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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 <linux/static_key.h>
27#include <net/tcp.h>
28#include <net/inet_common.h>
29#include <net/xfrm.h>
30#include <net/busy_poll.h>
31
32static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
33{
34 if (seq == s_win)
35 return true;
36 if (after(end_seq, s_win) && before(seq, e_win))
37 return true;
38 return seq == e_win && seq == end_seq;
39}
40
41static enum tcp_tw_status
42tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
43 const struct sk_buff *skb, int mib_idx)
44{
45 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
46
47 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
48 &tcptw->tw_last_oow_ack_time)) {
49 /* Send ACK. Note, we do not put the bucket,
50 * it will be released by caller.
51 */
52 return TCP_TW_ACK;
53 }
54
55 /* We are rate-limiting, so just release the tw sock and drop skb. */
56 inet_twsk_put(tw);
57 return TCP_TW_SUCCESS;
58}
59
60/*
61 * * Main purpose of TIME-WAIT state is to close connection gracefully,
62 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
63 * (and, probably, tail of data) and one or more our ACKs are lost.
64 * * What is TIME-WAIT timeout? It is associated with maximal packet
65 * lifetime in the internet, which results in wrong conclusion, that
66 * it is set to catch "old duplicate segments" wandering out of their path.
67 * It is not quite correct. This timeout is calculated so that it exceeds
68 * maximal retransmission timeout enough to allow to lose one (or more)
69 * segments sent by peer and our ACKs. This time may be calculated from RTO.
70 * * When TIME-WAIT socket receives RST, it means that another end
71 * finally closed and we are allowed to kill TIME-WAIT too.
72 * * Second purpose of TIME-WAIT is catching old duplicate segments.
73 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
74 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
75 * * If we invented some more clever way to catch duplicates
76 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
77 *
78 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
79 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
80 * from the very beginning.
81 *
82 * NOTE. With recycling (and later with fin-wait-2) TW bucket
83 * is _not_ stateless. It means, that strictly speaking we must
84 * spinlock it. I do not want! Well, probability of misbehaviour
85 * is ridiculously low and, seems, we could use some mb() tricks
86 * to avoid misread sequence numbers, states etc. --ANK
87 *
88 * We don't need to initialize tmp_out.sack_ok as we don't use the results
89 */
90enum tcp_tw_status
91tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
92 const struct tcphdr *th)
93{
94 struct tcp_options_received tmp_opt;
95 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
96 bool paws_reject = false;
97
98 tmp_opt.saw_tstamp = 0;
99 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
100 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);
101
102 if (tmp_opt.saw_tstamp) {
103 if (tmp_opt.rcv_tsecr)
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_timewait_check_oow_rate_limit(
120 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
121
122 if (th->rst)
123 goto kill;
124
125 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
126 return TCP_TW_RST;
127
128 /* Dup ACK? */
129 if (!th->ack ||
130 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
131 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
132 inet_twsk_put(tw);
133 return TCP_TW_SUCCESS;
134 }
135
136 /* New data or FIN. If new data arrive after half-duplex close,
137 * reset.
138 */
139 if (!th->fin ||
140 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
141 return TCP_TW_RST;
142
143 /* FIN arrived, enter true time-wait state. */
144 tw->tw_substate = TCP_TIME_WAIT;
145 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
146 if (tmp_opt.saw_tstamp) {
147 tcptw->tw_ts_recent_stamp = get_seconds();
148 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
149 }
150
151 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
152 return TCP_TW_ACK;
153 }
154
155 /*
156 * Now real TIME-WAIT state.
157 *
158 * RFC 1122:
159 * "When a connection is [...] on TIME-WAIT state [...]
160 * [a TCP] MAY accept a new SYN from the remote TCP to
161 * reopen the connection directly, if it:
162 *
163 * (1) assigns its initial sequence number for the new
164 * connection to be larger than the largest sequence
165 * number it used on the previous connection incarnation,
166 * and
167 *
168 * (2) returns to TIME-WAIT state if the SYN turns out
169 * to be an old duplicate".
170 */
171
172 if (!paws_reject &&
173 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
174 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
175 /* In window segment, it may be only reset or bare ack. */
176
177 if (th->rst) {
178 /* This is TIME_WAIT assassination, in two flavors.
179 * Oh well... nobody has a sufficient solution to this
180 * protocol bug yet.
181 */
182 if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
183kill:
184 inet_twsk_deschedule_put(tw);
185 return TCP_TW_SUCCESS;
186 }
187 }
188 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
189
190 if (tmp_opt.saw_tstamp) {
191 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
192 tcptw->tw_ts_recent_stamp = get_seconds();
193 }
194
195 inet_twsk_put(tw);
196 return TCP_TW_SUCCESS;
197 }
198
199 /* Out of window segment.
200
201 All the segments are ACKed immediately.
202
203 The only exception is new SYN. We accept it, if it is
204 not old duplicate and we are not in danger to be killed
205 by delayed old duplicates. RFC check is that it has
206 newer sequence number works at rates <40Mbit/sec.
207 However, if paws works, it is reliable AND even more,
208 we even may relax silly seq space cutoff.
209
210 RED-PEN: we violate main RFC requirement, if this SYN will appear
211 old duplicate (i.e. we receive RST in reply to SYN-ACK),
212 we must return socket to time-wait state. It is not good,
213 but not fatal yet.
214 */
215
216 if (th->syn && !th->rst && !th->ack && !paws_reject &&
217 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
218 (tmp_opt.saw_tstamp &&
219 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
220 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
221 if (isn == 0)
222 isn++;
223 TCP_SKB_CB(skb)->tcp_tw_isn = isn;
224 return TCP_TW_SYN;
225 }
226
227 if (paws_reject)
228 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
229
230 if (!th->rst) {
231 /* In this case we must reset the TIMEWAIT timer.
232 *
233 * If it is ACKless SYN it may be both old duplicate
234 * and new good SYN with random sequence number <rcv_nxt.
235 * Do not reschedule in the last case.
236 */
237 if (paws_reject || th->ack)
238 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
239
240 return tcp_timewait_check_oow_rate_limit(
241 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
242 }
243 inet_twsk_put(tw);
244 return TCP_TW_SUCCESS;
245}
246EXPORT_SYMBOL(tcp_timewait_state_process);
247
248/*
249 * Move a socket to time-wait or dead fin-wait-2 state.
250 */
251void tcp_time_wait(struct sock *sk, int state, int timeo)
252{
253 const struct inet_connection_sock *icsk = inet_csk(sk);
254 const struct tcp_sock *tp = tcp_sk(sk);
255 struct inet_timewait_sock *tw;
256 struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
257
258 tw = inet_twsk_alloc(sk, tcp_death_row, state);
259
260 if (tw) {
261 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
262 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
263 struct inet_sock *inet = inet_sk(sk);
264
265 tw->tw_transparent = inet->transparent;
266 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
267 tcptw->tw_rcv_nxt = tp->rcv_nxt;
268 tcptw->tw_snd_nxt = tp->snd_nxt;
269 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
270 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
271 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
272 tcptw->tw_ts_offset = tp->tsoffset;
273 tcptw->tw_last_oow_ack_time = 0;
274
275#if IS_ENABLED(CONFIG_IPV6)
276 if (tw->tw_family == PF_INET6) {
277 struct ipv6_pinfo *np = inet6_sk(sk);
278
279 tw->tw_v6_daddr = sk->sk_v6_daddr;
280 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
281 tw->tw_tclass = np->tclass;
282 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
283 tw->tw_ipv6only = sk->sk_ipv6only;
284 }
285#endif
286
287#ifdef CONFIG_TCP_MD5SIG
288 /*
289 * The timewait bucket does not have the key DB from the
290 * sock structure. We just make a quick copy of the
291 * md5 key being used (if indeed we are using one)
292 * so the timewait ack generating code has the key.
293 */
294 do {
295 struct tcp_md5sig_key *key;
296 tcptw->tw_md5_key = NULL;
297 key = tp->af_specific->md5_lookup(sk, sk);
298 if (key) {
299 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
300 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
301 }
302 } while (0);
303#endif
304
305 /* Get the TIME_WAIT timeout firing. */
306 if (timeo < rto)
307 timeo = rto;
308
309 tw->tw_timeout = TCP_TIMEWAIT_LEN;
310 if (state == TCP_TIME_WAIT)
311 timeo = TCP_TIMEWAIT_LEN;
312
313 /* tw_timer is pinned, so we need to make sure BH are disabled
314 * in following section, otherwise timer handler could run before
315 * we complete the initialization.
316 */
317 local_bh_disable();
318 inet_twsk_schedule(tw, timeo);
319 /* Linkage updates.
320 * Note that access to tw after this point is illegal.
321 */
322 inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
323 local_bh_enable();
324 } else {
325 /* Sorry, if we're out of memory, just CLOSE this
326 * socket up. We've got bigger problems than
327 * non-graceful socket closings.
328 */
329 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
330 }
331
332 tcp_update_metrics(sk);
333 tcp_done(sk);
334}
335EXPORT_SYMBOL(tcp_time_wait);
336
337void tcp_twsk_destructor(struct sock *sk)
338{
339#ifdef CONFIG_TCP_MD5SIG
340 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
341
342 if (twsk->tw_md5_key)
343 kfree_rcu(twsk->tw_md5_key, rcu);
344#endif
345}
346EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
347
348/* Warning : This function is called without sk_listener being locked.
349 * Be sure to read socket fields once, as their value could change under us.
350 */
351void tcp_openreq_init_rwin(struct request_sock *req,
352 const struct sock *sk_listener,
353 const struct dst_entry *dst)
354{
355 struct inet_request_sock *ireq = inet_rsk(req);
356 const struct tcp_sock *tp = tcp_sk(sk_listener);
357 int full_space = tcp_full_space(sk_listener);
358 u32 window_clamp;
359 __u8 rcv_wscale;
360 u32 rcv_wnd;
361 int mss;
362
363 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
364 window_clamp = READ_ONCE(tp->window_clamp);
365 /* Set this up on the first call only */
366 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
367
368 /* limit the window selection if the user enforce a smaller rx buffer */
369 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
370 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
371 req->rsk_window_clamp = full_space;
372
373 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
374 if (rcv_wnd == 0)
375 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
376 else if (full_space < rcv_wnd * mss)
377 full_space = rcv_wnd * mss;
378
379 /* tcp_full_space because it is guaranteed to be the first packet */
380 tcp_select_initial_window(sk_listener, full_space,
381 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
382 &req->rsk_rcv_wnd,
383 &req->rsk_window_clamp,
384 ireq->wscale_ok,
385 &rcv_wscale,
386 rcv_wnd);
387 ireq->rcv_wscale = rcv_wscale;
388}
389EXPORT_SYMBOL(tcp_openreq_init_rwin);
390
391static void tcp_ecn_openreq_child(struct tcp_sock *tp,
392 const struct request_sock *req)
393{
394 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
395}
396
397void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
398{
399 struct inet_connection_sock *icsk = inet_csk(sk);
400 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
401 bool ca_got_dst = false;
402
403 if (ca_key != TCP_CA_UNSPEC) {
404 const struct tcp_congestion_ops *ca;
405
406 rcu_read_lock();
407 ca = tcp_ca_find_key(ca_key);
408 if (likely(ca && try_module_get(ca->owner))) {
409 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
410 icsk->icsk_ca_ops = ca;
411 ca_got_dst = true;
412 }
413 rcu_read_unlock();
414 }
415
416 /* If no valid choice made yet, assign current system default ca. */
417 if (!ca_got_dst &&
418 (!icsk->icsk_ca_setsockopt ||
419 !try_module_get(icsk->icsk_ca_ops->owner)))
420 tcp_assign_congestion_control(sk);
421
422 tcp_set_ca_state(sk, TCP_CA_Open);
423}
424EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
425
426static void smc_check_reset_syn_req(struct tcp_sock *oldtp,
427 struct request_sock *req,
428 struct tcp_sock *newtp)
429{
430#if IS_ENABLED(CONFIG_SMC)
431 struct inet_request_sock *ireq;
432
433 if (static_branch_unlikely(&tcp_have_smc)) {
434 ireq = inet_rsk(req);
435 if (oldtp->syn_smc && !ireq->smc_ok)
436 newtp->syn_smc = 0;
437 }
438#endif
439}
440
441/* This is not only more efficient than what we used to do, it eliminates
442 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
443 *
444 * Actually, we could lots of memory writes here. tp of listening
445 * socket contains all necessary default parameters.
