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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
30int sysctl_tcp_syncookies __read_mostly = 1;
31EXPORT_SYMBOL(sysctl_tcp_syncookies);
32
33int sysctl_tcp_abort_on_overflow __read_mostly;
34
35struct 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};
50EXPORT_SYMBOL_GPL(tcp_death_row);
51
52static 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 */
91enum tcp_tw_status
92tcp_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) {
140kill_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) {
193kill:
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}
261EXPORT_SYMBOL(tcp_timewait_state_process);
262
263/*
264 * Move a socket to time-wait or dead fin-wait-2 state.
265 */
266void 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
297 tw->tw_v6_daddr = sk->sk_v6_daddr;
298 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
299 tw->tw_tclass = np->tclass;
300 tw->tw_flowlabel = np->flow_label >> 12;
301 tw->tw_ipv6only = np->ipv6only;
302 }
303#endif
304
305#ifdef CONFIG_TCP_MD5SIG
306 /*
307 * The timewait bucket does not have the key DB from the
308 * sock structure. We just make a quick copy of the
309 * md5 key being used (if indeed we are using one)
310 * so the timewait ack generating code has the key.
311 */
312 do {
313 struct tcp_md5sig_key *key;
314 tcptw->tw_md5_key = NULL;
315 key = tp->af_specific->md5_lookup(sk, sk);
316 if (key != NULL) {
317 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
318 if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
319 BUG();
320 }
321 } while (0);
322#endif
323
324 /* Linkage updates. */
325 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
326
327 /* Get the TIME_WAIT timeout firing. */
328 if (timeo < rto)
329 timeo = rto;
330
331 if (recycle_ok) {
332 tw->tw_timeout = rto;
333 } else {
334 tw->tw_timeout = TCP_TIMEWAIT_LEN;
335 if (state == TCP_TIME_WAIT)
336 timeo = TCP_TIMEWAIT_LEN;
337 }
338
339 inet_twsk_schedule(tw, &tcp_death_row, timeo,
340 TCP_TIMEWAIT_LEN);
341 inet_twsk_put(tw);
342 } else {
343 /* Sorry, if we're out of memory, just CLOSE this
344 * socket up. We've got bigger problems than
345 * non-graceful socket closings.
346 */
347 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
348 }
349
350 tcp_update_metrics(sk);
351 tcp_done(sk);
352}
353
354void tcp_twsk_destructor(struct sock *sk)
355{
356#ifdef CONFIG_TCP_MD5SIG
357 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
358
359 if (twsk->tw_md5_key)
360 kfree_rcu(twsk->tw_md5_key, rcu);
361#endif
362}
363EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
364
365static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
366 struct request_sock *req)
367{
368 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
369}
370
371/* This is not only more efficient than what we used to do, it eliminates
372 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
373 *
374 * Actually, we could lots of memory writes here. tp of listening
375 * socket contains all necessary default parameters.
376 */
377struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
378{
379 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
380
381 if (newsk != NULL) {
382 const struct inet_request_sock *ireq = inet_rsk(req);
383 struct tcp_request_sock *treq = tcp_rsk(req);
384 struct inet_connection_sock *newicsk = inet_csk(newsk);
385 struct tcp_sock *newtp = tcp_sk(newsk);
386
387 /* Now setup tcp_sock */
388 newtp->pred_flags = 0;
389
390 newtp->rcv_wup = newtp->copied_seq =
391 newtp->rcv_nxt = treq->rcv_isn + 1;
392
393 newtp->snd_sml = newtp->snd_una =
394 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
395
396 tcp_prequeue_init(newtp);
397 INIT_LIST_HEAD(&newtp->tsq_node);
398
399 tcp_init_wl(newtp, treq->rcv_isn);
400
401 newtp->srtt_us = 0;
402 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
403 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
404
405 newtp->packets_out = 0;
406 newtp->retrans_out = 0;
407 newtp->sacked_out = 0;
408 newtp->fackets_out = 0;
409 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
410 tcp_enable_early_retrans(newtp);
411 newtp->tlp_high_seq = 0;
412 newtp->lsndtime = treq->snt_synack;
413 newtp->total_retrans = req->num_retrans;
414
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
419 */
420 newtp->snd_cwnd = TCP_INIT_CWND;
421 newtp->snd_cwnd_cnt = 0;
422
423 if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
424 !try_module_get(newicsk->icsk_ca_ops->owner))
425 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
426
427 tcp_set_ca_state(newsk, TCP_CA_Open);
428 tcp_init_xmit_timers(newsk);
429 __skb_queue_head_init(&newtp->out_of_order_queue);
430 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
431
432 newtp->rx_opt.saw_tstamp = 0;
433
434 newtp->rx_opt.dsack = 0;
435 newtp->rx_opt.num_sacks = 0;
436
437 newtp->urg_data = 0;
438
439 if (sock_flag(newsk, SOCK_KEEPOPEN))
440 inet_csk_reset_keepalive_timer(newsk,
441 keepalive_time_when(newtp));
442
443 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
444 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
