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.
6 * Implementation of the Transmission Control Protocol(TCP).
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>
22 #include <linux/module.h>
23 #include <linux/slab.h>
24 #include <linux/sysctl.h>
25 #include <linux/workqueue.h>
27 #include <net/inet_common.h>
30 int sysctl_tcp_syncookies __read_mostly = 1;
31 EXPORT_SYMBOL(sysctl_tcp_syncookies);
33 int sysctl_tcp_abort_on_overflow __read_mostly;
35 struct inet_timewait_death_row tcp_death_row = {
36 .sysctl_max_tw_buckets = NR_FILE * 2,
37 .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
38 .death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
39 .hashinfo = &tcp_hashinfo,
40 .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
41 (unsigned long)&tcp_death_row),
42 .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
43 inet_twdr_twkill_work),
44 /* Short-time timewait calendar */
47 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
48 (unsigned long)&tcp_death_row),
50 EXPORT_SYMBOL_GPL(tcp_death_row);
52 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
56 if (after(end_seq, s_win) && before(seq, e_win))
58 return seq == e_win && seq == end_seq;
62 * * Main purpose of TIME-WAIT state is to close connection gracefully,
63 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
64 * (and, probably, tail of data) and one or more our ACKs are lost.
65 * * What is TIME-WAIT timeout? It is associated with maximal packet
66 * lifetime in the internet, which results in wrong conclusion, that
67 * it is set to catch "old duplicate segments" wandering out of their path.
68 * It is not quite correct. This timeout is calculated so that it exceeds
69 * maximal retransmission timeout enough to allow to lose one (or more)
70 * segments sent by peer and our ACKs. This time may be calculated from RTO.
71 * * When TIME-WAIT socket receives RST, it means that another end
72 * finally closed and we are allowed to kill TIME-WAIT too.
73 * * Second purpose of TIME-WAIT is catching old duplicate segments.
74 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
75 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
76 * * If we invented some more clever way to catch duplicates
77 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
79 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
80 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
81 * from the very beginning.
83 * NOTE. With recycling (and later with fin-wait-2) TW bucket
84 * is _not_ stateless. It means, that strictly speaking we must
85 * spinlock it. I do not want! Well, probability of misbehaviour
86 * is ridiculously low and, seems, we could use some mb() tricks
87 * to avoid misread sequence numbers, states etc. --ANK
90 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
91 const struct tcphdr *th)
93 struct tcp_options_received tmp_opt;
94 const u8 *hash_location;
95 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
96 bool paws_reject = false;
98 tmp_opt.saw_tstamp = 0;
99 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
100 tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
102 if (tmp_opt.saw_tstamp) {
103 tmp_opt.ts_recent = tcptw->tw_ts_recent;
104 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
105 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
109 if (tw->tw_substate == TCP_FIN_WAIT2) {
110 /* Just repeat all the checks of tcp_rcv_state_process() */
112 /* Out of window, send ACK */
114 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
116 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
122 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
127 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
128 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
130 return TCP_TW_SUCCESS;
133 /* New data or FIN. If new data arrive after half-duplex close,
137 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
139 inet_twsk_deschedule(tw, &tcp_death_row);
144 /* FIN arrived, enter true time-wait state. */
145 tw->tw_substate = TCP_TIME_WAIT;
146 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
147 if (tmp_opt.saw_tstamp) {
148 tcptw->tw_ts_recent_stamp = get_seconds();
149 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
152 if (tcp_death_row.sysctl_tw_recycle &&
153 tcptw->tw_ts_recent_stamp &&
154 tcp_tw_remember_stamp(tw))
155 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
158 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
164 * Now real TIME-WAIT state.
167 * "When a connection is [...] on TIME-WAIT state [...]
168 * [a TCP] MAY accept a new SYN from the remote TCP to
169 * reopen the connection directly, if it:
171 * (1) assigns its initial sequence number for the new
172 * connection to be larger than the largest sequence
173 * number it used on the previous connection incarnation,
176 * (2) returns to TIME-WAIT state if the SYN turns out
177 * to be an old duplicate".
