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Linux/net/ipv4/tcp_input.c

  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              Implementation of the Transmission Control Protocol(TCP).
  7  *
  8  * Authors:     Ross Biro
  9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 10  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
 11  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
 12  *              Florian La Roche, <flla@stud.uni-sb.de>
 13  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 14  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
 15  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
 16  *              Matthew Dillon, <dillon@apollo.west.oic.com>
 17  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 18  *              Jorge Cwik, <jorge@laser.satlink.net>
 19  */
 20 
 21 /*
 22  * Changes:
 23  *              Pedro Roque     :       Fast Retransmit/Recovery.
 24  *                                      Two receive queues.
 25  *                                      Retransmit queue handled by TCP.
 26  *                                      Better retransmit timer handling.
 27  *                                      New congestion avoidance.
 28  *                                      Header prediction.
 29  *                                      Variable renaming.
 30  *
 31  *              Eric            :       Fast Retransmit.
 32  *              Randy Scott     :       MSS option defines.
 33  *              Eric Schenk     :       Fixes to slow start algorithm.
 34  *              Eric Schenk     :       Yet another double ACK bug.
 35  *              Eric Schenk     :       Delayed ACK bug fixes.
 36  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
 37  *              David S. Miller :       Don't allow zero congestion window.
 38  *              Eric Schenk     :       Fix retransmitter so that it sends
 39  *                                      next packet on ack of previous packet.
 40  *              Andi Kleen      :       Moved open_request checking here
 41  *                                      and process RSTs for open_requests.
 42  *              Andi Kleen      :       Better prune_queue, and other fixes.
 43  *              Andrey Savochkin:       Fix RTT measurements in the presence of
 44  *                                      timestamps.
 45  *              Andrey Savochkin:       Check sequence numbers correctly when
 46  *                                      removing SACKs due to in sequence incoming
 47  *                                      data segments.
 48  *              Andi Kleen:             Make sure we never ack data there is not
 49  *                                      enough room for. Also make this condition
 50  *                                      a fatal error if it might still happen.
 51  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
 52  *                                      connections with MSS<min(MTU,ann. MSS)
 53  *                                      work without delayed acks.
 54  *              Andi Kleen:             Process packets with PSH set in the
 55  *                                      fast path.
 56  *              J Hadi Salim:           ECN support
 57  *              Andrei Gurtov,
 58  *              Pasi Sarolahti,
 59  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
 60  *                                      engine. Lots of bugs are found.
 61  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
 62  */
 63 
 64 #define pr_fmt(fmt) "TCP: " fmt
 65 
 66 #include <linux/mm.h>
 67 #include <linux/slab.h>
 68 #include <linux/module.h>
 69 #include <linux/sysctl.h>
 70 #include <linux/kernel.h>
 71 #include <linux/prefetch.h>
 72 #include <net/dst.h>
 73 #include <net/tcp.h>
 74 #include <net/inet_common.h>
 75 #include <linux/ipsec.h>
 76 #include <asm/unaligned.h>
 77 #include <linux/errqueue.h>
 78 
 79 int sysctl_tcp_timestamps __read_mostly = 1;
 80 int sysctl_tcp_window_scaling __read_mostly = 1;
 81 int sysctl_tcp_sack __read_mostly = 1;
 82 int sysctl_tcp_fack __read_mostly = 1;
 83 int sysctl_tcp_max_reordering __read_mostly = 300;
 84 int sysctl_tcp_dsack __read_mostly = 1;
 85 int sysctl_tcp_app_win __read_mostly = 31;
 86 int sysctl_tcp_adv_win_scale __read_mostly = 1;
 87 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
 88 
 89 /* rfc5961 challenge ack rate limiting */
 90 int sysctl_tcp_challenge_ack_limit = 100;
 91 
 92 int sysctl_tcp_stdurg __read_mostly;
 93 int sysctl_tcp_rfc1337 __read_mostly;
 94 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
 95 int sysctl_tcp_frto __read_mostly = 2;
 96 int sysctl_tcp_min_rtt_wlen __read_mostly = 300;
 97 
 98 int sysctl_tcp_thin_dupack __read_mostly;
 99 
100 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
101 int sysctl_tcp_early_retrans __read_mostly = 3;
102 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
103 
104 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
105 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
106 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
107 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
108 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
109 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
110 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
111 #define FLAG_LOST_RETRANS       0x80 /* This ACK marks some retransmission lost */
112 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
113 #define FLAG_ORIG_SACK_ACKED    0x200 /* Never retransmitted data are (s)acked  */
114 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
115 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
116 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
117 #define FLAG_UPDATE_TS_RECENT   0x4000 /* tcp_replace_ts_recent() */
118 
119 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
120 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
121 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
122 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
123 
124 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
125 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
126 
127 #define REXMIT_NONE     0 /* no loss recovery to do */
128 #define REXMIT_LOST     1 /* retransmit packets marked lost */
129 #define REXMIT_NEW      2 /* FRTO-style transmit of unsent/new packets */
130 
131 /* Adapt the MSS value used to make delayed ack decision to the
132  * real world.
133  */
134 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
135 {
136         struct inet_connection_sock *icsk = inet_csk(sk);
137         const unsigned int lss = icsk->icsk_ack.last_seg_size;
138         unsigned int len;
139 
140         icsk->icsk_ack.last_seg_size = 0;
141 
142         /* skb->len may jitter because of SACKs, even if peer
143          * sends good full-sized frames.
144          */
145         len = skb_shinfo(skb)->gso_size ? : skb->len;
146         if (len >= icsk->icsk_ack.rcv_mss) {
147                 icsk->icsk_ack.rcv_mss = len;
148         } else {
149                 /* Otherwise, we make more careful check taking into account,
150                  * that SACKs block is variable.
151                  *
152                  * "len" is invariant segment length, including TCP header.
153                  */
154                 len += skb->data - skb_transport_header(skb);
155                 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
156                     /* If PSH is not set, packet should be
157                      * full sized, provided peer TCP is not badly broken.
158                      * This observation (if it is correct 8)) allows
159                      * to handle super-low mtu links fairly.
160                      */
161                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
162                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
163                         /* Subtract also invariant (if peer is RFC compliant),
164                          * tcp header plus fixed timestamp option length.
165                          * Resulting "len" is MSS free of SACK jitter.
166                          */
167                         len -= tcp_sk(sk)->tcp_header_len;
168                         icsk->icsk_ack.last_seg_size = len;
169                         if (len == lss) {
170                                 icsk->icsk_ack.rcv_mss = len;
171                                 return;
172                         }
173                 }
174                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
175                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
176                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
177         }
178 }
179 
180 static void tcp_incr_quickack(struct sock *sk)
181 {
182         struct inet_connection_sock *icsk = inet_csk(sk);
183         unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
184 
185         if (quickacks == 0)
186                 quickacks = 2;
187         if (quickacks > icsk->icsk_ack.quick)
188                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
189 }
190 
191 static void tcp_enter_quickack_mode(struct sock *sk)
192 {
193         struct inet_connection_sock *icsk = inet_csk(sk);
194         tcp_incr_quickack(sk);
195         icsk->icsk_ack.pingpong = 0;
196         icsk->icsk_ack.ato = TCP_ATO_MIN;
197 }
198 
199 /* Send ACKs quickly, if "quick" count is not exhausted
200  * and the session is not interactive.
201  */
202 
203 static bool tcp_in_quickack_mode(struct sock *sk)
204 {
205         const struct inet_connection_sock *icsk = inet_csk(sk);
206         const struct dst_entry *dst = __sk_dst_get(sk);
207 
208         return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
209                 (icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
210 }
211 
212 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
213 {
214         if (tp->ecn_flags & TCP_ECN_OK)
215                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
216 }
217 
218 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
219 {
220         if (tcp_hdr(skb)->cwr)
221                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
222 }
223 
224 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
225 {
226         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
227 }
228 
229 static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
230 {
231         switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
232         case INET_ECN_NOT_ECT:
233                 /* Funny extension: if ECT is not set on a segment,
234                  * and we already seen ECT on a previous segment,
235                  * it is probably a retransmit.
236                  */
237                 if (tp->ecn_flags & TCP_ECN_SEEN)
238                         tcp_enter_quickack_mode((struct sock *)tp);
239                 break;
240         case INET_ECN_CE:
241                 if (tcp_ca_needs_ecn((struct sock *)tp))
242                         tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
243 
244                 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
245                         /* Better not delay acks, sender can have a very low cwnd */
246                         tcp_enter_quickack_mode((struct sock *)tp);
247                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
248                 }
249                 tp->ecn_flags |= TCP_ECN_SEEN;
250                 break;
251         default:
252                 if (tcp_ca_needs_ecn((struct sock *)tp))
253                         tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
254                 tp->ecn_flags |= TCP_ECN_SEEN;
255                 break;
256         }
257 }
258 
259 static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
260 {
261         if (tp->ecn_flags & TCP_ECN_OK)
262                 __tcp_ecn_check_ce(tp, skb);
263 }
264 
265 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
266 {
267         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
268                 tp->ecn_flags &= ~TCP_ECN_OK;
269 }
270 
271 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
272 {
273         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
274                 tp->ecn_flags &= ~TCP_ECN_OK;
275 }
276 
277 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
278 {
279         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
280                 return true;
281         return false;
282 }
283 
284 /* Buffer size and advertised window tuning.
285  *
286  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
287  */
288 
289 static void tcp_sndbuf_expand(struct sock *sk)
290 {
291         const struct tcp_sock *tp = tcp_sk(sk);
292         int sndmem, per_mss;
293         u32 nr_segs;
294 
295         /* Worst case is non GSO/TSO : each frame consumes one skb
296          * and skb->head is kmalloced using power of two area of memory
297          */
298         per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
299                   MAX_TCP_HEADER +
300                   SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
301 
302         per_mss = roundup_pow_of_two(per_mss) +
303                   SKB_DATA_ALIGN(sizeof(struct sk_buff));
304 
305         nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
306         nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
307 
308         /* Fast Recovery (RFC 5681 3.2) :
309          * Cubic needs 1.7 factor, rounded to 2 to include
310          * extra cushion (application might react slowly to POLLOUT)
311          */
312         sndmem = 2 * nr_segs * per_mss;
313 
314         if (sk->sk_sndbuf < sndmem)
315                 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
316 }
317 
318 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
319  *
320  * All tcp_full_space() is split to two parts: "network" buffer, allocated
321  * forward and advertised in receiver window (tp->rcv_wnd) and
322  * "application buffer", required to isolate scheduling/application
323  * latencies from network.
324  * window_clamp is maximal advertised window. It can be less than
325  * tcp_full_space(), in this case tcp_full_space() - window_clamp
326  * is reserved for "application" buffer. The less window_clamp is
327  * the smoother our behaviour from viewpoint of network, but the lower
328  * throughput and the higher sensitivity of the connection to losses. 8)
329  *
330  * rcv_ssthresh is more strict window_clamp used at "slow start"
331  * phase to predict further behaviour of this connection.
332  * It is used for two goals:
333  * - to enforce header prediction at sender, even when application
334  *   requires some significant "application buffer". It is check #1.
335  * - to prevent pruning of receive queue because of misprediction
336  *   of receiver window. Check #2.
337  *
338  * The scheme does not work when sender sends good segments opening
339  * window and then starts to feed us spaghetti. But it should work
340  * in common situations. Otherwise, we have to rely on queue collapsing.
341  */
342 
343 /* Slow part of check#2. */
344 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
345 {
346         struct tcp_sock *tp = tcp_sk(sk);
347         /* Optimize this! */
348         int truesize = tcp_win_from_space(skb->truesize) >> 1;
349         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
350 
351         while (tp->rcv_ssthresh <= window) {
352                 if (truesize <= skb->len)
353                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
354 
355                 truesize >>= 1;
356                 window >>= 1;
357         }
358         return 0;
359 }
360 
361 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
362 {
363         struct tcp_sock *tp = tcp_sk(sk);
364 
365         /* Check #1 */
366         if (tp->rcv_ssthresh < tp->window_clamp &&
367             (int)tp->rcv_ssthresh < tcp_space(sk) &&
368             !tcp_under_memory_pressure(sk)) {
369                 int incr;
370 
371                 /* Check #2. Increase window, if skb with such overhead
372                  * will fit to rcvbuf in future.
373                  */
374                 if (tcp_win_from_space(skb->truesize) <= skb->len)
375                         incr = 2 * tp->advmss;
376                 else
377                         incr = __tcp_grow_window(sk, skb);
378 
379                 if (incr) {
380                         incr = max_t(int, incr, 2 * skb->len);
381                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
382                                                tp->window_clamp);
383                         inet_csk(sk)->icsk_ack.quick |= 1;
384                 }
385         }
386 }
387 
388 /* 3. Tuning rcvbuf, when connection enters established state. */
389 static void tcp_fixup_rcvbuf(struct sock *sk)
390 {
391         u32 mss = tcp_sk(sk)->advmss;
392         int rcvmem;
393 
394         rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
395                  tcp_default_init_rwnd(mss);
396 
397         /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
398          * Allow enough cushion so that sender is not limited by our window
399          */
400         if (sysctl_tcp_moderate_rcvbuf)
401                 rcvmem <<= 2;
402 
403         if (sk->sk_rcvbuf < rcvmem)
404                 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
405 }
406 
407 /* 4. Try to fixup all. It is made immediately after connection enters
408  *    established state.
409  */
410 void tcp_init_buffer_space(struct sock *sk)
411 {
412         struct tcp_sock *tp = tcp_sk(sk);
413         int maxwin;
414 
415         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
416                 tcp_fixup_rcvbuf(sk);
417         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
418                 tcp_sndbuf_expand(sk);
419 
420         tp->rcvq_space.space = tp->rcv_wnd;
421         tp->rcvq_space.time = tcp_time_stamp;
422         tp->rcvq_space.seq = tp->copied_seq;
423 
424         maxwin = tcp_full_space(sk);
425 
426         if (tp->window_clamp >= maxwin) {
427                 tp->window_clamp = maxwin;
428 
429                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
430                         tp->window_clamp = max(maxwin -
431                                                (maxwin >> sysctl_tcp_app_win),
432                                                4 * tp->advmss);
433         }
434 
435         /* Force reservation of one segment. */
436         if (sysctl_tcp_app_win &&
437             tp->window_clamp > 2 * tp->advmss &&
438             tp->window_clamp + tp->advmss > maxwin)
439                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
440 
441         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
442         tp->snd_cwnd_stamp = tcp_time_stamp;
443 }
444 
445 /* 5. Recalculate window clamp after socket hit its memory bounds. */
446 static void tcp_clamp_window(struct sock *sk)
447 {
448         struct tcp_sock *tp = tcp_sk(sk);
449         struct inet_connection_sock *icsk = inet_csk(sk);
450 
451         icsk->icsk_ack.quick = 0;
452 
453         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
454             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
455             !tcp_under_memory_pressure(sk) &&
456             sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
457                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
458                                     sysctl_tcp_rmem[2]);
459         }
460         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
461                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
462 }
463 
464 /* Initialize RCV_MSS value.
465  * RCV_MSS is an our guess about MSS used by the peer.
466  * We haven't any direct information about the MSS.
467  * It's better to underestimate the RCV_MSS rather than overestimate.
468  * Overestimations make us ACKing less frequently than needed.
469  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
470  */
471 void tcp_initialize_rcv_mss(struct sock *sk)
472 {
473         const struct tcp_sock *tp = tcp_sk(sk);
474         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
475 
476         hint = min(hint, tp->rcv_wnd / 2);
477         hint = min(hint, TCP_MSS_DEFAULT);
478         hint = max(hint, TCP_MIN_MSS);
479 
480         inet_csk(sk)->icsk_ack.rcv_mss = hint;
481 }
482 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
483 
484 /* Receiver "autotuning" code.
485  *
486  * The algorithm for RTT estimation w/o timestamps is based on
487  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
488  * <http://public.lanl.gov/radiant/pubs.html#DRS>
489  *
490  * More detail on this code can be found at
491  * <http://staff.psc.edu/jheffner/>,
492  * though this reference is out of date.  A new paper
493  * is pending.
494  */
495 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
496 {
497         u32 new_sample = tp->rcv_rtt_est.rtt;
498         long m = sample;
499 
500         if (m == 0)
501                 m = 1;
502 
503         if (new_sample != 0) {
504                 /* If we sample in larger samples in the non-timestamp
505                  * case, we could grossly overestimate the RTT especially
506                  * with chatty applications or bulk transfer apps which
507                  * are stalled on filesystem I/O.
508                  *
509                  * Also, since we are only going for a minimum in the
510                  * non-timestamp case, we do not smooth things out
511                  * else with timestamps disabled convergence takes too
512                  * long.
513                  */
514                 if (!win_dep) {
515                         m -= (new_sample >> 3);
516                         new_sample += m;
517                 } else {
518                         m <<= 3;
519                         if (m < new_sample)
520                                 new_sample = m;
521                 }
522         } else {
523                 /* No previous measure. */
524                 new_sample = m << 3;
525         }
526 
527         if (tp->rcv_rtt_est.rtt != new_sample)
528                 tp->rcv_rtt_est.rtt = new_sample;
529 }
530 
531 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
532 {
533         if (tp->rcv_rtt_est.time == 0)
534                 goto new_measure;
535         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
536                 return;
537         tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
538 
539 new_measure:
540         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
541         tp->rcv_rtt_est.time = tcp_time_stamp;
542 }
543 
544 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
545                                           const struct sk_buff *skb)
546 {
547         struct tcp_sock *tp = tcp_sk(sk);
548         if (tp->rx_opt.rcv_tsecr &&
549             (TCP_SKB_CB(skb)->end_seq -
550              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
551                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
552 }
553 
554 /*
555  * This function should be called every time data is copied to user space.
556  * It calculates the appropriate TCP receive buffer space.
557  */
558 void tcp_rcv_space_adjust(struct sock *sk)
559 {
560         struct tcp_sock *tp = tcp_sk(sk);
561         int time;
562         int copied;
563 
564         time = tcp_time_stamp - tp->rcvq_space.time;
565         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
566                 return;
567 
568         /* Number of bytes copied to user in last RTT */
569         copied = tp->copied_seq - tp->rcvq_space.seq;
570         if (copied <= tp->rcvq_space.space)
571                 goto new_measure;
572 
573         /* A bit of theory :
574          * copied = bytes received in previous RTT, our base window
575          * To cope with packet losses, we need a 2x factor
576          * To cope with slow start, and sender growing its cwin by 100 %
577          * every RTT, we need a 4x factor, because the ACK we are sending
578          * now is for the next RTT, not the current one :
579          * <prev RTT . ><current RTT .. ><next RTT .... >
580          */
581 
582         if (sysctl_tcp_moderate_rcvbuf &&
583             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
584                 int rcvwin, rcvmem, rcvbuf;
585 
586                 /* minimal window to cope with packet losses, assuming
587                  * steady state. Add some cushion because of small variations.
588                  */
589                 rcvwin = (copied << 1) + 16 * tp->advmss;
590 
591                 /* If rate increased by 25%,
592                  *      assume slow start, rcvwin = 3 * copied
593                  * If rate increased by 50%,
594                  *      assume sender can use 2x growth, rcvwin = 4 * copied
595                  */
596                 if (copied >=
597                     tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
598                         if (copied >=
599                             tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
600                                 rcvwin <<= 1;
601                         else
602                                 rcvwin += (rcvwin >> 1);
603                 }
604 
605                 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
606                 while (tcp_win_from_space(rcvmem) < tp->advmss)
607                         rcvmem += 128;
608 
609                 rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
610                 if (rcvbuf > sk->sk_rcvbuf) {
611                         sk->sk_rcvbuf = rcvbuf;
612 
613                         /* Make the window clamp follow along.  */
614                         tp->window_clamp = rcvwin;
615                 }
616         }
617         tp->rcvq_space.space = copied;
618 
619 new_measure:
620         tp->rcvq_space.seq = tp->copied_seq;
621         tp->rcvq_space.time = tcp_time_stamp;
622 }
623 
624 /* There is something which you must keep in mind when you analyze the
625  * behavior of the tp->ato delayed ack timeout interval.  When a
626  * connection starts up, we want to ack as quickly as possible.  The
627  * problem is that "good" TCP's do slow start at the beginning of data
628  * transmission.  The means that until we send the first few ACK's the
629  * sender will sit on his end and only queue most of his data, because
630  * he can only send snd_cwnd unacked packets at any given time.  For
631  * each ACK we send, he increments snd_cwnd and transmits more of his
632  * queue.  -DaveM
633  */
634 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
635 {
636         struct tcp_sock *tp = tcp_sk(sk);
637         struct inet_connection_sock *icsk = inet_csk(sk);
638         u32 now;
639 
640         inet_csk_schedule_ack(sk);
641 
642         tcp_measure_rcv_mss(sk, skb);
643 
644         tcp_rcv_rtt_measure(tp);
645 
646         now = tcp_time_stamp;
647 
648         if (!icsk->icsk_ack.ato) {
649                 /* The _first_ data packet received, initialize
650                  * delayed ACK engine.
651                  */
652                 tcp_incr_quickack(sk);
653                 icsk->icsk_ack.ato = TCP_ATO_MIN;
654         } else {
655                 int m = now - icsk->icsk_ack.lrcvtime;
656 
657                 if (m <= TCP_ATO_MIN / 2) {
658                         /* The fastest case is the first. */
659                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
660                 } else if (m < icsk->icsk_ack.ato) {
661                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
662                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
663                                 icsk->icsk_ack.ato = icsk->icsk_rto;
664                 } else if (m > icsk->icsk_rto) {
665                         /* Too long gap. Apparently sender failed to
666                          * restart window, so that we send ACKs quickly.
667                          */
668                         tcp_incr_quickack(sk);
669                         sk_mem_reclaim(sk);
670                 }
671         }
672         icsk->icsk_ack.lrcvtime = now;
673 
674         tcp_ecn_check_ce(tp, skb);
675 
676         if (skb->len >= 128)
677                 tcp_grow_window(sk, skb);
678 }
679 
680 /* Called to compute a smoothed rtt estimate. The data fed to this
681  * routine either comes from timestamps, or from segments that were
682  * known _not_ to have been retransmitted [see Karn/Partridge
683  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
684  * piece by Van Jacobson.
685  * NOTE: the next three routines used to be one big routine.
686  * To save cycles in the RFC 1323 implementation it was better to break
687  * it up into three procedures. -- erics
688  */
689 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
690 {
691         struct tcp_sock *tp = tcp_sk(sk);
692         long m = mrtt_us; /* RTT */
693         u32 srtt = tp->srtt_us;
694 
695         /*      The following amusing code comes from Jacobson's
696          *      article in SIGCOMM '88.  Note that rtt and mdev
697          *      are scaled versions of rtt and mean deviation.
698          *      This is designed to be as fast as possible
699          *      m stands for "measurement".
700          *
701          *      On a 1990 paper the rto value is changed to:
702          *      RTO = rtt + 4 * mdev
703          *
704          * Funny. This algorithm seems to be very broken.
705          * These formulae increase RTO, when it should be decreased, increase
706          * too slowly, when it should be increased quickly, decrease too quickly
707          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
708          * does not matter how to _calculate_ it. Seems, it was trap
709          * that VJ failed to avoid. 8)
710          */
711         if (srtt != 0) {
712                 m -= (srtt >> 3);       /* m is now error in rtt est */
713                 srtt += m;              /* rtt = 7/8 rtt + 1/8 new */
714                 if (m < 0) {
715                         m = -m;         /* m is now abs(error) */
716                         m -= (tp->mdev_us >> 2);   /* similar update on mdev */
717                         /* This is similar to one of Eifel findings.
718                          * Eifel blocks mdev updates when rtt decreases.
719                          * This solution is a bit different: we use finer gain
720                          * for mdev in this case (alpha*beta).
721                          * Like Eifel it also prevents growth of rto,
722                          * but also it limits too fast rto decreases,
723                          * happening in pure Eifel.
724                          */
725                         if (m > 0)
726                                 m >>= 3;
727                 } else {
728                         m -= (tp->mdev_us >> 2);   /* similar update on mdev */
729                 }
730                 tp->mdev_us += m;               /* mdev = 3/4 mdev + 1/4 new */
731                 if (tp->mdev_us > tp->mdev_max_us) {
732                         tp->mdev_max_us = tp->mdev_us;
733                         if (tp->mdev_max_us > tp->rttvar_us)
734                                 tp->rttvar_us = tp->mdev_max_us;
735                 }
736                 if (after(tp->snd_una, tp->rtt_seq)) {
737                         if (tp->mdev_max_us < tp->rttvar_us)
738                                 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
739                         tp->rtt_seq = tp->snd_nxt;
740                         tp->mdev_max_us = tcp_rto_min_us(sk);
741                 }
742         } else {
743                 /* no previous measure. */
744                 srtt = m << 3;          /* take the measured time to be rtt */
745                 tp->mdev_us = m << 1;   /* make sure rto = 3*rtt */
746                 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
747                 tp->mdev_max_us = tp->rttvar_us;
748                 tp->rtt_seq = tp->snd_nxt;
749         }
750         tp->srtt_us = max(1U, srtt);
751 }
752 
753 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
754  * Note: TCP stack does not yet implement pacing.
755  * FQ packet scheduler can be used to implement cheap but effective
756  * TCP pacing, to smooth the burst on large writes when packets
757  * in flight is significantly lower than cwnd (or rwin)
758  */
759 int sysctl_tcp_pacing_ss_ratio __read_mostly = 200;
760 int sysctl_tcp_pacing_ca_ratio __read_mostly = 120;
761 
762 static void tcp_update_pacing_rate(struct sock *sk)
763 {
764         const struct tcp_sock *tp = tcp_sk(sk);
765         u64 rate;
766 
767         /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
768         rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
769 
770         /* current rate is (cwnd * mss) / srtt
771          * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
772          * In Congestion Avoidance phase, set it to 120 % the current rate.
773          *
774          * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
775          *       If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
776          *       end of slow start and should slow down.
