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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// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * INET An implementation of the TCP/IP protocol suite for the LINUX
4 * operating system. INET is implemented using the BSD Socket
5 * interface as the means of communication with the user level.
6 *
7 * Implementation of the Transmission Control Protocol(TCP).
8 *
9 * Authors: Ross Biro
10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11 * Mark Evans, <evansmp@uhura.aston.ac.uk>
12 * Corey Minyard <wf-rch!minyard@relay.EU.net>
13 * Florian La Roche, <flla@stud.uni-sb.de>
14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15 * Linus Torvalds, <torvalds@cs.helsinki.fi>
16 * Alan Cox, <gw4pts@gw4pts.ampr.org>
17 * Matthew Dillon, <dillon@apollo.west.oic.com>
18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19 * Jorge Cwik, <jorge@laser.satlink.net>
20 */
21
22#include <net/tcp.h>
23#include <net/xfrm.h>
24#include <net/busy_poll.h>
25
26static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
27{
28 if (seq == s_win)
29 return true;
30 if (after(end_seq, s_win) && before(seq, e_win))
31 return true;
32 return seq == e_win && seq == end_seq;
33}
34
35static enum tcp_tw_status
36tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
37 const struct sk_buff *skb, int mib_idx)
38{
39 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
40
41 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
42 &tcptw->tw_last_oow_ack_time)) {
43 /* Send ACK. Note, we do not put the bucket,
44 * it will be released by caller.
45 */
46 return TCP_TW_ACK;
47 }
48
49 /* We are rate-limiting, so just release the tw sock and drop skb. */
50 inet_twsk_put(tw);
51 return TCP_TW_SUCCESS;
52}
53
54static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq)
55{
56#ifdef CONFIG_TCP_AO
57 struct tcp_ao_info *ao;
58
59 ao = rcu_dereference(tcptw->ao_info);
60 if (unlikely(ao && seq < tcptw->tw_rcv_nxt))
61 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1);
62#endif
63 tcptw->tw_rcv_nxt = seq;
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(twsk_net(tw), skb, &tmp_opt, 0, NULL);
107
108 if (tmp_opt.saw_tstamp) {
109 if (tmp_opt.rcv_tsecr)
110 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
111 tmp_opt.ts_recent = tcptw->tw_ts_recent;
112 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
113 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
114 }
115 }
116
117 if (tw->tw_substate == TCP_FIN_WAIT2) {
118 /* Just repeat all the checks of tcp_rcv_state_process() */
119
120 /* Out of window, send ACK */
121 if (paws_reject ||
122 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
123 tcptw->tw_rcv_nxt,
124 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
125 return tcp_timewait_check_oow_rate_limit(
126 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
127
128 if (th->rst)
129 goto kill;
130
131 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
132 return TCP_TW_RST;
133
134 /* Dup ACK? */
135 if (!th->ack ||
136 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
137 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
138 inet_twsk_put(tw);
139 return TCP_TW_SUCCESS;
140 }
141
142 /* New data or FIN. If new data arrive after half-duplex close,
143 * reset.
144 */
145 if (!th->fin ||
146 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
147 return TCP_TW_RST;
148
149 /* FIN arrived, enter true time-wait state. */
150 tw->tw_substate = TCP_TIME_WAIT;
151 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq);
152
153 if (tmp_opt.saw_tstamp) {
154 tcptw->tw_ts_recent_stamp = ktime_get_seconds();
155 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
156 }
157
158 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
159 return TCP_TW_ACK;
160 }
161
162 /*
163 * Now real TIME-WAIT state.
164 *
165 * RFC 1122:
166 * "When a connection is [...] on TIME-WAIT state [...]
167 * [a TCP] MAY accept a new SYN from the remote TCP to
168 * reopen the connection directly, if it:
169 *
170 * (1) assigns its initial sequence number for the new
171 * connection to be larger than the largest sequence
172 * number it used on the previous connection incarnation,
173 * and
174 *
175 * (2) returns to TIME-WAIT state if the SYN turns out
176 * to be an old duplicate".
177 */
178
179 if (!paws_reject &&
180 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
181 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
182 /* In window segment, it may be only reset or bare ack. */
183
184 if (th->rst) {
185 /* This is TIME_WAIT assassination, in two flavors.
