Version:  2.0.40 2.2.26 2.4.37 3.0 3.1 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

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 <net/dst.h>
 72 #include <net/tcp.h>
 73 #include <net/inet_common.h>
 74 #include <linux/ipsec.h>
 75 #include <asm/unaligned.h>
 76 #include <net/netdma.h>
 77 
 78 int sysctl_tcp_timestamps __read_mostly = 1;
 79 int sysctl_tcp_window_scaling __read_mostly = 1;
 80 int sysctl_tcp_sack __read_mostly = 1;
 81 int sysctl_tcp_fack __read_mostly = 1;
 82 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
 83 EXPORT_SYMBOL(sysctl_tcp_reordering);
 84 int sysctl_tcp_dsack __read_mostly = 1;
 85 int sysctl_tcp_app_win __read_mostly = 31;
 86 int sysctl_tcp_adv_win_scale __read_mostly = 1;
 87 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
 88 
 89 /* rfc5961 challenge ack rate limiting */
 90 int sysctl_tcp_challenge_ack_limit = 100;
 91 
 92 int sysctl_tcp_stdurg __read_mostly;
 93 int sysctl_tcp_rfc1337 __read_mostly;
 94 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
 95 int sysctl_tcp_frto __read_mostly = 2;
 96 
 97 int sysctl_tcp_thin_dupack __read_mostly;
 98 
 99 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
100 int sysctl_tcp_early_retrans __read_mostly = 3;
101 
102 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
103 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
104 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
105 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
106 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
107 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
108 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
109 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
110 #define FLAG_ORIG_SACK_ACKED    0x200 /* Never retransmitted data are (s)acked  */
111 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
112 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
113 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
114 #define FLAG_UPDATE_TS_RECENT   0x4000 /* tcp_replace_ts_recent() */
115 
116 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
117 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
118 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
119 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
120 
121 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
122 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
123 
124 /* Adapt the MSS value used to make delayed ack decision to the
125  * real world.
126  */
127 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
128 {
129         struct inet_connection_sock *icsk = inet_csk(sk);
130         const unsigned int lss = icsk->icsk_ack.last_seg_size;
131         unsigned int len;
132 
133         icsk->icsk_ack.last_seg_size = 0;
134 
135         /* skb->len may jitter because of SACKs, even if peer
136          * sends good full-sized frames.
137          */
138         len = skb_shinfo(skb)->gso_size ? : skb->len;
139         if (len >= icsk->icsk_ack.rcv_mss) {
140                 icsk->icsk_ack.rcv_mss = len;
141         } else {
142                 /* Otherwise, we make more careful check taking into account,
143                  * that SACKs block is variable.
144                  *
145                  * "len" is invariant segment length, including TCP header.
146                  */
147                 len += skb->data - skb_transport_header(skb);
148                 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
149                     /* If PSH is not set, packet should be
150                      * full sized, provided peer TCP is not badly broken.
151                      * This observation (if it is correct 8)) allows
152                      * to handle super-low mtu links fairly.
153                      */
154                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
155                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
156                         /* Subtract also invariant (if peer is RFC compliant),
157                          * tcp header plus fixed timestamp option length.
158                          * Resulting "len" is MSS free of SACK jitter.
159                          */
160                         len -= tcp_sk(sk)->tcp_header_len;
161                         icsk->icsk_ack.last_seg_size = len;
162                         if (len == lss) {
163                                 icsk->icsk_ack.rcv_mss = len;
164                                 return;
165                         }
166                 }
167                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
168                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
169                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
170         }
171 }
172 
173 static void tcp_incr_quickack(struct sock *sk)
174 {
175         struct inet_connection_sock *icsk = inet_csk(sk);
176         unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
177 
178         if (quickacks == 0)
179                 quickacks = 2;
180         if (quickacks > icsk->icsk_ack.quick)
181                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
182 }
183 
184 static void tcp_enter_quickack_mode(struct sock *sk)
185 {
186         struct inet_connection_sock *icsk = inet_csk(sk);
187         tcp_incr_quickack(sk);
188         icsk->icsk_ack.pingpong = 0;
189         icsk->icsk_ack.ato = TCP_ATO_MIN;
190 }
191 
192 /* Send ACKs quickly, if "quick" count is not exhausted
193  * and the session is not interactive.
194  */
195 
196 static inline bool tcp_in_quickack_mode(const struct sock *sk)
197 {
198         const struct inet_connection_sock *icsk = inet_csk(sk);
199 
200         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
201 }
202 
203 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
204 {
205         if (tp->ecn_flags & TCP_ECN_OK)
206                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
207 }
208 
209 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
210 {
211         if (tcp_hdr(skb)->cwr)
212                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
213 }
214 
215 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
216 {
217         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
218 }
219 
220 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
221 {
222         if (!(tp->ecn_flags & TCP_ECN_OK))
223                 return;
224 
225         switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
226         case INET_ECN_NOT_ECT:
227                 /* Funny extension: if ECT is not set on a segment,
228                  * and we already seen ECT on a previous segment,
229                  * it is probably a retransmit.
230                  */
231                 if (tp->ecn_flags & TCP_ECN_SEEN)
232                         tcp_enter_quickack_mode((struct sock *)tp);
233                 break;
234         case INET_ECN_CE:
235                 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
236                         /* Better not delay acks, sender can have a very low cwnd */
237                         tcp_enter_quickack_mode((struct sock *)tp);
238                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
239                 }
240                 /* fallinto */
241         default:
242                 tp->ecn_flags |= TCP_ECN_SEEN;
243         }
244 }
245 
246 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
247 {
248         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
249                 tp->ecn_flags &= ~TCP_ECN_OK;
250 }
251 
252 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
253 {
254         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
255                 tp->ecn_flags &= ~TCP_ECN_OK;
256 }
257 
258 static bool TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
259 {
260         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
261                 return true;
262         return false;
263 }
264 
265 /* Buffer size and advertised window tuning.
266  *
267  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
268  */
269 
270 static void tcp_sndbuf_expand(struct sock *sk)
271 {
272         const struct tcp_sock *tp = tcp_sk(sk);
273         int sndmem, per_mss;
274         u32 nr_segs;
275 
276         /* Worst case is non GSO/TSO : each frame consumes one skb
277          * and skb->head is kmalloced using power of two area of memory
278          */
279         per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
280                   MAX_TCP_HEADER +
281                   SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
282 
283         per_mss = roundup_pow_of_two(per_mss) +
284                   SKB_DATA_ALIGN(sizeof(struct sk_buff));
285 
286         nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
287         nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
288 
289         /* Fast Recovery (RFC 5681 3.2) :
290          * Cubic needs 1.7 factor, rounded to 2 to include
291          * extra cushion (application might react slowly to POLLOUT)
292          */
293         sndmem = 2 * nr_segs * per_mss;
294 
295         if (sk->sk_sndbuf < sndmem)
296                 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
297 }
298 
299 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
300  *
301  * All tcp_full_space() is split to two parts: "network" buffer, allocated
302  * forward and advertised in receiver window (tp->rcv_wnd) and
303  * "application buffer", required to isolate scheduling/application
304  * latencies from network.
305  * window_clamp is maximal advertised window. It can be less than
306  * tcp_full_space(), in this case tcp_full_space() - window_clamp
307  * is reserved for "application" buffer. The less window_clamp is
308  * the smoother our behaviour from viewpoint of network, but the lower
309  * throughput and the higher sensitivity of the connection to losses. 8)
310  *
311  * rcv_ssthresh is more strict window_clamp used at "slow start"
312  * phase to predict further behaviour of this connection.
313  * It is used for two goals:
314  * - to enforce header prediction at sender, even when application
315  *   requires some significant "application buffer". It is check #1.
316  * - to prevent pruning of receive queue because of misprediction
317  *   of receiver window. Check #2.
318  *
319  * The scheme does not work when sender sends good segments opening
320  * window and then starts to feed us spaghetti. But it should work
321  * in common situations. Otherwise, we have to rely on queue collapsing.
322  */
323 
324 /* Slow part of check#2. */
325 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
326 {
327         struct tcp_sock *tp = tcp_sk(sk);
328         /* Optimize this! */
329         int truesize = tcp_win_from_space(skb->truesize) >> 1;
330         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
331 
332         while (tp->rcv_ssthresh <= window) {
333                 if (truesize <= skb->len)
334                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
335 
336                 truesize >>= 1;
337                 window >>= 1;
338         }
339         return 0;
340 }
341 
342 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
343 {
344         struct tcp_sock *tp = tcp_sk(sk);
345 
346         /* Check #1 */
347         if (tp->rcv_ssthresh < tp->window_clamp &&
348             (int)tp->rcv_ssthresh < tcp_space(sk) &&
349             !sk_under_memory_pressure(sk)) {
350                 int incr;
351 
352                 /* Check #2. Increase window, if skb with such overhead
353                  * will fit to rcvbuf in future.
354                  */
355                 if (tcp_win_from_space(skb->truesize) <= skb->len)
356                         incr = 2 * tp->advmss;
357                 else
358                         incr = __tcp_grow_window(sk, skb);
359 
360                 if (incr) {
361                         incr = max_t(int, incr, 2 * skb->len);
362                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
363                                                tp->window_clamp);
364                         inet_csk(sk)->icsk_ack.quick |= 1;
365                 }
366         }
367 }
368 
369 /* 3. Tuning rcvbuf, when connection enters established state. */
370 static void tcp_fixup_rcvbuf(struct sock *sk)
371 {
372         u32 mss = tcp_sk(sk)->advmss;
373         int rcvmem;
374 
375         rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
376                  tcp_default_init_rwnd(mss);
377 
378         /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
379          * Allow enough cushion so that sender is not limited by our window
380          */
381         if (sysctl_tcp_moderate_rcvbuf)
382                 rcvmem <<= 2;
383 
384         if (sk->sk_rcvbuf < rcvmem)
385                 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
386 }
387 
388 /* 4. Try to fixup all. It is made immediately after connection enters
389  *    established state.
390  */
391 void tcp_init_buffer_space(struct sock *sk)
392 {
393         struct tcp_sock *tp = tcp_sk(sk);
394         int maxwin;
395 
396         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
397                 tcp_fixup_rcvbuf(sk);
398         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
399                 tcp_sndbuf_expand(sk);
400 
401         tp->rcvq_space.space = tp->rcv_wnd;
402         tp->rcvq_space.time = tcp_time_stamp;
403         tp->rcvq_space.seq = tp->copied_seq;
404 
405         maxwin = tcp_full_space(sk);
406 
407         if (tp->window_clamp >= maxwin) {
408                 tp->window_clamp = maxwin;
409 
410                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
411                         tp->window_clamp = max(maxwin -
412                                                (maxwin >> sysctl_tcp_app_win),
413                                                4 * tp->advmss);
414         }
415 
416         /* Force reservation of one segment. */
417         if (sysctl_tcp_app_win &&
418             tp->window_clamp > 2 * tp->advmss &&
419             tp->window_clamp + tp->advmss > maxwin)
420                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
421 
422         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
423         tp->snd_cwnd_stamp = tcp_time_stamp;
424 }
425 
426 /* 5. Recalculate window clamp after socket hit its memory bounds. */
427 static void tcp_clamp_window(struct sock *sk)
428 {
429         struct tcp_sock *tp = tcp_sk(sk);
430         struct inet_connection_sock *icsk = inet_csk(sk);
431 
432         icsk->icsk_ack.quick = 0;
433 
434         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
435             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
436             !sk_under_memory_pressure(sk) &&
437             sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
438                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
439                                     sysctl_tcp_rmem[2]);
440         }
441         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
442                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
443 }
444 
445 /* Initialize RCV_MSS value.
446  * RCV_MSS is an our guess about MSS used by the peer.
447  * We haven't any direct information about the MSS.
448  * It's better to underestimate the RCV_MSS rather than overestimate.
449  * Overestimations make us ACKing less frequently than needed.
450  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
451  */
452 void tcp_initialize_rcv_mss(struct sock *sk)
453 {
454         const struct tcp_sock *tp = tcp_sk(sk);
455         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
456 
457         hint = min(hint, tp->rcv_wnd / 2);
458         hint = min(hint, TCP_MSS_DEFAULT);
459         hint = max(hint, TCP_MIN_MSS);
460 
461         inet_csk(sk)->icsk_ack.rcv_mss = hint;
462 }
463 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
464 
465 /* Receiver "autotuning" code.
466  *
467  * The algorithm for RTT estimation w/o timestamps is based on
468  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
469  * <http://public.lanl.gov/radiant/pubs.html#DRS>
470  *
471  * More detail on this code can be found at
472  * <http://staff.psc.edu/jheffner/>,
473  * though this reference is out of date.  A new paper
474  * is pending.
475  */
476 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
477 {
478         u32 new_sample = tp->rcv_rtt_est.rtt;
479         long m = sample;
480 
481         if (m == 0)
482                 m = 1;
483 
484         if (new_sample != 0) {
485                 /* If we sample in larger samples in the non-timestamp
486                  * case, we could grossly overestimate the RTT especially
487                  * with chatty applications or bulk transfer apps which
488                  * are stalled on filesystem I/O.
489                  *
490                  * Also, since we are only going for a minimum in the
491                  * non-timestamp case, we do not smooth things out
492                  * else with timestamps disabled convergence takes too
493                  * long.
494                  */
495                 if (!win_dep) {
496                         m -= (new_sample >> 3);
497                         new_sample += m;
498                 } else {
499                         m <<= 3;
500                         if (m < new_sample)
501                                 new_sample = m;
502                 }
503         } else {
504                 /* No previous measure. */
505                 new_sample = m << 3;
506         }
507 
508         if (tp->rcv_rtt_est.rtt != new_sample)
509                 tp->rcv_rtt_est.rtt = new_sample;
510 }
511 
512 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
513 {
514         if (tp->rcv_rtt_est.time == 0)
515                 goto new_measure;
516         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
517                 return;
518         tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
519 
520 new_measure:
521         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
522         tp->rcv_rtt_est.time = tcp_time_stamp;
523 }
524 
525 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
526                                           const struct sk_buff *skb)
527 {
528         struct tcp_sock *tp = tcp_sk(sk);
529         if (tp->rx_opt.rcv_tsecr &&
530             (TCP_SKB_CB(skb)->end_seq -
531              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
532                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
533 }
534 
535 /*
536  * This function should be called every time data is copied to user space.
537  * It calculates the appropriate TCP receive buffer space.
538  */
539 void tcp_rcv_space_adjust(struct sock *sk)
540 {
541         struct tcp_sock *tp = tcp_sk(sk);
542         int time;
543         int copied;
544 
545         time = tcp_time_stamp - tp->rcvq_space.time;
546         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
547                 return;
548 
549         /* Number of bytes copied to user in last RTT */
550         copied = tp->copied_seq - tp->rcvq_space.seq;
551         if (copied <= tp->rcvq_space.space)
552                 goto new_measure;
553 
554         /* A bit of theory :
555          * copied = bytes received in previous RTT, our base window
556          * To cope with packet losses, we need a 2x factor
557          * To cope with slow start, and sender growing its cwin by 100 %
558          * every RTT, we need a 4x factor, because the ACK we are sending
559          * now is for the next RTT, not the current one :
560          * <prev RTT . ><current RTT .. ><next RTT .... >
561          */
562 
563         if (sysctl_tcp_moderate_rcvbuf &&
564             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
565                 int rcvwin, rcvmem, rcvbuf;
566 
567                 /* minimal window to cope with packet losses, assuming
568                  * steady state. Add some cushion because of small variations.
569                  */
570                 rcvwin = (copied << 1) + 16 * tp->advmss;
571 
572                 /* If rate increased by 25%,
573                  *      assume slow start, rcvwin = 3 * copied
574                  * If rate increased by 50%,
575                  *      assume sender can use 2x growth, rcvwin = 4 * copied
576                  */
577                 if (copied >=
578                     tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
579                         if (copied >=
580                             tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
581                                 rcvwin <<= 1;
582                         else
583                                 rcvwin += (rcvwin >> 1);
584                 }
585 
586                 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
587                 while (tcp_win_from_space(rcvmem) < tp->advmss)
588                         rcvmem += 128;
589 
590                 rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
591                 if (rcvbuf > sk->sk_rcvbuf) {
592                         sk->sk_rcvbuf = rcvbuf;
593 
594                         /* Make the window clamp follow along.  */
595                         tp->window_clamp = rcvwin;
596                 }
597         }
598         tp->rcvq_space.space = copied;
599 
600 new_measure:
601         tp->rcvq_space.seq = tp->copied_seq;
602         tp->rcvq_space.time = tcp_time_stamp;
603 }
604 
605 /* There is something which you must keep in mind when you analyze the
606  * behavior of the tp->ato delayed ack timeout interval.  When a
607  * connection starts up, we want to ack as quickly as possible.  The
608  * problem is that "good" TCP's do slow start at the beginning of data
609  * transmission.  The means that until we send the first few ACK's the
610  * sender will sit on his end and only queue most of his data, because
611  * he can only send snd_cwnd unacked packets at any given time.  For
612  * each ACK we send, he increments snd_cwnd and transmits more of his
613  * queue.  -DaveM
614  */
615 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
616 {
617         struct tcp_sock *tp = tcp_sk(sk);
618         struct inet_connection_sock *icsk = inet_csk(sk);
619         u32 now;
620 
621         inet_csk_schedule_ack(sk);
622 
623         tcp_measure_rcv_mss(sk, skb);
624 
625         tcp_rcv_rtt_measure(tp);
626 
627         now = tcp_time_stamp;
628 
629         if (!icsk->icsk_ack.ato) {
630                 /* The _first_ data packet received, initialize
631                  * delayed ACK engine.
632                  */
633                 tcp_incr_quickack(sk);
634                 icsk->icsk_ack.ato = TCP_ATO_MIN;
635         } else {
636                 int m = now - icsk->icsk_ack.lrcvtime;
637 
638                 if (m <= TCP_ATO_MIN / 2) {
639                         /* The fastest case is the first. */
640                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
641                 } else if (m < icsk->icsk_ack.ato) {
642                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
643                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
644                                 icsk->icsk_ack.ato = icsk->icsk_rto;
645                 } else if (m > icsk->icsk_rto) {
646                         /* Too long gap. Apparently sender failed to
647                          * restart window, so that we send ACKs quickly.
648                          */
649                         tcp_incr_quickack(sk);
650                         sk_mem_reclaim(sk);
651                 }
652         }
653         icsk->icsk_ack.lrcvtime = now;
654 
655         TCP_ECN_check_ce(tp, skb);
656 
657         if (skb->len >= 128)
658                 tcp_grow_window(sk, skb);
659 }
660 
661 /* Called to compute a smoothed rtt estimate. The data fed to this
662  * routine either comes from timestamps, or from segments that were
663  * known _not_ to have been retransmitted [see Karn/Partridge
664  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
665  * piece by Van Jacobson.
666  * NOTE: the next three routines used to be one big routine.
667  * To save cycles in the RFC 1323 implementation it was better to break
668  * it up into three procedures. -- erics
669  */
670 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
671 {
672         struct tcp_sock *tp = tcp_sk(sk);
673         long m = mrtt_us; /* RTT */
674         u32 srtt = tp->srtt_us;
675 
676         /*      The following amusing code comes from Jacobson's
677          *      article in SIGCOMM '88.  Note that rtt and mdev
678          *      are scaled versions of rtt and mean deviation.
679          *      This is designed to be as fast as possible
680          *      m stands for "measurement".
681          *
682          *      On a 1990 paper the rto value is changed to:
683          *      RTO = rtt + 4 * mdev
684          *
685          * Funny. This algorithm seems to be very broken.
686          * These formulae increase RTO, when it should be decreased, increase
687          * too slowly, when it should be increased quickly, decrease too quickly
688          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
689          * does not matter how to _calculate_ it. Seems, it was trap
690          * that VJ failed to avoid. 8)
691          */
692         if (srtt != 0) {
693                 m -= (srtt >> 3);       /* m is now error in rtt est */
694                 srtt += m;              /* rtt = 7/8 rtt + 1/8 new */
695                 if (m < 0) {
696                         m = -m;         /* m is now abs(error) */
697                         m -= (tp->mdev_us >> 2);   /* similar update on mdev */
698                         /* This is similar to one of Eifel findings.
699                          * Eifel blocks mdev updates when rtt decreases.
700                          * This solution is a bit different: we use finer gain
701                          * for mdev in this case (alpha*beta).
702                          * Like Eifel it also prevents growth of rto,
703                          * but also it limits too fast rto decreases,
704                          * happening in pure Eifel.
705                          */
706                         if (m > 0)
707                                 m >>= 3;
708                 } else {
709                         m -= (tp->mdev_us >> 2);   /* similar update on mdev */
710                 }
711                 tp->mdev_us += m;               /* mdev = 3/4 mdev + 1/4 new */
712                 if (tp->mdev_us > tp->mdev_max_us) {
713                         tp->mdev_max_us = tp->mdev_us;
714                         if (tp->mdev_max_us > tp->rttvar_us)
715                                 tp->rttvar_us = tp->mdev_max_us;
716                 }
717                 if (after(tp->snd_una, tp->rtt_seq)) {
718                         if (tp->mdev_max_us < tp->rttvar_us)
719                                 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
720                         tp->rtt_seq = tp->snd_nxt;
721                         tp->mdev_max_us = tcp_rto_min_us(sk);
722                 }
723         } else {
724                 /* no previous measure. */
725                 srtt = m << 3;          /* take the measured time to be rtt */
726                 tp->mdev_us = m << 1;   /* make sure rto = 3*rtt */
727                 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
728                 tp->mdev_max_us = tp->rttvar_us;
729                 tp->rtt_seq = tp->snd_nxt;
730         }
731         tp->srtt_us = max(1U, srtt);
732 }
733 
734 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
735  * Note: TCP stack does not yet implement pacing.
736  * FQ packet scheduler can be used to implement cheap but effective
737  * TCP pacing, to smooth the burst on large writes when packets
738  * in flight is significantly lower than cwnd (or rwin)
739  */
740 static void tcp_update_pacing_rate(struct sock *sk)
741 {
742         const struct tcp_sock *tp = tcp_sk(sk);
743         u64 rate;
744 
745         /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
746         rate = (u64)tp->mss_cache * 2 * (USEC_PER_SEC << 3);
747 
748         rate *= max(tp->snd_cwnd, tp->packets_out);
749 
750         if (likely(tp->srtt_us))
751                 do_div(rate, tp->srtt_us);
752 
753         /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
754          * without any lock. We want to make sure compiler wont store
755          * intermediate values in this location.
756          */
757         ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
758                                                 sk->sk_max_pacing_rate);
759 }
760 
761 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
762  * routine referred to above.
763  */
764 static void tcp_set_rto(struct sock *sk)
765 {
766         const struct tcp_sock *tp = tcp_sk(sk);
767         /* Old crap is replaced with new one. 8)
768          *
769          * More seriously:
770          * 1. If rtt variance happened to be less 50msec, it is hallucination.
771          *    It cannot be less due to utterly erratic ACK generation made
772          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
773          *    to do with delayed acks, because at cwnd>2 true delack timeout
774          *    is invisible. Actually, Linux-2.4 also generates erratic
775          *    ACKs in some circumstances.
776          */
777         inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
778 
779         /* 2. Fixups made earlier cannot be right.
780          *    If we do not estimate RTO correctly without them,
781          *    all the algo is pure shit and should be replaced
782          *    with correct one. It is exactly, which we pretend to do.
783          */
784 
785         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
786          * guarantees that rto is higher.
