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Linux/net/ipv4/tcp_input.c

  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              Implementation of the Transmission Control Protocol(TCP).
  7  *
  8  * Authors:     Ross Biro
  9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 10  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
 11  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
 12  *              Florian La Roche, <flla@stud.uni-sb.de>
 13  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 14  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
 15  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
 16  *              Matthew Dillon, <dillon@apollo.west.oic.com>
 17  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 18  *              Jorge Cwik, <jorge@laser.satlink.net>
 19  */
 20 
 21 /*
 22  * Changes:
 23  *              Pedro Roque     :       Fast Retransmit/Recovery.
 24  *                                      Two receive queues.
 25  *                                      Retransmit queue handled by TCP.
 26  *                                      Better retransmit timer handling.
 27  *                                      New congestion avoidance.
 28  *                                      Header prediction.
 29  *                                      Variable renaming.
 30  *
 31  *              Eric            :       Fast Retransmit.
 32  *              Randy Scott     :       MSS option defines.
 33  *              Eric Schenk     :       Fixes to slow start algorithm.
 34  *              Eric Schenk     :       Yet another double ACK bug.
 35  *              Eric Schenk     :       Delayed ACK bug fixes.
 36  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
 37  *              David S. Miller :       Don't allow zero congestion window.
 38  *              Eric Schenk     :       Fix retransmitter so that it sends
 39  *                                      next packet on ack of previous packet.
 40  *              Andi Kleen      :       Moved open_request checking here
 41  *                                      and process RSTs for open_requests.
 42  *              Andi Kleen      :       Better prune_queue, and other fixes.
 43  *              Andrey Savochkin:       Fix RTT measurements in the presence of
 44  *                                      timestamps.
 45  *              Andrey Savochkin:       Check sequence numbers correctly when
 46  *                                      removing SACKs due to in sequence incoming
 47  *                                      data segments.
 48  *              Andi Kleen:             Make sure we never ack data there is not
 49  *                                      enough room for. Also make this condition
 50  *                                      a fatal error if it might still happen.
 51  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
 52  *                                      connections with MSS<min(MTU,ann. MSS)
 53  *                                      work without delayed acks.
 54  *              Andi Kleen:             Process packets with PSH set in the
 55  *                                      fast path.
 56  *              J Hadi Salim:           ECN support
 57  *              Andrei Gurtov,
 58  *              Pasi Sarolahti,
 59  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
 60  *                                      engine. Lots of bugs are found.
 61  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
 62  */
 63 
 64 #define pr_fmt(fmt) "TCP: " fmt
 65 
 66 #include <linux/mm.h>
 67 #include <linux/slab.h>
 68 #include <linux/module.h>
 69 #include <linux/sysctl.h>
 70 #include <linux/kernel.h>
 71 #include <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, const __u32 mrtt)
671 {
672         struct tcp_sock *tp = tcp_sk(sk);
673         long m = mrtt; /* RTT */
674         u32 srtt = tp->srtt;
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 >> 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 >> 2);   /* similar update on mdev */
710                 }
711                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
712                 if (tp->mdev > tp->mdev_max) {
713                         tp->mdev_max = tp->mdev;
714                         if (tp->mdev_max > tp->rttvar)
715                                 tp->rttvar = tp->mdev_max;
716                 }
717                 if (after(tp->snd_una, tp->rtt_seq)) {
718                         if (tp->mdev_max < tp->rttvar)
719                                 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
720                         tp->rtt_seq = tp->snd_nxt;
721                         tp->mdev_max = tcp_rto_min(sk);
722                 }
723         } else {
724                 /* no previous measure. */
725                 srtt = m << 3;          /* take the measured time to be rtt */
726                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
727                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
728                 tp->rtt_seq = tp->snd_nxt;
729         }
730         tp->srtt = max(1U, srtt);
731 }
732 
733 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
734  * Note: TCP stack does not yet implement pacing.
735  * FQ packet scheduler can be used to implement cheap but effective
736  * TCP pacing, to smooth the burst on large writes when packets
737  * in flight is significantly lower than cwnd (or rwin)
738  */
739 static void tcp_update_pacing_rate(struct sock *sk)
740 {
741         const struct tcp_sock *tp = tcp_sk(sk);
742         u64 rate;
743 
744         /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
745         rate = (u64)tp->mss_cache * 2 * (HZ << 3);
746 
747         rate *= max(tp->snd_cwnd, tp->packets_out);
748 
749         /* Correction for small srtt and scheduling constraints.
750          * For small rtt, consider noise is too high, and use
751          * the minimal value (srtt = 1 -> 125 us for HZ=1000)
752          *
753          * We probably need usec resolution in the future.
754          * Note: This also takes care of possible srtt=0 case,
755          * when tcp_rtt_estimator() was not yet called.
756          */
757         if (tp->srtt > 8 + 2)
758                 do_div(rate, tp->srtt);
759 
760         /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
761          * without any lock. We want to make sure compiler wont store
762          * intermediate values in this location.
763          */
764         ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
765                                                 sk->sk_max_pacing_rate);
766 }
767 
768 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
769  * routine referred to above.
770  */
771 static void tcp_set_rto(struct sock *sk)
772 {
773         const struct tcp_sock *tp = tcp_sk(sk);
774         /* Old crap is replaced with new one. 8)
775          *
776          * More seriously:
777          * 1. If rtt variance happened to be less 50msec, it is hallucination.
778          *    It cannot be less due to utterly erratic ACK generation made
779          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
780          *    to do with delayed acks, because at cwnd>2 true delack timeout
781          *    is invisible. Actually, Linux-2.4 also generates erratic
782          *    ACKs in some circumstances.
783          */
784         inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
785 
786         /* 2. Fixups made earlier cannot be right.
787          *    If we do not estimate RTO correctly without them,
788          *    all the algo is pure shit and should be replaced
789          *    with correct one. It is exactly, which we pretend to do.
790          */
791 
792         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
793          * guarantees that rto is higher.
794          */
795         tcp_bound_rto(sk);
796 }
797 
798 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
799 {
800         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
801 
802         if (!cwnd)
803                 cwnd = TCP_INIT_CWND;
804         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
805 }
806 
807 /*
808  * Packet counting of FACK is based on in-order assumptions, therefore TCP
809  * disables it when reordering is detected
810  */
811 void tcp_disable_fack(struct tcp_sock *tp)
812 {
813         /* RFC3517 uses different metric in lost marker => reset on change */
814         if (tcp_is_fack(tp))
815                 tp->lost_skb_hint = NULL;
816         tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
817 }
818 
819 /* Take a notice that peer is sending D-SACKs */
820 static void tcp_dsack_seen(struct tcp_sock *tp)
821 {
822         tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
823 }
824 
825 static void tcp_update_reordering(struct sock *sk, const int metric,
826                                   const int ts)
827 {
828         struct tcp_sock *tp = tcp_sk(sk);
829         if (metric > tp->reordering) {
830                 int mib_idx;
831 
832                 tp->reordering = min(TCP_MAX_REORDERING, metric);
833 
834                 /* This exciting event is worth to be remembered. 8) */
835                 if (ts)
836                         mib_idx = LINUX_MIB_TCPTSREORDER;
837                 else if (tcp_is_reno(tp))
838                         mib_idx = LINUX_MIB_TCPRENOREORDER;
839                 else if (tcp_is_fack(tp))
840                         mib_idx = LINUX_MIB_TCPFACKREORDER;
841                 else
842                         mib_idx = LINUX_MIB_TCPSACKREORDER;
843 
844                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
845 #if FASTRETRANS_DEBUG > 1
846                 pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
847                          tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
848                          tp->reordering,
849                          tp->fackets_out,
850                          tp->sacked_out,
851                          tp->undo_marker ? tp->undo_retrans : 0);
852 #endif
853                 tcp_disable_fack(tp);
854         }
855 
856         if (metric > 0)
857                 tcp_disable_early_retrans(tp);
858 }
859 
860 /* This must be called before lost_out is incremented */
861 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
862 {
863         if ((tp->retransmit_skb_hint == NULL) ||
864             before(TCP_SKB_CB(skb)->seq,
865                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
866                 tp->retransmit_skb_hint = skb;
867 
868         if (!tp->lost_out ||
869             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
870                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
871 }
872 
873 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
874 {
875         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
876                 tcp_verify_retransmit_hint(tp, skb);
877 
878                 tp->lost_out += tcp_skb_pcount(skb);
879                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
880         }
881 }
882 
883 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
884                                             struct sk_buff *skb)
885 {
886         tcp_verify_retransmit_hint(tp, skb);
887 
888         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
889                 tp->lost_out += tcp_skb_pcount(skb);
890                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
891         }
892 }
893 
894 /* This procedure tags the retransmission queue when SACKs arrive.
895  *
896  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
897  * Packets in queue with these bits set are counted in variables
898  * sacked_out, retrans_out and lost_out, correspondingly.
899  *
900  * Valid combinations are:
901  * Tag  InFlight        Description
902  * 0    1               - orig segment is in flight.
903  * S    0               - nothing flies, orig reached receiver.
904  * L    0               - nothing flies, orig lost by net.
905  * R    2               - both orig and retransmit are in flight.
906  * L|R  1               - orig is lost, retransmit is in flight.
907  * S|R  1               - orig reached receiver, retrans is still in flight.
908  * (L|S|R is logically valid, it could occur when L|R is sacked,
909  *  but it is equivalent to plain S and code short-curcuits it to S.
910  *  L|S is logically invalid, it would mean -1 packet in flight 8))
911  *
912  * These 6 states form finite state machine, controlled by the following events:
913  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
914  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
915  * 3. Loss detection event of two flavors:
916  *      A. Scoreboard estimator decided the packet is lost.
917  *         A'. Reno "three dupacks" marks head of queue lost.
918  *         A''. Its FACK modification, head until snd.fack is lost.
919  *      B. SACK arrives sacking SND.NXT at the moment, when the
920  *         segment was retransmitted.
921  * 4. D-SACK added new rule: D-SACK changes any tag to S.
922  *
923  * It is pleasant to note, that state diagram turns out to be commutative,
924  * so that we are allowed not to be bothered by order of our actions,
925  * when multiple events arrive simultaneously. (see the function below).
926  *
927  * Reordering detection.
928  * --------------------
929  * Reordering metric is maximal distance, which a packet can be displaced
930  * in packet stream. With SACKs we can estimate it:
931  *
932  * 1. SACK fills old hole and the corresponding segment was not
933  *    ever retransmitted -> reordering. Alas, we cannot use it
934  *    when segment was retransmitted.
935  * 2. The last flaw is solved with D-SACK. D-SACK arrives
936  *    for retransmitted and already SACKed segment -> reordering..
937  * Both of these heuristics are not used in Loss state, when we cannot
938  * account for retransmits accurately.
939  *
940  * SACK block validation.
941  * ----------------------
942  *
943  * SACK block range validation checks that the received SACK block fits to
944  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
945  * Note that SND.UNA is not included to the range though being valid because
946  * it means that the receiver is rather inconsistent with itself reporting
947  * SACK reneging when it should advance SND.UNA. Such SACK block this is
948  * perfectly valid, however, in light of RFC2018 which explicitly states
949  * that "SACK block MUST reflect the newest segment.  Even if the newest
950  * segment is going to be discarded ...", not that it looks very clever
951  * in case of head skb. Due to potentional receiver driven attacks, we
952  * choose to avoid immediate execution of a walk in write queue due to
953  * reneging and defer head skb's loss recovery to standard loss recovery
954  * procedure that will eventually trigger (nothing forbids us doing this).
955  *
956  * Implements also blockage to start_seq wrap-around. Problem lies in the
957  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
958  * there's no guarantee that it will be before snd_nxt (n). The problem
959  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
960  * wrap (s_w):
961  *
962  *         <- outs wnd ->                          <- wrapzone ->
963  *         u     e      n                         u_w   e_w  s n_w
964  *         |     |      |                          |     |   |  |
965  * |<------------+------+----- TCP seqno space --------------+---------->|
966  * ...-- <2^31 ->|                                           |<--------...
967  * ...---- >2^31 ------>|                                    |<--------...
968  *
969  * Current code wouldn't be vulnerable but it's better still to discard such
970  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
971  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
972  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
973  * equal to the ideal case (infinite seqno space without wrap caused issues).
974  *
975  * With D-SACK the lower bound is extended to cover sequence space below
976  * SND.UNA down to undo_marker, which is the last point of interest. Yet
977  * again, D-SACK block must not to go across snd_una (for the same reason as
978  * for the normal SACK blocks, explained above). But there all simplicity
979  * ends, TCP might receive valid D-SACKs below that. As long as they reside
980  * fully below undo_marker they do not affect behavior in anyway and can
981  * therefore be safely ignored. In rare cases (which are more or less
982  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
983  * fragmentation and packet reordering past skb's retransmission. To consider
984  * them correctly, the acceptable range must be extended even more though
985  * the exact amount is rather hard to quantify. However, tp->max_window can
986  * be used as an exaggerated estimate.
987  */
988 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
989                                    u32 start_seq, u32 end_seq)
990 {
991         /* Too far in future, or reversed (interpretation is ambiguous) */
992         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
993                 return false;
994 
995         /* Nasty start_seq wrap-around check (see comments above) */
996         if (!before(start_seq, tp->snd_nxt))
997                 return false;
998 
999         /* In outstanding window? ...This is valid exit for D-SACKs too.
1000          * start_seq == snd_una is non-sensical (see comments above)
1001          */
1002         if (after(start_seq, tp->snd_una))
1003                 return true;
1004 
1005         if (!is_dsack || !tp->undo_marker)
1006                 return false;
1007 
1008         /* ...Then it's D-SACK, and must reside below snd_una completely */
1009         if (after(end_seq, tp->snd_una))
1010                 return false;
1011 
1012         if (!before(start_seq, tp->undo_marker))
1013                 return true;
1014 
1015         /* Too old */
1016         if (!after(end_seq, tp->undo_marker))
1017                 return false;
1018 
1019         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1020          *   start_seq < undo_marker and end_seq >= undo_marker.
1021          */
1022         return !before(start_seq, end_seq - tp->max_window);
1023 }
1024 
1025 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1026  * Event "B". Later note: FACK people cheated me again 8), we have to account
1027  * for reordering! Ugly, but should help.
1028  *
1029  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1030  * less than what is now known to be received by the other end (derived from
1031  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1032  * retransmitted skbs to avoid some costly processing per ACKs.
1033  */
1034 static void tcp_mark_lost_retrans(struct sock *sk)
1035 {
1036         const struct inet_connection_sock *icsk = inet_csk(sk);
1037         struct tcp_sock *tp = tcp_sk(sk);
1038         struct sk_buff *skb;
1039         int cnt = 0;
1040         u32 new_low_seq = tp->snd_nxt;
1041         u32 received_upto = tcp_highest_sack_seq(tp);
1042 
1043         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1044             !after(received_upto, tp->lost_retrans_low) ||
1045             icsk->icsk_ca_state != TCP_CA_Recovery)
1046                 return;
1047 
1048         tcp_for_write_queue(skb, sk) {
1049                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1050 
1051                 if (skb == tcp_send_head(sk))
1052                         break;
1053                 if (cnt == tp->retrans_out)
1054                         break;
1055                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1056                         continue;
1057 
1058                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1059                         continue;
1060 
1061                 /* TODO: We would like to get rid of tcp_is_fack(tp) only
1062                  * constraint here (see above) but figuring out that at
1063                  * least tp->reordering SACK blocks reside between ack_seq
1064                  * and received_upto is not easy task to do cheaply with
1065                  * the available datastructures.
1066                  *
1067                  * Whether FACK should check here for tp->reordering segs
1068                  * in-between one could argue for either way (it would be
1069                  * rather simple to implement as we could count fack_count
1070                  * during the walk and do tp->fackets_out - fack_count).
1071                  */
1072                 if (after(received_upto, ack_seq)) {
1073                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1074                         tp->retrans_out -= tcp_skb_pcount(skb);
1075 
1076                         tcp_skb_mark_lost_uncond_verify(tp, skb);
1077                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1078                 } else {
1079                         if (before(ack_seq, new_low_seq))
1080                                 new_low_seq = ack_seq;
1081                         cnt += tcp_skb_pcount(skb);
1082                 }
1083         }
1084 
1085         if (tp->retrans_out)
1086                 tp->lost_retrans_low = new_low_seq;
1087 }
1088 
1089 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1090                             struct tcp_sack_block_wire *sp, int num_sacks,
1091                             u32 prior_snd_una)
1092 {
1093         struct tcp_sock *tp = tcp_sk(sk);
1094         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1095         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1096         bool dup_sack = false;
1097 
1098         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1099                 dup_sack = true;
1100                 tcp_dsack_seen(tp);
1101                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1102         } else if (num_sacks > 1) {
1103                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1104                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1105 
1106                 if (!after(end_seq_0, end_seq_1) &&
1107                     !before(start_seq_0, start_seq_1)) {
1108                         dup_sack = true;
1109                         tcp_dsack_seen(tp);
1110                         NET_INC_STATS_BH(sock_net(sk),
1111                                         LINUX_MIB_TCPDSACKOFORECV);
1112                 }
1113         }
1114 
1115         /* D-SACK for already forgotten data... Do dumb counting. */
1116         if (dup_sack && tp->undo_marker && tp->undo_retrans &&
1117             !after(end_seq_0, prior_snd_una) &&
1118             after(end_seq_0, tp->undo_marker))
1119                 tp->undo_retrans--;
1120 
1121         return dup_sack;
1122 }
1123 
1124 struct tcp_sacktag_state {
1125         int reord;
1126         int fack_count;
1127         int flag;
1128         s32 rtt; /* RTT measured by SACKing never-retransmitted data */
1129 };
1130 
1131 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1132  * the incoming SACK may not exactly match but we can find smaller MSS
1133  * aligned portion of it that matches. Therefore we might need to fragment
1134  * which may fail and creates some hassle (caller must handle error case
1135  * returns).
1136  *
1137  * FIXME: this could be merged to shift decision code
1138  */
1139 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1140                                   u32 start_seq, u32 end_seq)
1141 {
1142         int err;
1143         bool in_sack;
1144         unsigned int pkt_len;
1145         unsigned int mss;
1146 
1147         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1148                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1149 
1150         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1151             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1152                 mss = tcp_skb_mss(skb);
1153                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1154 
1155                 if (!in_sack) {
1156                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1157                         if (pkt_len < mss)
1158                                 pkt_len = mss;
1159                 } else {
1160                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1161                         if (pkt_len < mss)
1162                                 return -EINVAL;
1163                 }
1164 
1165                 /* Round if necessary so that SACKs cover only full MSSes
1166                  * and/or the remaining small portion (if present)
1167                  */
1168                 if (pkt_len > mss) {
1169                         unsigned int new_len = (pkt_len / mss) * mss;
1170                         if (!in_sack && new_len < pkt_len) {
1171                                 new_len += mss;
1172                                 if (new_len > skb->len)
1173                                         return 0;
1174                         }
1175                         pkt_len = new_len;
1176                 }
1177                 err = tcp_fragment(sk, skb, pkt_len, mss);
1178                 if (err < 0)
1179                         return err;
1180         }
1181 
1182         return in_sack;
1183 }
1184 
1185 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1186 static u8 tcp_sacktag_one(struct sock *sk,
1187                           struct tcp_sacktag_state *state, u8 sacked,
1188                           u32 start_seq, u32 end_seq,
1189                           int dup_sack, int pcount, u32 xmit_time)
1190 {
1191         struct tcp_sock *tp = tcp_sk(sk);
1192         int fack_count = state->fack_count;
1193 
1194         /* Account D-SACK for retransmitted packet. */
1195         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1196                 if (tp->undo_marker && tp->undo_retrans &&
1197                     after(end_seq, tp->undo_marker))
1198                         tp->undo_retrans--;
1199                 if (sacked & TCPCB_SACKED_ACKED)
1200                         state->reord = min(fack_count, state->reord);
1201         }
1202 
1203         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1204         if (!after(end_seq, tp->snd_una))
1205                 return sacked;
1206 
1207         if (!(sacked & TCPCB_SACKED_ACKED)) {
1208                 if (sacked & TCPCB_SACKED_RETRANS) {
1209                         /* If the segment is not tagged as lost,
1210                          * we do not clear RETRANS, believing
1211                          * that retransmission is still in flight.
1212                          */
1213                         if (sacked & TCPCB_LOST) {
1214                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1215                                 tp->lost_out -= pcount;
1216                                 tp->retrans_out -= pcount;
1217                         }
1218                 } else {
1219                         if (!(sacked & TCPCB_RETRANS)) {
1220                                 /* New sack for not retransmitted frame,
1221                                  * which was in hole. It is reordering.
1222                                  */
1223                                 if (before(start_seq,
1224                                            tcp_highest_sack_seq(tp)))
1225                                         state->reord = min(fack_count,
1226                                                            state->reord);
1227                                 if (!after(end_seq, tp->high_seq))
1228                                         state->flag |= FLAG_ORIG_SACK_ACKED;
1229                                 /* Pick the earliest sequence sacked for RTT */
1230                                 if (state->rtt < 0)
1231                                         state->rtt = tcp_time_stamp - xmit_time;
1232                         }
1233 
1234                         if (sacked & TCPCB_LOST) {
1235                                 sacked &= ~TCPCB_LOST;
1236                                 tp->lost_out -= pcount;
1237                         }
1238                 }
1239 
1240                 sacked |= TCPCB_SACKED_ACKED;
1241                 state->flag |= FLAG_DATA_SACKED;
1242                 tp->sacked_out += pcount;
1243 
1244                 fack_count += pcount;
1245 
1246                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1247                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1248                     before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1249                         tp->lost_cnt_hint += pcount;
1250 
1251                 if (fack_count > tp->fackets_out)
1252                         tp->fackets_out = fack_count;
1253         }
1254 
1255         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1256          * frames and clear it. undo_retrans is decreased above, L|R frames
1257          * are accounted above as well.