186 * Oh well... nobody has a sufficient solution to this
187 * protocol bug yet.
188 */
189 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) {
190kill:
191 inet_twsk_deschedule_put(tw);
192 return TCP_TW_SUCCESS;
193 }
194 } else {
195 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
196 }
197
198 if (tmp_opt.saw_tstamp) {
199 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
200 tcptw->tw_ts_recent_stamp = ktime_get_seconds();
201 }
202
203 inet_twsk_put(tw);
204 return TCP_TW_SUCCESS;
205 }
206
207 /* Out of window segment.
208
209 All the segments are ACKed immediately.
210
211 The only exception is new SYN. We accept it, if it is
212 not old duplicate and we are not in danger to be killed
213 by delayed old duplicates. RFC check is that it has
214 newer sequence number works at rates <40Mbit/sec.
215 However, if paws works, it is reliable AND even more,
216 we even may relax silly seq space cutoff.
217
218 RED-PEN: we violate main RFC requirement, if this SYN will appear
219 old duplicate (i.e. we receive RST in reply to SYN-ACK),
220 we must return socket to time-wait state. It is not good,
221 but not fatal yet.
222 */
223
224 if (th->syn && !th->rst && !th->ack && !paws_reject &&
225 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
226 (tmp_opt.saw_tstamp &&
227 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
228 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
229 if (isn == 0)
230 isn++;
231 TCP_SKB_CB(skb)->tcp_tw_isn = isn;
232 return TCP_TW_SYN;
233 }
234
235 if (paws_reject)
236 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
237
238 if (!th->rst) {
239 /* In this case we must reset the TIMEWAIT timer.
240 *
241 * If it is ACKless SYN it may be both old duplicate
242 * and new good SYN with random sequence number <rcv_nxt.
243 * Do not reschedule in the last case.
244 */
245 if (paws_reject || th->ack)
246 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
247
248 return tcp_timewait_check_oow_rate_limit(
249 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
250 }
251 inet_twsk_put(tw);
252 return TCP_TW_SUCCESS;
253}
254EXPORT_SYMBOL(tcp_timewait_state_process);
255
256static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw)
257{
258#ifdef CONFIG_TCP_MD5SIG
259 const struct tcp_sock *tp = tcp_sk(sk);
260 struct tcp_md5sig_key *key;
261
262 /*
263 * The timewait bucket does not have the key DB from the
264 * sock structure. We just make a quick copy of the
265 * md5 key being used (if indeed we are using one)
266 * so the timewait ack generating code has the key.
267 */
268 tcptw->tw_md5_key = NULL;
269 if (!static_branch_unlikely(&tcp_md5_needed.key))
270 return;
271
272 key = tp->af_specific->md5_lookup(sk, sk);
273 if (key) {
274 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
275 if (!tcptw->tw_md5_key)
276 return;
277 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key))
278 goto out_free;
279 tcp_md5_add_sigpool();
280 }
281 return;
282out_free:
283 WARN_ON_ONCE(1);
284 kfree(tcptw->tw_md5_key);
285 tcptw->tw_md5_key = NULL;
286#endif
287}
288
289/*
290 * Move a socket to time-wait or dead fin-wait-2 state.