787          */
788         tcp_bound_rto(sk);
789 }
790 
791 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
792 {
793         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
794 
795         if (!cwnd)
796                 cwnd = TCP_INIT_CWND;
797         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
798 }
799 
800 /*
801  * Packet counting of FACK is based on in-order assumptions, therefore TCP
802  * disables it when reordering is detected
803  */
804 void tcp_disable_fack(struct tcp_sock *tp)
805 {
806         /* RFC3517 uses different metric in lost marker => reset on change */
807         if (tcp_is_fack(tp))
808                 tp->lost_skb_hint = NULL;
809         tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
810 }
811 
812 /* Take a notice that peer is sending D-SACKs */
813 static void tcp_dsack_seen(struct tcp_sock *tp)
814 {
815         tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
816 }
817 
818 static void tcp_update_reordering(struct sock *sk, const int metric,
819                                   const int ts)
820 {
821         struct tcp_sock *tp = tcp_sk(sk);
822         if (metric > tp->reordering) {
823                 int mib_idx;
824 
825                 tp->reordering = min(TCP_MAX_REORDERING, metric);
826 
827                 /* This exciting event is worth to be remembered. 8) */
828                 if (ts)
829                         mib_idx = LINUX_MIB_TCPTSREORDER;
830                 else if (tcp_is_reno(tp))
831                         mib_idx = LINUX_MIB_TCPRENOREORDER;
832                 else if (tcp_is_fack(tp))
833                         mib_idx = LINUX_MIB_TCPFACKREORDER;
834                 else
835                         mib_idx = LINUX_MIB_TCPSACKREORDER;
836 
837                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
838 #if FASTRETRANS_DEBUG > 1
839                 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
840                          tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
841                          tp->reordering,
842                          tp->fackets_out,
843                          tp->sacked_out,
844                          tp->undo_marker ? tp->undo_retrans : 0);
845 #endif
846                 tcp_disable_fack(tp);
847         }
848 
849         if (metric > 0)
850                 tcp_disable_early_retrans(tp);
851 }
852 
853 /* This must be called before lost_out is incremented */
854 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
855 {
856         if ((tp->retransmit_skb_hint == NULL) ||
857             before(TCP_SKB_CB(skb)->seq,
858                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
859                 tp->retransmit_skb_hint = skb;
860 
861         if (!tp->lost_out ||
862             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
863                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
864 }
865 
866 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
867 {
868         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
869                 tcp_verify_retransmit_hint(tp, skb);
870 
871                 tp->lost_out += tcp_skb_pcount(skb);
872                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
873         }
874 }
875 
876 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
877                                             struct sk_buff *skb)
878 {
879         tcp_verify_retransmit_hint(tp, skb);
880 
881         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
882                 tp->lost_out += tcp_skb_pcount(skb);
883                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
884         }
885 }
886 
887 /* This procedure tags the retransmission queue when SACKs arrive.
888  *
889  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
890  * Packets in queue with these bits set are counted in variables
891  * sacked_out, retrans_out and lost_out, correspondingly.
892  *
893  * Valid combinations are:
894  * Tag  InFlight        Description
895  * 0    1               - orig segment is in flight.
896  * S    0               - nothing flies, orig reached receiver.
897  * L    0               - nothing flies, orig lost by net.
898  * R    2               - both orig and retransmit are in flight.
899  * L|R  1               - orig is lost, retransmit is in flight.
900  * S|R  1               - orig reached receiver, retrans is still in flight.
901  * (L|S|R is logically valid, it could occur when L|R is sacked,
902  *  but it is equivalent to plain S and code short-curcuits it to S.
903  *  L|S is logically invalid, it would mean -1 packet in flight 8))
904  *
905  * These 6 states form finite state machine, controlled by the following events:
906  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
907  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
908  * 3. Loss detection event of two flavors:
909  *      A. Scoreboard estimator decided the packet is lost.
910  *         A'. Reno "three dupacks" marks head of queue lost.
911  *         A''. Its FACK modification, head until snd.fack is lost.
912  *      B. SACK arrives sacking SND.NXT at the moment, when the
913  *         segment was retransmitted.
914  * 4. D-SACK added new rule: D-SACK changes any tag to S.
915  *
916  * It is pleasant to note, that state diagram turns out to be commutative,
917  * so that we are allowed not to be bothered by order of our actions,
918  * when multiple events arrive simultaneously. (see the function below).
919  *
920  * Reordering detection.
921  * --------------------
922  * Reordering metric is maximal distance, which a packet can be displaced
923  * in packet stream. With SACKs we can estimate it:
924  *
925  * 1. SACK fills old hole and the corresponding segment was not
926  *    ever retransmitted -> reordering. Alas, we cannot use it
927  *    when segment was retransmitted.
928  * 2. The last flaw is solved with D-SACK. D-SACK arrives
929  *    for retransmitted and already SACKed segment -> reordering..
930  * Both of these heuristics are not used in Loss state, when we cannot
931  * account for retransmits accurately.
932  *
933  * SACK block validation.
934  * ----------------------
935  *
936  * SACK block range validation checks that the received SACK block fits to
937  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
938  * Note that SND.UNA is not included to the range though being valid because
939  * it means that the receiver is rather inconsistent with itself reporting
940  * SACK reneging when it should advance SND.UNA. Such SACK block this is
941  * perfectly valid, however, in light of RFC2018 which explicitly states
942  * that "SACK block MUST reflect the newest segment.  Even if the newest
943  * segment is going to be discarded ...", not that it looks very clever
944  * in case of head skb. Due to potentional receiver driven attacks, we
945  * choose to avoid immediate execution of a walk in write queue due to
946  * reneging and defer head skb's loss recovery to standard loss recovery
947  * procedure that will eventually trigger (nothing forbids us doing this).
948  *
949  * Implements also blockage to start_seq wrap-around. Problem lies in the
950  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
951  * there's no guarantee that it will be before snd_nxt (n). The problem
952  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
953  * wrap (s_w):
954  *
955  *         <- outs wnd ->                          <- wrapzone ->
956  *         u     e      n                         u_w   e_w  s n_w
957  *         |     |      |                          |     |   |  |
958  * |<------------+------+----- TCP seqno space --------------+---------->|
959  * ...-- <2^31 ->|                                           |<--------...
960  * ...---- >2^31 ------>|                                    |<--------...
961  *
962  * Current code wouldn't be vulnerable but it's better still to discard such
963  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
964  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
965  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
966  * equal to the ideal case (infinite seqno space without wrap caused issues).
967  *
968  * With D-SACK the lower bound is extended to cover sequence space below
969  * SND.UNA down to undo_marker, which is the last point of interest. Yet
970  * again, D-SACK block must not to go across snd_una (for the same reason as
971  * for the normal SACK blocks, explained above). But there all simplicity
972  * ends, TCP might receive valid D-SACKs below that. As long as they reside
973  * fully below undo_marker they do not affect behavior in anyway and can
974  * therefore be safely ignored. In rare cases (which are more or less
975  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
976  * fragmentation and packet reordering past skb's retransmission. To consider
977  * them correctly, the acceptable range must be extended even more though
978  * the exact amount is rather hard to quantify. However, tp->max_window can
979  * be used as an exaggerated estimate.
980  */
981 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
982                                    u32 start_seq, u32 end_seq)
983 {
984         /* Too far in future, or reversed (interpretation is ambiguous) */
985         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
986                 return false;
987 
988         /* Nasty start_seq wrap-around check (see comments above) */
989         if (!before(start_seq, tp->snd_nxt))
990                 return false;
991 
992         /* In outstanding window? ...This is valid exit for D-SACKs too.
993          * start_seq == snd_una is non-sensical (see comments above)
994          */
995         if (after(start_seq, tp->snd_una))
996                 return true;
997 
998         if (!is_dsack || !tp->undo_marker)
999                 return false;
1000 
1001         /* ...Then it's D-SACK, and must reside below snd_una completely */
1002         if (after(end_seq, tp->snd_una))
1003                 return false;
1004 
1005         if (!before(start_seq, tp->undo_marker))
1006                 return true;
1007 
1008         /* Too old */
1009         if (!after(end_seq, tp->undo_marker))
1010                 return false;
1011 
1012         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1013          *   start_seq < undo_marker and end_seq >= undo_marker.
1014          */
1015         return !before(start_seq, end_seq - tp->max_window);
1016 }
1017 
1018 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1019  * Event "B". Later note: FACK people cheated me again 8), we have to account
1020  * for reordering! Ugly, but should help.
1021  *
1022  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1023  * less than what is now known to be received by the other end (derived from
1024  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1025  * retransmitted skbs to avoid some costly processing per ACKs.
1026  */
1027 static void tcp_mark_lost_retrans(struct sock *sk)
1028 {
1029         const struct inet_connection_sock *icsk = inet_csk(sk);
1030         struct tcp_sock *tp = tcp_sk(sk);
1031         struct sk_buff *skb;
1032         int cnt = 0;
1033         u32 new_low_seq = tp->snd_nxt;
1034         u32 received_upto = tcp_highest_sack_seq(tp);
1035 
1036         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1037             !after(received_upto, tp->lost_retrans_low) ||
1038             icsk->icsk_ca_state != TCP_CA_Recovery)
1039                 return;
1040 
1041         tcp_for_write_queue(skb, sk) {
1042                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1043 
1044                 if (skb == tcp_send_head(sk))
1045                         break;
1046                 if (cnt == tp->retrans_out)
1047                         break;
1048                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1049                         continue;
1050 
1051                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1052                         continue;
1053 
1054                 /* TODO: We would like to get rid of tcp_is_fack(tp) only
1055                  * constraint here (see above) but figuring out that at
1056                  * least tp->reordering SACK blocks reside between ack_seq
1057                  * and received_upto is not easy task to do cheaply with
1058                  * the available datastructures.
1059                  *
1060                  * Whether FACK should check here for tp->reordering segs
1061                  * in-between one could argue for either way (it would be
1062                  * rather simple to implement as we could count fack_count
1063                  * during the walk and do tp->fackets_out - fack_count).
1064                  */
1065                 if (after(received_upto, ack_seq)) {
1066                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1067                         tp->retrans_out -= tcp_skb_pcount(skb);
1068 
1069                         tcp_skb_mark_lost_uncond_verify(tp, skb);
1070                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1071                 } else {
1072                         if (before(ack_seq, new_low_seq))
1073                                 new_low_seq = ack_seq;
1074                         cnt += tcp_skb_pcount(skb);
1075                 }
1076         }
1077 
1078         if (tp->retrans_out)
1079                 tp->lost_retrans_low = new_low_seq;
1080 }
1081 
1082 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1083                             struct tcp_sack_block_wire *sp, int num_sacks,
1084                             u32 prior_snd_una)
1085 {
1086         struct tcp_sock *tp = tcp_sk(sk);
1087         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1088         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1089         bool dup_sack = false;
1090 
1091         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1092                 dup_sack = true;
1093                 tcp_dsack_seen(tp);
1094                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1095         } else if (num_sacks > 1) {
1096                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1097                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1098 
1099                 if (!after(end_seq_0, end_seq_1) &&
1100                     !before(start_seq_0, start_seq_1)) {
1101                         dup_sack = true;
1102                         tcp_dsack_seen(tp);
1103                         NET_INC_STATS_BH(sock_net(sk),
1104                                         LINUX_MIB_TCPDSACKOFORECV);
1105                 }
1106         }
1107 
1108         /* D-SACK for already forgotten data... Do dumb counting. */
1109         if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1110             !after(end_seq_0, prior_snd_una) &&
1111             after(end_seq_0, tp->undo_marker))
1112                 tp->undo_retrans--;
1113 
1114         return dup_sack;
1115 }
1116 
1117 struct tcp_sacktag_state {
1118         int     reord;
1119         int     fack_count;
1120         long    rtt_us; /* RTT measured by SACKing never-retransmitted data */
1121         int     flag;
1122 };
1123 
1124 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1125  * the incoming SACK may not exactly match but we can find smaller MSS
1126  * aligned portion of it that matches. Therefore we might need to fragment
1127  * which may fail and creates some hassle (caller must handle error case
1128  * returns).
1129  *
1130  * FIXME: this could be merged to shift decision code
1131  */
1132 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1133                                   u32 start_seq, u32 end_seq)
1134 {
1135         int err;
1136         bool in_sack;
1137         unsigned int pkt_len;
1138         unsigned int mss;
1139 
1140         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1141                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1142 
1143         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1144             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1145                 mss = tcp_skb_mss(skb);
1146                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1147 
1148                 if (!in_sack) {
1149                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1150                         if (pkt_len < mss)
1151                                 pkt_len = mss;
1152                 } else {
1153                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1154                         if (pkt_len < mss)
1155                                 return -EINVAL;
1156                 }
1157 
1158                 /* Round if necessary so that SACKs cover only full MSSes
1159                  * and/or the remaining small portion (if present)
1160                  */
1161                 if (pkt_len > mss) {
1162                         unsigned int new_len = (pkt_len / mss) * mss;
1163                         if (!in_sack && new_len < pkt_len) {
1164                                 new_len += mss;
1165                                 if (new_len >= skb->len)
1166                                         return 0;
1167                         }
1168                         pkt_len = new_len;
1169                 }
1170                 err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1171                 if (err < 0)
1172                         return err;
1173         }
1174 
1175         return in_sack;
1176 }
1177 
1178 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1179 static u8 tcp_sacktag_one(struct sock *sk,
1180                           struct tcp_sacktag_state *state, u8 sacked,
1181                           u32 start_seq, u32 end_seq,
1182                           int dup_sack, int pcount,
1183                           const struct skb_mstamp *xmit_time)
1184 {
1185         struct tcp_sock *tp = tcp_sk(sk);
1186         int fack_count = state->fack_count;
1187 
1188         /* Account D-SACK for retransmitted packet. */
1189         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1190                 if (tp->undo_marker && tp->undo_retrans > 0 &&
1191                     after(end_seq, tp->undo_marker))
1192                         tp->undo_retrans--;
1193                 if (sacked & TCPCB_SACKED_ACKED)
1194                         state->reord = min(fack_count, state->reord);
1195         }
1196 
1197         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1198         if (!after(end_seq, tp->snd_una))
1199                 return sacked;
1200 
1201         if (!(sacked & TCPCB_SACKED_ACKED)) {
1202                 if (sacked & TCPCB_SACKED_RETRANS) {
1203                         /* If the segment is not tagged as lost,
1204                          * we do not clear RETRANS, believing
1205                          * that retransmission is still in flight.
1206                          */
1207                         if (sacked & TCPCB_LOST) {
1208                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1209                                 tp->lost_out -= pcount;
1210                                 tp->retrans_out -= pcount;
1211                         }
1212                 } else {
1213                         if (!(sacked & TCPCB_RETRANS)) {
1214                                 /* New sack for not retransmitted frame,
1215                                  * which was in hole. It is reordering.
1216                                  */
1217                                 if (before(start_seq,
1218                                            tcp_highest_sack_seq(tp)))
1219                                         state->reord = min(fack_count,
1220                                                            state->reord);
1221                                 if (!after(end_seq, tp->high_seq))
1222                                         state->flag |= FLAG_ORIG_SACK_ACKED;
1223                                 /* Pick the earliest sequence sacked for RTT */
1224                                 if (state->rtt_us < 0) {
1225                                         struct skb_mstamp now;
1226 
1227                                         skb_mstamp_get(&now);
1228                                         state->rtt_us = skb_mstamp_us_delta(&now,
1229                                                                 xmit_time);
1230                                 }
1231                         }
1232 
1233                         if (sacked & TCPCB_LOST) {
1234                                 sacked &= ~TCPCB_LOST;
1235                                 tp->lost_out -= pcount;
1236                         }
1237                 }
1238 
1239                 sacked |= TCPCB_SACKED_ACKED;
1240                 state->flag |= FLAG_DATA_SACKED;
1241                 tp->sacked_out += pcount;
1242 
1243                 fack_count += pcount;
1244 
1245                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1246                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1247                     before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1248                         tp->lost_cnt_hint += pcount;
1249 
1250                 if (fack_count > tp->fackets_out)
1251                         tp->fackets_out = fack_count;
1252         }
1253 
1254         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1255          * frames and clear it. undo_retrans is decreased above, L|R frames
1256          * are accounted above as well.
1257          */
1258         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1259                 sacked &= ~TCPCB_SACKED_RETRANS;
1260                 tp->retrans_out -= pcount;
1261         }
1262 
1263         return sacked;
1264 }
1265 
1266 /* Shift newly-SACKed bytes from this skb to the immediately previous
1267  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1268  */
1269 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1270                             struct tcp_sacktag_state *state,
1271                             unsigned int pcount, int shifted, int mss,
1272                             bool dup_sack)
1273 {
1274         struct tcp_sock *tp = tcp_sk(sk);
1275         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1276         u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
1277         u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
1278 
1279         BUG_ON(!pcount);
1280 
1281         /* Adjust counters and hints for the newly sacked sequence
1282          * range but discard the return value since prev is already
1283          * marked. We must tag the range first because the seq
1284          * advancement below implicitly advances
1285          * tcp_highest_sack_seq() when skb is highest_sack.
1286          */
1287         tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1288                         start_seq, end_seq, dup_sack, pcount,
1289                         &skb->skb_mstamp);
1290 
1291         if (skb == tp->lost_skb_hint)
1292                 tp->lost_cnt_hint += pcount;
1293 
1294         TCP_SKB_CB(prev)->end_seq += shifted;
1295         TCP_SKB_CB(skb)->seq += shifted;
1296 
1297         skb_shinfo(prev)->gso_segs += pcount;
1298         BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1299         skb_shinfo(skb)->gso_segs -= pcount;
1300 
1301         /* When we're adding to gso_segs == 1, gso_size will be zero,
1302          * in theory this shouldn't be necessary but as long as DSACK
1303          * code can come after this skb later on it's better to keep
1304          * setting gso_size to something.
1305          */
1306         if (!skb_shinfo(prev)->gso_size) {
1307                 skb_shinfo(prev)->gso_size = mss;
1308                 skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1309         }
1310 
1311         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1312         if (skb_shinfo(skb)->gso_segs <= 1) {
1313                 skb_shinfo(skb)->gso_size = 0;
1314                 skb_shinfo(skb)->gso_type = 0;
1315         }
1316 
1317         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1318         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1319 
1320         if (skb->len > 0) {
1321                 BUG_ON(!tcp_skb_pcount(skb));
1322                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1323                 return false;
1324         }
1325 
1326         /* Whole SKB was eaten :-) */
1327 
1328         if (skb == tp->retransmit_skb_hint)
1329                 tp->retransmit_skb_hint = prev;
1330         if (skb == tp->lost_skb_hint) {
1331                 tp->lost_skb_hint = prev;
1332                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1333         }
1334 
1335         TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1336         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1337                 TCP_SKB_CB(prev)->end_seq++;
1338 
1339         if (skb == tcp_highest_sack(sk))
1340                 tcp_advance_highest_sack(sk, skb);
1341 
1342         tcp_unlink_write_queue(skb, sk);
1343         sk_wmem_free_skb(sk, skb);
1344 
1345         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1346 
1347         return true;
1348 }
1349 
1350 /* I wish gso_size would have a bit more sane initialization than
1351  * something-or-zero which complicates things
1352  */
1353 static int tcp_skb_seglen(const struct sk_buff *skb)
1354 {
1355         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1356 }
1357 
1358 /* Shifting pages past head area doesn't work */
1359 static int skb_can_shift(const struct sk_buff *skb)
1360 {
1361         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1362 }
1363 
1364 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1365  * skb.
1366  */
1367 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1368                                           struct tcp_sacktag_state *state,
1369                                           u32 start_seq, u32 end_seq,
1370                                           bool dup_sack)
1371 {
1372         struct tcp_sock *tp = tcp_sk(sk);
1373         struct sk_buff *prev;
1374         int mss;
1375         int pcount = 0;
1376         int len;
1377         int in_sack;
1378 
1379         if (!sk_can_gso(sk))
1380                 goto fallback;
1381 
1382         /* Normally R but no L won't result in plain S */
1383         if (!dup_sack &&
1384             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1385                 goto fallback;
1386         if (!skb_can_shift(skb))
1387                 goto fallback;
1388         /* This frame is about to be dropped (was ACKed). */
1389         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1390                 goto fallback;
1391 
1392         /* Can only happen with delayed DSACK + discard craziness */
1393         if (unlikely(skb == tcp_write_queue_head(sk)))
1394                 goto fallback;
1395         prev = tcp_write_queue_prev(sk, skb);
1396 
1397         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1398                 goto fallback;
1399 
1400         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1401                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1402 
1403         if (in_sack) {
1404                 len = skb->len;
1405                 pcount = tcp_skb_pcount(skb);
1406                 mss = tcp_skb_seglen(skb);
1407 
1408                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1409                  * drop this restriction as unnecessary
1410                  */
1411                 if (mss != tcp_skb_seglen(prev))
1412                         goto fallback;
1413         } else {
1414                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1415                         goto noop;
1416                 /* CHECKME: This is non-MSS split case only?, this will
1417                  * cause skipped skbs due to advancing loop btw, original
1418                  * has that feature too
1419                  */
1420                 if (tcp_skb_pcount(skb) <= 1)
1421                         goto noop;
1422 
1423                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1424                 if (!in_sack) {
1425                         /* TODO: head merge to next could be attempted here
1426                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1427                          * though it might not be worth of the additional hassle
1428                          *
1429                          * ...we can probably just fallback to what was done
1430                          * previously. We could try merging non-SACKed ones
1431                          * as well but it probably isn't going to buy off
1432                          * because later SACKs might again split them, and
1433                          * it would make skb timestamp tracking considerably
1434                          * harder problem.
1435                          */
1436                         goto fallback;
1437                 }
1438 
1439                 len = end_seq - TCP_SKB_CB(skb)->seq;
1440                 BUG_ON(len < 0);
1441                 BUG_ON(len > skb->len);
1442 
1443                 /* MSS boundaries should be honoured or else pcount will
1444                  * severely break even though it makes things bit trickier.
1445                  * Optimize common case to avoid most of the divides
1446                  */
1447                 mss = tcp_skb_mss(skb);
1448 
1449                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1450                  * drop this restriction as unnecessary
1451                  */
1452                 if (mss != tcp_skb_seglen(prev))
1453                         goto fallback;
1454 
1455                 if (len == mss) {
1456                         pcount = 1;
1457                 } else if (len < mss) {
1458                         goto noop;
1459                 } else {
1460                         pcount = len / mss;
1461                         len = pcount * mss;
1462                 }
1463         }
1464 
1465         /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1466         if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1467                 goto fallback;
1468 
1469         if (!skb_shift(prev, skb, len))
1470                 goto fallback;
1471         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1472                 goto out;
1473 
1474         /* Hole filled allows collapsing with the next as well, this is very
1475          * useful when hole on every nth skb pattern happens
1476          */
1477         if (prev == tcp_write_queue_tail(sk))
1478                 goto out;
1479         skb = tcp_write_queue_next(sk, prev);
1480 
1481         if (!skb_can_shift(skb) ||
1482             (skb == tcp_send_head(sk)) ||
1483             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1484             (mss != tcp_skb_seglen(skb)))
1485                 goto out;
1486 
1487         len = skb->len;
1488         if (skb_shift(prev, skb, len)) {
1489                 pcount += tcp_skb_pcount(skb);
1490                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1491         }
1492 
1493 out:
1494         state->fack_count += pcount;
1495         return prev;
1496 
1497 noop:
1498         return skb;
1499 
1500 fallback:
1501         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1502         return NULL;
1503 }
1504 
1505 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1506                                         struct tcp_sack_block *next_dup,
1507                                         struct tcp_sacktag_state *state,
1508                                         u32 start_seq, u32 end_seq,
1509                                         bool dup_sack_in)
1510 {
1511         struct tcp_sock *tp = tcp_sk(sk);
1512         struct sk_buff *tmp;
1513 
1514         tcp_for_write_queue_from(skb, sk) {
1515                 int in_sack = 0;
1516                 bool dup_sack = dup_sack_in;
1517 
1518                 if (skb == tcp_send_head(sk))
1519                         break;
1520 
1521                 /* queue is in-order => we can short-circuit the walk early */
1522                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1523                         break;
1524 
1525                 if ((next_dup != NULL) &&
1526                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1527                         in_sack = tcp_match_skb_to_sack(sk, skb,
1528                                                         next_dup->start_seq,
1529                                                         next_dup->end_seq);
1530                         if (in_sack > 0)
1531                                 dup_sack = true;
1532                 }
1533 
1534                 /* skb reference here is a bit tricky to get right, since
1535                  * shifting can eat and free both this skb and the next,
1536                  * so not even _safe variant of the loop is enough.
