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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#include <net/rstreason.h>
26
27static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
28{
29 if (seq == s_win)
30 return true;
31 if (after(end_seq, s_win) && before(seq, e_win))
32 return true;
33 return seq == e_win && seq == end_seq;
34}
35
36static enum tcp_tw_status
37tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
38 const struct sk_buff *skb, int mib_idx)
39{
40 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
41
42 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
43 &tcptw->tw_last_oow_ack_time)) {
44 /* Send ACK. Note, we do not put the bucket,
45 * it will be released by caller.
46 */
47 return TCP_TW_ACK;
48 }
49
50 /* We are rate-limiting, so just release the tw sock and drop skb. */
51 inet_twsk_put(tw);
52 return TCP_TW_SUCCESS;
53}
54
55static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq,
56 u32 rcv_nxt)
57{
58#ifdef CONFIG_TCP_AO
59 struct tcp_ao_info *ao;
60
61 ao = rcu_dereference(tcptw->ao_info);
62 if (unlikely(ao && seq < rcv_nxt))
63 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1);
64#endif
65 WRITE_ONCE(tcptw->tw_rcv_nxt, seq);
66}
67
68/*
69 * * Main purpose of TIME-WAIT state is to close connection gracefully,
70 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
71 * (and, probably, tail of data) and one or more our ACKs are lost.
72 * * What is TIME-WAIT timeout? It is associated with maximal packet
73 * lifetime in the internet, which results in wrong conclusion, that
74 * it is set to catch "old duplicate segments" wandering out of their path.
75 * It is not quite correct. This timeout is calculated so that it exceeds
76 * maximal retransmission timeout enough to allow to lose one (or more)
77 * segments sent by peer and our ACKs. This time may be calculated from RTO.
78 * * When TIME-WAIT socket receives RST, it means that another end
79 * finally closed and we are allowed to kill TIME-WAIT too.
80 * * Second purpose of TIME-WAIT is catching old duplicate segments.
81 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
82 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
83 * * If we invented some more clever way to catch duplicates
84 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
85 *
86 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
87 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
88 * from the very beginning.
89 *
90 * NOTE. With recycling (and later with fin-wait-2) TW bucket
91 * is _not_ stateless. It means, that strictly speaking we must
92 * spinlock it. I do not want! Well, probability of misbehaviour
93 * is ridiculously low and, seems, we could use some mb() tricks
94 * to avoid misread sequence numbers, states etc. --ANK
95 *
96 * We don't need to initialize tmp_out.sack_ok as we don't use the results
97 */
98enum tcp_tw_status
99tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
100 const struct tcphdr *th, u32 *tw_isn)
101{
102 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
103 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt);
104 struct tcp_options_received tmp_opt;
105 bool paws_reject = false;
106 int ts_recent_stamp;
107
108 tmp_opt.saw_tstamp = 0;
109 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp);
110 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) {
111 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);
112
113 if (tmp_opt.saw_tstamp) {
114 if (tmp_opt.rcv_tsecr)
115 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
116 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent);
117 tmp_opt.ts_recent_stamp = ts_recent_stamp;
118 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
119 }
120 }
121
122 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) {
123 /* Just repeat all the checks of tcp_rcv_state_process() */
124
125 /* Out of window, send ACK */
126 if (paws_reject ||
127 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
128 rcv_nxt,
129 rcv_nxt + tcptw->tw_rcv_wnd))
130 return tcp_timewait_check_oow_rate_limit(
131 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
132
133 if (th->rst)
134 goto kill;
135
136 if (th->syn && !before(TCP_SKB_CB(skb)->seq, rcv_nxt))
137 return TCP_TW_RST;
138
139 /* Dup ACK? */
140 if (!th->ack ||
141 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) ||
142 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
143 inet_twsk_put(tw);
144 return TCP_TW_SUCCESS;
145 }
146
147 /* New data or FIN. If new data arrive after half-duplex close,
148 * reset.
149 */
150 if (!th->fin ||
151 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1)
152 return TCP_TW_RST;
153
154 /* FIN arrived, enter true time-wait state. */
155 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT);
156 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq,
157 rcv_nxt);
158
159 if (tmp_opt.saw_tstamp) {
160 WRITE_ONCE(tcptw->tw_ts_recent_stamp,
161 ktime_get_seconds());
162 WRITE_ONCE(tcptw->tw_ts_recent,
163 tmp_opt.rcv_tsval);
164 }
165
166 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
167 return TCP_TW_ACK;
168 }
169
170 /*
171 * Now real TIME-WAIT state.
