Version:  2.0.40 2.2.26 2.4.37 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18

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

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