1537                  */
1538                 if (in_sack <= 0) {
1539                         tmp = tcp_shift_skb_data(sk, skb, state,
1540                                                  start_seq, end_seq, dup_sack);
1541                         if (tmp != NULL) {
1542                                 if (tmp != skb) {
1543                                         skb = tmp;
1544                                         continue;
1545                                 }
1546 
1547                                 in_sack = 0;
1548                         } else {
1549                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1550                                                                 start_seq,
1551                                                                 end_seq);
1552                         }
1553                 }
1554 
1555                 if (unlikely(in_sack < 0))
1556                         break;
1557 
1558                 if (in_sack) {
1559                         TCP_SKB_CB(skb)->sacked =
1560                                 tcp_sacktag_one(sk,
1561                                                 state,
1562                                                 TCP_SKB_CB(skb)->sacked,
1563                                                 TCP_SKB_CB(skb)->seq,
1564                                                 TCP_SKB_CB(skb)->end_seq,
1565                                                 dup_sack,
1566                                                 tcp_skb_pcount(skb),
1567                                                 &skb->skb_mstamp);
1568 
1569                         if (!before(TCP_SKB_CB(skb)->seq,
1570                                     tcp_highest_sack_seq(tp)))
1571                                 tcp_advance_highest_sack(sk, skb);
1572                 }
1573 
1574                 state->fack_count += tcp_skb_pcount(skb);
1575         }
1576         return skb;
1577 }
1578 
1579 /* Avoid all extra work that is being done by sacktag while walking in
1580  * a normal way
1581  */
1582 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1583                                         struct tcp_sacktag_state *state,
1584                                         u32 skip_to_seq)
1585 {
1586         tcp_for_write_queue_from(skb, sk) {
1587                 if (skb == tcp_send_head(sk))
1588                         break;
1589 
1590                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1591                         break;
1592 
1593                 state->fack_count += tcp_skb_pcount(skb);
1594         }
1595         return skb;
1596 }
1597 
1598 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1599                                                 struct sock *sk,
1600                                                 struct tcp_sack_block *next_dup,
1601                                                 struct tcp_sacktag_state *state,
1602                                                 u32 skip_to_seq)
1603 {
1604         if (next_dup == NULL)
1605                 return skb;
1606 
1607         if (before(next_dup->start_seq, skip_to_seq)) {
1608                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1609                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1610                                        next_dup->start_seq, next_dup->end_seq,
1611                                        1);
1612         }
1613 
1614         return skb;
1615 }
1616 
1617 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1618 {
1619         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1620 }
1621 
1622 static int
1623 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1624                         u32 prior_snd_una, long *sack_rtt_us)
1625 {
1626         struct tcp_sock *tp = tcp_sk(sk);
1627         const unsigned char *ptr = (skb_transport_header(ack_skb) +
1628                                     TCP_SKB_CB(ack_skb)->sacked);
1629         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1630         struct tcp_sack_block sp[TCP_NUM_SACKS];
1631         struct tcp_sack_block *cache;
1632         struct tcp_sacktag_state state;
1633         struct sk_buff *skb;
1634         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1635         int used_sacks;
1636         bool found_dup_sack = false;
1637         int i, j;
1638         int first_sack_index;
1639 
1640         state.flag = 0;
1641         state.reord = tp->packets_out;
1642         state.rtt_us = -1L;
1643 
1644         if (!tp->sacked_out) {
1645                 if (WARN_ON(tp->fackets_out))
1646                         tp->fackets_out = 0;
1647                 tcp_highest_sack_reset(sk);
1648         }
1649 
1650         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1651                                          num_sacks, prior_snd_una);
1652         if (found_dup_sack)
1653                 state.flag |= FLAG_DSACKING_ACK;
1654 
1655         /* Eliminate too old ACKs, but take into
1656          * account more or less fresh ones, they can
1657          * contain valid SACK info.
1658          */
1659         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1660                 return 0;
1661 
1662         if (!tp->packets_out)
1663                 goto out;
1664 
1665         used_sacks = 0;
1666         first_sack_index = 0;
1667         for (i = 0; i < num_sacks; i++) {
1668                 bool dup_sack = !i && found_dup_sack;
1669 
1670                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1671                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1672 
1673                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1674                                             sp[used_sacks].start_seq,
1675                                             sp[used_sacks].end_seq)) {
1676                         int mib_idx;
1677 
1678                         if (dup_sack) {
1679                                 if (!tp->undo_marker)
1680                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1681                                 else
1682                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1683                         } else {
1684                                 /* Don't count olds caused by ACK reordering */
1685                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1686                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1687                                         continue;
1688                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1689                         }
1690 
1691                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1692                         if (i == 0)
1693                                 first_sack_index = -1;
1694                         continue;
1695                 }
1696 
1697                 /* Ignore very old stuff early */
1698                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1699                         continue;
1700 
1701                 used_sacks++;
1702         }
1703 
1704         /* order SACK blocks to allow in order walk of the retrans queue */
1705         for (i = used_sacks - 1; i > 0; i--) {
1706                 for (j = 0; j < i; j++) {
1707                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1708                                 swap(sp[j], sp[j + 1]);
1709 
1710                                 /* Track where the first SACK block goes to */
1711                                 if (j == first_sack_index)
1712                                         first_sack_index = j + 1;
1713                         }
1714                 }
1715         }
1716 
1717         skb = tcp_write_queue_head(sk);
1718         state.fack_count = 0;
1719         i = 0;
1720 
1721         if (!tp->sacked_out) {
1722                 /* It's already past, so skip checking against it */
1723                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1724         } else {
1725                 cache = tp->recv_sack_cache;
1726                 /* Skip empty blocks in at head of the cache */
1727                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1728                        !cache->end_seq)
1729                         cache++;
1730         }
1731 
1732         while (i < used_sacks) {
1733                 u32 start_seq = sp[i].start_seq;
1734                 u32 end_seq = sp[i].end_seq;
1735                 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1736                 struct tcp_sack_block *next_dup = NULL;
1737 
1738                 if (found_dup_sack && ((i + 1) == first_sack_index))
1739                         next_dup = &sp[i + 1];
1740 
1741                 /* Skip too early cached blocks */
1742                 while (tcp_sack_cache_ok(tp, cache) &&
1743                        !before(start_seq, cache->end_seq))
1744                         cache++;
1745 
1746                 /* Can skip some work by looking recv_sack_cache? */
1747                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1748                     after(end_seq, cache->start_seq)) {
1749 
1750                         /* Head todo? */
1751                         if (before(start_seq, cache->start_seq)) {
1752                                 skb = tcp_sacktag_skip(skb, sk, &state,
1753                                                        start_seq);
1754                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1755                                                        &state,
1756                                                        start_seq,
1757                                                        cache->start_seq,
1758                                                        dup_sack);
1759                         }
1760 
1761                         /* Rest of the block already fully processed? */
1762                         if (!after(end_seq, cache->end_seq))
1763                                 goto advance_sp;
1764 
1765                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1766                                                        &state,
1767                                                        cache->end_seq);
1768 
1769                         /* ...tail remains todo... */
1770                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1771                                 /* ...but better entrypoint exists! */
1772                                 skb = tcp_highest_sack(sk);
1773                                 if (skb == NULL)
1774                                         break;
1775                                 state.fack_count = tp->fackets_out;
1776                                 cache++;
1777                                 goto walk;
1778                         }
1779 
1780                         skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1781                         /* Check overlap against next cached too (past this one already) */
1782                         cache++;
1783                         continue;
1784                 }
1785 
1786                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1787                         skb = tcp_highest_sack(sk);
1788                         if (skb == NULL)
1789                                 break;
1790                         state.fack_count = tp->fackets_out;
1791                 }
1792                 skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1793 
1794 walk:
1795                 skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1796                                        start_seq, end_seq, dup_sack);
1797 
1798 advance_sp:
1799                 i++;
1800         }
1801 
1802         /* Clear the head of the cache sack blocks so we can skip it next time */
1803         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1804                 tp->recv_sack_cache[i].start_seq = 0;
1805                 tp->recv_sack_cache[i].end_seq = 0;
1806         }
1807         for (j = 0; j < used_sacks; j++)
1808                 tp->recv_sack_cache[i++] = sp[j];
1809 
1810         tcp_mark_lost_retrans(sk);
1811 
1812         tcp_verify_left_out(tp);
1813 
1814         if ((state.reord < tp->fackets_out) &&
1815             ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1816                 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1817 
1818 out:
1819 
1820 #if FASTRETRANS_DEBUG > 0
1821         WARN_ON((int)tp->sacked_out < 0);
1822         WARN_ON((int)tp->lost_out < 0);
1823         WARN_ON((int)tp->retrans_out < 0);
1824         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1825 #endif
1826         *sack_rtt_us = state.rtt_us;
1827         return state.flag;
1828 }
1829 
1830 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1831  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1832  */
1833 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1834 {
1835         u32 holes;
1836 
1837         holes = max(tp->lost_out, 1U);
1838         holes = min(holes, tp->packets_out);
1839 
1840         if ((tp->sacked_out + holes) > tp->packets_out) {
1841                 tp->sacked_out = tp->packets_out - holes;
1842                 return true;
1843         }
1844         return false;
1845 }
1846 
1847 /* If we receive more dupacks than we expected counting segments
1848  * in assumption of absent reordering, interpret this as reordering.
1849  * The only another reason could be bug in receiver TCP.
1850  */
1851 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1852 {
1853         struct tcp_sock *tp = tcp_sk(sk);
1854         if (tcp_limit_reno_sacked(tp))
1855                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1856 }
1857 
1858 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1859 
1860 static void tcp_add_reno_sack(struct sock *sk)
1861 {
1862         struct tcp_sock *tp = tcp_sk(sk);
1863         tp->sacked_out++;
1864         tcp_check_reno_reordering(sk, 0);
1865         tcp_verify_left_out(tp);
1866 }
1867 
1868 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1869 
1870 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1871 {
1872         struct tcp_sock *tp = tcp_sk(sk);
1873 
1874         if (acked > 0) {
1875                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1876                 if (acked - 1 >= tp->sacked_out)
1877                         tp->sacked_out = 0;
1878                 else
1879                         tp->sacked_out -= acked - 1;
1880         }
1881         tcp_check_reno_reordering(sk, acked);
1882         tcp_verify_left_out(tp);
1883 }
1884 
1885 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1886 {
1887         tp->sacked_out = 0;
1888 }
1889 
1890 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
1891 {
1892         tp->retrans_out = 0;
1893         tp->lost_out = 0;
1894 
1895         tp->undo_marker = 0;
1896         tp->undo_retrans = -1;
1897 }
1898 
1899 void tcp_clear_retrans(struct tcp_sock *tp)
1900 {
1901         tcp_clear_retrans_partial(tp);
1902 
1903         tp->fackets_out = 0;
1904         tp->sacked_out = 0;
1905 }
1906 
1907 /* Enter Loss state. If "how" is not zero, forget all SACK information
1908  * and reset tags completely, otherwise preserve SACKs. If receiver
1909  * dropped its ofo queue, we will know this due to reneging detection.
1910  */
1911 void tcp_enter_loss(struct sock *sk, int how)
1912 {
1913         const struct inet_connection_sock *icsk = inet_csk(sk);
1914         struct tcp_sock *tp = tcp_sk(sk);
1915         struct sk_buff *skb;
1916         bool new_recovery = false;
1917 
1918         /* Reduce ssthresh if it has not yet been made inside this window. */
1919         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1920             !after(tp->high_seq, tp->snd_una) ||
1921             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1922                 new_recovery = true;
1923                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1924                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1925                 tcp_ca_event(sk, CA_EVENT_LOSS);
1926         }
1927         tp->snd_cwnd       = 1;
1928         tp->snd_cwnd_cnt   = 0;
1929         tp->snd_cwnd_stamp = tcp_time_stamp;
1930 
1931         tcp_clear_retrans_partial(tp);
1932 
1933         if (tcp_is_reno(tp))
1934                 tcp_reset_reno_sack(tp);
1935 
1936         tp->undo_marker = tp->snd_una;
1937         if (how) {
1938                 tp->sacked_out = 0;
1939                 tp->fackets_out = 0;
1940         }
1941         tcp_clear_all_retrans_hints(tp);
1942 
1943         tcp_for_write_queue(skb, sk) {
1944                 if (skb == tcp_send_head(sk))
1945                         break;
1946 
1947                 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1948                         tp->undo_marker = 0;
1949 
1950                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1951                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1952                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1953                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1954                         tp->lost_out += tcp_skb_pcount(skb);
1955                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1956                 }
1957         }
1958         tcp_verify_left_out(tp);
1959 
1960         /* Timeout in disordered state after receiving substantial DUPACKs
1961          * suggests that the degree of reordering is over-estimated.
1962          */
1963         if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1964             tp->sacked_out >= sysctl_tcp_reordering)
1965                 tp->reordering = min_t(unsigned int, tp->reordering,
1966                                        sysctl_tcp_reordering);
1967         tcp_set_ca_state(sk, TCP_CA_Loss);
1968         tp->high_seq = tp->snd_nxt;
1969         TCP_ECN_queue_cwr(tp);
1970 
1971         /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1972          * loss recovery is underway except recurring timeout(s) on
1973          * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1974          */
1975         tp->frto = sysctl_tcp_frto &&
1976                    (new_recovery || icsk->icsk_retransmits) &&
1977                    !inet_csk(sk)->icsk_mtup.probe_size;
1978 }
1979 
1980 /* If ACK arrived pointing to a remembered SACK, it means that our
1981  * remembered SACKs do not reflect real state of receiver i.e.
1982  * receiver _host_ is heavily congested (or buggy).
1983  *
1984  * Do processing similar to RTO timeout.
1985  */
1986 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
1987 {
1988         if (flag & FLAG_SACK_RENEGING) {
1989                 struct inet_connection_sock *icsk = inet_csk(sk);
1990                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1991 
1992                 tcp_enter_loss(sk, 1);
1993                 icsk->icsk_retransmits++;
1994                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1995                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1996                                           icsk->icsk_rto, TCP_RTO_MAX);
1997                 return true;
1998         }
1999         return false;
2000 }
2001 
2002 static inline int tcp_fackets_out(const struct tcp_sock *tp)
2003 {
2004         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2005 }
2006 
2007 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2008  * counter when SACK is enabled (without SACK, sacked_out is used for
2009  * that purpose).
2010  *
2011  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2012  * segments up to the highest received SACK block so far and holes in
2013  * between them.
2014  *
2015  * With reordering, holes may still be in flight, so RFC3517 recovery
2016  * uses pure sacked_out (total number of SACKed segments) even though
2017  * it violates the RFC that uses duplicate ACKs, often these are equal
2018  * but when e.g. out-of-window ACKs or packet duplication occurs,
2019  * they differ. Since neither occurs due to loss, TCP should really
2020  * ignore them.
2021  */
2022 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2023 {
2024         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2025 }
2026 
2027 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
2028 {
2029         struct tcp_sock *tp = tcp_sk(sk);
2030         unsigned long delay;
2031 
2032         /* Delay early retransmit and entering fast recovery for
2033          * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
2034          * available, or RTO is scheduled to fire first.
2035          */
2036         if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2037             (flag & FLAG_ECE) || !tp->srtt_us)
2038                 return false;
2039 
2040         delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
2041                     msecs_to_jiffies(2));
2042 
2043         if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2044                 return false;
2045 
2046         inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2047                                   TCP_RTO_MAX);
2048         return true;
2049 }
2050 
2051 /* Linux NewReno/SACK/FACK/ECN state machine.
2052  * --------------------------------------
2053  *
2054  * "Open"       Normal state, no dubious events, fast path.
2055  * "Disorder"   In all the respects it is "Open",
2056  *              but requires a bit more attention. It is entered when
2057  *              we see some SACKs or dupacks. It is split of "Open"
2058  *              mainly to move some processing from fast path to slow one.
2059  * "CWR"        CWND was reduced due to some Congestion Notification event.
2060  *              It can be ECN, ICMP source quench, local device congestion.
2061  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2062  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2063  *
2064  * tcp_fastretrans_alert() is entered:
2065  * - each incoming ACK, if state is not "Open"
2066  * - when arrived ACK is unusual, namely:
2067  *      * SACK
2068  *      * Duplicate ACK.
2069  *      * ECN ECE.
2070  *
2071  * Counting packets in flight is pretty simple.
2072  *
2073  *      in_flight = packets_out - left_out + retrans_out
2074  *
2075  *      packets_out is SND.NXT-SND.UNA counted in packets.
2076  *
2077  *      retrans_out is number of retransmitted segments.
2078  *
2079  *      left_out is number of segments left network, but not ACKed yet.
2080  *
2081  *              left_out = sacked_out + lost_out
2082  *
2083  *     sacked_out: Packets, which arrived to receiver out of order
2084  *                 and hence not ACKed. With SACKs this number is simply
2085  *                 amount of SACKed data. Even without SACKs
2086  *                 it is easy to give pretty reliable estimate of this number,
2087  *                 counting duplicate ACKs.
2088  *
2089  *       lost_out: Packets lost by network. TCP has no explicit
2090  *                 "loss notification" feedback from network (for now).
2091  *                 It means that this number can be only _guessed_.
2092  *                 Actually, it is the heuristics to predict lossage that
2093  *                 distinguishes different algorithms.
2094  *
2095  *      F.e. after RTO, when all the queue is considered as lost,
2096  *      lost_out = packets_out and in_flight = retrans_out.
2097  *
2098  *              Essentially, we have now two algorithms counting
2099  *              lost packets.
2100  *
2101  *              FACK: It is the simplest heuristics. As soon as we decided
2102  *              that something is lost, we decide that _all_ not SACKed
2103  *              packets until the most forward SACK are lost. I.e.
2104  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2105  *              It is absolutely correct estimate, if network does not reorder
2106  *              packets. And it loses any connection to reality when reordering
2107  *              takes place. We use FACK by default until reordering
2108  *              is suspected on the path to this destination.
2109  *
2110  *              NewReno: when Recovery is entered, we assume that one segment
2111  *              is lost (classic Reno). While we are in Recovery and
2112  *              a partial ACK arrives, we assume that one more packet
2113  *              is lost (NewReno). This heuristics are the same in NewReno
2114  *              and SACK.
2115  *
2116  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2117  *  deflation etc. CWND is real congestion window, never inflated, changes
2118  *  only according to classic VJ rules.
2119  *
2120  * Really tricky (and requiring careful tuning) part of algorithm
2121  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2122  * The first determines the moment _when_ we should reduce CWND and,
2123  * hence, slow down forward transmission. In fact, it determines the moment
2124  * when we decide that hole is caused by loss, rather than by a reorder.
2125  *
2126  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2127  * holes, caused by lost packets.
2128  *
2129  * And the most logically complicated part of algorithm is undo
2130  * heuristics. We detect false retransmits due to both too early
2131  * fast retransmit (reordering) and underestimated RTO, analyzing
2132  * timestamps and D-SACKs. When we detect that some segments were
2133  * retransmitted by mistake and CWND reduction was wrong, we undo
2134  * window reduction and abort recovery phase. This logic is hidden
2135  * inside several functions named tcp_try_undo_<something>.
2136  */
2137 
2138 /* This function decides, when we should leave Disordered state
2139  * and enter Recovery phase, reducing congestion window.
2140  *
2141  * Main question: may we further continue forward transmission
2142  * with the same cwnd?
2143  */
2144 static bool tcp_time_to_recover(struct sock *sk, int flag)
2145 {
2146         struct tcp_sock *tp = tcp_sk(sk);
2147         __u32 packets_out;
2148 
2149         /* Trick#1: The loss is proven. */
2150         if (tp->lost_out)
2151                 return true;
2152 
2153         /* Not-A-Trick#2 : Classic rule... */
2154         if (tcp_dupack_heuristics(tp) > tp->reordering)
2155                 return true;
2156 
2157         /* Trick#4: It is still not OK... But will it be useful to delay
2158          * recovery more?
2159          */
2160         packets_out = tp->packets_out;
2161         if (packets_out <= tp->reordering &&
2162             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2163             !tcp_may_send_now(sk)) {
2164                 /* We have nothing to send. This connection is limited
2165                  * either by receiver window or by application.
2166                  */
2167                 return true;
2168         }
2169 
2170         /* If a thin stream is detected, retransmit after first
2171          * received dupack. Employ only if SACK is supported in order
2172          * to avoid possible corner-case series of spurious retransmissions
2173          * Use only if there are no unsent data.
2174          */
2175         if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2176             tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2177             tcp_is_sack(tp) && !tcp_send_head(sk))
2178                 return true;
2179 
2180         /* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
2181          * retransmissions due to small network reorderings, we implement
2182          * Mitigation A.3 in the RFC and delay the retransmission for a short
2183          * interval if appropriate.
2184          */
2185         if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2186             (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2187             !tcp_may_send_now(sk))
2188                 return !tcp_pause_early_retransmit(sk, flag);
2189 
2190         return false;
2191 }
2192 
2193 /* Detect loss in event "A" above by marking head of queue up as lost.
2194  * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2195  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2196  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2197  * the maximum SACKed segments to pass before reaching this limit.
