Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ryusuke...
[linux-2.6/mini2440.git] / net / ipv4 / tcp_minisocks.c
blob4c03598ed9248f29fa721b4a3473fca83b21b18f
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.
6 * Implementation of the Transmission Control Protocol(TCP).
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>
21 #include <linux/mm.h>
22 #include <linux/module.h>
23 #include <linux/sysctl.h>
24 #include <linux/workqueue.h>
25 #include <net/tcp.h>
26 #include <net/inet_common.h>
27 #include <net/xfrm.h>
29 #ifdef CONFIG_SYSCTL
30 #define SYNC_INIT 0 /* let the user enable it */
31 #else
32 #define SYNC_INIT 1
33 #endif
35 int sysctl_tcp_syncookies __read_mostly = SYNC_INIT;
36 EXPORT_SYMBOL(sysctl_tcp_syncookies);
38 int sysctl_tcp_abort_on_overflow __read_mostly;
40 struct inet_timewait_death_row tcp_death_row = {
41 .sysctl_max_tw_buckets = NR_FILE * 2,
42 .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
43 .death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
44 .hashinfo = &tcp_hashinfo,
45 .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
46 (unsigned long)&tcp_death_row),
47 .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
48 inet_twdr_twkill_work),
49 /* Short-time timewait calendar */
51 .twcal_hand = -1,
52 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
53 (unsigned long)&tcp_death_row),
56 EXPORT_SYMBOL_GPL(tcp_death_row);
58 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
60 if (seq == s_win)
61 return 1;
62 if (after(end_seq, s_win) && before(seq, e_win))
63 return 1;
64 return (seq == e_win && seq == end_seq);
68 * * Main purpose of TIME-WAIT state is to close connection gracefully,
69 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
70 * (and, probably, tail of data) and one or more our ACKs are lost.
71 * * What is TIME-WAIT timeout? It is associated with maximal packet
72 * lifetime in the internet, which results in wrong conclusion, that
73 * it is set to catch "old duplicate segments" wandering out of their path.
74 * It is not quite correct. This timeout is calculated so that it exceeds
75 * maximal retransmission timeout enough to allow to lose one (or more)
76 * segments sent by peer and our ACKs. This time may be calculated from RTO.
77 * * When TIME-WAIT socket receives RST, it means that another end
78 * finally closed and we are allowed to kill TIME-WAIT too.
79 * * Second purpose of TIME-WAIT is catching old duplicate segments.
80 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
81 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
82 * * If we invented some more clever way to catch duplicates
83 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
85 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
86 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
87 * from the very beginning.
89 * NOTE. With recycling (and later with fin-wait-2) TW bucket
90 * is _not_ stateless. It means, that strictly speaking we must
91 * spinlock it. I do not want! Well, probability of misbehaviour
92 * is ridiculously low and, seems, we could use some mb() tricks
93 * to avoid misread sequence numbers, states etc. --ANK
95 enum tcp_tw_status
96 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
97 const struct tcphdr *th)
99 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
100 struct tcp_options_received tmp_opt;
101 int paws_reject = 0;
103 tmp_opt.saw_tstamp = 0;
104 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
105 tcp_parse_options(skb, &tmp_opt, 0);
107 if (tmp_opt.saw_tstamp) {
108 tmp_opt.ts_recent = tcptw->tw_ts_recent;
109 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
110 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
114 if (tw->tw_substate == TCP_FIN_WAIT2) {
115 /* Just repeat all the checks of tcp_rcv_state_process() */
117 /* Out of window, send ACK */
118 if (paws_reject ||
119 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
120 tcptw->tw_rcv_nxt,
121 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
122 return TCP_TW_ACK;
124 if (th->rst)
125 goto kill;
127 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
128 goto kill_with_rst;
130 /* Dup ACK? */
131 if (!th->ack ||
132 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
133 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
134 inet_twsk_put(tw);
135 return TCP_TW_SUCCESS;
138 /* New data or FIN. If new data arrive after half-duplex close,
139 * reset.
141 if (!th->fin ||
142 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
143 kill_with_rst:
144 inet_twsk_deschedule(tw, &tcp_death_row);
145 inet_twsk_put(tw);
146 return TCP_TW_RST;
149 /* FIN arrived, enter true time-wait state. */
150 tw->tw_substate = TCP_TIME_WAIT;
151 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
152 if (tmp_opt.saw_tstamp) {
153 tcptw->tw_ts_recent_stamp = get_seconds();
154 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
157 /* I am shamed, but failed to make it more elegant.