172 *
173 * RFC 1122:
174 * "When a connection is [...] on TIME-WAIT state [...]
175 * [a TCP] MAY accept a new SYN from the remote TCP to
176 * reopen the connection directly, if it:
177 *
178 * (1) assigns its initial sequence number for the new
179 * connection to be larger than the largest sequence
180 * number it used on the previous connection incarnation,
181 * and
182 *
183 * (2) returns to TIME-WAIT state if the SYN turns out
184 * to be an old duplicate".
185 */
186
187 if (!paws_reject &&
188 (TCP_SKB_CB(skb)->seq == rcv_nxt &&
189 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
190 /* In window segment, it may be only reset or bare ack. */
191
192 if (th->rst) {
193 /* This is TIME_WAIT assassination, in two flavors.
194 * Oh well... nobody has a sufficient solution to this
195 * protocol bug yet.
196 */
197 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) {
198kill:
199 inet_twsk_deschedule_put(tw);
200 return TCP_TW_SUCCESS;
201 }
202 } else {
203 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
204 }
205
206 if (tmp_opt.saw_tstamp) {
207 WRITE_ONCE(tcptw->tw_ts_recent,
208 tmp_opt.rcv_tsval);
209 WRITE_ONCE(tcptw->tw_ts_recent_stamp,
210 ktime_get_seconds());
211 }
212
213 inet_twsk_put(tw);
214 return TCP_TW_SUCCESS;
215 }
216
217 /* Out of window segment.
218
219 All the segments are ACKed immediately.
220
221 The only exception is new SYN. We accept it, if it is
222 not old duplicate and we are not in danger to be killed
223 by delayed old duplicates. RFC check is that it has
224 newer sequence number works at rates <40Mbit/sec.
225 However, if paws works, it is reliable AND even more,
226 we even may relax silly seq space cutoff.
227
228 RED-PEN: we violate main RFC requirement, if this SYN will appear
229 old duplicate (i.e. we receive RST in reply to SYN-ACK),
230 we must return socket to time-wait state. It is not good,
231 but not fatal yet.
232 */
233
234 if (th->syn && !th->rst && !th->ack && !paws_reject &&
235 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) ||
236 (tmp_opt.saw_tstamp &&
237 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) {
238 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
239 if (isn == 0)
240 isn++;
241 *tw_isn = isn;
242 return TCP_TW_SYN;
243 }
244
245 if (paws_reject)
246 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
247
248 if (!th->rst) {
249 /* In this case we must reset the TIMEWAIT timer.
250 *
251 * If it is ACKless SYN it may be both old duplicate
252 * and new good SYN with random sequence number <rcv_nxt.
253 * Do not reschedule in the last case.
254 */
255 if (paws_reject || th->ack)
256 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
257
258 return tcp_timewait_check_oow_rate_limit(
259 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
260 }
261 inet_twsk_put(tw);
262 return TCP_TW_SUCCESS;
263}
264EXPORT_SYMBOL(tcp_timewait_state_process);
265
266static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw)
267{
268#ifdef CONFIG_TCP_MD5SIG
269 const struct tcp_sock *tp = tcp_sk(sk);
270 struct tcp_md5sig_key *key;
271
272 /*
273 * The timewait bucket does not have the key DB from the
274 * sock structure. We just make a quick copy of the
275 * md5 key being used (if indeed we are using one)
276 * so the timewait ack generating code has the key.
277 */
278 tcptw->tw_md5_key = NULL;
279 if (!static_branch_unlikely(&tcp_md5_needed.key))
280 return;
281
282 key = tp->af_specific->md5_lookup(sk, sk);
283 if (key) {
284 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
285 if (!tcptw->tw_md5_key)
286 return;
287 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key))
288 goto out_free;
289 tcp_md5_add_sigpool();
290 }
291 return;
292out_free:
293 WARN_ON_ONCE(1);
294 kfree(tcptw->tw_md5_key);
295 tcptw->tw_md5_key = NULL;
296#endif
297}
298
299/*
300 * Move a socket to time-wait or dead fin-wait-2 state.
