rxrpc: Fix several cases where a padded len isn't checked in ticket decode
[GitHub/mt8127/android_kernel_alcatel_ttab.git] / net / ipv4 / tcp_minisocks.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 #include <linux/mm.h>
22 #include <linux/module.h>
23 #include <linux/slab.h>
24 #include <linux/sysctl.h>
25 #include <linux/workqueue.h>
26 #include <net/tcp.h>
27 #include <net/inet_common.h>
28 #include <net/xfrm.h>
29
30 int sysctl_tcp_syncookies __read_mostly = 1;
31 EXPORT_SYMBOL(sysctl_tcp_syncookies);
32
33 int sysctl_tcp_abort_on_overflow __read_mostly;
34
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 */
45
46 .twcal_hand = -1,
47 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
48 (unsigned long)&tcp_death_row),
49 };
50 EXPORT_SYMBOL_GPL(tcp_death_row);
51
52 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
53 {
54 if (seq == s_win)
55 return true;
56 if (after(end_seq, s_win) && before(seq, e_win))
57 return true;
58 return seq == e_win && seq == end_seq;
59 }
60
61 /*
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.
78 *
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.
82 *
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
88 *
89 * We don't need to initialize tmp_out.sack_ok as we don't use the results
90 */
91 enum tcp_tw_status
92 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
93 const struct tcphdr *th)
94 {
95 struct tcp_options_received tmp_opt;
96 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
97 bool paws_reject = false;
98
99 tmp_opt.saw_tstamp = 0;
100 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
101 tcp_parse_options(skb, &tmp_opt, 0, NULL);
102
103 if (tmp_opt.saw_tstamp) {
104 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
105 tmp_opt.ts_recent = tcptw->tw_ts_recent;
106 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
107 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
108 }
109 }
110
111 if (tw->tw_substate == TCP_FIN_WAIT2) {
112 /* Just repeat all the checks of tcp_rcv_state_process() */
113
114 /* Out of window, send ACK */
115 if (paws_reject ||
116 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
117 tcptw->tw_rcv_nxt,
118 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
119 return TCP_TW_ACK;
120
121 if (th->rst)
122 goto kill;
123
124 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
125 goto kill_with_rst;
126
127 /* Dup ACK? */
128 if (!th->ack ||
129 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
130 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
131 inet_twsk_put(tw);
132 return TCP_TW_SUCCESS;
133 }
134
135 /* New data or FIN. If new data arrive after half-duplex close,
136 * reset.
137 */
138 if (!th->fin ||
139 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
140 kill_with_rst:
141 inet_twsk_deschedule(tw, &tcp_death_row);
142 inet_twsk_put(tw);
143 return TCP_TW_RST;
144 }
145
146 /* FIN arrived, enter true time-wait state. */
147 tw->tw_substate = TCP_TIME_WAIT;
148 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
149 if (tmp_opt.saw_tstamp) {
150 tcptw->tw_ts_recent_stamp = get_seconds();
151 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
152 }
153
154 if (tcp_death_row.sysctl_tw_recycle &&
155 tcptw->tw_ts_recent_stamp &&
156 tcp_tw_remember_stamp(tw))
157 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
158 TCP_TIMEWAIT_LEN);
159 else
160 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
161 TCP_TIMEWAIT_LEN);
162 return TCP_TW_ACK;
163 }
164
165 /*
166 * Now real TIME-WAIT state.
167 *
168 * RFC 1122:
169 * "When a connection is [...] on TIME-WAIT state [...]
170 * [a TCP] MAY accept a new SYN from the remote TCP to
171 * reopen the connection directly, if it:
172 *
173 * (1) assigns its initial sequence number for the new
174 * connection to be larger than the largest sequence
175 * number it used on the previous connection incarnation,
176 * and
177 *
178 * (2) returns to TIME-WAIT state if the SYN turns out
179 * to be an old duplicate".
180 */
181
182 if (!paws_reject &&
183 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
184 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
185 /* In window segment, it may be only reset or bare ack. */
186
187 if (th->rst) {
188 /* This is TIME_WAIT assassination, in two flavors.
189 * Oh well... nobody has a sufficient solution to this
190 * protocol bug yet.