181 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
182 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
183 /* In window segment, it may be only reset or bare ack. */
186 /* This is TIME_WAIT assassination, in two flavors.
187 * Oh well... nobody has a sufficient solution to this
190 if (sysctl_tcp_rfc1337 == 0) {
192 inet_twsk_deschedule(tw, &tcp_death_row);
194 return TCP_TW_SUCCESS;
197 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
200 if (tmp_opt.saw_tstamp) {
201 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
202 tcptw->tw_ts_recent_stamp = get_seconds();
206 return TCP_TW_SUCCESS;
209 /* Out of window segment.
211 All the segments are ACKed immediately.
213 The only exception is new SYN. We accept it, if it is
214 not old duplicate and we are not in danger to be killed
215 by delayed old duplicates. RFC check is that it has
216 newer sequence number works at rates <40Mbit/sec.
217 However, if paws works, it is reliable AND even more,
218 we even may relax silly seq space cutoff.
220 RED-PEN: we violate main RFC requirement, if this SYN will appear
221 old duplicate (i.e. we receive RST in reply to SYN-ACK),
222 we must return socket to time-wait state. It is not good,
226 if (th->syn && !th->rst && !th->ack && !paws_reject &&
227 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
228 (tmp_opt.saw_tstamp &&
229 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
230 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
233 TCP_SKB_CB(skb)->when = isn;
238 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
241 /* In this case we must reset the TIMEWAIT timer.
243 * If it is ACKless SYN it may be both old duplicate
244 * and new good SYN with random sequence number <rcv_nxt.
245 * Do not reschedule in the last case.
247 if (paws_reject || th->ack)
248 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
251 /* Send ACK. Note, we do not put the bucket,
252 * it will be released by caller.
257 return TCP_TW_SUCCESS;
259 EXPORT_SYMBOL(tcp_timewait_state_process);
262 * Move a socket to time-wait or dead fin-wait-2 state.
264 void tcp_time_wait(struct sock *sk, int state, int timeo)
266 struct inet_timewait_sock *tw = NULL;
267 const struct inet_connection_sock *icsk = inet_csk(sk);
268 const struct tcp_sock *tp = tcp_sk(sk);
269 bool recycle_ok = false;
271 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
272 recycle_ok = tcp_remember_stamp(sk);
274 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
275 tw = inet_twsk_alloc(sk, state);
278 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
279 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
280 struct inet_sock *inet = inet_sk(sk);
282 tw->tw_transparent = inet->transparent;
283 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
284 tcptw->tw_rcv_nxt = tp->rcv_nxt;
285 tcptw->tw_snd_nxt = tp->snd_nxt;
286 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
287 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
288 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
290 #if IS_ENABLED(CONFIG_IPV6)
291 if (tw->tw_family == PF_INET6) {
292 struct ipv6_pinfo *np = inet6_sk(sk);
293 struct inet6_timewait_sock *tw6;
295 tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
296 tw6 = inet6_twsk((struct sock *)tw);
297 tw6->tw_v6_daddr = np->daddr;
298 tw6->tw_v6_rcv_saddr = np->rcv_saddr;
299 tw->tw_tclass = np->tclass;
300 tw->tw_ipv6only = np->ipv6only;
304 #ifdef CONFIG_TCP_MD5SIG
306 * The timewait bucket does not have the key DB from the
307 * sock structure. We just make a quick copy of the
308 * md5 key being used (if indeed we are using one)
309 * so the timewait ack generating code has the key.