1258          */
1259         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1260                 sacked &= ~TCPCB_SACKED_RETRANS;
1261                 tp->retrans_out -= pcount;
1262         }
1263 
1264         return sacked;
1265 }
1266 
1267 /* Shift newly-SACKed bytes from this skb to the immediately previous
1268  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1269  */
1270 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1271                             struct tcp_sacktag_state *state,
1272                             unsigned int pcount, int shifted, int mss,
1273                             bool dup_sack)
1274 {
1275         struct tcp_sock *tp = tcp_sk(sk);
1276         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1277         u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
1278         u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
1279 
1280         BUG_ON(!pcount);
1281 
1282         /* Adjust counters and hints for the newly sacked sequence
1283          * range but discard the return value since prev is already
1284          * marked. We must tag the range first because the seq
1285          * advancement below implicitly advances
1286          * tcp_highest_sack_seq() when skb is highest_sack.
1287          */
1288         tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1289                         start_seq, end_seq, dup_sack, pcount,
1290                         TCP_SKB_CB(skb)->when);
1291 
1292         if (skb == tp->lost_skb_hint)
1293                 tp->lost_cnt_hint += pcount;
1294 
1295         TCP_SKB_CB(prev)->end_seq += shifted;
1296         TCP_SKB_CB(skb)->seq += shifted;
1297 
1298         skb_shinfo(prev)->gso_segs += pcount;
1299         BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1300         skb_shinfo(skb)->gso_segs -= pcount;
1301 
1302         /* When we're adding to gso_segs == 1, gso_size will be zero,
1303          * in theory this shouldn't be necessary but as long as DSACK
1304          * code can come after this skb later on it's better to keep
1305          * setting gso_size to something.
1306          */
1307         if (!skb_shinfo(prev)->gso_size) {
1308                 skb_shinfo(prev)->gso_size = mss;
1309                 skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1310         }
1311 
1312         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1313         if (skb_shinfo(skb)->gso_segs <= 1) {
1314                 skb_shinfo(skb)->gso_size = 0;
1315                 skb_shinfo(skb)->gso_type = 0;
1316         }
1317 
1318         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1319         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1320 
1321         if (skb->len > 0) {
1322                 BUG_ON(!tcp_skb_pcount(skb));
1323                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1324                 return false;
1325         }
1326 
1327         /* Whole SKB was eaten :-) */
1328 
1329         if (skb == tp->retransmit_skb_hint)
1330                 tp->retransmit_skb_hint = prev;
1331         if (skb == tp->lost_skb_hint) {
1332                 tp->lost_skb_hint = prev;
1333                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1334         }
1335 
1336         TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1337         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1338                 TCP_SKB_CB(prev)->end_seq++;
1339 
1340         if (skb == tcp_highest_sack(sk))
1341                 tcp_advance_highest_sack(sk, skb);
1342 
1343         tcp_unlink_write_queue(skb, sk);
1344         sk_wmem_free_skb(sk, skb);
1345 
1346         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1347 
1348         return true;
1349 }
1350 
1351 /* I wish gso_size would have a bit more sane initialization than
1352  * something-or-zero which complicates things
1353  */
1354 static int tcp_skb_seglen(const struct sk_buff *skb)
1355 {
1356         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1357 }
1358 
1359 /* Shifting pages past head area doesn't work */
1360 static int skb_can_shift(const struct sk_buff *skb)
1361 {
1362         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1363 }
1364 
1365 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1366  * skb.
1367  */
1368 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1369                                           struct tcp_sacktag_state *state,
1370                                           u32 start_seq, u32 end_seq,
1371                                           bool dup_sack)
1372 {
1373         struct tcp_sock *tp = tcp_sk(sk);
1374         struct sk_buff *prev;
1375         int mss;
1376         int pcount = 0;
1377         int len;
1378         int in_sack;
1379 
1380         if (!sk_can_gso(sk))
1381                 goto fallback;
1382 
1383         /* Normally R but no L won't result in plain S */
1384         if (!dup_sack &&
1385             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1386                 goto fallback;
1387         if (!skb_can_shift(skb))
1388                 goto fallback;
1389         /* This frame is about to be dropped (was ACKed). */
1390         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1391                 goto fallback;
1392 
1393         /* Can only happen with delayed DSACK + discard craziness */
1394         if (unlikely(skb == tcp_write_queue_head(sk)))
1395                 goto fallback;
1396         prev = tcp_write_queue_prev(sk, skb);
1397 
1398         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1399                 goto fallback;
1400 
1401         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1402                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1403 
1404         if (in_sack) {
1405                 len = skb->len;
1406                 pcount = tcp_skb_pcount(skb);
1407                 mss = tcp_skb_seglen(skb);
1408 
1409                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1410                  * drop this restriction as unnecessary
1411                  */
1412                 if (mss != tcp_skb_seglen(prev))
1413                         goto fallback;
1414         } else {
1415                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1416                         goto noop;
1417                 /* CHECKME: This is non-MSS split case only?, this will
1418                  * cause skipped skbs due to advancing loop btw, original
1419                  * has that feature too
1420                  */
1421                 if (tcp_skb_pcount(skb) <= 1)
1422                         goto noop;
1423 
1424                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1425                 if (!in_sack) {
1426                         /* TODO: head merge to next could be attempted here
1427                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1428                          * though it might not be worth of the additional hassle
1429                          *
1430                          * ...we can probably just fallback to what was done
1431                          * previously. We could try merging non-SACKed ones
1432                          * as well but it probably isn't going to buy off
1433                          * because later SACKs might again split them, and
1434                          * it would make skb timestamp tracking considerably
1435                          * harder problem.
1436                          */
1437                         goto fallback;
1438                 }
1439 
1440                 len = end_seq - TCP_SKB_CB(skb)->seq;
1441                 BUG_ON(len < 0);
1442                 BUG_ON(len > skb->len);
1443 
1444                 /* MSS boundaries should be honoured or else pcount will
1445                  * severely break even though it makes things bit trickier.
1446                  * Optimize common case to avoid most of the divides
1447                  */
1448                 mss = tcp_skb_mss(skb);
1449 
1450                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1451                  * drop this restriction as unnecessary
1452                  */
1453                 if (mss != tcp_skb_seglen(prev))
1454                         goto fallback;
1455 
1456                 if (len == mss) {
1457                         pcount = 1;
1458                 } else if (len < mss) {
1459                         goto noop;
1460                 } else {
1461                         pcount = len / mss;
1462                         len = pcount * mss;
1463                 }
1464         }
1465 
1466         /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1467         if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1468                 goto fallback;
1469 
1470         if (!skb_shift(prev, skb, len))
1471                 goto fallback;
1472         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1473                 goto out;
1474 
1475         /* Hole filled allows collapsing with the next as well, this is very
1476          * useful when hole on every nth skb pattern happens
1477          */
1478         if (prev == tcp_write_queue_tail(sk))
1479                 goto out;
1480         skb = tcp_write_queue_next(sk, prev);
1481 
1482         if (!skb_can_shift(skb) ||
1483             (skb == tcp_send_head(sk)) ||
1484             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1485             (mss != tcp_skb_seglen(skb)))
1486                 goto out;
1487 
1488         len = skb->len;
1489         if (skb_shift(prev, skb, len)) {
1490                 pcount += tcp_skb_pcount(skb);
1491                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1492         }
1493 
1494 out:
1495         state->fack_count += pcount;
1496         return prev;
1497 
1498 noop:
1499         return skb;
1500 
1501 fallback:
1502         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1503         return NULL;
1504 }
1505 
1506 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1507                                         struct tcp_sack_block *next_dup,
1508                                         struct tcp_sacktag_state *state,
1509                                         u32 start_seq, u32 end_seq,
1510                                         bool dup_sack_in)
1511 {
1512         struct tcp_sock *tp = tcp_sk(sk);
1513         struct sk_buff *tmp;
1514 
1515         tcp_for_write_queue_from(skb, sk) {
1516                 int in_sack = 0;
1517                 bool dup_sack = dup_sack_in;
1518 
1519                 if (skb == tcp_send_head(sk))
1520                         break;
1521 
1522                 /* queue is in-order => we can short-circuit the walk early */
1523                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1524                         break;
1525 
1526                 if ((next_dup != NULL) &&
1527                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1528                         in_sack = tcp_match_skb_to_sack(sk, skb,
1529                                                         next_dup->start_seq,
1530                                                         next_dup->end_seq);
1531                         if (in_sack > 0)
1532                                 dup_sack = true;
1533                 }
1534 
1535                 /* skb reference here is a bit tricky to get right, since
1536                  * shifting can eat and free both this skb and the next,
1537                  * so not even _safe variant of the loop is enough.
1538                  */
1539                 if (in_sack <= 0) {
1540                         tmp = tcp_shift_skb_data(sk, skb, state,
1541                                                  start_seq, end_seq, dup_sack);
1542                         if (tmp != NULL) {
1543                                 if (tmp != skb) {
1544                                         skb = tmp;
1545                                         continue;
1546                                 }
1547 
1548                                 in_sack = 0;
1549                         } else {
1550                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1551                                                                 start_seq,
1552                                                                 end_seq);
1553                         }
1554                 }
1555 
1556                 if (unlikely(in_sack < 0))
1557                         break;
1558 
1559                 if (in_sack) {
1560                         TCP_SKB_CB(skb)->sacked =
1561                                 tcp_sacktag_one(sk,
1562                                                 state,
1563                                                 TCP_SKB_CB(skb)->sacked,
1564                                                 TCP_SKB_CB(skb)->seq,
1565                                                 TCP_SKB_CB(skb)->end_seq,
1566                                                 dup_sack,
1567                                                 tcp_skb_pcount(skb),
1568                                                 TCP_SKB_CB(skb)->when);
1569 
1570                         if (!before(TCP_SKB_CB(skb)->seq,
1571                                     tcp_highest_sack_seq(tp)))
1572                                 tcp_advance_highest_sack(sk, skb);
1573                 }
1574 
1575                 state->fack_count += tcp_skb_pcount(skb);
1576         }
1577         return skb;
1578 }
1579 
1580 /* Avoid all extra work that is being done by sacktag while walking in
1581  * a normal way
1582  */
1583 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1584                                         struct tcp_sacktag_state *state,
1585                                         u32 skip_to_seq)
1586 {
1587         tcp_for_write_queue_from(skb, sk) {
1588                 if (skb == tcp_send_head(sk))
1589                         break;
1590 
1591                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1592                         break;
1593 
1594                 state->fack_count += tcp_skb_pcount(skb);
1595         }
1596         return skb;
1597 }
1598 
1599 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1600                                                 struct sock *sk,
1601                                                 struct tcp_sack_block *next_dup,
1602                                                 struct tcp_sacktag_state *state,
1603                                                 u32 skip_to_seq)
1604 {
1605         if (next_dup == NULL)
1606                 return skb;
1607 
1608         if (before(next_dup->start_seq, skip_to_seq)) {
1609                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1610                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1611                                        next_dup->start_seq, next_dup->end_seq,
1612                                        1);
1613         }
1614 
1615         return skb;
1616 }
1617 
1618 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1619 {
1620         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1621 }
1622 
1623 static int
1624 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1625                         u32 prior_snd_una, s32 *sack_rtt)
1626 {
1627         struct tcp_sock *tp = tcp_sk(sk);
1628         const unsigned char *ptr = (skb_transport_header(ack_skb) +
1629                                     TCP_SKB_CB(ack_skb)->sacked);
1630         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1631         struct tcp_sack_block sp[TCP_NUM_SACKS];
1632         struct tcp_sack_block *cache;
1633         struct tcp_sacktag_state state;
1634         struct sk_buff *skb;
1635         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1636         int used_sacks;
1637         bool found_dup_sack = false;
1638         int i, j;
1639         int first_sack_index;
1640 
1641         state.flag = 0;
1642         state.reord = tp->packets_out;
1643         state.rtt = -1;
1644 
1645         if (!tp->sacked_out) {
1646                 if (WARN_ON(tp->fackets_out))
1647                         tp->fackets_out = 0;
1648                 tcp_highest_sack_reset(sk);
1649         }
1650 
1651         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1652                                          num_sacks, prior_snd_una);
1653         if (found_dup_sack)
1654                 state.flag |= FLAG_DSACKING_ACK;
1655 
1656         /* Eliminate too old ACKs, but take into
1657          * account more or less fresh ones, they can
1658          * contain valid SACK info.
1659          */
1660         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1661                 return 0;
1662 
1663         if (!tp->packets_out)
1664                 goto out;
1665 
1666         used_sacks = 0;
1667         first_sack_index = 0;
1668         for (i = 0; i < num_sacks; i++) {
1669                 bool dup_sack = !i && found_dup_sack;
1670 
1671                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1672                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1673 
1674                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1675                                             sp[used_sacks].start_seq,
1676                                             sp[used_sacks].end_seq)) {
1677                         int mib_idx;
1678 
1679                         if (dup_sack) {
1680                                 if (!tp->undo_marker)
1681                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1682                                 else
1683                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1684                         } else {
1685                                 /* Don't count olds caused by ACK reordering */
1686                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1687                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1688                                         continue;
1689                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1690                         }
1691 
1692                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1693                         if (i == 0)
1694                                 first_sack_index = -1;
1695                         continue;
1696                 }
1697 
1698                 /* Ignore very old stuff early */
1699                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1700                         continue;
1701 
1702                 used_sacks++;
1703         }
1704 
1705         /* order SACK blocks to allow in order walk of the retrans queue */
1706         for (i = used_sacks - 1; i > 0; i--) {
1707                 for (j = 0; j < i; j++) {
1708                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1709                                 swap(sp[j], sp[j + 1]);
1710 
1711                                 /* Track where the first SACK block goes to */
1712                                 if (j == first_sack_index)
1713                                         first_sack_index = j + 1;
1714                         }
1715                 }
1716         }
1717 
1718         skb = tcp_write_queue_head(sk);
1719         state.fack_count = 0;
1720         i = 0;
1721 
1722         if (!tp->sacked_out) {
1723                 /* It's already past, so skip checking against it */
1724                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1725         } else {
1726                 cache = tp->recv_sack_cache;
1727                 /* Skip empty blocks in at head of the cache */
1728                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1729                        !cache->end_seq)
1730                         cache++;
1731         }
1732 
1733         while (i < used_sacks) {
1734                 u32 start_seq = sp[i].start_seq;
1735                 u32 end_seq = sp[i].end_seq;
1736                 bool dup_sack = (found_dup_sack && (i == first_sack_index));
1737                 struct tcp_sack_block *next_dup = NULL;
1738 
1739                 if (found_dup_sack && ((i + 1) == first_sack_index))
1740                         next_dup = &sp[i + 1];
1741 
1742                 /* Skip too early cached blocks */
1743                 while (tcp_sack_cache_ok(tp, cache) &&
1744                        !before(start_seq, cache->end_seq))
1745                         cache++;
1746 
1747                 /* Can skip some work by looking recv_sack_cache? */
1748                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1749                     after(end_seq, cache->start_seq)) {
1750 
1751                         /* Head todo? */
1752                         if (before(start_seq, cache->start_seq)) {
1753                                 skb = tcp_sacktag_skip(skb, sk, &state,
1754                                                        start_seq);
1755                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1756                                                        &state,
1757                                                        start_seq,
1758                                                        cache->start_seq,
1759                                                        dup_sack);
1760                         }
1761 
1762                         /* Rest of the block already fully processed? */
1763                         if (!after(end_seq, cache->end_seq))
1764                                 goto advance_sp;
1765 
1766                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1767                                                        &state,
1768                                                        cache->end_seq);
1769 
1770                         /* ...tail remains todo... */
1771                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1772                                 /* ...but better entrypoint exists! */
1773                                 skb = tcp_highest_sack(sk);
1774                                 if (skb == NULL)
1775                                         break;
1776                                 state.fack_count = tp->fackets_out;
1777                                 cache++;
1778                                 goto walk;
1779                         }
1780 
1781                         skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1782                         /* Check overlap against next cached too (past this one already) */
1783                         cache++;
1784                         continue;
1785                 }
1786 
1787                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1788                         skb = tcp_highest_sack(sk);
1789                         if (skb == NULL)
1790                                 break;
1791                         state.fack_count = tp->fackets_out;
1792                 }
1793                 skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1794 
1795 walk:
1796                 skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1797                                        start_seq, end_seq, dup_sack);
1798 
1799 advance_sp:
1800                 i++;
1801         }
1802 
1803         /* Clear the head of the cache sack blocks so we can skip it next time */
1804         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1805                 tp->recv_sack_cache[i].start_seq = 0;
1806                 tp->recv_sack_cache[i].end_seq = 0;
1807         }
1808         for (j = 0; j < used_sacks; j++)
1809                 tp->recv_sack_cache[i++] = sp[j];
1810 
1811         tcp_mark_lost_retrans(sk);
1812 
1813         tcp_verify_left_out(tp);
1814 
1815         if ((state.reord < tp->fackets_out) &&
1816             ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1817                 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1818 
1819 out:
1820 
1821 #if FASTRETRANS_DEBUG > 0
1822         WARN_ON((int)tp->sacked_out < 0);
1823         WARN_ON((int)tp->lost_out < 0);
1824         WARN_ON((int)tp->retrans_out < 0);
1825         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1826 #endif
1827         *sack_rtt = state.rtt;
1828         return state.flag;
1829 }
1830 
1831 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1832  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1833  */
1834 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1835 {
1836         u32 holes;
1837 
1838         holes = max(tp->lost_out, 1U);
1839         holes = min(holes, tp->packets_out);
1840 
1841         if ((tp->sacked_out + holes) > tp->packets_out) {
1842                 tp->sacked_out = tp->packets_out - holes;
1843                 return true;
1844         }
1845         return false;
1846 }
1847 
1848 /* If we receive more dupacks than we expected counting segments
1849  * in assumption of absent reordering, interpret this as reordering.
1850  * The only another reason could be bug in receiver TCP.
1851  */
1852 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1853 {
1854         struct tcp_sock *tp = tcp_sk(sk);
1855         if (tcp_limit_reno_sacked(tp))
1856                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1857 }
1858 
1859 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1860 
1861 static void tcp_add_reno_sack(struct sock *sk)
1862 {
1863         struct tcp_sock *tp = tcp_sk(sk);
1864         tp->sacked_out++;
1865         tcp_check_reno_reordering(sk, 0);
1866         tcp_verify_left_out(tp);
1867 }
1868 
1869 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1870 
1871 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1872 {
1873         struct tcp_sock *tp = tcp_sk(sk);
1874 
1875         if (acked > 0) {
1876                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1877                 if (acked - 1 >= tp->sacked_out)
1878                         tp->sacked_out = 0;
1879                 else
1880                         tp->sacked_out -= acked - 1;
1881         }
1882         tcp_check_reno_reordering(sk, acked);
1883         tcp_verify_left_out(tp);
1884 }
1885 
1886 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1887 {
1888         tp->sacked_out = 0;
1889 }
1890 
1891 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
1892 {
1893         tp->retrans_out = 0;
1894         tp->lost_out = 0;
1895 
1896         tp->undo_marker = 0;
1897         tp->undo_retrans = 0;
1898 }
1899 
1900 void tcp_clear_retrans(struct tcp_sock *tp)
1901 {
1902         tcp_clear_retrans_partial(tp);
1903 
1904         tp->fackets_out = 0;
1905         tp->sacked_out = 0;
1906 }
1907 
1908 /* Enter Loss state. If "how" is not zero, forget all SACK information
1909  * and reset tags completely, otherwise preserve SACKs. If receiver
1910  * dropped its ofo queue, we will know this due to reneging detection.
1911  */
1912 void tcp_enter_loss(struct sock *sk, int how)
1913 {
1914         const struct inet_connection_sock *icsk = inet_csk(sk);
1915         struct tcp_sock *tp = tcp_sk(sk);
1916         struct sk_buff *skb;
1917         bool new_recovery = false;
1918 
1919         /* Reduce ssthresh if it has not yet been made inside this window. */
1920         if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1921             !after(tp->high_seq, tp->snd_una) ||
1922             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1923                 new_recovery = true;
1924                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1925                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1926                 tcp_ca_event(sk, CA_EVENT_LOSS);
1927         }
1928         tp->snd_cwnd       = 1;
1929         tp->snd_cwnd_cnt   = 0;
1930         tp->snd_cwnd_stamp = tcp_time_stamp;
1931 
1932         tcp_clear_retrans_partial(tp);
1933 
1934         if (tcp_is_reno(tp))
1935                 tcp_reset_reno_sack(tp);
1936 
1937         tp->undo_marker = tp->snd_una;
1938         if (how) {
1939                 tp->sacked_out = 0;
1940                 tp->fackets_out = 0;
1941         }
1942         tcp_clear_all_retrans_hints(tp);
1943 
1944         tcp_for_write_queue(skb, sk) {
1945                 if (skb == tcp_send_head(sk))
1946                         break;
1947 
1948                 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1949                         tp->undo_marker = 0;
1950 
1951                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1952                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1953                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1954                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1955                         tp->lost_out += tcp_skb_pcount(skb);
1956                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1957                 }
1958         }
1959         tcp_verify_left_out(tp);
1960 
1961         /* Timeout in disordered state after receiving substantial DUPACKs
1962          * suggests that the degree of reordering is over-estimated.