301 */
302void tcp_time_wait(struct sock *sk, int state, int timeo)
303{
304 const struct inet_connection_sock *icsk = inet_csk(sk);
305 struct tcp_sock *tp = tcp_sk(sk);
306 struct net *net = sock_net(sk);
307 struct inet_timewait_sock *tw;
308
309 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state);
310
311 if (tw) {
312 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
313 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
314
315 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk);
316 tw->tw_mark = sk->sk_mark;
317 tw->tw_priority = READ_ONCE(sk->sk_priority);
318 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
319 tcptw->tw_rcv_nxt = tp->rcv_nxt;
320 tcptw->tw_snd_nxt = tp->snd_nxt;
321 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
322 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
323 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
324 tcptw->tw_ts_offset = tp->tsoffset;
325 tw->tw_usec_ts = tp->tcp_usec_ts;
326 tcptw->tw_last_oow_ack_time = 0;
327 tcptw->tw_tx_delay = tp->tcp_tx_delay;
328 tw->tw_txhash = sk->sk_txhash;
329 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping;
330#ifdef CONFIG_SOCK_RX_QUEUE_MAPPING
331 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping;
332#endif
333#if IS_ENABLED(CONFIG_IPV6)
334 if (tw->tw_family == PF_INET6) {
335 struct ipv6_pinfo *np = inet6_sk(sk);
336
337 tw->tw_v6_daddr = sk->sk_v6_daddr;
338 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
339 tw->tw_tclass = np->tclass;
340 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
341 tw->tw_ipv6only = sk->sk_ipv6only;
342 }
343#endif
344
345 tcp_time_wait_init(sk, tcptw);
346 tcp_ao_time_wait(tcptw, tp);
347
348 /* Get the TIME_WAIT timeout firing. */
349 if (timeo < rto)
350 timeo = rto;
351
352 if (state == TCP_TIME_WAIT)
353 timeo = TCP_TIMEWAIT_LEN;
354
355 /* Linkage updates.
356 * Note that access to tw after this point is illegal.
357 */
358 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo);
359 } else {
360 /* Sorry, if we're out of memory, just CLOSE this
361 * socket up. We've got bigger problems than
362 * non-graceful socket closings.
363 */
364 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW);
365 }
366
367 tcp_update_metrics(sk);
368 tcp_done(sk);
369}
370EXPORT_SYMBOL(tcp_time_wait);
371
372#ifdef CONFIG_TCP_MD5SIG
373static void tcp_md5_twsk_free_rcu(struct rcu_head *head)
374{
375 struct tcp_md5sig_key *key;
376
377 key = container_of(head, struct tcp_md5sig_key, rcu);
378 kfree(key);
379 static_branch_slow_dec_deferred(&tcp_md5_needed);
380 tcp_md5_release_sigpool();
381}
382#endif
383
384void tcp_twsk_destructor(struct sock *sk)
385{
386#ifdef CONFIG_TCP_MD5SIG
387 if (static_branch_unlikely(&tcp_md5_needed.key)) {
388 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
389
390 if (twsk->tw_md5_key)
391 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu);
392 }
393#endif
394 tcp_ao_destroy_sock(sk, true);
395}
396EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
397
398void tcp_twsk_purge(struct list_head *net_exit_list)
399{
400 bool purged_once = false;
401 struct net *net;
402
403 list_for_each_entry(net, net_exit_list, exit_list) {
404 if (net->ipv4.tcp_death_row.hashinfo->pernet) {
405 /* Even if tw_refcount == 1, we must clean up kernel reqsk */
406 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo);
407 } else if (!purged_once) {
408 inet_twsk_purge(&tcp_hashinfo);
409 purged_once = true;
410 }
411 }
412}
413
414/* Warning : This function is called without sk_listener being locked.
415 * Be sure to read socket fields once, as their value could change under us.