445 if (sysctl_tcp_fack)
446 tcp_enable_fack(newtp);
447 }
448 newtp->window_clamp = req->window_clamp;
449 newtp->rcv_ssthresh = req->rcv_wnd;
450 newtp->rcv_wnd = req->rcv_wnd;
451 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
452 if (newtp->rx_opt.wscale_ok) {
453 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
454 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
455 } else {
456 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
457 newtp->window_clamp = min(newtp->window_clamp, 65535U);
458 }
459 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
460 newtp->rx_opt.snd_wscale);
461 newtp->max_window = newtp->snd_wnd;
462
463 if (newtp->rx_opt.tstamp_ok) {
464 newtp->rx_opt.ts_recent = req->ts_recent;
465 newtp->rx_opt.ts_recent_stamp = get_seconds();
466 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
467 } else {
468 newtp->rx_opt.ts_recent_stamp = 0;
469 newtp->tcp_header_len = sizeof(struct tcphdr);
470 }
471 newtp->tsoffset = 0;
472#ifdef CONFIG_TCP_MD5SIG
473 newtp->md5sig_info = NULL; /*XXX*/
474 if (newtp->af_specific->md5_lookup(sk, newsk))
475 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
476#endif
477 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
478 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
479 newtp->rx_opt.mss_clamp = req->mss;
480 TCP_ECN_openreq_child(newtp, req);
481 newtp->fastopen_rsk = NULL;
482 newtp->syn_data_acked = 0;
483
484 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
485 }
486 return newsk;
487}
488EXPORT_SYMBOL(tcp_create_openreq_child);
489
490/*
491 * Process an incoming packet for SYN_RECV sockets represented as a
492 * request_sock. Normally sk is the listener socket but for TFO it
493 * points to the child socket.
494 *
495 * XXX (TFO) - The current impl contains a special check for ack
496 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
497 *
498 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
499 */
500
501struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
502 struct request_sock *req,
503 struct request_sock **prev,
504 bool fastopen)
505{
506 struct tcp_options_received tmp_opt;
507 struct sock *child;
508 const struct tcphdr *th = tcp_hdr(skb);
509 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
510 bool paws_reject = false;
511
512 BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
513
514 tmp_opt.saw_tstamp = 0;
515 if (th->doff > (sizeof(struct tcphdr)>>2)) {
516 tcp_parse_options(skb, &tmp_opt, 0, NULL);
517
518 if (tmp_opt.saw_tstamp) {
519 tmp_opt.ts_recent = req->ts_recent;
520 /* We do not store true stamp, but it is not required,
521 * it can be estimated (approximately)
522 * from another data.
523 */
524 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
525 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
526 }
527 }
528
529 /* Check for pure retransmitted SYN. */
530 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
531 flg == TCP_FLAG_SYN &&
532 !paws_reject) {
533 /*
534 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
535 * this case on figure 6 and figure 8, but formal
536 * protocol description says NOTHING.
537 * To be more exact, it says that we should send ACK,
538 * because this segment (at least, if it has no data)
539 * is out of window.
540 *
541 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
542 * describe SYN-RECV state. All the description
543 * is wrong, we cannot believe to it and should
544 * rely only on common sense and implementation
545 * experience.
546 *
547 * Enforce "SYN-ACK" according to figure 8, figure 6
548 * of RFC793, fixed by RFC1122.
549 *
550 * Note that even if there is new data in the SYN packet
551 * they will be thrown away too.
552 *
553 * Reset timer after retransmitting SYNACK, similar to
554 * the idea of fast retransmit in recovery.
555 */
556 if (!inet_rtx_syn_ack(sk, req))
557 req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
558 TCP_RTO_MAX) + jiffies;
559 return NULL;
560 }
561
562 /* Further reproduces section "SEGMENT ARRIVES"
563 for state SYN-RECEIVED of RFC793.
564 It is broken, however, it does not work only
565 when SYNs are crossed.
566
567 You would think that SYN crossing is impossible here, since
568 we should have a SYN_SENT socket (from connect()) on our end,
569 but this is not true if the crossed SYNs were sent to both
570 ends by a malicious third party. We must defend against this,
571 and to do that we first verify the ACK (as per RFC793, page
572 36) and reset if it is invalid. Is this a true full defense?
573 To convince ourselves, let us consider a way in which the ACK
574 test can still pass in this 'malicious crossed SYNs' case.
575 Malicious sender sends identical SYNs (and thus identical sequence
576 numbers) to both A and B:
577
578 A: gets SYN, seq=7
579 B: gets SYN, seq=7
580
581 By our good fortune, both A and B select the same initial
582 send sequence number of seven :-)
583
584 A: sends SYN|ACK, seq=7, ack_seq=8
585 B: sends SYN|ACK, seq=7, ack_seq=8
586
587 So we are now A eating this SYN|ACK, ACK test passes. So
588 does sequence test, SYN is truncated, and thus we consider
589 it a bare ACK.