158 * Yes, it is direct reference to IP, which is impossible
159 * to generalize to IPv6. Taking into account that IPv6
160 * do not understand recycling in any case, it not
161 * a big problem in practice. --ANK */
162 if (tw->tw_family == AF_INET &&
163 tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp &&
164 tcp_v4_tw_remember_stamp(tw))
165 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
166 TCP_TIMEWAIT_LEN);
167 else
168 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
169 TCP_TIMEWAIT_LEN);
170 return TCP_TW_ACK;
174 * Now real TIME-WAIT state.
176 * RFC 1122:
177 * "When a connection is [...] on TIME-WAIT state [...]
178 * [a TCP] MAY accept a new SYN from the remote TCP to
179 * reopen the connection directly, if it:
181 * (1) assigns its initial sequence number for the new
182 * connection to be larger than the largest sequence
183 * number it used on the previous connection incarnation,
184 * and
186 * (2) returns to TIME-WAIT state if the SYN turns out
187 * to be an old duplicate".
190 if (!paws_reject &&
191 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
192 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
193 /* In window segment, it may be only reset or bare ack. */
195 if (th->rst) {
196 /* This is TIME_WAIT assassination, in two flavors.
197 * Oh well... nobody has a sufficient solution to this
198 * protocol bug yet.
200 if (sysctl_tcp_rfc1337 == 0) {
201 kill:
202 inet_twsk_deschedule(tw, &tcp_death_row);
203 inet_twsk_put(tw);
204 return TCP_TW_SUCCESS;
207 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
208 TCP_TIMEWAIT_LEN);
210 if (tmp_opt.saw_tstamp) {
211 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
212 tcptw->tw_ts_recent_stamp = get_seconds();
215 inet_twsk_put(tw);
216 return TCP_TW_SUCCESS;
219 /* Out of window segment.
221 All the segments are ACKed immediately.
223 The only exception is new SYN. We accept it, if it is
224 not old duplicate and we are not in danger to be killed
225 by delayed old duplicates. RFC check is that it has
226 newer sequence number works at rates <40Mbit/sec.
227 However, if paws works, it is reliable AND even more,
228 we even may relax silly seq space cutoff.
230 RED-PEN: we violate main RFC requirement, if this SYN will appear
231 old duplicate (i.e. we receive RST in reply to SYN-ACK),
232 we must return socket to time-wait state. It is not good,
233 but not fatal yet.
236 if (th->syn && !th->rst && !th->ack && !paws_reject &&
237 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
238 (tmp_opt.saw_tstamp &&
239 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
240 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
241 if (isn == 0)
242 isn++;
243 TCP_SKB_CB(skb)->when = isn;
244 return TCP_TW_SYN;
247 if (paws_reject)
248 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
250 if (!th->rst) {
251 /* In this case we must reset the TIMEWAIT timer.
253 * If it is ACKless SYN it may be both old duplicate
254 * and new good SYN with random sequence number <rcv_nxt.
255 * Do not reschedule in the last case.
257 if (paws_reject || th->ack)
258 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
259 TCP_TIMEWAIT_LEN);
261 /* Send ACK. Note, we do not put the bucket,
262 * it will be released by caller.
264 return TCP_TW_ACK;
266 inet_twsk_put(tw);
267 return TCP_TW_SUCCESS;
271 * Move a socket to time-wait or dead fin-wait-2 state.
273 void tcp_time_wait(struct sock *sk, int state, int timeo)
275 struct inet_timewait_sock *tw = NULL;
276 const struct inet_connection_sock *icsk = inet_csk(sk);
277 const struct tcp_sock *tp = tcp_sk(sk);
278 int recycle_ok = 0;
280 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
281 recycle_ok = icsk->icsk_af_ops->remember_stamp(sk);
283 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
284 tw = inet_twsk_alloc(sk, state);
286 if (tw != NULL) {
287 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
288 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
290 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
291 tcptw->tw_rcv_nxt = tp->rcv_nxt;
292 tcptw->tw_snd_nxt = tp->snd_nxt;
293 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
294 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
295 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
297 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
298 if (tw->tw_family == PF_INET6) {
299 struct ipv6_pinfo *np = inet6_sk(sk);
300 struct inet6_timewait_sock *tw6;
302 tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
303 tw6 = inet6_twsk((struct sock *)tw);
304 ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr);
305 ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr);
306 tw->tw_ipv6only = np->ipv6only;
308 #endif
310 #ifdef CONFIG_TCP_MD5SIG
312 * The timewait bucket does not have the key DB from the
313 * sock structure. We just make a quick copy of the
314 * md5 key being used (if indeed we are using one)
315 * so the timewait ack generating code has the key.
