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/tcp_ecn.h>
24#include <net/xfrm.h>
25#include <net/busy_poll.h>
26#include <net/rstreason.h>
27#include <net/psp.h>
28
29static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
30{
31 if (seq == s_win)
32 return true;
33 if (after(end_seq, s_win) && before(seq1: seq, seq2: e_win))
34 return true;
35 return seq == e_win && seq == end_seq;
36}
37
38static enum tcp_tw_status
39tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
40 const struct sk_buff *skb, int mib_idx)
41{
42 struct tcp_timewait_sock *tcptw = tcp_twsk(sk: (struct sock *)tw);
43
44 if (!tcp_oow_rate_limited(net: twsk_net(twsk: tw), skb, mib_idx,
45 last_oow_ack_time: &tcptw->tw_last_oow_ack_time)) {
46 /* Send ACK. Note, we do not put the bucket,
47 * it will be released by caller.
48 */
49 return TCP_TW_ACK_OOW;
50 }
51
52 /* We are rate-limiting, so just release the tw sock and drop skb. */
53 inet_twsk_put(tw);
54 return TCP_TW_SUCCESS;
55}
56
57static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq,
58 u32 rcv_nxt)
59{
60#ifdef CONFIG_TCP_AO
61 struct tcp_ao_info *ao;
62
63 ao = rcu_dereference(tcptw->ao_info);
64 if (unlikely(ao && seq < rcv_nxt))
65 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1);
66#endif
67 WRITE_ONCE(tcptw->tw_rcv_nxt, seq);
68}
69
70/*
71 * * Main purpose of TIME-WAIT state is to close connection gracefully,
72 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
73 * (and, probably, tail of data) and one or more our ACKs are lost.
74 * * What is TIME-WAIT timeout? It is associated with maximal packet
75 * lifetime in the internet, which results in wrong conclusion, that
76 * it is set to catch "old duplicate segments" wandering out of their path.
77 * It is not quite correct. This timeout is calculated so that it exceeds
78 * maximal retransmission timeout enough to allow to lose one (or more)
79 * segments sent by peer and our ACKs. This time may be calculated from RTO.
80 * * When TIME-WAIT socket receives RST, it means that another end
81 * finally closed and we are allowed to kill TIME-WAIT too.
82 * * Second purpose of TIME-WAIT is catching old duplicate segments.
83 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
84 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
85 * * If we invented some more clever way to catch duplicates
86 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
87 *
88 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
89 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
90 * from the very beginning.
91 *
92 * NOTE. With recycling (and later with fin-wait-2) TW bucket
93 * is _not_ stateless. It means, that strictly speaking we must
94 * spinlock it. I do not want! Well, probability of misbehaviour
95 * is ridiculously low and, seems, we could use some mb() tricks
96 * to avoid misread sequence numbers, states etc. --ANK
97 *
98 * We don't need to initialize tmp_out.sack_ok as we don't use the results
99 */
100enum tcp_tw_status
101tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
102 const struct tcphdr *th, u32 *tw_isn,
103 enum skb_drop_reason *drop_reason)
104{
105 struct tcp_timewait_sock *tcptw = tcp_twsk(sk: (struct sock *)tw);
106 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt);
107 struct tcp_options_received tmp_opt;
108 enum skb_drop_reason psp_drop;
109 bool paws_reject = false;
110 int ts_recent_stamp;
111
112 /* Instead of dropping immediately, wait to see what value is
113 * returned. We will accept a non psp-encapsulated syn in the
114 * case where TCP_TW_SYN is returned.