590
591 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
592 bare ACK. Otherwise, we create an established connection. Both
593 ends (listening sockets) accept the new incoming connection and try
594 to talk to each other. 8-)
595
596 Note: This case is both harmless, and rare. Possibility is about the
597 same as us discovering intelligent life on another plant tomorrow.
598
599 But generally, we should (RFC lies!) to accept ACK
600 from SYNACK both here and in tcp_rcv_state_process().
601 tcp_rcv_state_process() does not, hence, we do not too.
602
603 Note that the case is absolutely generic:
604 we cannot optimize anything here without
605 violating protocol. All the checks must be made
606 before attempt to create socket.
607 */
608
609 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
610 * and the incoming segment acknowledges something not yet
611 * sent (the segment carries an unacceptable ACK) ...
612 * a reset is sent."
613 *
614 * Invalid ACK: reset will be sent by listening socket.
615 * Note that the ACK validity check for a Fast Open socket is done
616 * elsewhere and is checked directly against the child socket rather
617 * than req because user data may have been sent out.
618 */
619 if ((flg & TCP_FLAG_ACK) && !fastopen &&
620 (TCP_SKB_CB(skb)->ack_seq !=
621 tcp_rsk(req)->snt_isn + 1))
622 return sk;
623
624 /* Also, it would be not so bad idea to check rcv_tsecr, which
625 * is essentially ACK extension and too early or too late values
626 * should cause reset in unsynchronized states.
627 */
628
629 /* RFC793: "first check sequence number". */
630
631 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
632 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rcv_wnd)) {
633 /* Out of window: send ACK and drop. */
634 if (!(flg & TCP_FLAG_RST))
635 req->rsk_ops->send_ack(sk, skb, req);
636 if (paws_reject)
637 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
638 return NULL;
639 }
640
641 /* In sequence, PAWS is OK. */
642
643 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
644 req->ts_recent = tmp_opt.rcv_tsval;
645
646 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
647 /* Truncate SYN, it is out of window starting
648 at tcp_rsk(req)->rcv_isn + 1. */
649 flg &= ~TCP_FLAG_SYN;
650 }
651
652 /* RFC793: "second check the RST bit" and
653 * "fourth, check the SYN bit"
654 */
655 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
656 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
657 goto embryonic_reset;
658 }
659
660 /* ACK sequence verified above, just make sure ACK is
661 * set. If ACK not set, just silently drop the packet.
662 *
663 * XXX (TFO) - if we ever allow "data after SYN", the
664 * following check needs to be removed.
665 */
666 if (!(flg & TCP_FLAG_ACK))
667 return NULL;
668
669 /* For Fast Open no more processing is needed (sk is the
670 * child socket).
671 */
672 if (fastopen)
673 return sk;
674
675 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
676 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
677 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
678 inet_rsk(req)->acked = 1;
679 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
680 return NULL;
681 }
682
683 /* OK, ACK is valid, create big socket and
684 * feed this segment to it. It will repeat all
685 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
686 * ESTABLISHED STATE. If it will be dropped after
687 * socket is created, wait for troubles.
688 */
689 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
690 if (child == NULL)
691 goto listen_overflow;
692
693 inet_csk_reqsk_queue_unlink(sk, req, prev);
694 inet_csk_reqsk_queue_removed(sk, req);
695
696 inet_csk_reqsk_queue_add(sk, req, child);
697 return child;
698
699listen_overflow:
700 if (!sysctl_tcp_abort_on_overflow) {
701 inet_rsk(req)->acked = 1;
702 return NULL;
703 }
704
705embryonic_reset:
706 if (!(flg & TCP_FLAG_RST)) {
707 /* Received a bad SYN pkt - for TFO We try not to reset
708 * the local connection unless it's really necessary to
709 * avoid becoming vulnerable to outside attack aiming at
710 * resetting legit local connections.
711 */
712 req->rsk_ops->send_reset(sk, skb);
713 } else if (fastopen) { /* received a valid RST pkt */
714 reqsk_fastopen_remove(sk, req, true);
715 tcp_reset(sk);
716 }
717 if (!fastopen) {
718 inet_csk_reqsk_queue_drop(sk, req, prev);
719 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
720 }
721 return NULL;
722}
723EXPORT_SYMBOL(tcp_check_req);
724
725/*
726 * Queue segment on the new socket if the new socket is active,
727 * otherwise we just shortcircuit this and continue with
728 * the new socket.
729 *
730 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
731 * when entering. But other states are possible due to a race condition
732 * where after __inet_lookup_established() fails but before the listener
733 * locked is obtained, other packets cause the same connection to
734 * be created.
735 */
736
737int tcp_child_process(struct sock *parent, struct sock *child,
738 struct sk_buff *skb)
739{
740 int ret = 0;
741 int state = child->sk_state;
742
743 if (!sock_owned_by_user(child)) {
744 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
745 skb->len);
746 /* Wakeup parent, send SIGIO */
747 if (state == TCP_SYN_RECV && child->sk_state != state)
748 parent->sk_data_ready(parent);
749 } else {
750 /* Alas, it is possible again, because we do lookup
751 * in main socket hash table and lock on listening
752 * socket does not protect us more.