317 do {
318 struct tcp_md5sig_key *key;
319 memset(tcptw->tw_md5_key, 0, sizeof(tcptw->tw_md5_key));
320 tcptw->tw_md5_keylen = 0;
321 key = tp->af_specific->md5_lookup(sk, sk);
322 if (key != NULL) {
323 memcpy(&tcptw->tw_md5_key, key->key, key->keylen);
324 tcptw->tw_md5_keylen = key->keylen;
325 if (tcp_alloc_md5sig_pool(sk) == NULL)
326 BUG();
328 } while (0);
329 #endif
331 /* Linkage updates. */
332 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
334 /* Get the TIME_WAIT timeout firing. */
335 if (timeo < rto)
336 timeo = rto;
338 if (recycle_ok) {
339 tw->tw_timeout = rto;
340 } else {
341 tw->tw_timeout = TCP_TIMEWAIT_LEN;
342 if (state == TCP_TIME_WAIT)
343 timeo = TCP_TIMEWAIT_LEN;
346 inet_twsk_schedule(tw, &tcp_death_row, timeo,
347 TCP_TIMEWAIT_LEN);
348 inet_twsk_put(tw);
349 } else {
350 /* Sorry, if we're out of memory, just CLOSE this
351 * socket up. We've got bigger problems than
352 * non-graceful socket closings.
354 LIMIT_NETDEBUG(KERN_INFO "TCP: time wait bucket table overflow\n");
357 tcp_update_metrics(sk);
358 tcp_done(sk);
361 void tcp_twsk_destructor(struct sock *sk)
363 #ifdef CONFIG_TCP_MD5SIG
364 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
365 if (twsk->tw_md5_keylen)
366 tcp_free_md5sig_pool();
367 #endif
370 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
372 static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
373 struct request_sock *req)
375 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
378 /* This is not only more efficient than what we used to do, it eliminates
379 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
381 * Actually, we could lots of memory writes here. tp of listening
382 * socket contains all necessary default parameters.
384 struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
386 struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC);
388 if (newsk != NULL) {
389 const struct inet_request_sock *ireq = inet_rsk(req);
390 struct tcp_request_sock *treq = tcp_rsk(req);
391 struct inet_connection_sock *newicsk = inet_csk(newsk);
392 struct tcp_sock *newtp;
394 /* Now setup tcp_sock */
395 newtp = tcp_sk(newsk);
396 newtp->pred_flags = 0;
397 newtp->rcv_wup = newtp->copied_seq = newtp->rcv_nxt = treq->rcv_isn + 1;
398 newtp->snd_sml = newtp->snd_una = newtp->snd_nxt = treq->snt_isn + 1;
399 newtp->snd_up = treq->snt_isn + 1;
401 tcp_prequeue_init(newtp);
403 tcp_init_wl(newtp, treq->rcv_isn);
405 newtp->srtt = 0;
406 newtp->mdev = TCP_TIMEOUT_INIT;
407 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
409 newtp->packets_out = 0;
410 newtp->retrans_out = 0;
411 newtp->sacked_out = 0;
412 newtp->fackets_out = 0;
413 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
415 /* So many TCP implementations out there (incorrectly) count the
416 * initial SYN frame in their delayed-ACK and congestion control
417 * algorithms that we must have the following bandaid to talk
418 * efficiently to them. -DaveM
420 newtp->snd_cwnd = 2;
421 newtp->snd_cwnd_cnt = 0;
422 newtp->bytes_acked = 0;
424 newtp->frto_counter = 0;
425 newtp->frto_highmark = 0;
427 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
429 tcp_set_ca_state(newsk, TCP_CA_Open);
430 tcp_init_xmit_timers(newsk);
431 skb_queue_head_init(&newtp->out_of_order_queue);
432 newtp->write_seq = treq->snt_isn + 1;
433 newtp->pushed_seq = newtp->write_seq;
435 newtp->rx_opt.saw_tstamp = 0;
437 newtp->rx_opt.dsack = 0;
438 newtp->rx_opt.num_sacks = 0;
440 newtp->urg_data = 0;
442 if (sock_flag(newsk, SOCK_KEEPOPEN))
443 inet_csk_reset_keepalive_timer(newsk,
444 keepalive_time_when(newtp));
446 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
447 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
448 if (sysctl_tcp_fack)
449 tcp_enable_fack(newtp);
451 newtp->window_clamp = req->window_clamp;
452 newtp->rcv_ssthresh = req->rcv_wnd;
453 newtp->rcv_wnd = req->rcv_wnd;
454 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