416 */
417void tcp_openreq_init_rwin(struct request_sock *req,
418 const struct sock *sk_listener,
419 const struct dst_entry *dst)
420{
421 struct inet_request_sock *ireq = inet_rsk(req);
422 const struct tcp_sock *tp = tcp_sk(sk_listener);
423 int full_space = tcp_full_space(sk_listener);
424 u32 window_clamp;
425 __u8 rcv_wscale;
426 u32 rcv_wnd;
427 int mss;
428
429 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
430 window_clamp = READ_ONCE(tp->window_clamp);
431 /* Set this up on the first call only */
432 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
433
434 /* limit the window selection if the user enforce a smaller rx buffer */
435 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
436 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
437 req->rsk_window_clamp = full_space;
438
439 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
440 if (rcv_wnd == 0)
441 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
442 else if (full_space < rcv_wnd * mss)
443 full_space = rcv_wnd * mss;
444
445 /* tcp_full_space because it is guaranteed to be the first packet */
446 tcp_select_initial_window(sk_listener, full_space,
447 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
448 &req->rsk_rcv_wnd,
449 &req->rsk_window_clamp,
450 ireq->wscale_ok,
451 &rcv_wscale,
452 rcv_wnd);
453 ireq->rcv_wscale = rcv_wscale;
454}
455EXPORT_SYMBOL(tcp_openreq_init_rwin);
456
457static void tcp_ecn_openreq_child(struct tcp_sock *tp,
458 const struct request_sock *req)
459{
460 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
461}
462
463void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
464{
465 struct inet_connection_sock *icsk = inet_csk(sk);
466 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
467 bool ca_got_dst = false;
468
469 if (ca_key != TCP_CA_UNSPEC) {
470 const struct tcp_congestion_ops *ca;
471
472 rcu_read_lock();
473 ca = tcp_ca_find_key(ca_key);
474 if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
475 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
476 icsk->icsk_ca_ops = ca;
477 ca_got_dst = true;
478 }
479 rcu_read_unlock();
480 }
481
482 /* If no valid choice made yet, assign current system default ca. */
483 if (!ca_got_dst &&
484 (!icsk->icsk_ca_setsockopt ||
485 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner)))
486 tcp_assign_congestion_control(sk);
487
488 tcp_set_ca_state(sk, TCP_CA_Open);
489}
490EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
491
492static void smc_check_reset_syn_req(const struct tcp_sock *oldtp,
493 struct request_sock *req,
494 struct tcp_sock *newtp)
495{
496#if IS_ENABLED(CONFIG_SMC)
497 struct inet_request_sock *ireq;
498
499 if (static_branch_unlikely(&tcp_have_smc)) {
500 ireq = inet_rsk(req);
501 if (oldtp->syn_smc && !ireq->smc_ok)
502 newtp->syn_smc = 0;
503 }
504#endif
505}
506
507/* This is not only more efficient than what we used to do, it eliminates
508 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
509 *
510 * Actually, we could lots of memory writes here. tp of listening
511 * socket contains all necessary default parameters.
512 */
513struct sock *tcp_create_openreq_child(const struct sock *sk,
514 struct request_sock *req,
515 struct sk_buff *skb)
516{
517 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
518 const struct inet_request_sock *ireq = inet_rsk(req);
519 struct tcp_request_sock *treq = tcp_rsk(req);
520 struct inet_connection_sock *newicsk;
521 const struct tcp_sock *oldtp;
522 struct tcp_sock *newtp;
523 u32 seq;
524
525 if (!newsk)
526 return NULL;
527
528 newicsk = inet_csk(newsk);
529 newtp = tcp_sk(newsk);
530 oldtp = tcp_sk(sk);
531
532 smc_check_reset_syn_req(oldtp, req, newtp);
533
534 /* Now setup tcp_sock */
535 newtp->pred_flags = 0;
536
537 seq = treq->rcv_isn + 1;
538 newtp->rcv_wup = seq;
539 WRITE_ONCE(newtp->copied_seq, seq);
540 WRITE_ONCE(newtp->rcv_nxt, seq);
541 newtp->segs_in = 1;
542
543 seq = treq->snt_isn + 1;
544 newtp->snd_sml = newtp->snd_una = seq;
545 WRITE_ONCE(newtp->snd_nxt, seq);
546 newtp->snd_up = seq;
547
548 INIT_LIST_HEAD(&newtp->tsq_node);
549 INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
550
551 tcp_init_wl(newtp, treq->rcv_isn);
552
553 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
554 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
555
556 newtp->lsndtime = tcp_jiffies32;
557 newsk->sk_txhash = READ_ONCE(treq->txhash);
558 newtp->total_retrans = req->num_retrans;
559
560 tcp_init_xmit_timers(newsk);
561 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
562
563 if (sock_flag(newsk, SOCK_KEEPOPEN))
564 inet_csk_reset_keepalive_timer(newsk,
565 keepalive_time_when(newtp));
566
567 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
568 newtp->rx_opt.sack_ok = ireq->sack_ok;
569 newtp->window_clamp = req->rsk_window_clamp;
570 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
571 newtp->rcv_wnd = req->rsk_rcv_wnd;
572 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
573 if (newtp->rx_opt.wscale_ok) {
574 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
575 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
576 } else {
577 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
578 newtp->window_clamp = min(newtp->window_clamp, 65535U);
579 }
580 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
581 newtp->max_window = newtp->snd_wnd;
582
583 if (newtp->rx_opt.tstamp_ok) {
584 newtp->tcp_usec_ts = treq->req_usec_ts;
585 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent);
586 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
587 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
588 } else {
589 newtp->tcp_usec_ts = 0;
590 newtp->rx_opt.ts_recent_stamp = 0;
591 newtp->tcp_header_len = sizeof(struct tcphdr);
592 }
593 if (req->num_timeout) {
594 newtp->total_rto = req->num_timeout;
595 newtp->undo_marker = treq->snt_isn;
596 if (newtp->tcp_usec_ts) {
597 newtp->retrans_stamp = treq->snt_synack;
598 newtp->total_rto_time = (u32)(tcp_clock_us() -
599 newtp->retrans_stamp) / USEC_PER_MSEC;
600 } else {
601 newtp->retrans_stamp = div_u64(treq->snt_synack,
602 USEC_PER_SEC / TCP_TS_HZ);
603 newtp->total_rto_time = tcp_clock_ms() -
604 newtp->retrans_stamp;
605 }
606 newtp->total_rto_recoveries = 1;
607 }
608 newtp->tsoffset = treq->ts_off;
609#ifdef CONFIG_TCP_MD5SIG
610 newtp->md5sig_info = NULL; /*XXX*/
611#endif
612#ifdef CONFIG_TCP_AO
613 newtp->ao_info = NULL;
614
615 if (tcp_rsk_used_ao(req)) {
616 struct tcp_ao_key *ao_key;
617
618 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1);
619 if (ao_key)
620 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key);
621 }
622 #endif
623 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
624 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
625 newtp->rx_opt.mss_clamp = req->mss;
626 tcp_ecn_openreq_child(newtp, req);
627 newtp->fastopen_req = NULL;
628 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
629
630 newtp->bpf_chg_cc_inprogress = 0;
631 tcp_bpf_clone(sk, newsk);
632
633 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
634
635 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1);
636
637 return newsk;
638}
639EXPORT_SYMBOL(tcp_create_openreq_child);
640
641/*
642 * Process an incoming packet for SYN_RECV sockets represented as a
643 * request_sock. Normally sk is the listener socket but for TFO it
644 * points to the child socket.
645 *
646 * XXX (TFO) - The current impl contains a special check for ack
647 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
648 *
649 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
650 *
651 * Note: If @fastopen is true, this can be called from process context.
652 * Otherwise, this is from BH context.
653 */
654
655struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
656 struct request_sock *req,
657 bool fastopen, bool *req_stolen)
658{
659 struct tcp_options_received tmp_opt;
660 struct sock *child;
661 const struct tcphdr *th = tcp_hdr(skb);
662 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
663 bool paws_reject = false;
664 bool own_req;
665
666 tmp_opt.saw_tstamp = 0;
667 if (th->doff > (sizeof(struct tcphdr)>>2)) {
668 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
669
670 if (tmp_opt.saw_tstamp) {
671 tmp_opt.ts_recent = READ_ONCE(req->ts_recent);
672 if (tmp_opt.rcv_tsecr)
673 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
674 /* We do not store true stamp, but it is not required,
675 * it can be estimated (approximately)
676 * from another data.
677 */
678 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ;
679 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
680 }
681 }
682
683 /* Check for pure retransmitted SYN. */
684 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
685 flg == TCP_FLAG_SYN &&
686 !paws_reject) {
687 /*
688 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
689 * this case on figure 6 and figure 8, but formal
690 * protocol description says NOTHING.
691 * To be more exact, it says that we should send ACK,
692 * because this segment (at least, if it has no data)
693 * is out of window.
694 *
695 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
696 * describe SYN-RECV state. All the description
697 * is wrong, we cannot believe to it and should
698 * rely only on common sense and implementation
699 * experience.
700 *
701 * Enforce "SYN-ACK" according to figure 8, figure 6
702 * of RFC793, fixed by RFC1122.
703 *
704 * Note that even if there is new data in the SYN packet
705 * they will be thrown away too.
706 *
707 * Reset timer after retransmitting SYNACK, similar to
708 * the idea of fast retransmit in recovery.
709 */
710 if (!tcp_oow_rate_limited(sock_net(sk), skb,
711 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
712 &tcp_rsk(req)->last_oow_ack_time) &&
713
714 !inet_rtx_syn_ack(sk, req)) {
715 unsigned long expires = jiffies;
716
717 expires += reqsk_timeout(req, TCP_RTO_MAX);
718 if (!fastopen)
719 mod_timer_pending(&req->rsk_timer, expires);
720 else
721 req->rsk_timer.expires = expires;
722 }
723 return NULL;
724 }
725
726 /* Further reproduces section "SEGMENT ARRIVES"
727 for state SYN-RECEIVED of RFC793.
728 It is broken, however, it does not work only
729 when SYNs are crossed.
730
731 You would think that SYN crossing is impossible here, since
732 we should have a SYN_SENT socket (from connect()) on our end,
733 but this is not true if the crossed SYNs were sent to both
734 ends by a malicious third party. We must defend against this,
735 and to do that we first verify the ACK (as per RFC793, page
736 36) and reset if it is invalid. Is this a true full defense?
737 To convince ourselves, let us consider a way in which the ACK
738 test can still pass in this 'malicious crossed SYNs' case.
739 Malicious sender sends identical SYNs (and thus identical sequence
740 numbers) to both A and B:
741
742 A: gets SYN, seq=7
743 B: gets SYN, seq=7
744
745 By our good fortune, both A and B select the same initial
746 send sequence number of seven :-)
747
748 A: sends SYN|ACK, seq=7, ack_seq=8
749 B: sends SYN|ACK, seq=7, ack_seq=8
750
751 So we are now A eating this SYN|ACK, ACK test passes. So
752 does sequence test, SYN is truncated, and thus we consider
753 it a bare ACK.
754
755 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
756 bare ACK. Otherwise, we create an established connection. Both
757 ends (listening sockets) accept the new incoming connection and try
758 to talk to each other. 8-)
759
760 Note: This case is both harmless, and rare. Possibility is about the
761 same as us discovering intelligent life on another plant tomorrow.
762
763 But generally, we should (RFC lies!) to accept ACK
764 from SYNACK both here and in tcp_rcv_state_process().
765 tcp_rcv_state_process() does not, hence, we do not too.
766
767 Note that the case is absolutely generic:
768 we cannot optimize anything here without
769 violating protocol. All the checks must be made
770 before attempt to create socket.
771 */
772
773 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
774 * and the incoming segment acknowledges something not yet
775 * sent (the segment carries an unacceptable ACK) ...
776 * a reset is sent."
777 *
778 * Invalid ACK: reset will be sent by listening socket.
779 * Note that the ACK validity check for a Fast Open socket is done
780 * elsewhere and is checked directly against the child socket rather
781 * than req because user data may have been sent out.
782 */
783 if ((flg & TCP_FLAG_ACK) && !fastopen &&
784 (TCP_SKB_CB(skb)->ack_seq !=
785 tcp_rsk(req)->snt_isn + 1))
786 return sk;
787
788 /* Also, it would be not so bad idea to check rcv_tsecr, which
789 * is essentially ACK extension and too early or too late values
790 * should cause reset in unsynchronized states.