2198  */
2199 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2200 {
2201         struct tcp_sock *tp = tcp_sk(sk);
2202         struct sk_buff *skb;
2203         int cnt, oldcnt;
2204         int err;
2205         unsigned int mss;
2206         /* Use SACK to deduce losses of new sequences sent during recovery */
2207         const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2208 
2209         WARN_ON(packets > tp->packets_out);
2210         if (tp->lost_skb_hint) {
2211                 skb = tp->lost_skb_hint;
2212                 cnt = tp->lost_cnt_hint;
2213                 /* Head already handled? */
2214                 if (mark_head && skb != tcp_write_queue_head(sk))
2215                         return;
2216         } else {
2217                 skb = tcp_write_queue_head(sk);
2218                 cnt = 0;
2219         }
2220 
2221         tcp_for_write_queue_from(skb, sk) {
2222                 if (skb == tcp_send_head(sk))
2223                         break;
2224                 /* TODO: do this better */
2225                 /* this is not the most efficient way to do this... */
2226                 tp->lost_skb_hint = skb;
2227                 tp->lost_cnt_hint = cnt;
2228 
2229                 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2230                         break;
2231 
2232                 oldcnt = cnt;
2233                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2234                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2235                         cnt += tcp_skb_pcount(skb);
2236 
2237                 if (cnt > packets) {
2238                         if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2239                             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2240                             (oldcnt >= packets))
2241                                 break;
2242 
2243                         mss = skb_shinfo(skb)->gso_size;
2244                         err = tcp_fragment(sk, skb, (packets - oldcnt) * mss,
2245                                            mss, GFP_ATOMIC);
2246                         if (err < 0)
2247                                 break;
2248                         cnt = packets;
2249                 }
2250 
2251                 tcp_skb_mark_lost(tp, skb);
2252 
2253                 if (mark_head)
2254                         break;
2255         }
2256         tcp_verify_left_out(tp);
2257 }
2258 
2259 /* Account newly detected lost packet(s) */
2260 
2261 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2262 {
2263         struct tcp_sock *tp = tcp_sk(sk);
2264 
2265         if (tcp_is_reno(tp)) {
2266                 tcp_mark_head_lost(sk, 1, 1);
2267         } else if (tcp_is_fack(tp)) {
2268                 int lost = tp->fackets_out - tp->reordering;
2269                 if (lost <= 0)
2270                         lost = 1;
2271                 tcp_mark_head_lost(sk, lost, 0);
2272         } else {
2273                 int sacked_upto = tp->sacked_out - tp->reordering;
2274                 if (sacked_upto >= 0)
2275                         tcp_mark_head_lost(sk, sacked_upto, 0);
2276                 else if (fast_rexmit)
2277                         tcp_mark_head_lost(sk, 1, 1);
2278         }
2279 }
2280 
2281 /* CWND moderation, preventing bursts due to too big ACKs
2282  * in dubious situations.
2283  */
2284 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2285 {
2286         tp->snd_cwnd = min(tp->snd_cwnd,
2287                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2288         tp->snd_cwnd_stamp = tcp_time_stamp;
2289 }
2290 
2291 /* Nothing was retransmitted or returned timestamp is less
2292  * than timestamp of the first retransmission.
2293  */
2294 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2295 {
2296         return !tp->retrans_stamp ||
2297                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2298                  before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2299 }
2300 
2301 /* Undo procedures. */
2302 
2303 #if FASTRETRANS_DEBUG > 1
2304 static void DBGUNDO(struct sock *sk, const char *msg)
2305 {
2306         struct tcp_sock *tp = tcp_sk(sk);
2307         struct inet_sock *inet = inet_sk(sk);
2308 
2309         if (sk->sk_family == AF_INET) {
2310                 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2311                          msg,
2312                          &inet->inet_daddr, ntohs(inet->inet_dport),
2313                          tp->snd_cwnd, tcp_left_out(tp),
2314                          tp->snd_ssthresh, tp->prior_ssthresh,
2315                          tp->packets_out);
2316         }
2317 #if IS_ENABLED(CONFIG_IPV6)
2318         else if (sk->sk_family == AF_INET6) {
2319                 struct ipv6_pinfo *np = inet6_sk(sk);
2320                 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2321                          msg,
2322                          &np->daddr, ntohs(inet->inet_dport),
2323                          tp->snd_cwnd, tcp_left_out(tp),
2324                          tp->snd_ssthresh, tp->prior_ssthresh,
2325                          tp->packets_out);
2326         }
2327 #endif
2328 }
2329 #else
2330 #define DBGUNDO(x...) do { } while (0)
2331 #endif
2332 
2333 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2334 {
2335         struct tcp_sock *tp = tcp_sk(sk);
2336 
2337         if (unmark_loss) {
2338                 struct sk_buff *skb;
2339 
2340                 tcp_for_write_queue(skb, sk) {
2341                         if (skb == tcp_send_head(sk))
2342                                 break;
2343                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2344                 }
2345                 tp->lost_out = 0;
2346                 tcp_clear_all_retrans_hints(tp);
2347         }
2348 
2349         if (tp->prior_ssthresh) {
2350                 const struct inet_connection_sock *icsk = inet_csk(sk);
2351 
2352                 if (icsk->icsk_ca_ops->undo_cwnd)
2353                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2354                 else
2355                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2356 
2357                 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2358                         tp->snd_ssthresh = tp->prior_ssthresh;
2359                         TCP_ECN_withdraw_cwr(tp);
2360                 }
2361         } else {
2362                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2363         }
2364         tp->snd_cwnd_stamp = tcp_time_stamp;
2365         tp->undo_marker = 0;
2366 }
2367 
2368 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2369 {
2370         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2371 }
2372 
2373 /* People celebrate: "We love our President!" */
2374 static bool tcp_try_undo_recovery(struct sock *sk)
2375 {
2376         struct tcp_sock *tp = tcp_sk(sk);
2377 
2378         if (tcp_may_undo(tp)) {
2379                 int mib_idx;
2380 
2381                 /* Happy end! We did not retransmit anything
2382                  * or our original transmission succeeded.
2383                  */
2384                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2385                 tcp_undo_cwnd_reduction(sk, false);
2386                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2387                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2388                 else
2389                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2390 
2391                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2392         }
2393         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2394                 /* Hold old state until something *above* high_seq
2395                  * is ACKed. For Reno it is MUST to prevent false
2396                  * fast retransmits (RFC2582). SACK TCP is safe. */
2397                 tcp_moderate_cwnd(tp);
2398                 return true;
2399         }
2400         tcp_set_ca_state(sk, TCP_CA_Open);
2401         return false;
2402 }
2403 
2404 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2405 static bool tcp_try_undo_dsack(struct sock *sk)
2406 {
2407         struct tcp_sock *tp = tcp_sk(sk);
2408 
2409         if (tp->undo_marker && !tp->undo_retrans) {
2410                 DBGUNDO(sk, "D-SACK");
2411                 tcp_undo_cwnd_reduction(sk, false);
2412                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2413                 return true;
2414         }
2415         return false;
2416 }
2417 
2418 /* We can clear retrans_stamp when there are no retransmissions in the
2419  * window. It would seem that it is trivially available for us in
2420  * tp->retrans_out, however, that kind of assumptions doesn't consider
2421  * what will happen if errors occur when sending retransmission for the
2422  * second time. ...It could the that such segment has only
2423  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2424  * the head skb is enough except for some reneging corner cases that
2425  * are not worth the effort.
2426  *
2427  * Main reason for all this complexity is the fact that connection dying
2428  * time now depends on the validity of the retrans_stamp, in particular,
2429  * that successive retransmissions of a segment must not advance
2430  * retrans_stamp under any conditions.
2431  */
2432 static bool tcp_any_retrans_done(const struct sock *sk)
2433 {
2434         const struct tcp_sock *tp = tcp_sk(sk);
2435         struct sk_buff *skb;
2436 
2437         if (tp->retrans_out)
2438                 return true;
2439 
2440         skb = tcp_write_queue_head(sk);
2441         if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2442                 return true;
2443 
2444         return false;
2445 }
2446 
2447 /* Undo during loss recovery after partial ACK or using F-RTO. */
2448 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2449 {
2450         struct tcp_sock *tp = tcp_sk(sk);
2451 
2452         if (frto_undo || tcp_may_undo(tp)) {
2453                 tcp_undo_cwnd_reduction(sk, true);
2454 
2455                 DBGUNDO(sk, "partial loss");
2456                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2457                 if (frto_undo)
2458                         NET_INC_STATS_BH(sock_net(sk),
2459                                          LINUX_MIB_TCPSPURIOUSRTOS);
2460                 inet_csk(sk)->icsk_retransmits = 0;
2461                 if (frto_undo || tcp_is_sack(tp))
2462                         tcp_set_ca_state(sk, TCP_CA_Open);
2463                 return true;
2464         }
2465         return false;
2466 }
2467 
2468 /* The cwnd reduction in CWR and Recovery use the PRR algorithm
2469  * https://datatracker.ietf.org/doc/draft-ietf-tcpm-proportional-rate-reduction/
2470  * It computes the number of packets to send (sndcnt) based on packets newly
2471  * delivered:
2472  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2473  *      cwnd reductions across a full RTT.
2474  *   2) If packets in flight is lower than ssthresh (such as due to excess
2475  *      losses and/or application stalls), do not perform any further cwnd
2476  *      reductions, but instead slow start up to ssthresh.
2477  */
2478 static void tcp_init_cwnd_reduction(struct sock *sk, const bool set_ssthresh)
2479 {
2480         struct tcp_sock *tp = tcp_sk(sk);
2481 
2482         tp->high_seq = tp->snd_nxt;
2483         tp->tlp_high_seq = 0;
2484         tp->snd_cwnd_cnt = 0;
2485         tp->prior_cwnd = tp->snd_cwnd;
2486         tp->prr_delivered = 0;
2487         tp->prr_out = 0;
2488         if (set_ssthresh)
2489                 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2490         TCP_ECN_queue_cwr(tp);
2491 }
2492 
2493 static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
2494                                int fast_rexmit)
2495 {
2496         struct tcp_sock *tp = tcp_sk(sk);
2497         int sndcnt = 0;
2498         int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2499         int newly_acked_sacked = prior_unsacked -
2500                                  (tp->packets_out - tp->sacked_out);
2501 
2502         tp->prr_delivered += newly_acked_sacked;
2503         if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
2504                 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2505                                tp->prior_cwnd - 1;
2506                 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2507         } else {
2508                 sndcnt = min_t(int, delta,
2509                                max_t(int, tp->prr_delivered - tp->prr_out,
2510                                      newly_acked_sacked) + 1);
2511         }
2512 
2513         sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2514         tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2515 }
2516 
2517 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2518 {
2519         struct tcp_sock *tp = tcp_sk(sk);
2520 
2521         /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2522         if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2523             (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2524                 tp->snd_cwnd = tp->snd_ssthresh;
2525                 tp->snd_cwnd_stamp = tcp_time_stamp;
2526         }
2527         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2528 }
2529 
2530 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2531 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
2532 {
2533         struct tcp_sock *tp = tcp_sk(sk);
2534 
2535         tp->prior_ssthresh = 0;
2536         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2537                 tp->undo_marker = 0;
2538                 tcp_init_cwnd_reduction(sk, set_ssthresh);
2539                 tcp_set_ca_state(sk, TCP_CA_CWR);
2540         }
2541 }
2542 
2543 static void tcp_try_keep_open(struct sock *sk)
2544 {
2545         struct tcp_sock *tp = tcp_sk(sk);
2546         int state = TCP_CA_Open;
2547 
2548         if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2549                 state = TCP_CA_Disorder;
2550 
2551         if (inet_csk(sk)->icsk_ca_state != state) {
2552                 tcp_set_ca_state(sk, state);
2553                 tp->high_seq = tp->snd_nxt;
2554         }
2555 }
2556 
2557 static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
2558 {
2559         struct tcp_sock *tp = tcp_sk(sk);
2560 
2561         tcp_verify_left_out(tp);
2562 
2563         if (!tcp_any_retrans_done(sk))
2564                 tp->retrans_stamp = 0;
2565 
2566         if (flag & FLAG_ECE)
2567                 tcp_enter_cwr(sk, 1);
2568 
2569         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2570                 tcp_try_keep_open(sk);
2571         } else {
2572                 tcp_cwnd_reduction(sk, prior_unsacked, 0);
2573         }
2574 }
2575 
2576 static void tcp_mtup_probe_failed(struct sock *sk)
2577 {
2578         struct inet_connection_sock *icsk = inet_csk(sk);
2579 
2580         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2581         icsk->icsk_mtup.probe_size = 0;
2582 }
2583 
2584 static void tcp_mtup_probe_success(struct sock *sk)
2585 {
2586         struct tcp_sock *tp = tcp_sk(sk);
2587         struct inet_connection_sock *icsk = inet_csk(sk);
2588 
2589         /* FIXME: breaks with very large cwnd */
2590         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2591         tp->snd_cwnd = tp->snd_cwnd *
2592                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2593                        icsk->icsk_mtup.probe_size;
2594         tp->snd_cwnd_cnt = 0;
2595         tp->snd_cwnd_stamp = tcp_time_stamp;
2596         tp->snd_ssthresh = tcp_current_ssthresh(sk);
2597 
2598         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2599         icsk->icsk_mtup.probe_size = 0;
2600         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2601 }
2602 
2603 /* Do a simple retransmit without using the backoff mechanisms in
2604  * tcp_timer. This is used for path mtu discovery.
2605  * The socket is already locked here.
2606  */
2607 void tcp_simple_retransmit(struct sock *sk)
2608 {
2609         const struct inet_connection_sock *icsk = inet_csk(sk);
2610         struct tcp_sock *tp = tcp_sk(sk);
2611         struct sk_buff *skb;
2612         unsigned int mss = tcp_current_mss(sk);
2613         u32 prior_lost = tp->lost_out;
2614 
2615         tcp_for_write_queue(skb, sk) {
2616                 if (skb == tcp_send_head(sk))
2617                         break;
2618                 if (tcp_skb_seglen(skb) > mss &&
2619                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2620                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2621                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2622                                 tp->retrans_out -= tcp_skb_pcount(skb);
2623                         }
2624                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2625                 }
2626         }
2627 
2628         tcp_clear_retrans_hints_partial(tp);
2629 
2630         if (prior_lost == tp->lost_out)
2631                 return;
2632 
2633         if (tcp_is_reno(tp))
2634                 tcp_limit_reno_sacked(tp);
2635 
2636         tcp_verify_left_out(tp);
2637 
2638         /* Don't muck with the congestion window here.
2639          * Reason is that we do not increase amount of _data_
2640          * in network, but units changed and effective
2641          * cwnd/ssthresh really reduced now.
2642          */
2643         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2644                 tp->high_seq = tp->snd_nxt;
2645                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2646                 tp->prior_ssthresh = 0;
2647                 tp->undo_marker = 0;
2648                 tcp_set_ca_state(sk, TCP_CA_Loss);
2649         }
2650         tcp_xmit_retransmit_queue(sk);
2651 }
2652 EXPORT_SYMBOL(tcp_simple_retransmit);
2653 
2654 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2655 {
2656         struct tcp_sock *tp = tcp_sk(sk);
2657         int mib_idx;
2658 
2659         if (tcp_is_reno(tp))
2660                 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2661         else
2662                 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2663 
2664         NET_INC_STATS_BH(sock_net(sk), mib_idx);
2665 
2666         tp->prior_ssthresh = 0;
2667         tp->undo_marker = tp->snd_una;
2668         tp->undo_retrans = tp->retrans_out ? : -1;
2669 
2670         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2671                 if (!ece_ack)
2672                         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2673                 tcp_init_cwnd_reduction(sk, true);
2674         }
2675         tcp_set_ca_state(sk, TCP_CA_Recovery);
2676 }
2677 
2678 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2679  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2680  */
2681 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
2682 {
2683         struct inet_connection_sock *icsk = inet_csk(sk);
2684         struct tcp_sock *tp = tcp_sk(sk);
2685         bool recovered = !before(tp->snd_una, tp->high_seq);
2686 
2687         if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2688                 /* Step 3.b. A timeout is spurious if not all data are
2689                  * lost, i.e., never-retransmitted data are (s)acked.
2690                  */
2691                 if (tcp_try_undo_loss(sk, flag & FLAG_ORIG_SACK_ACKED))
2692                         return;
2693 
2694                 if (after(tp->snd_nxt, tp->high_seq) &&
2695                     (flag & FLAG_DATA_SACKED || is_dupack)) {
2696                         tp->frto = 0; /* Loss was real: 2nd part of step 3.a */
2697                 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2698                         tp->high_seq = tp->snd_nxt;
2699                         __tcp_push_pending_frames(sk, tcp_current_mss(sk),
2700                                                   TCP_NAGLE_OFF);
2701                         if (after(tp->snd_nxt, tp->high_seq))
2702                                 return; /* Step 2.b */
2703                         tp->frto = 0;
2704                 }
2705         }
2706 
2707         if (recovered) {
2708                 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2709                 icsk->icsk_retransmits = 0;
2710                 tcp_try_undo_recovery(sk);
2711                 return;
2712         }
2713         if (flag & FLAG_DATA_ACKED)
2714                 icsk->icsk_retransmits = 0;
2715         if (tcp_is_reno(tp)) {
2716                 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2717                  * delivered. Lower inflight to clock out (re)tranmissions.
2718                  */
2719                 if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2720                         tcp_add_reno_sack(sk);
2721                 else if (flag & FLAG_SND_UNA_ADVANCED)
2722                         tcp_reset_reno_sack(tp);
2723         }
2724         if (tcp_try_undo_loss(sk, false))
2725                 return;
2726         tcp_xmit_retransmit_queue(sk);
2727 }
2728 
2729 /* Undo during fast recovery after partial ACK. */
2730 static bool tcp_try_undo_partial(struct sock *sk, const int acked,
2731                                  const int prior_unsacked)
2732 {
2733         struct tcp_sock *tp = tcp_sk(sk);
2734 
2735         if (tp->undo_marker && tcp_packet_delayed(tp)) {
2736                 /* Plain luck! Hole if filled with delayed
2737                  * packet, rather than with a retransmit.
2738                  */
2739                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2740 
2741                 /* We are getting evidence that the reordering degree is higher
2742                  * than we realized. If there are no retransmits out then we
2743                  * can undo. Otherwise we clock out new packets but do not
2744                  * mark more packets lost or retransmit more.
2745                  */
2746                 if (tp->retrans_out) {
2747                         tcp_cwnd_reduction(sk, prior_unsacked, 0);
2748                         return true;
2749                 }
2750 
2751                 if (!tcp_any_retrans_done(sk))
2752                         tp->retrans_stamp = 0;
2753 
2754                 DBGUNDO(sk, "partial recovery");
2755                 tcp_undo_cwnd_reduction(sk, true);
2756                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2757                 tcp_try_keep_open(sk);
2758                 return true;
2759         }
2760         return false;
2761 }
2762 
2763 /* Process an event, which can update packets-in-flight not trivially.
2764  * Main goal of this function is to calculate new estimate for left_out,
2765  * taking into account both packets sitting in receiver's buffer and
2766  * packets lost by network.
2767  *
2768  * Besides that it does CWND reduction, when packet loss is detected
2769  * and changes state of machine.
2770  *
2771  * It does _not_ decide what to send, it is made in function
2772  * tcp_xmit_retransmit_queue().
2773  */
2774 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2775                                   const int prior_unsacked,
2776                                   bool is_dupack, int flag)
2777 {
2778         struct inet_connection_sock *icsk = inet_csk(sk);
2779         struct tcp_sock *tp = tcp_sk(sk);
2780         bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2781                                     (tcp_fackets_out(tp) > tp->reordering));
2782         int fast_rexmit = 0;
2783 
2784         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2785                 tp->sacked_out = 0;
2786         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2787                 tp->fackets_out = 0;
2788 
2789         /* Now state machine starts.
2790          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2791         if (flag & FLAG_ECE)
2792                 tp->prior_ssthresh = 0;
2793 
2794         /* B. In all the states check for reneging SACKs. */
2795         if (tcp_check_sack_reneging(sk, flag))
2796                 return;
2797 
2798         /* C. Check consistency of the current state. */
2799         tcp_verify_left_out(tp);
2800 
2801         /* D. Check state exit conditions. State can be terminated
2802          *    when high_seq is ACKed. */
2803         if (icsk->icsk_ca_state == TCP_CA_Open) {
2804                 WARN_ON(tp->retrans_out != 0);
2805                 tp->retrans_stamp = 0;
2806         } else if (!before(tp->snd_una, tp->high_seq)) {
2807                 switch (icsk->icsk_ca_state) {
2808                 case TCP_CA_CWR:
2809                         /* CWR is to be held something *above* high_seq
2810                          * is ACKed for CWR bit to reach receiver. */
2811                         if (tp->snd_una != tp->high_seq) {
2812                                 tcp_end_cwnd_reduction(sk);
2813                                 tcp_set_ca_state(sk, TCP_CA_Open);
2814                         }
2815                         break;
2816 
2817                 case TCP_CA_Recovery:
2818                         if (tcp_is_reno(tp))
2819                                 tcp_reset_reno_sack(tp);
2820                         if (tcp_try_undo_recovery(sk))
2821                                 return;
2822                         tcp_end_cwnd_reduction(sk);
2823                         break;
2824                 }
2825         }
2826 
2827         /* E. Process state. */
2828         switch (icsk->icsk_ca_state) {
2829         case TCP_CA_Recovery:
2830                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2831                         if (tcp_is_reno(tp) && is_dupack)
2832                                 tcp_add_reno_sack(sk);
2833                 } else {
2834                         if (tcp_try_undo_partial(sk, acked, prior_unsacked))
2835                                 return;
2836                         /* Partial ACK arrived. Force fast retransmit. */
2837                         do_lost = tcp_is_reno(tp) ||
2838                                   tcp_fackets_out(tp) > tp->reordering;
2839                 }
2840                 if (tcp_try_undo_dsack(sk)) {
2841                         tcp_try_keep_open(sk);
2842                         return;
2843                 }
2844                 break;
2845         case TCP_CA_Loss:
2846                 tcp_process_loss(sk, flag, is_dupack);
2847                 if (icsk->icsk_ca_state != TCP_CA_Open)
2848                         return;
2849                 /* Fall through to processing in Open state. */
2850         default:
2851                 if (tcp_is_reno(tp)) {
2852                         if (flag & FLAG_SND_UNA_ADVANCED)
2853                                 tcp_reset_reno_sack(tp);
2854                         if (is_dupack)
2855                                 tcp_add_reno_sack(sk);
2856                 }
2857 
2858                 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2859                         tcp_try_undo_dsack(sk);
2860 
2861                 if (!tcp_time_to_recover(sk, flag)) {
2862                         tcp_try_to_open(sk, flag, prior_unsacked);
2863                         return;
2864                 }
2865 
2866                 /* MTU probe failure: don't reduce cwnd */
2867                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2868                     icsk->icsk_mtup.probe_size &&
2869                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2870                         tcp_mtup_probe_failed(sk);
2871                         /* Restores the reduction we did in tcp_mtup_probe() */
2872                         tp->snd_cwnd++;
2873                         tcp_simple_retransmit(sk);
2874                         return;
2875                 }
2876 
2877                 /* Otherwise enter Recovery state */
2878                 tcp_enter_recovery(sk, (flag & FLAG_ECE));
2879                 fast_rexmit = 1;
2880         }
2881 
2882         if (do_lost)
2883                 tcp_update_scoreboard(sk, fast_rexmit);
2884         tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit);
2885         tcp_xmit_retransmit_queue(sk);
2886 }
2887 
2888 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2889                                       long seq_rtt_us, long sack_rtt_us)
2890 {
2891         const struct tcp_sock *tp = tcp_sk(sk);
2892 
2893         /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2894          * broken middle-boxes or peers may corrupt TS-ECR fields. But
2895          * Karn's algorithm forbids taking RTT if some retransmitted data
2896          * is acked (RFC6298).
2897          */
2898         if (flag & FLAG_RETRANS_DATA_ACKED)
2899                 seq_rtt_us = -1L;
2900 
2901         if (seq_rtt_us < 0)
2902                 seq_rtt_us = sack_rtt_us;
2903 
2904         /* RTTM Rule: A TSecr value received in a segment is used to
2905          * update the averaged RTT measurement only if the segment
2906          * acknowledges some new data, i.e., only if it advances the
2907          * left edge of the send window.