455 if (newtp->rx_opt.wscale_ok) {
456 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
457 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
458 } else {
459 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
460 newtp->window_clamp = min(newtp->window_clamp, 65535U);
462 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
463 newtp->rx_opt.snd_wscale);
464 newtp->max_window = newtp->snd_wnd;
466 if (newtp->rx_opt.tstamp_ok) {
467 newtp->rx_opt.ts_recent = req->ts_recent;
468 newtp->rx_opt.ts_recent_stamp = get_seconds();
469 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
470 } else {
471 newtp->rx_opt.ts_recent_stamp = 0;
472 newtp->tcp_header_len = sizeof(struct tcphdr);
474 #ifdef CONFIG_TCP_MD5SIG
475 newtp->md5sig_info = NULL; /*XXX*/
476 if (newtp->af_specific->md5_lookup(sk, newsk))
477 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
478 #endif
479 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len)
480 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
481 newtp->rx_opt.mss_clamp = req->mss;
482 TCP_ECN_openreq_child(newtp, req);
484 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
486 return newsk;
490 * Process an incoming packet for SYN_RECV sockets represented
491 * as a request_sock.
494 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
495 struct request_sock *req,
496 struct request_sock **prev)
498 const struct tcphdr *th = tcp_hdr(skb);
499 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
500 int paws_reject = 0;
501 struct tcp_options_received tmp_opt;
502 struct sock *child;
504 tmp_opt.saw_tstamp = 0;
505 if (th->doff > (sizeof(struct tcphdr)>>2)) {
506 tcp_parse_options(skb, &tmp_opt, 0);
508 if (tmp_opt.saw_tstamp) {
509 tmp_opt.ts_recent = req->ts_recent;
510 /* We do not store true stamp, but it is not required,
511 * it can be estimated (approximately)
512 * from another data.
514 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
515 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
519 /* Check for pure retransmitted SYN. */
520 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
521 flg == TCP_FLAG_SYN &&
522 !paws_reject) {
524 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
525 * this case on figure 6 and figure 8, but formal
526 * protocol description says NOTHING.
527 * To be more exact, it says that we should send ACK,
528 * because this segment (at least, if it has no data)
529 * is out of window.
531 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
532 * describe SYN-RECV state. All the description
533 * is wrong, we cannot believe to it and should
534 * rely only on common sense and implementation
535 * experience.
537 * Enforce "SYN-ACK" according to figure 8, figure 6
538 * of RFC793, fixed by RFC1122.
540 req->rsk_ops->rtx_syn_ack(sk, req);
541 return NULL;
544 /* Further reproduces section "SEGMENT ARRIVES"
545 for state SYN-RECEIVED of RFC793.
546 It is broken, however, it does not work only
547 when SYNs are crossed.
549 You would think that SYN crossing is impossible here, since
550 we should have a SYN_SENT socket (from connect()) on our end,
551 but this is not true if the crossed SYNs were sent to both
552 ends by a malicious third party. We must defend against this,
553 and to do that we first verify the ACK (as per RFC793, page
554 36) and reset if it is invalid. Is this a true full defense?
555 To convince ourselves, let us consider a way in which the ACK
556 test can still pass in this 'malicious crossed SYNs' case.
557 Malicious sender sends identical SYNs (and thus identical sequence
558 numbers) to both A and B:
560 A: gets SYN, seq=7
561 B: gets SYN, seq=7
563 By our good fortune, both A and B select the same initial
564 send sequence number of seven :-)
566 A: sends SYN|ACK, seq=7, ack_seq=8
567 B: sends SYN|ACK, seq=7, ack_seq=8
569 So we are now A eating this SYN|ACK, ACK test passes. So
570 does sequence test, SYN is truncated, and thus we consider
571 it a bare ACK.