1963          */
1964         if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1965             tp->sacked_out >= sysctl_tcp_reordering)
1966                 tp->reordering = min_t(unsigned int, tp->reordering,
1967                                        sysctl_tcp_reordering);
1968         tcp_set_ca_state(sk, TCP_CA_Loss);
1969         tp->high_seq = tp->snd_nxt;
1970         TCP_ECN_queue_cwr(tp);
1971 
1972         /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1973          * loss recovery is underway except recurring timeout(s) on
1974          * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1975          */
1976         tp->frto = sysctl_tcp_frto &&
1977                    (new_recovery || icsk->icsk_retransmits) &&
1978                    !inet_csk(sk)->icsk_mtup.probe_size;
1979 }
1980 
1981 /* If ACK arrived pointing to a remembered SACK, it means that our
1982  * remembered SACKs do not reflect real state of receiver i.e.
1983  * receiver _host_ is heavily congested (or buggy).
1984  *
1985  * Do processing similar to RTO timeout.
1986  */
1987 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
1988 {
1989         if (flag & FLAG_SACK_RENEGING) {
1990                 struct inet_connection_sock *icsk = inet_csk(sk);
1991                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1992 
1993                 tcp_enter_loss(sk, 1);
1994                 icsk->icsk_retransmits++;
1995                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1996                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1997                                           icsk->icsk_rto, TCP_RTO_MAX);
1998                 return true;
1999         }
2000         return false;
2001 }
2002 
2003 static inline int tcp_fackets_out(const struct tcp_sock *tp)
2004 {
2005         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2006 }
2007 
2008 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2009  * counter when SACK is enabled (without SACK, sacked_out is used for
2010  * that purpose).
2011  *
2012  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2013  * segments up to the highest received SACK block so far and holes in
2014  * between them.
2015  *
2016  * With reordering, holes may still be in flight, so RFC3517 recovery
2017  * uses pure sacked_out (total number of SACKed segments) even though
2018  * it violates the RFC that uses duplicate ACKs, often these are equal
2019  * but when e.g. out-of-window ACKs or packet duplication occurs,
2020  * they differ. Since neither occurs due to loss, TCP should really
2021  * ignore them.
2022  */
2023 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2024 {
2025         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2026 }
2027 
2028 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
2029 {
2030         struct tcp_sock *tp = tcp_sk(sk);
2031         unsigned long delay;
2032 
2033         /* Delay early retransmit and entering fast recovery for
2034          * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
2035          * available, or RTO is scheduled to fire first.
2036          */
2037         if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2038             (flag & FLAG_ECE) || !tp->srtt)
2039                 return false;
2040 
2041         delay = max_t(unsigned long, (tp->srtt >> 5), msecs_to_jiffies(2));
2042         if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2043                 return false;
2044 
2045         inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2046                                   TCP_RTO_MAX);
2047         return true;
2048 }
2049 
2050 /* Linux NewReno/SACK/FACK/ECN state machine.
2051  * --------------------------------------
2052  *
2053  * "Open"       Normal state, no dubious events, fast path.
2054  * "Disorder"   In all the respects it is "Open",
2055  *              but requires a bit more attention. It is entered when
2056  *              we see some SACKs or dupacks. It is split of "Open"
2057  *              mainly to move some processing from fast path to slow one.
2058  * "CWR"        CWND was reduced due to some Congestion Notification event.
2059  *              It can be ECN, ICMP source quench, local device congestion.
2060  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2061  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2062  *
2063  * tcp_fastretrans_alert() is entered:
2064  * - each incoming ACK, if state is not "Open"
2065  * - when arrived ACK is unusual, namely:
2066  *      * SACK
2067  *      * Duplicate ACK.
2068  *      * ECN ECE.
2069  *
2070  * Counting packets in flight is pretty simple.
2071  *
2072  *      in_flight = packets_out - left_out + retrans_out
2073  *
2074  *      packets_out is SND.NXT-SND.UNA counted in packets.
2075  *
2076  *      retrans_out is number of retransmitted segments.
2077  *
2078  *      left_out is number of segments left network, but not ACKed yet.
2079  *
2080  *              left_out = sacked_out + lost_out
2081  *
2082  *     sacked_out: Packets, which arrived to receiver out of order
2083  *                 and hence not ACKed. With SACKs this number is simply
2084  *                 amount of SACKed data. Even without SACKs
2085  *                 it is easy to give pretty reliable estimate of this number,
2086  *                 counting duplicate ACKs.
2087  *
2088  *       lost_out: Packets lost by network. TCP has no explicit
2089  *                 "loss notification" feedback from network (for now).
2090  *                 It means that this number can be only _guessed_.
2091  *                 Actually, it is the heuristics to predict lossage that
2092  *                 distinguishes different algorithms.
2093  *
2094  *      F.e. after RTO, when all the queue is considered as lost,
2095  *      lost_out = packets_out and in_flight = retrans_out.
2096  *
2097  *              Essentially, we have now two algorithms counting
2098  *              lost packets.
2099  *
2100  *              FACK: It is the simplest heuristics. As soon as we decided
2101  *              that something is lost, we decide that _all_ not SACKed
2102  *              packets until the most forward SACK are lost. I.e.
2103  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2104  *              It is absolutely correct estimate, if network does not reorder
2105  *              packets. And it loses any connection to reality when reordering
2106  *              takes place. We use FACK by default until reordering
2107  *              is suspected on the path to this destination.
2108  *
2109  *              NewReno: when Recovery is entered, we assume that one segment
2110  *              is lost (classic Reno). While we are in Recovery and
2111  *              a partial ACK arrives, we assume that one more packet
2112  *              is lost (NewReno). This heuristics are the same in NewReno
2113  *              and SACK.
2114  *
2115  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2116  *  deflation etc. CWND is real congestion window, never inflated, changes
2117  *  only according to classic VJ rules.
2118  *
2119  * Really tricky (and requiring careful tuning) part of algorithm
2120  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2121  * The first determines the moment _when_ we should reduce CWND and,
2122  * hence, slow down forward transmission. In fact, it determines the moment
2123  * when we decide that hole is caused by loss, rather than by a reorder.
2124  *
2125  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2126  * holes, caused by lost packets.
2127  *
2128  * And the most logically complicated part of algorithm is undo
2129  * heuristics. We detect false retransmits due to both too early
2130  * fast retransmit (reordering) and underestimated RTO, analyzing
2131  * timestamps and D-SACKs. When we detect that some segments were
2132  * retransmitted by mistake and CWND reduction was wrong, we undo
2133  * window reduction and abort recovery phase. This logic is hidden
2134  * inside several functions named tcp_try_undo_<something>.
2135  */
2136 
2137 /* This function decides, when we should leave Disordered state
2138  * and enter Recovery phase, reducing congestion window.
2139  *
2140  * Main question: may we further continue forward transmission
2141  * with the same cwnd?
2142  */
2143 static bool tcp_time_to_recover(struct sock *sk, int flag)
2144 {
2145         struct tcp_sock *tp = tcp_sk(sk);
2146         __u32 packets_out;
2147 
2148         /* Trick#1: The loss is proven. */
2149         if (tp->lost_out)
2150                 return true;
2151 
2152         /* Not-A-Trick#2 : Classic rule... */
2153         if (tcp_dupack_heuristics(tp) > tp->reordering)
2154                 return true;
2155 
2156         /* Trick#4: It is still not OK... But will it be useful to delay
2157          * recovery more?
2158          */
2159         packets_out = tp->packets_out;
2160         if (packets_out <= tp->reordering &&
2161             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2162             !tcp_may_send_now(sk)) {
2163                 /* We have nothing to send. This connection is limited
2164                  * either by receiver window or by application.
2165                  */
2166                 return true;
2167         }
2168 
2169         /* If a thin stream is detected, retransmit after first
2170          * received dupack. Employ only if SACK is supported in order
2171          * to avoid possible corner-case series of spurious retransmissions
2172          * Use only if there are no unsent data.
2173          */
2174         if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2175             tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2176             tcp_is_sack(tp) && !tcp_send_head(sk))
2177                 return true;
2178 
2179         /* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
2180          * retransmissions due to small network reorderings, we implement
2181          * Mitigation A.3 in the RFC and delay the retransmission for a short
2182          * interval if appropriate.
2183          */
2184         if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2185             (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2186             !tcp_may_send_now(sk))
2187                 return !tcp_pause_early_retransmit(sk, flag);
2188 
2189         return false;
2190 }
2191 
2192 /* Detect loss in event "A" above by marking head of queue up as lost.
2193  * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2194  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2195  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2196  * the maximum SACKed segments to pass before reaching this limit.
2197  */
2198 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2199 {
2200         struct tcp_sock *tp = tcp_sk(sk);
2201         struct sk_buff *skb;
2202         int cnt, oldcnt;
2203         int err;
2204         unsigned int mss;
2205         /* Use SACK to deduce losses of new sequences sent during recovery */
2206         const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2207 
2208         WARN_ON(packets > tp->packets_out);
2209         if (tp->lost_skb_hint) {
2210                 skb = tp->lost_skb_hint;
2211                 cnt = tp->lost_cnt_hint;
2212                 /* Head already handled? */
2213                 if (mark_head && skb != tcp_write_queue_head(sk))
2214                         return;
2215         } else {
2216                 skb = tcp_write_queue_head(sk);
2217                 cnt = 0;
2218         }
2219 
2220         tcp_for_write_queue_from(skb, sk) {
2221                 if (skb == tcp_send_head(sk))
2222                         break;
2223                 /* TODO: do this better */
2224                 /* this is not the most efficient way to do this... */
2225                 tp->lost_skb_hint = skb;
2226                 tp->lost_cnt_hint = cnt;
2227 
2228                 if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2229                         break;
2230 
2231                 oldcnt = cnt;
2232                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2233                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2234                         cnt += tcp_skb_pcount(skb);
2235 
2236                 if (cnt > packets) {
2237                         if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2238                             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2239                             (oldcnt >= packets))
2240                                 break;
2241 
2242                         mss = skb_shinfo(skb)->gso_size;
2243                         err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2244                         if (err < 0)
2245                                 break;
2246                         cnt = packets;
2247                 }
2248 
2249                 tcp_skb_mark_lost(tp, skb);
2250 
2251                 if (mark_head)
2252                         break;
2253         }
2254         tcp_verify_left_out(tp);
2255 }
2256 
2257 /* Account newly detected lost packet(s) */
2258 
2259 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2260 {
2261         struct tcp_sock *tp = tcp_sk(sk);
2262 
2263         if (tcp_is_reno(tp)) {
2264                 tcp_mark_head_lost(sk, 1, 1);
2265         } else if (tcp_is_fack(tp)) {
2266                 int lost = tp->fackets_out - tp->reordering;
2267                 if (lost <= 0)
2268                         lost = 1;
2269                 tcp_mark_head_lost(sk, lost, 0);
2270         } else {
2271                 int sacked_upto = tp->sacked_out - tp->reordering;
2272                 if (sacked_upto >= 0)
2273                         tcp_mark_head_lost(sk, sacked_upto, 0);
2274                 else if (fast_rexmit)
2275                         tcp_mark_head_lost(sk, 1, 1);
2276         }
2277 }
2278 
2279 /* CWND moderation, preventing bursts due to too big ACKs
2280  * in dubious situations.
2281  */
2282 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2283 {
2284         tp->snd_cwnd = min(tp->snd_cwnd,
2285                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2286         tp->snd_cwnd_stamp = tcp_time_stamp;
2287 }
2288 
2289 /* Nothing was retransmitted or returned timestamp is less
2290  * than timestamp of the first retransmission.
2291  */
2292 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2293 {
2294         return !tp->retrans_stamp ||
2295                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2296                  before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2297 }
2298 
2299 /* Undo procedures. */
2300 
2301 #if FASTRETRANS_DEBUG > 1
2302 static void DBGUNDO(struct sock *sk, const char *msg)
2303 {
2304         struct tcp_sock *tp = tcp_sk(sk);
2305         struct inet_sock *inet = inet_sk(sk);
2306 
2307         if (sk->sk_family == AF_INET) {
2308                 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2309                          msg,
2310                          &inet->inet_daddr, ntohs(inet->inet_dport),
2311                          tp->snd_cwnd, tcp_left_out(tp),
2312                          tp->snd_ssthresh, tp->prior_ssthresh,
2313                          tp->packets_out);
2314         }
2315 #if IS_ENABLED(CONFIG_IPV6)
2316         else if (sk->sk_family == AF_INET6) {
2317                 struct ipv6_pinfo *np = inet6_sk(sk);
2318                 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2319                          msg,
2320                          &np->daddr, ntohs(inet->inet_dport),
2321                          tp->snd_cwnd, tcp_left_out(tp),
2322                          tp->snd_ssthresh, tp->prior_ssthresh,
2323                          tp->packets_out);
2324         }
2325 #endif
2326 }
2327 #else
2328 #define DBGUNDO(x...) do { } while (0)
2329 #endif
2330 
2331 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2332 {
2333         struct tcp_sock *tp = tcp_sk(sk);
2334 
2335         if (unmark_loss) {
2336                 struct sk_buff *skb;
2337 
2338                 tcp_for_write_queue(skb, sk) {
2339                         if (skb == tcp_send_head(sk))
2340                                 break;
2341                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2342                 }
2343                 tp->lost_out = 0;
2344                 tcp_clear_all_retrans_hints(tp);
2345         }
2346 
2347         if (tp->prior_ssthresh) {
2348                 const struct inet_connection_sock *icsk = inet_csk(sk);
2349 
2350                 if (icsk->icsk_ca_ops->undo_cwnd)
2351                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2352                 else
2353                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2354 
2355                 if (tp->prior_ssthresh > tp->snd_ssthresh) {
2356                         tp->snd_ssthresh = tp->prior_ssthresh;
2357                         TCP_ECN_withdraw_cwr(tp);
2358                 }
2359         } else {
2360                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2361         }
2362         tp->snd_cwnd_stamp = tcp_time_stamp;
2363         tp->undo_marker = 0;
2364 }
2365 
2366 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2367 {
2368         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2369 }
2370 
2371 /* People celebrate: "We love our President!" */
2372 static bool tcp_try_undo_recovery(struct sock *sk)
2373 {
2374         struct tcp_sock *tp = tcp_sk(sk);
2375 
2376         if (tcp_may_undo(tp)) {
2377                 int mib_idx;
2378 
2379                 /* Happy end! We did not retransmit anything
2380                  * or our original transmission succeeded.
2381                  */
2382                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2383                 tcp_undo_cwnd_reduction(sk, false);
2384                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2385                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2386                 else
2387                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2388 
2389                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2390         }
2391         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2392                 /* Hold old state until something *above* high_seq
2393                  * is ACKed. For Reno it is MUST to prevent false
2394                  * fast retransmits (RFC2582). SACK TCP is safe. */
2395                 tcp_moderate_cwnd(tp);
2396                 return true;
2397         }
2398         tcp_set_ca_state(sk, TCP_CA_Open);
2399         return false;
2400 }
2401 
2402 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2403 static bool tcp_try_undo_dsack(struct sock *sk)
2404 {
2405         struct tcp_sock *tp = tcp_sk(sk);
2406 
2407         if (tp->undo_marker && !tp->undo_retrans) {
2408                 DBGUNDO(sk, "D-SACK");
2409                 tcp_undo_cwnd_reduction(sk, false);
2410                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2411                 return true;
2412         }
2413         return false;
2414 }
2415 
2416 /* We can clear retrans_stamp when there are no retransmissions in the
2417  * window. It would seem that it is trivially available for us in
2418  * tp->retrans_out, however, that kind of assumptions doesn't consider
2419  * what will happen if errors occur when sending retransmission for the
2420  * second time. ...It could the that such segment has only
2421  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2422  * the head skb is enough except for some reneging corner cases that
2423  * are not worth the effort.
2424  *
2425  * Main reason for all this complexity is the fact that connection dying
2426  * time now depends on the validity of the retrans_stamp, in particular,
2427  * that successive retransmissions of a segment must not advance
2428  * retrans_stamp under any conditions.
2429  */
2430 static bool tcp_any_retrans_done(const struct sock *sk)
2431 {
2432         const struct tcp_sock *tp = tcp_sk(sk);
2433         struct sk_buff *skb;
2434 
2435         if (tp->retrans_out)
2436                 return true;
2437 
2438         skb = tcp_write_queue_head(sk);
2439         if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2440                 return true;
2441 
2442         return false;
2443 }
2444 
2445 /* Undo during loss recovery after partial ACK or using F-RTO. */
2446 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2447 {
2448         struct tcp_sock *tp = tcp_sk(sk);
2449 
2450         if (frto_undo || tcp_may_undo(tp)) {
2451                 tcp_undo_cwnd_reduction(sk, true);
2452 
2453                 DBGUNDO(sk, "partial loss");
2454                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2455                 if (frto_undo)
2456                         NET_INC_STATS_BH(sock_net(sk),
2457                                          LINUX_MIB_TCPSPURIOUSRTOS);
2458                 inet_csk(sk)->icsk_retransmits = 0;
2459                 if (frto_undo || tcp_is_sack(tp))
2460                         tcp_set_ca_state(sk, TCP_CA_Open);
2461                 return true;
2462         }
2463         return false;
2464 }
2465 
2466 /* The cwnd reduction in CWR and Recovery use the PRR algorithm
2467  * https://datatracker.ietf.org/doc/draft-ietf-tcpm-proportional-rate-reduction/
2468  * It computes the number of packets to send (sndcnt) based on packets newly
2469  * delivered:
2470  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2471  *      cwnd reductions across a full RTT.
2472  *   2) If packets in flight is lower than ssthresh (such as due to excess
2473  *      losses and/or application stalls), do not perform any further cwnd
2474  *      reductions, but instead slow start up to ssthresh.
2475  */
2476 static void tcp_init_cwnd_reduction(struct sock *sk, const bool set_ssthresh)
2477 {
2478         struct tcp_sock *tp = tcp_sk(sk);
2479 
2480         tp->high_seq = tp->snd_nxt;
2481         tp->tlp_high_seq = 0;
2482         tp->snd_cwnd_cnt = 0;
2483         tp->prior_cwnd = tp->snd_cwnd;
2484         tp->prr_delivered = 0;
2485         tp->prr_out = 0;
2486         if (set_ssthresh)
2487                 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2488         TCP_ECN_queue_cwr(tp);
2489 }
2490 
2491 static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
2492                                int fast_rexmit)
2493 {
2494         struct tcp_sock *tp = tcp_sk(sk);
2495         int sndcnt = 0;
2496         int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2497         int newly_acked_sacked = prior_unsacked -
2498                                  (tp->packets_out - tp->sacked_out);
2499 
2500         tp->prr_delivered += newly_acked_sacked;
2501         if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
2502                 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2503                                tp->prior_cwnd - 1;
2504                 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2505         } else {
2506                 sndcnt = min_t(int, delta,
2507                                max_t(int, tp->prr_delivered - tp->prr_out,
2508                                      newly_acked_sacked) + 1);
2509         }
2510 
2511         sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2512         tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2513 }
2514 
2515 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2516 {
2517         struct tcp_sock *tp = tcp_sk(sk);
2518 
2519         /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2520         if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2521             (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2522                 tp->snd_cwnd = tp->snd_ssthresh;
2523                 tp->snd_cwnd_stamp = tcp_time_stamp;
2524         }
2525         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2526 }
2527 
2528 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2529 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
2530 {
2531         struct tcp_sock *tp = tcp_sk(sk);
2532 
2533         tp->prior_ssthresh = 0;
2534         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2535                 tp->undo_marker = 0;
2536                 tcp_init_cwnd_reduction(sk, set_ssthresh);
2537                 tcp_set_ca_state(sk, TCP_CA_CWR);
2538         }
2539 }
2540 
2541 static void tcp_try_keep_open(struct sock *sk)
2542 {
2543         struct tcp_sock *tp = tcp_sk(sk);
2544         int state = TCP_CA_Open;
2545 
2546         if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2547                 state = TCP_CA_Disorder;
2548 
2549         if (inet_csk(sk)->icsk_ca_state != state) {
2550                 tcp_set_ca_state(sk, state);
2551                 tp->high_seq = tp->snd_nxt;
2552         }
2553 }
2554 
2555 static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
2556 {
2557         struct tcp_sock *tp = tcp_sk(sk);
2558 
2559         tcp_verify_left_out(tp);
2560 
2561         if (!tcp_any_retrans_done(sk))
2562                 tp->retrans_stamp = 0;
2563 
2564         if (flag & FLAG_ECE)
2565                 tcp_enter_cwr(sk, 1);
2566 
2567         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2568                 tcp_try_keep_open(sk);
2569         } else {
2570                 tcp_cwnd_reduction(sk, prior_unsacked, 0);
2571         }
2572 }
2573 
2574 static void tcp_mtup_probe_failed(struct sock *sk)
2575 {
2576         struct inet_connection_sock *icsk = inet_csk(sk);
2577 
2578         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2579         icsk->icsk_mtup.probe_size = 0;
2580 }
2581 
2582 static void tcp_mtup_probe_success(struct sock *sk)
2583 {
2584         struct tcp_sock *tp = tcp_sk(sk);
2585         struct inet_connection_sock *icsk = inet_csk(sk);
2586 
2587         /* FIXME: breaks with very large cwnd */
2588         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2589         tp->snd_cwnd = tp->snd_cwnd *
2590                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2591                        icsk->icsk_mtup.probe_size;
2592         tp->snd_cwnd_cnt = 0;
2593         tp->snd_cwnd_stamp = tcp_time_stamp;
2594         tp->snd_ssthresh = tcp_current_ssthresh(sk);
2595 
2596         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2597         icsk->icsk_mtup.probe_size = 0;
2598         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2599 }
2600 
2601 /* Do a simple retransmit without using the backoff mechanisms in
2602  * tcp_timer. This is used for path mtu discovery.