777          */
778         if (tp->snd_cwnd < tp->snd_ssthresh / 2)
779                 rate *= sysctl_tcp_pacing_ss_ratio;
780         else
781                 rate *= sysctl_tcp_pacing_ca_ratio;
782 
783         rate *= max(tp->snd_cwnd, tp->packets_out);
784 
785         if (likely(tp->srtt_us))
786                 do_div(rate, tp->srtt_us);
787 
788         /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
789          * without any lock. We want to make sure compiler wont store
790          * intermediate values in this location.
791          */
792         ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
793                                                 sk->sk_max_pacing_rate);
794 }
795 
796 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
797  * routine referred to above.
798  */
799 static void tcp_set_rto(struct sock *sk)
800 {
801         const struct tcp_sock *tp = tcp_sk(sk);
802         /* Old crap is replaced with new one. 8)
803          *
804          * More seriously:
805          * 1. If rtt variance happened to be less 50msec, it is hallucination.
806          *    It cannot be less due to utterly erratic ACK generation made
807          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
808          *    to do with delayed acks, because at cwnd>2 true delack timeout
809          *    is invisible. Actually, Linux-2.4 also generates erratic
810          *    ACKs in some circumstances.
811          */
812         inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
813 
814         /* 2. Fixups made earlier cannot be right.
815          *    If we do not estimate RTO correctly without them,
816          *    all the algo is pure shit and should be replaced
817          *    with correct one. It is exactly, which we pretend to do.
818          */
819 
820         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
821          * guarantees that rto is higher.
822          */
823         tcp_bound_rto(sk);
824 }
825 
826 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
827 {
828         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
829 
830         if (!cwnd)
831                 cwnd = TCP_INIT_CWND;
832         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
833 }
834 
835 /*
836  * Packet counting of FACK is based on in-order assumptions, therefore TCP
837  * disables it when reordering is detected
838  */
839 void tcp_disable_fack(struct tcp_sock *tp)
840 {
841         /* RFC3517 uses different metric in lost marker => reset on change */
842         if (tcp_is_fack(tp))
843                 tp->lost_skb_hint = NULL;
844         tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
845 }
846 
847 /* Take a notice that peer is sending D-SACKs */
848 static void tcp_dsack_seen(struct tcp_sock *tp)
849 {
850         tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
851 }
852 
853 static void tcp_update_reordering(struct sock *sk, const int metric,
854                                   const int ts)
855 {
856         struct tcp_sock *tp = tcp_sk(sk);
857         if (metric > tp->reordering) {
858                 int mib_idx;
859 
860                 tp->reordering = min(sysctl_tcp_max_reordering, metric);
861 
862                 /* This exciting event is worth to be remembered. 8) */
863                 if (ts)
864                         mib_idx = LINUX_MIB_TCPTSREORDER;
865                 else if (tcp_is_reno(tp))
866                         mib_idx = LINUX_MIB_TCPRENOREORDER;
867                 else if (tcp_is_fack(tp))
868                         mib_idx = LINUX_MIB_TCPFACKREORDER;
869                 else
870                         mib_idx = LINUX_MIB_TCPSACKREORDER;
871 
872                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
873 #if FASTRETRANS_DEBUG > 1
874                 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
875                          tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
876                          tp->reordering,
877                          tp->fackets_out,
878                          tp->sacked_out,
879                          tp->undo_marker ? tp->undo_retrans : 0);
880 #endif
881                 tcp_disable_fack(tp);
882         }
883 
884         if (metric > 0)
885                 tcp_disable_early_retrans(tp);
886         tp->rack.reord = 1;
887 }
888 
889 /* This must be called before lost_out is incremented */
890 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
891 {
892         if (!tp->retransmit_skb_hint ||
893             before(TCP_SKB_CB(skb)->seq,
894                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
895                 tp->retransmit_skb_hint = skb;
896 
897         if (!tp->lost_out ||
898             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
899                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
900 }
901 
902 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
903 {
904         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
905                 tcp_verify_retransmit_hint(tp, skb);
906 
907                 tp->lost_out += tcp_skb_pcount(skb);
908                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
909         }
910 }
911 
912 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
913 {
914         tcp_verify_retransmit_hint(tp, skb);
915 
916         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
917                 tp->lost_out += tcp_skb_pcount(skb);
918                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
919         }
920 }
921 
922 /* This procedure tags the retransmission queue when SACKs arrive.
923  *
924  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
925  * Packets in queue with these bits set are counted in variables
926  * sacked_out, retrans_out and lost_out, correspondingly.
927  *
928  * Valid combinations are:
929  * Tag  InFlight        Description
930  * 0    1               - orig segment is in flight.
931  * S    0               - nothing flies, orig reached receiver.
932  * L    0               - nothing flies, orig lost by net.
933  * R    2               - both orig and retransmit are in flight.
934  * L|R  1               - orig is lost, retransmit is in flight.
935  * S|R  1               - orig reached receiver, retrans is still in flight.
936  * (L|S|R is logically valid, it could occur when L|R is sacked,
937  *  but it is equivalent to plain S and code short-curcuits it to S.
938  *  L|S is logically invalid, it would mean -1 packet in flight 8))
939  *
940  * These 6 states form finite state machine, controlled by the following events:
941  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
942  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
943  * 3. Loss detection event of two flavors:
944  *      A. Scoreboard estimator decided the packet is lost.
945  *         A'. Reno "three dupacks" marks head of queue lost.
946  *         A''. Its FACK modification, head until snd.fack is lost.
947  *      B. SACK arrives sacking SND.NXT at the moment, when the
948  *         segment was retransmitted.
949  * 4. D-SACK added new rule: D-SACK changes any tag to S.
950  *
951  * It is pleasant to note, that state diagram turns out to be commutative,
952  * so that we are allowed not to be bothered by order of our actions,
953  * when multiple events arrive simultaneously. (see the function below).
954  *
955  * Reordering detection.
956  * --------------------
957  * Reordering metric is maximal distance, which a packet can be displaced
958  * in packet stream. With SACKs we can estimate it:
959  *
960  * 1. SACK fills old hole and the corresponding segment was not
961  *    ever retransmitted -> reordering. Alas, we cannot use it
962  *    when segment was retransmitted.
963  * 2. The last flaw is solved with D-SACK. D-SACK arrives
964  *    for retransmitted and already SACKed segment -> reordering..
965  * Both of these heuristics are not used in Loss state, when we cannot
966  * account for retransmits accurately.
967  *
968  * SACK block validation.
969  * ----------------------
970  *
971  * SACK block range validation checks that the received SACK block fits to
972  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
973  * Note that SND.UNA is not included to the range though being valid because
974  * it means that the receiver is rather inconsistent with itself reporting
975  * SACK reneging when it should advance SND.UNA. Such SACK block this is
976  * perfectly valid, however, in light of RFC2018 which explicitly states
977  * that "SACK block MUST reflect the newest segment.  Even if the newest
978  * segment is going to be discarded ...", not that it looks very clever
979  * in case of head skb. Due to potentional receiver driven attacks, we
980  * choose to avoid immediate execution of a walk in write queue due to
981  * reneging and defer head skb's loss recovery to standard loss recovery
982  * procedure that will eventually trigger (nothing forbids us doing this).
983  *
984  * Implements also blockage to start_seq wrap-around. Problem lies in the
985  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
986  * there's no guarantee that it will be before snd_nxt (n). The problem
987  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
988  * wrap (s_w):
989  *
990  *         <- outs wnd ->                          <- wrapzone ->
991  *         u     e      n                         u_w   e_w  s n_w
992  *         |     |      |                          |     |   |  |
993  * |<------------+------+----- TCP seqno space --------------+---------->|
994  * ...-- <2^31 ->|                                           |<--------...
995  * ...---- >2^31 ------>|                                    |<--------...
996  *
997  * Current code wouldn't be vulnerable but it's better still to discard such
998  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
999  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1000  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1001  * equal to the ideal case (infinite seqno space without wrap caused issues).
1002  *
1003  * With D-SACK the lower bound is extended to cover sequence space below
1004  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1005  * again, D-SACK block must not to go across snd_una (for the same reason as
1006  * for the normal SACK blocks, explained above). But there all simplicity
1007  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1008  * fully below undo_marker they do not affect behavior in anyway and can
1009  * therefore be safely ignored. In rare cases (which are more or less
1010  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1011  * fragmentation and packet reordering past skb's retransmission. To consider
1012  * them correctly, the acceptable range must be extended even more though
1013  * the exact amount is rather hard to quantify. However, tp->max_window can
1014  * be used as an exaggerated estimate.
1015  */
1016 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1017                                    u32 start_seq, u32 end_seq)
1018 {
1019         /* Too far in future, or reversed (interpretation is ambiguous) */
1020         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1021                 return false;
1022 
1023         /* Nasty start_seq wrap-around check (see comments above) */
1024         if (!before(start_seq, tp->snd_nxt))
1025                 return false;
1026 
1027         /* In outstanding window? ...This is valid exit for D-SACKs too.
1028          * start_seq == snd_una is non-sensical (see comments above)
1029          */
1030         if (after(start_seq, tp->snd_una))
1031                 return true;
1032 
1033         if (!is_dsack || !tp->undo_marker)
1034                 return false;
1035 
1036         /* ...Then it's D-SACK, and must reside below snd_una completely */
1037         if (after(end_seq, tp->snd_una))
1038                 return false;
1039 
1040         if (!before(start_seq, tp->undo_marker))
1041                 return true;
1042 
1043         /* Too old */
1044         if (!after(end_seq, tp->undo_marker))
1045                 return false;
1046 
1047         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1048          *   start_seq < undo_marker and end_seq >= undo_marker.
1049          */
1050         return !before(start_seq, end_seq - tp->max_window);
1051 }
1052 
1053 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1054                             struct tcp_sack_block_wire *sp, int num_sacks,
1055                             u32 prior_snd_una)
1056 {
1057         struct tcp_sock *tp = tcp_sk(sk);
1058         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1059         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1060         bool dup_sack = false;
1061 
1062         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1063                 dup_sack = true;
1064                 tcp_dsack_seen(tp);
1065                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1066         } else if (num_sacks > 1) {
1067                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1068                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1069 
1070                 if (!after(end_seq_0, end_seq_1) &&
1071                     !before(start_seq_0, start_seq_1)) {
1072                         dup_sack = true;
1073                         tcp_dsack_seen(tp);
1074                         NET_INC_STATS_BH(sock_net(sk),
1075                                         LINUX_MIB_TCPDSACKOFORECV);
1076                 }
1077         }
1078 
1079         /* D-SACK for already forgotten data... Do dumb counting. */
1080         if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1081             !after(end_seq_0, prior_snd_una) &&
1082             after(end_seq_0, tp->undo_marker))
1083                 tp->undo_retrans--;
1084 
1085         return dup_sack;
1086 }
1087 
1088 struct tcp_sacktag_state {
1089         int     reord;
1090         int     fack_count;
1091         /* Timestamps for earliest and latest never-retransmitted segment
1092          * that was SACKed. RTO needs the earliest RTT to stay conservative,
1093          * but congestion control should still get an accurate delay signal.
1094          */
1095         struct skb_mstamp first_sackt;
1096         struct skb_mstamp last_sackt;
1097         int     flag;
1098 };
1099 
1100 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1101  * the incoming SACK may not exactly match but we can find smaller MSS
1102  * aligned portion of it that matches. Therefore we might need to fragment
1103  * which may fail and creates some hassle (caller must handle error case
1104  * returns).
1105  *
1106  * FIXME: this could be merged to shift decision code
1107  */
1108 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1109                                   u32 start_seq, u32 end_seq)
1110 {
1111         int err;
1112         bool in_sack;
1113         unsigned int pkt_len;
1114         unsigned int mss;
1115 
1116         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1117                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1118 
1119         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1120             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1121                 mss = tcp_skb_mss(skb);
1122                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1123 
1124                 if (!in_sack) {
1125                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1126                         if (pkt_len < mss)
1127                                 pkt_len = mss;
1128                 } else {
1129                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1130                         if (pkt_len < mss)
1131                                 return -EINVAL;
1132                 }
1133 
1134                 /* Round if necessary so that SACKs cover only full MSSes
1135                  * and/or the remaining small portion (if present)
1136                  */
1137                 if (pkt_len > mss) {
1138                         unsigned int new_len = (pkt_len / mss) * mss;
1139                         if (!in_sack && new_len < pkt_len) {
1140                                 new_len += mss;
1141                                 if (new_len >= skb->len)
1142                                         return 0;
1143                         }
1144                         pkt_len = new_len;
1145                 }
1146                 err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1147                 if (err < 0)
1148                         return err;
1149         }
1150 
1151         return in_sack;
1152 }
1153 
1154 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1155 static u8 tcp_sacktag_one(struct sock *sk,
1156                           struct tcp_sacktag_state *state, u8 sacked,
1157                           u32 start_seq, u32 end_seq,
1158                           int dup_sack, int pcount,
1159                           const struct skb_mstamp *xmit_time)
1160 {
1161         struct tcp_sock *tp = tcp_sk(sk);
1162         int fack_count = state->fack_count;
1163 
1164         /* Account D-SACK for retransmitted packet. */
1165         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1166                 if (tp->undo_marker && tp->undo_retrans > 0 &&
1167                     after(end_seq, tp->undo_marker))
1168                         tp->undo_retrans--;
1169                 if (sacked & TCPCB_SACKED_ACKED)
1170                         state->reord = min(fack_count, state->reord);
1171         }
1172 
1173         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1174         if (!after(end_seq, tp->snd_una))
1175                 return sacked;
1176 
1177         if (!(sacked & TCPCB_SACKED_ACKED)) {
1178                 tcp_rack_advance(tp, xmit_time, sacked);
1179 
1180                 if (sacked & TCPCB_SACKED_RETRANS) {
1181                         /* If the segment is not tagged as lost,
1182                          * we do not clear RETRANS, believing
1183                          * that retransmission is still in flight.
1184                          */
1185                         if (sacked & TCPCB_LOST) {
1186                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1187                                 tp->lost_out -= pcount;
1188                                 tp->retrans_out -= pcount;
1189                         }
1190                 } else {
1191                         if (!(sacked & TCPCB_RETRANS)) {
1192                                 /* New sack for not retransmitted frame,
1193                                  * which was in hole. It is reordering.
1194                                  */
1195                                 if (before(start_seq,
1196                                            tcp_highest_sack_seq(tp)))
1197                                         state->reord = min(fack_count,
1198                                                            state->reord);
1199                                 if (!after(end_seq, tp->high_seq))
1200                                         state->flag |= FLAG_ORIG_SACK_ACKED;
1201                                 if (state->first_sackt.v64 == 0)
1202                                         state->first_sackt = *xmit_time;
1203                                 state->last_sackt = *xmit_time;
1204                         }
1205 
1206                         if (sacked & TCPCB_LOST) {
1207                                 sacked &= ~TCPCB_LOST;
1208                                 tp->lost_out -= pcount;
1209                         }
1210                 }
1211 
1212                 sacked |= TCPCB_SACKED_ACKED;
1213                 state->flag |= FLAG_DATA_SACKED;
1214                 tp->sacked_out += pcount;
1215                 tp->delivered += pcount;  /* Out-of-order packets delivered */
1216 
1217                 fack_count += pcount;
1218 
1219                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1220                 if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
1221                     before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1222                         tp->lost_cnt_hint += pcount;
1223 
1224                 if (fack_count > tp->fackets_out)
1225                         tp->fackets_out = fack_count;
1226         }
1227 
1228         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1229          * frames and clear it. undo_retrans is decreased above, L|R frames
1230          * are accounted above as well.
1231          */
1232         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1233                 sacked &= ~TCPCB_SACKED_RETRANS;
1234                 tp->retrans_out -= pcount;
1235         }
1236 
1237         return sacked;
1238 }
1239 
1240 /* Shift newly-SACKed bytes from this skb to the immediately previous
1241  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1242  */
1243 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1244                             struct tcp_sacktag_state *state,
1245                             unsigned int pcount, int shifted, int mss,
1246                             bool dup_sack)
1247 {
1248         struct tcp_sock *tp = tcp_sk(sk);
1249         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1250         u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
1251         u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
1252 
1253         BUG_ON(!pcount);
1254 
1255         /* Adjust counters and hints for the newly sacked sequence
1256          * range but discard the return value since prev is already
1257          * marked. We must tag the range first because the seq
1258          * advancement below implicitly advances
1259          * tcp_highest_sack_seq() when skb is highest_sack.
1260          */
1261         tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1262                         start_seq, end_seq, dup_sack, pcount,
1263                         &skb->skb_mstamp);
1264 
1265         if (skb == tp->lost_skb_hint)
1266                 tp->lost_cnt_hint += pcount;
1267 
1268         TCP_SKB_CB(prev)->end_seq += shifted;
1269         TCP_SKB_CB(skb)->seq += shifted;
1270 
1271         tcp_skb_pcount_add(prev, pcount);
1272         BUG_ON(tcp_skb_pcount(skb) < pcount);
1273         tcp_skb_pcount_add(skb, -pcount);
1274 
1275         /* When we're adding to gso_segs == 1, gso_size will be zero,
1276          * in theory this shouldn't be necessary but as long as DSACK
1277          * code can come after this skb later on it's better to keep
1278          * setting gso_size to something.
1279          */
1280         if (!TCP_SKB_CB(prev)->tcp_gso_size)
1281                 TCP_SKB_CB(prev)->tcp_gso_size = mss;
1282 
1283         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1284         if (tcp_skb_pcount(skb) <= 1)
1285                 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1286 
1287         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1288         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1289 
1290         if (skb->len > 0) {
1291                 BUG_ON(!tcp_skb_pcount(skb));
1292                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1293                 return false;
1294         }
1295 
1296         /* Whole SKB was eaten :-) */
1297 
1298         if (skb == tp->retransmit_skb_hint)
1299                 tp->retransmit_skb_hint = prev;
1300         if (skb == tp->lost_skb_hint) {
1301                 tp->lost_skb_hint = prev;
1302                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1303         }
1304 
1305         TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1306         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1307                 TCP_SKB_CB(prev)->end_seq++;
1308 
1309         if (skb == tcp_highest_sack(sk))
1310                 tcp_advance_highest_sack(sk, skb);
1311 
1312         tcp_skb_collapse_tstamp(prev, skb);
1313         tcp_unlink_write_queue(skb, sk);
1314         sk_wmem_free_skb(sk, skb);
1315 
1316         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1317 
1318         return true;
1319 }
1320 
1321 /* I wish gso_size would have a bit more sane initialization than
1322  * something-or-zero which complicates things
1323  */
1324 static int tcp_skb_seglen(const struct sk_buff *skb)
1325 {
1326         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1327 }
1328 
1329 /* Shifting pages past head area doesn't work */
1330 static int skb_can_shift(const struct sk_buff *skb)
1331 {
1332         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1333 }
1334 
1335 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1336  * skb.
1337  */
1338 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1339                                           struct tcp_sacktag_state *state,
1340                                           u32 start_seq, u32 end_seq,
1341                                           bool dup_sack)
1342 {
1343         struct tcp_sock *tp = tcp_sk(sk);
1344         struct sk_buff *prev;
1345         int mss;
1346         int pcount = 0;
1347         int len;
1348         int in_sack;
1349 
1350         if (!sk_can_gso(sk))
1351                 goto fallback;
1352 
1353         /* Normally R but no L won't result in plain S */
1354         if (!dup_sack &&
1355             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1356                 goto fallback;
1357         if (!skb_can_shift(skb))
1358                 goto fallback;
1359         /* This frame is about to be dropped (was ACKed). */
1360         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1361                 goto fallback;
1362 
1363         /* Can only happen with delayed DSACK + discard craziness */
1364         if (unlikely(skb == tcp_write_queue_head(sk)))
1365                 goto fallback;
1366         prev = tcp_write_queue_prev(sk, skb);
1367 
1368         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1369                 goto fallback;
1370 
1371         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1372                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1373 
1374         if (in_sack) {
1375                 len = skb->len;
1376                 pcount = tcp_skb_pcount(skb);
1377                 mss = tcp_skb_seglen(skb);
1378 
1379                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1380                  * drop this restriction as unnecessary
1381                  */
1382                 if (mss != tcp_skb_seglen(prev))
1383                         goto fallback;
1384         } else {
1385                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1386                         goto noop;
1387                 /* CHECKME: This is non-MSS split case only?, this will
1388                  * cause skipped skbs due to advancing loop btw, original
1389                  * has that feature too
1390                  */
1391                 if (tcp_skb_pcount(skb) <= 1)
1392                         goto noop;
1393 
1394                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1395                 if (!in_sack) {
1396                         /* TODO: head merge to next could be attempted here
1397                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1398                          * though it might not be worth of the additional hassle
1399                          *
1400                          * ...we can probably just fallback to what was done
1401                          * previously. We could try merging non-SACKed ones
1402                          * as well but it probably isn't going to buy off
1403                          * because later SACKs might again split them, and
1404                          * it would make skb timestamp tracking considerably
1405                          * harder problem.
1406                          */
1407                         goto fallback;
1408                 }
1409 
1410                 len = end_seq - TCP_SKB_CB(skb)->seq;
1411                 BUG_ON(len < 0);
1412                 BUG_ON(len > skb->len);
1413 
1414                 /* MSS boundaries should be honoured or else pcount will
1415                  * severely break even though it makes things bit trickier.
1416                  * Optimize common case to avoid most of the divides
1417                  */
1418                 mss = tcp_skb_mss(skb);
1419 
1420                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1421                  * drop this restriction as unnecessary
1422                  */
1423                 if (mss != tcp_skb_seglen(prev))
1424                         goto fallback;
1425 
1426                 if (len == mss) {
1427                         pcount = 1;
1428                 } else if (len < mss) {
1429                         goto noop;
1430                 } else {
1431                         pcount = len / mss;
1432                         len = pcount * mss;
1433                 }
1434         }
1435 
1436         /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1437         if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1438                 goto fallback;
1439 
1440         if (!skb_shift(prev, skb, len))
1441                 goto fallback;
1442         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1443                 goto out;
1444 
1445         /* Hole filled allows collapsing with the next as well, this is very
1446          * useful when hole on every nth skb pattern happens
1447          */
1448         if (prev == tcp_write_queue_tail(sk))
1449                 goto out;
1450         skb = tcp_write_queue_next(sk, prev);
1451 
1452         if (!skb_can_shift(skb) ||
1453             (skb == tcp_send_head(sk)) ||
1454             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1455             (mss != tcp_skb_seglen(skb)))
1456                 goto out;
1457 
1458         len = skb->len;
1459         if (skb_shift(prev, skb, len)) {
1460                 pcount += tcp_skb_pcount(skb);
1461                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1462         }
1463 
1464 out:
1465         state->fack_count += pcount;
1466         return prev;
1467 
1468 noop:
1469         return skb;
1470 
1471 fallback:
1472         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1473         return NULL;
1474 }
1475 
1476 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1477                                         struct tcp_sack_block *next_dup,
1478                                         struct tcp_sacktag_state *state,
1479                                         u32 start_seq, u32 end_seq,
1480                                         bool dup_sack_in)
1481 {
1482         struct tcp_sock *tp = tcp_sk(sk);
1483         struct sk_buff *tmp;
1484 
1485         tcp_for_write_queue_from(skb, sk) {
1486                 int in_sack = 0;
1487                 bool dup_sack = dup_sack_in;
1488 
1489                 if (skb == tcp_send_head(sk))
1490                         break;
1491 
1492                 /* queue is in-order => we can short-circuit the walk early */
1493                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1494                         break;
1495 
1496                 if (next_dup  &&
1497                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1498                         in_sack = tcp_match_skb_to_sack(sk, skb,
1499                                                         next_dup->start_seq,
1500                                                         next_dup->end_seq);
1501                         if (in_sack > 0)
1502                                 dup_sack = true;
1503                 }
1504 
1505                 /* skb reference here is a bit tricky to get right, since
1506                  * shifting can eat and free both this skb and the next,
1507                  * so not even _safe variant of the loop is enough.
1508                  */
1509                 if (in_sack <= 0) {
1510                         tmp = tcp_shift_skb_data(sk, skb, state,
1511                                                  start_seq, end_seq, dup_sack);
1512                         if (tmp) {
1513                                 if (tmp != skb) {
1514                                         skb = tmp;
1515                                         continue;
1516                                 }
1517 
1518                                 in_sack = 0;
1519                         } else {
1520                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1521                                                                 start_seq,
1522                                                                 end_seq);
1523                         }
1524                 }
1525 
1526                 if (unlikely(in_sack < 0))
1527                         break;
1528 
1529                 if (in_sack) {
1530                         TCP_SKB_CB(skb)->sacked =
1531                                 tcp_sacktag_one(sk,
1532                                                 state,
1533                                                 TCP_SKB_CB(skb)->sacked,
1534                                                 TCP_SKB_CB(skb)->seq,
1535                                                 TCP_SKB_CB(skb)->end_seq,
1536                                                 dup_sack,
1537                                                 tcp_skb_pcount(skb),
1538                                                 &skb->skb_mstamp);
1539 
1540                         if (!before(TCP_SKB_CB(skb)->seq,
1541                                     tcp_highest_sack_seq(tp)))
1542                                 tcp_advance_highest_sack(sk, skb);
1543                 }
1544 
1545                 state->fack_count += tcp_skb_pcount(skb);
1546         }
1547         return skb;
1548 }
1549 
1550 /* Avoid all extra work that is being done by sacktag while walking in
1551  * a normal way
1552  */
1553 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1554                                         struct tcp_sacktag_state *state,
1555                                         u32 skip_to_seq)
1556 {
1557         tcp_for_write_queue_from(skb, sk) {
1558                 if (skb == tcp_send_head(sk))
1559                         break;
1560 
1561                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1562                         break;
1563 
1564                 state->fack_count += tcp_skb_pcount(skb);
1565         }
1566         return skb;
1567 }
1568 
1569 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1570                                                 struct sock *sk,
1571                                                 struct tcp_sack_block *next_dup,
1572                                                 struct tcp_sacktag_state *state,
1573                                                 u32 skip_to_seq)
1574 {
1575         if (!next_dup)
1576                 return skb;
1577 
1578         if (before(next_dup->start_seq, skip_to_seq)) {
1579                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1580                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1581                                        next_dup->start_seq, next_dup->end_seq,
1582                                        1);
1583         }
1584 
1585         return skb;
1586 }
1587 
1588 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1589 {
1590         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1591 }
1592 
1593 static int
1594 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1595                         u32 prior_snd_una, struct tcp_sacktag_state *state)
1596 {
1597         struct tcp_sock *tp = tcp_sk(sk);
1598         const unsigned char *ptr = (skb_transport_header(ack_skb) +
1599                                     TCP_SKB_CB(ack_skb)->sacked);
1600         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1601         struct tcp_sack_block sp[TCP_NUM_SACKS];
1602         struct tcp_sack_block *cache;
1603         struct sk_buff *skb;
1604         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1605         int used_sacks;
1606         bool found_dup_sack = false;
1607         int i, j;
1608         int first_sack_index;
1609 
1610         state->flag = 0;
1611         state->reord = tp->packets_out;
1612 
1613         if (!tp->sacked_out) {
1614                 if (WARN_ON(tp->fackets_out))
1615                         tp->fackets_out = 0;
1616                 tcp_highest_sack_reset(sk);
1617         }
1618 
1619         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1620                                          num_sacks, prior_snd_una);
1621         if (found_dup_sack)
1622                 state->flag |= FLAG_DSACKING_ACK;
1623 
1624         /* Eliminate too old ACKs, but take into
1625          * account more or less fresh ones, they can
1626          * contain valid SACK info.