573 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
574 bare ACK. Otherwise, we create an established connection. Both
575 ends (listening sockets) accept the new incoming connection and try
576 to talk to each other. 8-)
578 Note: This case is both harmless, and rare. Possibility is about the
579 same as us discovering intelligent life on another plant tomorrow.
581 But generally, we should (RFC lies!) to accept ACK
582 from SYNACK both here and in tcp_rcv_state_process().
583 tcp_rcv_state_process() does not, hence, we do not too.
585 Note that the case is absolutely generic:
586 we cannot optimize anything here without
587 violating protocol. All the checks must be made
588 before attempt to create socket.
591 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
592 * and the incoming segment acknowledges something not yet
593 * sent (the segment carries an unacceptable ACK) ...
594 * a reset is sent."
596 * Invalid ACK: reset will be sent by listening socket
598 if ((flg & TCP_FLAG_ACK) &&
599 (TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1))
600 return sk;
602 /* Also, it would be not so bad idea to check rcv_tsecr, which
603 * is essentially ACK extension and too early or too late values
604 * should cause reset in unsynchronized states.
607 /* RFC793: "first check sequence number". */
609 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
610 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) {
611 /* Out of window: send ACK and drop. */
612 if (!(flg & TCP_FLAG_RST))
613 req->rsk_ops->send_ack(sk, skb, req);
614 if (paws_reject)
615 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
616 return NULL;
619 /* In sequence, PAWS is OK. */
621 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1))
622 req->ts_recent = tmp_opt.rcv_tsval;
624 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
625 /* Truncate SYN, it is out of window starting
626 at tcp_rsk(req)->rcv_isn + 1. */
627 flg &= ~TCP_FLAG_SYN;
630 /* RFC793: "second check the RST bit" and
631 * "fourth, check the SYN bit"
633 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
634 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
635 goto embryonic_reset;
638 /* ACK sequence verified above, just make sure ACK is
639 * set. If ACK not set, just silently drop the packet.
641 if (!(flg & TCP_FLAG_ACK))
642 return NULL;
644 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
645 if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
646 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
647 inet_rsk(req)->acked = 1;
648 return NULL;
651 /* OK, ACK is valid, create big socket and
652 * feed this segment to it. It will repeat all
653 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
654 * ESTABLISHED STATE. If it will be dropped after
655 * socket is created, wait for troubles.
657 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
658 if (child == NULL)
659 goto listen_overflow;
661 inet_csk_reqsk_queue_unlink(sk, req, prev);
662 inet_csk_reqsk_queue_removed(sk, req);
664 inet_csk_reqsk_queue_add(sk, req, child);
665 return child;
667 listen_overflow:
668 if (!sysctl_tcp_abort_on_overflow) {
669 inet_rsk(req)->acked = 1;
670 return NULL;
673 embryonic_reset:
674 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
675 if (!(flg & TCP_FLAG_RST))
676 req->rsk_ops->send_reset(sk, skb);
678 inet_csk_reqsk_queue_drop(sk, req, prev);
679 return NULL;
683 * Queue segment on the new socket if the new socket is active,
684 * otherwise we just shortcircuit this and continue with
685 * the new socket.
688 int tcp_child_process(struct sock *parent, struct sock *child,
689 struct sk_buff *skb)
691 int ret = 0;
692 int state = child->sk_state;
694 if (!sock_owned_by_user(child)) {
695 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
696 skb->len);
697 /* Wakeup parent, send SIGIO */
698 if (state == TCP_SYN_RECV && child->sk_state != state)
699 parent->sk_data_ready(parent, 0);
700 } else {
701 /* Alas, it is possible again, because we do lookup
702 * in main socket hash table and lock on listening
703 * socket does not protect us more.
705 sk_add_backlog(child, skb);
708 bh_unlock_sock(child);
709 sock_put(child);
710 return ret;
713 EXPORT_SYMBOL(tcp_check_req);
714 EXPORT_SYMBOL(tcp_child_process);
715 EXPORT_SYMBOL(tcp_create_openreq_child);
716 EXPORT_SYMBOL(tcp_timewait_state_process);