2908          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2909          */
2910         if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2911             flag & FLAG_ACKED)
2912                 seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - tp->rx_opt.rcv_tsecr);
2913 
2914         if (seq_rtt_us < 0)
2915                 return false;
2916 
2917         tcp_rtt_estimator(sk, seq_rtt_us);
2918         tcp_set_rto(sk);
2919 
2920         /* RFC6298: only reset backoff on valid RTT measurement. */
2921         inet_csk(sk)->icsk_backoff = 0;
2922         return true;
2923 }
2924 
2925 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2926 static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)
2927 {
2928         struct tcp_sock *tp = tcp_sk(sk);
2929         long seq_rtt_us = -1L;
2930 
2931         if (synack_stamp && !tp->total_retrans)
2932                 seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - synack_stamp);
2933 
2934         /* If the ACK acks both the SYNACK and the (Fast Open'd) data packets
2935          * sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()
2936          */
2937         if (!tp->srtt_us)
2938                 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt_us, -1L);
2939 }
2940 
2941 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2942 {
2943         const struct inet_connection_sock *icsk = inet_csk(sk);
2944 
2945         icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2946         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2947 }
2948 
2949 /* Restart timer after forward progress on connection.
2950  * RFC2988 recommends to restart timer to now+rto.
2951  */
2952 void tcp_rearm_rto(struct sock *sk)
2953 {
2954         const struct inet_connection_sock *icsk = inet_csk(sk);
2955         struct tcp_sock *tp = tcp_sk(sk);
2956 
2957         /* If the retrans timer is currently being used by Fast Open
2958          * for SYN-ACK retrans purpose, stay put.
2959          */
2960         if (tp->fastopen_rsk)
2961                 return;
2962 
2963         if (!tp->packets_out) {
2964                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2965         } else {
2966                 u32 rto = inet_csk(sk)->icsk_rto;
2967                 /* Offset the time elapsed after installing regular RTO */
2968                 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
2969                     icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
2970                         struct sk_buff *skb = tcp_write_queue_head(sk);
2971                         const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
2972                         s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
2973                         /* delta may not be positive if the socket is locked
2974                          * when the retrans timer fires and is rescheduled.
2975                          */
2976                         if (delta > 0)
2977                                 rto = delta;
2978                 }
2979                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
2980                                           TCP_RTO_MAX);
2981         }
2982 }
2983 
2984 /* This function is called when the delayed ER timer fires. TCP enters
2985  * fast recovery and performs fast-retransmit.
2986  */
2987 void tcp_resume_early_retransmit(struct sock *sk)
2988 {
2989         struct tcp_sock *tp = tcp_sk(sk);
2990 
2991         tcp_rearm_rto(sk);
2992 
2993         /* Stop if ER is disabled after the delayed ER timer is scheduled */
2994         if (!tp->do_early_retrans)
2995                 return;
2996 
2997         tcp_enter_recovery(sk, false);
2998         tcp_update_scoreboard(sk, 1);
2999         tcp_xmit_retransmit_queue(sk);
3000 }
3001 
3002 /* If we get here, the whole TSO packet has not been acked. */
3003 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3004 {
3005         struct tcp_sock *tp = tcp_sk(sk);
3006         u32 packets_acked;
3007 
3008         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3009 
3010         packets_acked = tcp_skb_pcount(skb);
3011         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3012                 return 0;
3013         packets_acked -= tcp_skb_pcount(skb);
3014 
3015         if (packets_acked) {
3016                 BUG_ON(tcp_skb_pcount(skb) == 0);
3017                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3018         }
3019 
3020         return packets_acked;
3021 }
3022 
3023 /* Remove acknowledged frames from the retransmission queue. If our packet
3024  * is before the ack sequence we can discard it as it's confirmed to have
3025  * arrived at the other end.
3026  */
3027 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3028                                u32 prior_snd_una, long sack_rtt_us)
3029 {
3030         const struct inet_connection_sock *icsk = inet_csk(sk);
3031         struct skb_mstamp first_ackt, last_ackt, now;
3032         struct tcp_sock *tp = tcp_sk(sk);
3033         u32 prior_sacked = tp->sacked_out;
3034         u32 reord = tp->packets_out;
3035         bool fully_acked = true;
3036         long ca_seq_rtt_us = -1L;
3037         long seq_rtt_us = -1L;
3038         struct sk_buff *skb;
3039         u32 pkts_acked = 0;
3040         bool rtt_update;
3041         int flag = 0;
3042 
3043         first_ackt.v64 = 0;
3044 
3045         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3046                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3047                 u8 sacked = scb->sacked;
3048                 u32 acked_pcount;
3049 
3050                 /* Determine how many packets and what bytes were acked, tso and else */
3051                 if (after(scb->end_seq, tp->snd_una)) {
3052                         if (tcp_skb_pcount(skb) == 1 ||
3053                             !after(tp->snd_una, scb->seq))
3054                                 break;
3055 
3056                         acked_pcount = tcp_tso_acked(sk, skb);
3057                         if (!acked_pcount)
3058                                 break;
3059 
3060                         fully_acked = false;
3061                 } else {
3062                         acked_pcount = tcp_skb_pcount(skb);
3063                 }
3064 
3065                 if (sacked & TCPCB_RETRANS) {
3066                         if (sacked & TCPCB_SACKED_RETRANS)
3067                                 tp->retrans_out -= acked_pcount;
3068                         flag |= FLAG_RETRANS_DATA_ACKED;
3069                 } else {
3070                         last_ackt = skb->skb_mstamp;
3071                         WARN_ON_ONCE(last_ackt.v64 == 0);
3072                         if (!first_ackt.v64)
3073                                 first_ackt = last_ackt;
3074 
3075                         if (!(sacked & TCPCB_SACKED_ACKED))
3076                                 reord = min(pkts_acked, reord);
3077                         if (!after(scb->end_seq, tp->high_seq))
3078                                 flag |= FLAG_ORIG_SACK_ACKED;
3079                 }
3080 
3081                 if (sacked & TCPCB_SACKED_ACKED)
3082                         tp->sacked_out -= acked_pcount;
3083                 if (sacked & TCPCB_LOST)
3084                         tp->lost_out -= acked_pcount;
3085 
3086                 tp->packets_out -= acked_pcount;
3087                 pkts_acked += acked_pcount;
3088 
3089                 /* Initial outgoing SYN's get put onto the write_queue
3090                  * just like anything else we transmit.  It is not
3091                  * true data, and if we misinform our callers that
3092                  * this ACK acks real data, we will erroneously exit
3093                  * connection startup slow start one packet too
3094                  * quickly.  This is severely frowned upon behavior.
3095                  */
3096                 if (!(scb->tcp_flags & TCPHDR_SYN)) {
3097                         flag |= FLAG_DATA_ACKED;
3098                 } else {
3099                         flag |= FLAG_SYN_ACKED;
3100                         tp->retrans_stamp = 0;
3101                 }
3102 
3103                 if (!fully_acked)
3104                         break;
3105 
3106                 tcp_unlink_write_queue(skb, sk);
3107                 sk_wmem_free_skb(sk, skb);
3108                 if (skb == tp->retransmit_skb_hint)
3109                         tp->retransmit_skb_hint = NULL;
3110                 if (skb == tp->lost_skb_hint)
3111                         tp->lost_skb_hint = NULL;
3112         }
3113 
3114         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3115                 tp->snd_up = tp->snd_una;
3116 
3117         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3118                 flag |= FLAG_SACK_RENEGING;
3119 
3120         skb_mstamp_get(&now);
3121         if (first_ackt.v64) {
3122                 seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
3123                 ca_seq_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
3124         }
3125 
3126         rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us);
3127 
3128         if (flag & FLAG_ACKED) {
3129                 const struct tcp_congestion_ops *ca_ops
3130                         = inet_csk(sk)->icsk_ca_ops;
3131 
3132                 tcp_rearm_rto(sk);
3133                 if (unlikely(icsk->icsk_mtup.probe_size &&
3134                              !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3135                         tcp_mtup_probe_success(sk);
3136                 }
3137 
3138                 if (tcp_is_reno(tp)) {
3139                         tcp_remove_reno_sacks(sk, pkts_acked);
3140                 } else {
3141                         int delta;
3142 
3143                         /* Non-retransmitted hole got filled? That's reordering */
3144                         if (reord < prior_fackets)
3145                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3146 
3147                         delta = tcp_is_fack(tp) ? pkts_acked :
3148                                                   prior_sacked - tp->sacked_out;
3149                         tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3150                 }
3151 
3152                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3153 
3154                 if (ca_ops->pkts_acked)
3155                         ca_ops->pkts_acked(sk, pkts_acked, ca_seq_rtt_us);
3156 
3157         } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3158                    sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
3159                 /* Do not re-arm RTO if the sack RTT is measured from data sent
3160                  * after when the head was last (re)transmitted. Otherwise the
3161                  * timeout may continue to extend in loss recovery.
3162                  */
3163                 tcp_rearm_rto(sk);
3164         }
3165 
3166 #if FASTRETRANS_DEBUG > 0
3167         WARN_ON((int)tp->sacked_out < 0);
3168         WARN_ON((int)tp->lost_out < 0);
3169         WARN_ON((int)tp->retrans_out < 0);
3170         if (!tp->packets_out && tcp_is_sack(tp)) {
3171                 icsk = inet_csk(sk);
3172                 if (tp->lost_out) {
3173                         pr_debug("Leak l=%u %d\n",
3174                                  tp->lost_out, icsk->icsk_ca_state);
3175                         tp->lost_out = 0;
3176                 }
3177                 if (tp->sacked_out) {
3178                         pr_debug("Leak s=%u %d\n",
3179                                  tp->sacked_out, icsk->icsk_ca_state);
3180                         tp->sacked_out = 0;
3181                 }
3182                 if (tp->retrans_out) {
3183                         pr_debug("Leak r=%u %d\n",
3184                                  tp->retrans_out, icsk->icsk_ca_state);
3185                         tp->retrans_out = 0;
3186                 }
3187         }
3188 #endif
3189         return flag;
3190 }
3191 
3192 static void tcp_ack_probe(struct sock *sk)
3193 {
3194         const struct tcp_sock *tp = tcp_sk(sk);
3195         struct inet_connection_sock *icsk = inet_csk(sk);
3196 
3197         /* Was it a usable window open? */
3198 
3199         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3200                 icsk->icsk_backoff = 0;
3201                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3202                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3203                  * This function is not for random using!
3204                  */
3205         } else {
3206                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3207                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3208                                           TCP_RTO_MAX);
3209         }
3210 }
3211 
3212 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3213 {
3214         return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3215                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3216 }
3217 
3218 /* Decide wheather to run the increase function of congestion control. */
3219 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3220 {
3221         if (tcp_in_cwnd_reduction(sk))
3222                 return false;
3223 
3224         /* If reordering is high then always grow cwnd whenever data is
3225          * delivered regardless of its ordering. Otherwise stay conservative
3226          * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3227          * new SACK or ECE mark may first advance cwnd here and later reduce
3228          * cwnd in tcp_fastretrans_alert() based on more states.
3229          */
3230         if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
3231                 return flag & FLAG_FORWARD_PROGRESS;
3232 
3233         return flag & FLAG_DATA_ACKED;
3234 }
3235 
3236 /* Check that window update is acceptable.
3237  * The function assumes that snd_una<=ack<=snd_next.
3238  */
3239 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3240                                         const u32 ack, const u32 ack_seq,
3241                                         const u32 nwin)
3242 {
3243         return  after(ack, tp->snd_una) ||
3244                 after(ack_seq, tp->snd_wl1) ||
3245                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3246 }
3247 
3248 /* Update our send window.
3249  *
3250  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3251  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3252  */
3253 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3254                                  u32 ack_seq)
3255 {
3256         struct tcp_sock *tp = tcp_sk(sk);
3257         int flag = 0;
3258         u32 nwin = ntohs(tcp_hdr(skb)->window);
3259 
3260         if (likely(!tcp_hdr(skb)->syn))
3261                 nwin <<= tp->rx_opt.snd_wscale;
3262 
3263         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3264                 flag |= FLAG_WIN_UPDATE;
3265                 tcp_update_wl(tp, ack_seq);
3266 
3267                 if (tp->snd_wnd != nwin) {
3268                         tp->snd_wnd = nwin;
3269 
3270                         /* Note, it is the only place, where
3271                          * fast path is recovered for sending TCP.
3272                          */
3273                         tp->pred_flags = 0;
3274                         tcp_fast_path_check(sk);
3275 
3276                         if (nwin > tp->max_window) {
3277                                 tp->max_window = nwin;
3278                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3279                         }
3280                 }
3281         }
3282 
3283         tp->snd_una = ack;
3284 
3285         return flag;
3286 }
3287 
3288 /* RFC 5961 7 [ACK Throttling] */
3289 static void tcp_send_challenge_ack(struct sock *sk)
3290 {
3291         /* unprotected vars, we dont care of overwrites */
3292         static u32 challenge_timestamp;
3293         static unsigned int challenge_count;
3294         u32 now = jiffies / HZ;
3295 
3296         if (now != challenge_timestamp) {
3297                 challenge_timestamp = now;
3298                 challenge_count = 0;
3299         }
3300         if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3301                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3302                 tcp_send_ack(sk);
3303         }
3304 }
3305 
3306 static void tcp_store_ts_recent(struct tcp_sock *tp)
3307 {
3308         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3309         tp->rx_opt.ts_recent_stamp = get_seconds();
3310 }
3311 
3312 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3313 {
3314         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3315                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3316                  * extra check below makes sure this can only happen
3317                  * for pure ACK frames.  -DaveM
3318                  *
3319                  * Not only, also it occurs for expired timestamps.
3320                  */
3321 
3322                 if (tcp_paws_check(&tp->rx_opt, 0))
3323                         tcp_store_ts_recent(tp);
3324         }
3325 }
3326 
3327 /* This routine deals with acks during a TLP episode.
3328  * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3329  */
3330 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3331 {
3332         struct tcp_sock *tp = tcp_sk(sk);
3333         bool is_tlp_dupack = (ack == tp->tlp_high_seq) &&
3334                              !(flag & (FLAG_SND_UNA_ADVANCED |
3335                                        FLAG_NOT_DUP | FLAG_DATA_SACKED));
3336 
3337         /* Mark the end of TLP episode on receiving TLP dupack or when
3338          * ack is after tlp_high_seq.
3339          */
3340         if (is_tlp_dupack) {
3341                 tp->tlp_high_seq = 0;
3342                 return;
3343         }
3344 
3345         if (after(ack, tp->tlp_high_seq)) {
3346                 tp->tlp_high_seq = 0;
3347                 /* Don't reduce cwnd if DSACK arrives for TLP retrans. */
3348                 if (!(flag & FLAG_DSACKING_ACK)) {
3349                         tcp_init_cwnd_reduction(sk, true);
3350                         tcp_set_ca_state(sk, TCP_CA_CWR);
3351                         tcp_end_cwnd_reduction(sk);
3352                         tcp_try_keep_open(sk);
3353                         NET_INC_STATS_BH(sock_net(sk),
3354                                          LINUX_MIB_TCPLOSSPROBERECOVERY);
3355                 }
3356         }
3357 }
3358 
3359 /* This routine deals with incoming acks, but not outgoing ones. */
3360 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3361 {
3362         struct inet_connection_sock *icsk = inet_csk(sk);
3363         struct tcp_sock *tp = tcp_sk(sk);
3364         u32 prior_snd_una = tp->snd_una;
3365         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3366         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3367         bool is_dupack = false;
3368         u32 prior_fackets;
3369         int prior_packets = tp->packets_out;
3370         const int prior_unsacked = tp->packets_out - tp->sacked_out;
3371         int acked = 0; /* Number of packets newly acked */
3372         long sack_rtt_us = -1L;
3373 
3374         /* If the ack is older than previous acks
3375          * then we can probably ignore it.
3376          */
3377         if (before(ack, prior_snd_una)) {
3378                 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3379                 if (before(ack, prior_snd_una - tp->max_window)) {
3380                         tcp_send_challenge_ack(sk);
3381                         return -1;
3382                 }
3383                 goto old_ack;
3384         }
3385 
3386         /* If the ack includes data we haven't sent yet, discard
3387          * this segment (RFC793 Section 3.9).
3388          */
3389         if (after(ack, tp->snd_nxt))
3390                 goto invalid_ack;
3391 
3392         if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3393             icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3394                 tcp_rearm_rto(sk);
3395 
3396         if (after(ack, prior_snd_una))
3397                 flag |= FLAG_SND_UNA_ADVANCED;
3398 
3399         prior_fackets = tp->fackets_out;
3400 
3401         /* ts_recent update must be made after we are sure that the packet
3402          * is in window.
3403          */
3404         if (flag & FLAG_UPDATE_TS_RECENT)
3405                 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3406 
3407         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3408                 /* Window is constant, pure forward advance.
3409                  * No more checks are required.
3410                  * Note, we use the fact that SND.UNA>=SND.WL2.
3411                  */
3412                 tcp_update_wl(tp, ack_seq);
3413                 tp->snd_una = ack;
3414                 flag |= FLAG_WIN_UPDATE;
3415 
3416                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3417 
3418                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3419         } else {
3420                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3421                         flag |= FLAG_DATA;
3422                 else
3423                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3424 
3425                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3426 
3427                 if (TCP_SKB_CB(skb)->sacked)
3428                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3429                                                         &sack_rtt_us);
3430 
3431                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3432                         flag |= FLAG_ECE;
3433 
3434                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3435         }
3436 
3437         /* We passed data and got it acked, remove any soft error
3438          * log. Something worked...
3439          */
3440         sk->sk_err_soft = 0;
3441         icsk->icsk_probes_out = 0;
3442         tp->rcv_tstamp = tcp_time_stamp;
3443         if (!prior_packets)
3444                 goto no_queue;
3445 
3446         /* See if we can take anything off of the retransmit queue. */
3447         acked = tp->packets_out;
3448         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una,
3449                                     sack_rtt_us);
3450         acked -= tp->packets_out;
3451 
3452         /* Advance cwnd if state allows */
3453         if (tcp_may_raise_cwnd(sk, flag))
3454                 tcp_cong_avoid(sk, ack, acked);
3455 
3456         if (tcp_ack_is_dubious(sk, flag)) {
3457                 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3458                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3459                                       is_dupack, flag);
3460         }
3461         if (tp->tlp_high_seq)
3462                 tcp_process_tlp_ack(sk, ack, flag);
3463 
3464         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3465                 struct dst_entry *dst = __sk_dst_get(sk);
3466                 if (dst)
3467                         dst_confirm(dst);
3468         }
3469 
3470         if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3471                 tcp_schedule_loss_probe(sk);
3472         tcp_update_pacing_rate(sk);
3473         return 1;
3474 
3475 no_queue:
3476         /* If data was DSACKed, see if we can undo a cwnd reduction. */
3477         if (flag & FLAG_DSACKING_ACK)
3478                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3479                                       is_dupack, flag);
3480         /* If this ack opens up a zero window, clear backoff.  It was
3481          * being used to time the probes, and is probably far higher than
3482          * it needs to be for normal retransmission.
3483          */
3484         if (tcp_send_head(sk))
3485                 tcp_ack_probe(sk);
3486 
3487         if (tp->tlp_high_seq)
3488                 tcp_process_tlp_ack(sk, ack, flag);
3489         return 1;
3490 
3491 invalid_ack:
3492         SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3493         return -1;
3494 
3495 old_ack:
3496         /* If data was SACKed, tag it and see if we should send more data.
3497          * If data was DSACKed, see if we can undo a cwnd reduction.
3498          */
3499         if (TCP_SKB_CB(skb)->sacked) {
3500                 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3501                                                 &sack_rtt_us);
3502                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3503                                       is_dupack, flag);
3504         }
3505 
3506         SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3507         return 0;
3508 }
3509 
3510 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3511  * But, this can also be called on packets in the established flow when
3512  * the fast version below fails.
3513  */
3514 void tcp_parse_options(const struct sk_buff *skb,
3515                        struct tcp_options_received *opt_rx, int estab,
3516                        struct tcp_fastopen_cookie *foc)
3517 {
3518         const unsigned char *ptr;
3519         const struct tcphdr *th = tcp_hdr(skb);
3520         int length = (th->doff * 4) - sizeof(struct tcphdr);
3521 
3522         ptr = (const unsigned char *)(th + 1);
3523         opt_rx->saw_tstamp = 0;
3524 
3525         while (length > 0) {
3526                 int opcode = *ptr++;
3527                 int opsize;
3528 
3529                 switch (opcode) {
3530                 case TCPOPT_EOL:
3531                         return;
3532                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3533                         length--;
3534                         continue;
3535                 default:
3536                         opsize = *ptr++;
3537                         if (opsize < 2) /* "silly options" */
3538                                 return;
3539                         if (opsize > length)
3540                                 return; /* don't parse partial options */
3541                         switch (opcode) {
3542                         case TCPOPT_MSS:
3543                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3544                                         u16 in_mss = get_unaligned_be16(ptr);
3545                                         if (in_mss) {
3546                                                 if (opt_rx->user_mss &&
3547                                                     opt_rx->user_mss < in_mss)
3548                                                         in_mss = opt_rx->user_mss;
3549                                                 opt_rx->mss_clamp = in_mss;
3550                                         }
3551                                 }
3552                                 break;
3553                         case TCPOPT_WINDOW:
3554                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3555                                     !estab && sysctl_tcp_window_scaling) {
3556                                         __u8 snd_wscale = *(__u8 *)ptr;
3557                                         opt_rx->wscale_ok = 1;
3558                                         if (snd_wscale > 14) {
3559                                                 net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3560                                                                      __func__,
3561                                                                      snd_wscale);
3562                                                 snd_wscale = 14;
3563                                         }
3564                                         opt_rx->snd_wscale = snd_wscale;
3565                                 }
3566                                 break;
3567                         case TCPOPT_TIMESTAMP:
3568                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3569                                     ((estab && opt_rx->tstamp_ok) ||
3570                                      (!estab && sysctl_tcp_timestamps))) {
3571                                         opt_rx->saw_tstamp = 1;
3572                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3573                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3574                                 }
3575                                 break;
3576                         case TCPOPT_SACK_PERM:
3577                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3578                                     !estab && sysctl_tcp_sack) {
3579                                         opt_rx->sack_ok = TCP_SACK_SEEN;
3580                                         tcp_sack_reset(opt_rx);
3581                                 }
3582                                 break;
3583 
3584                         case TCPOPT_SACK:
3585                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3586                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3587                                    opt_rx->sack_ok) {
3588                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3589                                 }
3590                                 break;
3591 #ifdef CONFIG_TCP_MD5SIG
3592                         case TCPOPT_MD5SIG:
3593                                 /*
3594                                  * The MD5 Hash has already been
3595                                  * checked (see tcp_v{4,6}_do_rcv()).
3596                                  */
3597                                 break;
3598 #endif
3599                         case TCPOPT_EXP:
3600                                 /* Fast Open option shares code 254 using a
3601                                  * 16 bits magic number. It's valid only in
3602                                  * SYN or SYN-ACK with an even size.
3603                                  */
3604                                 if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
3605                                     get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
3606                                     foc == NULL || !th->syn || (opsize & 1))
3607                                         break;
3608                                 foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
3609                                 if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
3610                                     foc->len <= TCP_FASTOPEN_COOKIE_MAX)
3611                                         memcpy(foc->val, ptr + 2, foc->len);
3612                                 else if (foc->len != 0)
3613                                         foc->len = -1;
3614                                 break;
3615 
3616                         }
3617                         ptr += opsize-2;
3618                         length -= opsize;
3619                 }
3620         }
3621 }
3622 EXPORT_SYMBOL(tcp_parse_options);
3623 
3624 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3625 {
3626         const __be32 *ptr = (const __be32 *)(th + 1);
3627 
3628         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3629                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3630                 tp->rx_opt.saw_tstamp = 1;
3631                 ++ptr;
3632                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3633                 ++ptr;
3634                 if (*ptr)
3635                         tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3636                 else
3637                         tp->rx_opt.rcv_tsecr = 0;
3638                 return true;
3639         }
3640         return false;
3641 }
3642 
3643 /* Fast parse options. This hopes to only see timestamps.