291 */
292void tcp_time_wait(struct sock *sk, int state, int timeo)
293{
294 const struct inet_connection_sock *icsk = inet_csk(sk);
295 struct tcp_sock *tp = tcp_sk(sk);
296 struct net *net = sock_net(sk);
297 struct inet_timewait_sock *tw;
298
299 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state);
300
301 if (tw) {
302 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
303 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
304
305 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk);
306 tw->tw_mark = sk->sk_mark;
307 tw->tw_priority = READ_ONCE(sk->sk_priority);
308 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
309 tcptw->tw_rcv_nxt = tp->rcv_nxt;
310 tcptw->tw_snd_nxt = tp->snd_nxt;
311 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
312 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
313 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
314 tcptw->tw_ts_offset = tp->tsoffset;
315 tw->tw_usec_ts = tp->tcp_usec_ts;
316 tcptw->tw_last_oow_ack_time = 0;
317 tcptw->tw_tx_delay = tp->tcp_tx_delay;
318 tw->tw_txhash = sk->sk_txhash;
319#if IS_ENABLED(CONFIG_IPV6)
320 if (tw->tw_family == PF_INET6) {
321 struct ipv6_pinfo *np = inet6_sk(sk);
322
323 tw->tw_v6_daddr = sk->sk_v6_daddr;
324 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
325 tw->tw_tclass = np->tclass;
326 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
327 tw->tw_ipv6only = sk->sk_ipv6only;
328 }
329#endif
330
331 tcp_time_wait_init(sk, tcptw);
332 tcp_ao_time_wait(tcptw, tp);
333
334 /* Get the TIME_WAIT timeout firing. */
335 if (timeo < rto)
336 timeo = rto;
337
338 if (state == TCP_TIME_WAIT)
339 timeo = TCP_TIMEWAIT_LEN;
340
341 /* tw_timer is pinned, so we need to make sure BH are disabled
342 * in following section, otherwise timer handler could run before
343 * we complete the initialization.
344 */
345 local_bh_disable();
346 inet_twsk_schedule(tw, timeo);
347 /* Linkage updates.
348 * Note that access to tw after this point is illegal.
349 */
350 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo);
351 local_bh_enable();
352 } else {
353 /* Sorry, if we're out of memory, just CLOSE this
354 * socket up. We've got bigger problems than
355 * non-graceful socket closings.
356 */
357 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW);
358 }
359
360 tcp_update_metrics(sk);
361 tcp_done(sk);
362}
363EXPORT_SYMBOL(tcp_time_wait);
364
365#ifdef CONFIG_TCP_MD5SIG
366static void tcp_md5_twsk_free_rcu(struct rcu_head *head)
367{
368 struct tcp_md5sig_key *key;
369
370 key = container_of(head, struct tcp_md5sig_key, rcu);
371 kfree(key);
372 static_branch_slow_dec_deferred(&tcp_md5_needed);
373 tcp_md5_release_sigpool();
374}
375#endif
376
377void tcp_twsk_destructor(struct sock *sk)
378{
379#ifdef CONFIG_TCP_MD5SIG
380 if (static_branch_unlikely(&tcp_md5_needed.key)) {
381 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
382
383 if (twsk->tw_md5_key)
384 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu);
385 }
386#endif
387 tcp_ao_destroy_sock(sk, true);
388}
389EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
390
391void tcp_twsk_purge(struct list_head *net_exit_list, int family)
392{
393 bool purged_once = false;
394 struct net *net;
395
396 list_for_each_entry(net, net_exit_list, exit_list) {
397 if (net->ipv4.tcp_death_row.hashinfo->pernet) {
398 /* Even if tw_refcount == 1, we must clean up kernel reqsk */
399 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family);
400 } else if (!purged_once) {
401 /* The last refcount is decremented in tcp_sk_exit_batch() */
402 if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1)
403 continue;
404
405 inet_twsk_purge(&tcp_hashinfo, family);
406 purged_once = true;
407 }
408 }
409}
410EXPORT_SYMBOL_GPL(tcp_twsk_purge);
411
412/* Warning : This function is called without sk_listener being locked.
413 * Be sure to read socket fields once, as their value could change under us.