115 */
116 psp_drop = psp_twsk_rx_policy_check(tw, skb);
117
118 tmp_opt.saw_tstamp = 0;
119 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp);
120 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) {
121 tcp_parse_options(net: twsk_net(twsk: tw), skb, opt_rx: &tmp_opt, estab: 0, NULL);
122
123 if (tmp_opt.saw_tstamp) {
124 if (tmp_opt.rcv_tsecr)
125 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
126 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent);
127 tmp_opt.ts_recent_stamp = ts_recent_stamp;
128 paws_reject = tcp_paws_reject(rx_opt: &tmp_opt, rst: th->rst);
129 }
130 }
131
132 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) {
133 /* Just repeat all the checks of tcp_rcv_state_process() */
134
135 if (psp_drop)
136 goto out_put;
137
138 /* Out of window, send ACK */
139 if (paws_reject ||
140 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
141 s_win: rcv_nxt,
142 e_win: rcv_nxt + tcptw->tw_rcv_wnd))
143 return tcp_timewait_check_oow_rate_limit(
144 tw, skb, mib_idx: LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
145
146 if (th->rst)
147 goto kill;
148
149 if (th->syn && !before(TCP_SKB_CB(skb)->seq, seq2: rcv_nxt))
150 return TCP_TW_RST;
151
152 /* Dup ACK? */
153 if (!th->ack ||
154 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) ||
155 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
156 inet_twsk_put(tw);
157 return TCP_TW_SUCCESS;
158 }
159
160 /* New data or FIN. If new data arrive after half-duplex close,
161 * reset.
162 */
163 if (!th->fin ||
164 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1)
165 return TCP_TW_RST;
166
167 /* FIN arrived, enter true time-wait state. */
168 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT);
169 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq,
170 rcv_nxt);
171
172 if (tmp_opt.saw_tstamp) {
173 u64 ts = tcp_clock_ms();
174
175 WRITE_ONCE(tw->tw_entry_stamp, ts);
176 WRITE_ONCE(tcptw->tw_ts_recent_stamp,
177 div_u64(ts, MSEC_PER_SEC));
178 WRITE_ONCE(tcptw->tw_ts_recent,
179 tmp_opt.rcv_tsval);
180 }
181
182 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
183 return TCP_TW_ACK;
184 }
185
186 /*
187 * Now real TIME-WAIT state.
188 *
189 * RFC 1122:
190 * "When a connection is [...] on TIME-WAIT state [...]
191 * [a TCP] MAY accept a new SYN from the remote TCP to
192 * reopen the connection directly, if it:
193 *
194 * (1) assigns its initial sequence number for the new
195 * connection to be larger than the largest sequence
196 * number it used on the previous connection incarnation,
197 * and
198 *
199 * (2) returns to TIME-WAIT state if the SYN turns out
200 * to be an old duplicate".
201 */
202
203 if (!paws_reject &&
204 (TCP_SKB_CB(skb)->seq == rcv_nxt &&
205 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
206 /* In window segment, it may be only reset or bare ack. */
207
208 if (psp_drop)
209 goto out_put;
210
211 if (th->rst) {
212 /* This is TIME_WAIT assassination, in two flavors.
213 * Oh well... nobody has a sufficient solution to this
214 * protocol bug yet.
215 */
216 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) {
217kill:
218 inet_twsk_deschedule_put(tw);
219 return TCP_TW_SUCCESS;
220 }
221 } else {
222 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
223 }
224
225 if (tmp_opt.saw_tstamp) {
226 WRITE_ONCE(tcptw->tw_ts_recent,
227 tmp_opt.rcv_tsval);
228 WRITE_ONCE(tcptw->tw_ts_recent_stamp,
229 ktime_get_seconds());
230 }
231
232 inet_twsk_put(tw);
233 return TCP_TW_SUCCESS;
234 }
235
236 /* Out of window segment.
237
238 All the segments are ACKed immediately.
239
240 The only exception is new SYN. We accept it, if it is
241 not old duplicate and we are not in danger to be killed
242 by delayed old duplicates. RFC check is that it has
243 newer sequence number works at rates <40Mbit/sec.
244 However, if paws works, it is reliable AND even more,
245 we even may relax silly seq space cutoff.
246
247 RED-PEN: we violate main RFC requirement, if this SYN will appear
248 old duplicate (i.e. we receive RST in reply to SYN-ACK),
249 we must return socket to time-wait state. It is not good,
250 but not fatal yet.
251 */
252
253 if (th->syn && !th->rst && !th->ack && !paws_reject &&
254 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) ||
255 (tmp_opt.saw_tstamp &&
256 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) {
257 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
258 if (isn == 0)
259 isn++;
260 *tw_isn = isn;
261 return TCP_TW_SYN;
262 }
263
264 if (psp_drop)
265 goto out_put;
266
267 if (paws_reject) {
268 *drop_reason = SKB_DROP_REASON_TCP_RFC7323_TW_PAWS;
269 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWS_TW_REJECTED);
270 }
271
272 if (!th->rst) {
273 /* In this case we must reset the TIMEWAIT timer.
274 *
275 * If it is ACKless SYN it may be both old duplicate
276 * and new good SYN with random sequence number <rcv_nxt.
277 * Do not reschedule in the last case.
278 */
279 if (paws_reject || th->ack)
280 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
281
282 return tcp_timewait_check_oow_rate_limit(
283 tw, skb, mib_idx: LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
284 }
285
286out_put:
287 inet_twsk_put(tw);
288 return TCP_TW_SUCCESS;
289}
290EXPORT_IPV6_MOD(tcp_timewait_state_process);
291
292static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw)
293{
294#ifdef CONFIG_TCP_MD5SIG
295 const struct tcp_sock *tp = tcp_sk(sk);
296 struct tcp_md5sig_key *key;
297
298 /*
299 * The timewait bucket does not have the key DB from the
300 * sock structure. We just make a quick copy of the
301 * md5 key being used (if indeed we are using one)
302 * so the timewait ack generating code has the key.
303 */
304 tcptw->tw_md5_key = NULL;
305 if (!static_branch_unlikely(&tcp_md5_needed.key))
306 return;
307
308 key = tp->af_specific->md5_lookup(sk, sk);
309 if (key) {
310 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
311 if (!tcptw->tw_md5_key)
312 return;
313 if (!static_key_fast_inc_not_disabled(key: &tcp_md5_needed.key.key))
314 goto out_free;
315 tcp_md5_add_sigpool();
316 }
317 return;
318out_free:
319 WARN_ON_ONCE(1);
320 kfree(objp: tcptw->tw_md5_key);
321 tcptw->tw_md5_key = NULL;
322#endif
323}
324
325/*
326 * Move a socket to time-wait or dead fin-wait-2 state.
327 */
328void tcp_time_wait(struct sock *sk, int state, int timeo)
329{
330 const struct inet_connection_sock *icsk = inet_csk(sk);
331 struct tcp_sock *tp = tcp_sk(sk);
332 struct net *net = sock_net(sk);
333 struct inet_timewait_sock *tw;
334
335 tw = inet_twsk_alloc(sk, dr: &net->ipv4.tcp_death_row, state);
336
337 if (tw) {
338 struct tcp_timewait_sock *tcptw = tcp_twsk(sk: (struct sock *)tw);
339 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
340
341 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk);
342 tw->tw_mark = sk->sk_mark;
343 tw->tw_priority = READ_ONCE(sk->sk_priority);
344 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
345 /* refreshed when we enter true TIME-WAIT state */
346 tw->tw_entry_stamp = tcp_time_stamp_ms(tp);
347 tcptw->tw_rcv_nxt = tp->rcv_nxt;
348 tcptw->tw_snd_nxt = tp->snd_nxt;
349 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
350 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
351 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
352 tcptw->tw_ts_offset = tp->tsoffset;
353 tw->tw_usec_ts = tp->tcp_usec_ts;
354 tcptw->tw_last_oow_ack_time = 0;
355 tcptw->tw_tx_delay = tp->tcp_tx_delay;
356 tw->tw_txhash = sk->sk_txhash;
357 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping;
358#ifdef CONFIG_SOCK_RX_QUEUE_MAPPING
359 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping;
360#endif
361#if IS_ENABLED(CONFIG_IPV6)
362 if (tw->tw_family == PF_INET6) {
363 struct ipv6_pinfo *np = inet6_sk(sk: sk);
364
365 tw->tw_v6_daddr = sk->sk_v6_daddr;
366 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
367 tw->tw_tclass = np->tclass;
368 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
369 tw->tw_ipv6only = sk->sk_ipv6only;
370 }
371#endif
372
373 tcp_time_wait_init(sk, tcptw);
374 tcp_ao_time_wait(tcptw, tp);
375
376 /* Get the TIME_WAIT timeout firing. */
377 if (timeo < rto)
378 timeo = rto;
379
380 if (state == TCP_TIME_WAIT)
381 timeo = TCP_TIMEWAIT_LEN;
382
383 /* Linkage updates.
384 * Note that access to tw after this point is illegal.
385 */
386 inet_twsk_hashdance_schedule(tw, sk, hashinfo: net->ipv4.tcp_death_row.hashinfo, timeo);
387 } else {
388 /* Sorry, if we're out of memory, just CLOSE this
389 * socket up. We've got bigger problems than
390 * non-graceful socket closings.
391 */
392 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW);
393 }
394
395 tcp_update_metrics(sk);
396 tcp_done(sk);
397}
398EXPORT_SYMBOL(tcp_time_wait);
399
400void tcp_twsk_destructor(struct sock *sk)
401{
402#ifdef CONFIG_TCP_MD5SIG
403 if (static_branch_unlikely(&tcp_md5_needed.key)) {
404 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
405
406 if (twsk->tw_md5_key) {
407 kfree(objp: twsk->tw_md5_key);
408 static_branch_slow_dec_deferred(&tcp_md5_needed);
409 tcp_md5_release_sigpool();
410 }
411 }
412#endif
413 tcp_ao_destroy_sock(sk, twsk: true);
414 psp_twsk_assoc_free(tw: inet_twsk(sk));
415}
416
417void tcp_twsk_purge(struct list_head *net_exit_list)
418{
419 bool purged_once = false;
420 struct net *net;
421
422 list_for_each_entry(net, net_exit_list, exit_list) {
423 if (net->ipv4.tcp_death_row.hashinfo->pernet) {
424 /* Even if tw_refcount == 1, we must clean up kernel reqsk */
425 inet_twsk_purge(hashinfo: net->ipv4.tcp_death_row.hashinfo);
426 } else if (!purged_once) {
427 inet_twsk_purge(hashinfo: &tcp_hashinfo);
428 purged_once = true;
429 }
430 }
431}
432
433/* Warning : This function is called without sk_listener being locked.
434 * Be sure to read socket fields once, as their value could change under us.
435 */
436void tcp_openreq_init_rwin(struct request_sock *req,
437 const struct sock *sk_listener,
438 const struct dst_entry *dst)
439{
440 struct inet_request_sock *ireq = inet_rsk(sk: req);
441 const struct tcp_sock *tp = tcp_sk(sk_listener);
442 int full_space = tcp_full_space(sk: sk_listener);
443 u32 window_clamp;
444 __u8 rcv_wscale;
445 u32 rcv_wnd;
446 int mss;
447
448 mss = tcp_mss_clamp(tp, mss: dst_metric_advmss(dst));
449 window_clamp = READ_ONCE(tp->window_clamp);
450 /* Set this up on the first call only */
451 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
452
453 /* limit the window selection if the user enforce a smaller rx buffer */
454 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
455 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
456 req->rsk_window_clamp = full_space;
457
458 rcv_wnd = tcp_rwnd_init_bpf(sk: (struct sock *)req);
459 if (rcv_wnd == 0)
460 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
461 else if (full_space < rcv_wnd * mss)
462 full_space = rcv_wnd * mss;
463
464 /* tcp_full_space because it is guaranteed to be the first packet */
465 tcp_select_initial_window(sk: sk_listener, space: full_space,
466 mss: mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
467 rcv_wnd: &req->rsk_rcv_wnd,
468 window_clamp: &req->rsk_window_clamp,
469 wscale_ok: ireq->wscale_ok,
470 rcv_wscale: &rcv_wscale,
471 init_rcv_wnd: rcv_wnd);
472 ireq->rcv_wscale = rcv_wscale;
473}
474
475static void tcp_ecn_openreq_child(struct sock *sk,
476 const struct request_sock *req,
477 const struct sk_buff *skb)
478{
479 const struct tcp_request_sock *treq = tcp_rsk(req);
480 struct tcp_sock *tp = tcp_sk(sk);
481
482 if (treq->accecn_ok) {
483 tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
484 tp->syn_ect_snt = treq->syn_ect_snt;
485 tcp_accecn_third_ack(sk, skb, sent_ect: treq->syn_ect_snt);
486 tp->saw_accecn_opt = treq->saw_accecn_opt;
487 tp->prev_ecnfield = treq->syn_ect_rcv;
488 tp->accecn_opt_demand = 1;
489 tcp_ecn_received_counters_payload(sk, skb);
490 } else {
491 tcp_ecn_mode_set(tp, mode: inet_rsk(sk: req)->ecn_ok ?
492 TCP_ECN_MODE_RFC3168 :
493 TCP_ECN_DISABLED);
494 }
495}
496
497void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
498{
499 struct inet_connection_sock *icsk = inet_csk(sk);
500 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
501 bool ca_got_dst = false;
502
503 if (ca_key != TCP_CA_UNSPEC) {
504 const struct tcp_congestion_ops *ca;
505
506 rcu_read_lock();
507 ca = tcp_ca_find_key(key: ca_key);
508 if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
509 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
510 icsk->icsk_ca_ops = ca;
511 ca_got_dst = true;
512 }
513 rcu_read_unlock();
514 }
515
516 /* If no valid choice made yet, assign current system default ca. */
517 if (!ca_got_dst &&
518 (!icsk->icsk_ca_setsockopt ||
519 !bpf_try_module_get(data: icsk->icsk_ca_ops, owner: icsk->icsk_ca_ops->owner)))
520 tcp_assign_congestion_control(sk);
521
522 tcp_set_ca_state(sk, ca_state: TCP_CA_Open);
523}
524EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child);
525
526static void smc_check_reset_syn_req(const struct tcp_sock *oldtp,
527 struct request_sock *req,
528 struct tcp_sock *newtp)
529{
530#if IS_ENABLED(CONFIG_SMC)
531 struct inet_request_sock *ireq;
532
533 if (static_branch_unlikely(&tcp_have_smc)) {
534 ireq = inet_rsk(req);
535 if (oldtp->syn_smc && !ireq->smc_ok)
536 newtp->syn_smc = 0;
537 }
538#endif
539}
540
541/* This is not only more efficient than what we used to do, it eliminates
542 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
543 *
544 * Actually, we could lots of memory writes here. tp of listening
545 * socket contains all necessary default parameters.
546 */
547struct sock *tcp_create_openreq_child(const struct sock *sk,
548 struct request_sock *req,
549 struct sk_buff *skb)
550{
551 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
552 const struct inet_request_sock *ireq = inet_rsk(sk: req);
553 struct tcp_request_sock *treq = tcp_rsk(req);
554 struct inet_connection_sock *newicsk;
555 const struct tcp_sock *oldtp;
556 struct tcp_sock *newtp;
557 u32 seq;
558
559 if (!newsk)
560 return NULL;
561
562 newicsk = inet_csk(newsk);
563 newtp = tcp_sk(newsk);
564 oldtp = tcp_sk(sk);
565
566 smc_check_reset_syn_req(oldtp, req, newtp);
567
568 /* Now setup tcp_sock */
569 newtp->pred_flags = 0;
570
571 seq = treq->rcv_isn + 1;
572 newtp->rcv_wup = seq;
573 WRITE_ONCE(newtp->copied_seq, seq);
574 WRITE_ONCE(newtp->rcv_nxt, seq);
575 newtp->segs_in = 1;
576
577 seq = treq->snt_isn + 1;
578 newtp->snd_sml = newtp->snd_una = seq;
579 WRITE_ONCE(newtp->snd_nxt, seq);
580 newtp->snd_up = seq;
581
582 INIT_LIST_HEAD(list: &newtp->tsq_node);
583 INIT_LIST_HEAD(list: &newtp->tsorted_sent_queue);
584
585 tcp_init_wl(tp: newtp, seq: treq->rcv_isn);
586
587 minmax_reset(m: &newtp->rtt_min, tcp_jiffies32, meas: ~0U);
588 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
589
590 newtp->lsndtime = tcp_jiffies32;
591 newsk->sk_txhash = READ_ONCE(treq->txhash);
592 newtp->total_retrans = req->num_retrans;
593
594 tcp_init_xmit_timers(newsk);
595 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
596
597 if (sock_flag(sk: newsk, flag: SOCK_KEEPOPEN))
598 tcp_reset_keepalive_timer(sk: newsk, timeout: keepalive_time_when(tp: newtp));
599
600 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
601 newtp->rx_opt.sack_ok = ireq->sack_ok;
602 newtp->window_clamp = req->rsk_window_clamp;
603 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
604 newtp->rcv_wnd = req->rsk_rcv_wnd;
605 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
606 if (newtp->rx_opt.wscale_ok) {
607 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
608 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
609 } else {
610 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
611 newtp->window_clamp = min(newtp->window_clamp, 65535U);
612 }
613 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
614 newtp->max_window = newtp->snd_wnd;
615
616 if (newtp->rx_opt.tstamp_ok) {
617 newtp->tcp_usec_ts = treq->req_usec_ts;
618 newtp->rx_opt.ts_recent = req->ts_recent;
619 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
620 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
621 } else {
622 newtp->tcp_usec_ts = 0;
623 newtp->rx_opt.ts_recent_stamp = 0;
624 newtp->tcp_header_len = sizeof(struct tcphdr);
625 }
626 if (req->num_timeout) {
627 newtp->total_rto = req->num_timeout;
628 newtp->undo_marker = treq->snt_isn;
629 if (newtp->tcp_usec_ts) {
630 newtp->retrans_stamp = treq->snt_synack;
631 newtp->total_rto_time = (u32)(tcp_clock_us() -
632 newtp->retrans_stamp) / USEC_PER_MSEC;
633 } else {
634 newtp->retrans_stamp = div_u64(dividend: treq->snt_synack,
635 USEC_PER_SEC / TCP_TS_HZ);
636 newtp->total_rto_time = tcp_clock_ms() -
637 newtp->retrans_stamp;
638 }
639 newtp->total_rto_recoveries = 1;
640 }
641 newtp->tsoffset = treq->ts_off;
642#ifdef CONFIG_TCP_MD5SIG
643 newtp->md5sig_info = NULL; /*XXX*/
644#endif
645#ifdef CONFIG_TCP_AO
646 newtp->ao_info = NULL;
647
648 if (tcp_rsk_used_ao(req)) {
649 struct tcp_ao_key *ao_key;
650
651 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1);
652 if (ao_key)
653 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key);
654 }
655 #endif
656 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
657 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
658 newtp->rx_opt.mss_clamp = req->mss;
659 tcp_ecn_openreq_child(sk: newsk, req, skb);
660 newtp->fastopen_req = NULL;
661 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
662
663 newtp->bpf_chg_cc_inprogress = 0;
664 tcp_bpf_clone(sk, newsk);
665
666 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
667
668 xa_init_flags(xa: &newsk->sk_user_frags, XA_FLAGS_ALLOC1);
669
670 return newsk;
671}
672EXPORT_SYMBOL(tcp_create_openreq_child);
673
674/*
675 * Process an incoming packet for SYN_RECV sockets represented as a
676 * request_sock. Normally sk is the listener socket but for TFO it
677 * points to the child socket.
678 *
679 * XXX (TFO) - The current impl contains a special check for ack
680 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
681 *
682 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
683 *
684 * Note: If @fastopen is true, this can be called from process context.
685 * Otherwise, this is from BH context.
686 */
687
688struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
689 struct request_sock *req,
690 bool fastopen, bool *req_stolen,
691 enum skb_drop_reason *drop_reason)
692{
693 struct tcp_options_received tmp_opt;
694 struct sock *child;
695 const struct tcphdr *th = tcp_hdr(skb);
696 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
697 bool tsecr_reject = false;
698 bool paws_reject = false;
699 bool own_req;
700
701 tmp_opt.saw_tstamp = 0;
702 tmp_opt.accecn = 0;
703 if (th->doff > (sizeof(struct tcphdr)>>2)) {
704 tcp_parse_options(net: sock_net(sk), skb, opt_rx: &tmp_opt, estab: 0, NULL);
705
706 if (tmp_opt.saw_tstamp) {
707 tmp_opt.ts_recent = req->ts_recent;
708 if (tmp_opt.rcv_tsecr) {
709 if (inet_rsk(sk: req)->tstamp_ok && !fastopen)
710 tsecr_reject = !between(seq1: tmp_opt.rcv_tsecr,
711 seq2: tcp_rsk(req)->snt_tsval_first,
712 READ_ONCE(tcp_rsk(req)->snt_tsval_last));
713 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
714 }
715 /* We do not store true stamp, but it is not required,
716 * it can be estimated (approximately)
717 * from another data.
718 */
719 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ;
720 paws_reject = tcp_paws_reject(rx_opt: &tmp_opt, rst: th->rst);
721 }
722 }
723
724 /* Check for pure retransmitted SYN. */
725 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
726 flg == TCP_FLAG_SYN &&
727 !paws_reject) {
728 /*
729 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
730 * this case on figure 6 and figure 8, but formal
731 * protocol description says NOTHING.
732 * To be more exact, it says that we should send ACK,
733 * because this segment (at least, if it has no data)
734 * is out of window.
735 *
736 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
737 * describe SYN-RECV state. All the description
738 * is wrong, we cannot believe to it and should
739 * rely only on common sense and implementation
740 * experience.
741 *
742 * Enforce "SYN-ACK" according to figure 8, figure 6
743 * of RFC793, fixed by RFC1122.
744 *
745 * Note that even if there is new data in the SYN packet
746 * they will be thrown away too.
747 *
748 * Reset timer after retransmitting SYNACK, similar to
749 * the idea of fast retransmit in recovery.
750 */
751 if (!tcp_oow_rate_limited(net: sock_net(sk), skb,
752 mib_idx: LINUX_MIB_TCPACKSKIPPEDSYNRECV,
753 last_oow_ack_time: &tcp_rsk(req)->last_oow_ack_time) &&
754
755 !tcp_rtx_synack(sk, req)) {
756 unsigned long expires = jiffies;
757
758 expires += reqsk_timeout(req, TCP_RTO_MAX);
759 if (!fastopen)
760 mod_timer_pending(timer: &req->rsk_timer, expires);
761 else
762 req->rsk_timer.expires = expires;
763 }
764 return NULL;
765 }
766
767 /* Further reproduces section "SEGMENT ARRIVES"
768 for state SYN-RECEIVED of RFC793.
769 It is broken, however, it does not work only
770 when SYNs are crossed.
771
772 You would think that SYN crossing is impossible here, since
773 we should have a SYN_SENT socket (from connect()) on our end,
774 but this is not true if the crossed SYNs were sent to both
775 ends by a malicious third party. We must defend against this,
776 and to do that we first verify the ACK (as per RFC793, page
777 36) and reset if it is invalid. Is this a true full defense?
778 To convince ourselves, let us consider a way in which the ACK
779 test can still pass in this 'malicious crossed SYNs' case.
780 Malicious sender sends identical SYNs (and thus identical sequence
781 numbers) to both A and B:
782
783 A: gets SYN, seq=7
784 B: gets SYN, seq=7
785
786 By our good fortune, both A and B select the same initial
787 send sequence number of seven :-)
788
789 A: sends SYN|ACK, seq=7, ack_seq=8
790 B: sends SYN|ACK, seq=7, ack_seq=8
791
792 So we are now A eating this SYN|ACK, ACK test passes. So
793 does sequence test, SYN is truncated, and thus we consider
794 it a bare ACK.
795
796 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
797 bare ACK. