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

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