414 */
415void tcp_openreq_init_rwin(struct request_sock *req,
416 const struct sock *sk_listener,
417 const struct dst_entry *dst)
418{
419 struct inet_request_sock *ireq = inet_rsk(req);
420 const struct tcp_sock *tp = tcp_sk(sk_listener);
421 int full_space = tcp_full_space(sk_listener);
422 u32 window_clamp;
423 __u8 rcv_wscale;
424 u32 rcv_wnd;
425 int mss;
426
427 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
428 window_clamp = READ_ONCE(tp->window_clamp);
429 /* Set this up on the first call only */
430 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
431
432 /* limit the window selection if the user enforce a smaller rx buffer */
433 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
434 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
435 req->rsk_window_clamp = full_space;
436
437 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
438 if (rcv_wnd == 0)
439 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
440 else if (full_space < rcv_wnd * mss)
441 full_space = rcv_wnd * mss;
442
443 /* tcp_full_space because it is guaranteed to be the first packet */
444 tcp_select_initial_window(sk_listener, full_space,
445 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
446 &req->rsk_rcv_wnd,
447 &req->rsk_window_clamp,
448 ireq->wscale_ok,
449 &rcv_wscale,
450 rcv_wnd);
451 ireq->rcv_wscale = rcv_wscale;
452}
453EXPORT_SYMBOL(tcp_openreq_init_rwin);
454
455static void tcp_ecn_openreq_child(struct tcp_sock *tp,
456 const struct request_sock *req)
457{
458 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
459}
460
461void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
462{
463 struct inet_connection_sock *icsk = inet_csk(sk);
464 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
465 bool ca_got_dst = false;
466
467 if (ca_key != TCP_CA_UNSPEC) {
468 const struct tcp_congestion_ops *ca;
469
470 rcu_read_lock();
471 ca = tcp_ca_find_key(ca_key);
472 if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
473 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
474 icsk->icsk_ca_ops = ca;
475 ca_got_dst = true;
476 }
477 rcu_read_unlock();
478 }
479
480 /* If no valid choice made yet, assign current system default ca. */
481 if (!ca_got_dst &&
482 (!icsk->icsk_ca_setsockopt ||
483 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner)))
484 tcp_assign_congestion_control(sk);
485
486 tcp_set_ca_state(sk, TCP_CA_Open);
487}
488EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
489
490static void smc_check_reset_syn_req(const struct tcp_sock *oldtp,
491 struct request_sock *req,
492 struct tcp_sock *newtp)
493{
494#if IS_ENABLED(CONFIG_SMC)
495 struct inet_request_sock *ireq;
496
497 if (static_branch_unlikely(&tcp_have_smc)) {
498 ireq = inet_rsk(req);
499 if (oldtp->syn_smc && !ireq->smc_ok)
500 newtp->syn_smc = 0;
501 }
502#endif
503}
504
505/* This is not only more efficient than what we used to do, it eliminates
506 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
507 *
508 * Actually, we could lots of memory writes here. tp of listening
509 * socket contains all necessary default parameters.
510 */
511struct sock *tcp_create_openreq_child(const struct sock *sk,
512 struct request_sock *req,
513 struct sk_buff *skb)
514{
515 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
516 const struct inet_request_sock *ireq = inet_rsk(req);
517 struct tcp_request_sock *treq = tcp_rsk(req);
518 struct inet_connection_sock *newicsk;
519 const struct tcp_sock *oldtp;
520 struct tcp_sock *newtp;
521 u32 seq;
522#ifdef CONFIG_TCP_AO
523 struct tcp_ao_key *ao_key;
524#endif
525
526 if (!newsk)
527 return NULL;
528
529 newicsk = inet_csk(newsk);
530 newtp = tcp_sk(newsk);
531 oldtp = tcp_sk(sk);
532
533 smc_check_reset_syn_req(oldtp, req, newtp);
534
535 /* Now setup tcp_sock */
536 newtp->pred_flags = 0;
537
538 seq = treq->rcv_isn + 1;
539 newtp->rcv_wup = seq;
540 WRITE_ONCE(newtp->copied_seq, seq);
541 WRITE_ONCE(newtp->rcv_nxt, seq);
542 newtp->segs_in = 1;
543
544 seq = treq->snt_isn + 1;
545 newtp->snd_sml = newtp->snd_una = seq;
546 WRITE_ONCE(newtp->snd_nxt, seq);
547 newtp->snd_up = seq;
548
549 INIT_LIST_HEAD(&newtp->tsq_node);
550 INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
551
552 tcp_init_wl(newtp, treq->rcv_isn);
553
554 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
555 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
556
557 newtp->lsndtime = tcp_jiffies32;
558 newsk->sk_txhash = READ_ONCE(treq->txhash);
559 newtp->total_retrans = req->num_retrans;
560
561 tcp_init_xmit_timers(newsk);
562 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
563
564 if (sock_flag(newsk, SOCK_KEEPOPEN))
565 inet_csk_reset_keepalive_timer(newsk,
566 keepalive_time_when(newtp));
567
568 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
569 newtp->rx_opt.sack_ok = ireq->sack_ok;
570 newtp->window_clamp = req->rsk_window_clamp;
571 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
572 newtp->rcv_wnd = req->rsk_rcv_wnd;
573 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
574 if (newtp->rx_opt.wscale_ok) {
575 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
576 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
577 } else {
578 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
579 newtp->window_clamp = min(newtp->window_clamp, 65535U);
580 }
581 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
582 newtp->max_window = newtp->snd_wnd;
583
584 if (newtp->rx_opt.tstamp_ok) {
585 newtp->tcp_usec_ts = treq->req_usec_ts;
586 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent);
587 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
588 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
589 } else {
590 newtp->tcp_usec_ts = 0;
591 newtp->rx_opt.ts_recent_stamp = 0;
592 newtp->tcp_header_len = sizeof(struct tcphdr);
593 }
594 if (req->num_timeout) {
595 newtp->total_rto = req->num_timeout;
596 newtp->undo_marker = treq->snt_isn;
597 if (newtp->tcp_usec_ts) {
598 newtp->retrans_stamp = treq->snt_synack;
599 newtp->total_rto_time = (u32)(tcp_clock_us() -
600 newtp->retrans_stamp) / USEC_PER_MSEC;
601 } else {
602 newtp->retrans_stamp = div_u64(treq->snt_synack,
603 USEC_PER_SEC / TCP_TS_HZ);
604 newtp->total_rto_time = tcp_clock_ms() -
605 newtp->retrans_stamp;
606 }
607 newtp->total_rto_recoveries = 1;
608 }
609 newtp->tsoffset = treq->ts_off;
610#ifdef CONFIG_TCP_MD5SIG
611 newtp->md5sig_info = NULL; /*XXX*/
612#endif
613#ifdef CONFIG_TCP_AO
614 newtp->ao_info = NULL;
615 ao_key = treq->af_specific->ao_lookup(sk, req,
616 tcp_rsk(req)->ao_keyid, -1);
617 if (ao_key)
618 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key);
619 #endif
620 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
621 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
622 newtp->rx_opt.mss_clamp = req->mss;
623 tcp_ecn_openreq_child(newtp, req);
624 newtp->fastopen_req = NULL;
625 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
626
627 newtp->bpf_chg_cc_inprogress = 0;
628 tcp_bpf_clone(sk, newsk);
629
630 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
631
632 return newsk;
633}
634EXPORT_SYMBOL(tcp_create_openreq_child);
635
636/*
637 * Process an incoming packet for SYN_RECV sockets represented as a
638 * request_sock. Normally sk is the listener socket but for TFO it
639 * points to the child socket.
640 *
641 * XXX (TFO) - The current impl contains a special check for ack
642 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
643 *
644 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
645 *
646 * Note: If @fastopen is true, this can be called from process context.
647 * Otherwise, this is from BH context.
648 */
649
650struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
651 struct request_sock *req,
652 bool fastopen, bool *req_stolen)
653{
654 struct tcp_options_received tmp_opt;
655 struct sock *child;
656 const struct tcphdr *th = tcp_hdr(skb);
657 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
658 bool paws_reject = false;
659 bool own_req;
660
661 tmp_opt.saw_tstamp = 0;
662 if (th->doff > (sizeof(struct tcphdr)>>2)) {
663 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
664
665 if (tmp_opt.saw_tstamp) {
666 tmp_opt.ts_recent = READ_ONCE(req->ts_recent);
667 if (tmp_opt.rcv_tsecr)
668 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
669 /* We do not store true stamp, but it is not required,
670 * it can be estimated (approximately)
671 * from another data.
672 */
673 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ;
674 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
675 }
676 }
677
678 /* Check for pure retransmitted SYN. */
679 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
680 flg == TCP_FLAG_SYN &&
681 !paws_reject) {
682 /*
683 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
684 * this case on figure 6 and figure 8, but formal
685 * protocol description says NOTHING.
686 * To be more exact, it says that we should send ACK,
687 * because this segment (at least, if it has no data)
688 * is out of window.
689 *
690 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
691 * describe SYN-RECV state. All the description
692 * is wrong, we cannot believe to it and should
693 * rely only on common sense and implementation
694 * experience.
695 *
696 * Enforce "SYN-ACK" according to figure 8, figure 6
697 * of RFC793, fixed by RFC1122.
698 *
699 * Note that even if there is new data in the SYN packet
700 * they will be thrown away too.
701 *
702 * Reset timer after retransmitting SYNACK, similar to
703 * the idea of fast retransmit in recovery.
704 */
705 if (!tcp_oow_rate_limited(sock_net(sk), skb,
706 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
707 &tcp_rsk(req)->last_oow_ack_time) &&
708
709 !inet_rtx_syn_ack(sk, req)) {
710 unsigned long expires = jiffies;
711
712 expires += reqsk_timeout(req, TCP_RTO_MAX);
713 if (!fastopen)
714 mod_timer_pending(&req->rsk_timer, expires);
715 else
716 req->rsk_timer.expires = expires;
717 }
718 return NULL;
719 }
720
721 /* Further reproduces section "SEGMENT ARRIVES"
722 for state SYN-RECEIVED of RFC793.
723 It is broken, however, it does not work only
724 when SYNs are crossed.
725
726 You would think that SYN crossing is impossible here, since
727 we should have a SYN_SENT socket (from connect()) on our end,
728 but this is not true if the crossed SYNs were sent to both
729 ends by a malicious third party. We must defend against this,
730 and to do that we first verify the ACK (as per RFC793, page
731 36) and reset if it is invalid. Is this a true full defense?
732 To convince ourselves, let us consider a way in which the ACK
733 test can still pass in this 'malicious crossed SYNs' case.
734 Malicious sender sends identical SYNs (and thus identical sequence
735 numbers) to both A and B:
736
737 A: gets SYN, seq=7
738 B: gets SYN, seq=7
739
740 By our good fortune, both A and B select the same initial
741 send sequence number of seven :-)
742
743 A: sends SYN|ACK, seq=7, ack_seq=8
744 B: sends SYN|ACK, seq=7, ack_seq=8
745
746 So we are now A eating this SYN|ACK, ACK test passes. So
747 does sequence test, SYN is truncated, and thus we consider
748 it a bare ACK.
749
750 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
751 bare ACK. Otherwise, we create an established connection. Both
752 ends (listening sockets) accept the new incoming connection and try
753 to talk to each other. 8-)
754
755 Note: This case is both harmless, and rare. Possibility is about the
756 same as us discovering intelligent life on another plant tomorrow.
757
758 But generally, we should (RFC lies!) to accept ACK
759 from SYNACK both here and in tcp_rcv_state_process().
760 tcp_rcv_state_process() does not, hence, we do not too.
761
762 Note that the case is absolutely generic:
763 we cannot optimize anything here without
764 violating protocol. All the checks must be made
765 before attempt to create socket.
766 */
767
768 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
769 * and the incoming segment acknowledges something not yet
770 * sent (the segment carries an unacceptable ACK) ...
771 * a reset is sent."
772 *
773 * Invalid ACK: reset will be sent by listening socket.
774 * Note that the ACK validity check for a Fast Open socket is done
775 * elsewhere and is checked directly against the child socket rather
776 * than req because user data may have been sent out.
777 */
778 if ((flg & TCP_FLAG_ACK) && !fastopen &&
779 (TCP_SKB_CB(skb)->ack_seq !=
780 tcp_rsk(req)->snt_isn + 1))
781 return sk;
782
783 /* Also, it would be not so bad idea to check rcv_tsecr, which
784 * is essentially ACK extension and too early or too late values
785 * should cause reset in unsynchronized states.
786 */
787
788 /* RFC793: "first check sequence number". */
789
790 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
791 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
792 /* Out of window: send ACK and drop. */
793 if (!(flg & TCP_FLAG_RST) &&
794 !tcp_oow_rate_limited(sock_net(sk), skb,
795 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
796 &tcp_rsk(req)->last_oow_ack_time))
797 req->rsk_ops->send_ack(sk, skb, req);
798 if (paws_reject)
799 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
800 return NULL;
801 }
802
803 /* In sequence, PAWS is OK. */
804
805 /* TODO: We probably should defer ts_recent change once
806 * we take ownership of @req.