753 */
754 __sk_add_backlog(child, skb);
755 }
756
757 bh_unlock_sock(child);
758 sock_put(child);
759 return ret;
760}
761EXPORT_SYMBOL(tcp_child_process);
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
30int sysctl_tcp_abort_on_overflow __read_mostly;
31
32struct inet_timewait_death_row tcp_death_row = {
33 .sysctl_max_tw_buckets = NR_FILE * 2,
34 .hashinfo = &tcp_hashinfo,
35};
36EXPORT_SYMBOL_GPL(tcp_death_row);
37
38static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
39{
40 if (seq == s_win)
41 return true;
42 if (after(end_seq, s_win) && before(seq, e_win))
43 return true;
44 return seq == e_win && seq == end_seq;
45}
46
47static enum tcp_tw_status
48tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
49 const struct sk_buff *skb, int mib_idx)
50{
51 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
52
53 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
54 &tcptw->tw_last_oow_ack_time)) {
55 /* Send ACK. Note, we do not put the bucket,
56 * it will be released by caller.
57 */
58 return TCP_TW_ACK;
59 }
60
61 /* We are rate-limiting, so just release the tw sock and drop skb. */
62 inet_twsk_put(tw);
63 return TCP_TW_SUCCESS;
64}
65
66/*
67 * * Main purpose of TIME-WAIT state is to close connection gracefully,
68 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
69 * (and, probably, tail of data) and one or more our ACKs are lost.
70 * * What is TIME-WAIT timeout? It is associated with maximal packet
71 * lifetime in the internet, which results in wrong conclusion, that
72 * it is set to catch "old duplicate segments" wandering out of their path.
73 * It is not quite correct. This timeout is calculated so that it exceeds
74 * maximal retransmission timeout enough to allow to lose one (or more)
75 * segments sent by peer and our ACKs. This time may be calculated from RTO.
76 * * When TIME-WAIT socket receives RST, it means that another end
77 * finally closed and we are allowed to kill TIME-WAIT too.
78 * * Second purpose of TIME-WAIT is catching old duplicate segments.
79 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
80 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
81 * * If we invented some more clever way to catch duplicates
82 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
83 *
84 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
85 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
86 * from the very beginning.
87 *
88 * NOTE. With recycling (and later with fin-wait-2) TW bucket
89 * is _not_ stateless. It means, that strictly speaking we must
90 * spinlock it. I do not want! Well, probability of misbehaviour
91 * is ridiculously low and, seems, we could use some mb() tricks
92 * to avoid misread sequence numbers, states etc. --ANK
93 *
94 * We don't need to initialize tmp_out.sack_ok as we don't use the results
95 */
96enum tcp_tw_status
97tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
98 const struct tcphdr *th)
99{
100 struct tcp_options_received tmp_opt;
101 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
102 bool paws_reject = false;
103
104 tmp_opt.saw_tstamp = 0;
105 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
106 tcp_parse_options(skb, &tmp_opt, 0, NULL);
107
108 if (tmp_opt.saw_tstamp) {
109 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
110 tmp_opt.ts_recent = tcptw->tw_ts_recent;
111 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
112 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
113 }
114 }
115
116 if (tw->tw_substate == TCP_FIN_WAIT2) {
117 /* Just repeat all the checks of tcp_rcv_state_process() */
118
119 /* Out of window, send ACK */
120 if (paws_reject ||
121 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
122 tcptw->tw_rcv_nxt,
123 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
124 return tcp_timewait_check_oow_rate_limit(
125 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
126
127 if (th->rst)
128 goto kill;
129
130 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
131 return TCP_TW_RST;
132
133 /* Dup ACK? */
134 if (!th->ack ||
135 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
136 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
137 inet_twsk_put(tw);
138 return TCP_TW_SUCCESS;
139 }
140
141 /* New data or FIN. If new data arrive after half-duplex close,
142 * reset.
143 */
144 if (!th->fin ||
145 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
146 return TCP_TW_RST;
147
148 /* FIN arrived, enter true time-wait state. */
149 tw->tw_substate = TCP_TIME_WAIT;
150 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
151 if (tmp_opt.saw_tstamp) {
152 tcptw->tw_ts_recent_stamp = get_seconds();
153 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
154 }
155
156 if (tcp_death_row.sysctl_tw_recycle &&
157 tcptw->tw_ts_recent_stamp &&
158 tcp_tw_remember_stamp(tw))
159 inet_twsk_reschedule(tw, tw->tw_timeout);
160 else
161 inet_twsk_reschedule(tw, 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) {
193kill:
194 inet_twsk_deschedule_put(tw);
195 return TCP_TW_SUCCESS;
196 }
197 }
198 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
199
200 if (tmp_opt.saw_tstamp) {
201 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
202 tcptw->tw_ts_recent_stamp = get_seconds();
203 }
204
205 inet_twsk_put(tw);
206 return TCP_TW_SUCCESS;
207 }
208
209 /* Out of window segment.
210
211 All the segments are ACKed immediately.
212
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.
219
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,
223 but not fatal yet.
224 */
225
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;
231 if (isn == 0)
232 isn++;
233 TCP_SKB_CB(skb)->tcp_tw_isn = isn;
234 return TCP_TW_SYN;
235 }
236
237 if (paws_reject)
238 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
239
240 if (!th->rst) {
241 /* In this case we must reset the TIMEWAIT timer.
242 *
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.
246 */
247 if (paws_reject || th->ack)
248 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
249
250 return tcp_timewait_check_oow_rate_limit(
251 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
252 }
253 inet_twsk_put(tw);
254 return TCP_TW_SUCCESS;
255}
256EXPORT_SYMBOL(tcp_timewait_state_process);
257
258/*
259 * Move a socket to time-wait or dead fin-wait-2 state.
260 */
261void tcp_time_wait(struct sock *sk, int state, int timeo)
262{
263 const struct inet_connection_sock *icsk = inet_csk(sk);
264 const struct tcp_sock *tp = tcp_sk(sk);
265 struct inet_timewait_sock *tw;
266 bool recycle_ok = false;
267
268 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
269 recycle_ok = tcp_remember_stamp(sk);
270
271 tw = inet_twsk_alloc(sk, &tcp_death_row, state);
272
273 if (tw) {
274 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
275 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
276 struct inet_sock *inet = inet_sk(sk);
277
278 tw->tw_transparent = inet->transparent;
279 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
280 tcptw->tw_rcv_nxt = tp->rcv_nxt;
281 tcptw->tw_snd_nxt = tp->snd_nxt;
282 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
283 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
284 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
285 tcptw->tw_ts_offset = tp->tsoffset;
286 tcptw->tw_last_oow_ack_time = 0;
287
288#if IS_ENABLED(CONFIG_IPV6)
289 if (tw->tw_family == PF_INET6) {
290 struct ipv6_pinfo *np = inet6_sk(sk);
291
292 tw->tw_v6_daddr = sk->sk_v6_daddr;
293 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
294 tw->tw_tclass = np->tclass;
295 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
296 tw->tw_ipv6only = sk->sk_ipv6only;
297 }
298#endif
299
300#ifdef CONFIG_TCP_MD5SIG
301 /*
302 * The timewait bucket does not have the key DB from the
303 * sock structure. We just make a quick copy of the
304 * md5 key being used (if indeed we are using one)
305 * so the timewait ack generating code has the key.
306 */
307 do {
308 struct tcp_md5sig_key *key;
309 tcptw->tw_md5_key = NULL;
310 key = tp->af_specific->md5_lookup(sk, sk);
311 if (key) {
312 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
313 if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
314 BUG();
315 }
316 } while (0);
317#endif
318
319 /* Get the TIME_WAIT timeout firing. */
320 if (timeo < rto)
321 timeo = rto;
322
323 if (recycle_ok) {
324 tw->tw_timeout = rto;
325 } else {
326 tw->tw_timeout = TCP_TIMEWAIT_LEN;
327 if (state == TCP_TIME_WAIT)
328 timeo = TCP_TIMEWAIT_LEN;
329 }
330
331 inet_twsk_schedule(tw, timeo);
332 /* Linkage updates. */
333 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
334 inet_twsk_put(tw);
335 } else {
336 /* Sorry, if we're out of memory, just CLOSE this
337 * socket up. We've got bigger problems than
338 * non-graceful socket closings.
339 */
340 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
341 }
342
343 tcp_update_metrics(sk);
344 tcp_done(sk);
345}
346
347void tcp_twsk_destructor(struct sock *sk)
348{
349#ifdef CONFIG_TCP_MD5SIG
350 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
351
352 if (twsk->tw_md5_key)
353 kfree_rcu(twsk->tw_md5_key, rcu);
354#endif
355}
356EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
357
358/* Warning : This function is called without sk_listener being locked.
359 * Be sure to read socket fields once, as their value could change under us.