1627          */
1628         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1629                 return 0;
1630 
1631         if (!tp->packets_out)
1632                 goto out;
1633 
1634         used_sacks = 0;
1635         first_sack_index = 0;
1636         for (i = 0; i < num_sacks; i++) {
1637                 bool dup_sack = !i && found_dup_sack;
1638 
1639                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1640                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1641 
1642                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1643                                             sp[used_sacks].start_seq,
1644                                             sp[used_sacks].end_seq)) {
1645                         int mib_idx;
1646 
1647                         if (dup_sack) {
1648                                 if (!tp->undo_marker)
1649                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1650                                 else
1651                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1652                         } else {
1653                                 /* Don't count olds caused by ACK reordering */
1654                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1655                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1656                                         continue;
1657                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1658                         }
1659 
1660                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1661                         if (i == 0)
1662                                 first_sack_index = -1;
1663                         continue;
1664                 }
1665 
1666                 /* Ignore very old stuff early */
1667                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1668                         continue;
1669 
1670                 used_sacks++;
1671         }
1672 
1673         /* order SACK blocks to allow in order walk of the retrans queue */
1674         for (i = used_sacks - 1; i > 0; i--) {
1675                 for (j = 0; j < i; j++) {
1676                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1677                                 swap(sp[j], sp[j + 1]);
1678 
1679                                 /* Track where the first SACK block goes to */
1680                                 if (j == first_sack_index)
1681                                         first_sack_index = j + 1;
1682                         }
1683                 }
1684         }
1685 
1686         skb = tcp_write_queue_head(sk);
1687         state->fack_count = 0;
1688         i = 0;
1689 
1690         if (!tp->sacked_out) {
1691                 /* It's already past, so skip checking against it */
1692                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1693         } else {
1694                 cache = tp->recv_sack_cache;
1695                 /* Skip empty blocks in at head of the cache */
1696                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1697                        !cache->end_seq)
1698                         cache++;
1699         }
1700 
1701         while (i < used_sacks) {
1702                 u32 start_seq = sp[i].start_seq;
1703                 u32 end_seq = sp[i].end_seq;
1704                 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1705                 struct tcp_sack_block *next_dup = NULL;
1706 
1707                 if (found_dup_sack && ((i + 1) == first_sack_index))
1708                         next_dup = &sp[i + 1];
1709 
1710                 /* Skip too early cached blocks */
1711                 while (tcp_sack_cache_ok(tp, cache) &&
1712                        !before(start_seq, cache->end_seq))
1713                         cache++;
1714 
1715                 /* Can skip some work by looking recv_sack_cache? */
1716                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1717                     after(end_seq, cache->start_seq)) {
1718 
1719                         /* Head todo? */
1720                         if (before(start_seq, cache->start_seq)) {
1721                                 skb = tcp_sacktag_skip(skb, sk, state,
1722                                                        start_seq);
1723                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1724                                                        state,
1725                                                        start_seq,
1726                                                        cache->start_seq,
1727                                                        dup_sack);
1728                         }
1729 
1730                         /* Rest of the block already fully processed? */
1731                         if (!after(end_seq, cache->end_seq))
1732                                 goto advance_sp;
1733 
1734                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1735                                                        state,
1736                                                        cache->end_seq);
1737 
1738                         /* ...tail remains todo... */
1739                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1740                                 /* ...but better entrypoint exists! */
1741                                 skb = tcp_highest_sack(sk);
1742                                 if (!skb)
1743                                         break;
1744                                 state->fack_count = tp->fackets_out;
1745                                 cache++;
1746                                 goto walk;
1747                         }
1748 
1749                         skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
1750                         /* Check overlap against next cached too (past this one already) */
1751                         cache++;
1752                         continue;
1753                 }
1754 
1755                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1756                         skb = tcp_highest_sack(sk);
1757                         if (!skb)
1758                                 break;
1759                         state->fack_count = tp->fackets_out;
1760                 }
1761                 skb = tcp_sacktag_skip(skb, sk, state, start_seq);
1762 
1763 walk:
1764                 skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1765                                        start_seq, end_seq, dup_sack);
1766 
1767 advance_sp:
1768                 i++;
1769         }
1770 
1771         /* Clear the head of the cache sack blocks so we can skip it next time */
1772         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1773                 tp->recv_sack_cache[i].start_seq = 0;
1774                 tp->recv_sack_cache[i].end_seq = 0;
1775         }
1776         for (j = 0; j < used_sacks; j++)
1777                 tp->recv_sack_cache[i++] = sp[j];
1778 
1779         if ((state->reord < tp->fackets_out) &&
1780             ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1781                 tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
1782 
1783         tcp_verify_left_out(tp);
1784 out:
1785 
1786 #if FASTRETRANS_DEBUG > 0
1787         WARN_ON((int)tp->sacked_out < 0);
1788         WARN_ON((int)tp->lost_out < 0);
1789         WARN_ON((int)tp->retrans_out < 0);
1790         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1791 #endif
1792         return state->flag;
1793 }
1794 
1795 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1796  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1797  */
1798 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1799 {
1800         u32 holes;
1801 
1802         holes = max(tp->lost_out, 1U);
1803         holes = min(holes, tp->packets_out);
1804 
1805         if ((tp->sacked_out + holes) > tp->packets_out) {
1806                 tp->sacked_out = tp->packets_out - holes;
1807                 return true;
1808         }
1809         return false;
1810 }
1811 
1812 /* If we receive more dupacks than we expected counting segments
1813  * in assumption of absent reordering, interpret this as reordering.
1814  * The only another reason could be bug in receiver TCP.
1815  */
1816 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1817 {
1818         struct tcp_sock *tp = tcp_sk(sk);
1819         if (tcp_limit_reno_sacked(tp))
1820                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1821 }
1822 
1823 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1824 
1825 static void tcp_add_reno_sack(struct sock *sk)
1826 {
1827         struct tcp_sock *tp = tcp_sk(sk);
1828         u32 prior_sacked = tp->sacked_out;
1829 
1830         tp->sacked_out++;
1831         tcp_check_reno_reordering(sk, 0);
1832         if (tp->sacked_out > prior_sacked)
1833                 tp->delivered++; /* Some out-of-order packet is delivered */
1834         tcp_verify_left_out(tp);
1835 }
1836 
1837 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1838 
1839 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1840 {
1841         struct tcp_sock *tp = tcp_sk(sk);
1842 
1843         if (acked > 0) {
1844                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1845                 tp->delivered += max_t(int, acked - tp->sacked_out, 1);
1846                 if (acked - 1 >= tp->sacked_out)
1847                         tp->sacked_out = 0;
1848                 else
1849                         tp->sacked_out -= acked - 1;
1850         }
1851         tcp_check_reno_reordering(sk, acked);
1852         tcp_verify_left_out(tp);
1853 }
1854 
1855 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1856 {
1857         tp->sacked_out = 0;
1858 }
1859 
1860 void tcp_clear_retrans(struct tcp_sock *tp)
1861 {
1862         tp->retrans_out = 0;
1863         tp->lost_out = 0;
1864         tp->undo_marker = 0;
1865         tp->undo_retrans = -1;
1866         tp->fackets_out = 0;
1867         tp->sacked_out = 0;
1868 }
1869 
1870 static inline void tcp_init_undo(struct tcp_sock *tp)
1871 {
1872         tp->undo_marker = tp->snd_una;
1873         /* Retransmission still in flight may cause DSACKs later. */
1874         tp->undo_retrans = tp->retrans_out ? : -1;
1875 }
1876 
1877 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
1878  * and reset tags completely, otherwise preserve SACKs. If receiver
1879  * dropped its ofo queue, we will know this due to reneging detection.
1880  */
1881 void tcp_enter_loss(struct sock *sk)
1882 {
1883         const struct inet_connection_sock *icsk = inet_csk(sk);
1884         struct tcp_sock *tp = tcp_sk(sk);
1885         struct net *net = sock_net(sk);
1886         struct sk_buff *skb;
1887         bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1888         bool is_reneg;                  /* is receiver reneging on SACKs? */
1889 
1890         /* Reduce ssthresh if it has not yet been made inside this window. */
1891         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1892             !after(tp->high_seq, tp->snd_una) ||
1893             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1894                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1895                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1896                 tcp_ca_event(sk, CA_EVENT_LOSS);
1897                 tcp_init_undo(tp);
1898         }
1899         tp->snd_cwnd       = 1;
1900         tp->snd_cwnd_cnt   = 0;
1901         tp->snd_cwnd_stamp = tcp_time_stamp;
1902 
1903         tp->retrans_out = 0;
1904         tp->lost_out = 0;
1905 
1906         if (tcp_is_reno(tp))
1907                 tcp_reset_reno_sack(tp);
1908 
1909         skb = tcp_write_queue_head(sk);
1910         is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
1911         if (is_reneg) {
1912                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1913                 tp->sacked_out = 0;
1914                 tp->fackets_out = 0;
1915         }
1916         tcp_clear_all_retrans_hints(tp);
1917 
1918         tcp_for_write_queue(skb, sk) {
1919                 if (skb == tcp_send_head(sk))
1920                         break;
1921 
1922                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1923                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
1924                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1925                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1926                         tp->lost_out += tcp_skb_pcount(skb);
1927                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1928                 }
1929         }
1930         tcp_verify_left_out(tp);
1931 
1932         /* Timeout in disordered state after receiving substantial DUPACKs
1933          * suggests that the degree of reordering is over-estimated.
1934          */
1935         if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1936             tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
1937                 tp->reordering = min_t(unsigned int, tp->reordering,
1938                                        net->ipv4.sysctl_tcp_reordering);
1939         tcp_set_ca_state(sk, TCP_CA_Loss);
1940         tp->high_seq = tp->snd_nxt;
1941         tcp_ecn_queue_cwr(tp);
1942 
1943         /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1944          * loss recovery is underway except recurring timeout(s) on
1945          * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1946          */
1947         tp->frto = sysctl_tcp_frto &&
1948                    (new_recovery || icsk->icsk_retransmits) &&
1949                    !inet_csk(sk)->icsk_mtup.probe_size;
1950 }
1951 
1952 /* If ACK arrived pointing to a remembered SACK, it means that our
1953  * remembered SACKs do not reflect real state of receiver i.e.
1954  * receiver _host_ is heavily congested (or buggy).
1955  *
1956  * To avoid big spurious retransmission bursts due to transient SACK
1957  * scoreboard oddities that look like reneging, we give the receiver a
1958  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
1959  * restore sanity to the SACK scoreboard. If the apparent reneging
1960  * persists until this RTO then we'll clear the SACK scoreboard.
1961  */
1962 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
1963 {
1964         if (flag & FLAG_SACK_RENEGING) {
1965                 struct tcp_sock *tp = tcp_sk(sk);
1966                 unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
1967                                           msecs_to_jiffies(10));
1968 
1969                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1970                                           delay, TCP_RTO_MAX);
1971                 return true;
1972         }
1973         return false;
1974 }
1975 
1976 static inline int tcp_fackets_out(const struct tcp_sock *tp)
1977 {
1978         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
1979 }
1980 
1981 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
1982  * counter when SACK is enabled (without SACK, sacked_out is used for
1983  * that purpose).
1984  *
1985  * Instead, with FACK TCP uses fackets_out that includes both SACKed
1986  * segments up to the highest received SACK block so far and holes in
1987  * between them.
1988  *
1989  * With reordering, holes may still be in flight, so RFC3517 recovery
1990  * uses pure sacked_out (total number of SACKed segments) even though
1991  * it violates the RFC that uses duplicate ACKs, often these are equal
1992  * but when e.g. out-of-window ACKs or packet duplication occurs,
1993  * they differ. Since neither occurs due to loss, TCP should really
1994  * ignore them.
1995  */
1996 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
1997 {
1998         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
1999 }
2000 
2001 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
2002 {
2003         struct tcp_sock *tp = tcp_sk(sk);
2004         unsigned long delay;
2005 
2006         /* Delay early retransmit and entering fast recovery for
2007          * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
2008          * available, or RTO is scheduled to fire first.
2009          */
2010         if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2011             (flag & FLAG_ECE) || !tp->srtt_us)
2012                 return false;
2013 
2014         delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
2015                     msecs_to_jiffies(2));
2016 
2017         if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2018                 return false;
2019 
2020         inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2021                                   TCP_RTO_MAX);
2022         return true;
2023 }
2024 
2025 /* Linux NewReno/SACK/FACK/ECN state machine.
2026  * --------------------------------------
2027  *
2028  * "Open"       Normal state, no dubious events, fast path.
2029  * "Disorder"   In all the respects it is "Open",
2030  *              but requires a bit more attention. It is entered when
2031  *              we see some SACKs or dupacks. It is split of "Open"
2032  *              mainly to move some processing from fast path to slow one.
2033  * "CWR"        CWND was reduced due to some Congestion Notification event.
2034  *              It can be ECN, ICMP source quench, local device congestion.
2035  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2036  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2037  *
2038  * tcp_fastretrans_alert() is entered:
2039  * - each incoming ACK, if state is not "Open"
2040  * - when arrived ACK is unusual, namely:
2041  *      * SACK
2042  *      * Duplicate ACK.
2043  *      * ECN ECE.
2044  *
2045  * Counting packets in flight is pretty simple.
2046  *
2047  *      in_flight = packets_out - left_out + retrans_out
2048  *
2049  *      packets_out is SND.NXT-SND.UNA counted in packets.
2050  *
2051  *      retrans_out is number of retransmitted segments.
2052  *
2053  *      left_out is number of segments left network, but not ACKed yet.
2054  *
2055  *              left_out = sacked_out + lost_out
2056  *
2057  *     sacked_out: Packets, which arrived to receiver out of order
2058  *                 and hence not ACKed. With SACKs this number is simply
2059  *                 amount of SACKed data. Even without SACKs
2060  *                 it is easy to give pretty reliable estimate of this number,
2061  *                 counting duplicate ACKs.
2062  *
2063  *       lost_out: Packets lost by network. TCP has no explicit
2064  *                 "loss notification" feedback from network (for now).
2065  *                 It means that this number can be only _guessed_.
2066  *                 Actually, it is the heuristics to predict lossage that
2067  *                 distinguishes different algorithms.
2068  *
2069  *      F.e. after RTO, when all the queue is considered as lost,
2070  *      lost_out = packets_out and in_flight = retrans_out.
2071  *
2072  *              Essentially, we have now two algorithms counting
2073  *              lost packets.
2074  *
2075  *              FACK: It is the simplest heuristics. As soon as we decided
2076  *              that something is lost, we decide that _all_ not SACKed
2077  *              packets until the most forward SACK are lost. I.e.
2078  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2079  *              It is absolutely correct estimate, if network does not reorder
2080  *              packets. And it loses any connection to reality when reordering
2081  *              takes place. We use FACK by default until reordering
2082  *              is suspected on the path to this destination.
2083  *
2084  *              NewReno: when Recovery is entered, we assume that one segment
2085  *              is lost (classic Reno). While we are in Recovery and
2086  *              a partial ACK arrives, we assume that one more packet
2087  *              is lost (NewReno). This heuristics are the same in NewReno
2088  *              and SACK.
2089  *
2090  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2091  *  deflation etc. CWND is real congestion window, never inflated, changes
2092  *  only according to classic VJ rules.
2093  *
2094  * Really tricky (and requiring careful tuning) part of algorithm
2095  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2096  * The first determines the moment _when_ we should reduce CWND and,
2097  * hence, slow down forward transmission. In fact, it determines the moment
2098  * when we decide that hole is caused by loss, rather than by a reorder.
2099  *
2100  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2101  * holes, caused by lost packets.
2102  *
2103  * And the most logically complicated part of algorithm is undo
2104  * heuristics. We detect false retransmits due to both too early
2105  * fast retransmit (reordering) and underestimated RTO, analyzing
2106  * timestamps and D-SACKs. When we detect that some segments were
2107  * retransmitted by mistake and CWND reduction was wrong, we undo
2108  * window reduction and abort recovery phase. This logic is hidden
2109  * inside several functions named tcp_try_undo_<something>.
2110  */
2111 
2112 /* This function decides, when we should leave Disordered state
2113  * and enter Recovery phase, reducing congestion window.
2114  *
2115  * Main question: may we further continue forward transmission
2116  * with the same cwnd?
2117  */
2118 static bool tcp_time_to_recover(struct sock *sk, int flag)
2119 {
2120         struct tcp_sock *tp = tcp_sk(sk);
2121         __u32 packets_out;
2122         int tcp_reordering = sock_net(sk)->ipv4.sysctl_tcp_reordering;
2123 
2124         /* Trick#1: The loss is proven. */
2125         if (tp->lost_out)
2126                 return true;
2127 
2128         /* Not-A-Trick#2 : Classic rule... */
2129         if (tcp_dupack_heuristics(tp) > tp->reordering)
2130                 return true;
2131 
2132         /* Trick#4: It is still not OK... But will it be useful to delay
2133          * recovery more?
2134          */
2135         packets_out = tp->packets_out;
2136         if (packets_out <= tp->reordering &&
2137             tp->sacked_out >= max_t(__u32, packets_out/2, tcp_reordering) &&
2138             !tcp_may_send_now(sk)) {
2139                 /* We have nothing to send. This connection is limited
2140                  * either by receiver window or by application.
2141                  */
2142                 return true;
2143         }
2144 
2145         /* If a thin stream is detected, retransmit after first
2146          * received dupack. Employ only if SACK is supported in order
2147          * to avoid possible corner-case series of spurious retransmissions
2148          * Use only if there are no unsent data.
2149          */
2150         if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2151             tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2152             tcp_is_sack(tp) && !tcp_send_head(sk))
2153                 return true;
2154 
2155         /* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
2156          * retransmissions due to small network reorderings, we implement
2157          * Mitigation A.3 in the RFC and delay the retransmission for a short
2158          * interval if appropriate.
2159          */
2160         if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2161             (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2162             !tcp_may_send_now(sk))
2163                 return !tcp_pause_early_retransmit(sk, flag);
2164 
2165         return false;
2166 }
2167 
2168 /* Detect loss in event "A" above by marking head of queue up as lost.
2169  * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2170  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2171  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2172  * the maximum SACKed segments to pass before reaching this limit.
2173  */
2174 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2175 {
2176         struct tcp_sock *tp = tcp_sk(sk);
2177         struct sk_buff *skb;
2178         int cnt, oldcnt, lost;
2179         unsigned int mss;
2180         /* Use SACK to deduce losses of new sequences sent during recovery */
2181         const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2182 
2183         WARN_ON(packets > tp->packets_out);
2184         if (tp->lost_skb_hint) {
2185                 skb = tp->lost_skb_hint;
2186                 cnt = tp->lost_cnt_hint;
2187                 /* Head already handled? */
2188                 if (mark_head && skb != tcp_write_queue_head(sk))
2189                         return;
2190         } else {
2191                 skb = tcp_write_queue_head(sk);
2192                 cnt = 0;
2193         }
2194 
2195         tcp_for_write_queue_from(skb, sk) {
2196                 if (skb == tcp_send_head(sk))
2197                         break;
2198                 /* TODO: do this better */
2199                 /* this is not the most efficient way to do this... */
2200                 tp->lost_skb_hint = skb;
2201                 tp->lost_cnt_hint = cnt;
2202 
2203                 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2204                         break;
2205 
2206                 oldcnt = cnt;
2207                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2208                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2209                         cnt += tcp_skb_pcount(skb);
2210 
2211                 if (cnt > packets) {
2212                         if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2213                             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2214                             (oldcnt >= packets))
2215                                 break;
2216 
2217                         mss = tcp_skb_mss(skb);
2218                         /* If needed, chop off the prefix to mark as lost. */
2219                         lost = (packets - oldcnt) * mss;
2220                         if (lost < skb->len &&
2221                             tcp_fragment(sk, skb, lost, mss, GFP_ATOMIC) < 0)
2222                                 break;
2223                         cnt = packets;
2224                 }
2225 
2226                 tcp_skb_mark_lost(tp, skb);
2227 
2228                 if (mark_head)
2229                         break;
2230         }
2231         tcp_verify_left_out(tp);
2232 }
2233 
2234 /* Account newly detected lost packet(s) */
2235 
2236 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2237 {
2238         struct tcp_sock *tp = tcp_sk(sk);
2239 
2240         if (tcp_is_reno(tp)) {
2241                 tcp_mark_head_lost(sk, 1, 1);
2242         } else if (tcp_is_fack(tp)) {
2243                 int lost = tp->fackets_out - tp->reordering;
2244                 if (lost <= 0)
2245                         lost = 1;
2246                 tcp_mark_head_lost(sk, lost, 0);
2247         } else {
2248                 int sacked_upto = tp->sacked_out - tp->reordering;
2249                 if (sacked_upto >= 0)
2250                         tcp_mark_head_lost(sk, sacked_upto, 0);
2251                 else if (fast_rexmit)
2252                         tcp_mark_head_lost(sk, 1, 1);
2253         }
2254 }
2255 
2256 /* CWND moderation, preventing bursts due to too big ACKs
2257  * in dubious situations.
2258  */
2259 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2260 {
2261         tp->snd_cwnd = min(tp->snd_cwnd,
2262                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2263         tp->snd_cwnd_stamp = tcp_time_stamp;
2264 }
2265 
2266 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2267 {
2268         return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2269                before(tp->rx_opt.rcv_tsecr, when);
2270 }
2271 
2272 /* skb is spurious retransmitted if the returned timestamp echo
2273  * reply is prior to the skb transmission time
2274  */
2275 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2276                                      const struct sk_buff *skb)
2277 {
2278         return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2279                tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2280 }
2281 
2282 /* Nothing was retransmitted or returned timestamp is less
2283  * than timestamp of the first retransmission.
2284  */
2285 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2286 {
2287         return !tp->retrans_stamp ||
2288                tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2289 }
2290 
2291 /* Undo procedures. */
2292 
2293 /* We can clear retrans_stamp when there are no retransmissions in the
2294  * window. It would seem that it is trivially available for us in
2295  * tp->retrans_out, however, that kind of assumptions doesn't consider
2296  * what will happen if errors occur when sending retransmission for the
2297  * second time. ...It could the that such segment has only
2298  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2299  * the head skb is enough except for some reneging corner cases that
2300  * are not worth the effort.
2301  *
2302  * Main reason for all this complexity is the fact that connection dying
2303  * time now depends on the validity of the retrans_stamp, in particular,
2304  * that successive retransmissions of a segment must not advance
2305  * retrans_stamp under any conditions.
2306  */
2307 static bool tcp_any_retrans_done(const struct sock *sk)
2308 {
2309         const struct tcp_sock *tp = tcp_sk(sk);
2310         struct sk_buff *skb;
2311 
2312         if (tp->retrans_out)
2313                 return true;
2314 
2315         skb = tcp_write_queue_head(sk);
2316         if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2317                 return true;
2318 
2319         return false;
2320 }
2321 
2322 #if FASTRETRANS_DEBUG > 1
2323 static void DBGUNDO(struct sock *sk, const char *msg)
2324 {
2325         struct tcp_sock *tp = tcp_sk(sk);
2326         struct inet_sock *inet = inet_sk(sk);
2327 
2328         if (sk->sk_family == AF_INET) {
2329                 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2330                          msg,
2331                          &inet->inet_daddr, ntohs(inet->inet_dport),
2332                          tp->snd_cwnd, tcp_left_out(tp),
2333                          tp->snd_ssthresh, tp->prior_ssthresh,
2334                          tp->packets_out);
2335         }
2336 #if IS_ENABLED(CONFIG_IPV6)
2337         else if (sk->sk_family == AF_INET6) {
2338                 struct ipv6_pinfo *np = inet6_sk(sk);
2339                 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2340                          msg,
2341                          &np->daddr, ntohs(inet->inet_dport),
2342                          tp->snd_cwnd, tcp_left_out(tp),
2343                          tp->snd_ssthresh, tp->prior_ssthresh,
2344                          tp->packets_out);
2345         }
2346 #endif
2347 }
2348 #else
2349 #define DBGUNDO(x...) do { } while (0)
2350 #endif
2351 
2352 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2353 {
2354         struct tcp_sock *tp = tcp_sk(sk);
2355 
2356         if (unmark_loss) {
2357                 struct sk_buff *skb;
2358 
2359                 tcp_for_write_queue(skb, sk) {
2360                         if (skb == tcp_send_head(sk))
2361                                 break;
2362                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2363                 }
2364                 tp->lost_out = 0;
2365                 tcp_clear_all_retrans_hints(tp);
2366         }
2367 
2368         if (tp->prior_ssthresh) {
2369                 const struct inet_connection_sock *icsk = inet_csk(sk);
2370 
2371                 if (icsk->icsk_ca_ops->undo_cwnd)
2372                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2373                 else
2374                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2375 
2376                 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2377                         tp->snd_ssthresh = tp->prior_ssthresh;
2378                         tcp_ecn_withdraw_cwr(tp);
2379                 }
2380         }
2381         tp->snd_cwnd_stamp = tcp_time_stamp;
2382         tp->undo_marker = 0;
2383 }
2384 
2385 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2386 {
2387         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2388 }
2389 
2390 /* People celebrate: "We love our President!" */
2391 static bool tcp_try_undo_recovery(struct sock *sk)
2392 {
2393         struct tcp_sock *tp = tcp_sk(sk);
2394 
2395         if (tcp_may_undo(tp)) {
2396                 int mib_idx;
2397 
2398                 /* Happy end! We did not retransmit anything
2399                  * or our original transmission succeeded.