807 */
808 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
809 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval);
810
811 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
812 /* Truncate SYN, it is out of window starting
813 at tcp_rsk(req)->rcv_isn + 1. */
814 flg &= ~TCP_FLAG_SYN;
815 }
816
817 /* RFC793: "second check the RST bit" and
818 * "fourth, check the SYN bit"
819 */
820 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
821 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
822 goto embryonic_reset;
823 }
824
825 /* ACK sequence verified above, just make sure ACK is
826 * set. If ACK not set, just silently drop the packet.
827 *
828 * XXX (TFO) - if we ever allow "data after SYN", the
829 * following check needs to be removed.
830 */
831 if (!(flg & TCP_FLAG_ACK))
832 return NULL;
833
834 /* For Fast Open no more processing is needed (sk is the
835 * child socket).
836 */
837 if (fastopen)
838 return sk;
839
840 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
841 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
842 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
843 inet_rsk(req)->acked = 1;
844 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
845 return NULL;
846 }
847
848 /* OK, ACK is valid, create big socket and
849 * feed this segment to it. It will repeat all
850 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
851 * ESTABLISHED STATE. If it will be dropped after
852 * socket is created, wait for troubles.
853 */
854 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
855 req, &own_req);
856 if (!child)
857 goto listen_overflow;
858
859 if (own_req && rsk_drop_req(req)) {
860 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req);
861 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
862 return child;
863 }
864
865 sock_rps_save_rxhash(child, skb);
866 tcp_synack_rtt_meas(child, req);
867 *req_stolen = !own_req;
868 return inet_csk_complete_hashdance(sk, child, req, own_req);
869
870listen_overflow:
871 if (sk != req->rsk_listener)
872 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
873
874 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) {
875 inet_rsk(req)->acked = 1;
876 return NULL;
877 }
878
879embryonic_reset:
880 if (!(flg & TCP_FLAG_RST)) {
881 /* Received a bad SYN pkt - for TFO We try not to reset
882 * the local connection unless it's really necessary to
883 * avoid becoming vulnerable to outside attack aiming at
884 * resetting legit local connections.
885 */
886 req->rsk_ops->send_reset(sk, skb);
887 } else if (fastopen) { /* received a valid RST pkt */
888 reqsk_fastopen_remove(sk, req, true);
889 tcp_reset(sk, skb);
890 }
891 if (!fastopen) {
892 bool unlinked = inet_csk_reqsk_queue_drop(sk, req);
893
894 if (unlinked)
895 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
896 *req_stolen = !unlinked;
897 }
898 return NULL;
899}
900EXPORT_SYMBOL(tcp_check_req);
901
902/*
903 * Queue segment on the new socket if the new socket is active,
904 * otherwise we just shortcircuit this and continue with
905 * the new socket.
906 *
907 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
908 * when entering. But other states are possible due to a race condition
909 * where after __inet_lookup_established() fails but before the listener
910 * locked is obtained, other packets cause the same connection to
911 * be created.
912 */
913
914int tcp_child_process(struct sock *parent, struct sock *child,
915 struct sk_buff *skb)
916 __releases(&((child)->sk_lock.slock))
917{
918 int ret = 0;
919 int state = child->sk_state;
920
921 /* record sk_napi_id and sk_rx_queue_mapping of child. */
922 sk_mark_napi_id_set(child, skb);
923
924 tcp_segs_in(tcp_sk(child), skb);
925 if (!sock_owned_by_user(child)) {
926 ret = tcp_rcv_state_process(child, skb);
927 /* Wakeup parent, send SIGIO */
928 if (state == TCP_SYN_RECV && child->sk_state != state)
929 parent->sk_data_ready(parent);
930 } else {
931 /* Alas, it is possible again, because we do lookup
932 * in main socket hash table and lock on listening
933 * socket does not protect us more.
934 */
935 __sk_add_backlog(child, skb);
936 }
937
938 bh_unlock_sock(child);
939 sock_put(child);
940 return ret;
941}
942EXPORT_SYMBOL(tcp_child_process);