3644  * If it is wrong it falls back on tcp_parse_options().
3645  */
3646 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3647                                    const struct tcphdr *th, struct tcp_sock *tp)
3648 {
3649         /* In the spirit of fast parsing, compare doff directly to constant
3650          * values.  Because equality is used, short doff can be ignored here.
3651          */
3652         if (th->doff == (sizeof(*th) / 4)) {
3653                 tp->rx_opt.saw_tstamp = 0;
3654                 return false;
3655         } else if (tp->rx_opt.tstamp_ok &&
3656                    th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3657                 if (tcp_parse_aligned_timestamp(tp, th))
3658                         return true;
3659         }
3660 
3661         tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3662         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3663                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3664 
3665         return true;
3666 }
3667 
3668 #ifdef CONFIG_TCP_MD5SIG
3669 /*
3670  * Parse MD5 Signature option
3671  */
3672 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3673 {
3674         int length = (th->doff << 2) - sizeof(*th);
3675         const u8 *ptr = (const u8 *)(th + 1);
3676 
3677         /* If the TCP option is too short, we can short cut */
3678         if (length < TCPOLEN_MD5SIG)
3679                 return NULL;
3680 
3681         while (length > 0) {
3682                 int opcode = *ptr++;
3683                 int opsize;
3684 
3685                 switch (opcode) {
3686                 case TCPOPT_EOL:
3687                         return NULL;
3688                 case TCPOPT_NOP:
3689                         length--;
3690                         continue;
3691                 default:
3692                         opsize = *ptr++;
3693                         if (opsize < 2 || opsize > length)
3694                                 return NULL;
3695                         if (opcode == TCPOPT_MD5SIG)
3696                                 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3697                 }
3698                 ptr += opsize - 2;
3699                 length -= opsize;
3700         }
3701         return NULL;
3702 }
3703 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3704 #endif
3705 
3706 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3707  *
3708  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3709  * it can pass through stack. So, the following predicate verifies that
3710  * this segment is not used for anything but congestion avoidance or
3711  * fast retransmit. Moreover, we even are able to eliminate most of such
3712  * second order effects, if we apply some small "replay" window (~RTO)
3713  * to timestamp space.
3714  *
3715  * All these measures still do not guarantee that we reject wrapped ACKs
3716  * on networks with high bandwidth, when sequence space is recycled fastly,
3717  * but it guarantees that such events will be very rare and do not affect
3718  * connection seriously. This doesn't look nice, but alas, PAWS is really
3719  * buggy extension.
3720  *
3721  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3722  * states that events when retransmit arrives after original data are rare.
3723  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3724  * the biggest problem on large power networks even with minor reordering.
3725  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3726  * up to bandwidth of 18Gigabit/sec. 8) ]
3727  */
3728 
3729 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3730 {
3731         const struct tcp_sock *tp = tcp_sk(sk);
3732         const struct tcphdr *th = tcp_hdr(skb);
3733         u32 seq = TCP_SKB_CB(skb)->seq;
3734         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3735 
3736         return (/* 1. Pure ACK with correct sequence number. */
3737                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3738 
3739                 /* 2. ... and duplicate ACK. */
3740                 ack == tp->snd_una &&
3741 
3742                 /* 3. ... and does not update window. */
3743                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3744 
3745                 /* 4. ... and sits in replay window. */
3746                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3747 }
3748 
3749 static inline bool tcp_paws_discard(const struct sock *sk,
3750                                    const struct sk_buff *skb)
3751 {
3752         const struct tcp_sock *tp = tcp_sk(sk);
3753 
3754         return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3755                !tcp_disordered_ack(sk, skb);
3756 }
3757 
3758 /* Check segment sequence number for validity.
3759  *
3760  * Segment controls are considered valid, if the segment
3761  * fits to the window after truncation to the window. Acceptability
3762  * of data (and SYN, FIN, of course) is checked separately.
3763  * See tcp_data_queue(), for example.
3764  *
3765  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3766  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3767  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3768  * (borrowed from freebsd)
3769  */
3770 
3771 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3772 {
3773         return  !before(end_seq, tp->rcv_wup) &&
3774                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3775 }
3776 
3777 /* When we get a reset we do this. */
3778 void tcp_reset(struct sock *sk)
3779 {
3780         /* We want the right error as BSD sees it (and indeed as we do). */
3781         switch (sk->sk_state) {
3782         case TCP_SYN_SENT:
3783                 sk->sk_err = ECONNREFUSED;
3784                 break;
3785         case TCP_CLOSE_WAIT:
3786                 sk->sk_err = EPIPE;
3787                 break;
3788         case TCP_CLOSE:
3789                 return;
3790         default:
3791                 sk->sk_err = ECONNRESET;
3792         }
3793         /* This barrier is coupled with smp_rmb() in tcp_poll() */
3794         smp_wmb();
3795 
3796         if (!sock_flag(sk, SOCK_DEAD))
3797                 sk->sk_error_report(sk);
3798 
3799         tcp_done(sk);
3800 }
3801 
3802 /*
3803  *      Process the FIN bit. This now behaves as it is supposed to work
3804  *      and the FIN takes effect when it is validly part of sequence
3805  *      space. Not before when we get holes.
3806  *
3807  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3808  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3809  *      TIME-WAIT)
3810  *
3811  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3812  *      close and we go into CLOSING (and later onto TIME-WAIT)
3813  *
3814  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3815  */
3816 static void tcp_fin(struct sock *sk)
3817 {
3818         struct tcp_sock *tp = tcp_sk(sk);
3819         const struct dst_entry *dst;
3820 
3821         inet_csk_schedule_ack(sk);
3822 
3823         sk->sk_shutdown |= RCV_SHUTDOWN;
3824         sock_set_flag(sk, SOCK_DONE);
3825 
3826         switch (sk->sk_state) {
3827         case TCP_SYN_RECV:
3828         case TCP_ESTABLISHED:
3829                 /* Move to CLOSE_WAIT */
3830                 tcp_set_state(sk, TCP_CLOSE_WAIT);
3831                 dst = __sk_dst_get(sk);
3832                 if (!dst || !dst_metric(dst, RTAX_QUICKACK))
3833                         inet_csk(sk)->icsk_ack.pingpong = 1;
3834                 break;
3835 
3836         case TCP_CLOSE_WAIT:
3837         case TCP_CLOSING:
3838                 /* Received a retransmission of the FIN, do
3839                  * nothing.
3840                  */
3841                 break;
3842         case TCP_LAST_ACK:
3843                 /* RFC793: Remain in the LAST-ACK state. */
3844                 break;
3845 
3846         case TCP_FIN_WAIT1:
3847                 /* This case occurs when a simultaneous close
3848                  * happens, we must ack the received FIN and
3849                  * enter the CLOSING state.
3850                  */
3851                 tcp_send_ack(sk);
3852                 tcp_set_state(sk, TCP_CLOSING);
3853                 break;
3854         case TCP_FIN_WAIT2:
3855                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
3856                 tcp_send_ack(sk);
3857                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3858                 break;
3859         default:
3860                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3861                  * cases we should never reach this piece of code.
3862                  */
3863                 pr_err("%s: Impossible, sk->sk_state=%d\n",
3864                        __func__, sk->sk_state);
3865                 break;
3866         }
3867 
3868         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3869          * Probably, we should reset in this case. For now drop them.
3870          */
3871         __skb_queue_purge(&tp->out_of_order_queue);
3872         if (tcp_is_sack(tp))
3873                 tcp_sack_reset(&tp->rx_opt);
3874         sk_mem_reclaim(sk);
3875 
3876         if (!sock_flag(sk, SOCK_DEAD)) {
3877                 sk->sk_state_change(sk);
3878 
3879                 /* Do not send POLL_HUP for half duplex close. */
3880                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3881                     sk->sk_state == TCP_CLOSE)
3882                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
3883                 else
3884                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
3885         }
3886 }
3887 
3888 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
3889                                   u32 end_seq)
3890 {
3891         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3892                 if (before(seq, sp->start_seq))
3893                         sp->start_seq = seq;
3894                 if (after(end_seq, sp->end_seq))
3895                         sp->end_seq = end_seq;
3896                 return true;
3897         }
3898         return false;
3899 }
3900 
3901 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
3902 {
3903         struct tcp_sock *tp = tcp_sk(sk);
3904 
3905         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3906                 int mib_idx;
3907 
3908                 if (before(seq, tp->rcv_nxt))
3909                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
3910                 else
3911                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
3912 
3913                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
3914 
3915                 tp->rx_opt.dsack = 1;
3916                 tp->duplicate_sack[0].start_seq = seq;
3917                 tp->duplicate_sack[0].end_seq = end_seq;
3918         }
3919 }
3920 
3921 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
3922 {
3923         struct tcp_sock *tp = tcp_sk(sk);
3924 
3925         if (!tp->rx_opt.dsack)
3926                 tcp_dsack_set(sk, seq, end_seq);
3927         else
3928                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3929 }
3930 
3931 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
3932 {
3933         struct tcp_sock *tp = tcp_sk(sk);
3934 
3935         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3936             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3937                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
3938                 tcp_enter_quickack_mode(sk);
3939 
3940                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3941                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3942 
3943                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3944                                 end_seq = tp->rcv_nxt;
3945                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
3946                 }
3947         }
3948 
3949         tcp_send_ack(sk);
3950 }
3951 
3952 /* These routines update the SACK block as out-of-order packets arrive or
3953  * in-order packets close up the sequence space.
3954  */
3955 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3956 {
3957         int this_sack;
3958         struct tcp_sack_block *sp = &tp->selective_acks[0];
3959         struct tcp_sack_block *swalk = sp + 1;
3960 
3961         /* See if the recent change to the first SACK eats into
3962          * or hits the sequence space of other SACK blocks, if so coalesce.
3963          */
3964         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
3965                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3966                         int i;
3967 
3968                         /* Zap SWALK, by moving every further SACK up by one slot.
3969                          * Decrease num_sacks.
3970                          */
3971                         tp->rx_opt.num_sacks--;
3972                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
3973                                 sp[i] = sp[i + 1];
3974                         continue;
3975                 }
3976                 this_sack++, swalk++;
3977         }
3978 }
3979 
3980 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3981 {
3982         struct tcp_sock *tp = tcp_sk(sk);
3983         struct tcp_sack_block *sp = &tp->selective_acks[0];
3984         int cur_sacks = tp->rx_opt.num_sacks;
3985         int this_sack;
3986 
3987         if (!cur_sacks)
3988                 goto new_sack;
3989 
3990         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
3991                 if (tcp_sack_extend(sp, seq, end_seq)) {
3992                         /* Rotate this_sack to the first one. */
3993                         for (; this_sack > 0; this_sack--, sp--)
3994                                 swap(*sp, *(sp - 1));
3995                         if (cur_sacks > 1)
3996                                 tcp_sack_maybe_coalesce(tp);
3997                         return;
3998                 }
3999         }
4000 
4001         /* Could not find an adjacent existing SACK, build a new one,
4002          * put it at the front, and shift everyone else down.  We
4003          * always know there is at least one SACK present already here.
4004          *
4005          * If the sack array is full, forget about the last one.
4006          */
4007         if (this_sack >= TCP_NUM_SACKS) {
4008                 this_sack--;
4009                 tp->rx_opt.num_sacks--;
4010                 sp--;
4011         }
4012         for (; this_sack > 0; this_sack--, sp--)
4013                 *sp = *(sp - 1);
4014 
4015 new_sack:
4016         /* Build the new head SACK, and we're done. */
4017         sp->start_seq = seq;
4018         sp->end_seq = end_seq;
4019         tp->rx_opt.num_sacks++;
4020 }
4021 
4022 /* RCV.NXT advances, some SACKs should be eaten. */
4023 
4024 static void tcp_sack_remove(struct tcp_sock *tp)
4025 {
4026         struct tcp_sack_block *sp = &tp->selective_acks[0];
4027         int num_sacks = tp->rx_opt.num_sacks;
4028         int this_sack;
4029 
4030         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4031         if (skb_queue_empty(&tp->out_of_order_queue)) {
4032                 tp->rx_opt.num_sacks = 0;
4033                 return;
4034         }
4035 
4036         for (this_sack = 0; this_sack < num_sacks;) {
4037                 /* Check if the start of the sack is covered by RCV.NXT. */
4038                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4039                         int i;
4040 
4041                         /* RCV.NXT must cover all the block! */
4042                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4043 
4044                         /* Zap this SACK, by moving forward any other SACKS. */
4045                         for (i = this_sack+1; i < num_sacks; i++)
4046                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4047                         num_sacks--;
4048                         continue;
4049                 }
4050                 this_sack++;
4051                 sp++;
4052         }
4053         tp->rx_opt.num_sacks = num_sacks;
4054 }
4055 
4056 /* This one checks to see if we can put data from the
4057  * out_of_order queue into the receive_queue.
4058  */
4059 static void tcp_ofo_queue(struct sock *sk)
4060 {
4061         struct tcp_sock *tp = tcp_sk(sk);
4062         __u32 dsack_high = tp->rcv_nxt;
4063         struct sk_buff *skb;
4064 
4065         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4066                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4067                         break;
4068 
4069                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4070                         __u32 dsack = dsack_high;
4071                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4072                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4073                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4074                 }
4075 
4076                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4077                         SOCK_DEBUG(sk, "ofo packet was already received\n");
4078                         __skb_unlink(skb, &tp->out_of_order_queue);
4079                         __kfree_skb(skb);
4080                         continue;
4081                 }
4082                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4083                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4084                            TCP_SKB_CB(skb)->end_seq);
4085 
4086                 __skb_unlink(skb, &tp->out_of_order_queue);
4087                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4088                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4089                 if (tcp_hdr(skb)->fin)
4090                         tcp_fin(sk);
4091         }
4092 }
4093 
4094 static bool tcp_prune_ofo_queue(struct sock *sk);
4095 static int tcp_prune_queue(struct sock *sk);
4096 
4097 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4098                                  unsigned int size)
4099 {
4100         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4101             !sk_rmem_schedule(sk, skb, size)) {
4102 
4103                 if (tcp_prune_queue(sk) < 0)
4104                         return -1;
4105 
4106                 if (!sk_rmem_schedule(sk, skb, size)) {
4107                         if (!tcp_prune_ofo_queue(sk))
4108                                 return -1;
4109 
4110                         if (!sk_rmem_schedule(sk, skb, size))
4111                                 return -1;
4112                 }
4113         }
4114         return 0;
4115 }
4116 
4117 /**
4118  * tcp_try_coalesce - try to merge skb to prior one
4119  * @sk: socket
4120  * @to: prior buffer
4121  * @from: buffer to add in queue
4122  * @fragstolen: pointer to boolean
4123  *
4124  * Before queueing skb @from after @to, try to merge them
4125  * to reduce overall memory use and queue lengths, if cost is small.
4126  * Packets in ofo or receive queues can stay a long time.
4127  * Better try to coalesce them right now to avoid future collapses.
4128  * Returns true if caller should free @from instead of queueing it
4129  */
4130 static bool tcp_try_coalesce(struct sock *sk,
4131                              struct sk_buff *to,
4132                              struct sk_buff *from,
4133                              bool *fragstolen)
4134 {
4135         int delta;
4136 
4137         *fragstolen = false;
4138 
4139         if (tcp_hdr(from)->fin)
4140                 return false;
4141 
4142         /* Its possible this segment overlaps with prior segment in queue */
4143         if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4144                 return false;
4145 
4146         if (!skb_try_coalesce(to, from, fragstolen, &delta))
4147                 return false;
4148 
4149         atomic_add(delta, &sk->sk_rmem_alloc);
4150         sk_mem_charge(sk, delta);
4151         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4152         TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4153         TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4154         return true;
4155 }
4156 
4157 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4158 {
4159         struct tcp_sock *tp = tcp_sk(sk);
4160         struct sk_buff *skb1;
4161         u32 seq, end_seq;
4162 
4163         TCP_ECN_check_ce(tp, skb);
4164 
4165         if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4166                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4167                 __kfree_skb(skb);
4168                 return;
4169         }
4170 
4171         /* Disable header prediction. */
4172         tp->pred_flags = 0;
4173         inet_csk_schedule_ack(sk);
4174 
4175         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4176         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4177                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4178 
4179         skb1 = skb_peek_tail(&tp->out_of_order_queue);
4180         if (!skb1) {
4181                 /* Initial out of order segment, build 1 SACK. */
4182                 if (tcp_is_sack(tp)) {
4183                         tp->rx_opt.num_sacks = 1;
4184                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4185                         tp->selective_acks[0].end_seq =
4186                                                 TCP_SKB_CB(skb)->end_seq;
4187                 }
4188                 __skb_queue_head(&tp->out_of_order_queue, skb);
4189                 goto end;
4190         }
4191 
4192         seq = TCP_SKB_CB(skb)->seq;
4193         end_seq = TCP_SKB_CB(skb)->end_seq;
4194 
4195         if (seq == TCP_SKB_CB(skb1)->end_seq) {
4196                 bool fragstolen;
4197 
4198                 if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4199                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4200                 } else {
4201                         tcp_grow_window(sk, skb);
4202                         kfree_skb_partial(skb, fragstolen);
4203                         skb = NULL;
4204                 }
4205 
4206                 if (!tp->rx_opt.num_sacks ||
4207                     tp->selective_acks[0].end_seq != seq)
4208                         goto add_sack;
4209 
4210                 /* Common case: data arrive in order after hole. */
4211                 tp->selective_acks[0].end_seq = end_seq;
4212                 goto end;
4213         }
4214 
4215         /* Find place to insert this segment. */
4216         while (1) {
4217                 if (!after(TCP_SKB_CB(skb1)->seq, seq))
4218                         break;
4219                 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4220                         skb1 = NULL;
4221                         break;
4222                 }
4223                 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4224         }
4225 
4226         /* Do skb overlap to previous one? */
4227         if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4228                 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4229                         /* All the bits are present. Drop. */
4230                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4231                         __kfree_skb(skb);
4232                         skb = NULL;
4233                         tcp_dsack_set(sk, seq, end_seq);
4234                         goto add_sack;
4235                 }
4236                 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4237                         /* Partial overlap. */
4238                         tcp_dsack_set(sk, seq,
4239                                       TCP_SKB_CB(skb1)->end_seq);
4240                 } else {
4241                         if (skb_queue_is_first(&tp->out_of_order_queue,
4242                                                skb1))
4243                                 skb1 = NULL;
4244                         else
4245                                 skb1 = skb_queue_prev(
4246                                         &tp->out_of_order_queue,
4247                                         skb1);
4248                 }
4249         }
4250         if (!skb1)
4251                 __skb_queue_head(&tp->out_of_order_queue, skb);
4252         else
4253                 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4254 
4255         /* And clean segments covered by new one as whole. */
4256         while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4257                 skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4258 
4259                 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4260                         break;
4261                 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4262                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4263                                          end_seq);
4264                         break;
4265                 }
4266                 __skb_unlink(skb1, &tp->out_of_order_queue);
4267                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4268                                  TCP_SKB_CB(skb1)->end_seq);
4269                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4270                 __kfree_skb(skb1);
4271         }
4272 
4273 add_sack:
4274         if (tcp_is_sack(tp))
4275                 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4276 end:
4277         if (skb) {
4278                 tcp_grow_window(sk, skb);
4279                 skb_set_owner_r(skb, sk);
4280         }
4281 }
4282 
4283 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4284                   bool *fragstolen)
4285 {
4286         int eaten;
4287         struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4288 
4289         __skb_pull(skb, hdrlen);
4290         eaten = (tail &&
4291                  tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4292         tcp_sk(sk)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4293         if (!eaten) {
4294                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4295                 skb_set_owner_r(skb, sk);
4296         }
4297         return eaten;
4298 }
4299 
4300 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4301 {
4302         struct sk_buff *skb = NULL;
4303         struct tcphdr *th;
4304         bool fragstolen;
4305 
4306         if (size == 0)
4307                 return 0;
4308 
4309         skb = alloc_skb(size + sizeof(*th), sk->sk_allocation);
4310         if (!skb)
4311                 goto err;
4312 
4313         if (tcp_try_rmem_schedule(sk, skb, size + sizeof(*th)))
4314                 goto err_free;
4315 
4316         th = (struct tcphdr *)skb_put(skb, sizeof(*th));
4317         skb_reset_transport_header(skb);
4318         memset(th, 0, sizeof(*th));
4319 
4320         if (memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size))
4321                 goto err_free;
4322 
4323         TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4324         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4325         TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4326 
4327         if (tcp_queue_rcv(sk, skb, sizeof(*th), &fragstolen)) {
4328                 WARN_ON_ONCE(fragstolen); /* should not happen */
4329                 __kfree_skb(skb);
4330         }
4331         return size;
4332 
4333 err_free:
4334         kfree_skb(skb);
4335 err:
4336         return -ENOMEM;
4337 }
4338 
4339 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4340 {
4341         const struct tcphdr *th = tcp_hdr(skb);
4342         struct tcp_sock *tp = tcp_sk(sk);
4343         int eaten = -1;
4344         bool fragstolen = false;
4345 
4346         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4347                 goto drop;
4348 
4349         skb_dst_drop(skb);
4350         __skb_pull(skb, th->doff * 4);
4351 
4352         TCP_ECN_accept_cwr(tp, skb);
4353 
4354         tp->rx_opt.dsack = 0;
4355 
4356         /*  Queue data for delivery to the user.
4357          *  Packets in sequence go to the receive queue.
4358          *  Out of sequence packets to the out_of_order_queue.
4359          */
4360         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4361                 if (tcp_receive_window(tp) == 0)
4362                         goto out_of_window;
4363 
4364                 /* Ok. In sequence. In window. */
4365                 if (tp->ucopy.task == current &&
4366                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4367                     sock_owned_by_user(sk) && !tp->urg_data) {
4368                         int chunk = min_t(unsigned int, skb->len,
4369                                           tp->ucopy.len);
4370 
4371                         __set_current_state(TASK_RUNNING);
4372 
4373                         local_bh_enable();
4374                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4375                                 tp->ucopy.len -= chunk;
4376                                 tp->copied_seq += chunk;
4377                                 eaten = (chunk == skb->len);
4378                                 tcp_rcv_space_adjust(sk);
4379                         }
4380                         local_bh_disable();
4381                 }
4382 
4383                 if (eaten <= 0) {
4384 queue_and_out:
4385                         if (eaten < 0 &&
4386                             tcp_try_rmem_schedule(sk, skb, skb->truesize))
4387                                 goto drop;
4388 
4389                         eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4390                 }
4391                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4392                 if (skb->len)
4393                         tcp_event_data_recv(sk, skb);
4394                 if (th->fin)
4395                         tcp_fin(sk);
4396 
4397                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4398                         tcp_ofo_queue(sk);
4399 
4400                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4401                          * gap in queue is filled.