2603  * The socket is already locked here.
2604  */
2605 void tcp_simple_retransmit(struct sock *sk)
2606 {
2607         const struct inet_connection_sock *icsk = inet_csk(sk);
2608         struct tcp_sock *tp = tcp_sk(sk);
2609         struct sk_buff *skb;
2610         unsigned int mss = tcp_current_mss(sk);
2611         u32 prior_lost = tp->lost_out;
2612 
2613         tcp_for_write_queue(skb, sk) {
2614                 if (skb == tcp_send_head(sk))
2615                         break;
2616                 if (tcp_skb_seglen(skb) > mss &&
2617                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2618                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2619                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2620                                 tp->retrans_out -= tcp_skb_pcount(skb);
2621                         }
2622                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2623                 }
2624         }
2625 
2626         tcp_clear_retrans_hints_partial(tp);
2627 
2628         if (prior_lost == tp->lost_out)
2629                 return;
2630 
2631         if (tcp_is_reno(tp))
2632                 tcp_limit_reno_sacked(tp);
2633 
2634         tcp_verify_left_out(tp);
2635 
2636         /* Don't muck with the congestion window here.
2637          * Reason is that we do not increase amount of _data_
2638          * in network, but units changed and effective
2639          * cwnd/ssthresh really reduced now.
2640          */
2641         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2642                 tp->high_seq = tp->snd_nxt;
2643                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2644                 tp->prior_ssthresh = 0;
2645                 tp->undo_marker = 0;
2646                 tcp_set_ca_state(sk, TCP_CA_Loss);
2647         }
2648         tcp_xmit_retransmit_queue(sk);
2649 }
2650 EXPORT_SYMBOL(tcp_simple_retransmit);
2651 
2652 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2653 {
2654         struct tcp_sock *tp = tcp_sk(sk);
2655         int mib_idx;
2656 
2657         if (tcp_is_reno(tp))
2658                 mib_idx = LINUX_MIB_TCPRENORECOVERY;
2659         else
2660                 mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2661 
2662         NET_INC_STATS_BH(sock_net(sk), mib_idx);
2663 
2664         tp->prior_ssthresh = 0;
2665         tp->undo_marker = tp->snd_una;
2666         tp->undo_retrans = tp->retrans_out;
2667 
2668         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2669                 if (!ece_ack)
2670                         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2671                 tcp_init_cwnd_reduction(sk, true);
2672         }
2673         tcp_set_ca_state(sk, TCP_CA_Recovery);
2674 }
2675 
2676 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2677  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2678  */
2679 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
2680 {
2681         struct inet_connection_sock *icsk = inet_csk(sk);
2682         struct tcp_sock *tp = tcp_sk(sk);
2683         bool recovered = !before(tp->snd_una, tp->high_seq);
2684 
2685         if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2686                 if (flag & FLAG_ORIG_SACK_ACKED) {
2687                         /* Step 3.b. A timeout is spurious if not all data are
2688                          * lost, i.e., never-retransmitted data are (s)acked.
2689                          */
2690                         tcp_try_undo_loss(sk, true);
2691                         return;
2692                 }
2693                 if (after(tp->snd_nxt, tp->high_seq) &&
2694                     (flag & FLAG_DATA_SACKED || is_dupack)) {
2695                         tp->frto = 0; /* Loss was real: 2nd part of step 3.a */
2696                 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2697                         tp->high_seq = tp->snd_nxt;
2698                         __tcp_push_pending_frames(sk, tcp_current_mss(sk),
2699                                                   TCP_NAGLE_OFF);
2700                         if (after(tp->snd_nxt, tp->high_seq))
2701                                 return; /* Step 2.b */
2702                         tp->frto = 0;
2703                 }
2704         }
2705 
2706         if (recovered) {
2707                 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2708                 icsk->icsk_retransmits = 0;
2709                 tcp_try_undo_recovery(sk);
2710                 return;
2711         }
2712         if (flag & FLAG_DATA_ACKED)
2713                 icsk->icsk_retransmits = 0;
2714         if (tcp_is_reno(tp)) {
2715                 /* A Reno DUPACK means new data in F-RTO step 2.b above are
2716                  * delivered. Lower inflight to clock out (re)tranmissions.
2717                  */
2718                 if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2719                         tcp_add_reno_sack(sk);
2720                 else if (flag & FLAG_SND_UNA_ADVANCED)
2721                         tcp_reset_reno_sack(tp);
2722         }
2723         if (tcp_try_undo_loss(sk, false))
2724                 return;
2725         tcp_xmit_retransmit_queue(sk);
2726 }
2727 
2728 /* Undo during fast recovery after partial ACK. */
2729 static bool tcp_try_undo_partial(struct sock *sk, const int acked,
2730                                  const int prior_unsacked)
2731 {
2732         struct tcp_sock *tp = tcp_sk(sk);
2733 
2734         if (tp->undo_marker && tcp_packet_delayed(tp)) {
2735                 /* Plain luck! Hole if filled with delayed
2736                  * packet, rather than with a retransmit.
2737                  */
2738                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2739 
2740                 /* We are getting evidence that the reordering degree is higher
2741                  * than we realized. If there are no retransmits out then we
2742                  * can undo. Otherwise we clock out new packets but do not
2743                  * mark more packets lost or retransmit more.
2744                  */
2745                 if (tp->retrans_out) {
2746                         tcp_cwnd_reduction(sk, prior_unsacked, 0);
2747                         return true;
2748                 }
2749 
2750                 if (!tcp_any_retrans_done(sk))
2751                         tp->retrans_stamp = 0;
2752 
2753                 DBGUNDO(sk, "partial recovery");
2754                 tcp_undo_cwnd_reduction(sk, true);
2755                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2756                 tcp_try_keep_open(sk);
2757                 return true;
2758         }
2759         return false;
2760 }
2761 
2762 /* Process an event, which can update packets-in-flight not trivially.
2763  * Main goal of this function is to calculate new estimate for left_out,
2764  * taking into account both packets sitting in receiver's buffer and
2765  * packets lost by network.
2766  *
2767  * Besides that it does CWND reduction, when packet loss is detected
2768  * and changes state of machine.
2769  *
2770  * It does _not_ decide what to send, it is made in function
2771  * tcp_xmit_retransmit_queue().
2772  */
2773 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2774                                   const int prior_unsacked,
2775                                   bool is_dupack, int flag)
2776 {
2777         struct inet_connection_sock *icsk = inet_csk(sk);
2778         struct tcp_sock *tp = tcp_sk(sk);
2779         bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2780                                     (tcp_fackets_out(tp) > tp->reordering));
2781         int fast_rexmit = 0;
2782 
2783         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2784                 tp->sacked_out = 0;
2785         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2786                 tp->fackets_out = 0;
2787 
2788         /* Now state machine starts.
2789          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2790         if (flag & FLAG_ECE)
2791                 tp->prior_ssthresh = 0;
2792 
2793         /* B. In all the states check for reneging SACKs. */
2794         if (tcp_check_sack_reneging(sk, flag))
2795                 return;
2796 
2797         /* C. Check consistency of the current state. */
2798         tcp_verify_left_out(tp);
2799 
2800         /* D. Check state exit conditions. State can be terminated
2801          *    when high_seq is ACKed. */
2802         if (icsk->icsk_ca_state == TCP_CA_Open) {
2803                 WARN_ON(tp->retrans_out != 0);
2804                 tp->retrans_stamp = 0;
2805         } else if (!before(tp->snd_una, tp->high_seq)) {
2806                 switch (icsk->icsk_ca_state) {
2807                 case TCP_CA_CWR:
2808                         /* CWR is to be held something *above* high_seq
2809                          * is ACKed for CWR bit to reach receiver. */
2810                         if (tp->snd_una != tp->high_seq) {
2811                                 tcp_end_cwnd_reduction(sk);
2812                                 tcp_set_ca_state(sk, TCP_CA_Open);
2813                         }
2814                         break;
2815 
2816                 case TCP_CA_Recovery:
2817                         if (tcp_is_reno(tp))
2818                                 tcp_reset_reno_sack(tp);
2819                         if (tcp_try_undo_recovery(sk))
2820                                 return;
2821                         tcp_end_cwnd_reduction(sk);
2822                         break;
2823                 }
2824         }
2825 
2826         /* E. Process state. */
2827         switch (icsk->icsk_ca_state) {
2828         case TCP_CA_Recovery:
2829                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2830                         if (tcp_is_reno(tp) && is_dupack)
2831                                 tcp_add_reno_sack(sk);
2832                 } else {
2833                         if (tcp_try_undo_partial(sk, acked, prior_unsacked))
2834                                 return;
2835                         /* Partial ACK arrived. Force fast retransmit. */
2836                         do_lost = tcp_is_reno(tp) ||
2837                                   tcp_fackets_out(tp) > tp->reordering;
2838                 }
2839                 if (tcp_try_undo_dsack(sk)) {
2840                         tcp_try_keep_open(sk);
2841                         return;
2842                 }
2843                 break;
2844         case TCP_CA_Loss:
2845                 tcp_process_loss(sk, flag, is_dupack);
2846                 if (icsk->icsk_ca_state != TCP_CA_Open)
2847                         return;
2848                 /* Fall through to processing in Open state. */
2849         default:
2850                 if (tcp_is_reno(tp)) {
2851                         if (flag & FLAG_SND_UNA_ADVANCED)
2852                                 tcp_reset_reno_sack(tp);
2853                         if (is_dupack)
2854                                 tcp_add_reno_sack(sk);
2855                 }
2856 
2857                 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2858                         tcp_try_undo_dsack(sk);
2859 
2860                 if (!tcp_time_to_recover(sk, flag)) {
2861                         tcp_try_to_open(sk, flag, prior_unsacked);
2862                         return;
2863                 }
2864 
2865                 /* MTU probe failure: don't reduce cwnd */
2866                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2867                     icsk->icsk_mtup.probe_size &&
2868                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2869                         tcp_mtup_probe_failed(sk);
2870                         /* Restores the reduction we did in tcp_mtup_probe() */
2871                         tp->snd_cwnd++;
2872                         tcp_simple_retransmit(sk);
2873                         return;
2874                 }
2875 
2876                 /* Otherwise enter Recovery state */
2877                 tcp_enter_recovery(sk, (flag & FLAG_ECE));
2878                 fast_rexmit = 1;
2879         }
2880 
2881         if (do_lost)
2882                 tcp_update_scoreboard(sk, fast_rexmit);
2883         tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit);
2884         tcp_xmit_retransmit_queue(sk);
2885 }
2886 
2887 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2888                                       s32 seq_rtt, s32 sack_rtt)
2889 {
2890         const struct tcp_sock *tp = tcp_sk(sk);
2891 
2892         /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2893          * broken middle-boxes or peers may corrupt TS-ECR fields. But
2894          * Karn's algorithm forbids taking RTT if some retransmitted data
2895          * is acked (RFC6298).
2896          */
2897         if (flag & FLAG_RETRANS_DATA_ACKED)
2898                 seq_rtt = -1;
2899 
2900         if (seq_rtt < 0)
2901                 seq_rtt = sack_rtt;
2902 
2903         /* RTTM Rule: A TSecr value received in a segment is used to
2904          * update the averaged RTT measurement only if the segment
2905          * acknowledges some new data, i.e., only if it advances the
2906          * left edge of the send window.
2907          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2908          */
2909         if (seq_rtt < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2910             flag & FLAG_ACKED)
2911                 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2912 
2913         if (seq_rtt < 0)
2914                 return false;
2915 
2916         tcp_rtt_estimator(sk, seq_rtt);
2917         tcp_set_rto(sk);
2918 
2919         /* RFC6298: only reset backoff on valid RTT measurement. */
2920         inet_csk(sk)->icsk_backoff = 0;
2921         return true;
2922 }
2923 
2924 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2925 static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)
2926 {
2927         struct tcp_sock *tp = tcp_sk(sk);
2928         s32 seq_rtt = -1;
2929 
2930         if (synack_stamp && !tp->total_retrans)
2931                 seq_rtt = tcp_time_stamp - synack_stamp;
2932 
2933         /* If the ACK acks both the SYNACK and the (Fast Open'd) data packets
2934          * sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()
2935          */
2936         if (!tp->srtt)
2937                 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt, -1);
2938 }
2939 
2940 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight)
2941 {
2942         const struct inet_connection_sock *icsk = inet_csk(sk);
2943         icsk->icsk_ca_ops->cong_avoid(sk, ack, acked, in_flight);
2944         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2945 }
2946 
2947 /* Restart timer after forward progress on connection.
2948  * RFC2988 recommends to restart timer to now+rto.
2949  */
2950 void tcp_rearm_rto(struct sock *sk)
2951 {
2952         const struct inet_connection_sock *icsk = inet_csk(sk);
2953         struct tcp_sock *tp = tcp_sk(sk);
2954 
2955         /* If the retrans timer is currently being used by Fast Open
2956          * for SYN-ACK retrans purpose, stay put.
2957          */
2958         if (tp->fastopen_rsk)
2959                 return;
2960 
2961         if (!tp->packets_out) {
2962                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2963         } else {
2964                 u32 rto = inet_csk(sk)->icsk_rto;
2965                 /* Offset the time elapsed after installing regular RTO */
2966                 if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
2967                     icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
2968                         struct sk_buff *skb = tcp_write_queue_head(sk);
2969                         const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
2970                         s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
2971                         /* delta may not be positive if the socket is locked
2972                          * when the retrans timer fires and is rescheduled.
2973                          */
2974                         if (delta > 0)
2975                                 rto = delta;
2976                 }
2977                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
2978                                           TCP_RTO_MAX);
2979         }
2980 }
2981 
2982 /* This function is called when the delayed ER timer fires. TCP enters
2983  * fast recovery and performs fast-retransmit.
2984  */
2985 void tcp_resume_early_retransmit(struct sock *sk)
2986 {
2987         struct tcp_sock *tp = tcp_sk(sk);
2988 
2989         tcp_rearm_rto(sk);
2990 
2991         /* Stop if ER is disabled after the delayed ER timer is scheduled */
2992         if (!tp->do_early_retrans)
2993                 return;
2994 
2995         tcp_enter_recovery(sk, false);
2996         tcp_update_scoreboard(sk, 1);
2997         tcp_xmit_retransmit_queue(sk);
2998 }
2999 
3000 /* If we get here, the whole TSO packet has not been acked. */
3001 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3002 {
3003         struct tcp_sock *tp = tcp_sk(sk);
3004         u32 packets_acked;
3005 
3006         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3007 
3008         packets_acked = tcp_skb_pcount(skb);
3009         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3010                 return 0;
3011         packets_acked -= tcp_skb_pcount(skb);
3012 
3013         if (packets_acked) {
3014                 BUG_ON(tcp_skb_pcount(skb) == 0);
3015                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3016         }
3017 
3018         return packets_acked;
3019 }
3020 
3021 /* Remove acknowledged frames from the retransmission queue. If our packet
3022  * is before the ack sequence we can discard it as it's confirmed to have
3023  * arrived at the other end.
3024  */
3025 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3026                                u32 prior_snd_una, s32 sack_rtt)
3027 {
3028         struct tcp_sock *tp = tcp_sk(sk);
3029         const struct inet_connection_sock *icsk = inet_csk(sk);
3030         struct sk_buff *skb;
3031         u32 now = tcp_time_stamp;
3032         bool fully_acked = true;
3033         int flag = 0;
3034         u32 pkts_acked = 0;
3035         u32 reord = tp->packets_out;
3036         u32 prior_sacked = tp->sacked_out;
3037         s32 seq_rtt = -1;
3038         s32 ca_seq_rtt = -1;
3039         ktime_t last_ackt = net_invalid_timestamp();
3040         bool rtt_update;
3041 
3042         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3043                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3044                 u32 acked_pcount;
3045                 u8 sacked = scb->sacked;
3046 
3047                 /* Determine how many packets and what bytes were acked, tso and else */
3048                 if (after(scb->end_seq, tp->snd_una)) {
3049                         if (tcp_skb_pcount(skb) == 1 ||
3050                             !after(tp->snd_una, scb->seq))
3051                                 break;
3052 
3053                         acked_pcount = tcp_tso_acked(sk, skb);
3054                         if (!acked_pcount)
3055                                 break;
3056 
3057                         fully_acked = false;
3058                 } else {
3059                         acked_pcount = tcp_skb_pcount(skb);
3060                 }
3061 
3062                 if (sacked & TCPCB_RETRANS) {
3063                         if (sacked & TCPCB_SACKED_RETRANS)
3064                                 tp->retrans_out -= acked_pcount;
3065                         flag |= FLAG_RETRANS_DATA_ACKED;
3066                 } else {
3067                         ca_seq_rtt = now - scb->when;
3068                         last_ackt = skb->tstamp;
3069                         if (seq_rtt < 0) {
3070                                 seq_rtt = ca_seq_rtt;
3071                         }
3072                         if (!(sacked & TCPCB_SACKED_ACKED))
3073                                 reord = min(pkts_acked, reord);
3074                         if (!after(scb->end_seq, tp->high_seq))
3075                                 flag |= FLAG_ORIG_SACK_ACKED;
3076                 }
3077 
3078                 if (sacked & TCPCB_SACKED_ACKED)
3079                         tp->sacked_out -= acked_pcount;
3080                 if (sacked & TCPCB_LOST)
3081                         tp->lost_out -= acked_pcount;
3082 
3083                 tp->packets_out -= acked_pcount;
3084                 pkts_acked += acked_pcount;
3085 
3086                 /* Initial outgoing SYN's get put onto the write_queue
3087                  * just like anything else we transmit.  It is not
3088                  * true data, and if we misinform our callers that
3089                  * this ACK acks real data, we will erroneously exit
3090                  * connection startup slow start one packet too
3091                  * quickly.  This is severely frowned upon behavior.
3092                  */
3093                 if (!(scb->tcp_flags & TCPHDR_SYN)) {
3094                         flag |= FLAG_DATA_ACKED;
3095                 } else {
3096                         flag |= FLAG_SYN_ACKED;
3097                         tp->retrans_stamp = 0;
3098                 }
3099 
3100                 if (!fully_acked)
3101                         break;
3102 
3103                 tcp_unlink_write_queue(skb, sk);
3104                 sk_wmem_free_skb(sk, skb);
3105                 if (skb == tp->retransmit_skb_hint)
3106                         tp->retransmit_skb_hint = NULL;
3107                 if (skb == tp->lost_skb_hint)
3108                         tp->lost_skb_hint = NULL;
3109         }
3110 
3111         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3112                 tp->snd_up = tp->snd_una;
3113 
3114         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3115                 flag |= FLAG_SACK_RENEGING;
3116 
3117         rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt, sack_rtt);
3118 
3119         if (flag & FLAG_ACKED) {
3120                 const struct tcp_congestion_ops *ca_ops
3121                         = inet_csk(sk)->icsk_ca_ops;
3122 
3123                 tcp_rearm_rto(sk);
3124                 if (unlikely(icsk->icsk_mtup.probe_size &&
3125                              !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3126                         tcp_mtup_probe_success(sk);
3127                 }
3128 
3129                 if (tcp_is_reno(tp)) {
3130                         tcp_remove_reno_sacks(sk, pkts_acked);
3131                 } else {
3132                         int delta;
3133 
3134                         /* Non-retransmitted hole got filled? That's reordering */
3135                         if (reord < prior_fackets)
3136                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3137 
3138                         delta = tcp_is_fack(tp) ? pkts_acked :
3139                                                   prior_sacked - tp->sacked_out;
3140                         tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3141                 }
3142 
3143                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3144 
3145                 if (ca_ops->pkts_acked) {
3146                         s32 rtt_us = -1;
3147 
3148                         /* Is the ACK triggering packet unambiguous? */
3149                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3150                                 /* High resolution needed and available? */
3151                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3152                                     !ktime_equal(last_ackt,
3153                                                  net_invalid_timestamp()))
3154                                         rtt_us = ktime_us_delta(ktime_get_real(),
3155                                                                 last_ackt);
3156                                 else if (ca_seq_rtt >= 0)
3157                                         rtt_us = jiffies_to_usecs(ca_seq_rtt);
3158                         }
3159 
3160                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3161                 }
3162         } else if (skb && rtt_update && sack_rtt >= 0 &&
3163                    sack_rtt > (s32)(now - TCP_SKB_CB(skb)->when)) {
3164                 /* Do not re-arm RTO if the sack RTT is measured from data sent
3165                  * after when the head was last (re)transmitted. Otherwise the
3166                  * timeout may continue to extend in loss recovery.
3167                  */
3168                 tcp_rearm_rto(sk);
3169         }
3170 
3171 #if FASTRETRANS_DEBUG > 0
3172         WARN_ON((int)tp->sacked_out < 0);
3173         WARN_ON((int)tp->lost_out < 0);
3174         WARN_ON((int)tp->retrans_out < 0);
3175         if (!tp->packets_out && tcp_is_sack(tp)) {
3176                 icsk = inet_csk(sk);
3177                 if (tp->lost_out) {
3178                         pr_debug("Leak l=%u %d\n",
3179                                  tp->lost_out, icsk->icsk_ca_state);
3180                         tp->lost_out = 0;
3181                 }
3182                 if (tp->sacked_out) {
3183                         pr_debug("Leak s=%u %d\n",
3184                                  tp->sacked_out, icsk->icsk_ca_state);
3185                         tp->sacked_out = 0;
3186                 }
3187                 if (tp->retrans_out) {
3188                         pr_debug("Leak r=%u %d\n",
3189                                  tp->retrans_out, icsk->icsk_ca_state);
3190                         tp->retrans_out = 0;
3191                 }
3192         }
3193 #endif
3194         return flag;
3195 }
3196 
3197 static void tcp_ack_probe(struct sock *sk)
3198 {
3199         const struct tcp_sock *tp = tcp_sk(sk);
3200         struct inet_connection_sock *icsk = inet_csk(sk);
3201 
3202         /* Was it a usable window open? */
3203 
3204         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3205                 icsk->icsk_backoff = 0;
3206                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3207                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3208                  * This function is not for random using!
3209                  */
3210         } else {
3211                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3212                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3213                                           TCP_RTO_MAX);
3214         }
3215 }
3216 
3217 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3218 {
3219         return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3220                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3221 }
3222 
3223 /* Decide wheather to run the increase function of congestion control. */
3224 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3225 {
3226         if (tcp_in_cwnd_reduction(sk))
3227                 return false;
3228 
3229         /* If reordering is high then always grow cwnd whenever data is
3230          * delivered regardless of its ordering. Otherwise stay conservative
3231          * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3232          * new SACK or ECE mark may first advance cwnd here and later reduce
3233          * cwnd in tcp_fastretrans_alert() based on more states.
3234          */
3235         if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
3236                 return flag & FLAG_FORWARD_PROGRESS;
3237 
3238         return flag & FLAG_DATA_ACKED;
3239 }
3240 
3241 /* Check that window update is acceptable.
3242  * The function assumes that snd_una<=ack<=snd_next.
3243  */
3244 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3245                                         const u32 ack, const u32 ack_seq,
3246                                         const u32 nwin)
3247 {
3248         return  after(ack, tp->snd_una) ||
3249                 after(ack_seq, tp->snd_wl1) ||
3250                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3251 }
3252 
3253 /* Update our send window.
3254  *
3255  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3256  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3257  */
3258 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3259                                  u32 ack_seq)
3260 {
3261         struct tcp_sock *tp = tcp_sk(sk);
3262         int flag = 0;
3263         u32 nwin = ntohs(tcp_hdr(skb)->window);
3264 
3265         if (likely(!tcp_hdr(skb)->syn))
3266                 nwin <<= tp->rx_opt.snd_wscale;
3267 
3268         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3269                 flag |= FLAG_WIN_UPDATE;
3270                 tcp_update_wl(tp, ack_seq);
3271 
3272                 if (tp->snd_wnd != nwin) {
3273                         tp->snd_wnd = nwin;
3274 
3275                         /* Note, it is the only place, where
3276                          * fast path is recovered for sending TCP.
3277                          */
3278                         tp->pred_flags = 0;
3279                         tcp_fast_path_check(sk);
3280 
3281                         if (nwin > tp->max_window) {
3282                                 tp->max_window = nwin;
3283                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3284                         }
3285                 }
3286         }
3287 
3288         tp->snd_una = ack;
3289 
3290         return flag;
3291 }
3292 
3293 /* RFC 5961 7 [ACK Throttling] */
3294 static void tcp_send_challenge_ack(struct sock *sk)
3295 {
3296         /* unprotected vars, we dont care of overwrites */
3297         static u32 challenge_timestamp;
3298         static unsigned int challenge_count;
3299         u32 now = jiffies / HZ;
3300 
3301         if (now != challenge_timestamp) {
3302                 challenge_timestamp = now;
3303                 challenge_count = 0;
3304         }
3305         if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3306                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3307                 tcp_send_ack(sk);
3308         }
3309 }
3310 
3311 static void tcp_store_ts_recent(struct tcp_sock *tp)
3312 {
3313         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3314         tp->rx_opt.ts_recent_stamp = get_seconds();
3315 }
3316 
3317 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3318 {
3319         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3320                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3321                  * extra check below makes sure this can only happen
3322                  * for pure ACK frames.  -DaveM
3323                  *
3324                  * Not only, also it occurs for expired timestamps.
3325                  */
3326 
3327                 if (tcp_paws_check(&tp->rx_opt, 0))
3328                         tcp_store_ts_recent(tp);
3329         }
3330 }
3331 
3332 /* This routine deals with acks during a TLP episode.
3333  * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3334  */
3335 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3336 {
3337         struct tcp_sock *tp = tcp_sk(sk);
3338         bool is_tlp_dupack = (ack == tp->tlp_high_seq) &&
3339                              !(flag & (FLAG_SND_UNA_ADVANCED |
3340                                        FLAG_NOT_DUP | FLAG_DATA_SACKED));
3341 
3342         /* Mark the end of TLP episode on receiving TLP dupack or when
3343          * ack is after tlp_high_seq.
3344          */
3345         if (is_tlp_dupack) {
3346                 tp->tlp_high_seq = 0;
3347                 return;
3348         }
3349 
3350         if (after(ack, tp->tlp_high_seq)) {
3351                 tp->tlp_high_seq = 0;
3352                 /* Don't reduce cwnd if DSACK arrives for TLP retrans. */
3353                 if (!(flag & FLAG_DSACKING_ACK)) {
3354                         tcp_init_cwnd_reduction(sk, true);
3355                         tcp_set_ca_state(sk, TCP_CA_CWR);
3356                         tcp_end_cwnd_reduction(sk);
3357                         tcp_try_keep_open(sk);
3358                         NET_INC_STATS_BH(sock_net(sk),
3359                                          LINUX_MIB_TCPLOSSPROBERECOVERY);
3360                 }
3361         }
3362 }
3363 
3364 /* This routine deals with incoming acks, but not outgoing ones. */
3365 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3366 {
3367         struct inet_connection_sock *icsk = inet_csk(sk);
3368         struct tcp_sock *tp = tcp_sk(sk);
3369         u32 prior_snd_una = tp->snd_una;
3370         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3371         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3372         bool is_dupack = false;
3373         u32 prior_in_flight, prior_cwnd = tp->snd_cwnd, prior_rtt = tp->srtt;
3374         u32 prior_fackets;
3375         int prior_packets = tp->packets_out;
3376         const int prior_unsacked = tp->packets_out - tp->sacked_out;
3377         int acked = 0; /* Number of packets newly acked */
3378         s32 sack_rtt = -1;
3379 
3380         /* If the ack is older than previous acks
3381          * then we can probably ignore it.
3382          */
3383         if (before(ack, prior_snd_una)) {
3384                 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3385                 if (before(ack, prior_snd_una - tp->max_window)) {
3386                         tcp_send_challenge_ack(sk);
3387                         return -1;
3388                 }
3389                 goto old_ack;
3390         }
3391 
3392         /* If the ack includes data we haven't sent yet, discard
3393          * this segment (RFC793 Section 3.9).
3394          */
3395         if (after(ack, tp->snd_nxt))
3396                 goto invalid_ack;
3397 
3398         if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3399             icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3400                 tcp_rearm_rto(sk);
3401 
3402         if (after(ack, prior_snd_una))
3403                 flag |= FLAG_SND_UNA_ADVANCED;
3404 
3405         prior_fackets = tp->fackets_out;
3406         prior_in_flight = tcp_packets_in_flight(tp);
3407 
3408         /* ts_recent update must be made after we are sure that the packet
3409          * is in window.
3410          */
3411         if (flag & FLAG_UPDATE_TS_RECENT)
3412                 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3413 
3414         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3415                 /* Window is constant, pure forward advance.
3416                  * No more checks are required.
3417                  * Note, we use the fact that SND.UNA>=SND.WL2.
3418                  */
3419                 tcp_update_wl(tp, ack_seq);
3420                 tp->snd_una = ack;
3421                 flag |= FLAG_WIN_UPDATE;
3422 
3423                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3424 
3425                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3426         } else {
3427                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3428                         flag |= FLAG_DATA;
3429                 else
3430                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3431 
3432                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3433 
3434                 if (TCP_SKB_CB(skb)->sacked)
3435                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3436                                                         &sack_rtt);
3437 
3438                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3439                         flag |= FLAG_ECE;
3440 
3441                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3442         }
3443 
3444         /* We passed data and got it acked, remove any soft error
3445          * log. Something worked...
3446          */
3447         sk->sk_err_soft = 0;
3448         icsk->icsk_probes_out = 0;
3449         tp->rcv_tstamp = tcp_time_stamp;
3450         if (!prior_packets)
3451                 goto no_queue;
3452 
3453         /* See if we can take anything off of the retransmit queue. */
3454         acked = tp->packets_out;
3455         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, sack_rtt);
3456         acked -= tp->packets_out;
3457 
3458         /* Advance cwnd if state allows */
3459         if (tcp_may_raise_cwnd(sk, flag))
3460                 tcp_cong_avoid(sk, ack, acked, prior_in_flight);
3461 
3462         if (tcp_ack_is_dubious(sk, flag)) {
3463                 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3464                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3465                                       is_dupack, flag);
3466         }
3467         if (tp->tlp_high_seq)
3468                 tcp_process_tlp_ack(sk, ack, flag);
3469 
3470         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3471                 struct dst_entry *dst = __sk_dst_get(sk);
3472                 if (dst)
3473                         dst_confirm(dst);
3474         }
3475 
3476         if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3477                 tcp_schedule_loss_probe(sk);
3478         if (tp->srtt != prior_rtt || tp->snd_cwnd != prior_cwnd)
3479                 tcp_update_pacing_rate(sk);
3480         return 1;
3481 
3482 no_queue:
3483         /* If data was DSACKed, see if we can undo a cwnd reduction. */
3484         if (flag & FLAG_DSACKING_ACK)
3485                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3486                                       is_dupack, flag);
3487         /* If this ack opens up a zero window, clear backoff.  It was
3488          * being used to time the probes, and is probably far higher than
3489          * it needs to be for normal retransmission.
3490          */
3491         if (tcp_send_head(sk))
3492                 tcp_ack_probe(sk);
3493 
3494         if (tp->tlp_high_seq)
3495                 tcp_process_tlp_ack(sk, ack, flag);
3496         return 1;
3497 
3498 invalid_ack:
3499         SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3500         return -1;
3501 
3502 old_ack:
3503         /* If data was SACKed, tag it and see if we should send more data.
3504          * If data was DSACKed, see if we can undo a cwnd reduction.
3505          */
3506         if (TCP_SKB_CB(skb)->sacked) {
3507                 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3508                                                 &sack_rtt);
3509                 tcp_fastretrans_alert(sk, acked, prior_unsacked,
3510                                       is_dupack, flag);
3511         }
3512 
3513         SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3514         return 0;
3515 }
3516 
3517 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3518  * But, this can also be called on packets in the established flow when
3519  * the fast version below fails.
3520  */
3521 void tcp_parse_options(const struct sk_buff *skb,
3522                        struct tcp_options_received *opt_rx, int estab,
3523                        struct tcp_fastopen_cookie *foc)
3524 {
3525         const unsigned char *ptr;
3526         const struct tcphdr *th = tcp_hdr(skb);
3527         int length = (th->doff * 4) - sizeof(struct tcphdr);
3528 
3529         ptr = (const unsigned char *)(th + 1);
3530         opt_rx->saw_tstamp = 0;
3531 
3532         while (length > 0) {
3533                 int opcode = *ptr++;
3534                 int opsize;
3535 
3536                 switch (opcode) {
3537                 case TCPOPT_EOL:
3538                         return;
3539                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3540                         length--;
3541                         continue;
3542                 default:
3543                         opsize = *ptr++;
3544                         if (opsize < 2) /* "silly options" */
3545                                 return;
3546                         if (opsize > length)
3547                                 return; /* don't parse partial options */
3548                         switch (opcode) {
3549                         case TCPOPT_MSS:
3550                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3551                                         u16 in_mss = get_unaligned_be16(ptr);
3552                                         if (in_mss) {
3553                                                 if (opt_rx->user_mss &&
3554                                                     opt_rx->user_mss < in_mss)
3555                                                         in_mss = opt_rx->user_mss;
3556                                                 opt_rx->mss_clamp = in_mss;
3557                                         }
3558                                 }
3559                                 break;
3560                         case TCPOPT_WINDOW:
3561                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3562                                     !estab && sysctl_tcp_window_scaling) {
3563                                         __u8 snd_wscale = *(__u8 *)ptr;
3564                                         opt_rx->wscale_ok = 1;
3565                                         if (snd_wscale > 14) {
3566                                                 net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3567                                                                      __func__,
3568                                                                      snd_wscale);
3569                                                 snd_wscale = 14;
3570                                         }
3571                                         opt_rx->snd_wscale = snd_wscale;
3572                                 }
3573                                 break;
3574                         case TCPOPT_TIMESTAMP:
3575                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3576                                     ((estab && opt_rx->tstamp_ok) ||
3577                                      (!estab && sysctl_tcp_timestamps))) {
3578                                         opt_rx->saw_tstamp = 1;
3579                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3580                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3581                                 }
3582                                 break;
3583                         case TCPOPT_SACK_PERM:
3584                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3585                                     !estab && sysctl_tcp_sack) {
3586                                         opt_rx->sack_ok = TCP_SACK_SEEN;
3587                                         tcp_sack_reset(opt_rx);
3588                                 }
3589                                 break;
3590 
3591                         case TCPOPT_SACK:
3592                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3593                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3594                                    opt_rx->sack_ok) {
3595                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3596                                 }
3597                                 break;
3598 #ifdef CONFIG_TCP_MD5SIG
3599                         case TCPOPT_MD5SIG:
3600                                 /*
3601                                  * The MD5 Hash has already been
3602                                  * checked (see tcp_v{4,6}_do_rcv()).
3603                                  */
3604                                 break;
3605 #endif
3606                         case TCPOPT_EXP:
3607                                 /* Fast Open option shares code 254 using a
3608                                  * 16 bits magic number. It's valid only in
3609                                  * SYN or SYN-ACK with an even size.
3610                                  */
3611                                 if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
3612                                     get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
3613                                     foc == NULL || !th->syn || (opsize & 1))
3614                                         break;
3615                                 foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
3616                                 if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
3617                                     foc->len <= TCP_FASTOPEN_COOKIE_MAX)
3618                                         memcpy(foc->val, ptr + 2, foc->len);
3619                                 else if (foc->len != 0)
3620                                         foc->len = -1;
3621                                 break;
3622 
3623                         }
3624                         ptr += opsize-2;
3625                         length -= opsize;
3626                 }
3627         }
3628 }
3629 EXPORT_SYMBOL(tcp_parse_options);
3630 
3631 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3632 {
3633         const __be32 *ptr = (const __be32 *)(th + 1);
3634 
3635         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3636                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3637                 tp->rx_opt.saw_tstamp = 1;
3638                 ++ptr;
3639                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3640                 ++ptr;
3641                 if (*ptr)
3642                         tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3643                 else
3644                         tp->rx_opt.rcv_tsecr = 0;
3645                 return true;
3646         }
3647         return false;
3648 }
3649 
3650 /* Fast parse options. This hopes to only see timestamps.
3651  * If it is wrong it falls back on tcp_parse_options().
3652  */
3653 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3654                                    const struct tcphdr *th, struct tcp_sock *tp)
3655 {
3656         /* In the spirit of fast parsing, compare doff directly to constant
3657          * values.  Because equality is used, short doff can be ignored here.
3658          */
3659         if (th->doff == (sizeof(*th) / 4)) {
3660                 tp->rx_opt.saw_tstamp = 0;
3661                 return false;
3662         } else if (tp->rx_opt.tstamp_ok &&
3663                    th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3664                 if (tcp_parse_aligned_timestamp(tp, th))
3665                         return true;
3666         }
3667 
3668         tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3669         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3670                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3671 
3672         return true;
3673 }
3674 
3675 #ifdef CONFIG_TCP_MD5SIG
3676 /*
3677  * Parse MD5 Signature option
3678  */
3679 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3680 {
3681         int length = (th->doff << 2) - sizeof(*th);
3682         const u8 *ptr = (const u8 *)(th + 1);
3683 
3684         /* If the TCP option is too short, we can short cut */
3685         if (length < TCPOLEN_MD5SIG)
3686                 return NULL;
3687 
3688         while (length > 0) {
3689                 int opcode = *ptr++;
3690                 int opsize;
3691 
3692                 switch (opcode) {
3693                 case TCPOPT_EOL:
3694                         return NULL;
3695                 case TCPOPT_NOP:
3696                         length--;
3697                         continue;
3698                 default:
3699                         opsize = *ptr++;
3700                         if (opsize < 2 || opsize > length)
3701                                 return NULL;
3702                         if (opcode == TCPOPT_MD5SIG)
3703                                 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3704                 }
3705                 ptr += opsize - 2;
3706                 length -= opsize;
3707         }
3708         return NULL;
3709 }
3710 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3711 #endif
3712 
3713 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3714  *
3715  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3716  * it can pass through stack. So, the following predicate verifies that
3717  * this segment is not used for anything but congestion avoidance or
3718  * fast retransmit. Moreover, we even are able to eliminate most of such
3719  * second order effects, if we apply some small "replay" window (~RTO)
3720  * to timestamp space.
3721  *
3722  * All these measures still do not guarantee that we reject wrapped ACKs
3723  * on networks with high bandwidth, when sequence space is recycled fastly,
3724  * but it guarantees that such events will be very rare and do not affect
3725  * connection seriously. This doesn't look nice, but alas, PAWS is really
3726  * buggy extension.
3727  *
3728  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3729  * states that events when retransmit arrives after original data are rare.
3730  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3731  * the biggest problem on large power networks even with minor reordering.
3732  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3733  * up to bandwidth of 18Gigabit/sec. 8) ]
3734  */
3735 
3736 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3737 {
3738         const struct tcp_sock *tp = tcp_sk(sk);
3739         const struct tcphdr *th = tcp_hdr(skb);
3740         u32 seq = TCP_SKB_CB(skb)->seq;
3741         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3742 
3743         return (/* 1. Pure ACK with correct sequence number. */
3744                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3745 
3746                 /* 2. ... and duplicate ACK. */
3747                 ack == tp->snd_una &&
3748 
3749                 /* 3. ... and does not update window. */
3750                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3751 
3752                 /* 4. ... and sits in replay window. */
3753                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3754 }
3755 
3756 static inline bool tcp_paws_discard(const struct sock *sk,
3757                                    const struct sk_buff *skb)
3758 {
3759         const struct tcp_sock *tp = tcp_sk(sk);
3760 
3761         return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3762                !tcp_disordered_ack(sk, skb);
3763 }
3764 
3765 /* Check segment sequence number for validity.
3766  *
3767  * Segment controls are considered valid, if the segment
3768  * fits to the window after truncation to the window. Acceptability
3769  * of data (and SYN, FIN, of course) is checked separately.
3770  * See tcp_data_queue(), for example.
3771  *
3772  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3773  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3774  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3775  * (borrowed from freebsd)
3776  */
3777 
3778 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3779 {
3780         return  !before(end_seq, tp->rcv_wup) &&
3781                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3782 }
3783 
3784 /* When we get a reset we do this. */
3785 void tcp_reset(struct sock *sk)
3786 {
3787         /* We want the right error as BSD sees it (and indeed as we do). */
3788         switch (sk->sk_state) {
3789         case TCP_SYN_SENT:
3790                 sk->sk_err = ECONNREFUSED;
3791                 break;
3792         case TCP_CLOSE_WAIT:
3793                 sk->sk_err = EPIPE;
3794                 break;
3795         case TCP_CLOSE:
3796                 return;
3797         default:
3798                 sk->sk_err = ECONNRESET;
3799         }
3800         /* This barrier is coupled with smp_rmb() in tcp_poll() */
3801         smp_wmb();
3802 
3803         if (!sock_flag(sk, SOCK_DEAD))
3804                 sk->sk_error_report(sk);
3805 
3806         tcp_done(sk);
3807 }
3808 
3809 /*
3810  *      Process the FIN bit. This now behaves as it is supposed to work
3811  *      and the FIN takes effect when it is validly part of sequence
3812  *      space. Not before when we get holes.
3813  *
3814  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3815  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3816  *      TIME-WAIT)
3817  *
3818  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3819  *      close and we go into CLOSING (and later onto TIME-WAIT)
3820  *
3821  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3822  */
3823 static void tcp_fin(struct sock *sk)
3824 {
3825         struct tcp_sock *tp = tcp_sk(sk);
3826         const struct dst_entry *dst;
3827 
3828         inet_csk_schedule_ack(sk);
3829 
3830         sk->sk_shutdown |= RCV_SHUTDOWN;
3831         sock_set_flag(sk, SOCK_DONE);
3832 
3833         switch (sk->sk_state) {
3834         case TCP_SYN_RECV:
3835         case TCP_ESTABLISHED:
3836                 /* Move to CLOSE_WAIT */
3837                 tcp_set_state(sk, TCP_CLOSE_WAIT);
3838                 dst = __sk_dst_get(sk);
3839                 if (!dst || !dst_metric(dst, RTAX_QUICKACK))
3840                         inet_csk(sk)->icsk_ack.pingpong = 1;
3841                 break;
3842 
3843         case TCP_CLOSE_WAIT:
3844         case TCP_CLOSING:
3845                 /* Received a retransmission of the FIN, do
3846                  * nothing.