2400                  */
2401                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2402                 tcp_undo_cwnd_reduction(sk, false);
2403                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2404                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2405                 else
2406                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2407 
2408                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2409         }
2410         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2411                 /* Hold old state until something *above* high_seq
2412                  * is ACKed. For Reno it is MUST to prevent false
2413                  * fast retransmits (RFC2582). SACK TCP is safe. */
2414                 tcp_moderate_cwnd(tp);
2415                 if (!tcp_any_retrans_done(sk))
2416                         tp->retrans_stamp = 0;
2417                 return true;
2418         }
2419         tcp_set_ca_state(sk, TCP_CA_Open);
2420         return false;
2421 }
2422 
2423 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2424 static bool tcp_try_undo_dsack(struct sock *sk)
2425 {
2426         struct tcp_sock *tp = tcp_sk(sk);
2427 
2428         if (tp->undo_marker && !tp->undo_retrans) {
2429                 DBGUNDO(sk, "D-SACK");
2430                 tcp_undo_cwnd_reduction(sk, false);
2431                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2432                 return true;
2433         }
2434         return false;
2435 }
2436 
2437 /* Undo during loss recovery after partial ACK or using F-RTO. */
2438 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2439 {
2440         struct tcp_sock *tp = tcp_sk(sk);
2441 
2442         if (frto_undo || tcp_may_undo(tp)) {
2443                 tcp_undo_cwnd_reduction(sk, true);
2444 
2445                 DBGUNDO(sk, "partial loss");
2446                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2447                 if (frto_undo)
2448                         NET_INC_STATS_BH(sock_net(sk),
2449                                          LINUX_MIB_TCPSPURIOUSRTOS);
2450                 inet_csk(sk)->icsk_retransmits = 0;
2451                 if (frto_undo || tcp_is_sack(tp))
2452                         tcp_set_ca_state(sk, TCP_CA_Open);
2453                 return true;
2454         }
2455         return false;
2456 }
2457 
2458 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2459  * It computes the number of packets to send (sndcnt) based on packets newly
2460  * delivered:
2461  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2462  *      cwnd reductions across a full RTT.
2463  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2464  *      But when the retransmits are acked without further losses, PRR
2465  *      slow starts cwnd up to ssthresh to speed up the recovery.
2466  */
2467 static void tcp_init_cwnd_reduction(struct sock *sk)
2468 {
2469         struct tcp_sock *tp = tcp_sk(sk);
2470 
2471         tp->high_seq = tp->snd_nxt;
2472         tp->tlp_high_seq = 0;
2473         tp->snd_cwnd_cnt = 0;
2474         tp->prior_cwnd = tp->snd_cwnd;
2475         tp->prr_delivered = 0;
2476         tp->prr_out = 0;
2477         tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2478         tcp_ecn_queue_cwr(tp);
2479 }
2480 
2481 static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
2482                                int flag)
2483 {
2484         struct tcp_sock *tp = tcp_sk(sk);
2485         int sndcnt = 0;
2486         int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2487 
2488         if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2489                 return;
2490 
2491         tp->prr_delivered += newly_acked_sacked;
2492         if (delta < 0) {
2493                 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2494                                tp->prior_cwnd - 1;
2495                 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2496         } else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
2497                    !(flag & FLAG_LOST_RETRANS)) {
2498                 sndcnt = min_t(int, delta,
2499                                max_t(int, tp->prr_delivered - tp->prr_out,
2500                                      newly_acked_sacked) + 1);
2501         } else {
2502                 sndcnt = min(delta, newly_acked_sacked);
2503         }
2504         /* Force a fast retransmit upon entering fast recovery */
2505         sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2506         tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2507 }
2508 
2509 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2510 {
2511         struct tcp_sock *tp = tcp_sk(sk);
2512 
2513         /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2514         if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2515             (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2516                 tp->snd_cwnd = tp->snd_ssthresh;
2517                 tp->snd_cwnd_stamp = tcp_time_stamp;
2518         }
2519         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2520 }
2521 
2522 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2523 void tcp_enter_cwr(struct sock *sk)
2524 {
2525         struct tcp_sock *tp = tcp_sk(sk);
2526 
2527         tp->prior_ssthresh = 0;
2528         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2529                 tp->undo_marker = 0;
2530                 tcp_init_cwnd_reduction(sk);
2531                 tcp_set_ca_state(sk, TCP_CA_CWR);
2532         }
2533 }
2534 EXPORT_SYMBOL(tcp_enter_cwr);
2535 
2536 static void tcp_try_keep_open(struct sock *sk)
2537 {
2538         struct tcp_sock *tp = tcp_sk(sk);
2539         int state = TCP_CA_Open;
2540 
2541         if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2542                 state = TCP_CA_Disorder;
2543 
2544         if (inet_csk(sk)->icsk_ca_state != state) {
2545                 tcp_set_ca_state(sk, state);
2546                 tp->high_seq = tp->snd_nxt;
2547         }
2548 }
2549 
2550 static void tcp_try_to_open(struct sock *sk, int flag)
2551 {
2552         struct tcp_sock *tp = tcp_sk(sk);
2553 
2554         tcp_verify_left_out(tp);
2555 
2556         if (!tcp_any_retrans_done(sk))
2557                 tp->retrans_stamp = 0;
2558 
2559         if (flag & FLAG_ECE)
2560                 tcp_enter_cwr(sk);
2561 
2562         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2563                 tcp_try_keep_open(sk);
2564         }
2565 }
2566 
2567 static void tcp_mtup_probe_failed(struct sock *sk)
2568 {
2569         struct inet_connection_sock *icsk = inet_csk(sk);
2570 
2571         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2572         icsk->icsk_mtup.probe_size = 0;
2573         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2574 }
2575 
2576 static void tcp_mtup_probe_success(struct sock *sk)
2577 {
2578         struct tcp_sock *tp = tcp_sk(sk);
2579         struct inet_connection_sock *icsk = inet_csk(sk);
2580 
2581         /* FIXME: breaks with very large cwnd */
2582         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2583         tp->snd_cwnd = tp->snd_cwnd *
2584                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2585                        icsk->icsk_mtup.probe_size;
2586         tp->snd_cwnd_cnt = 0;
2587         tp->snd_cwnd_stamp = tcp_time_stamp;
2588         tp->snd_ssthresh = tcp_current_ssthresh(sk);
2589 
2590         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2591         icsk->icsk_mtup.probe_size = 0;
2592         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2593         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2594 }
2595 
2596 /* Do a simple retransmit without using the backoff mechanisms in
2597  * tcp_timer. This is used for path mtu discovery.
2598  * The socket is already locked here.
2599  */
2600 void tcp_simple_retransmit(struct sock *sk)
2601 {
2602         const struct inet_connection_sock *icsk = inet_csk(sk);
2603         struct tcp_sock *tp = tcp_sk(sk);
2604         struct sk_buff *skb;
2605         unsigned int mss = tcp_current_mss(sk);
2606         u32 prior_lost = tp->lost_out;
2607 
2608         tcp_for_write_queue(skb, sk) {
2609                 if (skb == tcp_send_head(sk))
2610                         break;
2611                 if (tcp_skb_seglen(skb) > mss &&
2612                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2613                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2614                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2615                                 tp->retrans_out -= tcp_skb_pcount(skb);
2616                         }
2617                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2618                 }
2619         }
2620 
2621         tcp_clear_retrans_hints_partial(tp);
2622 
2623         if (prior_lost == tp->lost_out)
2624                 return;
2625 
2626         if (tcp_is_reno(tp))
2627                 tcp_limit_reno_sacked(tp);
2628 
2629         tcp_verify_left_out(tp);
2630 
2631         /* Don't muck with the congestion window here.
2632          * Reason is that we do not increase amount of _data_
2633          * in network, but units changed and effective
2634          * cwnd/ssthresh really reduced now.
2635          */
2636         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2637                 tp->high_seq = tp->snd_nxt;
2638                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2639                 tp->prior_ssthresh = 0;
2640                 tp->undo_marker = 0;
2641                 tcp_set_ca_state(sk, TCP_CA_Loss);
2642         }
2643         tcp_xmit_retransmit_queue(sk);
2644 }
2645 EXPORT_SYMBOL(tcp_simple_retransmit);
2646 
2647 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2648 {
2649         struct tcp_sock *tp = tcp_sk(sk);
2650         int mib_idx;
2651 
2652         if (tcp_is_reno(tp))
2653                 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2654         else
2655                 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2656 
2657         NET_INC_STATS_BH(sock_net(sk), mib_idx);
2658 
2659         tp->prior_ssthresh = 0;
2660         tcp_init_undo(tp);
2661 
2662         if (!tcp_in_cwnd_reduction(sk)) {
2663                 if (!ece_ack)
2664                         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2665                 tcp_init_cwnd_reduction(sk);
2666         }
2667         tcp_set_ca_state(sk, TCP_CA_Recovery);
2668 }
2669 
2670 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2671  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2672  */
2673 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
2674                              int *rexmit)
2675 {
2676         struct tcp_sock *tp = tcp_sk(sk);
2677         bool recovered = !before(tp->snd_una, tp->high_seq);
2678 
2679         if ((flag & FLAG_SND_UNA_ADVANCED) &&
2680             tcp_try_undo_loss(sk, false))
2681                 return;
2682 
2683         if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2684                 /* Step 3.b. A timeout is spurious if not all data are
2685                  * lost, i.e., never-retransmitted data are (s)acked.
2686                  */
2687                 if ((flag & FLAG_ORIG_SACK_ACKED) &&
2688                     tcp_try_undo_loss(sk, true))
2689                         return;
2690 
2691                 if (after(tp->snd_nxt, tp->high_seq)) {
2692                         if (flag & FLAG_DATA_SACKED || is_dupack)
2693                                 tp->frto = 0; /* Step 3.a. loss was real */
2694                 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2695                         tp->high_seq = tp->snd_nxt;
2696                         /* Step 2.b. Try send new data (but deferred until cwnd
2697                          * is updated in tcp_ack()). Otherwise fall back to
2698                          * the conventional recovery.
2699                          */
2700                         if (tcp_send_head(sk) &&
2701                             after(tcp_wnd_end(tp), tp->snd_nxt)) {
2702                                 *rexmit = REXMIT_NEW;
2703                                 return;
2704                         }
2705                         tp->frto = 0;
2706                 }
2707         }
2708 
2709         if (recovered) {
2710                 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2711                 tcp_try_undo_recovery(sk);
2712                 return;
2713         }
2714         if (tcp_is_reno(tp)) {
2715                 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2716                  * delivered. Lower inflight to clock out (re)tranmissions.
2717                  */
2718                 if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2719                         tcp_add_reno_sack(sk);
2720                 else if (flag & FLAG_SND_UNA_ADVANCED)
2721                         tcp_reset_reno_sack(tp);
2722         }
2723         *rexmit = REXMIT_LOST;
2724 }
2725 
2726 /* Undo during fast recovery after partial ACK. */
2727 static bool tcp_try_undo_partial(struct sock *sk, const int acked)
2728 {
2729         struct tcp_sock *tp = tcp_sk(sk);
2730 
2731         if (tp->undo_marker && tcp_packet_delayed(tp)) {
2732                 /* Plain luck! Hole if filled with delayed
2733                  * packet, rather than with a retransmit.
2734                  */
2735                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2736 
2737                 /* We are getting evidence that the reordering degree is higher
2738                  * than we realized. If there are no retransmits out then we
2739                  * can undo. Otherwise we clock out new packets but do not
2740                  * mark more packets lost or retransmit more.
2741                  */
2742                 if (tp->retrans_out)
2743                         return true;
2744 
2745                 if (!tcp_any_retrans_done(sk))
2746                         tp->retrans_stamp = 0;
2747 
2748                 DBGUNDO(sk, "partial recovery");
2749                 tcp_undo_cwnd_reduction(sk, true);
2750                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2751                 tcp_try_keep_open(sk);
2752                 return true;
2753         }
2754         return false;
2755 }
2756 
2757 /* Process an event, which can update packets-in-flight not trivially.
2758  * Main goal of this function is to calculate new estimate for left_out,
2759  * taking into account both packets sitting in receiver's buffer and
2760  * packets lost by network.
2761  *
2762  * Besides that it updates the congestion state when packet loss or ECN
2763  * is detected. But it does not reduce the cwnd, it is done by the
2764  * congestion control later.
2765  *
2766  * It does _not_ decide what to send, it is made in function
2767  * tcp_xmit_retransmit_queue().
2768  */
2769 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2770                                   bool is_dupack, int *ack_flag, int *rexmit)
2771 {
2772         struct inet_connection_sock *icsk = inet_csk(sk);
2773         struct tcp_sock *tp = tcp_sk(sk);
2774         int fast_rexmit = 0, flag = *ack_flag;
2775         bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2776                                     (tcp_fackets_out(tp) > tp->reordering));
2777 
2778         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2779                 tp->sacked_out = 0;
2780         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2781                 tp->fackets_out = 0;
2782 
2783         /* Now state machine starts.
2784          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2785         if (flag & FLAG_ECE)
2786                 tp->prior_ssthresh = 0;
2787 
2788         /* B. In all the states check for reneging SACKs. */
2789         if (tcp_check_sack_reneging(sk, flag))
2790                 return;
2791 
2792         /* C. Check consistency of the current state. */
2793         tcp_verify_left_out(tp);
2794 
2795         /* D. Check state exit conditions. State can be terminated
2796          *    when high_seq is ACKed. */
2797         if (icsk->icsk_ca_state == TCP_CA_Open) {
2798                 WARN_ON(tp->retrans_out != 0);
2799                 tp->retrans_stamp = 0;
2800         } else if (!before(tp->snd_una, tp->high_seq)) {
2801                 switch (icsk->icsk_ca_state) {
2802                 case TCP_CA_CWR:
2803                         /* CWR is to be held something *above* high_seq
2804                          * is ACKed for CWR bit to reach receiver. */
2805                         if (tp->snd_una != tp->high_seq) {
2806                                 tcp_end_cwnd_reduction(sk);
2807                                 tcp_set_ca_state(sk, TCP_CA_Open);
2808                         }
2809                         break;
2810 
2811                 case TCP_CA_Recovery:
2812                         if (tcp_is_reno(tp))
2813                                 tcp_reset_reno_sack(tp);
2814                         if (tcp_try_undo_recovery(sk))
2815                                 return;
2816                         tcp_end_cwnd_reduction(sk);
2817                         break;
2818                 }
2819         }
2820 
2821         /* Use RACK to detect loss */
2822         if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
2823             tcp_rack_mark_lost(sk)) {
2824                 flag |= FLAG_LOST_RETRANS;
2825                 *ack_flag |= FLAG_LOST_RETRANS;
2826         }
2827 
2828         /* E. Process state. */
2829         switch (icsk->icsk_ca_state) {
2830         case TCP_CA_Recovery:
2831                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2832                         if (tcp_is_reno(tp) && is_dupack)
2833                                 tcp_add_reno_sack(sk);
2834                 } else {
2835                         if (tcp_try_undo_partial(sk, acked))
2836                                 return;
2837                         /* Partial ACK arrived. Force fast retransmit. */
2838                         do_lost = tcp_is_reno(tp) ||
2839                                   tcp_fackets_out(tp) > tp->reordering;
2840                 }
2841                 if (tcp_try_undo_dsack(sk)) {
2842                         tcp_try_keep_open(sk);
2843                         return;
2844                 }
2845                 break;
2846         case TCP_CA_Loss:
2847                 tcp_process_loss(sk, flag, is_dupack, rexmit);
2848                 if (icsk->icsk_ca_state != TCP_CA_Open &&
2849                     !(flag & FLAG_LOST_RETRANS))
2850                         return;
2851                 /* Change state if cwnd is undone or retransmits are lost */
2852         default:
2853                 if (tcp_is_reno(tp)) {
2854                         if (flag & FLAG_SND_UNA_ADVANCED)
2855                                 tcp_reset_reno_sack(tp);
2856                         if (is_dupack)
2857                                 tcp_add_reno_sack(sk);
2858                 }
2859 
2860                 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2861                         tcp_try_undo_dsack(sk);
2862 
2863                 if (!tcp_time_to_recover(sk, flag)) {
2864                         tcp_try_to_open(sk, flag);
2865                         return;
2866                 }
2867 
2868                 /* MTU probe failure: don't reduce cwnd */
2869                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2870                     icsk->icsk_mtup.probe_size &&
2871                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2872                         tcp_mtup_probe_failed(sk);
2873                         /* Restores the reduction we did in tcp_mtup_probe() */
2874                         tp->snd_cwnd++;
2875                         tcp_simple_retransmit(sk);
2876                         return;
2877                 }
2878 
2879                 /* Otherwise enter Recovery state */
2880                 tcp_enter_recovery(sk, (flag & FLAG_ECE));
2881                 fast_rexmit = 1;
2882         }
2883 
2884         if (do_lost)
2885                 tcp_update_scoreboard(sk, fast_rexmit);
2886         *rexmit = REXMIT_LOST;
2887 }
2888 
2889 /* Kathleen Nichols' algorithm for tracking the minimum value of
2890  * a data stream over some fixed time interval. (E.g., the minimum
2891  * RTT over the past five minutes.) It uses constant space and constant
2892  * time per update yet almost always delivers the same minimum as an
2893  * implementation that has to keep all the data in the window.
2894  *
2895  * The algorithm keeps track of the best, 2nd best & 3rd best min
2896  * values, maintaining an invariant that the measurement time of the
2897  * n'th best >= n-1'th best. It also makes sure that the three values
2898  * are widely separated in the time window since that bounds the worse
2899  * case error when that data is monotonically increasing over the window.
2900  *
2901  * Upon getting a new min, we can forget everything earlier because it
2902  * has no value - the new min is <= everything else in the window by
2903  * definition and it's the most recent. So we restart fresh on every new min
2904  * and overwrites 2nd & 3rd choices. The same property holds for 2nd & 3rd
2905  * best.
2906  */
2907 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
2908 {
2909         const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ;
2910         struct rtt_meas *m = tcp_sk(sk)->rtt_min;
2911         struct rtt_meas rttm = {
2912                 .rtt = likely(rtt_us) ? rtt_us : jiffies_to_usecs(1),
2913                 .ts = now,
2914         };
2915         u32 elapsed;
2916 
2917         /* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
2918         if (unlikely(rttm.rtt <= m[0].rtt))
2919                 m[0] = m[1] = m[2] = rttm;
2920         else if (rttm.rtt <= m[1].rtt)
2921                 m[1] = m[2] = rttm;
2922         else if (rttm.rtt <= m[2].rtt)
2923                 m[2] = rttm;
2924 
2925         elapsed = now - m[0].ts;
2926         if (unlikely(elapsed > wlen)) {
2927                 /* Passed entire window without a new min so make 2nd choice
2928                  * the new min & 3rd choice the new 2nd. So forth and so on.
2929                  */
2930                 m[0] = m[1];
2931                 m[1] = m[2];
2932                 m[2] = rttm;
2933                 if (now - m[0].ts > wlen) {
2934                         m[0] = m[1];
2935                         m[1] = rttm;
2936                         if (now - m[0].ts > wlen)
2937                                 m[0] = rttm;
2938                 }
2939         } else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
2940                 /* Passed a quarter of the window without a new min so
2941                  * take 2nd choice from the 2nd quarter of the window.
2942                  */
2943                 m[2] = m[1] = rttm;
2944         } else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
2945                 /* Passed half the window without a new min so take the 3rd
2946                  * choice from the last half of the window.
2947                  */
2948                 m[2] = rttm;
2949         }
2950 }
2951 
2952 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2953                                       long seq_rtt_us, long sack_rtt_us,
2954                                       long ca_rtt_us)
2955 {
2956         const struct tcp_sock *tp = tcp_sk(sk);
2957 
2958         /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2959          * broken middle-boxes or peers may corrupt TS-ECR fields. But
2960          * Karn's algorithm forbids taking RTT if some retransmitted data
2961          * is acked (RFC6298).
2962          */
2963         if (seq_rtt_us < 0)
2964                 seq_rtt_us = sack_rtt_us;
2965 
2966         /* RTTM Rule: A TSecr value received in a segment is used to
2967          * update the averaged RTT measurement only if the segment
2968          * acknowledges some new data, i.e., only if it advances the
2969          * left edge of the send window.
2970          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2971          */
2972         if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2973             flag & FLAG_ACKED)
2974                 seq_rtt_us = ca_rtt_us = jiffies_to_usecs(tcp_time_stamp -
2975                                                           tp->rx_opt.rcv_tsecr);
2976         if (seq_rtt_us < 0)
2977                 return false;
2978 
2979         /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2980          * always taken together with ACK, SACK, or TS-opts. Any negative
2981          * values will be skipped with the seq_rtt_us < 0 check above.
2982          */
2983         tcp_update_rtt_min(sk, ca_rtt_us);
2984         tcp_rtt_estimator(sk, seq_rtt_us);
2985         tcp_set_rto(sk);
2986 
2987         /* RFC6298: only reset backoff on valid RTT measurement. */
2988         inet_csk(sk)->icsk_backoff = 0;
2989         return true;
2990 }
2991 
2992 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2993 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2994 {
2995         long rtt_us = -1L;
2996 
2997         if (req && !req->num_retrans && tcp_rsk(req)->snt_synack.v64) {
2998                 struct skb_mstamp now;
2999 
3000                 skb_mstamp_get(&now);
3001                 rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack);
3002         }
3003 
3004         tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us);
3005 }
3006 
3007 
3008 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3009 {
3010         const struct inet_connection_sock *icsk = inet_csk(sk);
3011 
3012         icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3013         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3014 }
3015 
3016 /* Restart timer after forward progress on connection.
3017  * RFC2988 recommends to restart timer to now+rto.
3018  */
3019 void tcp_rearm_rto(struct sock *sk)
3020 {
3021         const struct inet_connection_sock *icsk = inet_csk(sk);
3022         struct tcp_sock *tp = tcp_sk(sk);
3023 
3024         /* If the retrans timer is currently being used by Fast Open
3025          * for SYN-ACK retrans purpose, stay put.
3026          */
3027         if (tp->fastopen_rsk)
3028                 return;
3029 
3030         if (!tp->packets_out) {
3031                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3032         } else {
3033                 u32 rto = inet_csk(sk)->icsk_rto;
3034                 /* Offset the time elapsed after installing regular RTO */
3035                 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3036                     icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3037                         struct sk_buff *skb = tcp_write_queue_head(sk);
3038                         const u32 rto_time_stamp =
3039                                 tcp_skb_timestamp(skb) + rto;
3040                         s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
3041                         /* delta may not be positive if the socket is locked
3042                          * when the retrans timer fires and is rescheduled.
3043                          */
3044                         if (delta > 0)
3045                                 rto = delta;
3046                 }
3047                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3048                                           TCP_RTO_MAX);
3049         }
3050 }
3051 
3052 /* This function is called when the delayed ER timer fires. TCP enters
3053  * fast recovery and performs fast-retransmit.
3054  */
3055 void tcp_resume_early_retransmit(struct sock *sk)
3056 {
3057         struct tcp_sock *tp = tcp_sk(sk);
3058 
3059         tcp_rearm_rto(sk);
3060 
3061         /* Stop if ER is disabled after the delayed ER timer is scheduled */
3062         if (!tp->do_early_retrans)
3063                 return;
3064 
3065         tcp_enter_recovery(sk, false);
3066         tcp_update_scoreboard(sk, 1);
3067         tcp_xmit_retransmit_queue(sk);
3068 }
3069 
3070 /* If we get here, the whole TSO packet has not been acked. */
3071 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3072 {
3073         struct tcp_sock *tp = tcp_sk(sk);
3074         u32 packets_acked;
3075 
3076         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3077 
3078         packets_acked = tcp_skb_pcount(skb);
3079         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3080                 return 0;
3081         packets_acked -= tcp_skb_pcount(skb);
3082 
3083         if (packets_acked) {
3084                 BUG_ON(tcp_skb_pcount(skb) == 0);
3085                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3086         }
3087 
3088         return packets_acked;
3089 }
3090 
3091 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3092                            u32 prior_snd_una)
3093 {
3094         const struct skb_shared_info *shinfo;
3095 
3096         /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3097         if (likely(!(sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK)))
3098                 return;
3099 
3100         shinfo = skb_shinfo(skb);
3101         if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
3102             !before(shinfo->tskey, prior_snd_una) &&
3103             before(shinfo->tskey, tcp_sk(sk)->snd_una))
3104                 __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3105 }
3106 
3107 /* Remove acknowledged frames from the retransmission queue. If our packet
3108  * is before the ack sequence we can discard it as it's confirmed to have
3109  * arrived at the other end.