360 */
361void tcp_openreq_init_rwin(struct request_sock *req,
362 const struct sock *sk_listener,
363 const struct dst_entry *dst)
364{
365 struct inet_request_sock *ireq = inet_rsk(req);
366 const struct tcp_sock *tp = tcp_sk(sk_listener);
367 u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
368 int full_space = tcp_full_space(sk_listener);
369 int mss = dst_metric_advmss(dst);
370 u32 window_clamp;
371 __u8 rcv_wscale;
372
373 if (user_mss && user_mss < mss)
374 mss = user_mss;
375
376 window_clamp = READ_ONCE(tp->window_clamp);
377 /* Set this up on the first call only */
378 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
379
380 /* limit the window selection if the user enforce a smaller rx buffer */
381 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
382 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
383 req->rsk_window_clamp = full_space;
384
385 /* tcp_full_space because it is guaranteed to be the first packet */
386 tcp_select_initial_window(full_space,
387 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
388 &req->rsk_rcv_wnd,
389 &req->rsk_window_clamp,
390 ireq->wscale_ok,
391 &rcv_wscale,
392 dst_metric(dst, RTAX_INITRWND));
393 ireq->rcv_wscale = rcv_wscale;
394}
395EXPORT_SYMBOL(tcp_openreq_init_rwin);
396
397static void tcp_ecn_openreq_child(struct tcp_sock *tp,
398 const struct request_sock *req)
399{
400 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
401}
402
403void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
404{
405 struct inet_connection_sock *icsk = inet_csk(sk);
406 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
407 bool ca_got_dst = false;
408
409 if (ca_key != TCP_CA_UNSPEC) {
410 const struct tcp_congestion_ops *ca;
411
412 rcu_read_lock();
413 ca = tcp_ca_find_key(ca_key);
414 if (likely(ca && try_module_get(ca->owner))) {
415 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
416 icsk->icsk_ca_ops = ca;
417 ca_got_dst = true;
418 }
419 rcu_read_unlock();
420 }
421
422 /* If no valid choice made yet, assign current system default ca. */
423 if (!ca_got_dst &&
424 (!icsk->icsk_ca_setsockopt ||
425 !try_module_get(icsk->icsk_ca_ops->owner)))
426 tcp_assign_congestion_control(sk);
427
428 tcp_set_ca_state(sk, TCP_CA_Open);
429}
430EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
431
432/* This is not only more efficient than what we used to do, it eliminates
433 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
434 *
435 * Actually, we could lots of memory writes here. tp of listening
436 * socket contains all necessary default parameters.
437 */
438struct sock *tcp_create_openreq_child(const struct sock *sk,
439 struct request_sock *req,
440 struct sk_buff *skb)
441{
442 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
443
444 if (newsk) {
445 const struct inet_request_sock *ireq = inet_rsk(req);
446 struct tcp_request_sock *treq = tcp_rsk(req);
447 struct inet_connection_sock *newicsk = inet_csk(newsk);
448 struct tcp_sock *newtp = tcp_sk(newsk);
449
450 /* Now setup tcp_sock */
451 newtp->pred_flags = 0;
452
453 newtp->rcv_wup = newtp->copied_seq =
454 newtp->rcv_nxt = treq->rcv_isn + 1;
455 newtp->segs_in = 1;
456
457 newtp->snd_sml = newtp->snd_una =
458 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
459
460 tcp_prequeue_init(newtp);
461 INIT_LIST_HEAD(&newtp->tsq_node);
462
463 tcp_init_wl(newtp, treq->rcv_isn);
464
465 newtp->srtt_us = 0;
466 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
467 newtp->rtt_min[0].rtt = ~0U;
468 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
469
470 newtp->packets_out = 0;
471 newtp->retrans_out = 0;
472 newtp->sacked_out = 0;
473 newtp->fackets_out = 0;
474 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
475 tcp_enable_early_retrans(newtp);
476 newtp->tlp_high_seq = 0;
477 newtp->lsndtime = treq->snt_synack.stamp_jiffies;
478 newsk->sk_txhash = treq->txhash;
479 newtp->last_oow_ack_time = 0;
480 newtp->total_retrans = req->num_retrans;
481
482 /* So many TCP implementations out there (incorrectly) count the
483 * initial SYN frame in their delayed-ACK and congestion control
484 * algorithms that we must have the following bandaid to talk
485 * efficiently to them. -DaveM
486 */
487 newtp->snd_cwnd = TCP_INIT_CWND;
488 newtp->snd_cwnd_cnt = 0;
489
490 tcp_init_xmit_timers(newsk);
491 __skb_queue_head_init(&newtp->out_of_order_queue);
492 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
493
494 newtp->rx_opt.saw_tstamp = 0;
495
496 newtp->rx_opt.dsack = 0;
497 newtp->rx_opt.num_sacks = 0;
498
499 newtp->urg_data = 0;
500
501 if (sock_flag(newsk, SOCK_KEEPOPEN))
502 inet_csk_reset_keepalive_timer(newsk,
503 keepalive_time_when(newtp));
504
505 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
506 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
507 if (sysctl_tcp_fack)
508 tcp_enable_fack(newtp);
509 }
510 newtp->window_clamp = req->rsk_window_clamp;
511 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
512 newtp->rcv_wnd = req->rsk_rcv_wnd;
513 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
514 if (newtp->rx_opt.wscale_ok) {
515 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
516 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
517 } else {
518 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
519 newtp->window_clamp = min(newtp->window_clamp, 65535U);
520 }
521 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
522 newtp->rx_opt.snd_wscale);
523 newtp->max_window = newtp->snd_wnd;
524
525 if (newtp->rx_opt.tstamp_ok) {
526 newtp->rx_opt.ts_recent = req->ts_recent;
527 newtp->rx_opt.ts_recent_stamp = get_seconds();
528 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
529 } else {
530 newtp->rx_opt.ts_recent_stamp = 0;
531 newtp->tcp_header_len = sizeof(struct tcphdr);
532 }
533 newtp->tsoffset = 0;
534#ifdef CONFIG_TCP_MD5SIG
535 newtp->md5sig_info = NULL; /*XXX*/
536 if (newtp->af_specific->md5_lookup(sk, newsk))
537 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
538#endif
539 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
540 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
541 newtp->rx_opt.mss_clamp = req->mss;
542 tcp_ecn_openreq_child(newtp, req);
543 newtp->fastopen_rsk = NULL;
544 newtp->syn_data_acked = 0;
545 newtp->rack.mstamp.v64 = 0;
546 newtp->rack.advanced = 0;
547
548 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
549 }
550 return newsk;
551}
552EXPORT_SYMBOL(tcp_create_openreq_child);
553
554/*
555 * Process an incoming packet for SYN_RECV sockets represented as a
556 * request_sock. Normally sk is the listener socket but for TFO it
557 * points to the child socket.