3847                  */
3848                 break;
3849         case TCP_LAST_ACK:
3850                 /* RFC793: Remain in the LAST-ACK state. */
3851                 break;
3852 
3853         case TCP_FIN_WAIT1:
3854                 /* This case occurs when a simultaneous close
3855                  * happens, we must ack the received FIN and
3856                  * enter the CLOSING state.
3857                  */
3858                 tcp_send_ack(sk);
3859                 tcp_set_state(sk, TCP_CLOSING);
3860                 break;
3861         case TCP_FIN_WAIT2:
3862                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
3863                 tcp_send_ack(sk);
3864                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3865                 break;
3866         default:
3867                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3868                  * cases we should never reach this piece of code.
3869                  */
3870                 pr_err("%s: Impossible, sk->sk_state=%d\n",
3871                        __func__, sk->sk_state);
3872                 break;
3873         }
3874 
3875         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3876          * Probably, we should reset in this case. For now drop them.
3877          */
3878         __skb_queue_purge(&tp->out_of_order_queue);
3879         if (tcp_is_sack(tp))
3880                 tcp_sack_reset(&tp->rx_opt);
3881         sk_mem_reclaim(sk);
3882 
3883         if (!sock_flag(sk, SOCK_DEAD)) {
3884                 sk->sk_state_change(sk);
3885 
3886                 /* Do not send POLL_HUP for half duplex close. */
3887                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3888                     sk->sk_state == TCP_CLOSE)
3889                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
3890                 else
3891                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
3892         }
3893 }
3894 
3895 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
3896                                   u32 end_seq)
3897 {
3898         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3899                 if (before(seq, sp->start_seq))
3900                         sp->start_seq = seq;
3901                 if (after(end_seq, sp->end_seq))
3902                         sp->end_seq = end_seq;
3903                 return true;
3904         }
3905         return false;
3906 }
3907 
3908 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
3909 {
3910         struct tcp_sock *tp = tcp_sk(sk);
3911 
3912         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3913                 int mib_idx;
3914 
3915                 if (before(seq, tp->rcv_nxt))
3916                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
3917                 else
3918                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
3919 
3920                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
3921 
3922                 tp->rx_opt.dsack = 1;
3923                 tp->duplicate_sack[0].start_seq = seq;
3924                 tp->duplicate_sack[0].end_seq = end_seq;
3925         }
3926 }
3927 
3928 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
3929 {
3930         struct tcp_sock *tp = tcp_sk(sk);
3931 
3932         if (!tp->rx_opt.dsack)
3933                 tcp_dsack_set(sk, seq, end_seq);
3934         else
3935                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3936 }
3937 
3938 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
3939 {
3940         struct tcp_sock *tp = tcp_sk(sk);
3941 
3942         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3943             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3944                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
3945                 tcp_enter_quickack_mode(sk);
3946 
3947                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3948                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3949 
3950                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3951                                 end_seq = tp->rcv_nxt;
3952                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
3953                 }
3954         }
3955 
3956         tcp_send_ack(sk);
3957 }
3958 
3959 /* These routines update the SACK block as out-of-order packets arrive or
3960  * in-order packets close up the sequence space.
3961  */
3962 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3963 {
3964         int this_sack;
3965         struct tcp_sack_block *sp = &tp->selective_acks[0];
3966         struct tcp_sack_block *swalk = sp + 1;
3967 
3968         /* See if the recent change to the first SACK eats into
3969          * or hits the sequence space of other SACK blocks, if so coalesce.
3970          */
3971         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
3972                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3973                         int i;
3974 
3975                         /* Zap SWALK, by moving every further SACK up by one slot.
3976                          * Decrease num_sacks.
3977                          */
3978                         tp->rx_opt.num_sacks--;
3979                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
3980                                 sp[i] = sp[i + 1];
3981                         continue;
3982                 }
3983                 this_sack++, swalk++;
3984         }
3985 }
3986 
3987 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3988 {
3989         struct tcp_sock *tp = tcp_sk(sk);
3990         struct tcp_sack_block *sp = &tp->selective_acks[0];
3991         int cur_sacks = tp->rx_opt.num_sacks;
3992         int this_sack;
3993 
3994         if (!cur_sacks)
3995                 goto new_sack;
3996 
3997         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
3998                 if (tcp_sack_extend(sp, seq, end_seq)) {
3999                         /* Rotate this_sack to the first one. */
4000                         for (; this_sack > 0; this_sack--, sp--)
4001                                 swap(*sp, *(sp - 1));
4002                         if (cur_sacks > 1)
4003                                 tcp_sack_maybe_coalesce(tp);
4004                         return;
4005                 }
4006         }
4007 
4008         /* Could not find an adjacent existing SACK, build a new one,
4009          * put it at the front, and shift everyone else down.  We
4010          * always know there is at least one SACK present already here.
4011          *
4012          * If the sack array is full, forget about the last one.
4013          */
4014         if (this_sack >= TCP_NUM_SACKS) {
4015                 this_sack--;
4016                 tp->rx_opt.num_sacks--;
4017                 sp--;
4018         }
4019         for (; this_sack > 0; this_sack--, sp--)
4020                 *sp = *(sp - 1);
4021 
4022 new_sack:
4023         /* Build the new head SACK, and we're done. */
4024         sp->start_seq = seq;
4025         sp->end_seq = end_seq;
4026         tp->rx_opt.num_sacks++;
4027 }
4028 
4029 /* RCV.NXT advances, some SACKs should be eaten. */
4030 
4031 static void tcp_sack_remove(struct tcp_sock *tp)
4032 {
4033         struct tcp_sack_block *sp = &tp->selective_acks[0];
4034         int num_sacks = tp->rx_opt.num_sacks;
4035         int this_sack;
4036 
4037         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4038         if (skb_queue_empty(&tp->out_of_order_queue)) {
4039                 tp->rx_opt.num_sacks = 0;
4040                 return;
4041         }
4042 
4043         for (this_sack = 0; this_sack < num_sacks;) {
4044                 /* Check if the start of the sack is covered by RCV.NXT. */
4045                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4046                         int i;
4047 
4048                         /* RCV.NXT must cover all the block! */
4049                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4050 
4051                         /* Zap this SACK, by moving forward any other SACKS. */
4052                         for (i = this_sack+1; i < num_sacks; i++)
4053                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4054                         num_sacks--;
4055                         continue;
4056                 }
4057                 this_sack++;
4058                 sp++;
4059         }
4060         tp->rx_opt.num_sacks = num_sacks;
4061 }
4062 
4063 /* This one checks to see if we can put data from the
4064  * out_of_order queue into the receive_queue.
4065  */
4066 static void tcp_ofo_queue(struct sock *sk)
4067 {
4068         struct tcp_sock *tp = tcp_sk(sk);
4069         __u32 dsack_high = tp->rcv_nxt;
4070         struct sk_buff *skb;
4071 
4072         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4073                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4074                         break;
4075 
4076                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4077                         __u32 dsack = dsack_high;
4078                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4079                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4080                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4081                 }
4082 
4083                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4084                         SOCK_DEBUG(sk, "ofo packet was already received\n");
4085                         __skb_unlink(skb, &tp->out_of_order_queue);
4086                         __kfree_skb(skb);
4087                         continue;
4088                 }
4089                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4090                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4091                            TCP_SKB_CB(skb)->end_seq);
4092 
4093                 __skb_unlink(skb, &tp->out_of_order_queue);
4094                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4095                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4096                 if (tcp_hdr(skb)->fin)
4097                         tcp_fin(sk);
4098         }
4099 }
4100 
4101 static bool tcp_prune_ofo_queue(struct sock *sk);
4102 static int tcp_prune_queue(struct sock *sk);
4103 
4104 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4105                                  unsigned int size)
4106 {
4107         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4108             !sk_rmem_schedule(sk, skb, size)) {
4109 
4110                 if (tcp_prune_queue(sk) < 0)
4111                         return -1;
4112 
4113                 if (!sk_rmem_schedule(sk, skb, size)) {
4114                         if (!tcp_prune_ofo_queue(sk))
4115                                 return -1;
4116 
4117                         if (!sk_rmem_schedule(sk, skb, size))
4118                                 return -1;
4119                 }
4120         }
4121         return 0;
4122 }
4123 
4124 /**
4125  * tcp_try_coalesce - try to merge skb to prior one
4126  * @sk: socket
4127  * @to: prior buffer
4128  * @from: buffer to add in queue
4129  * @fragstolen: pointer to boolean
4130  *
4131  * Before queueing skb @from after @to, try to merge them
4132  * to reduce overall memory use and queue lengths, if cost is small.
4133  * Packets in ofo or receive queues can stay a long time.
4134  * Better try to coalesce them right now to avoid future collapses.
4135  * Returns true if caller should free @from instead of queueing it
4136  */
4137 static bool tcp_try_coalesce(struct sock *sk,
4138                              struct sk_buff *to,
4139                              struct sk_buff *from,
4140                              bool *fragstolen)
4141 {
4142         int delta;
4143 
4144         *fragstolen = false;
4145 
4146         if (tcp_hdr(from)->fin)
4147                 return false;
4148 
4149         /* Its possible this segment overlaps with prior segment in queue */
4150         if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4151                 return false;
4152 
4153         if (!skb_try_coalesce(to, from, fragstolen, &delta))
4154                 return false;
4155 
4156         atomic_add(delta, &sk->sk_rmem_alloc);
4157         sk_mem_charge(sk, delta);
4158         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4159         TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4160         TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4161         return true;
4162 }
4163 
4164 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4165 {
4166         struct tcp_sock *tp = tcp_sk(sk);
4167         struct sk_buff *skb1;
4168         u32 seq, end_seq;
4169 
4170         TCP_ECN_check_ce(tp, skb);
4171 
4172         if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4173                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4174                 __kfree_skb(skb);
4175                 return;
4176         }
4177 
4178         /* Disable header prediction. */
4179         tp->pred_flags = 0;
4180         inet_csk_schedule_ack(sk);
4181 
4182         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4183         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4184                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4185 
4186         skb1 = skb_peek_tail(&tp->out_of_order_queue);
4187         if (!skb1) {
4188                 /* Initial out of order segment, build 1 SACK. */
4189                 if (tcp_is_sack(tp)) {
4190                         tp->rx_opt.num_sacks = 1;
4191                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4192                         tp->selective_acks[0].end_seq =
4193                                                 TCP_SKB_CB(skb)->end_seq;
4194                 }
4195                 __skb_queue_head(&tp->out_of_order_queue, skb);
4196                 goto end;
4197         }
4198 
4199         seq = TCP_SKB_CB(skb)->seq;
4200         end_seq = TCP_SKB_CB(skb)->end_seq;
4201 
4202         if (seq == TCP_SKB_CB(skb1)->end_seq) {
4203                 bool fragstolen;
4204 
4205                 if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4206                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4207                 } else {
4208                         tcp_grow_window(sk, skb);
4209                         kfree_skb_partial(skb, fragstolen);
4210                         skb = NULL;
4211                 }
4212 
4213                 if (!tp->rx_opt.num_sacks ||
4214                     tp->selective_acks[0].end_seq != seq)
4215                         goto add_sack;
4216 
4217                 /* Common case: data arrive in order after hole. */
4218                 tp->selective_acks[0].end_seq = end_seq;
4219                 goto end;
4220         }
4221 
4222         /* Find place to insert this segment. */
4223         while (1) {
4224                 if (!after(TCP_SKB_CB(skb1)->seq, seq))
4225                         break;
4226                 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4227                         skb1 = NULL;
4228                         break;
4229                 }
4230                 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4231         }
4232 
4233         /* Do skb overlap to previous one? */
4234         if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4235                 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4236                         /* All the bits are present. Drop. */
4237                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4238                         __kfree_skb(skb);
4239                         skb = NULL;
4240                         tcp_dsack_set(sk, seq, end_seq);
4241                         goto add_sack;
4242                 }
4243                 if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4244                         /* Partial overlap. */
4245                         tcp_dsack_set(sk, seq,
4246                                       TCP_SKB_CB(skb1)->end_seq);
4247                 } else {
4248                         if (skb_queue_is_first(&tp->out_of_order_queue,
4249                                                skb1))
4250                                 skb1 = NULL;
4251                         else
4252                                 skb1 = skb_queue_prev(
4253                                         &tp->out_of_order_queue,
4254                                         skb1);
4255                 }
4256         }
4257         if (!skb1)
4258                 __skb_queue_head(&tp->out_of_order_queue, skb);
4259         else
4260                 __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4261 
4262         /* And clean segments covered by new one as whole. */
4263         while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4264                 skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4265 
4266                 if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4267                         break;
4268                 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4269                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4270                                          end_seq);
4271                         break;
4272                 }
4273                 __skb_unlink(skb1, &tp->out_of_order_queue);
4274                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4275                                  TCP_SKB_CB(skb1)->end_seq);
4276                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4277                 __kfree_skb(skb1);
4278         }
4279 
4280 add_sack:
4281         if (tcp_is_sack(tp))
4282                 tcp_sack_new_ofo_skb(sk, seq, end_seq);
4283 end:
4284         if (skb) {
4285                 tcp_grow_window(sk, skb);
4286                 skb_set_owner_r(skb, sk);
4287         }
4288 }
4289 
4290 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4291                   bool *fragstolen)
4292 {
4293         int eaten;
4294         struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4295 
4296         __skb_pull(skb, hdrlen);
4297         eaten = (tail &&
4298                  tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4299         tcp_sk(sk)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4300         if (!eaten) {
4301                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4302                 skb_set_owner_r(skb, sk);
4303         }
4304         return eaten;
4305 }
4306 
4307 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4308 {
4309         struct sk_buff *skb = NULL;
4310         struct tcphdr *th;
4311         bool fragstolen;
4312 
4313         if (size == 0)
4314                 return 0;
4315 
4316         skb = alloc_skb(size + sizeof(*th), sk->sk_allocation);
4317         if (!skb)
4318                 goto err;
4319 
4320         if (tcp_try_rmem_schedule(sk, skb, size + sizeof(*th)))
4321                 goto err_free;
4322 
4323         th = (struct tcphdr *)skb_put(skb, sizeof(*th));
4324         skb_reset_transport_header(skb);
4325         memset(th, 0, sizeof(*th));
4326 
4327         if (memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size))
4328                 goto err_free;
4329 
4330         TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4331         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4332         TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4333 
4334         if (tcp_queue_rcv(sk, skb, sizeof(*th), &fragstolen)) {
4335                 WARN_ON_ONCE(fragstolen); /* should not happen */
4336                 __kfree_skb(skb);
4337         }
4338         return size;
4339 
4340 err_free:
4341         kfree_skb(skb);
4342 err:
4343         return -ENOMEM;
4344 }
4345 
4346 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4347 {
4348         const struct tcphdr *th = tcp_hdr(skb);
4349         struct tcp_sock *tp = tcp_sk(sk);
4350         int eaten = -1;
4351         bool fragstolen = false;
4352 
4353         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4354                 goto drop;
4355 
4356         skb_dst_drop(skb);
4357         __skb_pull(skb, th->doff * 4);
4358 
4359         TCP_ECN_accept_cwr(tp, skb);
4360 
4361         tp->rx_opt.dsack = 0;
4362 
4363         /*  Queue data for delivery to the user.
4364          *  Packets in sequence go to the receive queue.
4365          *  Out of sequence packets to the out_of_order_queue.
4366          */
4367         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4368                 if (tcp_receive_window(tp) == 0)
4369                         goto out_of_window;
4370 
4371                 /* Ok. In sequence. In window. */
4372                 if (tp->ucopy.task == current &&
4373                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4374                     sock_owned_by_user(sk) && !tp->urg_data) {
4375                         int chunk = min_t(unsigned int, skb->len,
4376                                           tp->ucopy.len);
4377 
4378                         __set_current_state(TASK_RUNNING);
4379 
4380                         local_bh_enable();
4381                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4382                                 tp->ucopy.len -= chunk;
4383                                 tp->copied_seq += chunk;
4384                                 eaten = (chunk == skb->len);
4385                                 tcp_rcv_space_adjust(sk);
4386                         }
4387                         local_bh_disable();
4388                 }
4389 
4390                 if (eaten <= 0) {
4391 queue_and_out:
4392                         if (eaten < 0 &&
4393                             tcp_try_rmem_schedule(sk, skb, skb->truesize))
4394                                 goto drop;
4395 
4396                         eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4397                 }
4398                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4399                 if (skb->len)
4400                         tcp_event_data_recv(sk, skb);
4401                 if (th->fin)
4402                         tcp_fin(sk);
4403 
4404                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4405                         tcp_ofo_queue(sk);
4406 
4407                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4408                          * gap in queue is filled.
4409                          */
4410                         if (skb_queue_empty(&tp->out_of_order_queue))
4411                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4412                 }
4413 
4414                 if (tp->rx_opt.num_sacks)
4415                         tcp_sack_remove(tp);
4416 
4417                 tcp_fast_path_check(sk);
4418 
4419                 if (eaten > 0)
4420                         kfree_skb_partial(skb, fragstolen);
4421                 if (!sock_flag(sk, SOCK_DEAD))
4422                         sk->sk_data_ready(sk, 0);
4423                 return;
4424         }
4425 
4426         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4427                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4428                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4429                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4430 
4431 out_of_window:
4432                 tcp_enter_quickack_mode(sk);
4433                 inet_csk_schedule_ack(sk);
4434 drop:
4435                 __kfree_skb(skb);
4436                 return;
4437         }
4438 
4439         /* Out of window. F.e. zero window probe. */
4440         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4441                 goto out_of_window;
4442 
4443         tcp_enter_quickack_mode(sk);
4444 
4445         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4446                 /* Partial packet, seq < rcv_next < end_seq */
4447                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4448                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4449                            TCP_SKB_CB(skb)->end_seq);
4450 
4451                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4452 
4453                 /* If window is closed, drop tail of packet. But after
4454                  * remembering D-SACK for its head made in previous line.
4455                  */
4456                 if (!tcp_receive_window(tp))
4457                         goto out_of_window;
4458                 goto queue_and_out;
4459         }
4460 
4461         tcp_data_queue_ofo(sk, skb);
4462 }
4463 
4464 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4465                                         struct sk_buff_head *list)
4466 {
4467         struct sk_buff *next = NULL;
4468 
4469         if (!skb_queue_is_last(list, skb))
4470                 next = skb_queue_next(list, skb);
4471 
4472         __skb_unlink(skb, list);
4473         __kfree_skb(skb);
4474         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4475 
4476         return next;
4477 }
4478 
4479 /* Collapse contiguous sequence of skbs head..tail with
4480  * sequence numbers start..end.
4481  *
4482  * If tail is NULL, this means until the end of the list.
4483  *
4484  * Segments with FIN/SYN are not collapsed (only because this
4485  * simplifies code)
4486  */
4487 static void
4488 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4489              struct sk_buff *head, struct sk_buff *tail,
4490              u32 start, u32 end)
4491 {
4492         struct sk_buff *skb, *n;
4493         bool end_of_skbs;
4494 
4495         /* First, check that queue is collapsible and find
4496          * the point where collapsing can be useful. */
4497         skb = head;
4498 restart:
4499         end_of_skbs = true;
4500         skb_queue_walk_from_safe(list, skb, n) {
4501                 if (skb == tail)
4502                         break;
4503                 /* No new bits? It is possible on ofo queue. */
4504                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4505                         skb = tcp_collapse_one(sk, skb, list);
4506                         if (!skb)
4507                                 break;
4508                         goto restart;
4509                 }
4510 
4511                 /* The first skb to collapse is:
4512                  * - not SYN/FIN and
4513                  * - bloated or contains data before "start" or
4514                  *   overlaps to the next one.
4515                  */
4516                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4517                     (tcp_win_from_space(skb->truesize) > skb->len ||
4518                      before(TCP_SKB_CB(skb)->seq, start))) {
4519                         end_of_skbs = false;
4520                         break;
4521                 }
4522 
4523                 if (!skb_queue_is_last(list, skb)) {
4524                         struct sk_buff *next = skb_queue_next(list, skb);
4525                         if (next != tail &&
4526                             TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4527                                 end_of_skbs = false;
4528                                 break;
4529                         }
4530                 }
4531 
4532                 /* Decided to skip this, advance start seq. */
4533                 start = TCP_SKB_CB(skb)->end_seq;
4534         }
4535         if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4536                 return;
4537 
4538         while (before(start, end)) {
4539                 struct sk_buff *nskb;
4540                 unsigned int header = skb_headroom(skb);
4541                 int copy = SKB_MAX_ORDER(header, 0);
4542 
4543                 /* Too big header? This can happen with IPv6. */
4544                 if (copy < 0)
4545                         return;
4546                 if (end - start < copy)
4547                         copy = end - start;
4548                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4549                 if (!nskb)
4550                         return;
4551 
4552                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4553                 skb_set_network_header(nskb, (skb_network_header(skb) -
4554                                               skb->head));
4555                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4556                                                 skb->head));
4557                 skb_reserve(nskb, header);
4558                 memcpy(nskb->head, skb->head, header);
4559                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4560                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4561                 __skb_queue_before(list, skb, nskb);
4562                 skb_set_owner_r(nskb, sk);
4563 
4564                 /* Copy data, releasing collapsed skbs. */
4565                 while (copy > 0) {
4566                         int offset = start - TCP_SKB_CB(skb)->seq;
4567                         int size = TCP_SKB_CB(skb)->end_seq - start;
4568 
4569                         BUG_ON(offset < 0);
4570                         if (size > 0) {
4571                                 size = min(copy, size);
4572                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4573                                         BUG();
4574                                 TCP_SKB_CB(nskb)->end_seq += size;
4575                                 copy -= size;
4576                                 start += size;
4577                         }
4578                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4579                                 skb = tcp_collapse_one(sk, skb, list);
4580                                 if (!skb ||
4581                                     skb == tail ||
4582                                     tcp_hdr(skb)->syn ||
4583                                     tcp_hdr(skb)->fin)
4584                                         return;
4585                         }
4586                 }
4587         }
4588 }
4589 
4590 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4591  * and tcp_collapse() them until all the queue is collapsed.