312 struct tcp_md5sig_key *key;
313 tcptw->tw_md5_key = NULL;
314 key = tp->af_specific->md5_lookup(sk, sk);
316 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
317 if (tcptw->tw_md5_key && tcp_alloc_md5sig_pool(sk) == NULL)
323 /* Linkage updates. */
324 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
326 /* Get the TIME_WAIT timeout firing. */
331 tw->tw_timeout = rto;
333 tw->tw_timeout = TCP_TIMEWAIT_LEN;
334 if (state == TCP_TIME_WAIT)
335 timeo = TCP_TIMEWAIT_LEN;
338 inet_twsk_schedule(tw, &tcp_death_row, timeo,
342 /* Sorry, if we're out of memory, just CLOSE this
343 * socket up. We've got bigger problems than
344 * non-graceful socket closings.
346 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
349 tcp_update_metrics(sk);
353 void tcp_twsk_destructor(struct sock *sk)
355 #ifdef CONFIG_TCP_MD5SIG
356 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
358 if (twsk->tw_md5_key) {
359 tcp_free_md5sig_pool();
360 kfree_rcu(twsk->tw_md5_key, rcu);
364 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
366 static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
367 struct request_sock *req)
369 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
372 /* This is not only more efficient than what we used to do, it eliminates
373 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
375 * Actually, we could lots of memory writes here. tp of listening
376 * socket contains all necessary default parameters.
378 struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
380 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
383 const struct inet_request_sock *ireq = inet_rsk(req);
384 struct tcp_request_sock *treq = tcp_rsk(req);
385 struct inet_connection_sock *newicsk = inet_csk(newsk);
386 struct tcp_sock *newtp = tcp_sk(newsk);
387 struct tcp_sock *oldtp = tcp_sk(sk);
388 struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
390 /* TCP Cookie Transactions require space for the cookie pair,
391 * as it differs for each connection. There is no need to
392 * copy any s_data_payload stored at the original socket.
393 * Failure will prevent resuming the connection.
395 * Presumed copied, in order of appearance:
396 * cookie_in_always, cookie_out_never
398 if (oldcvp != NULL) {
399 struct tcp_cookie_values *newcvp =
400 kzalloc(sizeof(*newtp->cookie_values),
403 if (newcvp != NULL) {
404 kref_init(&newcvp->kref);
405 newcvp->cookie_desired =
406 oldcvp->cookie_desired;
407 newtp->cookie_values = newcvp;
409 /* Not Yet Implemented */
410 newtp->cookie_values = NULL;
414 /* Now setup tcp_sock */
415 newtp->pred_flags = 0;
417 newtp->rcv_wup = newtp->copied_seq =
418 newtp->rcv_nxt = treq->rcv_isn + 1;
420 newtp->snd_sml = newtp->snd_una =
421 newtp->snd_nxt = newtp->snd_up =
422 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
424 tcp_prequeue_init(newtp);
425 INIT_LIST_HEAD(&newtp->tsq_node);
427 tcp_init_wl(newtp, treq->rcv_isn);
430 newtp->mdev = TCP_TIMEOUT_INIT;
431 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
433 newtp->packets_out = 0;
434 newtp->retrans_out = 0;
435 newtp->sacked_out = 0;
436 newtp->fackets_out = 0;
437 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
438 tcp_enable_early_retrans(newtp);
440 /* So many TCP implementations out there (incorrectly) count the
441 * initial SYN frame in their delayed-ACK and congestion control
442 * algorithms that we must have the following bandaid to talk
443 * efficiently to them. -DaveM
445 newtp->snd_cwnd = TCP_INIT_CWND;
446 newtp->snd_cwnd_cnt = 0;
447 newtp->bytes_acked = 0;
449 newtp->frto_counter = 0;
450 newtp->frto_highmark = 0;
452 if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
453 !try_module_get(newicsk->icsk_ca_ops->owner))
454 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
456 tcp_set_ca_state(newsk, TCP_CA_Open);
457 tcp_init_xmit_timers(newsk);
458 skb_queue_head_init(&newtp->out_of_order_queue);
459 newtp->write_seq = newtp->pushed_seq =
460 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
462 newtp->rx_opt.saw_tstamp = 0;
464 newtp->rx_opt.dsack = 0;
465 newtp->rx_opt.num_sacks = 0;
469 if (sock_flag(newsk, SOCK_KEEPOPEN))
470 inet_csk_reset_keepalive_timer(newsk,
471 keepalive_time_when(newtp));
473 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
474 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
476 tcp_enable_fack(newtp);