3110  */
3111 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3112                                u32 prior_snd_una, int *acked,
3113                                struct tcp_sacktag_state *sack)
3114 {
3115         const struct inet_connection_sock *icsk = inet_csk(sk);
3116         struct skb_mstamp first_ackt, last_ackt, now;
3117         struct tcp_sock *tp = tcp_sk(sk);
3118         u32 prior_sacked = tp->sacked_out;
3119         u32 reord = tp->packets_out;
3120         bool fully_acked = true;
3121         long sack_rtt_us = -1L;
3122         long seq_rtt_us = -1L;
3123         long ca_rtt_us = -1L;
3124         struct sk_buff *skb;
3125         u32 pkts_acked = 0;
3126         bool rtt_update;
3127         int flag = 0;
3128 
3129         first_ackt.v64 = 0;
3130 
3131         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3132                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3133                 u8 sacked = scb->sacked;
3134                 u32 acked_pcount;
3135 
3136                 tcp_ack_tstamp(sk, skb, prior_snd_una);
3137 
3138                 /* Determine how many packets and what bytes were acked, tso and else */
3139                 if (after(scb->end_seq, tp->snd_una)) {
3140                         if (tcp_skb_pcount(skb) == 1 ||
3141                             !after(tp->snd_una, scb->seq))
3142                                 break;
3143 
3144                         acked_pcount = tcp_tso_acked(sk, skb);
3145                         if (!acked_pcount)
3146                                 break;
3147 
3148                         fully_acked = false;
3149                 } else {
3150                         /* Speedup tcp_unlink_write_queue() and next loop */
3151                         prefetchw(skb->next);
3152                         acked_pcount = tcp_skb_pcount(skb);
3153                 }
3154 
3155                 if (unlikely(sacked & TCPCB_RETRANS)) {
3156                         if (sacked & TCPCB_SACKED_RETRANS)
3157                                 tp->retrans_out -= acked_pcount;
3158                         flag |= FLAG_RETRANS_DATA_ACKED;
3159                 } else if (!(sacked & TCPCB_SACKED_ACKED)) {
3160                         last_ackt = skb->skb_mstamp;
3161                         WARN_ON_ONCE(last_ackt.v64 == 0);
3162                         if (!first_ackt.v64)
3163                                 first_ackt = last_ackt;
3164 
3165                         reord = min(pkts_acked, reord);
3166                         if (!after(scb->end_seq, tp->high_seq))
3167                                 flag |= FLAG_ORIG_SACK_ACKED;
3168                 }
3169 
3170                 if (sacked & TCPCB_SACKED_ACKED) {
3171                         tp->sacked_out -= acked_pcount;
3172                 } else if (tcp_is_sack(tp)) {
3173                         tp->delivered += acked_pcount;
3174                         if (!tcp_skb_spurious_retrans(tp, skb))
3175                                 tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
3176                 }
3177                 if (sacked & TCPCB_LOST)
3178                         tp->lost_out -= acked_pcount;
3179 
3180                 tp->packets_out -= acked_pcount;
3181                 pkts_acked += acked_pcount;
3182 
3183                 /* Initial outgoing SYN's get put onto the write_queue
3184                  * just like anything else we transmit.  It is not
3185                  * true data, and if we misinform our callers that
3186                  * this ACK acks real data, we will erroneously exit
3187                  * connection startup slow start one packet too
3188                  * quickly.  This is severely frowned upon behavior.
3189                  */
3190                 if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3191                         flag |= FLAG_DATA_ACKED;
3192                 } else {
3193                         flag |= FLAG_SYN_ACKED;
3194                         tp->retrans_stamp = 0;
3195                 }
3196 
3197                 if (!fully_acked)
3198                         break;
3199 
3200                 tcp_unlink_write_queue(skb, sk);
3201                 sk_wmem_free_skb(sk, skb);
3202                 if (unlikely(skb == tp->retransmit_skb_hint))
3203                         tp->retransmit_skb_hint = NULL;
3204                 if (unlikely(skb == tp->lost_skb_hint))
3205                         tp->lost_skb_hint = NULL;
3206         }
3207 
3208         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3209                 tp->snd_up = tp->snd_una;
3210 
3211         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3212                 flag |= FLAG_SACK_RENEGING;
3213 
3214         skb_mstamp_get(&now);
3215         if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3216                 seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
3217                 ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
3218         }
3219         if (sack->first_sackt.v64) {
3220                 sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
3221                 ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
3222         }
3223 
3224         rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3225                                         ca_rtt_us);
3226 
3227         if (flag & FLAG_ACKED) {
3228                 tcp_rearm_rto(sk);
3229                 if (unlikely(icsk->icsk_mtup.probe_size &&
3230                              !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3231                         tcp_mtup_probe_success(sk);
3232                 }
3233 
3234                 if (tcp_is_reno(tp)) {
3235                         tcp_remove_reno_sacks(sk, pkts_acked);
3236                 } else {
3237                         int delta;
3238 
3239                         /* Non-retransmitted hole got filled? That's reordering */
3240                         if (reord < prior_fackets)
3241                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3242 
3243                         delta = tcp_is_fack(tp) ? pkts_acked :
3244                                                   prior_sacked - tp->sacked_out;
3245                         tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3246                 }
3247 
3248                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3249 
3250         } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3251                    sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
3252                 /* Do not re-arm RTO if the sack RTT is measured from data sent
3253                  * after when the head was last (re)transmitted. Otherwise the
3254                  * timeout may continue to extend in loss recovery.
3255                  */
3256                 tcp_rearm_rto(sk);
3257         }
3258 
3259         if (icsk->icsk_ca_ops->pkts_acked)
3260                 icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
3261 
3262 #if FASTRETRANS_DEBUG > 0
3263         WARN_ON((int)tp->sacked_out < 0);
3264         WARN_ON((int)tp->lost_out < 0);
3265         WARN_ON((int)tp->retrans_out < 0);
3266         if (!tp->packets_out && tcp_is_sack(tp)) {
3267                 icsk = inet_csk(sk);
3268                 if (tp->lost_out) {
3269                         pr_debug("Leak l=%u %d\n",
3270                                  tp->lost_out, icsk->icsk_ca_state);
3271                         tp->lost_out = 0;
3272                 }
3273                 if (tp->sacked_out) {
3274                         pr_debug("Leak s=%u %d\n",
3275                                  tp->sacked_out, icsk->icsk_ca_state);
3276                         tp->sacked_out = 0;
3277                 }
3278                 if (tp->retrans_out) {
3279                         pr_debug("Leak r=%u %d\n",
3280                                  tp->retrans_out, icsk->icsk_ca_state);
3281                         tp->retrans_out = 0;
3282                 }
3283         }
3284 #endif
3285         *acked = pkts_acked;
3286         return flag;
3287 }
3288 
3289 static void tcp_ack_probe(struct sock *sk)
3290 {
3291         const struct tcp_sock *tp = tcp_sk(sk);
3292         struct inet_connection_sock *icsk = inet_csk(sk);
3293 
3294         /* Was it a usable window open? */
3295 
3296         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3297                 icsk->icsk_backoff = 0;
3298                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3299                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3300                  * This function is not for random using!
3301                  */
3302         } else {
3303                 unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3304 
3305                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3306                                           when, TCP_RTO_MAX);
3307         }
3308 }
3309 
3310 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3311 {
3312         return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3313                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3314 }
3315 
3316 /* Decide wheather to run the increase function of congestion control. */
3317 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3318 {
3319         /* If reordering is high then always grow cwnd whenever data is
3320          * delivered regardless of its ordering. Otherwise stay conservative
3321          * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3322          * new SACK or ECE mark may first advance cwnd here and later reduce
3323          * cwnd in tcp_fastretrans_alert() based on more states.
3324          */
3325         if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
3326                 return flag & FLAG_FORWARD_PROGRESS;
3327 
3328         return flag & FLAG_DATA_ACKED;
3329 }
3330 
3331 /* The "ultimate" congestion control function that aims to replace the rigid
3332  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3333  * It's called toward the end of processing an ACK with precise rate
3334  * information. All transmission or retransmission are delayed afterwards.
3335  */
3336 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3337                              int flag)
3338 {
3339         if (tcp_in_cwnd_reduction(sk)) {
3340                 /* Reduce cwnd if state mandates */
3341                 tcp_cwnd_reduction(sk, acked_sacked, flag);
3342         } else if (tcp_may_raise_cwnd(sk, flag)) {
3343                 /* Advance cwnd if state allows */
3344                 tcp_cong_avoid(sk, ack, acked_sacked);
3345         }
3346         tcp_update_pacing_rate(sk);
3347 }
3348 
3349 /* Check that window update is acceptable.
3350  * The function assumes that snd_una<=ack<=snd_next.
3351  */
3352 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3353                                         const u32 ack, const u32 ack_seq,
3354                                         const u32 nwin)
3355 {
3356         return  after(ack, tp->snd_una) ||
3357                 after(ack_seq, tp->snd_wl1) ||
3358                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3359 }
3360 
3361 /* If we update tp->snd_una, also update tp->bytes_acked */
3362 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3363 {
3364         u32 delta = ack - tp->snd_una;
3365 
3366         u64_stats_update_begin(&tp->syncp);
3367         tp->bytes_acked += delta;
3368         u64_stats_update_end(&tp->syncp);
3369         tp->snd_una = ack;
3370 }
3371 
3372 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3373 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3374 {
3375         u32 delta = seq - tp->rcv_nxt;
3376 
3377         u64_stats_update_begin(&tp->syncp);
3378         tp->bytes_received += delta;
3379         u64_stats_update_end(&tp->syncp);
3380         tp->rcv_nxt = seq;
3381 }
3382 
3383 /* Update our send window.
3384  *
3385  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3386  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3387  */
3388 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3389                                  u32 ack_seq)
3390 {
3391         struct tcp_sock *tp = tcp_sk(sk);
3392         int flag = 0;
3393         u32 nwin = ntohs(tcp_hdr(skb)->window);
3394 
3395         if (likely(!tcp_hdr(skb)->syn))
3396                 nwin <<= tp->rx_opt.snd_wscale;
3397 
3398         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3399                 flag |= FLAG_WIN_UPDATE;
3400                 tcp_update_wl(tp, ack_seq);
3401 
3402                 if (tp->snd_wnd != nwin) {
3403                         tp->snd_wnd = nwin;
3404 
3405                         /* Note, it is the only place, where
3406                          * fast path is recovered for sending TCP.
3407                          */
3408                         tp->pred_flags = 0;
3409                         tcp_fast_path_check(sk);
3410 
3411                         if (tcp_send_head(sk))
3412                                 tcp_slow_start_after_idle_check(sk);
3413 
3414                         if (nwin > tp->max_window) {
3415                                 tp->max_window = nwin;
3416                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3417                         }
3418                 }
3419         }
3420 
3421         tcp_snd_una_update(tp, ack);
3422 
3423         return flag;
3424 }
3425 
3426 /* Return true if we're currently rate-limiting out-of-window ACKs and
3427  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3428  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3429  * attacks that send repeated SYNs or ACKs for the same connection. To
3430  * do this, we do not send a duplicate SYNACK or ACK if the remote
3431  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3432  */
3433 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3434                           int mib_idx, u32 *last_oow_ack_time)
3435 {
3436         /* Data packets without SYNs are not likely part of an ACK loop. */
3437         if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3438             !tcp_hdr(skb)->syn)
3439                 goto not_rate_limited;
3440 
3441         if (*last_oow_ack_time) {
3442                 s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
3443 
3444                 if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
3445                         NET_INC_STATS_BH(net, mib_idx);
3446                         return true;    /* rate-limited: don't send yet! */
3447                 }
3448         }
3449 
3450         *last_oow_ack_time = tcp_time_stamp;
3451 
3452 not_rate_limited:
3453         return false;   /* not rate-limited: go ahead, send dupack now! */
3454 }
3455 
3456 /* RFC 5961 7 [ACK Throttling] */
3457 static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3458 {
3459         /* unprotected vars, we dont care of overwrites */
3460         static u32 challenge_timestamp;
3461         static unsigned int challenge_count;
3462         struct tcp_sock *tp = tcp_sk(sk);
3463         u32 now;
3464 
3465         /* First check our per-socket dupack rate limit. */
3466         if (tcp_oow_rate_limited(sock_net(sk), skb,
3467                                  LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3468                                  &tp->last_oow_ack_time))
3469                 return;
3470 
3471         /* Then check the check host-wide RFC 5961 rate limit. */
3472         now = jiffies / HZ;
3473         if (now != challenge_timestamp) {
3474                 challenge_timestamp = now;
3475                 challenge_count = 0;
3476         }
3477         if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3478                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3479                 tcp_send_ack(sk);
3480         }
3481 }
3482 
3483 static void tcp_store_ts_recent(struct tcp_sock *tp)
3484 {
3485         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3486         tp->rx_opt.ts_recent_stamp = get_seconds();
3487 }
3488 
3489 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3490 {
3491         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3492                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3493                  * extra check below makes sure this can only happen
3494                  * for pure ACK frames.  -DaveM
3495                  *
3496                  * Not only, also it occurs for expired timestamps.
3497                  */
3498 
3499                 if (tcp_paws_check(&tp->rx_opt, 0))
3500                         tcp_store_ts_recent(tp);
3501         }
3502 }
3503 
3504 /* This routine deals with acks during a TLP episode.
3505  * We mark the end of a TLP episode on receiving TLP dupack or when
3506  * ack is after tlp_high_seq.
3507  * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3508  */
3509 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3510 {
3511         struct tcp_sock *tp = tcp_sk(sk);
3512 
3513         if (before(ack, tp->tlp_high_seq))
3514                 return;
3515 
3516         if (flag & FLAG_DSACKING_ACK) {
3517                 /* This DSACK means original and TLP probe arrived; no loss */
3518                 tp->tlp_high_seq = 0;
3519         } else if (after(ack, tp->tlp_high_seq)) {
3520                 /* ACK advances: there was a loss, so reduce cwnd. Reset
3521                  * tlp_high_seq in tcp_init_cwnd_reduction()
3522                  */
3523                 tcp_init_cwnd_reduction(sk);
3524                 tcp_set_ca_state(sk, TCP_CA_CWR);
3525                 tcp_end_cwnd_reduction(sk);
3526                 tcp_try_keep_open(sk);
3527                 NET_INC_STATS_BH(sock_net(sk),
3528                                  LINUX_MIB_TCPLOSSPROBERECOVERY);
3529         } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3530                              FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3531                 /* Pure dupack: original and TLP probe arrived; no loss */
3532                 tp->tlp_high_seq = 0;
3533         }
3534 }
3535 
3536 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3537 {
3538         const struct inet_connection_sock *icsk = inet_csk(sk);
3539 
3540         if (icsk->icsk_ca_ops->in_ack_event)
3541                 icsk->icsk_ca_ops->in_ack_event(sk, flags);
3542 }
3543 
3544 /* Congestion control has updated the cwnd already. So if we're in
3545  * loss recovery then now we do any new sends (for FRTO) or
3546  * retransmits (for CA_Loss or CA_recovery) that make sense.
3547  */
3548 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3549 {
3550         struct tcp_sock *tp = tcp_sk(sk);
3551 
3552         if (rexmit == REXMIT_NONE)
3553                 return;
3554 
3555         if (unlikely(rexmit == 2)) {
3556                 __tcp_push_pending_frames(sk, tcp_current_mss(sk),
3557                                           TCP_NAGLE_OFF);
3558                 if (after(tp->snd_nxt, tp->high_seq))
3559                         return;
3560                 tp->frto = 0;
3561         }
3562         tcp_xmit_retransmit_queue(sk);
3563 }
3564 
3565 /* This routine deals with incoming acks, but not outgoing ones. */
3566 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3567 {
3568         struct inet_connection_sock *icsk = inet_csk(sk);
3569         struct tcp_sock *tp = tcp_sk(sk);
3570         struct tcp_sacktag_state sack_state;
3571         u32 prior_snd_una = tp->snd_una;
3572         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3573         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3574         bool is_dupack = false;
3575         u32 prior_fackets;
3576         int prior_packets = tp->packets_out;
3577         u32 prior_delivered = tp->delivered;
3578         int acked = 0; /* Number of packets newly acked */
3579         int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3580 
3581         sack_state.first_sackt.v64 = 0;
3582 
3583         /* We very likely will need to access write queue head. */
3584         prefetchw(sk->sk_write_queue.next);
3585 
3586         /* If the ack is older than previous acks
3587          * then we can probably ignore it.
3588          */
3589         if (before(ack, prior_snd_una)) {
3590                 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3591                 if (before(ack, prior_snd_una - tp->max_window)) {
3592                         tcp_send_challenge_ack(sk, skb);
3593                         return -1;
3594                 }
3595                 goto old_ack;
3596         }
3597 
3598         /* If the ack includes data we haven't sent yet, discard
3599          * this segment (RFC793 Section 3.9).
3600          */
3601         if (after(ack, tp->snd_nxt))
3602                 goto invalid_ack;
3603 
3604         if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3605             icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3606                 tcp_rearm_rto(sk);
3607 
3608         if (after(ack, prior_snd_una)) {
3609                 flag |= FLAG_SND_UNA_ADVANCED;
3610                 icsk->icsk_retransmits = 0;
3611         }
3612 
3613         prior_fackets = tp->fackets_out;
3614 
3615         /* ts_recent update must be made after we are sure that the packet
3616          * is in window.
3617          */
3618         if (flag & FLAG_UPDATE_TS_RECENT)
3619                 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3620 
3621         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3622                 /* Window is constant, pure forward advance.
3623                  * No more checks are required.
3624                  * Note, we use the fact that SND.UNA>=SND.WL2.
3625                  */
3626                 tcp_update_wl(tp, ack_seq);
3627                 tcp_snd_una_update(tp, ack);
3628                 flag |= FLAG_WIN_UPDATE;
3629 
3630                 tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3631 
3632                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3633         } else {
3634                 u32 ack_ev_flags = CA_ACK_SLOWPATH;
3635 
3636                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3637                         flag |= FLAG_DATA;
3638                 else
3639                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3640 
3641                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3642 
3643                 if (TCP_SKB_CB(skb)->sacked)
3644                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3645                                                         &sack_state);
3646 
3647                 if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3648                         flag |= FLAG_ECE;
3649                         ack_ev_flags |= CA_ACK_ECE;
3650                 }
3651 
3652                 if (flag & FLAG_WIN_UPDATE)
3653                         ack_ev_flags |= CA_ACK_WIN_UPDATE;
3654 
3655                 tcp_in_ack_event(sk, ack_ev_flags);
3656         }
3657 
3658         /* We passed data and got it acked, remove any soft error
3659          * log. Something worked...
3660          */
3661         sk->sk_err_soft = 0;
3662         icsk->icsk_probes_out = 0;
3663         tp->rcv_tstamp = tcp_time_stamp;
3664         if (!prior_packets)
3665                 goto no_queue;
3666 
3667         /* See if we can take anything off of the retransmit queue. */
3668         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
3669                                     &sack_state);
3670 
3671         if (tcp_ack_is_dubious(sk, flag)) {
3672                 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3673                 tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3674         }
3675         if (tp->tlp_high_seq)
3676                 tcp_process_tlp_ack(sk, ack, flag);
3677 
3678         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3679                 struct dst_entry *dst = __sk_dst_get(sk);
3680                 if (dst)
3681                         dst_confirm(dst);
3682         }
3683 
3684         if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3685                 tcp_schedule_loss_probe(sk);
3686         tcp_cong_control(sk, ack, tp->delivered - prior_delivered, flag);
3687         tcp_xmit_recovery(sk, rexmit);
3688         return 1;
3689 
3690 no_queue:
3691         /* If data was DSACKed, see if we can undo a cwnd reduction. */
3692         if (flag & FLAG_DSACKING_ACK)
3693                 tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3694         /* If this ack opens up a zero window, clear backoff.  It was
3695          * being used to time the probes, and is probably far higher than
3696          * it needs to be for normal retransmission.
3697          */
3698         if (tcp_send_head(sk))
3699                 tcp_ack_probe(sk);
3700 
3701         if (tp->tlp_high_seq)
3702                 tcp_process_tlp_ack(sk, ack, flag);
3703         return 1;
3704 
3705 invalid_ack:
3706         SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3707         return -1;
3708 
3709 old_ack:
3710         /* If data was SACKed, tag it and see if we should send more data.
3711          * If data was DSACKed, see if we can undo a cwnd reduction.
3712          */
3713         if (TCP_SKB_CB(skb)->sacked) {
3714                 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3715                                                 &sack_state);
3716                 tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3717                 tcp_xmit_recovery(sk, rexmit);
3718         }
3719 
3720         SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3721         return 0;
3722 }
3723 
3724 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3725                                       bool syn, struct tcp_fastopen_cookie *foc,
3726                                       bool exp_opt)
3727 {
3728         /* Valid only in SYN or SYN-ACK with an even length.  */
3729         if (!foc || !syn || len < 0 || (len & 1))
3730                 return;
3731 
3732         if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3733             len <= TCP_FASTOPEN_COOKIE_MAX)
3734                 memcpy(foc->val, cookie, len);
3735         else if (len != 0)
3736                 len = -1;
3737         foc->len = len;
3738         foc->exp = exp_opt;
3739 }
3740 
3741 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3742  * But, this can also be called on packets in the established flow when
3743  * the fast version below fails.
3744  */
3745 void tcp_parse_options(const struct sk_buff *skb,
3746                        struct tcp_options_received *opt_rx, int estab,
3747                        struct tcp_fastopen_cookie *foc)
3748 {
3749         const unsigned char *ptr;
3750         const struct tcphdr *th = tcp_hdr(skb);
3751         int length = (th->doff * 4) - sizeof(struct tcphdr);
3752 
3753         ptr = (const unsigned char *)(th + 1);
3754         opt_rx->saw_tstamp = 0;
3755 
3756         while (length > 0) {
3757                 int opcode = *ptr++;
3758                 int opsize;
3759 
3760                 switch (opcode) {
3761                 case TCPOPT_EOL:
3762                         return;
3763                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3764                         length--;
3765                         continue;
3766                 default:
3767                         opsize = *ptr++;
3768                         if (opsize < 2) /* "silly options" */
3769                                 return;
3770                         if (opsize > length)
3771                                 return; /* don't parse partial options */
3772                         switch (opcode) {
3773                         case TCPOPT_MSS:
3774                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3775                                         u16 in_mss = get_unaligned_be16(ptr);
3776                                         if (in_mss) {
3777                                                 if (opt_rx->user_mss &&
3778                                                     opt_rx->user_mss < in_mss)
3779                                                         in_mss = opt_rx->user_mss;
3780                                                 opt_rx->mss_clamp = in_mss;
3781                                         }
3782                                 }
3783                                 break;
3784                         case TCPOPT_WINDOW:
3785                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3786                                     !estab && sysctl_tcp_window_scaling) {
3787                                         __u8 snd_wscale = *(__u8 *)ptr;
3788                                         opt_rx->wscale_ok = 1;
3789                                         if (snd_wscale > 14) {
3790                                                 net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3791                                                                      __func__,
3792                                                                      snd_wscale);
3793                                                 snd_wscale = 14;
3794                                         }
3795                                         opt_rx->snd_wscale = snd_wscale;
3796                                 }
3797                                 break;
3798                         case TCPOPT_TIMESTAMP:
3799                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3800                                     ((estab && opt_rx->tstamp_ok) ||
3801                                      (!estab && sysctl_tcp_timestamps))) {
3802                                         opt_rx->saw_tstamp = 1;
3803                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3804                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3805                                 }
3806                                 break;
3807                         case TCPOPT_SACK_PERM:
3808                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3809                                     !estab && sysctl_tcp_sack) {
3810                                         opt_rx->sack_ok = TCP_SACK_SEEN;
3811                                         tcp_sack_reset(opt_rx);
3812                                 }
3813                                 break;
3814 
3815                         case TCPOPT_SACK:
3816                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3817                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3818                                    opt_rx->sack_ok) {
3819                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3820                                 }
3821                                 break;
3822 #ifdef CONFIG_TCP_MD5SIG
3823                         case TCPOPT_MD5SIG:
3824                                 /*
3825                                  * The MD5 Hash has already been
3826                                  * checked (see tcp_v{4,6}_do_rcv()).
3827                                  */
3828                                 break;
3829 #endif
3830                         case TCPOPT_FASTOPEN:
3831                                 tcp_parse_fastopen_option(
3832                                         opsize - TCPOLEN_FASTOPEN_BASE,
3833                                         ptr, th->syn, foc, false);
3834                                 break;
3835 
3836                         case TCPOPT_EXP:
3837                                 /* Fast Open option shares code 254 using a
3838                                  * 16 bits magic number.
3839                                  */
3840                                 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3841                                     get_unaligned_be16(ptr) ==
3842                                     TCPOPT_FASTOPEN_MAGIC)
3843                                         tcp_parse_fastopen_option(opsize -
3844                                                 TCPOLEN_EXP_FASTOPEN_BASE,
3845                                                 ptr + 2, th->syn, foc, true);
3846                                 break;
3847 
3848                         }
3849                         ptr += opsize-2;
3850                         length -= opsize;
3851                 }
3852         }
3853 }
3854 EXPORT_SYMBOL(tcp_parse_options);
3855 
3856 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3857 {
3858         const __be32 *ptr = (const __be32 *)(th + 1);
3859 
3860         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3861                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3862                 tp->rx_opt.saw_tstamp = 1;
3863                 ++ptr;
3864                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3865                 ++ptr;
3866                 if (*ptr)
3867                         tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3868                 else
3869                         tp->rx_opt.rcv_tsecr = 0;
3870                 return true;
3871         }
3872         return false;
3873 }
3874 
3875 /* Fast parse options. This hopes to only see timestamps.
3876  * If it is wrong it falls back on tcp_parse_options().
3877  */
3878 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3879                                    const struct tcphdr *th, struct tcp_sock *tp)
3880 {
3881         /* In the spirit of fast parsing, compare doff directly to constant
3882          * values.  Because equality is used, short doff can be ignored here.