446 */
447struct sock *tcp_create_openreq_child(const struct sock *sk,
448 struct request_sock *req,
449 struct sk_buff *skb)
450{
451 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
452
453 if (newsk) {
454 const struct inet_request_sock *ireq = inet_rsk(req);
455 struct tcp_request_sock *treq = tcp_rsk(req);
456 struct inet_connection_sock *newicsk = inet_csk(newsk);
457 struct tcp_sock *newtp = tcp_sk(newsk);
458 struct tcp_sock *oldtp = tcp_sk(sk);
459
460 smc_check_reset_syn_req(oldtp, req, newtp);
461
462 /* Now setup tcp_sock */
463 newtp->pred_flags = 0;
464
465 newtp->rcv_wup = newtp->copied_seq =
466 newtp->rcv_nxt = treq->rcv_isn + 1;
467 newtp->segs_in = 1;
468
469 newtp->snd_sml = newtp->snd_una =
470 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
471
472 INIT_LIST_HEAD(&newtp->tsq_node);
473 INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
474
475 tcp_init_wl(newtp, treq->rcv_isn);
476
477 newtp->srtt_us = 0;
478 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
479 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
480 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
481 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
482
483 newtp->packets_out = 0;
484 newtp->retrans_out = 0;
485 newtp->sacked_out = 0;
486 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
487 newtp->tlp_high_seq = 0;
488 newtp->lsndtime = tcp_jiffies32;
489 newsk->sk_txhash = treq->txhash;
490 newtp->last_oow_ack_time = 0;
491 newtp->total_retrans = req->num_retrans;
492
493 /* So many TCP implementations out there (incorrectly) count the
494 * initial SYN frame in their delayed-ACK and congestion control
495 * algorithms that we must have the following bandaid to talk
496 * efficiently to them. -DaveM
497 */
498 newtp->snd_cwnd = TCP_INIT_CWND;
499 newtp->snd_cwnd_cnt = 0;
500
501 /* There's a bubble in the pipe until at least the first ACK. */
502 newtp->app_limited = ~0U;
503
504 tcp_init_xmit_timers(newsk);
505 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
506
507 newtp->rx_opt.saw_tstamp = 0;
508
509 newtp->rx_opt.dsack = 0;
510 newtp->rx_opt.num_sacks = 0;
511
512 newtp->urg_data = 0;
513
514 if (sock_flag(newsk, SOCK_KEEPOPEN))
515 inet_csk_reset_keepalive_timer(newsk,
516 keepalive_time_when(newtp));
517
518 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
519 newtp->rx_opt.sack_ok = ireq->sack_ok;
520 newtp->window_clamp = req->rsk_window_clamp;
521 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
522 newtp->rcv_wnd = req->rsk_rcv_wnd;
523 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
524 if (newtp->rx_opt.wscale_ok) {
525 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
526 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
527 } else {
528 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
529 newtp->window_clamp = min(newtp->window_clamp, 65535U);
530 }
531 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
532 newtp->rx_opt.snd_wscale);
533 newtp->max_window = newtp->snd_wnd;
534
535 if (newtp->rx_opt.tstamp_ok) {
536 newtp->rx_opt.ts_recent = req->ts_recent;
537 newtp->rx_opt.ts_recent_stamp = get_seconds();
538 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
539 } else {
540 newtp->rx_opt.ts_recent_stamp = 0;
541 newtp->tcp_header_len = sizeof(struct tcphdr);
542 }
543 newtp->tsoffset = treq->ts_off;
544#ifdef CONFIG_TCP_MD5SIG
545 newtp->md5sig_info = NULL; /*XXX*/
546 if (newtp->af_specific->md5_lookup(sk, newsk))
547 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
548#endif
549 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
550 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
551 newtp->rx_opt.mss_clamp = req->mss;
552 tcp_ecn_openreq_child(newtp, req);
553 newtp->fastopen_req = NULL;
554 newtp->fastopen_rsk = NULL;
555 newtp->syn_data_acked = 0;
556 newtp->rack.mstamp = 0;
557 newtp->rack.advanced = 0;
558 newtp->rack.reo_wnd_steps = 1;
559 newtp->rack.last_delivered = 0;
560 newtp->rack.reo_wnd_persist = 0;
561 newtp->rack.dsack_seen = 0;
562
563 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
564 }
565 return newsk;
566}
567EXPORT_SYMBOL(tcp_create_openreq_child);
568
569/*
570 * Process an incoming packet for SYN_RECV sockets represented as a
571 * request_sock. Normally sk is the listener socket but for TFO it
572 * points to the child socket.