4592  */
4593 static void tcp_collapse_ofo_queue(struct sock *sk)
4594 {
4595         struct tcp_sock *tp = tcp_sk(sk);
4596         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4597         struct sk_buff *head;
4598         u32 start, end;
4599 
4600         if (skb == NULL)
4601                 return;
4602 
4603         start = TCP_SKB_CB(skb)->seq;
4604         end = TCP_SKB_CB(skb)->end_seq;
4605         head = skb;
4606 
4607         for (;;) {
4608                 struct sk_buff *next = NULL;
4609 
4610                 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4611                         next = skb_queue_next(&tp->out_of_order_queue, skb);
4612                 skb = next;
4613 
4614                 /* Segment is terminated when we see gap or when
4615                  * we are at the end of all the queue. */
4616                 if (!skb ||
4617                     after(TCP_SKB_CB(skb)->seq, end) ||
4618                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4619                         tcp_collapse(sk, &tp->out_of_order_queue,
4620                                      head, skb, start, end);
4621                         head = skb;
4622                         if (!skb)
4623                                 break;
4624                         /* Start new segment */
4625                         start = TCP_SKB_CB(skb)->seq;
4626                         end = TCP_SKB_CB(skb)->end_seq;
4627                 } else {
4628                         if (before(TCP_SKB_CB(skb)->seq, start))
4629                                 start = TCP_SKB_CB(skb)->seq;
4630                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4631                                 end = TCP_SKB_CB(skb)->end_seq;
4632                 }
4633         }
4634 }
4635 
4636 /*
4637  * Purge the out-of-order queue.
4638  * Return true if queue was pruned.
4639  */
4640 static bool tcp_prune_ofo_queue(struct sock *sk)
4641 {
4642         struct tcp_sock *tp = tcp_sk(sk);
4643         bool res = false;
4644 
4645         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4646                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4647                 __skb_queue_purge(&tp->out_of_order_queue);
4648 
4649                 /* Reset SACK state.  A conforming SACK implementation will
4650                  * do the same at a timeout based retransmit.  When a connection
4651                  * is in a sad state like this, we care only about integrity
4652                  * of the connection not performance.
4653                  */
4654                 if (tp->rx_opt.sack_ok)
4655                         tcp_sack_reset(&tp->rx_opt);
4656                 sk_mem_reclaim(sk);
4657                 res = true;
4658         }
4659         return res;
4660 }
4661 
4662 /* Reduce allocated memory if we can, trying to get
4663  * the socket within its memory limits again.
4664  *
4665  * Return less than zero if we should start dropping frames
4666  * until the socket owning process reads some of the data
4667  * to stabilize the situation.
4668  */
4669 static int tcp_prune_queue(struct sock *sk)
4670 {
4671         struct tcp_sock *tp = tcp_sk(sk);
4672 
4673         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4674 
4675         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4676 
4677         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4678                 tcp_clamp_window(sk);
4679         else if (sk_under_memory_pressure(sk))
4680                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4681 
4682         tcp_collapse_ofo_queue(sk);
4683         if (!skb_queue_empty(&sk->sk_receive_queue))
4684                 tcp_collapse(sk, &sk->sk_receive_queue,
4685                              skb_peek(&sk->sk_receive_queue),
4686                              NULL,
4687                              tp->copied_seq, tp->rcv_nxt);
4688         sk_mem_reclaim(sk);
4689 
4690         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4691                 return 0;
4692 
4693         /* Collapsing did not help, destructive actions follow.
4694          * This must not ever occur. */
4695 
4696         tcp_prune_ofo_queue(sk);
4697 
4698         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4699                 return 0;
4700 
4701         /* If we are really being abused, tell the caller to silently
4702          * drop receive data on the floor.  It will get retransmitted
4703          * and hopefully then we'll have sufficient space.
4704          */
4705         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4706 
4707         /* Massive buffer overcommit. */
4708         tp->pred_flags = 0;
4709         return -1;
4710 }
4711 
4712 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4713  * As additional protections, we do not touch cwnd in retransmission phases,
4714  * and if application hit its sndbuf limit recently.
4715  */
4716 void tcp_cwnd_application_limited(struct sock *sk)
4717 {
4718         struct tcp_sock *tp = tcp_sk(sk);
4719 
4720         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4721             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4722                 /* Limited by application or receiver window. */
4723                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4724                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4725                 if (win_used < tp->snd_cwnd) {
4726                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4727                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4728                 }
4729                 tp->snd_cwnd_used = 0;
4730         }
4731         tp->snd_cwnd_stamp = tcp_time_stamp;
4732 }
4733 
4734 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4735 {
4736         const struct tcp_sock *tp = tcp_sk(sk);
4737 
4738         /* If the user specified a specific send buffer setting, do
4739          * not modify it.
4740          */
4741         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4742                 return false;
4743 
4744         /* If we are under global TCP memory pressure, do not expand.  */
4745         if (sk_under_memory_pressure(sk))
4746                 return false;
4747 
4748         /* If we are under soft global TCP memory pressure, do not expand.  */
4749         if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4750                 return false;
4751 
4752         /* If we filled the congestion window, do not expand.  */
4753         if (tp->packets_out >= tp->snd_cwnd)
4754                 return false;
4755 
4756         return true;
4757 }
4758 
4759 /* When incoming ACK allowed to free some skb from write_queue,
4760  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4761  * on the exit from tcp input handler.
4762  *
4763  * PROBLEM: sndbuf expansion does not work well with largesend.
4764  */
4765 static void tcp_new_space(struct sock *sk)
4766 {
4767         struct tcp_sock *tp = tcp_sk(sk);
4768 
4769         if (tcp_should_expand_sndbuf(sk)) {
4770                 tcp_sndbuf_expand(sk);
4771                 tp->snd_cwnd_stamp = tcp_time_stamp;
4772         }
4773 
4774         sk->sk_write_space(sk);
4775 }
4776 
4777 static void tcp_check_space(struct sock *sk)
4778 {
4779         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4780                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4781                 if (sk->sk_socket &&
4782                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4783                         tcp_new_space(sk);
4784         }
4785 }
4786 
4787 static inline void tcp_data_snd_check(struct sock *sk)
4788 {
4789         tcp_push_pending_frames(sk);
4790         tcp_check_space(sk);
4791 }
4792 
4793 /*
4794  * Check if sending an ack is needed.
4795  */
4796 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4797 {
4798         struct tcp_sock *tp = tcp_sk(sk);
4799 
4800             /* More than one full frame received... */
4801         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4802              /* ... and right edge of window advances far enough.
4803               * (tcp_recvmsg() will send ACK otherwise). Or...
4804               */
4805              __tcp_select_window(sk) >= tp->rcv_wnd) ||
4806             /* We ACK each frame or... */
4807             tcp_in_quickack_mode(sk) ||
4808             /* We have out of order data. */
4809             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4810                 /* Then ack it now */
4811                 tcp_send_ack(sk);
4812         } else {
4813                 /* Else, send delayed ack. */
4814                 tcp_send_delayed_ack(sk);
4815         }
4816 }
4817 
4818 static inline void tcp_ack_snd_check(struct sock *sk)
4819 {
4820         if (!inet_csk_ack_scheduled(sk)) {
4821                 /* We sent a data segment already. */
4822                 return;
4823         }
4824         __tcp_ack_snd_check(sk, 1);
4825 }
4826 
4827 /*
4828  *      This routine is only called when we have urgent data
4829  *      signaled. Its the 'slow' part of tcp_urg. It could be
4830  *      moved inline now as tcp_urg is only called from one
4831  *      place. We handle URGent data wrong. We have to - as
4832  *      BSD still doesn't use the correction from RFC961.
4833  *      For 1003.1g we should support a new option TCP_STDURG to permit
4834  *      either form (or just set the sysctl tcp_stdurg).
4835  */
4836 
4837 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
4838 {
4839         struct tcp_sock *tp = tcp_sk(sk);
4840         u32 ptr = ntohs(th->urg_ptr);
4841 
4842         if (ptr && !sysctl_tcp_stdurg)
4843                 ptr--;
4844         ptr += ntohl(th->seq);
4845 
4846         /* Ignore urgent data that we've already seen and read. */
4847         if (after(tp->copied_seq, ptr))
4848                 return;
4849 
4850         /* Do not replay urg ptr.
4851          *
4852          * NOTE: interesting situation not covered by specs.
4853          * Misbehaving sender may send urg ptr, pointing to segment,
4854          * which we already have in ofo queue. We are not able to fetch
4855          * such data and will stay in TCP_URG_NOTYET until will be eaten
4856          * by recvmsg(). Seems, we are not obliged to handle such wicked
4857          * situations. But it is worth to think about possibility of some
4858          * DoSes using some hypothetical application level deadlock.
4859          */
4860         if (before(ptr, tp->rcv_nxt))
4861                 return;
4862 
4863         /* Do we already have a newer (or duplicate) urgent pointer? */
4864         if (tp->urg_data && !after(ptr, tp->urg_seq))
4865                 return;
4866 
4867         /* Tell the world about our new urgent pointer. */
4868         sk_send_sigurg(sk);
4869 
4870         /* We may be adding urgent data when the last byte read was
4871          * urgent. To do this requires some care. We cannot just ignore
4872          * tp->copied_seq since we would read the last urgent byte again
4873          * as data, nor can we alter copied_seq until this data arrives
4874          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4875          *
4876          * NOTE. Double Dutch. Rendering to plain English: author of comment
4877          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4878          * and expect that both A and B disappear from stream. This is _wrong_.
4879          * Though this happens in BSD with high probability, this is occasional.
4880          * Any application relying on this is buggy. Note also, that fix "works"
4881          * only in this artificial test. Insert some normal data between A and B and we will
4882          * decline of BSD again. Verdict: it is better to remove to trap
4883          * buggy users.
4884          */
4885         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4886             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4887                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4888                 tp->copied_seq++;
4889                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4890                         __skb_unlink(skb, &sk->sk_receive_queue);
4891                         __kfree_skb(skb);
4892                 }
4893         }
4894 
4895         tp->urg_data = TCP_URG_NOTYET;
4896         tp->urg_seq = ptr;
4897 
4898         /* Disable header prediction. */
4899         tp->pred_flags = 0;
4900 }
4901 
4902 /* This is the 'fast' part of urgent handling. */
4903 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
4904 {
4905         struct tcp_sock *tp = tcp_sk(sk);
4906 
4907         /* Check if we get a new urgent pointer - normally not. */
4908         if (th->urg)
4909                 tcp_check_urg(sk, th);
4910 
4911         /* Do we wait for any urgent data? - normally not... */
4912         if (tp->urg_data == TCP_URG_NOTYET) {
4913                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4914                           th->syn;
4915 
4916                 /* Is the urgent pointer pointing into this packet? */
4917                 if (ptr < skb->len) {
4918                         u8 tmp;
4919                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4920                                 BUG();
4921                         tp->urg_data = TCP_URG_VALID | tmp;
4922                         if (!sock_flag(sk, SOCK_DEAD))
4923                                 sk->sk_data_ready(sk, 0);
4924                 }
4925         }
4926 }
4927 
4928 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4929 {
4930         struct tcp_sock *tp = tcp_sk(sk);
4931         int chunk = skb->len - hlen;
4932         int err;
4933 
4934         local_bh_enable();
4935         if (skb_csum_unnecessary(skb))
4936                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4937         else
4938                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4939                                                        tp->ucopy.iov);
4940 
4941         if (!err) {
4942                 tp->ucopy.len -= chunk;
4943                 tp->copied_seq += chunk;
4944                 tcp_rcv_space_adjust(sk);
4945         }
4946 
4947         local_bh_disable();
4948         return err;
4949 }
4950 
4951 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
4952                                             struct sk_buff *skb)
4953 {
4954         __sum16 result;
4955 
4956         if (sock_owned_by_user(sk)) {
4957                 local_bh_enable();
4958                 result = __tcp_checksum_complete(skb);
4959                 local_bh_disable();
4960         } else {
4961                 result = __tcp_checksum_complete(skb);
4962         }
4963         return result;
4964 }
4965 
4966 static inline bool tcp_checksum_complete_user(struct sock *sk,
4967                                              struct sk_buff *skb)
4968 {
4969         return !skb_csum_unnecessary(skb) &&
4970                __tcp_checksum_complete_user(sk, skb);
4971 }
4972 
4973 #ifdef CONFIG_NET_DMA
4974 static bool tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
4975                                   int hlen)
4976 {
4977         struct tcp_sock *tp = tcp_sk(sk);
4978         int chunk = skb->len - hlen;
4979         int dma_cookie;
4980         bool copied_early = false;
4981 
4982         if (tp->ucopy.wakeup)
4983                 return false;
4984 
4985         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4986                 tp->ucopy.dma_chan = net_dma_find_channel();
4987 
4988         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4989 
4990                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4991                                                          skb, hlen,
4992                                                          tp->ucopy.iov, chunk,
4993                                                          tp->ucopy.pinned_list);
4994 
4995                 if (dma_cookie < 0)
4996                         goto out;
4997 
4998                 tp->ucopy.dma_cookie = dma_cookie;
4999                 copied_early = true;
5000 
5001                 tp->ucopy.len -= chunk;
5002                 tp->copied_seq += chunk;
5003                 tcp_rcv_space_adjust(sk);
5004 
5005                 if ((tp->ucopy.len == 0) ||
5006                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5007                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5008                         tp->ucopy.wakeup = 1;
5009                         sk->sk_data_ready(sk, 0);
5010                 }
5011         } else if (chunk > 0) {
5012                 tp->ucopy.wakeup = 1;
5013                 sk->sk_data_ready(sk, 0);
5014         }
5015 out:
5016         return copied_early;
5017 }
5018 #endif /* CONFIG_NET_DMA */
5019 
5020 /* Does PAWS and seqno based validation of an incoming segment, flags will
5021  * play significant role here.
5022  */
5023 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5024                                   const struct tcphdr *th, int syn_inerr)
5025 {
5026         struct tcp_sock *tp = tcp_sk(sk);
5027 
5028         /* RFC1323: H1. Apply PAWS check first. */
5029         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5030             tcp_paws_discard(sk, skb)) {
5031                 if (!th->rst) {
5032                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5033                         tcp_send_dupack(sk, skb);
5034                         goto discard;
5035                 }
5036                 /* Reset is accepted even if it did not pass PAWS. */
5037         }
5038 
5039         /* Step 1: check sequence number */
5040         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5041                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5042                  * (RST) segments are validated by checking their SEQ-fields."
5043                  * And page 69: "If an incoming segment is not acceptable,
5044                  * an acknowledgment should be sent in reply (unless the RST
5045                  * bit is set, if so drop the segment and return)".
5046                  */
5047                 if (!th->rst) {
5048                         if (th->syn)
5049                                 goto syn_challenge;
5050                         tcp_send_dupack(sk, skb);
5051                 }
5052                 goto discard;
5053         }
5054 
5055         /* Step 2: check RST bit */
5056         if (th->rst) {
5057                 /* RFC 5961 3.2 :
5058                  * If sequence number exactly matches RCV.NXT, then
5059                  *     RESET the connection
5060                  * else
5061                  *     Send a challenge ACK
5062                  */
5063                 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5064                         tcp_reset(sk);
5065                 else
5066                         tcp_send_challenge_ack(sk);
5067                 goto discard;
5068         }
5069 
5070         /* step 3: check security and precedence [ignored] */
5071 
5072         /* step 4: Check for a SYN
5073          * RFC 5691 4.2 : Send a challenge ack
5074          */
5075         if (th->syn) {
5076 syn_challenge:
5077                 if (syn_inerr)
5078                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5079                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5080                 tcp_send_challenge_ack(sk);
5081                 goto discard;
5082         }
5083 
5084         return true;
5085 
5086 discard:
5087         __kfree_skb(skb);
5088         return false;
5089 }
5090 
5091 /*
5092  *      TCP receive function for the ESTABLISHED state.
5093  *
5094  *      It is split into a fast path and a slow path. The fast path is
5095  *      disabled when:
5096  *      - A zero window was announced from us - zero window probing
5097  *        is only handled properly in the slow path.
5098  *      - Out of order segments arrived.
5099  *      - Urgent data is expected.
5100  *      - There is no buffer space left
5101  *      - Unexpected TCP flags/window values/header lengths are received
5102  *        (detected by checking the TCP header against pred_flags)
5103  *      - Data is sent in both directions. Fast path only supports pure senders
5104  *        or pure receivers (this means either the sequence number or the ack
5105  *        value must stay constant)
5106  *      - Unexpected TCP option.
5107  *
5108  *      When these conditions are not satisfied it drops into a standard
5109  *      receive procedure patterned after RFC793 to handle all cases.
5110  *      The first three cases are guaranteed by proper pred_flags setting,
5111  *      the rest is checked inline. Fast processing is turned on in
5112  *      tcp_data_queue when everything is OK.
5113  */
5114 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5115                          const struct tcphdr *th, unsigned int len)
5116 {
5117         struct tcp_sock *tp = tcp_sk(sk);
5118 
5119         if (unlikely(sk->sk_rx_dst == NULL))
5120                 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5121         /*
5122          *      Header prediction.
5123          *      The code loosely follows the one in the famous
5124          *      "30 instruction TCP receive" Van Jacobson mail.
5125          *
5126          *      Van's trick is to deposit buffers into socket queue
5127          *      on a device interrupt, to call tcp_recv function
5128          *      on the receive process context and checksum and copy
5129          *      the buffer to user space. smart...
5130          *
5131          *      Our current scheme is not silly either but we take the
5132          *      extra cost of the net_bh soft interrupt processing...
5133          *      We do checksum and copy also but from device to kernel.
5134          */
5135 
5136         tp->rx_opt.saw_tstamp = 0;
5137 
5138         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5139          *      if header_prediction is to be made
5140          *      'S' will always be tp->tcp_header_len >> 2
5141          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5142          *  turn it off (when there are holes in the receive
5143          *       space for instance)
5144          *      PSH flag is ignored.
5145          */
5146 
5147         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5148             TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5149             !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5150                 int tcp_header_len = tp->tcp_header_len;
5151 
5152                 /* Timestamp header prediction: tcp_header_len
5153                  * is automatically equal to th->doff*4 due to pred_flags
5154                  * match.
5155                  */
5156 
5157                 /* Check timestamp */
5158                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5159                         /* No? Slow path! */
5160                         if (!tcp_parse_aligned_timestamp(tp, th))
5161                                 goto slow_path;
5162 
5163                         /* If PAWS failed, check it more carefully in slow path */
5164                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5165                                 goto slow_path;
5166 
5167                         /* DO NOT update ts_recent here, if checksum fails
5168                          * and timestamp was corrupted part, it will result
5169                          * in a hung connection since we will drop all
5170                          * future packets due to the PAWS test.
5171                          */
5172                 }
5173 
5174                 if (len <= tcp_header_len) {
5175                         /* Bulk data transfer: sender */
5176                         if (len == tcp_header_len) {
5177                                 /* Predicted packet is in window by definition.
5178                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5179                                  * Hence, check seq<=rcv_wup reduces to:
5180                                  */
5181                                 if (tcp_header_len ==
5182                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5183                                     tp->rcv_nxt == tp->rcv_wup)
5184                                         tcp_store_ts_recent(tp);
5185 
5186                                 /* We know that such packets are checksummed
5187                                  * on entry.
5188                                  */
5189                                 tcp_ack(sk, skb, 0);
5190                                 __kfree_skb(skb);
5191                                 tcp_data_snd_check(sk);
5192                                 return;
5193                         } else { /* Header too small */
5194                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5195                                 goto discard;
5196                         }
5197                 } else {
5198                         int eaten = 0;
5199                         int copied_early = 0;
5200                         bool fragstolen = false;
5201 
5202                         if (tp->copied_seq == tp->rcv_nxt &&
5203                             len - tcp_header_len <= tp->ucopy.len) {
5204 #ifdef CONFIG_NET_DMA
5205                                 if (tp->ucopy.task == current &&
5206                                     sock_owned_by_user(sk) &&
5207                                     tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5208                                         copied_early = 1;
5209                                         eaten = 1;
5210                                 }
5211 #endif
5212                                 if (tp->ucopy.task == current &&
5213                                     sock_owned_by_user(sk) && !copied_early) {
5214                                         __set_current_state(TASK_RUNNING);
5215 
5216                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5217                                                 eaten = 1;
5218                                 }
5219                                 if (eaten) {
5220                                         /* Predicted packet is in window by definition.
5221                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5222                                          * Hence, check seq<=rcv_wup reduces to:
5223                                          */
5224                                         if (tcp_header_len ==
5225                                             (sizeof(struct tcphdr) +
5226                                              TCPOLEN_TSTAMP_ALIGNED) &&
5227                                             tp->rcv_nxt == tp->rcv_wup)
5228                                                 tcp_store_ts_recent(tp);
5229 
5230                                         tcp_rcv_rtt_measure_ts(sk, skb);
5231 
5232                                         __skb_pull(skb, tcp_header_len);
5233                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5234                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5235                                 }
5236                                 if (copied_early)
5237                                         tcp_cleanup_rbuf(sk, skb->len);
5238                         }
5239                         if (!eaten) {
5240                                 if (tcp_checksum_complete_user(sk, skb))
5241                                         goto csum_error;
5242 
5243                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5244                                         goto step5;
5245 
5246                                 /* Predicted packet is in window by definition.