3883          */
3884         if (th->doff == (sizeof(*th) / 4)) {
3885                 tp->rx_opt.saw_tstamp = 0;
3886                 return false;
3887         } else if (tp->rx_opt.tstamp_ok &&
3888                    th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3889                 if (tcp_parse_aligned_timestamp(tp, th))
3890                         return true;
3891         }
3892 
3893         tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3894         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3895                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3896 
3897         return true;
3898 }
3899 
3900 #ifdef CONFIG_TCP_MD5SIG
3901 /*
3902  * Parse MD5 Signature option
3903  */
3904 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3905 {
3906         int length = (th->doff << 2) - sizeof(*th);
3907         const u8 *ptr = (const u8 *)(th + 1);
3908 
3909         /* If the TCP option is too short, we can short cut */
3910         if (length < TCPOLEN_MD5SIG)
3911                 return NULL;
3912 
3913         while (length > 0) {
3914                 int opcode = *ptr++;
3915                 int opsize;
3916 
3917                 switch (opcode) {
3918                 case TCPOPT_EOL:
3919                         return NULL;
3920                 case TCPOPT_NOP:
3921                         length--;
3922                         continue;
3923                 default:
3924                         opsize = *ptr++;
3925                         if (opsize < 2 || opsize > length)
3926                                 return NULL;
3927                         if (opcode == TCPOPT_MD5SIG)
3928                                 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3929                 }
3930                 ptr += opsize - 2;
3931                 length -= opsize;
3932         }
3933         return NULL;
3934 }
3935 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3936 #endif
3937 
3938 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3939  *
3940  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3941  * it can pass through stack. So, the following predicate verifies that
3942  * this segment is not used for anything but congestion avoidance or
3943  * fast retransmit. Moreover, we even are able to eliminate most of such
3944  * second order effects, if we apply some small "replay" window (~RTO)
3945  * to timestamp space.
3946  *
3947  * All these measures still do not guarantee that we reject wrapped ACKs
3948  * on networks with high bandwidth, when sequence space is recycled fastly,
3949  * but it guarantees that such events will be very rare and do not affect
3950  * connection seriously. This doesn't look nice, but alas, PAWS is really
3951  * buggy extension.
3952  *
3953  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3954  * states that events when retransmit arrives after original data are rare.
3955  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3956  * the biggest problem on large power networks even with minor reordering.
3957  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3958  * up to bandwidth of 18Gigabit/sec. 8) ]
3959  */
3960 
3961 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3962 {
3963         const struct tcp_sock *tp = tcp_sk(sk);
3964         const struct tcphdr *th = tcp_hdr(skb);
3965         u32 seq = TCP_SKB_CB(skb)->seq;
3966         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3967 
3968         return (/* 1. Pure ACK with correct sequence number. */
3969                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3970 
3971                 /* 2. ... and duplicate ACK. */
3972                 ack == tp->snd_una &&
3973 
3974                 /* 3. ... and does not update window. */
3975                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3976 
3977                 /* 4. ... and sits in replay window. */
3978                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3979 }
3980 
3981 static inline bool tcp_paws_discard(const struct sock *sk,
3982                                    const struct sk_buff *skb)
3983 {
3984         const struct tcp_sock *tp = tcp_sk(sk);
3985 
3986         return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3987                !tcp_disordered_ack(sk, skb);
3988 }
3989 
3990 /* Check segment sequence number for validity.
3991  *
3992  * Segment controls are considered valid, if the segment
3993  * fits to the window after truncation to the window. Acceptability
3994  * of data (and SYN, FIN, of course) is checked separately.
3995  * See tcp_data_queue(), for example.
3996  *
3997  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3998  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3999  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4000  * (borrowed from freebsd)
4001  */
4002 
4003 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4004 {
4005         return  !before(end_seq, tp->rcv_wup) &&
4006                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4007 }
4008 
4009 /* When we get a reset we do this. */
4010 void tcp_reset(struct sock *sk)
4011 {
4012         /* We want the right error as BSD sees it (and indeed as we do). */
4013         switch (sk->sk_state) {
4014         case TCP_SYN_SENT:
4015                 sk->sk_err = ECONNREFUSED;
4016                 break;
4017         case TCP_CLOSE_WAIT:
4018                 sk->sk_err = EPIPE;
4019                 break;
4020         case TCP_CLOSE:
4021                 return;
4022         default:
4023                 sk->sk_err = ECONNRESET;
4024         }
4025         /* This barrier is coupled with smp_rmb() in tcp_poll() */
4026         smp_wmb();
4027 
4028         if (!sock_flag(sk, SOCK_DEAD))
4029                 sk->sk_error_report(sk);
4030 
4031         tcp_done(sk);
4032 }
4033 
4034 /*
4035  *      Process the FIN bit. This now behaves as it is supposed to work
4036  *      and the FIN takes effect when it is validly part of sequence
4037  *      space. Not before when we get holes.
4038  *
4039  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4040  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
4041  *      TIME-WAIT)
4042  *
4043  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
4044  *      close and we go into CLOSING (and later onto TIME-WAIT)
4045  *
4046  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4047  */
4048 void tcp_fin(struct sock *sk)
4049 {
4050         struct tcp_sock *tp = tcp_sk(sk);
4051 
4052         inet_csk_schedule_ack(sk);
4053 
4054         sk->sk_shutdown |= RCV_SHUTDOWN;
4055         sock_set_flag(sk, SOCK_DONE);
4056 
4057         switch (sk->sk_state) {
4058         case TCP_SYN_RECV:
4059         case TCP_ESTABLISHED:
4060                 /* Move to CLOSE_WAIT */
4061                 tcp_set_state(sk, TCP_CLOSE_WAIT);
4062                 inet_csk(sk)->icsk_ack.pingpong = 1;
4063                 break;
4064 
4065         case TCP_CLOSE_WAIT:
4066         case TCP_CLOSING:
4067                 /* Received a retransmission of the FIN, do
4068                  * nothing.
4069                  */
4070                 break;
4071         case TCP_LAST_ACK:
4072                 /* RFC793: Remain in the LAST-ACK state. */
4073                 break;
4074 
4075         case TCP_FIN_WAIT1:
4076                 /* This case occurs when a simultaneous close
4077                  * happens, we must ack the received FIN and
4078                  * enter the CLOSING state.
4079                  */
4080                 tcp_send_ack(sk);
4081                 tcp_set_state(sk, TCP_CLOSING);
4082                 break;
4083         case TCP_FIN_WAIT2:
4084                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4085                 tcp_send_ack(sk);
4086                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4087                 break;
4088         default:
4089                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4090                  * cases we should never reach this piece of code.
4091                  */
4092                 pr_err("%s: Impossible, sk->sk_state=%d\n",
4093                        __func__, sk->sk_state);
4094                 break;
4095         }
4096 
4097         /* It _is_ possible, that we have something out-of-order _after_ FIN.
4098          * Probably, we should reset in this case. For now drop them.
4099          */
4100         __skb_queue_purge(&tp->out_of_order_queue);
4101         if (tcp_is_sack(tp))
4102                 tcp_sack_reset(&tp->rx_opt);
4103         sk_mem_reclaim(sk);
4104 
4105         if (!sock_flag(sk, SOCK_DEAD)) {
4106                 sk->sk_state_change(sk);
4107 
4108                 /* Do not send POLL_HUP for half duplex close. */
4109                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4110                     sk->sk_state == TCP_CLOSE)
4111                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4112                 else
4113                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4114         }
4115 }
4116 
4117 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4118                                   u32 end_seq)
4119 {
4120         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4121                 if (before(seq, sp->start_seq))
4122                         sp->start_seq = seq;
4123                 if (after(end_seq, sp->end_seq))
4124                         sp->end_seq = end_seq;
4125                 return true;
4126         }
4127         return false;
4128 }
4129 
4130 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4131 {
4132         struct tcp_sock *tp = tcp_sk(sk);
4133 
4134         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4135                 int mib_idx;
4136 
4137                 if (before(seq, tp->rcv_nxt))
4138                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4139                 else
4140                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4141 
4142                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4143 
4144                 tp->rx_opt.dsack = 1;
4145                 tp->duplicate_sack[0].start_seq = seq;
4146                 tp->duplicate_sack[0].end_seq = end_seq;
4147         }
4148 }
4149 
4150 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4151 {
4152         struct tcp_sock *tp = tcp_sk(sk);
4153 
4154         if (!tp->rx_opt.dsack)
4155                 tcp_dsack_set(sk, seq, end_seq);
4156         else
4157                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4158 }
4159 
4160 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4161 {
4162         struct tcp_sock *tp = tcp_sk(sk);
4163 
4164         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4165             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4166                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4167                 tcp_enter_quickack_mode(sk);
4168 
4169                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4170                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4171 
4172                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4173                                 end_seq = tp->rcv_nxt;
4174                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4175                 }
4176         }
4177 
4178         tcp_send_ack(sk);
4179 }
4180 
4181 /* These routines update the SACK block as out-of-order packets arrive or
4182  * in-order packets close up the sequence space.
4183  */
4184 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4185 {
4186         int this_sack;
4187         struct tcp_sack_block *sp = &tp->selective_acks[0];
4188         struct tcp_sack_block *swalk = sp + 1;
4189 
4190         /* See if the recent change to the first SACK eats into
4191          * or hits the sequence space of other SACK blocks, if so coalesce.
4192          */
4193         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4194                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4195                         int i;
4196 
4197                         /* Zap SWALK, by moving every further SACK up by one slot.
4198                          * Decrease num_sacks.
4199                          */
4200                         tp->rx_opt.num_sacks--;
4201                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4202                                 sp[i] = sp[i + 1];
4203                         continue;
4204                 }
4205                 this_sack++, swalk++;
4206         }
4207 }
4208 
4209 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4210 {
4211         struct tcp_sock *tp = tcp_sk(sk);
4212         struct tcp_sack_block *sp = &tp->selective_acks[0];
4213         int cur_sacks = tp->rx_opt.num_sacks;
4214         int this_sack;
4215 
4216         if (!cur_sacks)
4217                 goto new_sack;
4218 
4219         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4220                 if (tcp_sack_extend(sp, seq, end_seq)) {
4221                         /* Rotate this_sack to the first one. */
4222                         for (; this_sack > 0; this_sack--, sp--)
4223                                 swap(*sp, *(sp - 1));
4224                         if (cur_sacks > 1)
4225                                 tcp_sack_maybe_coalesce(tp);
4226                         return;
4227                 }
4228         }
4229 
4230         /* Could not find an adjacent existing SACK, build a new one,
4231          * put it at the front, and shift everyone else down.  We
4232          * always know there is at least one SACK present already here.
4233          *
4234          * If the sack array is full, forget about the last one.
4235          */
4236         if (this_sack >= TCP_NUM_SACKS) {
4237                 this_sack--;
4238                 tp->rx_opt.num_sacks--;
4239                 sp--;
4240         }
4241         for (; this_sack > 0; this_sack--, sp--)
4242                 *sp = *(sp - 1);
4243 
4244 new_sack:
4245         /* Build the new head SACK, and we're done. */
4246         sp->start_seq = seq;
4247         sp->end_seq = end_seq;
4248         tp->rx_opt.num_sacks++;
4249 }
4250 
4251 /* RCV.NXT advances, some SACKs should be eaten. */
4252 
4253 static void tcp_sack_remove(struct tcp_sock *tp)
4254 {
4255         struct tcp_sack_block *sp = &tp->selective_acks[0];
4256         int num_sacks = tp->rx_opt.num_sacks;
4257         int this_sack;
4258 
4259         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4260         if (skb_queue_empty(&tp->out_of_order_queue)) {
4261                 tp->rx_opt.num_sacks = 0;
4262                 return;
4263         }
4264 
4265         for (this_sack = 0; this_sack < num_sacks;) {
4266                 /* Check if the start of the sack is covered by RCV.NXT. */
4267                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4268                         int i;
4269 
4270                         /* RCV.NXT must cover all the block! */
4271                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4272 
4273                         /* Zap this SACK, by moving forward any other SACKS. */
4274                         for (i = this_sack+1; i < num_sacks; i++)
4275                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4276                         num_sacks--;
4277                         continue;
4278                 }
4279                 this_sack++;
4280                 sp++;
4281         }
4282         tp->rx_opt.num_sacks = num_sacks;
4283 }
4284 
4285 /**
4286  * tcp_try_coalesce - try to merge skb to prior one
4287  * @sk: socket
4288  * @to: prior buffer
4289  * @from: buffer to add in queue
4290  * @fragstolen: pointer to boolean
4291  *
4292  * Before queueing skb @from after @to, try to merge them
4293  * to reduce overall memory use and queue lengths, if cost is small.
4294  * Packets in ofo or receive queues can stay a long time.
4295  * Better try to coalesce them right now to avoid future collapses.
4296  * Returns true if caller should free @from instead of queueing it
4297  */
4298 static bool tcp_try_coalesce(struct sock *sk,
4299                              struct sk_buff *to,
4300                              struct sk_buff *from,
4301                              bool *fragstolen)
4302 {
4303         int delta;
4304 
4305         *fragstolen = false;
4306 
4307         /* Its possible this segment overlaps with prior segment in queue */
4308         if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4309                 return false;
4310 
4311         if (!skb_try_coalesce(to, from, fragstolen, &delta))
4312                 return false;
4313 
4314         atomic_add(delta, &sk->sk_rmem_alloc);
4315         sk_mem_charge(sk, delta);
4316         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4317         TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4318         TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4319         TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4320         return true;
4321 }
4322 
4323 /* This one checks to see if we can put data from the
4324  * out_of_order queue into the receive_queue.
4325  */
4326 static void tcp_ofo_queue(struct sock *sk)
4327 {
4328         struct tcp_sock *tp = tcp_sk(sk);
4329         __u32 dsack_high = tp->rcv_nxt;
4330         struct sk_buff *skb, *tail;
4331         bool fragstolen, eaten;
4332 
4333         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4334                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4335                         break;
4336 
4337                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4338                         __u32 dsack = dsack_high;
4339                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4340                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4341                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4342                 }
4343 
4344                 __skb_unlink(skb, &tp->out_of_order_queue);
4345                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4346                         SOCK_DEBUG(sk, "ofo packet was already received\n");
4347                         __kfree_skb(skb);
4348                         continue;
4349                 }
4350                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4351                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4352                            TCP_SKB_CB(skb)->end_seq);
4353 
4354                 tail = skb_peek_tail(&sk->sk_receive_queue);
4355                 eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4356                 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4357                 if (!eaten)
4358                         __skb_queue_tail(&sk->sk_receive_queue, skb);
4359                 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4360                         tcp_fin(sk);
4361                 if (eaten)
4362                         kfree_skb_partial(skb, fragstolen);
4363         }
4364 }
4365 
4366 static bool tcp_prune_ofo_queue(struct sock *sk);
4367 static int tcp_prune_queue(struct sock *sk);
4368 
4369 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4370                                  unsigned int size)
4371 {
4372         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4373             !sk_rmem_schedule(sk, skb, size)) {
4374 
4375                 if (tcp_prune_queue(sk) < 0)
4376                         return -1;
4377 
4378                 if (!sk_rmem_schedule(sk, skb, size)) {
4379                         if (!tcp_prune_ofo_queue(sk))
4380                                 return -1;
4381 
4382                         if (!sk_rmem_schedule(sk, skb, size))
4383                                 return -1;
4384                 }
4385         }
4386         return 0;
4387 }
4388 
4389 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4390 {
4391         struct tcp_sock *tp = tcp_sk(sk);
4392         struct sk_buff *skb1;
4393         u32 seq, end_seq;
4394 
4395         tcp_ecn_check_ce(tp, skb);
4396 
4397         if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4398                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4399                 __kfree_skb(skb);
4400                 return;
4401         }
4402 
4403         /* Disable header prediction. */
4404         tp->pred_flags = 0;
4405         inet_csk_schedule_ack(sk);
4406 
4407         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4408         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4409                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4410 
4411         skb1 = skb_peek_tail(&tp->out_of_order_queue);
4412         if (!skb1) {
4413                 /* Initial out of order segment, build 1 SACK. */
4414                 if (tcp_is_sack(tp)) {
4415                         tp->rx_opt.num_sacks = 1;
4416                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4417                         tp->selective_acks[0].end_seq =
4418                                                 TCP_SKB_CB(skb)->end_seq;
4419                 }
4420                 __skb_queue_head(&tp->out_of_order_queue, skb);
4421                 goto end;
4422         }
4423 
4424         seq = TCP_SKB_CB(skb)->seq;
4425         end_seq = TCP_SKB_CB(skb)->end_seq;
4426 
4427         if (seq == TCP_SKB_CB(skb1)->end_seq) {
4428                 bool fragstolen;
4429 
4430                 if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4431                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4432                 } else {
4433                         tcp_grow_window(sk, skb);
4434                         kfree_skb_partial(skb, fragstolen);
4435                         skb = NULL;
4436                 }
4437 
4438                 if (!tp->rx_opt.num_sacks ||
4439                     tp->selective_acks[0].end_seq != seq)
4440                         goto add_sack;
4441 
4442                 /* Common case: data arrive in order after hole. */
4443                 tp->selective_acks[0].end_seq = end_seq;
4444                 goto end;
4445         }
4446 
4447         /* Find place to insert this segment. */
4448         while (1) {
4449                 if (!after(TCP_SKB_CB(skb1)->seq, seq))
4450                         break;
4451                 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4452                         skb1 = NULL;
4453                         break;
4454                 }
4455                 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4456         }
4457 
4458         /* Do skb overlap to previous one? */
4459         if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4460                 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4461                         /* All the bits are present. Drop. */
4462                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4463                         __kfree_skb(skb);
4464                         skb = NULL;
4465                         tcp_dsack_set(sk, seq, end_seq);
4466                         goto add_sack;
4467                 }
4468                 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4469                         /* Partial overlap. */
4470                         tcp_dsack_set(sk, seq,
4471                                       TCP_SKB_CB(skb1)->end_seq);
4472                 } else {
4473                         if (skb_queue_is_first(&tp->out_of_order_queue,
4474                                                skb1))
4475                                 skb1 = NULL;
4476                         else
4477                                 skb1 = skb_queue_prev(
4478                                         &tp->out_of_order_queue,
4479                                         skb1);
4480                 }
4481         }
4482         if (!skb1)
4483                 __skb_queue_head(&tp->out_of_order_queue, skb);
4484         else
4485                 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4486 
4487         /* And clean segments covered by new one as whole. */
4488         while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4489                 skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4490 
4491                 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4492                         break;
4493                 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4494                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4495                                          end_seq);
4496                         break;
4497                 }
4498                 __skb_unlink(skb1, &tp->out_of_order_queue);
4499                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4500                                  TCP_SKB_CB(skb1)->end_seq);
4501                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4502                 __kfree_skb(skb1);
4503         }
4504 
4505 add_sack:
4506         if (tcp_is_sack(tp))
4507                 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4508 end:
4509         if (skb) {
4510                 tcp_grow_window(sk, skb);
4511                 skb_set_owner_r(skb, sk);
4512         }
4513 }
4514 
4515 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4516                   bool *fragstolen)
4517 {
4518         int eaten;
4519         struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4520 
4521         __skb_pull(skb, hdrlen);
4522         eaten = (tail &&
4523                  tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4524         tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4525         if (!eaten) {
4526                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4527                 skb_set_owner_r(skb, sk);
4528         }
4529         return eaten;
4530 }
4531 
4532 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4533 {
4534         struct sk_buff *skb;
4535         int err = -ENOMEM;
4536         int data_len = 0;
4537         bool fragstolen;
4538 
4539         if (size == 0)
4540                 return 0;
4541 
4542         if (size > PAGE_SIZE) {
4543                 int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4544 
4545                 data_len = npages << PAGE_SHIFT;
4546                 size = data_len + (size & ~PAGE_MASK);
4547         }
4548         skb = alloc_skb_with_frags(size - data_len, data_len,
4549                                    PAGE_ALLOC_COSTLY_ORDER,
4550                                    &err, sk->sk_allocation);
4551         if (!skb)
4552                 goto err;
4553 
4554         skb_put(skb, size - data_len);
4555         skb->data_len = data_len;
4556         skb->len = size;
4557 
4558         if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4559                 goto err_free;
4560 
4561         err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4562         if (err)
4563                 goto err_free;
4564 
4565         TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4566         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4567         TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4568 
4569         if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
4570                 WARN_ON_ONCE(fragstolen); /* should not happen */
4571                 __kfree_skb(skb);
4572         }
4573         return size;
4574 
4575 err_free:
4576         kfree_skb(skb);
4577 err:
4578         return err;
4579 
4580 }
4581 
4582 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4583 {
4584         struct tcp_sock *tp = tcp_sk(sk);
4585         int eaten = -1;
4586         bool fragstolen = false;
4587 
4588         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4589                 goto drop;
4590 
4591         skb_dst_drop(skb);
4592         __skb_pull(skb, tcp_hdr(skb)->doff * 4);
4593 
4594         tcp_ecn_accept_cwr(tp, skb);
4595 
4596         tp->rx_opt.dsack = 0;
4597 
4598         /*  Queue data for delivery to the user.
4599          *  Packets in sequence go to the receive queue.
4600          *  Out of sequence packets to the out_of_order_queue.
4601          */
4602         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4603                 if (tcp_receive_window(tp) == 0)
4604                         goto out_of_window;
4605 
4606                 /* Ok. In sequence. In window. */
4607                 if (tp->ucopy.task == current &&
4608                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4609                     sock_owned_by_user(sk) && !tp->urg_data) {
4610                         int chunk = min_t(unsigned int, skb->len,
4611                                           tp->ucopy.len);
4612 
4613                         __set_current_state(TASK_RUNNING);
4614 
4615                         local_bh_enable();
4616                         if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
4617                                 tp->ucopy.len -= chunk;
4618                                 tp->copied_seq += chunk;
4619                                 eaten = (chunk == skb->len);
4620                                 tcp_rcv_space_adjust(sk);
4621                         }
4622                         local_bh_disable();
4623                 }
4624 
4625                 if (eaten <= 0) {
4626 queue_and_out:
4627                         if (eaten < 0) {
4628                                 if (skb_queue_len(&sk->sk_receive_queue) == 0)
4629                                         sk_forced_mem_schedule(sk, skb->truesize);
4630                                 else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4631                                         goto drop;
4632                         }
4633                         eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4634                 }
4635                 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4636                 if (skb->len)
4637                         tcp_event_data_recv(sk, skb);
4638                 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4639                         tcp_fin(sk);
4640 
4641                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4642                         tcp_ofo_queue(sk);
4643 
4644                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4645                          * gap in queue is filled.
4646                          */
4647                         if (skb_queue_empty(&tp->out_of_order_queue))
4648                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4649                 }
4650 
4651                 if (tp->rx_opt.num_sacks)
4652                         tcp_sack_remove(tp);
4653 
4654                 tcp_fast_path_check(sk);
4655 
4656                 if (eaten > 0)
4657                         kfree_skb_partial(skb, fragstolen);
4658                 if (!sock_flag(sk, SOCK_DEAD))
4659                         sk->sk_data_ready(sk);
4660                 return;
4661         }
4662 
4663         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4664                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4665                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4666                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4667 
4668 out_of_window:
4669                 tcp_enter_quickack_mode(sk);
4670                 inet_csk_schedule_ack(sk);
4671 drop:
4672                 __kfree_skb(skb);
4673                 return;
4674         }
4675 
4676         /* Out of window. F.e. zero window probe. */
4677         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4678                 goto out_of_window;
4679 
4680         tcp_enter_quickack_mode(sk);
4681 
4682         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4683                 /* Partial packet, seq < rcv_next < end_seq */
4684                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4685                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4686                            TCP_SKB_CB(skb)->end_seq);
4687 
4688                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4689 
4690                 /* If window is closed, drop tail of packet. But after
4691                  * remembering D-SACK for its head made in previous line.
4692                  */
4693                 if (!tcp_receive_window(tp))
4694                         goto out_of_window;
4695                 goto queue_and_out;
4696         }
4697 
4698         tcp_data_queue_ofo(sk, skb);
4699 }
4700 
4701 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4702                                         struct sk_buff_head *list)
4703 {
4704         struct sk_buff *next = NULL;
4705 
4706         if (!skb_queue_is_last(list, skb))
4707                 next = skb_queue_next(list, skb);
4708 
4709         __skb_unlink(skb, list);
4710         __kfree_skb(skb);
4711         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4712 
4713         return next;
4714 }
4715 
4716 /* Collapse contiguous sequence of skbs head..tail with
4717  * sequence numbers start..end.
4718  *
4719  * If tail is NULL, this means until the end of the list.
4720  *
4721  * Segments with FIN/SYN are not collapsed (only because this
4722  * simplifies code)
4723  */
4724 static void
4725 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4726              struct sk_buff *head, struct sk_buff *tail,
4727              u32 start, u32 end)
4728 {
4729         struct sk_buff *skb, *n;
4730         bool end_of_skbs;
4731 
4732         /* First, check that queue is collapsible and find
4733          * the point where collapsing can be useful. */
4734         skb = head;
4735 restart:
4736         end_of_skbs = true;
4737         skb_queue_walk_from_safe(list, skb, n) {
4738                 if (skb == tail)
4739                         break;
4740                 /* No new bits? It is possible on ofo queue. */
4741                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4742                         skb = tcp_collapse_one(sk, skb, list);
4743                         if (!skb)
4744                                 break;
4745                         goto restart;
4746                 }
4747 
4748                 /* The first skb to collapse is:
4749                  * - not SYN/FIN and
4750                  * - bloated or contains data before "start" or
4751                  *   overlaps to the next one.
4752                  */
4753                 if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4754                     (tcp_win_from_space(skb->truesize) > skb->len ||
4755                      before(TCP_SKB_CB(skb)->seq, start))) {
4756                         end_of_skbs = false;
4757                         break;
4758                 }
4759 
4760                 if (!skb_queue_is_last(list, skb)) {
4761                         struct sk_buff *next = skb_queue_next(list, skb);
4762                         if (next != tail &&
4763                             TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4764                                 end_of_skbs = false;
4765                                 break;
4766                         }
4767                 }
4768 
4769                 /* Decided to skip this, advance start seq. */
4770                 start = TCP_SKB_CB(skb)->end_seq;
4771         }
4772         if (end_of_skbs ||
4773             (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4774                 return;
4775 
4776         while (before(start, end)) {
4777                 int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4778                 struct sk_buff *nskb;
4779 
4780                 nskb = alloc_skb(copy, GFP_ATOMIC);
4781                 if (!nskb)
4782                         return;
4783 
4784                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4785                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4786                 __skb_queue_before(list, skb, nskb);
4787                 skb_set_owner_r(nskb, sk);
4788 
4789                 /* Copy data, releasing collapsed skbs. */
4790                 while (copy > 0) {
4791                         int offset = start - TCP_SKB_CB(skb)->seq;
4792                         int size = TCP_SKB_CB(skb)->end_seq - start;
4793 
4794                         BUG_ON(offset < 0);
4795                         if (size > 0) {
4796                                 size = min(copy, size);
4797                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4798                                         BUG();
4799                                 TCP_SKB_CB(nskb)->end_seq += size;
4800                                 copy -= size;
4801                                 start += size;
4802                         }
4803                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4804                                 skb = tcp_collapse_one(sk, skb, list);
4805                                 if (!skb ||
4806                                     skb == tail ||
4807                                     (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4808                                         return;
4809                         }
4810                 }
4811         }
4812 }
4813 
4814 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4815  * and tcp_collapse() them until all the queue is collapsed.