558 *
559 * XXX (TFO) - The current impl contains a special check for ack
560 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
561 *
562 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
563 */
564
565struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
566 struct request_sock *req,
567 bool fastopen)
568{
569 struct tcp_options_received tmp_opt;
570 struct sock *child;
571 const struct tcphdr *th = tcp_hdr(skb);
572 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
573 bool paws_reject = false;
574 bool own_req;
575
576 tmp_opt.saw_tstamp = 0;
577 if (th->doff > (sizeof(struct tcphdr)>>2)) {
578 tcp_parse_options(skb, &tmp_opt, 0, NULL);
579
580 if (tmp_opt.saw_tstamp) {
581 tmp_opt.ts_recent = req->ts_recent;
582 /* We do not store true stamp, but it is not required,
583 * it can be estimated (approximately)
584 * from another data.
585 */
586 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
587 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
588 }
589 }
590
591 /* Check for pure retransmitted SYN. */
592 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
593 flg == TCP_FLAG_SYN &&
594 !paws_reject) {
595 /*
596 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
597 * this case on figure 6 and figure 8, but formal
598 * protocol description says NOTHING.
599 * To be more exact, it says that we should send ACK,
600 * because this segment (at least, if it has no data)
601 * is out of window.
602 *
603 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
604 * describe SYN-RECV state. All the description
605 * is wrong, we cannot believe to it and should
606 * rely only on common sense and implementation
607 * experience.
608 *
609 * Enforce "SYN-ACK" according to figure 8, figure 6
610 * of RFC793, fixed by RFC1122.
611 *
612 * Note that even if there is new data in the SYN packet
613 * they will be thrown away too.
614 *
615 * Reset timer after retransmitting SYNACK, similar to
616 * the idea of fast retransmit in recovery.
617 */
618 if (!tcp_oow_rate_limited(sock_net(sk), skb,
619 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
620 &tcp_rsk(req)->last_oow_ack_time) &&
621
622 !inet_rtx_syn_ack(sk, req)) {
623 unsigned long expires = jiffies;
624
625 expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
626 TCP_RTO_MAX);
627 if (!fastopen)
628 mod_timer_pending(&req->rsk_timer, expires);
629 else
630 req->rsk_timer.expires = expires;
631 }
632 return NULL;
633 }
634
635 /* Further reproduces section "SEGMENT ARRIVES"
636 for state SYN-RECEIVED of RFC793.
637 It is broken, however, it does not work only
638 when SYNs are crossed.
639
640 You would think that SYN crossing is impossible here, since
641 we should have a SYN_SENT socket (from connect()) on our end,
642 but this is not true if the crossed SYNs were sent to both
643 ends by a malicious third party. We must defend against this,
644 and to do that we first verify the ACK (as per RFC793, page
645 36) and reset if it is invalid. Is this a true full defense?
646 To convince ourselves, let us consider a way in which the ACK
647 test can still pass in this 'malicious crossed SYNs' case.
648 Malicious sender sends identical SYNs (and thus identical sequence
649 numbers) to both A and B:
650
651 A: gets SYN, seq=7
652 B: gets SYN, seq=7
653
654 By our good fortune, both A and B select the same initial
655 send sequence number of seven :-)
656
657 A: sends SYN|ACK, seq=7, ack_seq=8
658 B: sends SYN|ACK, seq=7, ack_seq=8
659
660 So we are now A eating this SYN|ACK, ACK test passes. So
661 does sequence test, SYN is truncated, and thus we consider
662 it a bare ACK.
663
664 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
665 bare ACK. Otherwise, we create an established connection. Both
666 ends (listening sockets) accept the new incoming connection and try
667 to talk to each other. 8-)
668
669 Note: This case is both harmless, and rare. Possibility is about the
670 same as us discovering intelligent life on another plant tomorrow.
671
672 But generally, we should (RFC lies!) to accept ACK
673 from SYNACK both here and in tcp_rcv_state_process().