5247                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5248                                  * Hence, check seq<=rcv_wup reduces to:
5249                                  */
5250                                 if (tcp_header_len ==
5251                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5252                                     tp->rcv_nxt == tp->rcv_wup)
5253                                         tcp_store_ts_recent(tp);
5254 
5255                                 tcp_rcv_rtt_measure_ts(sk, skb);
5256 
5257                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5258 
5259                                 /* Bulk data transfer: receiver */
5260                                 eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5261                                                       &fragstolen);
5262                         }
5263 
5264                         tcp_event_data_recv(sk, skb);
5265 
5266                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5267                                 /* Well, only one small jumplet in fast path... */
5268                                 tcp_ack(sk, skb, FLAG_DATA);
5269                                 tcp_data_snd_check(sk);
5270                                 if (!inet_csk_ack_scheduled(sk))
5271                                         goto no_ack;
5272                         }
5273 
5274                         if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5275                                 __tcp_ack_snd_check(sk, 0);
5276 no_ack:
5277 #ifdef CONFIG_NET_DMA
5278                         if (copied_early)
5279                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5280                         else
5281 #endif
5282                         if (eaten)
5283                                 kfree_skb_partial(skb, fragstolen);
5284                         sk->sk_data_ready(sk, 0);
5285                         return;
5286                 }
5287         }
5288 
5289 slow_path:
5290         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5291                 goto csum_error;
5292 
5293         if (!th->ack && !th->rst)
5294                 goto discard;
5295 
5296         /*
5297          *      Standard slow path.
5298          */
5299 
5300         if (!tcp_validate_incoming(sk, skb, th, 1))
5301                 return;
5302 
5303 step5:
5304         if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5305                 goto discard;
5306 
5307         tcp_rcv_rtt_measure_ts(sk, skb);
5308 
5309         /* Process urgent data. */
5310         tcp_urg(sk, skb, th);
5311 
5312         /* step 7: process the segment text */
5313         tcp_data_queue(sk, skb);
5314 
5315         tcp_data_snd_check(sk);
5316         tcp_ack_snd_check(sk);
5317         return;
5318 
5319 csum_error:
5320         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5321         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5322 
5323 discard:
5324         __kfree_skb(skb);
5325 }
5326 EXPORT_SYMBOL(tcp_rcv_established);
5327 
5328 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5329 {
5330         struct tcp_sock *tp = tcp_sk(sk);
5331         struct inet_connection_sock *icsk = inet_csk(sk);
5332 
5333         tcp_set_state(sk, TCP_ESTABLISHED);
5334 
5335         if (skb != NULL) {
5336                 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5337                 security_inet_conn_established(sk, skb);
5338         }
5339 
5340         /* Make sure socket is routed, for correct metrics.  */
5341         icsk->icsk_af_ops->rebuild_header(sk);
5342 
5343         tcp_init_metrics(sk);
5344 
5345         tcp_init_congestion_control(sk);
5346 
5347         /* Prevent spurious tcp_cwnd_restart() on first data
5348          * packet.
5349          */
5350         tp->lsndtime = tcp_time_stamp;
5351 
5352         tcp_init_buffer_space(sk);
5353 
5354         if (sock_flag(sk, SOCK_KEEPOPEN))
5355                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5356 
5357         if (!tp->rx_opt.snd_wscale)
5358                 __tcp_fast_path_on(tp, tp->snd_wnd);
5359         else
5360                 tp->pred_flags = 0;
5361 
5362         if (!sock_flag(sk, SOCK_DEAD)) {
5363                 sk->sk_state_change(sk);
5364                 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5365         }
5366 }
5367 
5368 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5369                                     struct tcp_fastopen_cookie *cookie)
5370 {
5371         struct tcp_sock *tp = tcp_sk(sk);
5372         struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5373         u16 mss = tp->rx_opt.mss_clamp;
5374         bool syn_drop;
5375 
5376         if (mss == tp->rx_opt.user_mss) {
5377                 struct tcp_options_received opt;
5378 
5379                 /* Get original SYNACK MSS value if user MSS sets mss_clamp */
5380                 tcp_clear_options(&opt);
5381                 opt.user_mss = opt.mss_clamp = 0;
5382                 tcp_parse_options(synack, &opt, 0, NULL);
5383                 mss = opt.mss_clamp;
5384         }
5385 
5386         if (!tp->syn_fastopen)  /* Ignore an unsolicited cookie */
5387                 cookie->len = -1;
5388 
5389         /* The SYN-ACK neither has cookie nor acknowledges the data. Presumably
5390          * the remote receives only the retransmitted (regular) SYNs: either
5391          * the original SYN-data or the corresponding SYN-ACK is lost.
5392          */
5393         syn_drop = (cookie->len <= 0 && data && tp->total_retrans);
5394 
5395         tcp_fastopen_cache_set(sk, mss, cookie, syn_drop);
5396 
5397         if (data) { /* Retransmit unacked data in SYN */
5398                 tcp_for_write_queue_from(data, sk) {
5399                         if (data == tcp_send_head(sk) ||
5400                             __tcp_retransmit_skb(sk, data))
5401                                 break;
5402                 }
5403                 tcp_rearm_rto(sk);
5404                 return true;
5405         }
5406         tp->syn_data_acked = tp->syn_data;
5407         return false;
5408 }
5409 
5410 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5411                                          const struct tcphdr *th, unsigned int len)
5412 {
5413         struct inet_connection_sock *icsk = inet_csk(sk);
5414         struct tcp_sock *tp = tcp_sk(sk);
5415         struct tcp_fastopen_cookie foc = { .len = -1 };
5416         int saved_clamp = tp->rx_opt.mss_clamp;
5417 
5418         tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5419         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5420                 tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5421 
5422         if (th->ack) {
5423                 /* rfc793:
5424                  * "If the state is SYN-SENT then
5425                  *    first check the ACK bit
5426                  *      If the ACK bit is set
5427                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5428                  *        a reset (unless the RST bit is set, if so drop
5429                  *        the segment and return)"
5430                  */
5431                 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5432                     after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5433                         goto reset_and_undo;
5434 
5435                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5436                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5437                              tcp_time_stamp)) {
5438                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5439                         goto reset_and_undo;
5440                 }
5441 
5442                 /* Now ACK is acceptable.
5443                  *
5444                  * "If the RST bit is set
5445                  *    If the ACK was acceptable then signal the user "error:
5446                  *    connection reset", drop the segment, enter CLOSED state,
5447                  *    delete TCB, and return."
5448                  */
5449 
5450                 if (th->rst) {
5451                         tcp_reset(sk);
5452                         goto discard;
5453                 }
5454 
5455                 /* rfc793:
5456                  *   "fifth, if neither of the SYN or RST bits is set then
5457                  *    drop the segment and return."
5458                  *
5459                  *    See note below!
5460                  *                                        --ANK(990513)
5461                  */
5462                 if (!th->syn)
5463                         goto discard_and_undo;
5464 
5465                 /* rfc793:
5466                  *   "If the SYN bit is on ...
5467                  *    are acceptable then ...
5468                  *    (our SYN has been ACKed), change the connection
5469                  *    state to ESTABLISHED..."
5470                  */
5471 
5472                 TCP_ECN_rcv_synack(tp, th);
5473 
5474                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5475                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5476 
5477                 /* Ok.. it's good. Set up sequence numbers and
5478                  * move to established.
5479                  */
5480                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5481                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5482 
5483                 /* RFC1323: The window in SYN & SYN/ACK segments is
5484                  * never scaled.
5485                  */
5486                 tp->snd_wnd = ntohs(th->window);
5487 
5488                 if (!tp->rx_opt.wscale_ok) {
5489                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5490                         tp->window_clamp = min(tp->window_clamp, 65535U);
5491                 }
5492 
5493                 if (tp->rx_opt.saw_tstamp) {
5494                         tp->rx_opt.tstamp_ok       = 1;
5495                         tp->tcp_header_len =
5496                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5497                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5498                         tcp_store_ts_recent(tp);
5499                 } else {
5500                         tp->tcp_header_len = sizeof(struct tcphdr);
5501                 }
5502 
5503                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5504                         tcp_enable_fack(tp);
5505 
5506                 tcp_mtup_init(sk);
5507                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5508                 tcp_initialize_rcv_mss(sk);
5509 
5510                 /* Remember, tcp_poll() does not lock socket!
5511                  * Change state from SYN-SENT only after copied_seq
5512                  * is initialized. */
5513                 tp->copied_seq = tp->rcv_nxt;
5514 
5515                 smp_mb();
5516 
5517                 tcp_finish_connect(sk, skb);
5518 
5519                 if ((tp->syn_fastopen || tp->syn_data) &&
5520                     tcp_rcv_fastopen_synack(sk, skb, &foc))
5521                         return -1;
5522 
5523                 if (sk->sk_write_pending ||
5524                     icsk->icsk_accept_queue.rskq_defer_accept ||
5525                     icsk->icsk_ack.pingpong) {
5526                         /* Save one ACK. Data will be ready after
5527                          * several ticks, if write_pending is set.
5528                          *
5529                          * It may be deleted, but with this feature tcpdumps
5530                          * look so _wonderfully_ clever, that I was not able
5531                          * to stand against the temptation 8)     --ANK
5532                          */
5533                         inet_csk_schedule_ack(sk);
5534                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5535                         tcp_enter_quickack_mode(sk);
5536                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5537                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5538 
5539 discard:
5540                         __kfree_skb(skb);
5541                         return 0;
5542                 } else {
5543                         tcp_send_ack(sk);
5544                 }
5545                 return -1;
5546         }
5547 
5548         /* No ACK in the segment */
5549 
5550         if (th->rst) {
5551                 /* rfc793:
5552                  * "If the RST bit is set
5553                  *
5554                  *      Otherwise (no ACK) drop the segment and return."
5555                  */
5556 
5557                 goto discard_and_undo;
5558         }
5559 
5560         /* PAWS check. */
5561         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5562             tcp_paws_reject(&tp->rx_opt, 0))
5563                 goto discard_and_undo;
5564 
5565         if (th->syn) {
5566                 /* We see SYN without ACK. It is attempt of
5567                  * simultaneous connect with crossed SYNs.
5568                  * Particularly, it can be connect to self.
5569                  */
5570                 tcp_set_state(sk, TCP_SYN_RECV);
5571 
5572                 if (tp->rx_opt.saw_tstamp) {
5573                         tp->rx_opt.tstamp_ok = 1;
5574                         tcp_store_ts_recent(tp);
5575                         tp->tcp_header_len =
5576                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5577                 } else {
5578                         tp->tcp_header_len = sizeof(struct tcphdr);
5579                 }
5580 
5581                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5582                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5583 
5584                 /* RFC1323: The window in SYN & SYN/ACK segments is
5585                  * never scaled.
5586                  */
5587                 tp->snd_wnd    = ntohs(th->window);
5588                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5589                 tp->max_window = tp->snd_wnd;
5590 
5591                 TCP_ECN_rcv_syn(tp, th);
5592 
5593                 tcp_mtup_init(sk);
5594                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5595                 tcp_initialize_rcv_mss(sk);
5596 
5597                 tcp_send_synack(sk);
5598 #if 0
5599                 /* Note, we could accept data and URG from this segment.
5600                  * There are no obstacles to make this (except that we must
5601                  * either change tcp_recvmsg() to prevent it from returning data
5602                  * before 3WHS completes per RFC793, or employ TCP Fast Open).
5603                  *
5604                  * However, if we ignore data in ACKless segments sometimes,
5605                  * we have no reasons to accept it sometimes.
5606                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5607                  * is not flawless. So, discard packet for sanity.
5608                  * Uncomment this return to process the data.
5609                  */
5610                 return -1;
5611 #else
5612                 goto discard;
5613 #endif
5614         }
5615         /* "fifth, if neither of the SYN or RST bits is set then
5616          * drop the segment and return."
5617          */
5618 
5619 discard_and_undo:
5620         tcp_clear_options(&tp->rx_opt);
5621         tp->rx_opt.mss_clamp = saved_clamp;
5622         goto discard;
5623 
5624 reset_and_undo:
5625         tcp_clear_options(&tp->rx_opt);
5626         tp->rx_opt.mss_clamp = saved_clamp;
5627         return 1;
5628 }
5629 
5630 /*
5631  *      This function implements the receiving procedure of RFC 793 for
5632  *      all states except ESTABLISHED and TIME_WAIT.
5633  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5634  *      address independent.
5635  */
5636 
5637 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5638                           const struct tcphdr *th, unsigned int len)
5639 {
5640         struct tcp_sock *tp = tcp_sk(sk);
5641         struct inet_connection_sock *icsk = inet_csk(sk);
5642         struct request_sock *req;
5643         int queued = 0;
5644         bool acceptable;
5645         u32 synack_stamp;
5646 
5647         tp->rx_opt.saw_tstamp = 0;
5648 
5649         switch (sk->sk_state) {
5650         case TCP_CLOSE:
5651                 goto discard;
5652 
5653         case TCP_LISTEN:
5654                 if (th->ack)
5655                         return 1;
5656 
5657                 if (th->rst)
5658                         goto discard;
5659 
5660                 if (th->syn) {
5661                         if (th->fin)
5662                                 goto discard;
5663                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5664                                 return 1;
5665 
5666                         /* Now we have several options: In theory there is
5667                          * nothing else in the frame. KA9Q has an option to
5668                          * send data with the syn, BSD accepts data with the
5669                          * syn up to the [to be] advertised window and
5670                          * Solaris 2.1 gives you a protocol error. For now
5671                          * we just ignore it, that fits the spec precisely
5672                          * and avoids incompatibilities. It would be nice in
5673                          * future to drop through and process the data.
5674                          *
5675                          * Now that TTCP is starting to be used we ought to
5676                          * queue this data.
5677                          * But, this leaves one open to an easy denial of
5678                          * service attack, and SYN cookies can't defend
5679                          * against this problem. So, we drop the data
5680                          * in the interest of security over speed unless
5681                          * it's still in use.
5682                          */
5683                         kfree_skb(skb);
5684                         return 0;
5685                 }
5686                 goto discard;
5687 
5688         case TCP_SYN_SENT:
5689                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5690                 if (queued >= 0)
5691                         return queued;
5692 
5693                 /* Do step6 onward by hand. */
5694                 tcp_urg(sk, skb, th);
5695                 __kfree_skb(skb);
5696                 tcp_data_snd_check(sk);
5697                 return 0;
5698         }
5699 
5700         req = tp->fastopen_rsk;
5701         if (req != NULL) {
5702                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5703                     sk->sk_state != TCP_FIN_WAIT1);
5704 
5705                 if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
5706                         goto discard;
5707         }
5708 
5709         if (!th->ack && !th->rst)
5710                 goto discard;
5711 
5712         if (!tcp_validate_incoming(sk, skb, th, 0))
5713                 return 0;
5714 
5715         /* step 5: check the ACK field */
5716         acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5717                                       FLAG_UPDATE_TS_RECENT) > 0;
5718 
5719         switch (sk->sk_state) {
5720         case TCP_SYN_RECV:
5721                 if (!acceptable)
5722                         return 1;
5723 
5724                 /* Once we leave TCP_SYN_RECV, we no longer need req
5725                  * so release it.
5726                  */
5727                 if (req) {
5728                         synack_stamp = tcp_rsk(req)->snt_synack;
5729                         tp->total_retrans = req->num_retrans;
5730                         reqsk_fastopen_remove(sk, req, false);
5731                 } else {
5732                         synack_stamp = tp->lsndtime;
5733                         /* Make sure socket is routed, for correct metrics. */
5734                         icsk->icsk_af_ops->rebuild_header(sk);
5735                         tcp_init_congestion_control(sk);
5736 
5737                         tcp_mtup_init(sk);
5738                         tp->copied_seq = tp->rcv_nxt;
5739                         tcp_init_buffer_space(sk);
5740                 }
5741                 smp_mb();
5742                 tcp_set_state(sk, TCP_ESTABLISHED);
5743                 sk->sk_state_change(sk);
5744 
5745                 /* Note, that this wakeup is only for marginal crossed SYN case.
5746                  * Passively open sockets are not waked up, because
5747                  * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5748                  */
5749                 if (sk->sk_socket)
5750                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5751 
5752                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5753                 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5754                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5755                 tcp_synack_rtt_meas(sk, synack_stamp);
5756 
5757                 if (tp->rx_opt.tstamp_ok)
5758                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5759 
5760                 if (req) {
5761                         /* Re-arm the timer because data may have been sent out.
5762                          * This is similar to the regular data transmission case
5763                          * when new data has just been ack'ed.
5764                          *
5765                          * (TFO) - we could try to be more aggressive and
5766                          * retransmitting any data sooner based on when they
5767                          * are sent out.
5768                          */
5769                         tcp_rearm_rto(sk);
5770                 } else
5771                         tcp_init_metrics(sk);
5772 
5773                 tcp_update_pacing_rate(sk);
5774 
5775                 /* Prevent spurious tcp_cwnd_restart() on first data packet */
5776                 tp->lsndtime = tcp_time_stamp;
5777 
5778                 tcp_initialize_rcv_mss(sk);
5779                 tcp_fast_path_on(tp);
5780                 break;
5781 
5782         case TCP_FIN_WAIT1: {
5783                 struct dst_entry *dst;
5784                 int tmo;
5785 
5786                 /* If we enter the TCP_FIN_WAIT1 state and we are a
5787                  * Fast Open socket and this is the first acceptable
5788                  * ACK we have received, this would have acknowledged
5789                  * our SYNACK so stop the SYNACK timer.
5790                  */
5791                 if (req != NULL) {
5792                         /* Return RST if ack_seq is invalid.
5793                          * Note that RFC793 only says to generate a
5794                          * DUPACK for it but for TCP Fast Open it seems
5795                          * better to treat this case like TCP_SYN_RECV
5796                          * above.
5797                          */
5798                         if (!acceptable)
5799                                 return 1;
5800                         /* We no longer need the request sock. */
5801                         reqsk_fastopen_remove(sk, req, false);
5802                         tcp_rearm_rto(sk);
5803                 }
5804                 if (tp->snd_una != tp->write_seq)
5805                         break;
5806 
5807                 tcp_set_state(sk, TCP_FIN_WAIT2);
5808                 sk->sk_shutdown |= SEND_SHUTDOWN;
5809 
5810                 dst = __sk_dst_get(sk);
5811                 if (dst)
5812                         dst_confirm(dst);
5813 
5814                 if (!sock_flag(sk, SOCK_DEAD)) {
5815                         /* Wake up lingering close() */
5816                         sk->sk_state_change(sk);
5817                         break;
5818                 }
5819 
5820                 if (tp->linger2 < 0 ||
5821                     (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5822                      after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5823                         tcp_done(sk);
5824                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5825                         return 1;
5826                 }
5827 
5828                 tmo = tcp_fin_time(sk);
5829                 if (tmo > TCP_TIMEWAIT_LEN) {
5830                         inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5831                 } else if (th->fin || sock_owned_by_user(sk)) {
5832                         /* Bad case. We could lose such FIN otherwise.
5833                          * It is not a big problem, but it looks confusing
5834                          * and not so rare event. We still can lose it now,
5835                          * if it spins in bh_lock_sock(), but it is really
5836                          * marginal case.
5837                          */
5838                         inet_csk_reset_keepalive_timer(sk, tmo);
5839                 } else {
5840                         tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5841                         goto discard;
5842                 }
5843                 break;
5844         }
5845 
5846         case TCP_CLOSING:
5847                 if (tp->snd_una == tp->write_seq) {
5848                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5849                         goto discard;
5850                 }
5851                 break;
5852 
5853         case TCP_LAST_ACK:
5854                 if (tp->snd_una == tp->write_seq) {
5855                         tcp_update_metrics(sk);
5856                         tcp_done(sk);
5857                         goto discard;
5858                 }
5859                 break;
5860         }
5861 
5862         /* step 6: check the URG bit */
5863         tcp_urg(sk, skb, th);
5864 
5865         /* step 7: process the segment text */
5866         switch (sk->sk_state) {
5867         case TCP_CLOSE_WAIT:
5868         case TCP_CLOSING:
5869         case TCP_LAST_ACK:
5870                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5871                         break;
5872         case TCP_FIN_WAIT1:
5873         case TCP_FIN_WAIT2:
5874                 /* RFC 793 says to queue data in these states,
5875                  * RFC 1122 says we MUST send a reset.
5876                  * BSD 4.4 also does reset.
5877                  */
5878                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5879                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5880                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5881                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5882                                 tcp_reset(sk);
5883                                 return 1;
5884                         }
5885                 }
5886                 /* Fall through */
5887         case TCP_ESTABLISHED:
5888                 tcp_data_queue(sk, skb);
5889                 queued = 1;
5890                 break;
5891         }
5892 
5893         /* tcp_data could move socket to TIME-WAIT */
5894         if (sk->sk_state != TCP_CLOSE) {
5895                 tcp_data_snd_check(sk);
5896                 tcp_ack_snd_check(sk);
5897         }
5898 
5899         if (!queued) {
5900 discard:
5901                 __kfree_skb(skb);
5902         }
5903         return 0;
5904 }
5905 EXPORT_SYMBOL(tcp_rcv_state_process);
5906 

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