4816  */
4817 static void tcp_collapse_ofo_queue(struct sock *sk)
4818 {
4819         struct tcp_sock *tp = tcp_sk(sk);
4820         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4821         struct sk_buff *head;
4822         u32 start, end;
4823 
4824         if (!skb)
4825                 return;
4826 
4827         start = TCP_SKB_CB(skb)->seq;
4828         end = TCP_SKB_CB(skb)->end_seq;
4829         head = skb;
4830 
4831         for (;;) {
4832                 struct sk_buff *next = NULL;
4833 
4834                 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4835                         next = skb_queue_next(&tp->out_of_order_queue, skb);
4836                 skb = next;
4837 
4838                 /* Segment is terminated when we see gap or when
4839                  * we are at the end of all the queue. */
4840                 if (!skb ||
4841                     after(TCP_SKB_CB(skb)->seq, end) ||
4842                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4843                         tcp_collapse(sk, &tp->out_of_order_queue,
4844                                      head, skb, start, end);
4845                         head = skb;
4846                         if (!skb)
4847                                 break;
4848                         /* Start new segment */
4849                         start = TCP_SKB_CB(skb)->seq;
4850                         end = TCP_SKB_CB(skb)->end_seq;
4851                 } else {
4852                         if (before(TCP_SKB_CB(skb)->seq, start))
4853                                 start = TCP_SKB_CB(skb)->seq;
4854                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4855                                 end = TCP_SKB_CB(skb)->end_seq;
4856                 }
4857         }
4858 }
4859 
4860 /*
4861  * Purge the out-of-order queue.
4862  * Return true if queue was pruned.
4863  */
4864 static bool tcp_prune_ofo_queue(struct sock *sk)
4865 {
4866         struct tcp_sock *tp = tcp_sk(sk);
4867         bool res = false;
4868 
4869         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4870                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4871                 __skb_queue_purge(&tp->out_of_order_queue);
4872 
4873                 /* Reset SACK state.  A conforming SACK implementation will
4874                  * do the same at a timeout based retransmit.  When a connection
4875                  * is in a sad state like this, we care only about integrity
4876                  * of the connection not performance.
4877                  */
4878                 if (tp->rx_opt.sack_ok)
4879                         tcp_sack_reset(&tp->rx_opt);
4880                 sk_mem_reclaim(sk);
4881                 res = true;
4882         }
4883         return res;
4884 }
4885 
4886 /* Reduce allocated memory if we can, trying to get
4887  * the socket within its memory limits again.
4888  *
4889  * Return less than zero if we should start dropping frames
4890  * until the socket owning process reads some of the data
4891  * to stabilize the situation.
4892  */
4893 static int tcp_prune_queue(struct sock *sk)
4894 {
4895         struct tcp_sock *tp = tcp_sk(sk);
4896 
4897         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4898 
4899         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4900 
4901         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4902                 tcp_clamp_window(sk);
4903         else if (tcp_under_memory_pressure(sk))
4904                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4905 
4906         tcp_collapse_ofo_queue(sk);
4907         if (!skb_queue_empty(&sk->sk_receive_queue))
4908                 tcp_collapse(sk, &sk->sk_receive_queue,
4909                              skb_peek(&sk->sk_receive_queue),
4910                              NULL,
4911                              tp->copied_seq, tp->rcv_nxt);
4912         sk_mem_reclaim(sk);
4913 
4914         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4915                 return 0;
4916 
4917         /* Collapsing did not help, destructive actions follow.
4918          * This must not ever occur. */
4919 
4920         tcp_prune_ofo_queue(sk);
4921 
4922         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4923                 return 0;
4924 
4925         /* If we are really being abused, tell the caller to silently
4926          * drop receive data on the floor.  It will get retransmitted
4927          * and hopefully then we'll have sufficient space.
4928          */
4929         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4930 
4931         /* Massive buffer overcommit. */
4932         tp->pred_flags = 0;
4933         return -1;
4934 }
4935 
4936 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4937 {
4938         const struct tcp_sock *tp = tcp_sk(sk);
4939 
4940         /* If the user specified a specific send buffer setting, do
4941          * not modify it.
4942          */
4943         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4944                 return false;
4945 
4946         /* If we are under global TCP memory pressure, do not expand.  */
4947         if (tcp_under_memory_pressure(sk))
4948                 return false;
4949 
4950         /* If we are under soft global TCP memory pressure, do not expand.  */
4951         if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4952                 return false;
4953 
4954         /* If we filled the congestion window, do not expand.  */
4955         if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
4956                 return false;
4957 
4958         return true;
4959 }
4960 
4961 /* When incoming ACK allowed to free some skb from write_queue,
4962  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4963  * on the exit from tcp input handler.
4964  *
4965  * PROBLEM: sndbuf expansion does not work well with largesend.
4966  */
4967 static void tcp_new_space(struct sock *sk)
4968 {
4969         struct tcp_sock *tp = tcp_sk(sk);
4970 
4971         if (tcp_should_expand_sndbuf(sk)) {
4972                 tcp_sndbuf_expand(sk);
4973                 tp->snd_cwnd_stamp = tcp_time_stamp;
4974         }
4975 
4976         sk->sk_write_space(sk);
4977 }
4978 
4979 static void tcp_check_space(struct sock *sk)
4980 {
4981         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4982                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4983                 /* pairs with tcp_poll() */
4984                 smp_mb__after_atomic();
4985                 if (sk->sk_socket &&
4986                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4987                         tcp_new_space(sk);
4988         }
4989 }
4990 
4991 static inline void tcp_data_snd_check(struct sock *sk)
4992 {
4993         tcp_push_pending_frames(sk);
4994         tcp_check_space(sk);
4995 }
4996 
4997 /*
4998  * Check if sending an ack is needed.
4999  */
5000 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5001 {
5002         struct tcp_sock *tp = tcp_sk(sk);
5003 
5004             /* More than one full frame received... */
5005         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5006              /* ... and right edge of window advances far enough.
5007               * (tcp_recvmsg() will send ACK otherwise). Or...
5008               */
5009              __tcp_select_window(sk) >= tp->rcv_wnd) ||
5010             /* We ACK each frame or... */
5011             tcp_in_quickack_mode(sk) ||
5012             /* We have out of order data. */
5013             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
5014                 /* Then ack it now */
5015                 tcp_send_ack(sk);
5016         } else {
5017                 /* Else, send delayed ack. */
5018                 tcp_send_delayed_ack(sk);
5019         }
5020 }
5021 
5022 static inline void tcp_ack_snd_check(struct sock *sk)
5023 {
5024         if (!inet_csk_ack_scheduled(sk)) {
5025                 /* We sent a data segment already. */
5026                 return;
5027         }
5028         __tcp_ack_snd_check(sk, 1);
5029 }
5030 
5031 /*
5032  *      This routine is only called when we have urgent data
5033  *      signaled. Its the 'slow' part of tcp_urg. It could be
5034  *      moved inline now as tcp_urg is only called from one
5035  *      place. We handle URGent data wrong. We have to - as
5036  *      BSD still doesn't use the correction from RFC961.
5037  *      For 1003.1g we should support a new option TCP_STDURG to permit
5038  *      either form (or just set the sysctl tcp_stdurg).
5039  */
5040 
5041 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5042 {
5043         struct tcp_sock *tp = tcp_sk(sk);
5044         u32 ptr = ntohs(th->urg_ptr);
5045 
5046         if (ptr && !sysctl_tcp_stdurg)
5047                 ptr--;
5048         ptr += ntohl(th->seq);
5049 
5050         /* Ignore urgent data that we've already seen and read. */
5051         if (after(tp->copied_seq, ptr))
5052                 return;
5053 
5054         /* Do not replay urg ptr.
5055          *
5056          * NOTE: interesting situation not covered by specs.
5057          * Misbehaving sender may send urg ptr, pointing to segment,
5058          * which we already have in ofo queue. We are not able to fetch
5059          * such data and will stay in TCP_URG_NOTYET until will be eaten
5060          * by recvmsg(). Seems, we are not obliged to handle such wicked
5061          * situations. But it is worth to think about possibility of some
5062          * DoSes using some hypothetical application level deadlock.
5063          */
5064         if (before(ptr, tp->rcv_nxt))
5065                 return;
5066 
5067         /* Do we already have a newer (or duplicate) urgent pointer? */
5068         if (tp->urg_data && !after(ptr, tp->urg_seq))
5069                 return;
5070 
5071         /* Tell the world about our new urgent pointer. */
5072         sk_send_sigurg(sk);
5073 
5074         /* We may be adding urgent data when the last byte read was
5075          * urgent. To do this requires some care. We cannot just ignore
5076          * tp->copied_seq since we would read the last urgent byte again
5077          * as data, nor can we alter copied_seq until this data arrives
5078          * or we break the semantics of SIOCATMARK (and thus sockatmark())
5079          *
5080          * NOTE. Double Dutch. Rendering to plain English: author of comment
5081          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
5082          * and expect that both A and B disappear from stream. This is _wrong_.
5083          * Though this happens in BSD with high probability, this is occasional.
5084          * Any application relying on this is buggy. Note also, that fix "works"
5085          * only in this artificial test. Insert some normal data between A and B and we will
5086          * decline of BSD again. Verdict: it is better to remove to trap
5087          * buggy users.
5088          */
5089         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5090             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5091                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5092                 tp->copied_seq++;
5093                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5094                         __skb_unlink(skb, &sk->sk_receive_queue);
5095                         __kfree_skb(skb);
5096                 }
5097         }
5098 
5099         tp->urg_data = TCP_URG_NOTYET;
5100         tp->urg_seq = ptr;
5101 
5102         /* Disable header prediction. */
5103         tp->pred_flags = 0;
5104 }
5105 
5106 /* This is the 'fast' part of urgent handling. */
5107 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5108 {
5109         struct tcp_sock *tp = tcp_sk(sk);
5110 
5111         /* Check if we get a new urgent pointer - normally not. */
5112         if (th->urg)
5113                 tcp_check_urg(sk, th);
5114 
5115         /* Do we wait for any urgent data? - normally not... */
5116         if (tp->urg_data == TCP_URG_NOTYET) {
5117                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5118                           th->syn;
5119 
5120                 /* Is the urgent pointer pointing into this packet? */
5121                 if (ptr < skb->len) {
5122                         u8 tmp;
5123                         if (skb_copy_bits(skb, ptr, &tmp, 1))
5124                                 BUG();
5125                         tp->urg_data = TCP_URG_VALID | tmp;
5126                         if (!sock_flag(sk, SOCK_DEAD))
5127                                 sk->sk_data_ready(sk);
5128                 }
5129         }
5130 }
5131 
5132 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5133 {
5134         struct tcp_sock *tp = tcp_sk(sk);
5135         int chunk = skb->len - hlen;
5136         int err;
5137 
5138         local_bh_enable();
5139         if (skb_csum_unnecessary(skb))
5140                 err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
5141         else
5142                 err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
5143 
5144         if (!err) {
5145                 tp->ucopy.len -= chunk;
5146                 tp->copied_seq += chunk;
5147                 tcp_rcv_space_adjust(sk);
5148         }
5149 
5150         local_bh_disable();
5151         return err;
5152 }
5153 
5154 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5155                                             struct sk_buff *skb)
5156 {
5157         __sum16 result;
5158 
5159         if (sock_owned_by_user(sk)) {
5160                 local_bh_enable();
5161                 result = __tcp_checksum_complete(skb);
5162                 local_bh_disable();
5163         } else {
5164                 result = __tcp_checksum_complete(skb);
5165         }
5166         return result;
5167 }
5168 
5169 static inline bool tcp_checksum_complete_user(struct sock *sk,
5170                                              struct sk_buff *skb)
5171 {
5172         return !skb_csum_unnecessary(skb) &&
5173                __tcp_checksum_complete_user(sk, skb);
5174 }
5175 
5176 /* Does PAWS and seqno based validation of an incoming segment, flags will
5177  * play significant role here.
5178  */
5179 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5180                                   const struct tcphdr *th, int syn_inerr)
5181 {
5182         struct tcp_sock *tp = tcp_sk(sk);
5183 
5184         /* RFC1323: H1. Apply PAWS check first. */
5185         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5186             tcp_paws_discard(sk, skb)) {
5187                 if (!th->rst) {
5188                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5189                         if (!tcp_oow_rate_limited(sock_net(sk), skb,
5190                                                   LINUX_MIB_TCPACKSKIPPEDPAWS,
5191                                                   &tp->last_oow_ack_time))
5192                                 tcp_send_dupack(sk, skb);
5193                         goto discard;
5194                 }
5195                 /* Reset is accepted even if it did not pass PAWS. */
5196         }
5197 
5198         /* Step 1: check sequence number */
5199         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5200                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5201                  * (RST) segments are validated by checking their SEQ-fields."
5202                  * And page 69: "If an incoming segment is not acceptable,
5203                  * an acknowledgment should be sent in reply (unless the RST
5204                  * bit is set, if so drop the segment and return)".
5205                  */
5206                 if (!th->rst) {
5207                         if (th->syn)
5208                                 goto syn_challenge;
5209                         if (!tcp_oow_rate_limited(sock_net(sk), skb,
5210                                                   LINUX_MIB_TCPACKSKIPPEDSEQ,
5211                                                   &tp->last_oow_ack_time))
5212                                 tcp_send_dupack(sk, skb);
5213                 }
5214                 goto discard;
5215         }
5216 
5217         /* Step 2: check RST bit */
5218         if (th->rst) {
5219                 /* RFC 5961 3.2 :
5220                  * If sequence number exactly matches RCV.NXT, then
5221                  *     RESET the connection
5222                  * else
5223                  *     Send a challenge ACK
5224                  */
5225                 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5226                         tcp_reset(sk);
5227                 else
5228                         tcp_send_challenge_ack(sk, skb);
5229                 goto discard;
5230         }
5231 
5232         /* step 3: check security and precedence [ignored] */
5233 
5234         /* step 4: Check for a SYN
5235          * RFC 5961 4.2 : Send a challenge ack
5236          */
5237         if (th->syn) {
5238 syn_challenge:
5239                 if (syn_inerr)
5240                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5241                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5242                 tcp_send_challenge_ack(sk, skb);
5243                 goto discard;
5244         }
5245 
5246         return true;
5247 
5248 discard:
5249         __kfree_skb(skb);
5250         return false;
5251 }
5252 
5253 /*
5254  *      TCP receive function for the ESTABLISHED state.
5255  *
5256  *      It is split into a fast path and a slow path. The fast path is
5257  *      disabled when:
5258  *      - A zero window was announced from us - zero window probing
5259  *        is only handled properly in the slow path.
5260  *      - Out of order segments arrived.
5261  *      - Urgent data is expected.
5262  *      - There is no buffer space left
5263  *      - Unexpected TCP flags/window values/header lengths are received
5264  *        (detected by checking the TCP header against pred_flags)
5265  *      - Data is sent in both directions. Fast path only supports pure senders
5266  *        or pure receivers (this means either the sequence number or the ack
5267  *        value must stay constant)
5268  *      - Unexpected TCP option.
5269  *
5270  *      When these conditions are not satisfied it drops into a standard
5271  *      receive procedure patterned after RFC793 to handle all cases.
5272  *      The first three cases are guaranteed by proper pred_flags setting,
5273  *      the rest is checked inline. Fast processing is turned on in
5274  *      tcp_data_queue when everything is OK.
5275  */
5276 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5277                          const struct tcphdr *th, unsigned int len)
5278 {
5279         struct tcp_sock *tp = tcp_sk(sk);
5280 
5281         if (unlikely(!sk->sk_rx_dst))
5282                 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5283         /*
5284          *      Header prediction.
5285          *      The code loosely follows the one in the famous
5286          *      "30 instruction TCP receive" Van Jacobson mail.
5287          *
5288          *      Van's trick is to deposit buffers into socket queue
5289          *      on a device interrupt, to call tcp_recv function
5290          *      on the receive process context and checksum and copy
5291          *      the buffer to user space. smart...
5292          *
5293          *      Our current scheme is not silly either but we take the
5294          *      extra cost of the net_bh soft interrupt processing...
5295          *      We do checksum and copy also but from device to kernel.
5296          */
5297 
5298         tp->rx_opt.saw_tstamp = 0;
5299 
5300         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5301          *      if header_prediction is to be made
5302          *      'S' will always be tp->tcp_header_len >> 2
5303          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5304          *  turn it off (when there are holes in the receive
5305          *       space for instance)
5306          *      PSH flag is ignored.
5307          */
5308 
5309         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5310             TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5311             !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5312                 int tcp_header_len = tp->tcp_header_len;
5313 
5314                 /* Timestamp header prediction: tcp_header_len
5315                  * is automatically equal to th->doff*4 due to pred_flags
5316                  * match.
5317                  */
5318 
5319                 /* Check timestamp */
5320                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5321                         /* No? Slow path! */
5322                         if (!tcp_parse_aligned_timestamp(tp, th))
5323                                 goto slow_path;
5324 
5325                         /* If PAWS failed, check it more carefully in slow path */
5326                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5327                                 goto slow_path;
5328 
5329                         /* DO NOT update ts_recent here, if checksum fails
5330                          * and timestamp was corrupted part, it will result
5331                          * in a hung connection since we will drop all
5332                          * future packets due to the PAWS test.
5333                          */
5334                 }
5335 
5336                 if (len <= tcp_header_len) {
5337                         /* Bulk data transfer: sender */
5338                         if (len == tcp_header_len) {
5339                                 /* Predicted packet is in window by definition.
5340                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5341                                  * Hence, check seq<=rcv_wup reduces to:
5342                                  */
5343                                 if (tcp_header_len ==
5344                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5345                                     tp->rcv_nxt == tp->rcv_wup)
5346                                         tcp_store_ts_recent(tp);
5347 
5348                                 /* We know that such packets are checksummed
5349                                  * on entry.
5350                                  */
5351                                 tcp_ack(sk, skb, 0);
5352                                 __kfree_skb(skb);
5353                                 tcp_data_snd_check(sk);
5354                                 return;
5355                         } else { /* Header too small */
5356                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5357                                 goto discard;
5358                         }
5359                 } else {
5360                         int eaten = 0;
5361                         bool fragstolen = false;
5362 
5363                         if (tp->ucopy.task == current &&
5364                             tp->copied_seq == tp->rcv_nxt &&
5365                             len - tcp_header_len <= tp->ucopy.len &&
5366                             sock_owned_by_user(sk)) {
5367                                 __set_current_state(TASK_RUNNING);
5368 
5369                                 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
5370                                         /* Predicted packet is in window by definition.
5371                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5372                                          * Hence, check seq<=rcv_wup reduces to:
5373                                          */
5374                                         if (tcp_header_len ==
5375                                             (sizeof(struct tcphdr) +
5376                                              TCPOLEN_TSTAMP_ALIGNED) &&
5377                                             tp->rcv_nxt == tp->rcv_wup)
5378                                                 tcp_store_ts_recent(tp);
5379 
5380                                         tcp_rcv_rtt_measure_ts(sk, skb);
5381 
5382                                         __skb_pull(skb, tcp_header_len);
5383                                         tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5384                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5385                                         eaten = 1;
5386                                 }
5387                         }
5388                         if (!eaten) {
5389                                 if (tcp_checksum_complete_user(sk, skb))
5390                                         goto csum_error;
5391 
5392                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5393                                         goto step5;
5394 
5395                                 /* Predicted packet is in window by definition.
5396                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5397                                  * Hence, check seq<=rcv_wup reduces to:
5398                                  */
5399                                 if (tcp_header_len ==
5400                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5401                                     tp->rcv_nxt == tp->rcv_wup)
5402                                         tcp_store_ts_recent(tp);
5403 
5404                                 tcp_rcv_rtt_measure_ts(sk, skb);
5405 
5406                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5407 
5408                                 /* Bulk data transfer: receiver */
5409                                 eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5410                                                       &fragstolen);
5411                         }
5412 
5413                         tcp_event_data_recv(sk, skb);
5414 
5415                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5416                                 /* Well, only one small jumplet in fast path... */
5417                                 tcp_ack(sk, skb, FLAG_DATA);
5418                                 tcp_data_snd_check(sk);
5419                                 if (!inet_csk_ack_scheduled(sk))
5420                                         goto no_ack;
5421                         }
5422 
5423                         __tcp_ack_snd_check(sk, 0);
5424 no_ack:
5425                         if (eaten)
5426                                 kfree_skb_partial(skb, fragstolen);
5427                         sk->sk_data_ready(sk);
5428                         return;
5429                 }
5430         }
5431 
5432 slow_path:
5433         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5434                 goto csum_error;
5435 
5436         if (!th->ack && !th->rst && !th->syn)
5437                 goto discard;
5438 
5439         /*
5440          *      Standard slow path.
5441          */
5442 
5443         if (!tcp_validate_incoming(sk, skb, th, 1))
5444                 return;
5445 
5446 step5:
5447         if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5448                 goto discard;
5449 
5450         tcp_rcv_rtt_measure_ts(sk, skb);
5451 
5452         /* Process urgent data. */
5453         tcp_urg(sk, skb, th);
5454 
5455         /* step 7: process the segment text */
5456         tcp_data_queue(sk, skb);
5457 
5458         tcp_data_snd_check(sk);
5459         tcp_ack_snd_check(sk);
5460         return;
5461 
5462 csum_error:
5463         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5464         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5465 
5466 discard:
5467         __kfree_skb(skb);
5468 }
5469 EXPORT_SYMBOL(tcp_rcv_established);
5470 
5471 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5472 {
5473         struct tcp_sock *tp = tcp_sk(sk);
5474         struct inet_connection_sock *icsk = inet_csk(sk);
5475 
5476         tcp_set_state(sk, TCP_ESTABLISHED);
5477 
5478         if (skb) {
5479                 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5480                 security_inet_conn_established(sk, skb);
5481         }
5482 
5483         /* Make sure socket is routed, for correct metrics.  */
5484         icsk->icsk_af_ops->rebuild_header(sk);
5485 
5486         tcp_init_metrics(sk);
5487 
5488         tcp_init_congestion_control(sk);
5489 
5490         /* Prevent spurious tcp_cwnd_restart() on first data
5491          * packet.
5492          */
5493         tp->lsndtime = tcp_time_stamp;
5494 
5495         tcp_init_buffer_space(sk);
5496 
5497         if (sock_flag(sk, SOCK_KEEPOPEN))
5498                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5499 
5500         if (!tp->rx_opt.snd_wscale)
5501                 __tcp_fast_path_on(tp, tp->snd_wnd);
5502         else
5503                 tp->pred_flags = 0;
5504 
5505         if (!sock_flag(sk, SOCK_DEAD)) {
5506                 sk->sk_state_change(sk);
5507                 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5508         }
5509 }
5510 
5511 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5512                                     struct tcp_fastopen_cookie *cookie)
5513 {
5514         struct tcp_sock *tp = tcp_sk(sk);
5515         struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5516         u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5517         bool syn_drop = false;
5518 
5519         if (mss == tp->rx_opt.user_mss) {
5520                 struct tcp_options_received opt;
5521 
5522                 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
5523                 tcp_clear_options(&opt);
5524                 opt.user_mss = opt.mss_clamp = 0;
5525                 tcp_parse_options(synack, &opt, 0, NULL);
5526                 mss = opt.mss_clamp;
5527         }
5528 
5529         if (!tp->syn_fastopen) {
5530                 /* Ignore an unsolicited cookie */
5531                 cookie->len = -1;
5532         } else if (tp->total_retrans) {
5533                 /* SYN timed out and the SYN-ACK neither has a cookie nor
5534                  * acknowledges data. Presumably the remote received only
5535                  * the retransmitted (regular) SYNs: either the original
5536                  * SYN-data or the corresponding SYN-ACK was dropped.
5537                  */
5538                 syn_drop = (cookie->len < 0 && data);
5539         } else if (cookie->len < 0 && !tp->syn_data) {
5540                 /* We requested a cookie but didn't get it. If we did not use
5541                  * the (old) exp opt format then try so next time (try_exp=1).
5542                  * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5543                  */
5544                 try_exp = tp->syn_fastopen_exp ? 2 : 1;
5545         }
5546 
5547         tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5548 
5549         if (data) { /* Retransmit unacked data in SYN */
5550                 tcp_for_write_queue_from(data, sk) {
5551                         if (data == tcp_send_head(sk) ||
5552                             __tcp_retransmit_skb(sk, data))
5553                                 break;
5554                 }
5555                 tcp_rearm_rto(sk);
5556                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5557                 return true;
5558         }
5559         tp->syn_data_acked = tp->syn_data;
5560         if (tp->syn_data_acked)
5561                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5562 
5563         tcp_fastopen_add_skb(sk, synack);
5564 
5565         return false;
5566 }
5567 
5568 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5569                                          const struct tcphdr *th)
5570 {
5571         struct inet_connection_sock *icsk = inet_csk(sk);
5572         struct tcp_sock *tp = tcp_sk(sk);
5573         struct tcp_fastopen_cookie foc = { .len = -1 };
5574         int saved_clamp = tp->rx_opt.mss_clamp;
5575 
5576         tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5577         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5578                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5579 
5580         if (th->ack) {
5581                 /* rfc793:
5582                  * "If the state is SYN-SENT then
5583                  *    first check the ACK bit
5584                  *      If the ACK bit is set
5585                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5586                  *        a reset (unless the RST bit is set, if so drop
5587                  *        the segment and return)"
5588                  */
5589                 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5590                     after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5591                         goto reset_and_undo;
5592 
5593                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5594                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5595                              tcp_time_stamp)) {
5596                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5597                         goto reset_and_undo;
5598                 }
5599 
5600                 /* Now ACK is acceptable.