191 */
192 if (sysctl_tcp_rfc1337 == 0) {
193 kill:
194 inet_twsk_deschedule(tw, &tcp_death_row);
195 inet_twsk_put(tw);
196 return TCP_TW_SUCCESS;
197 }
198 }
199 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
200 TCP_TIMEWAIT_LEN);
201
202 if (tmp_opt.saw_tstamp) {
203 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
204 tcptw->tw_ts_recent_stamp = get_seconds();
205 }
206
207 inet_twsk_put(tw);
208 return TCP_TW_SUCCESS;
209 }
210
211 /* Out of window segment.
212
213 All the segments are ACKed immediately.
214
215 The only exception is new SYN. We accept it, if it is
216 not old duplicate and we are not in danger to be killed
217 by delayed old duplicates. RFC check is that it has
218 newer sequence number works at rates <40Mbit/sec.
219 However, if paws works, it is reliable AND even more,
220 we even may relax silly seq space cutoff.
221
222 RED-PEN: we violate main RFC requirement, if this SYN will appear
223 old duplicate (i.e. we receive RST in reply to SYN-ACK),
224 we must return socket to time-wait state. It is not good,
225 but not fatal yet.
226 */
227
228 if (th->syn && !th->rst && !th->ack && !paws_reject &&
229 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
230 (tmp_opt.saw_tstamp &&
231 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
232 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
233 if (isn == 0)
234 isn++;
235 TCP_SKB_CB(skb)->when = isn;
236 return TCP_TW_SYN;
237 }
238
239 if (paws_reject)
240 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
241
242 if (!th->rst) {
243 /* In this case we must reset the TIMEWAIT timer.
244 *
245 * If it is ACKless SYN it may be both old duplicate
246 * and new good SYN with random sequence number <rcv_nxt.
247 * Do not reschedule in the last case.
248 */
249 if (paws_reject || th->ack)
250 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
251 TCP_TIMEWAIT_LEN);
252
253 /* Send ACK. Note, we do not put the bucket,
254 * it will be released by caller.
255 */
256 return TCP_TW_ACK;
257 }
258 inet_twsk_put(tw);
259 return TCP_TW_SUCCESS;
260 }
261 EXPORT_SYMBOL(tcp_timewait_state_process);
262
263 /*
264 * Move a socket to time-wait or dead fin-wait-2 state.
265 */
266 void tcp_time_wait(struct sock *sk, int state, int timeo)
267 {
268 struct inet_timewait_sock *tw = NULL;
269 const struct inet_connection_sock *icsk = inet_csk(sk);
270 const struct tcp_sock *tp = tcp_sk(sk);
271 bool recycle_ok = false;
272
273 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
274 recycle_ok = tcp_remember_stamp(sk);
275
276 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
277 tw = inet_twsk_alloc(sk, state);
278
279 if (tw != NULL) {
280 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
281 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
282 struct inet_sock *inet = inet_sk(sk);
283
284 tw->tw_transparent = inet->transparent;
285 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
286 tcptw->tw_rcv_nxt = tp->rcv_nxt;
287 tcptw->tw_snd_nxt = tp->snd_nxt;
288 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
289 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
290 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
291 tcptw->tw_ts_offset = tp->tsoffset;
292
293 #if IS_ENABLED(CONFIG_IPV6)
294 if (tw->tw_family == PF_INET6) {
295 struct ipv6_pinfo *np = inet6_sk(sk);
296 struct inet6_timewait_sock *tw6;
297
298 tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
299 tw6 = inet6_twsk((struct sock *)tw);
300 tw6->tw_v6_daddr = np->daddr;
301 tw6->tw_v6_rcv_saddr = np->rcv_saddr;
302 tw->tw_tclass = np->tclass;
303 tw->tw_ipv6only = np->ipv6only;
304 }
305 #endif
306
307 #ifdef CONFIG_TCP_MD5SIG
308 /*
309 * The timewait bucket does not have the key DB from the
310 * sock structure. We just make a quick copy of the
311 * md5 key being used (if indeed we are using one)
312 * so the timewait ack generating code has the key.
313 */
314 do {
315 struct tcp_md5sig_key *key;
316 tcptw->tw_md5_key = NULL;
317 key = tp->af_specific->md5_lookup(sk, sk);
318 if (key != NULL) {
319 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
320 if (tcptw->tw_md5_key && tcp_alloc_md5sig_pool(sk) == NULL)
321 BUG();
322 }
323 } while (0);
324 #endif
325
326 /* Linkage updates. */
327 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
328
329 /* Get the TIME_WAIT timeout firing. */
330 if (timeo < rto)
331 timeo = rto;
332
333 if (recycle_ok) {
334 tw->tw_timeout = rto;
335 } else {
336 tw->tw_timeout = TCP_TIMEWAIT_LEN;
337 if (state == TCP_TIME_WAIT)
338 timeo = TCP_TIMEWAIT_LEN;
339 }
340
341 inet_twsk_schedule(tw, &tcp_death_row, timeo,
342 TCP_TIMEWAIT_LEN);
343 inet_twsk_put(tw);
344 } else {
345 /* Sorry, if we're out of memory, just CLOSE this
346 * socket up. We've got bigger problems than
347 * non-graceful socket closings.