4402                          */
4403                         if (skb_queue_empty(&tp->out_of_order_queue))
4404                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4405                 }
4406 
4407                 if (tp->rx_opt.num_sacks)
4408                         tcp_sack_remove(tp);
4409 
4410                 tcp_fast_path_check(sk);
4411 
4412                 if (eaten > 0)
4413                         kfree_skb_partial(skb, fragstolen);
4414                 if (!sock_flag(sk, SOCK_DEAD))
4415                         sk->sk_data_ready(sk);
4416                 return;
4417         }
4418 
4419         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4420                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4421                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4422                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4423 
4424 out_of_window:
4425                 tcp_enter_quickack_mode(sk);
4426                 inet_csk_schedule_ack(sk);
4427 drop:
4428                 __kfree_skb(skb);
4429                 return;
4430         }
4431 
4432         /* Out of window. F.e. zero window probe. */
4433         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4434                 goto out_of_window;
4435 
4436         tcp_enter_quickack_mode(sk);
4437 
4438         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4439                 /* Partial packet, seq < rcv_next < end_seq */
4440                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4441                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4442                            TCP_SKB_CB(skb)->end_seq);
4443 
4444                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4445 
4446                 /* If window is closed, drop tail of packet. But after
4447                  * remembering D-SACK for its head made in previous line.
4448                  */
4449                 if (!tcp_receive_window(tp))
4450                         goto out_of_window;
4451                 goto queue_and_out;
4452         }
4453 
4454         tcp_data_queue_ofo(sk, skb);
4455 }
4456 
4457 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4458                                         struct sk_buff_head *list)
4459 {
4460         struct sk_buff *next = NULL;
4461 
4462         if (!skb_queue_is_last(list, skb))
4463                 next = skb_queue_next(list, skb);
4464 
4465         __skb_unlink(skb, list);
4466         __kfree_skb(skb);
4467         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4468 
4469         return next;
4470 }
4471 
4472 /* Collapse contiguous sequence of skbs head..tail with
4473  * sequence numbers start..end.
4474  *
4475  * If tail is NULL, this means until the end of the list.
4476  *
4477  * Segments with FIN/SYN are not collapsed (only because this
4478  * simplifies code)
4479  */
4480 static void
4481 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4482              struct sk_buff *head, struct sk_buff *tail,
4483              u32 start, u32 end)
4484 {
4485         struct sk_buff *skb, *n;
4486         bool end_of_skbs;
4487 
4488         /* First, check that queue is collapsible and find
4489          * the point where collapsing can be useful. */
4490         skb = head;
4491 restart:
4492         end_of_skbs = true;
4493         skb_queue_walk_from_safe(list, skb, n) {
4494                 if (skb == tail)
4495                         break;
4496                 /* No new bits? It is possible on ofo queue. */
4497                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4498                         skb = tcp_collapse_one(sk, skb, list);
4499                         if (!skb)
4500                                 break;
4501                         goto restart;
4502                 }
4503 
4504                 /* The first skb to collapse is:
4505                  * - not SYN/FIN and
4506                  * - bloated or contains data before "start" or
4507                  *   overlaps to the next one.
4508                  */
4509                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4510                     (tcp_win_from_space(skb->truesize) > skb->len ||
4511                      before(TCP_SKB_CB(skb)->seq, start))) {
4512                         end_of_skbs = false;
4513                         break;
4514                 }
4515 
4516                 if (!skb_queue_is_last(list, skb)) {
4517                         struct sk_buff *next = skb_queue_next(list, skb);
4518                         if (next != tail &&
4519                             TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4520                                 end_of_skbs = false;
4521                                 break;
4522                         }
4523                 }
4524 
4525                 /* Decided to skip this, advance start seq. */
4526                 start = TCP_SKB_CB(skb)->end_seq;
4527         }
4528         if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4529                 return;
4530 
4531         while (before(start, end)) {
4532                 struct sk_buff *nskb;
4533                 unsigned int header = skb_headroom(skb);
4534                 int copy = SKB_MAX_ORDER(header, 0);
4535 
4536                 /* Too big header? This can happen with IPv6. */
4537                 if (copy < 0)
4538                         return;
4539                 if (end - start < copy)
4540                         copy = end - start;
4541                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4542                 if (!nskb)
4543                         return;
4544 
4545                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4546                 skb_set_network_header(nskb, (skb_network_header(skb) -
4547                                               skb->head));
4548                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4549                                                 skb->head));
4550                 skb_reserve(nskb, header);
4551                 memcpy(nskb->head, skb->head, header);
4552                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4553                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4554                 __skb_queue_before(list, skb, nskb);
4555                 skb_set_owner_r(nskb, sk);
4556 
4557                 /* Copy data, releasing collapsed skbs. */
4558                 while (copy > 0) {
4559                         int offset = start - TCP_SKB_CB(skb)->seq;
4560                         int size = TCP_SKB_CB(skb)->end_seq - start;
4561 
4562                         BUG_ON(offset < 0);
4563                         if (size > 0) {
4564                                 size = min(copy, size);
4565                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4566                                         BUG();
4567                                 TCP_SKB_CB(nskb)->end_seq += size;
4568                                 copy -= size;
4569                                 start += size;
4570                         }
4571                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4572                                 skb = tcp_collapse_one(sk, skb, list);
4573                                 if (!skb ||
4574                                     skb == tail ||
4575                                     tcp_hdr(skb)->syn ||
4576                                     tcp_hdr(skb)->fin)
4577                                         return;
4578                         }
4579                 }
4580         }
4581 }
4582 
4583 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4584  * and tcp_collapse() them until all the queue is collapsed.
4585  */
4586 static void tcp_collapse_ofo_queue(struct sock *sk)
4587 {
4588         struct tcp_sock *tp = tcp_sk(sk);
4589         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4590         struct sk_buff *head;
4591         u32 start, end;
4592 
4593         if (skb == NULL)
4594                 return;
4595 
4596         start = TCP_SKB_CB(skb)->seq;
4597         end = TCP_SKB_CB(skb)->end_seq;
4598         head = skb;
4599 
4600         for (;;) {
4601                 struct sk_buff *next = NULL;
4602 
4603                 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4604                         next = skb_queue_next(&tp->out_of_order_queue, skb);
4605                 skb = next;
4606 
4607                 /* Segment is terminated when we see gap or when
4608                  * we are at the end of all the queue. */
4609                 if (!skb ||
4610                     after(TCP_SKB_CB(skb)->seq, end) ||
4611                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4612                         tcp_collapse(sk, &tp->out_of_order_queue,
4613                                      head, skb, start, end);
4614                         head = skb;
4615                         if (!skb)
4616                                 break;
4617                         /* Start new segment */
4618                         start = TCP_SKB_CB(skb)->seq;
4619                         end = TCP_SKB_CB(skb)->end_seq;
4620                 } else {
4621                         if (before(TCP_SKB_CB(skb)->seq, start))
4622                                 start = TCP_SKB_CB(skb)->seq;
4623                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4624                                 end = TCP_SKB_CB(skb)->end_seq;
4625                 }
4626         }
4627 }
4628 
4629 /*
4630  * Purge the out-of-order queue.
4631  * Return true if queue was pruned.
4632  */
4633 static bool tcp_prune_ofo_queue(struct sock *sk)
4634 {
4635         struct tcp_sock *tp = tcp_sk(sk);
4636         bool res = false;
4637 
4638         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4639                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4640                 __skb_queue_purge(&tp->out_of_order_queue);
4641 
4642                 /* Reset SACK state.  A conforming SACK implementation will
4643                  * do the same at a timeout based retransmit.  When a connection
4644                  * is in a sad state like this, we care only about integrity
4645                  * of the connection not performance.
4646                  */
4647                 if (tp->rx_opt.sack_ok)
4648                         tcp_sack_reset(&tp->rx_opt);
4649                 sk_mem_reclaim(sk);
4650                 res = true;
4651         }
4652         return res;
4653 }
4654 
4655 /* Reduce allocated memory if we can, trying to get
4656  * the socket within its memory limits again.
4657  *
4658  * Return less than zero if we should start dropping frames
4659  * until the socket owning process reads some of the data
4660  * to stabilize the situation.
4661  */
4662 static int tcp_prune_queue(struct sock *sk)
4663 {
4664         struct tcp_sock *tp = tcp_sk(sk);
4665 
4666         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4667 
4668         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4669 
4670         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4671                 tcp_clamp_window(sk);
4672         else if (sk_under_memory_pressure(sk))
4673                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4674 
4675         tcp_collapse_ofo_queue(sk);
4676         if (!skb_queue_empty(&sk->sk_receive_queue))
4677                 tcp_collapse(sk, &sk->sk_receive_queue,
4678                              skb_peek(&sk->sk_receive_queue),
4679                              NULL,
4680                              tp->copied_seq, tp->rcv_nxt);
4681         sk_mem_reclaim(sk);
4682 
4683         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4684                 return 0;
4685 
4686         /* Collapsing did not help, destructive actions follow.
4687          * This must not ever occur. */
4688 
4689         tcp_prune_ofo_queue(sk);
4690 
4691         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4692                 return 0;
4693 
4694         /* If we are really being abused, tell the caller to silently
4695          * drop receive data on the floor.  It will get retransmitted
4696          * and hopefully then we'll have sufficient space.
4697          */
4698         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4699 
4700         /* Massive buffer overcommit. */
4701         tp->pred_flags = 0;
4702         return -1;
4703 }
4704 
4705 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4706 {
4707         const struct tcp_sock *tp = tcp_sk(sk);
4708 
4709         /* If the user specified a specific send buffer setting, do
4710          * not modify it.
4711          */
4712         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4713                 return false;
4714 
4715         /* If we are under global TCP memory pressure, do not expand.  */
4716         if (sk_under_memory_pressure(sk))
4717                 return false;
4718 
4719         /* If we are under soft global TCP memory pressure, do not expand.  */
4720         if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4721                 return false;
4722 
4723         /* If we filled the congestion window, do not expand.  */
4724         if (tp->packets_out >= tp->snd_cwnd)
4725                 return false;
4726 
4727         return true;
4728 }
4729 
4730 /* When incoming ACK allowed to free some skb from write_queue,
4731  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4732  * on the exit from tcp input handler.
4733  *
4734  * PROBLEM: sndbuf expansion does not work well with largesend.
4735  */
4736 static void tcp_new_space(struct sock *sk)
4737 {
4738         struct tcp_sock *tp = tcp_sk(sk);
4739 
4740         if (tcp_should_expand_sndbuf(sk)) {
4741                 tcp_sndbuf_expand(sk);
4742                 tp->snd_cwnd_stamp = tcp_time_stamp;
4743         }
4744 
4745         sk->sk_write_space(sk);
4746 }
4747 
4748 static void tcp_check_space(struct sock *sk)
4749 {
4750         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4751                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4752                 if (sk->sk_socket &&
4753                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4754                         tcp_new_space(sk);
4755         }
4756 }
4757 
4758 static inline void tcp_data_snd_check(struct sock *sk)
4759 {
4760         tcp_push_pending_frames(sk);
4761         tcp_check_space(sk);
4762 }
4763 
4764 /*
4765  * Check if sending an ack is needed.
4766  */
4767 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4768 {
4769         struct tcp_sock *tp = tcp_sk(sk);
4770 
4771             /* More than one full frame received... */
4772         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4773              /* ... and right edge of window advances far enough.
4774               * (tcp_recvmsg() will send ACK otherwise). Or...
4775               */
4776              __tcp_select_window(sk) >= tp->rcv_wnd) ||
4777             /* We ACK each frame or... */
4778             tcp_in_quickack_mode(sk) ||
4779             /* We have out of order data. */
4780             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4781                 /* Then ack it now */
4782                 tcp_send_ack(sk);
4783         } else {
4784                 /* Else, send delayed ack. */
4785                 tcp_send_delayed_ack(sk);
4786         }
4787 }
4788 
4789 static inline void tcp_ack_snd_check(struct sock *sk)
4790 {
4791         if (!inet_csk_ack_scheduled(sk)) {
4792                 /* We sent a data segment already. */
4793                 return;
4794         }
4795         __tcp_ack_snd_check(sk, 1);
4796 }
4797 
4798 /*
4799  *      This routine is only called when we have urgent data
4800  *      signaled. Its the 'slow' part of tcp_urg. It could be
4801  *      moved inline now as tcp_urg is only called from one
4802  *      place. We handle URGent data wrong. We have to - as
4803  *      BSD still doesn't use the correction from RFC961.
4804  *      For 1003.1g we should support a new option TCP_STDURG to permit
4805  *      either form (or just set the sysctl tcp_stdurg).
4806  */
4807 
4808 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
4809 {
4810         struct tcp_sock *tp = tcp_sk(sk);
4811         u32 ptr = ntohs(th->urg_ptr);
4812 
4813         if (ptr && !sysctl_tcp_stdurg)
4814                 ptr--;
4815         ptr += ntohl(th->seq);
4816 
4817         /* Ignore urgent data that we've already seen and read. */
4818         if (after(tp->copied_seq, ptr))
4819                 return;
4820 
4821         /* Do not replay urg ptr.
4822          *
4823          * NOTE: interesting situation not covered by specs.
4824          * Misbehaving sender may send urg ptr, pointing to segment,
4825          * which we already have in ofo queue. We are not able to fetch
4826          * such data and will stay in TCP_URG_NOTYET until will be eaten
4827          * by recvmsg(). Seems, we are not obliged to handle such wicked
4828          * situations. But it is worth to think about possibility of some
4829          * DoSes using some hypothetical application level deadlock.
4830          */
4831         if (before(ptr, tp->rcv_nxt))
4832                 return;
4833 
4834         /* Do we already have a newer (or duplicate) urgent pointer? */
4835         if (tp->urg_data && !after(ptr, tp->urg_seq))
4836                 return;
4837 
4838         /* Tell the world about our new urgent pointer. */
4839         sk_send_sigurg(sk);
4840 
4841         /* We may be adding urgent data when the last byte read was
4842          * urgent. To do this requires some care. We cannot just ignore
4843          * tp->copied_seq since we would read the last urgent byte again
4844          * as data, nor can we alter copied_seq until this data arrives
4845          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4846          *
4847          * NOTE. Double Dutch. Rendering to plain English: author of comment
4848          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4849          * and expect that both A and B disappear from stream. This is _wrong_.
4850          * Though this happens in BSD with high probability, this is occasional.
4851          * Any application relying on this is buggy. Note also, that fix "works"
4852          * only in this artificial test. Insert some normal data between A and B and we will
4853          * decline of BSD again. Verdict: it is better to remove to trap
4854          * buggy users.
4855          */
4856         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4857             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4858                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4859                 tp->copied_seq++;
4860                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4861                         __skb_unlink(skb, &sk->sk_receive_queue);
4862                         __kfree_skb(skb);
4863                 }
4864         }
4865 
4866         tp->urg_data = TCP_URG_NOTYET;
4867         tp->urg_seq = ptr;
4868 
4869         /* Disable header prediction. */
4870         tp->pred_flags = 0;
4871 }
4872 
4873 /* This is the 'fast' part of urgent handling. */
4874 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
4875 {
4876         struct tcp_sock *tp = tcp_sk(sk);
4877 
4878         /* Check if we get a new urgent pointer - normally not. */
4879         if (th->urg)
4880                 tcp_check_urg(sk, th);
4881 
4882         /* Do we wait for any urgent data? - normally not... */
4883         if (tp->urg_data == TCP_URG_NOTYET) {
4884                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4885                           th->syn;
4886 
4887                 /* Is the urgent pointer pointing into this packet? */
4888                 if (ptr < skb->len) {
4889                         u8 tmp;
4890                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4891                                 BUG();
4892                         tp->urg_data = TCP_URG_VALID | tmp;
4893                         if (!sock_flag(sk, SOCK_DEAD))
4894                                 sk->sk_data_ready(sk);
4895                 }
4896         }
4897 }
4898 
4899 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4900 {
4901         struct tcp_sock *tp = tcp_sk(sk);
4902         int chunk = skb->len - hlen;
4903         int err;
4904 
4905         local_bh_enable();
4906         if (skb_csum_unnecessary(skb))
4907                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4908         else
4909                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4910                                                        tp->ucopy.iov);
4911 
4912         if (!err) {
4913                 tp->ucopy.len -= chunk;
4914                 tp->copied_seq += chunk;
4915                 tcp_rcv_space_adjust(sk);
4916         }
4917 
4918         local_bh_disable();
4919         return err;
4920 }
4921 
4922 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
4923                                             struct sk_buff *skb)
4924 {
4925         __sum16 result;
4926 
4927         if (sock_owned_by_user(sk)) {
4928                 local_bh_enable();
4929                 result = __tcp_checksum_complete(skb);
4930                 local_bh_disable();
4931         } else {
4932                 result = __tcp_checksum_complete(skb);
4933         }
4934         return result;
4935 }
4936 
4937 static inline bool tcp_checksum_complete_user(struct sock *sk,
4938                                              struct sk_buff *skb)
4939 {
4940         return !skb_csum_unnecessary(skb) &&
4941                __tcp_checksum_complete_user(sk, skb);
4942 }
4943 
4944 #ifdef CONFIG_NET_DMA
4945 static bool tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
4946                                   int hlen)
4947 {
4948         struct tcp_sock *tp = tcp_sk(sk);
4949         int chunk = skb->len - hlen;
4950         int dma_cookie;
4951         bool copied_early = false;
4952 
4953         if (tp->ucopy.wakeup)
4954                 return false;
4955 
4956         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4957                 tp->ucopy.dma_chan = net_dma_find_channel();
4958 
4959         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4960 
4961                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4962                                                          skb, hlen,
4963                                                          tp->ucopy.iov, chunk,
4964                                                          tp->ucopy.pinned_list);
4965 
4966                 if (dma_cookie < 0)
4967                         goto out;
4968 
4969                 tp->ucopy.dma_cookie = dma_cookie;
4970                 copied_early = true;
4971 
4972                 tp->ucopy.len -= chunk;
4973                 tp->copied_seq += chunk;
4974                 tcp_rcv_space_adjust(sk);
4975 
4976                 if ((tp->ucopy.len == 0) ||
4977                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
4978                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
4979                         tp->ucopy.wakeup = 1;
4980                         sk->sk_data_ready(sk);
4981                 }
4982         } else if (chunk > 0) {
4983                 tp->ucopy.wakeup = 1;
4984                 sk->sk_data_ready(sk);
4985         }
4986 out:
4987         return copied_early;
4988 }
4989 #endif /* CONFIG_NET_DMA */
4990 
4991 /* Does PAWS and seqno based validation of an incoming segment, flags will
4992  * play significant role here.
4993  */
4994 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
4995                                   const struct tcphdr *th, int syn_inerr)
4996 {
4997         struct tcp_sock *tp = tcp_sk(sk);
4998 
4999         /* RFC1323: H1. Apply PAWS check first. */
5000         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5001             tcp_paws_discard(sk, skb)) {
5002                 if (!th->rst) {
5003                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5004                         tcp_send_dupack(sk, skb);
5005                         goto discard;
5006                 }
5007                 /* Reset is accepted even if it did not pass PAWS. */
5008         }
5009 
5010         /* Step 1: check sequence number */
5011         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5012                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5013                  * (RST) segments are validated by checking their SEQ-fields."
5014                  * And page 69: "If an incoming segment is not acceptable,
5015                  * an acknowledgment should be sent in reply (unless the RST
5016                  * bit is set, if so drop the segment and return)".
5017                  */
5018                 if (!th->rst) {
5019                         if (th->syn)
5020                                 goto syn_challenge;
5021                         tcp_send_dupack(sk, skb);
5022                 }
5023                 goto discard;
5024         }
5025 
5026         /* Step 2: check RST bit */
5027         if (th->rst) {
5028                 /* RFC 5961 3.2 :
5029                  * If sequence number exactly matches RCV.NXT, then
5030                  *     RESET the connection
5031                  * else
5032                  *     Send a challenge ACK
5033                  */
5034                 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5035                         tcp_reset(sk);
5036                 else
5037                         tcp_send_challenge_ack(sk);
5038                 goto discard;
5039         }
5040 
5041         /* step 3: check security and precedence [ignored] */
5042 
5043         /* step 4: Check for a SYN
5044          * RFC 5691 4.2 : Send a challenge ack
5045          */
5046         if (th->syn) {
5047 syn_challenge:
5048                 if (syn_inerr)
5049                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5050                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5051                 tcp_send_challenge_ack(sk);
5052                 goto discard;
5053         }
5054 
5055         return true;
5056 
5057 discard:
5058         __kfree_skb(skb);
5059         return false;
5060 }
5061 
5062 /*
5063  *      TCP receive function for the ESTABLISHED state.
5064  *
5065  *      It is split into a fast path and a slow path. The fast path is
5066  *      disabled when:
5067  *      - A zero window was announced from us - zero window probing
5068  *        is only handled properly in the slow path.
5069  *      - Out of order segments arrived.
5070  *      - Urgent data is expected.
5071  *      - There is no buffer space left
5072  *      - Unexpected TCP flags/window values/header lengths are received
5073  *        (detected by checking the TCP header against pred_flags)
5074  *      - Data is sent in both directions. Fast path only supports pure senders
5075  *        or pure receivers (this means either the sequence number or the ack
5076  *        value must stay constant)
5077  *      - Unexpected TCP option.
5078  *
5079  *      When these conditions are not satisfied it drops into a standard
5080  *      receive procedure patterned after RFC793 to handle all cases.
5081  *      The first three cases are guaranteed by proper pred_flags setting,
5082  *      the rest is checked inline. Fast processing is turned on in
5083  *      tcp_data_queue when everything is OK.
5084  */
5085 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5086                          const struct tcphdr *th, unsigned int len)
5087 {
5088         struct tcp_sock *tp = tcp_sk(sk);
5089 
5090         if (unlikely(sk->sk_rx_dst == NULL))
5091                 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5092         /*
5093          *      Header prediction.
5094          *      The code loosely follows the one in the famous
5095          *      "30 instruction TCP receive" Van Jacobson mail.
5096          *
5097          *      Van's trick is to deposit buffers into socket queue
5098          *      on a device interrupt, to call tcp_recv function
5099          *      on the receive process context and checksum and copy
5100          *      the buffer to user space. smart...
5101          *
5102          *      Our current scheme is not silly either but we take the
5103          *      extra cost of the net_bh soft interrupt processing...
5104          *      We do checksum and copy also but from device to kernel.
5105          */
5106 
5107         tp->rx_opt.saw_tstamp = 0;
5108 
5109         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5110          *      if header_prediction is to be made
5111          *      'S' will always be tp->tcp_header_len >> 2
5112          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5113          *  turn it off (when there are holes in the receive
5114          *       space for instance)
5115          *      PSH flag is ignored.
5116          */
5117 
5118         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5119             TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5120             !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5121                 int tcp_header_len = tp->tcp_header_len;
5122 
5123                 /* Timestamp header prediction: tcp_header_len
5124                  * is automatically equal to th->doff*4 due to pred_flags
5125                  * match.
5126                  */
5127 
5128                 /* Check timestamp */
5129                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5130                         /* No? Slow path! */
5131                         if (!tcp_parse_aligned_timestamp(tp, th))
5132                                 goto slow_path;
5133 
5134                         /* If PAWS failed, check it more carefully in slow path */
5135                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5136                                 goto slow_path;
5137 
5138                         /* DO NOT update ts_recent here, if checksum fails
5139                          * and timestamp was corrupted part, it will result
5140                          * in a hung connection since we will drop all
5141                          * future packets due to the PAWS test.
5142                          */
5143                 }
5144 
5145                 if (len <= tcp_header_len) {
5146                         /* Bulk data transfer: sender */
5147                         if (len == tcp_header_len) {
5148                                 /* Predicted packet is in window by definition.
5149                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5150                                  * Hence, check seq<=rcv_wup reduces to:
5151                                  */
5152                                 if (tcp_header_len ==
5153                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5154                                     tp->rcv_nxt == tp->rcv_wup)
5155                                         tcp_store_ts_recent(tp);
5156 
5157                                 /* We know that such packets are checksummed
5158                                  * on entry.
5159                                  */
5160                                 tcp_ack(sk, skb, 0);
5161                                 __kfree_skb(skb);
5162                                 tcp_data_snd_check(sk);
5163                                 return;
5164                         } else { /* Header too small */
5165                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5166                                 goto discard;
5167                         }
5168                 } else {
5169                         int eaten = 0;
5170                         int copied_early = 0;
5171                         bool fragstolen = false;
5172 
5173                         if (tp->copied_seq == tp->rcv_nxt &&
5174                             len - tcp_header_len <= tp->ucopy.len) {
5175 #ifdef CONFIG_NET_DMA
5176                                 if (tp->ucopy.task == current &&
5177                                     sock_owned_by_user(sk) &&
5178                                     tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5179                                         copied_early = 1;
5180                                         eaten = 1;
5181                                 }
5182 #endif
5183                                 if (tp->ucopy.task == current &&
5184                                     sock_owned_by_user(sk) && !copied_early) {
5185                                         __set_current_state(TASK_RUNNING);
5186 
5187                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5188                                                 eaten = 1;
5189                                 }
5190                                 if (eaten) {
5191                                         /* Predicted packet is in window by definition.
5192                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5193                                          * Hence, check seq<=rcv_wup reduces to:
5194                                          */
5195                                         if (tcp_header_len ==
5196                                             (sizeof(struct tcphdr) +
5197                                              TCPOLEN_TSTAMP_ALIGNED) &&
5198                                             tp->rcv_nxt == tp->rcv_wup)
5199                                                 tcp_store_ts_recent(tp);
5200 
5201                                         tcp_rcv_rtt_measure_ts(sk, skb);
5202 
5203                                         __skb_pull(skb, tcp_header_len);
5204                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5205                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5206                                 }
5207                                 if (copied_early)
5208                                         tcp_cleanup_rbuf(sk, skb->len);
5209                         }
5210                         if (!eaten) {
5211                                 if (tcp_checksum_complete_user(sk, skb))
5212                                         goto csum_error;
5213 
5214                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5215                                         goto step5;
5216 
5217                                 /* Predicted packet is in window by definition.
5218                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5219                                  * Hence, check seq<=rcv_wup reduces to:
5220                                  */
5221                                 if (tcp_header_len ==
5222                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5223                                     tp->rcv_nxt == tp->rcv_wup)
5224                                         tcp_store_ts_recent(tp);
5225 
5226                                 tcp_rcv_rtt_measure_ts(sk, skb);
5227 
5228                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5229 
5230                                 /* Bulk data transfer: receiver */
5231                                 eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5232                                                       &fragstolen);
5233                         }
5234 
5235                         tcp_event_data_recv(sk, skb);
5236 
5237                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5238                                 /* Well, only one small jumplet in fast path... */
5239                                 tcp_ack(sk, skb, FLAG_DATA);
5240                                 tcp_data_snd_check(sk);
5241                                 if (!inet_csk_ack_scheduled(sk))
5242                                         goto no_ack;
5243                         }
5244 
5245                         if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5246                                 __tcp_ack_snd_check(sk, 0);
5247 no_ack:
5248 #ifdef CONFIG_NET_DMA
5249                         if (copied_early)
5250                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5251                         else
5252 #endif
5253                         if (eaten)
5254                                 kfree_skb_partial(skb, fragstolen);
5255                         sk->sk_data_ready(sk);
5256                         return;
5257                 }
5258         }
5259 
5260 slow_path:
5261         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5262                 goto csum_error;
5263 
5264         if (!th->ack && !th->rst)
5265                 goto discard;
5266 
5267         /*
5268          *      Standard slow path.
5269          */
5270 
5271         if (!tcp_validate_incoming(sk, skb, th, 1))
5272                 return;
5273 
5274 step5:
5275         if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5276                 goto discard;
5277 
5278         tcp_rcv_rtt_measure_ts(sk, skb);
5279 
5280         /* Process urgent data. */
5281         tcp_urg(sk, skb, th);
5282 
5283         /* step 7: process the segment text */
5284         tcp_data_queue(sk, skb);
5285 
5286         tcp_data_snd_check(sk);
5287         tcp_ack_snd_check(sk);
5288         return;
5289 
5290 csum_error:
5291         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5292         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5293 
5294 discard:
5295         __kfree_skb(skb);
5296 }
5297 EXPORT_SYMBOL(tcp_rcv_established);
5298 
5299 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5300 {
5301         struct tcp_sock *tp = tcp_sk(sk);
5302         struct inet_connection_sock *icsk = inet_csk(sk);
5303 
5304         tcp_set_state(sk, TCP_ESTABLISHED);
5305 
5306         if (skb != NULL) {
5307                 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5308                 security_inet_conn_established(sk, skb);
5309         }
5310 
5311         /* Make sure socket is routed, for correct metrics.  */
5312         icsk->icsk_af_ops->rebuild_header(sk);
5313 
5314         tcp_init_metrics(sk);
5315 
5316         tcp_init_congestion_control(sk);
5317 
5318         /* Prevent spurious tcp_cwnd_restart() on first data
5319          * packet.
5320          */
5321         tp->lsndtime = tcp_time_stamp;
5322 
5323         tcp_init_buffer_space(sk);
5324 
5325         if (sock_flag(sk, SOCK_KEEPOPEN))
5326                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5327 
5328         if (!tp->rx_opt.snd_wscale)
5329                 __tcp_fast_path_on(tp, tp->snd_wnd);
5330         else
5331                 tp->pred_flags = 0;
5332 
5333         if (!sock_flag(sk, SOCK_DEAD)) {
5334                 sk->sk_state_change(sk);
5335                 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5336         }
5337 }
5338 
5339 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5340                                     struct tcp_fastopen_cookie *cookie)
5341 {
5342         struct tcp_sock *tp = tcp_sk(sk);
5343         struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5344         u16 mss = tp->rx_opt.mss_clamp;
5345         bool syn_drop;
5346 
5347         if (mss == tp->rx_opt.user_mss) {
5348                 struct tcp_options_received opt;
5349 
5350                 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
5351                 tcp_clear_options(&opt);
5352                 opt.user_mss = opt.mss_clamp = 0;
5353                 tcp_parse_options(synack, &opt, 0, NULL);
5354                 mss = opt.mss_clamp;
5355         }
5356 
5357         if (!tp->syn_fastopen)  /* Ignore an unsolicited cookie */
5358                 cookie->len = -1;
5359 
5360         /* The SYN-ACK neither has cookie nor acknowledges the data. Presumably
5361          * the remote receives only the retransmitted (regular) SYNs: either
5362          * the original SYN-data or the corresponding SYN-ACK is lost.
5363          */
5364         syn_drop = (cookie->len <= 0 && data && tp->total_retrans);
5365 
5366         tcp_fastopen_cache_set(sk, mss, cookie, syn_drop);
5367 
5368         if (data) { /* Retransmit unacked data in SYN */
5369                 tcp_for_write_queue_from(data, sk) {
5370                         if (data == tcp_send_head(sk) ||
5371                             __tcp_retransmit_skb(sk, data))
5372                                 break;
5373                 }
5374                 tcp_rearm_rto(sk);
5375                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5376                 return true;
5377         }
5378         tp->syn_data_acked = tp->syn_data;
5379         if (tp->syn_data_acked)
5380                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5381         return false;
5382 }
5383 
5384 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5385                                          const struct tcphdr *th, unsigned int len)
5386 {
5387         struct inet_connection_sock *icsk = inet_csk(sk);
5388         struct tcp_sock *tp = tcp_sk(sk);
5389         struct tcp_fastopen_cookie foc = { .len = -1 };
5390         int saved_clamp = tp->rx_opt.mss_clamp;
5391 
5392         tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5393         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5394                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5395 
5396         if (th->ack) {
5397                 /* rfc793:
5398                  * "If the state is SYN-SENT then
5399                  *    first check the ACK bit
5400                  *      If the ACK bit is set
5401                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5402                  *        a reset (unless the RST bit is set, if so drop
5403                  *        the segment and return)"
5404                  */
5405                 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5406                     after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5407                         goto reset_and_undo;
5408 
5409                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5410                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5411                              tcp_time_stamp)) {
5412                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5413                         goto reset_and_undo;
5414                 }
5415 
5416                 /* Now ACK is acceptable.
5417                  *
5418                  * "If the RST bit is set
5419                  *    If the ACK was acceptable then signal the user "error:
5420                  *    connection reset", drop the segment, enter CLOSED state,
5421                  *    delete TCB, and return."
5422                  */
5423 
5424                 if (th->rst) {
5425                         tcp_reset(sk);
5426                         goto discard;
5427                 }
5428 
5429                 /* rfc793:
5430                  *   "fifth, if neither of the SYN or RST bits is set then
5431                  *    drop the segment and return."
5432                  *
5433                  *    See note below!
5434                  *                                        --ANK(990513)
5435                  */
5436                 if (!th->syn)
5437                         goto discard_and_undo;
5438 
5439                 /* rfc793:
5440                  *   "If the SYN bit is on ...
5441                  *    are acceptable then ...
5442                  *    (our SYN has been ACKed), change the connection
5443                  *    state to ESTABLISHED..."
5444                  */
5445 
5446                 TCP_ECN_rcv_synack(tp, th);
5447 
5448                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5449                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5450 
5451                 /* Ok.. it's good. Set up sequence numbers and
5452                  * move to established.
5453                  */
5454                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5455                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5456 
5457                 /* RFC1323: The window in SYN & SYN/ACK segments is
5458                  * never scaled.
5459                  */
5460                 tp->snd_wnd = ntohs(th->window);
5461 
5462                 if (!tp->rx_opt.wscale_ok) {
5463                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5464                         tp->window_clamp = min(tp->window_clamp, 65535U);
5465                 }
5466 
5467                 if (tp->rx_opt.saw_tstamp) {
5468                         tp->rx_opt.tstamp_ok       = 1;
5469                         tp->tcp_header_len =
5470                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5471                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5472                         tcp_store_ts_recent(tp);
5473                 } else {
5474                         tp->tcp_header_len = sizeof(struct tcphdr);
5475                 }
5476 
5477                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5478                         tcp_enable_fack(tp);
5479 
5480                 tcp_mtup_init(sk);
5481                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5482                 tcp_initialize_rcv_mss(sk);
5483 
5484                 /* Remember, tcp_poll() does not lock socket!
5485                  * Change state from SYN-SENT only after copied_seq
5486                  * is initialized. */
5487                 tp->copied_seq = tp->rcv_nxt;
5488 
5489                 smp_mb();
5490 
5491                 tcp_finish_connect(sk, skb);
5492 
5493                 if ((tp->syn_fastopen || tp->syn_data) &&
5494                     tcp_rcv_fastopen_synack(sk, skb, &foc))
5495                         return -1;
5496 
5497                 if (sk->sk_write_pending ||
5498                     icsk->icsk_accept_queue.rskq_defer_accept ||
5499                     icsk->icsk_ack.pingpong) {
5500                         /* Save one ACK. Data will be ready after
5501                          * several ticks, if write_pending is set.
5502                          *
5503                          * It may be deleted, but with this feature tcpdumps
5504                          * look so _wonderfully_ clever, that I was not able
5505                          * to stand against the temptation 8)     --ANK
5506                          */
5507                         inet_csk_schedule_ack(sk);
5508                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5509                         tcp_enter_quickack_mode(sk);
5510                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5511                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5512 
5513 discard:
5514                         __kfree_skb(skb);
5515                         return 0;
5516                 } else {
5517                         tcp_send_ack(sk);
5518                 }
5519                 return -1;
5520         }
5521 
5522         /* No ACK in the segment */
5523 
5524         if (th->rst) {
5525                 /* rfc793:
5526                  * "If the RST bit is set
5527                  *
5528                  *      Otherwise (no ACK) drop the segment and return."
5529                  */
5530 
5531                 goto discard_and_undo;
5532         }
5533 
5534         /* PAWS check. */
5535         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5536             tcp_paws_reject(&tp->rx_opt, 0))
5537                 goto discard_and_undo;
5538 
5539         if (th->syn) {
5540                 /* We see SYN without ACK. It is attempt of
5541                  * simultaneous connect with crossed SYNs.
5542                  * Particularly, it can be connect to self.
5543                  */
5544                 tcp_set_state(sk, TCP_SYN_RECV);
5545 
5546                 if (tp->rx_opt.saw_tstamp) {
5547                         tp->rx_opt.tstamp_ok = 1;
5548                         tcp_store_ts_recent(tp);
5549                         tp->tcp_header_len =
5550                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5551                 } else {
5552                         tp->tcp_header_len = sizeof(struct tcphdr);
5553                 }
5554 
5555                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5556                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5557 
5558                 /* RFC1323: The window in SYN & SYN/ACK segments is
5559                  * never scaled.
5560                  */
5561                 tp->snd_wnd    = ntohs(th->window);
5562                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5563                 tp->max_window = tp->snd_wnd;
5564 
5565                 TCP_ECN_rcv_syn(tp, th);
5566 
5567                 tcp_mtup_init(sk);
5568                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5569                 tcp_initialize_rcv_mss(sk);
5570 
5571                 tcp_send_synack(sk);
5572 #if 0
5573                 /* Note, we could accept data and URG from this segment.
5574                  * There are no obstacles to make this (except that we must
5575                  * either change tcp_recvmsg() to prevent it from returning data
5576                  * before 3WHS completes per RFC793, or employ TCP Fast Open).
5577                  *
5578                  * However, if we ignore data in ACKless segments sometimes,
5579                  * we have no reasons to accept it sometimes.
5580                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5581                  * is not flawless. So, discard packet for sanity.
5582                  * Uncomment this return to process the data.
5583                  */
5584                 return -1;
5585 #else
5586                 goto discard;
5587 #endif
5588         }
5589         /* "fifth, if neither of the SYN or RST bits is set then
5590          * drop the segment and return."
5591          */
5592 
5593 discard_and_undo:
5594         tcp_clear_options(&tp->rx_opt);
5595         tp->rx_opt.mss_clamp = saved_clamp;
5596         goto discard;
5597 
5598 reset_and_undo:
5599         tcp_clear_options(&tp->rx_opt);
5600         tp->rx_opt.mss_clamp = saved_clamp;
5601         return 1;
5602 }
5603 
5604 /*
5605  *      This function implements the receiving procedure of RFC 793 for
5606  *      all states except ESTABLISHED and TIME_WAIT.
5607  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5608  *      address independent.
5609  */
5610 
5611 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5612                           const struct tcphdr *th, unsigned int len)
5613 {
5614         struct tcp_sock *tp = tcp_sk(sk);
5615         struct inet_connection_sock *icsk = inet_csk(sk);
5616         struct request_sock *req;
5617         int queued = 0;
5618         bool acceptable;
5619         u32 synack_stamp;
5620 
5621         tp->rx_opt.saw_tstamp = 0;
5622 
5623         switch (sk->sk_state) {
5624         case TCP_CLOSE:
5625                 goto discard;
5626 
5627         case TCP_LISTEN:
5628                 if (th->ack)
5629                         return 1;
5630 
5631                 if (th->rst)
5632                         goto discard;
5633 
5634                 if (th->syn) {
5635                         if (th->fin)
5636                                 goto discard;
5637                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5638                                 return 1;
5639 
5640                         /* Now we have several options: In theory there is
5641                          * nothing else in the frame. KA9Q has an option to
5642                          * send data with the syn, BSD accepts data with the
5643                          * syn up to the [to be] advertised window and
5644                          * Solaris 2.1 gives you a protocol error. For now
5645                          * we just ignore it, that fits the spec precisely
5646                          * and avoids incompatibilities. It would be nice in
5647                          * future to drop through and process the data.
5648                          *
5649                          * Now that TTCP is starting to be used we ought to
5650                          * queue this data.
5651                          * But, this leaves one open to an easy denial of
5652                          * service attack, and SYN cookies can't defend
5653                          * against this problem. So, we drop the data
5654                          * in the interest of security over speed unless
5655                          * it's still in use.
5656                          */
5657                         kfree_skb(skb);
5658                         return 0;
5659                 }
5660                 goto discard;
5661 
5662         case TCP_SYN_SENT:
5663                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5664                 if (queued >= 0)
5665                         return queued;
5666 
5667                 /* Do step6 onward by hand. */
5668                 tcp_urg(sk, skb, th);
5669                 __kfree_skb(skb);
5670                 tcp_data_snd_check(sk);
5671                 return 0;
5672         }
5673 
5674         req = tp->fastopen_rsk;
5675         if (req != NULL) {
5676                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5677                     sk->sk_state != TCP_FIN_WAIT1);
5678 
5679                 if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
5680                         goto discard;
5681         }
5682 
5683         if (!th->ack && !th->rst)
5684                 goto discard;
5685 
5686         if (!tcp_validate_incoming(sk, skb, th, 0))
5687                 return 0;
5688 
5689         /* step 5: check the ACK field */
5690         acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5691                                       FLAG_UPDATE_TS_RECENT) > 0;
5692 
5693         switch (sk->sk_state) {
5694         case TCP_SYN_RECV:
5695                 if (!acceptable)
5696                         return 1;
5697 
5698                 /* Once we leave TCP_SYN_RECV, we no longer need req
5699                  * so release it.
5700                  */
5701                 if (req) {
5702                         synack_stamp = tcp_rsk(req)->snt_synack;
5703                         tp->total_retrans = req->num_retrans;
5704                         reqsk_fastopen_remove(sk, req, false);
5705                 } else {
5706                         synack_stamp = tp->lsndtime;
5707                         /* Make sure socket is routed, for correct metrics. */
5708                         icsk->icsk_af_ops->rebuild_header(sk);
5709                         tcp_init_congestion_control(sk);
5710 
5711                         tcp_mtup_init(sk);
5712                         tp->copied_seq = tp->rcv_nxt;
5713                         tcp_init_buffer_space(sk);
5714                 }
5715                 smp_mb();
5716                 tcp_set_state(sk, TCP_ESTABLISHED);
5717                 sk->sk_state_change(sk);
5718 
5719                 /* Note, that this wakeup is only for marginal crossed SYN case.
5720                  * Passively open sockets are not waked up, because
5721                  * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5722                  */
5723                 if (sk->sk_socket)
5724                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5725 
5726                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5727                 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5728                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5729                 tcp_synack_rtt_meas(sk, synack_stamp);
5730 
5731                 if (tp->rx_opt.tstamp_ok)
5732                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5733 
5734                 if (req) {
5735                         /* Re-arm the timer because data may have been sent out.
5736                          * This is similar to the regular data transmission case
5737                          * when new data has just been ack'ed.
5738                          *
5739                          * (TFO) - we could try to be more aggressive and
5740                          * retransmitting any data sooner based on when they
5741                          * are sent out.
5742                          */
5743                         tcp_rearm_rto(sk);
5744                 } else
5745                         tcp_init_metrics(sk);
5746 
5747                 tcp_update_pacing_rate(sk);
5748 
5749                 /* Prevent spurious tcp_cwnd_restart() on first data packet */
5750                 tp->lsndtime = tcp_time_stamp;
5751 
5752                 tcp_initialize_rcv_mss(sk);
5753                 tcp_fast_path_on(tp);
5754                 break;
5755 
5756         case TCP_FIN_WAIT1: {
5757                 struct dst_entry *dst;
5758                 int tmo;
5759 
5760                 /* If we enter the TCP_FIN_WAIT1 state and we are a
5761                  * Fast Open socket and this is the first acceptable
5762                  * ACK we have received, this would have acknowledged
5763                  * our SYNACK so stop the SYNACK timer.
5764                  */
5765                 if (req != NULL) {
5766                         /* Return RST if ack_seq is invalid.
5767                          * Note that RFC793 only says to generate a
5768                          * DUPACK for it but for TCP Fast Open it seems
5769                          * better to treat this case like TCP_SYN_RECV
5770                          * above.
5771                          */
5772                         if (!acceptable)
5773                                 return 1;
5774                         /* We no longer need the request sock. */
5775                         reqsk_fastopen_remove(sk, req, false);
5776                         tcp_rearm_rto(sk);
5777                 }
5778                 if (tp->snd_una != tp->write_seq)
5779                         break;
5780 
5781                 tcp_set_state(sk, TCP_FIN_WAIT2);
5782                 sk->sk_shutdown |= SEND_SHUTDOWN;
5783 
5784                 dst = __sk_dst_get(sk);
5785                 if (dst)
5786                         dst_confirm(dst);
5787 
5788                 if (!sock_flag(sk, SOCK_DEAD)) {
5789                         /* Wake up lingering close() */
5790                         sk->sk_state_change(sk);
5791                         break;
5792                 }
5793 
5794                 if (tp->linger2 < 0 ||
5795                     (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5796                      after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5797                         tcp_done(sk);
5798                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5799                         return 1;
5800                 }
5801 
5802                 tmo = tcp_fin_time(sk);
5803                 if (tmo > TCP_TIMEWAIT_LEN) {
5804                         inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5805                 } else if (th->fin || sock_owned_by_user(sk)) {
5806                         /* Bad case. We could lose such FIN otherwise.
5807                          * It is not a big problem, but it looks confusing
5808                          * and not so rare event. We still can lose it now,
5809                          * if it spins in bh_lock_sock(), but it is really
5810                          * marginal case.
5811                          */
5812                         inet_csk_reset_keepalive_timer(sk, tmo);
5813                 } else {
5814                         tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5815                         goto discard;
5816                 }
5817                 break;
5818         }
5819 
5820         case TCP_CLOSING:
5821                 if (tp->snd_una == tp->write_seq) {
5822                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5823                         goto discard;
5824                 }
5825                 break;
5826 
5827         case TCP_LAST_ACK:
5828                 if (tp->snd_una == tp->write_seq) {
5829                         tcp_update_metrics(sk);
5830                         tcp_done(sk);
5831                         goto discard;
5832                 }
5833                 break;
5834         }
5835 
5836         /* step 6: check the URG bit */
5837         tcp_urg(sk, skb, th);
5838 
5839         /* step 7: process the segment text */
5840         switch (sk->sk_state) {
5841         case TCP_CLOSE_WAIT:
5842         case TCP_CLOSING:
5843         case TCP_LAST_ACK:
5844                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5845                         break;
5846         case TCP_FIN_WAIT1:
5847         case TCP_FIN_WAIT2:
5848                 /* RFC 793 says to queue data in these states,
5849                  * RFC 1122 says we MUST send a reset.
5850                  * BSD 4.4 also does reset.
5851                  */
5852                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5853                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5854                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5855                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5856                                 tcp_reset(sk);
5857                                 return 1;
5858                         }
5859                 }
5860                 /* Fall through */
5861         case TCP_ESTABLISHED:
5862                 tcp_data_queue(sk, skb);
5863                 queued = 1;
5864                 break;
5865         }
5866 
5867         /* tcp_data could move socket to TIME-WAIT */
5868         if (sk->sk_state != TCP_CLOSE) {
5869                 tcp_data_snd_check(sk);
5870                 tcp_ack_snd_check(sk);
5871         }
5872 
5873         if (!queued) {
5874 discard:
5875                 __kfree_skb(skb);
5876         }
5877         return 0;
5878 }
5879 EXPORT_SYMBOL(tcp_rcv_state_process);
5880 

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