573 *
574 * XXX (TFO) - The current impl contains a special check for ack
575 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
576 *
577 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
578 */
579
580struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
581 struct request_sock *req,
582 bool fastopen, bool *req_stolen)
583{
584 struct tcp_options_received tmp_opt;
585 struct sock *child;
586 const struct tcphdr *th = tcp_hdr(skb);
587 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
588 bool paws_reject = false;
589 bool own_req;
590
591 tmp_opt.saw_tstamp = 0;
592 if (th->doff > (sizeof(struct tcphdr)>>2)) {
593 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
594
595 if (tmp_opt.saw_tstamp) {
596 tmp_opt.ts_recent = req->ts_recent;
597 if (tmp_opt.rcv_tsecr)
598 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
599 /* We do not store true stamp, but it is not required,
600 * it can be estimated (approximately)
601 * from another data.
602 */
603 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
604 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
605 }
606 }
607
608 /* Check for pure retransmitted SYN. */
609 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
610 flg == TCP_FLAG_SYN &&
611 !paws_reject) {
612 /*
613 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
614 * this case on figure 6 and figure 8, but formal
615 * protocol description says NOTHING.
616 * To be more exact, it says that we should send ACK,
617 * because this segment (at least, if it has no data)
618 * is out of window.
619 *
620 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
621 * describe SYN-RECV state. All the description
622 * is wrong, we cannot believe to it and should
623 * rely only on common sense and implementation
624 * experience.
625 *
626 * Enforce "SYN-ACK" according to figure 8, figure 6
627 * of RFC793, fixed by RFC1122.
628 *
629 * Note that even if there is new data in the SYN packet
630 * they will be thrown away too.
631 *
632 * Reset timer after retransmitting SYNACK, similar to
633 * the idea of fast retransmit in recovery.
634 */
635 if (!tcp_oow_rate_limited(sock_net(sk), skb,
636 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
637 &tcp_rsk(req)->last_oow_ack_time) &&
638
639 !inet_rtx_syn_ack(sk, req)) {
640 unsigned long expires = jiffies;
641
642 expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
643 TCP_RTO_MAX);
644 if (!fastopen)
645 mod_timer_pending(&req->rsk_timer, expires);
646 else
647 req->rsk_timer.expires = expires;
648 }
649 return NULL;
650 }
651
652 /* Further reproduces section "SEGMENT ARRIVES"
653 for state SYN-RECEIVED of RFC793.
654 It is broken, however, it does not work only
655 when SYNs are crossed.
656
657 You would think that SYN crossing is impossible here, since
658 we should have a SYN_SENT socket (from connect()) on our end,
659 but this is not true if the crossed SYNs were sent to both
660 ends by a malicious third party. We must defend against this,
661 and to do that we first verify the ACK (as per RFC793, page
662 36) and reset if it is invalid. Is this a true full defense?
663 To convince ourselves, let us consider a way in which the ACK
664 test can still pass in this 'malicious crossed SYNs' case.
665 Malicious sender sends identical SYNs (and thus identical sequence
666 numbers) to both A and B:
667
668 A: gets SYN, seq=7
669 B: gets SYN, seq=7
670
671 By our good fortune, both A and B select the same initial
672 send sequence number of seven :-)
673
674 A: sends SYN|ACK, seq=7, ack_seq=8
675 B: sends SYN|ACK, seq=7, ack_seq=8
676
677 So we are now A eating this SYN|ACK, ACK test passes. So
678 does sequence test, SYN is truncated, and thus we consider
679 it a bare ACK.
680
681 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
682 bare ACK. Otherwise, we create an established connection. Both
683 ends (listening sockets) accept the new incoming connection and try
684 to talk to each other. 8-)
685
686 Note: This case is both harmless, and rare. Possibility is about the
687 same as us discovering intelligent life on another plant tomorrow.
688
689 But generally, we should (RFC lies!) to accept ACK
690 from SYNACK both here and in tcp_rcv_state_process().
691 tcp_rcv_state_process() does not, hence, we do not too.
692
693 Note that the case is absolutely generic:
694 we cannot optimize anything here without
695 violating protocol. All the checks must be made
696 before attempt to create socket.
697 */
698
699 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
700 * and the incoming segment acknowledges something not yet
701 * sent (the segment carries an unacceptable ACK) ...
702 * a reset is sent."
703 *
704 * Invalid ACK: reset will be sent by listening socket.
705 * Note that the ACK validity check for a Fast Open socket is done
706 * elsewhere and is checked directly against the child socket rather
707 * than req because user data may have been sent out.
708 */
709 if ((flg & TCP_FLAG_ACK) && !fastopen &&
710 (TCP_SKB_CB(skb)->ack_seq !=
711 tcp_rsk(req)->snt_isn + 1))
712 return sk;
713
714 /* Also, it would be not so bad idea to check rcv_tsecr, which
715 * is essentially ACK extension and too early or too late values
716 * should cause reset in unsynchronized states.