791 */
792
793 /* RFC793: "first check sequence number". */
794
795 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq,
796 TCP_SKB_CB(skb)->end_seq,
797 tcp_rsk(req)->rcv_nxt,
798 tcp_rsk(req)->rcv_nxt +
799 tcp_synack_window(req))) {
800 /* Out of window: send ACK and drop. */
801 if (!(flg & TCP_FLAG_RST) &&
802 !tcp_oow_rate_limited(sock_net(sk), skb,
803 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
804 &tcp_rsk(req)->last_oow_ack_time))
805 req->rsk_ops->send_ack(sk, skb, req);
806 if (paws_reject)
807 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
808 return NULL;
809 }
810
811 /* In sequence, PAWS is OK. */
812
813 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
814 /* Truncate SYN, it is out of window starting
815 at tcp_rsk(req)->rcv_isn + 1. */
816 flg &= ~TCP_FLAG_SYN;
817 }
818
819 /* RFC793: "second check the RST bit" and
820 * "fourth, check the SYN bit"
821 */
822 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
823 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
824 goto embryonic_reset;
825 }
826
827 /* ACK sequence verified above, just make sure ACK is
828 * set. If ACK not set, just silently drop the packet.
829 *
830 * XXX (TFO) - if we ever allow "data after SYN", the
831 * following check needs to be removed.
832 */
833 if (!(flg & TCP_FLAG_ACK))
834 return NULL;
835
836 /* For Fast Open no more processing is needed (sk is the
837 * child socket).
838 */
839 if (fastopen)
840 return sk;
841
842 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
843 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
844 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
845 inet_rsk(req)->acked = 1;
846 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
847 return NULL;
848 }
849
850 /* OK, ACK is valid, create big socket and
851 * feed this segment to it. It will repeat all
852 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
853 * ESTABLISHED STATE. If it will be dropped after
854 * socket is created, wait for troubles.
855 */
856 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
857 req, &own_req);
858 if (!child)
859 goto listen_overflow;
860
861 if (own_req && tmp_opt.saw_tstamp &&
862 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
863 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval;
864
865 if (own_req && rsk_drop_req(req)) {
866 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req);
867 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
868 return child;
869 }
870
871 sock_rps_save_rxhash(child, skb);
872 tcp_synack_rtt_meas(child, req);
873 *req_stolen = !own_req;
874 return inet_csk_complete_hashdance(sk, child, req, own_req);
875
876listen_overflow:
877 if (sk != req->rsk_listener)
878 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
879
880 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) {
881 inet_rsk(req)->acked = 1;
882 return NULL;
883 }
884
885embryonic_reset:
886 if (!(flg & TCP_FLAG_RST)) {
887 /* Received a bad SYN pkt - for TFO We try not to reset
888 * the local connection unless it's really necessary to
889 * avoid becoming vulnerable to outside attack aiming at
890 * resetting legit local connections.
891 */
892 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN);
893 } else if (fastopen) { /* received a valid RST pkt */
894 reqsk_fastopen_remove(sk, req, true);
895 tcp_reset(sk, skb);
896 }
897 if (!fastopen) {
898 bool unlinked = inet_csk_reqsk_queue_drop(sk, req);
899
900 if (unlinked)
901 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
902 *req_stolen = !unlinked;
903 }
904 return NULL;
905}
906EXPORT_SYMBOL(tcp_check_req);
907
908/*
909 * Queue segment on the new socket if the new socket is active,
910 * otherwise we just shortcircuit this and continue with
911 * the new socket.
912 *
913 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
914 * when entering. But other states are possible due to a race condition
915 * where after __inet_lookup_established() fails but before the listener
916 * locked is obtained, other packets cause the same connection to
917 * be created.
918 */
919
920enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child,
921 struct sk_buff *skb)
922 __releases(&((child)->sk_lock.slock))
923{
924 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET;
925 int state = child->sk_state;
926
927 /* record sk_napi_id and sk_rx_queue_mapping of child. */
928 sk_mark_napi_id_set(child, skb);
929
930 tcp_segs_in(tcp_sk(child), skb);
931 if (!sock_owned_by_user(child)) {
932 reason = tcp_rcv_state_process(child, skb);
933 /* Wakeup parent, send SIGIO */
934 if (state == TCP_SYN_RECV && child->sk_state != state)
935 parent->sk_data_ready(parent);
936 } else {
937 /* Alas, it is possible again, because we do lookup
938 * in main socket hash table and lock on listening
939 * socket does not protect us more.
940 */
941 __sk_add_backlog(child, skb);
942 }
943
944 bh_unlock_sock(child);
945 sock_put(child);
946 return reason;
947}
948EXPORT_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);