478 newtp->window_clamp = req->window_clamp;
479 newtp->rcv_ssthresh = req->rcv_wnd;
480 newtp->rcv_wnd = req->rcv_wnd;
481 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
482 if (newtp->rx_opt.wscale_ok) {
483 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
484 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
486 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
487 newtp->window_clamp = min(newtp->window_clamp, 65535U);
489 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
490 newtp->rx_opt.snd_wscale);
491 newtp->max_window = newtp->snd_wnd;
493 if (newtp->rx_opt.tstamp_ok) {
494 newtp->rx_opt.ts_recent = req->ts_recent;
495 newtp->rx_opt.ts_recent_stamp = get_seconds();
496 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
498 newtp->rx_opt.ts_recent_stamp = 0;
499 newtp->tcp_header_len = sizeof(struct tcphdr);
501 #ifdef CONFIG_TCP_MD5SIG
502 newtp->md5sig_info = NULL; /*XXX*/
503 if (newtp->af_specific->md5_lookup(sk, newsk))
504 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
506 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
507 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
508 newtp->rx_opt.mss_clamp = req->mss;
509 TCP_ECN_openreq_child(newtp, req);
511 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
515 EXPORT_SYMBOL(tcp_create_openreq_child);
518 * Process an incoming packet for SYN_RECV sockets represented
522 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
523 struct request_sock *req,
524 struct request_sock **prev)
526 struct tcp_options_received tmp_opt;
527 const u8 *hash_location;
529 const struct tcphdr *th = tcp_hdr(skb);
530 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
531 bool paws_reject = false;
533 tmp_opt.saw_tstamp = 0;
534 if (th->doff > (sizeof(struct tcphdr)>>2)) {
535 tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
537 if (tmp_opt.saw_tstamp) {
538 tmp_opt.ts_recent = req->ts_recent;
539 /* We do not store true stamp, but it is not required,
540 * it can be estimated (approximately)
543 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
544 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
548 /* Check for pure retransmitted SYN. */
549 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
550 flg == TCP_FLAG_SYN &&
553 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
554 * this case on figure 6 and figure 8, but formal
555 * protocol description says NOTHING.
556 * To be more exact, it says that we should send ACK,
557 * because this segment (at least, if it has no data)
560 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
561 * describe SYN-RECV state. All the description
562 * is wrong, we cannot believe to it and should
563 * rely only on common sense and implementation
566 * Enforce "SYN-ACK" according to figure 8, figure 6
567 * of RFC793, fixed by RFC1122.
569 req->rsk_ops->rtx_syn_ack(sk, req, NULL);
573 /* Further reproduces section "SEGMENT ARRIVES"
574 for state SYN-RECEIVED of RFC793.
575 It is broken, however, it does not work only
576 when SYNs are crossed.
578 You would think that SYN crossing is impossible here, since
579 we should have a SYN_SENT socket (from connect()) on our end,
580 but this is not true if the crossed SYNs were sent to both
581 ends by a malicious third party. We must defend against this,
582 and to do that we first verify the ACK (as per RFC793, page
583 36) and reset if it is invalid. Is this a true full defense?
584 To convince ourselves, let us consider a way in which the ACK
585 test can still pass in this 'malicious crossed SYNs' case.
586 Malicious sender sends identical SYNs (and thus identical sequence
587 numbers) to both A and B:
592 By our good fortune, both A and B select the same initial
593 send sequence number of seven :-)
595 A: sends SYN|ACK, seq=7, ack_seq=8
596 B: sends SYN|ACK, seq=7, ack_seq=8
598 So we are now A eating this SYN|ACK, ACK test passes. So
599 does sequence test, SYN is truncated, and thus we consider
602 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
603 bare ACK. Otherwise, we create an established connection. Both
604 ends (listening sockets) accept the new incoming connection and try
605 to talk to each other. 8-)
607 Note: This case is both harmless, and rare. Possibility is about the
608 same as us discovering intelligent life on another plant tomorrow.
610 But generally, we should (RFC lies!) to accept ACK
611 from SYNACK both here and in tcp_rcv_state_process().
612 tcp_rcv_state_process() does not, hence, we do not too.
614 Note that the case is absolutely generic:
615 we cannot optimize anything here without
616 violating protocol. All the checks must be made
617 before attempt to create socket.
620 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
621 * and the incoming segment acknowledges something not yet
622 * sent (the segment carries an unacceptable ACK) ...
625 * Invalid ACK: reset will be sent by listening socket
627 if ((flg & TCP_FLAG_ACK) &&
628 (TCP_SKB_CB(skb)->ack_seq !=
629 tcp_rsk(req)->snt_isn + 1 + tcp_s_data_size(tcp_sk(sk))))
632 /* Also, it would be not so bad idea to check rcv_tsecr, which
633 * is essentially ACK extension and too early or too late values
634 * should cause reset in unsynchronized states.
637 /* RFC793: "first check sequence number". */
639 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
640 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) {
641 /* Out of window: send ACK and drop. */
642 if (!(flg & TCP_FLAG_RST))
643 req->rsk_ops->send_ack(sk, skb, req);
645 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
649 /* In sequence, PAWS is OK. */
651 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1))
652 req->ts_recent = tmp_opt.rcv_tsval;
654 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
655 /* Truncate SYN, it is out of window starting
656 at tcp_rsk(req)->rcv_isn + 1. */
657 flg &= ~TCP_FLAG_SYN;
660 /* RFC793: "second check the RST bit" and
661 * "fourth, check the SYN bit"
663 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
664 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
665 goto embryonic_reset;
668 /* ACK sequence verified above, just make sure ACK is
669 * set. If ACK not set, just silently drop the packet.
671 if (!(flg & TCP_FLAG_ACK))
674 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
675 if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
676 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
677 inet_rsk(req)->acked = 1;
678 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
681 if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
682 tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
683 else if (req->retrans) /* don't take RTT sample if retrans && ~TS */
684 tcp_rsk(req)->snt_synack = 0;
686 /* OK, ACK is valid, create big socket and
687 * feed this segment to it. It will repeat all
688 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
689 * ESTABLISHED STATE. If it will be dropped after
690 * socket is created, wait for troubles.
692 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
694 goto listen_overflow;
696 inet_csk_reqsk_queue_unlink(sk, req, prev);
697 inet_csk_reqsk_queue_removed(sk, req);
699 inet_csk_reqsk_queue_add(sk, req, child);
703 if (!sysctl_tcp_abort_on_overflow) {
704 inet_rsk(req)->acked = 1;
709 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
710 if (!(flg & TCP_FLAG_RST))
711 req->rsk_ops->send_reset(sk, skb);
713 inet_csk_reqsk_queue_drop(sk, req, prev);
716 EXPORT_SYMBOL(tcp_check_req);
719 * Queue segment on the new socket if the new socket is active,
720 * otherwise we just shortcircuit this and continue with
724 int tcp_child_process(struct sock *parent, struct sock *child,
728 int state = child->sk_state;
730 if (!sock_owned_by_user(child)) {
731 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
733 /* Wakeup parent, send SIGIO */
734 if (state == TCP_SYN_RECV && child->sk_state != state)
735 parent->sk_data_ready(parent, 0);
737 /* Alas, it is possible again, because we do lookup
738 * in main socket hash table and lock on listening
739 * socket does not protect us more.
741 __sk_add_backlog(child, skb);
744 bh_unlock_sock(child);
748 EXPORT_SYMBOL(tcp_child_process);