717 */
718
719 /* RFC793: "first check sequence number". */
720
721 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
722 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
723 /* Out of window: send ACK and drop. */
724 if (!(flg & TCP_FLAG_RST) &&
725 !tcp_oow_rate_limited(sock_net(sk), skb,
726 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
727 &tcp_rsk(req)->last_oow_ack_time))
728 req->rsk_ops->send_ack(sk, skb, req);
729 if (paws_reject)
730 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
731 return NULL;
732 }
733
734 /* In sequence, PAWS is OK. */
735
736 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
737 req->ts_recent = tmp_opt.rcv_tsval;
738
739 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
740 /* Truncate SYN, it is out of window starting
741 at tcp_rsk(req)->rcv_isn + 1. */
742 flg &= ~TCP_FLAG_SYN;
743 }
744
745 /* RFC793: "second check the RST bit" and
746 * "fourth, check the SYN bit"
747 */
748 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
749 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
750 goto embryonic_reset;
751 }
752
753 /* ACK sequence verified above, just make sure ACK is
754 * set. If ACK not set, just silently drop the packet.
755 *
756 * XXX (TFO) - if we ever allow "data after SYN", the
757 * following check needs to be removed.
758 */
759 if (!(flg & TCP_FLAG_ACK))
760 return NULL;
761
762 /* For Fast Open no more processing is needed (sk is the
763 * child socket).
764 */
765 if (fastopen)
766 return sk;
767
768 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
769 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
770 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
771 inet_rsk(req)->acked = 1;
772 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
773 return NULL;
774 }
775
776 /* OK, ACK is valid, create big socket and
777 * feed this segment to it. It will repeat all
778 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
779 * ESTABLISHED STATE. If it will be dropped after
780 * socket is created, wait for troubles.
781 */
782 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
783 req, &own_req);
784 if (!child)
785 goto listen_overflow;
786
787 sock_rps_save_rxhash(child, skb);
788 tcp_synack_rtt_meas(child, req);
789 *req_stolen = !own_req;
790 return inet_csk_complete_hashdance(sk, child, req, own_req);
791
792listen_overflow:
793 if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
794 inet_rsk(req)->acked = 1;
795 return NULL;
796 }
797
798embryonic_reset:
799 if (!(flg & TCP_FLAG_RST)) {
800 /* Received a bad SYN pkt - for TFO We try not to reset
801 * the local connection unless it's really necessary to
802 * avoid becoming vulnerable to outside attack aiming at
803 * resetting legit local connections.
804 */
805 req->rsk_ops->send_reset(sk, skb);
806 } else if (fastopen) { /* received a valid RST pkt */
807 reqsk_fastopen_remove(sk, req, true);
808 tcp_reset(sk);
809 }
810 if (!fastopen) {
811 inet_csk_reqsk_queue_drop(sk, req);
812 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
813 }
814 return NULL;
815}
816EXPORT_SYMBOL(tcp_check_req);
817
818/*
819 * Queue segment on the new socket if the new socket is active,
820 * otherwise we just shortcircuit this and continue with
821 * the new socket.
822 *
823 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
824 * when entering. But other states are possible due to a race condition
825 * where after __inet_lookup_established() fails but before the listener
826 * locked is obtained, other packets cause the same connection to
827 * be created.
828 */
829
830int tcp_child_process(struct sock *parent, struct sock *child,
831 struct sk_buff *skb)
832{
833 int ret = 0;
834 int state = child->sk_state;
835
836 /* record NAPI ID of child */
837 sk_mark_napi_id(child, skb);
838
839 tcp_segs_in(tcp_sk(child), skb);
840 if (!sock_owned_by_user(child)) {
841 ret = tcp_rcv_state_process(child, skb);
842 /* Wakeup parent, send SIGIO */
843 if (state == TCP_SYN_RECV && child->sk_state != state)
844 parent->sk_data_ready(parent);
845 } else {
846 /* Alas, it is possible again, because we do lookup
847 * in main socket hash table and lock on listening
848 * socket does not protect us more.
849 */
850 __sk_add_backlog(child, skb);
851 }
852
853 bh_unlock_sock(child);
854 sock_put(child);
855 return ret;
856}
857EXPORT_SYMBOL(tcp_child_process);