348 */
349 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
350 }
351
352 tcp_update_metrics(sk);
353 tcp_done(sk);
354 }
355
356 void tcp_twsk_destructor(struct sock *sk)
357 {
358 #ifdef CONFIG_TCP_MD5SIG
359 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
360
361 if (twsk->tw_md5_key) {
362 tcp_free_md5sig_pool();
363 kfree_rcu(twsk->tw_md5_key, rcu);
364 }
365 #endif
366 }
367 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
368
369 static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
370 struct request_sock *req)
371 {
372 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
373 }
374
375 /* This is not only more efficient than what we used to do, it eliminates
376 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
377 *
378 * Actually, we could lots of memory writes here. tp of listening
379 * socket contains all necessary default parameters.
380 */
381 struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
382 {
383 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
384
385 if (newsk != NULL) {
386 const struct inet_request_sock *ireq = inet_rsk(req);
387 struct tcp_request_sock *treq = tcp_rsk(req);
388 struct inet_connection_sock *newicsk = inet_csk(newsk);
389 struct tcp_sock *newtp = tcp_sk(newsk);
390
391 /* Now setup tcp_sock */
392 newtp->pred_flags = 0;
393
394 newtp->rcv_wup = newtp->copied_seq =
395 newtp->rcv_nxt = treq->rcv_isn + 1;
396
397 newtp->snd_sml = newtp->snd_una =
398 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
399
400 tcp_prequeue_init(newtp);
401 INIT_LIST_HEAD(&newtp->tsq_node);
402
403 tcp_init_wl(newtp, treq->rcv_isn);
404
405 newtp->srtt = 0;
406 newtp->mdev = TCP_TIMEOUT_INIT;
407 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
408 newicsk->icsk_ack.lrcvtime = tcp_time_stamp;
409
410 newtp->packets_out = 0;
411 newtp->retrans_out = 0;
412 newtp->sacked_out = 0;
413 newtp->fackets_out = 0;
414 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
415 tcp_enable_early_retrans(newtp);
416 newtp->tlp_high_seq = 0;
417
418 /* So many TCP implementations out there (incorrectly) count the
419 * initial SYN frame in their delayed-ACK and congestion control
420 * algorithms that we must have the following bandaid to talk
421 * efficiently to them. -DaveM
422 */
423 newtp->snd_cwnd = TCP_INIT_CWND;
424 newtp->snd_cwnd_cnt = 0;
425
426 if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
427 !try_module_get(newicsk->icsk_ca_ops->owner))
428 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
429
430 tcp_set_ca_state(newsk, TCP_CA_Open);
431 tcp_init_xmit_timers(newsk);
432 skb_queue_head_init(&newtp->out_of_order_queue);
433 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
434
435 newtp->rx_opt.saw_tstamp = 0;
436
437 newtp->rx_opt.dsack = 0;
438 newtp->rx_opt.num_sacks = 0;
439
440 newtp->urg_data = 0;
441
442 if (sock_flag(newsk, SOCK_KEEPOPEN))
443 inet_csk_reset_keepalive_timer(newsk,
444 keepalive_time_when(newtp));
445
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);
450 }
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);
461 }
462 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
463 newtp->rx_opt.snd_wscale);
464 newtp->max_window = newtp->snd_wnd;
465
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);
473 }
474 newtp->tsoffset = 0;
475 #ifdef CONFIG_TCP_MD5SIG
476 newtp->md5sig_info = NULL; /*XXX*/
477 if (newtp->af_specific->md5_lookup(sk, newsk))
478 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
479 #endif
480 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
481 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
482 newtp->rx_opt.mss_clamp = req->mss;
483 TCP_ECN_openreq_child(newtp, req);
484 newtp->fastopen_rsk = NULL;
485 newtp->syn_data_acked = 0;
486
487 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
488 }
489 return newsk;
490 }
491 EXPORT_SYMBOL(tcp_create_openreq_child);
492
493 /*
494 * Process an incoming packet for SYN_RECV sockets represented as a
495 * request_sock. Normally sk is the listener socket but for TFO it
496 * points to the child socket.