674 tcp_rcv_state_process() does not, hence, we do not too.
675
676 Note that the case is absolutely generic:
677 we cannot optimize anything here without
678 violating protocol. All the checks must be made
679 before attempt to create socket.
680 */
681
682 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
683 * and the incoming segment acknowledges something not yet
684 * sent (the segment carries an unacceptable ACK) ...
685 * a reset is sent."
686 *
687 * Invalid ACK: reset will be sent by listening socket.
688 * Note that the ACK validity check for a Fast Open socket is done
689 * elsewhere and is checked directly against the child socket rather
690 * than req because user data may have been sent out.
691 */
692 if ((flg & TCP_FLAG_ACK) && !fastopen &&
693 (TCP_SKB_CB(skb)->ack_seq !=
694 tcp_rsk(req)->snt_isn + 1))
695 return sk;
696
697 /* Also, it would be not so bad idea to check rcv_tsecr, which
698 * is essentially ACK extension and too early or too late values
699 * should cause reset in unsynchronized states.
700 */
701
702 /* RFC793: "first check sequence number". */
703
704 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
705 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
706 /* Out of window: send ACK and drop. */
707 if (!(flg & TCP_FLAG_RST))
708 req->rsk_ops->send_ack(sk, skb, req);
709 if (paws_reject)
710 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
711 return NULL;
712 }
713
714 /* In sequence, PAWS is OK. */
715
716 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
717 req->ts_recent = tmp_opt.rcv_tsval;
718
719 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
720 /* Truncate SYN, it is out of window starting
721 at tcp_rsk(req)->rcv_isn + 1. */
722 flg &= ~TCP_FLAG_SYN;
723 }
724
725 /* RFC793: "second check the RST bit" and
726 * "fourth, check the SYN bit"
727 */
728 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
729 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
730 goto embryonic_reset;
731 }
732
733 /* ACK sequence verified above, just make sure ACK is
734 * set. If ACK not set, just silently drop the packet.
735 *
736 * XXX (TFO) - if we ever allow "data after SYN", the
737 * following check needs to be removed.
738 */
739 if (!(flg & TCP_FLAG_ACK))
740 return NULL;
741
742 /* For Fast Open no more processing is needed (sk is the
743 * child socket).
744 */
745 if (fastopen)
746 return sk;
747
748 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
749 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
750 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
751 inet_rsk(req)->acked = 1;
752 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
753 return NULL;
754 }
755
756 /* OK, ACK is valid, create big socket and
757 * feed this segment to it. It will repeat all
758 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
759 * ESTABLISHED STATE. If it will be dropped after
760 * socket is created, wait for troubles.
761 */
762 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
763 req, &own_req);
764 if (!child)
765 goto listen_overflow;
766
767 sock_rps_save_rxhash(child, skb);
768 tcp_synack_rtt_meas(child, req);
769 return inet_csk_complete_hashdance(sk, child, req, own_req);
770
771listen_overflow:
772 if (!sysctl_tcp_abort_on_overflow) {
773 inet_rsk(req)->acked = 1;
774 return NULL;
775 }
776
777embryonic_reset:
778 if (!(flg & TCP_FLAG_RST)) {
779 /* Received a bad SYN pkt - for TFO We try not to reset
780 * the local connection unless it's really necessary to
781 * avoid becoming vulnerable to outside attack aiming at
782 * resetting legit local connections.
783 */
784 req->rsk_ops->send_reset(sk, skb);
785 } else if (fastopen) { /* received a valid RST pkt */
786 reqsk_fastopen_remove(sk, req, true);
787 tcp_reset(sk);
788 }
789 if (!fastopen) {
790 inet_csk_reqsk_queue_drop(sk, req);
791 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
792 }
793 return NULL;
794}
795EXPORT_SYMBOL(tcp_check_req);
796
797/*
798 * Queue segment on the new socket if the new socket is active,
799 * otherwise we just shortcircuit this and continue with
800 * the new socket.
801 *
802 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
803 * when entering. But other states are possible due to a race condition
804 * where after __inet_lookup_established() fails but before the listener
805 * locked is obtained, other packets cause the same connection to
806 * be created.
807 */
808
809int tcp_child_process(struct sock *parent, struct sock *child,
810 struct sk_buff *skb)
811{
812 int ret = 0;
813 int state = child->sk_state;
814
815 tcp_segs_in(tcp_sk(child), skb);
816 if (!sock_owned_by_user(child)) {
817 ret = tcp_rcv_state_process(child, skb);
818 /* Wakeup parent, send SIGIO */
819 if (state == TCP_SYN_RECV && child->sk_state != state)
820 parent->sk_data_ready(parent);
821 } else {
822 /* Alas, it is possible again, because we do lookup
823 * in main socket hash table and lock on listening
824 * socket does not protect us more.
825 */
826 __sk_add_backlog(child, skb);
827 }
828
829 bh_unlock_sock(child);
830 sock_put(child);
831 return ret;
832}
833EXPORT_SYMBOL(tcp_child_process);