5601                  *
5602                  * "If the RST bit is set
5603                  *    If the ACK was acceptable then signal the user "error:
5604                  *    connection reset", drop the segment, enter CLOSED state,
5605                  *    delete TCB, and return."
5606                  */
5607 
5608                 if (th->rst) {
5609                         tcp_reset(sk);
5610                         goto discard;
5611                 }
5612 
5613                 /* rfc793:
5614                  *   "fifth, if neither of the SYN or RST bits is set then
5615                  *    drop the segment and return."
5616                  *
5617                  *    See note below!
5618                  *                                        --ANK(990513)
5619                  */
5620                 if (!th->syn)
5621                         goto discard_and_undo;
5622 
5623                 /* rfc793:
5624                  *   "If the SYN bit is on ...
5625                  *    are acceptable then ...
5626                  *    (our SYN has been ACKed), change the connection
5627                  *    state to ESTABLISHED..."
5628                  */
5629 
5630                 tcp_ecn_rcv_synack(tp, th);
5631 
5632                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5633                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5634 
5635                 /* Ok.. it's good. Set up sequence numbers and
5636                  * move to established.
5637                  */
5638                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5639                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5640 
5641                 /* RFC1323: The window in SYN & SYN/ACK segments is
5642                  * never scaled.
5643                  */
5644                 tp->snd_wnd = ntohs(th->window);
5645 
5646                 if (!tp->rx_opt.wscale_ok) {
5647                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5648                         tp->window_clamp = min(tp->window_clamp, 65535U);
5649                 }
5650 
5651                 if (tp->rx_opt.saw_tstamp) {
5652                         tp->rx_opt.tstamp_ok       = 1;
5653                         tp->tcp_header_len =
5654                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5655                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5656                         tcp_store_ts_recent(tp);
5657                 } else {
5658                         tp->tcp_header_len = sizeof(struct tcphdr);
5659                 }
5660 
5661                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5662                         tcp_enable_fack(tp);
5663 
5664                 tcp_mtup_init(sk);
5665                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5666                 tcp_initialize_rcv_mss(sk);
5667 
5668                 /* Remember, tcp_poll() does not lock socket!
5669                  * Change state from SYN-SENT only after copied_seq
5670                  * is initialized. */
5671                 tp->copied_seq = tp->rcv_nxt;
5672 
5673                 smp_mb();
5674 
5675                 tcp_finish_connect(sk, skb);
5676 
5677                 if ((tp->syn_fastopen || tp->syn_data) &&
5678                     tcp_rcv_fastopen_synack(sk, skb, &foc))
5679                         return -1;
5680 
5681                 if (sk->sk_write_pending ||
5682                     icsk->icsk_accept_queue.rskq_defer_accept ||
5683                     icsk->icsk_ack.pingpong) {
5684                         /* Save one ACK. Data will be ready after
5685                          * several ticks, if write_pending is set.
5686                          *
5687                          * It may be deleted, but with this feature tcpdumps
5688                          * look so _wonderfully_ clever, that I was not able
5689                          * to stand against the temptation 8)     --ANK
5690                          */
5691                         inet_csk_schedule_ack(sk);
5692                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5693                         tcp_enter_quickack_mode(sk);
5694                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5695                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5696 
5697 discard:
5698                         __kfree_skb(skb);
5699                         return 0;
5700                 } else {
5701                         tcp_send_ack(sk);
5702                 }
5703                 return -1;
5704         }
5705 
5706         /* No ACK in the segment */
5707 
5708         if (th->rst) {
5709                 /* rfc793:
5710                  * "If the RST bit is set
5711                  *
5712                  *      Otherwise (no ACK) drop the segment and return."
5713                  */
5714 
5715                 goto discard_and_undo;
5716         }
5717 
5718         /* PAWS check. */
5719         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5720             tcp_paws_reject(&tp->rx_opt, 0))
5721                 goto discard_and_undo;
5722 
5723         if (th->syn) {
5724                 /* We see SYN without ACK. It is attempt of
5725                  * simultaneous connect with crossed SYNs.
5726                  * Particularly, it can be connect to self.
5727                  */
5728                 tcp_set_state(sk, TCP_SYN_RECV);
5729 
5730                 if (tp->rx_opt.saw_tstamp) {
5731                         tp->rx_opt.tstamp_ok = 1;
5732                         tcp_store_ts_recent(tp);
5733                         tp->tcp_header_len =
5734                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5735                 } else {
5736                         tp->tcp_header_len = sizeof(struct tcphdr);
5737                 }
5738 
5739                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5740                 tp->copied_seq = tp->rcv_nxt;
5741                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5742 
5743                 /* RFC1323: The window in SYN & SYN/ACK segments is
5744                  * never scaled.
5745                  */
5746                 tp->snd_wnd    = ntohs(th->window);
5747                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5748                 tp->max_window = tp->snd_wnd;
5749 
5750                 tcp_ecn_rcv_syn(tp, th);
5751 
5752                 tcp_mtup_init(sk);
5753                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5754                 tcp_initialize_rcv_mss(sk);
5755 
5756                 tcp_send_synack(sk);
5757 #if 0
5758                 /* Note, we could accept data and URG from this segment.
5759                  * There are no obstacles to make this (except that we must
5760                  * either change tcp_recvmsg() to prevent it from returning data
5761                  * before 3WHS completes per RFC793, or employ TCP Fast Open).
5762                  *
5763                  * However, if we ignore data in ACKless segments sometimes,
5764                  * we have no reasons to accept it sometimes.
5765                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5766                  * is not flawless. So, discard packet for sanity.
5767                  * Uncomment this return to process the data.
5768                  */
5769                 return -1;
5770 #else
5771                 goto discard;
5772 #endif
5773         }
5774         /* "fifth, if neither of the SYN or RST bits is set then
5775          * drop the segment and return."
5776          */
5777 
5778 discard_and_undo:
5779         tcp_clear_options(&tp->rx_opt);
5780         tp->rx_opt.mss_clamp = saved_clamp;
5781         goto discard;
5782 
5783 reset_and_undo:
5784         tcp_clear_options(&tp->rx_opt);
5785         tp->rx_opt.mss_clamp = saved_clamp;
5786         return 1;
5787 }
5788 
5789 /*
5790  *      This function implements the receiving procedure of RFC 793 for
5791  *      all states except ESTABLISHED and TIME_WAIT.
5792  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5793  *      address independent.
5794  */
5795 
5796 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
5797 {
5798         struct tcp_sock *tp = tcp_sk(sk);
5799         struct inet_connection_sock *icsk = inet_csk(sk);
5800         const struct tcphdr *th = tcp_hdr(skb);
5801         struct request_sock *req;
5802         int queued = 0;
5803         bool acceptable;
5804 
5805         tp->rx_opt.saw_tstamp = 0;
5806 
5807         switch (sk->sk_state) {
5808         case TCP_CLOSE:
5809                 goto discard;
5810 
5811         case TCP_LISTEN:
5812                 if (th->ack)
5813                         return 1;
5814 
5815                 if (th->rst)
5816                         goto discard;
5817 
5818                 if (th->syn) {
5819                         if (th->fin)
5820                                 goto discard;
5821                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5822                                 return 1;
5823 
5824                         /* Now we have several options: In theory there is
5825                          * nothing else in the frame. KA9Q has an option to
5826                          * send data with the syn, BSD accepts data with the
5827                          * syn up to the [to be] advertised window and
5828                          * Solaris 2.1 gives you a protocol error. For now
5829                          * we just ignore it, that fits the spec precisely
5830                          * and avoids incompatibilities. It would be nice in
5831                          * future to drop through and process the data.
5832                          *
5833                          * Now that TTCP is starting to be used we ought to
5834                          * queue this data.
5835                          * But, this leaves one open to an easy denial of
5836                          * service attack, and SYN cookies can't defend
5837                          * against this problem. So, we drop the data
5838                          * in the interest of security over speed unless
5839                          * it's still in use.
5840                          */
5841                         kfree_skb(skb);
5842                         return 0;
5843                 }
5844                 goto discard;
5845 
5846         case TCP_SYN_SENT:
5847                 queued = tcp_rcv_synsent_state_process(sk, skb, th);
5848                 if (queued >= 0)
5849                         return queued;
5850 
5851                 /* Do step6 onward by hand. */
5852                 tcp_urg(sk, skb, th);
5853                 __kfree_skb(skb);
5854                 tcp_data_snd_check(sk);
5855                 return 0;
5856         }
5857 
5858         req = tp->fastopen_rsk;
5859         if (req) {
5860                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5861                     sk->sk_state != TCP_FIN_WAIT1);
5862 
5863                 if (!tcp_check_req(sk, skb, req, true))
5864                         goto discard;
5865         }
5866 
5867         if (!th->ack && !th->rst && !th->syn)
5868                 goto discard;
5869 
5870         if (!tcp_validate_incoming(sk, skb, th, 0))
5871                 return 0;
5872 
5873         /* step 5: check the ACK field */
5874         acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5875                                       FLAG_UPDATE_TS_RECENT) > 0;
5876 
5877         switch (sk->sk_state) {
5878         case TCP_SYN_RECV:
5879                 if (!acceptable)
5880                         return 1;
5881 
5882                 if (!tp->srtt_us)
5883                         tcp_synack_rtt_meas(sk, req);
5884 
5885                 /* Once we leave TCP_SYN_RECV, we no longer need req
5886                  * so release it.
5887                  */
5888                 if (req) {
5889                         tp->total_retrans = req->num_retrans;
5890                         reqsk_fastopen_remove(sk, req, false);
5891                 } else {
5892                         /* Make sure socket is routed, for correct metrics. */
5893                         icsk->icsk_af_ops->rebuild_header(sk);
5894                         tcp_init_congestion_control(sk);
5895 
5896                         tcp_mtup_init(sk);
5897                         tp->copied_seq = tp->rcv_nxt;
5898                         tcp_init_buffer_space(sk);
5899                 }
5900                 smp_mb();
5901                 tcp_set_state(sk, TCP_ESTABLISHED);
5902                 sk->sk_state_change(sk);
5903 
5904                 /* Note, that this wakeup is only for marginal crossed SYN case.
5905                  * Passively open sockets are not waked up, because
5906                  * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5907                  */
5908                 if (sk->sk_socket)
5909                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5910 
5911                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5912                 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5913                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5914 
5915                 if (tp->rx_opt.tstamp_ok)
5916                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5917 
5918                 if (req) {
5919                         /* Re-arm the timer because data may have been sent out.
5920                          * This is similar to the regular data transmission case
5921                          * when new data has just been ack'ed.
5922                          *
5923                          * (TFO) - we could try to be more aggressive and
5924                          * retransmitting any data sooner based on when they
5925                          * are sent out.
5926                          */
5927                         tcp_rearm_rto(sk);
5928                 } else
5929                         tcp_init_metrics(sk);
5930 
5931                 tcp_update_pacing_rate(sk);
5932 
5933                 /* Prevent spurious tcp_cwnd_restart() on first data packet */
5934                 tp->lsndtime = tcp_time_stamp;
5935 
5936                 tcp_initialize_rcv_mss(sk);
5937                 tcp_fast_path_on(tp);
5938                 break;
5939 
5940         case TCP_FIN_WAIT1: {
5941                 struct dst_entry *dst;
5942                 int tmo;
5943 
5944                 /* If we enter the TCP_FIN_WAIT1 state and we are a
5945                  * Fast Open socket and this is the first acceptable
5946                  * ACK we have received, this would have acknowledged
5947                  * our SYNACK so stop the SYNACK timer.
5948                  */
5949                 if (req) {
5950                         /* Return RST if ack_seq is invalid.
5951                          * Note that RFC793 only says to generate a
5952                          * DUPACK for it but for TCP Fast Open it seems
5953                          * better to treat this case like TCP_SYN_RECV
5954                          * above.
5955                          */
5956                         if (!acceptable)
5957                                 return 1;
5958                         /* We no longer need the request sock. */
5959                         reqsk_fastopen_remove(sk, req, false);
5960                         tcp_rearm_rto(sk);
5961                 }
5962                 if (tp->snd_una != tp->write_seq)
5963                         break;
5964 
5965                 tcp_set_state(sk, TCP_FIN_WAIT2);
5966                 sk->sk_shutdown |= SEND_SHUTDOWN;
5967 
5968                 dst = __sk_dst_get(sk);
5969                 if (dst)
5970                         dst_confirm(dst);
5971 
5972                 if (!sock_flag(sk, SOCK_DEAD)) {
5973                         /* Wake up lingering close() */
5974                         sk->sk_state_change(sk);
5975                         break;
5976                 }
5977 
5978                 if (tp->linger2 < 0 ||
5979                     (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5980                      after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5981                         tcp_done(sk);
5982                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5983                         return 1;
5984                 }
5985 
5986                 tmo = tcp_fin_time(sk);
5987                 if (tmo > TCP_TIMEWAIT_LEN) {
5988                         inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5989                 } else if (th->fin || sock_owned_by_user(sk)) {
5990                         /* Bad case. We could lose such FIN otherwise.
5991                          * It is not a big problem, but it looks confusing
5992                          * and not so rare event. We still can lose it now,
5993                          * if it spins in bh_lock_sock(), but it is really
5994                          * marginal case.
5995                          */
5996                         inet_csk_reset_keepalive_timer(sk, tmo);
5997                 } else {
5998                         tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5999                         goto discard;
6000                 }
6001                 break;
6002         }
6003 
6004         case TCP_CLOSING:
6005                 if (tp->snd_una == tp->write_seq) {
6006                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6007                         goto discard;
6008                 }
6009                 break;
6010 
6011         case TCP_LAST_ACK:
6012                 if (tp->snd_una == tp->write_seq) {
6013                         tcp_update_metrics(sk);
6014                         tcp_done(sk);
6015                         goto discard;
6016                 }
6017                 break;
6018         }
6019 
6020         /* step 6: check the URG bit */
6021         tcp_urg(sk, skb, th);
6022 
6023         /* step 7: process the segment text */
6024         switch (sk->sk_state) {
6025         case TCP_CLOSE_WAIT:
6026         case TCP_CLOSING:
6027         case TCP_LAST_ACK:
6028                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
6029                         break;
6030         case TCP_FIN_WAIT1:
6031         case TCP_FIN_WAIT2:
6032                 /* RFC 793 says to queue data in these states,
6033                  * RFC 1122 says we MUST send a reset.
6034                  * BSD 4.4 also does reset.
6035                  */
6036                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
6037                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6038                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6039                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6040                                 tcp_reset(sk);
6041                                 return 1;
6042                         }
6043                 }
6044                 /* Fall through */
6045         case TCP_ESTABLISHED:
6046                 tcp_data_queue(sk, skb);
6047                 queued = 1;
6048                 break;
6049         }
6050 
6051         /* tcp_data could move socket to TIME-WAIT */
6052         if (sk->sk_state != TCP_CLOSE) {
6053                 tcp_data_snd_check(sk);
6054                 tcp_ack_snd_check(sk);
6055         }
6056 
6057         if (!queued) {
6058 discard:
6059                 __kfree_skb(skb);
6060         }
6061         return 0;
6062 }
6063 EXPORT_SYMBOL(tcp_rcv_state_process);
6064 
6065 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6066 {
6067         struct inet_request_sock *ireq = inet_rsk(req);
6068 
6069         if (family == AF_INET)
6070                 net_dbg_ratelimited("drop open request from %pI4/%u\n",
6071                                     &ireq->ir_rmt_addr, port);
6072 #if IS_ENABLED(CONFIG_IPV6)
6073         else if (family == AF_INET6)
6074                 net_dbg_ratelimited("drop open request from %pI6/%u\n",
6075                                     &ireq->ir_v6_rmt_addr, port);
6076 #endif
6077 }
6078 
6079 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6080  *
6081  * If we receive a SYN packet with these bits set, it means a
6082  * network is playing bad games with TOS bits. In order to
6083  * avoid possible false congestion notifications, we disable
6084  * TCP ECN negotiation.
6085  *
6086  * Exception: tcp_ca wants ECN. This is required for DCTCP
6087  * congestion control: Linux DCTCP asserts ECT on all packets,
6088  * including SYN, which is most optimal solution; however,
6089  * others, such as FreeBSD do not.
6090  */
6091 static void tcp_ecn_create_request(struct request_sock *req,
6092                                    const struct sk_buff *skb,
6093                                    const struct sock *listen_sk,
6094                                    const struct dst_entry *dst)
6095 {
6096         const struct tcphdr *th = tcp_hdr(skb);
6097         const struct net *net = sock_net(listen_sk);
6098         bool th_ecn = th->ece && th->cwr;
6099         bool ect, ecn_ok;
6100         u32 ecn_ok_dst;
6101 
6102         if (!th_ecn)
6103                 return;
6104 
6105         ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6106         ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6107         ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
6108 
6109         if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6110             (ecn_ok_dst & DST_FEATURE_ECN_CA))
6111                 inet_rsk(req)->ecn_ok = 1;
6112 }
6113 
6114 static void tcp_openreq_init(struct request_sock *req,
6115                              const struct tcp_options_received *rx_opt,
6116                              struct sk_buff *skb, const struct sock *sk)
6117 {
6118         struct inet_request_sock *ireq = inet_rsk(req);
6119 
6120         req->rsk_rcv_wnd = 0;           /* So that tcp_send_synack() knows! */
6121         req->cookie_ts = 0;
6122         tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6123         tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6124         skb_mstamp_get(&tcp_rsk(req)->snt_synack);
6125         tcp_rsk(req)->last_oow_ack_time = 0;
6126         req->mss = rx_opt->mss_clamp;
6127         req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6128         ireq->tstamp_ok = rx_opt->tstamp_ok;
6129         ireq->sack_ok = rx_opt->sack_ok;
6130         ireq->snd_wscale = rx_opt->snd_wscale;
6131         ireq->wscale_ok = rx_opt->wscale_ok;
6132         ireq->acked = 0;
6133         ireq->ecn_ok = 0;
6134         ireq->ir_rmt_port = tcp_hdr(skb)->source;
6135         ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6136         ireq->ir_mark = inet_request_mark(sk, skb);
6137 }
6138 
6139 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6140                                       struct sock *sk_listener,
6141                                       bool attach_listener)
6142 {
6143         struct request_sock *req = reqsk_alloc(ops, sk_listener,
6144                                                attach_listener);
6145 
6146         if (req) {
6147                 struct inet_request_sock *ireq = inet_rsk(req);
6148 
6149                 kmemcheck_annotate_bitfield(ireq, flags);
6150                 ireq->opt = NULL;
6151                 atomic64_set(&ireq->ir_cookie, 0);
6152                 ireq->ireq_state = TCP_NEW_SYN_RECV;
6153                 write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6154                 ireq->ireq_family = sk_listener->sk_family;
6155         }
6156 
6157         return req;
6158 }
6159 EXPORT_SYMBOL(inet_reqsk_alloc);
6160 
6161 /*
6162  * Return true if a syncookie should be sent
6163  */
6164 static bool tcp_syn_flood_action(const struct sock *sk,
6165                                  const struct sk_buff *skb,
6166                                  const char *proto)
6167 {
6168         struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6169         const char *msg = "Dropping request";
6170         bool want_cookie = false;
6171         struct net *net = sock_net(sk);
6172 
6173 #ifdef CONFIG_SYN_COOKIES
6174         if (net->ipv4.sysctl_tcp_syncookies) {
6175                 msg = "Sending cookies";
6176                 want_cookie = true;
6177                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6178         } else
6179 #endif
6180                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6181 
6182         if (!queue->synflood_warned &&
6183             net->ipv4.sysctl_tcp_syncookies != 2 &&
6184             xchg(&queue->synflood_warned, 1) == 0)
6185                 pr_info("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
6186                         proto, ntohs(tcp_hdr(skb)->dest), msg);
6187 
6188         return want_cookie;
6189 }
6190 
6191 static void tcp_reqsk_record_syn(const struct sock *sk,
6192                                  struct request_sock *req,
6193                                  const struct sk_buff *skb)
6194 {
6195         if (tcp_sk(sk)->save_syn) {
6196                 u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6197                 u32 *copy;
6198 
6199                 copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6200                 if (copy) {
6201                         copy[0] = len;
6202                         memcpy(&copy[1], skb_network_header(skb), len);
6203                         req->saved_syn = copy;
6204                 }
6205         }
6206 }
6207 
6208 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6209                      const struct tcp_request_sock_ops *af_ops,
6210                      struct sock *sk, struct sk_buff *skb)
6211 {
6212         struct tcp_fastopen_cookie foc = { .len = -1 };
6213         __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6214         struct tcp_options_received tmp_opt;
6215         struct tcp_sock *tp = tcp_sk(sk);
6216         struct net *net = sock_net(sk);
6217         struct sock *fastopen_sk = NULL;
6218         struct dst_entry *dst = NULL;
6219         struct request_sock *req;
6220         bool want_cookie = false;
6221         struct flowi fl;
6222 
6223         /* TW buckets are converted to open requests without
6224          * limitations, they conserve resources and peer is
6225          * evidently real one.
6226          */
6227         if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
6228              inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6229                 want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
6230                 if (!want_cookie)
6231                         goto drop;
6232         }
6233 
6234 
6235         /* Accept backlog is full. If we have already queued enough
6236          * of warm entries in syn queue, drop request. It is better than
6237          * clogging syn queue with openreqs with exponentially increasing
6238          * timeout.
6239          */
6240         if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
6241                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6242                 goto drop;
6243         }
6244 
6245         req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6246         if (!req)
6247                 goto drop;
6248 
6249         tcp_rsk(req)->af_specific = af_ops;
6250 
6251         tcp_clear_options(&tmp_opt);
6252         tmp_opt.mss_clamp = af_ops->mss_clamp;
6253         tmp_opt.user_mss  = tp->rx_opt.user_mss;
6254         tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
6255 
6256         if (want_cookie && !tmp_opt.saw_tstamp)
6257                 tcp_clear_options(&tmp_opt);
6258 
6259         tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6260         tcp_openreq_init(req, &tmp_opt, skb, sk);
6261 
6262         /* Note: tcp_v6_init_req() might override ir_iif for link locals */
6263         inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6264 
6265         af_ops->init_req(req, sk, skb);
6266 
6267         if (security_inet_conn_request(sk, skb, req))
6268                 goto drop_and_free;
6269 
6270         if (!want_cookie && !isn) {
6271                 /* VJ's idea. We save last timestamp seen
6272                  * from the destination in peer table, when entering
6273                  * state TIME-WAIT, and check against it before
6274                  * accepting new connection request.
6275                  *
6276                  * If "isn" is not zero, this request hit alive
6277                  * timewait bucket, so that all the necessary checks
6278                  * are made in the function processing timewait state.
6279                  */
6280                 if (tcp_death_row.sysctl_tw_recycle) {
6281                         bool strict;
6282 
6283                         dst = af_ops->route_req(sk, &fl, req, &strict);
6284 
6285                         if (dst && strict &&
6286                             !tcp_peer_is_proven(req, dst, true,
6287                                                 tmp_opt.saw_tstamp)) {
6288                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
6289                                 goto drop_and_release;
6290                         }
6291                 }
6292                 /* Kill the following clause, if you dislike this way. */
6293                 else if (!net->ipv4.sysctl_tcp_syncookies &&
6294                          (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6295                           (sysctl_max_syn_backlog >> 2)) &&
6296                          !tcp_peer_is_proven(req, dst, false,
6297                                              tmp_opt.saw_tstamp)) {
6298                         /* Without syncookies last quarter of
6299                          * backlog is filled with destinations,
6300                          * proven to be alive.
6301                          * It means that we continue to communicate
6302                          * to destinations, already remembered
6303                          * to the moment of synflood.
6304                          */
6305                         pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6306                                     rsk_ops->family);
6307                         goto drop_and_release;
6308                 }
6309 
6310                 isn = af_ops->init_seq(skb);
6311         }
6312         if (!dst) {
6313                 dst = af_ops->route_req(sk, &fl, req, NULL);
6314                 if (!dst)
6315                         goto drop_and_free;
6316         }
6317 
6318         tcp_ecn_create_request(req, skb, sk, dst);
6319 
6320         if (want_cookie) {
6321                 isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6322                 req->cookie_ts = tmp_opt.tstamp_ok;
6323                 if (!tmp_opt.tstamp_ok)
6324                         inet_rsk(req)->ecn_ok = 0;
6325         }
6326 
6327         tcp_rsk(req)->snt_isn = isn;
6328         tcp_rsk(req)->txhash = net_tx_rndhash();
6329         tcp_openreq_init_rwin(req, sk, dst);
6330         if (!want_cookie) {
6331                 tcp_reqsk_record_syn(sk, req, skb);
6332                 fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
6333         }
6334         if (fastopen_sk) {
6335                 af_ops->send_synack(fastopen_sk, dst, &fl, req,
6336                                     &foc, false);
6337                 /* Add the child socket directly into the accept queue */
6338                 inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
6339                 sk->sk_data_ready(sk);
6340                 bh_unlock_sock(fastopen_sk);
6341                 sock_put(fastopen_sk);
6342         } else {
6343                 tcp_rsk(req)->tfo_listener = false;
6344                 if (!want_cookie)
6345                         inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
6346                 af_ops->send_synack(sk, dst, &fl, req,
6347                                     &foc, !want_cookie);
6348                 if (want_cookie)
6349                         goto drop_and_free;
6350         }
6351         reqsk_put(req);
6352         return 0;
6353 
6354 drop_and_release:
6355         dst_release(dst);
6356 drop_and_free:
6357         reqsk_free(req);
6358 drop:
6359         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
6360         return 0;
6361 }
6362 EXPORT_SYMBOL(tcp_conn_request);
6363 

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