497 *
498 * XXX (TFO) - The current impl contains a special check for ack
499 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
500 *
501 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
502 */
503
504 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
505 struct request_sock *req,
506 struct request_sock **prev,
507 bool fastopen)
508 {
509 struct tcp_options_received tmp_opt;
510 struct sock *child;
511 const struct tcphdr *th = tcp_hdr(skb);
512 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
513 bool paws_reject = false;
514
515 BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
516
517 tmp_opt.saw_tstamp = 0;
518 if (th->doff > (sizeof(struct tcphdr)>>2)) {
519 tcp_parse_options(skb, &tmp_opt, 0, NULL);
520
521 if (tmp_opt.saw_tstamp) {
522 tmp_opt.ts_recent = req->ts_recent;
523 /* We do not store true stamp, but it is not required,
524 * it can be estimated (approximately)
525 * from another data.
526 */
527 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
528 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
529 }
530 }
531
532 /* Check for pure retransmitted SYN. */
533 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
534 flg == TCP_FLAG_SYN &&
535 !paws_reject) {
536 /*
537 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
538 * this case on figure 6 and figure 8, but formal
539 * protocol description says NOTHING.
540 * To be more exact, it says that we should send ACK,
541 * because this segment (at least, if it has no data)
542 * is out of window.
543 *
544 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
545 * describe SYN-RECV state. All the description
546 * is wrong, we cannot believe to it and should
547 * rely only on common sense and implementation
548 * experience.
549 *
550 * Enforce "SYN-ACK" according to figure 8, figure 6
551 * of RFC793, fixed by RFC1122.
552 *
553 * Note that even if there is new data in the SYN packet
554 * they will be thrown away too.
555 *
556 * Reset timer after retransmitting SYNACK, similar to
557 * the idea of fast retransmit in recovery.
558 */
559 if (!inet_rtx_syn_ack(sk, req))
560 req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
561 TCP_RTO_MAX) + jiffies;
562 return NULL;
563 }
564
565 /* Further reproduces section "SEGMENT ARRIVES"
566 for state SYN-RECEIVED of RFC793.
567 It is broken, however, it does not work only
568 when SYNs are crossed.
569
570 You would think that SYN crossing is impossible here, since
571 we should have a SYN_SENT socket (from connect()) on our end,
572 but this is not true if the crossed SYNs were sent to both
573 ends by a malicious third party. We must defend against this,
574 and to do that we first verify the ACK (as per RFC793, page
575 36) and reset if it is invalid. Is this a true full defense?
576 To convince ourselves, let us consider a way in which the ACK
577 test can still pass in this 'malicious crossed SYNs' case.
578 Malicious sender sends identical SYNs (and thus identical sequence
579 numbers) to both A and B:
580
581 A: gets SYN, seq=7
582 B: gets SYN, seq=7
583
584 By our good fortune, both A and B select the same initial
585 send sequence number of seven :-)
586
587 A: sends SYN|ACK, seq=7, ack_seq=8
588 B: sends SYN|ACK, seq=7, ack_seq=8
589
590 So we are now A eating this SYN|ACK, ACK test passes. So
591 does sequence test, SYN is truncated, and thus we consider
592 it a bare ACK.
593
594 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
595 bare ACK. Otherwise, we create an established connection. Both
596 ends (listening sockets) accept the new incoming connection and try
597 to talk to each other. 8-)
598
599 Note: This case is both harmless, and rare. Possibility is about the
600 same as us discovering intelligent life on another plant tomorrow.
601
602 But generally, we should (RFC lies!) to accept ACK
603 from SYNACK both here and in tcp_rcv_state_process().
604 tcp_rcv_state_process() does not, hence, we do not too.
605
606 Note that the case is absolutely generic:
607 we cannot optimize anything here without
608 violating protocol. All the checks must be made
609 before attempt to create socket.
610 */
611
612 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
613 * and the incoming segment acknowledges something not yet
614 * sent (the segment carries an unacceptable ACK) ...
615 * a reset is sent."
616 *
617 * Invalid ACK: reset will be sent by listening socket.
618 * Note that the ACK validity check for a Fast Open socket is done
619 * elsewhere and is checked directly against the child socket rather
620 * than req because user data may have been sent out.
621 */
622 if ((flg & TCP_FLAG_ACK) && !fastopen &&
623 (TCP_SKB_CB(skb)->ack_seq !=
624 tcp_rsk(req)->snt_isn + 1))
625 return sk;
626
627 /* Also, it would be not so bad idea to check rcv_tsecr, which
628 * is essentially ACK extension and too early or too late values
629 * should cause reset in unsynchronized states.
630 */
631
632 /* RFC793: "first check sequence number". */
633
634 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
635 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rcv_wnd)) {
636 /* Out of window: send ACK and drop. */
637 if (!(flg & TCP_FLAG_RST))
638 req->rsk_ops->send_ack(sk, skb, req);
639 if (paws_reject)
640 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
641 return NULL;
642 }
643
644 /* In sequence, PAWS is OK. */
645
646 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
647 req->ts_recent = tmp_opt.rcv_tsval;
648
649 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
650 /* Truncate SYN, it is out of window starting
651 at tcp_rsk(req)->rcv_isn + 1. */
652 flg &= ~TCP_FLAG_SYN;
653 }
654
655 /* RFC793: "second check the RST bit" and
656 * "fourth, check the SYN bit"
657 */
658 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
659 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
660 goto embryonic_reset;
661 }
662
663 /* ACK sequence verified above, just make sure ACK is
664 * set. If ACK not set, just silently drop the packet.
665 *
666 * XXX (TFO) - if we ever allow "data after SYN", the
667 * following check needs to be removed.
668 */
669 if (!(flg & TCP_FLAG_ACK))
670 return NULL;
671
672 /* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */
673 if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
674 tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
675 else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */
676 tcp_rsk(req)->snt_synack = 0;
677
678 /* For Fast Open no more processing is needed (sk is the
679 * child socket).
680 */
681 if (fastopen)
682 return sk;
683
684 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
685 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
686 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
687 inet_rsk(req)->acked = 1;
688 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
689 return NULL;
690 }
691
692 /* OK, ACK is valid, create big socket and
693 * feed this segment to it. It will repeat all
694 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
695 * ESTABLISHED STATE. If it will be dropped after
696 * socket is created, wait for troubles.
697 */
698 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
699 if (child == NULL)
700 goto listen_overflow;
701
702 inet_csk_reqsk_queue_unlink(sk, req, prev);
703 inet_csk_reqsk_queue_removed(sk, req);
704
705 inet_csk_reqsk_queue_add(sk, req, child);
706 return child;
707
708 listen_overflow:
709 if (!sysctl_tcp_abort_on_overflow) {
710 inet_rsk(req)->acked = 1;
711 return NULL;
712 }
713
714 embryonic_reset:
715 if (!(flg & TCP_FLAG_RST)) {
716 /* Received a bad SYN pkt - for TFO We try not to reset
717 * the local connection unless it's really necessary to
718 * avoid becoming vulnerable to outside attack aiming at
719 * resetting legit local connections.
720 */
721 req->rsk_ops->send_reset(sk, skb);
722 } else if (fastopen) { /* received a valid RST pkt */
723 reqsk_fastopen_remove(sk, req, true);
724 tcp_reset(sk);
725 }
726 if (!fastopen) {
727 inet_csk_reqsk_queue_drop(sk, req, prev);
728 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
729 }
730 return NULL;
731 }
732 EXPORT_SYMBOL(tcp_check_req);
733
734 /*
735 * Queue segment on the new socket if the new socket is active,
736 * otherwise we just shortcircuit this and continue with
737 * the new socket.
738 *
739 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
740 * when entering. But other states are possible due to a race condition
741 * where after __inet_lookup_established() fails but before the listener
742 * locked is obtained, other packets cause the same connection to
743 * be created.
744 */
745
746 int tcp_child_process(struct sock *parent, struct sock *child,
747 struct sk_buff *skb)
748 {
749 int ret = 0;
750 int state = child->sk_state;
751
752 if (!sock_owned_by_user(child)) {
753 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
754 skb->len);
755 /* Wakeup parent, send SIGIO */
756 if (state == TCP_SYN_RECV && child->sk_state != state)
757 parent->sk_data_ready(parent, 0);
758 } else {
759 /* Alas, it is possible again, because we do lookup
760 * in main socket hash table and lock on listening
761 * socket does not protect us more.
762 */
763 __sk_add_backlog(child, skb);
764 }
765
766 bh_unlock_sock(child);
767 sock_put(child);
768 return ret;
769 }
770 EXPORT_SYMBOL(tcp_child_process);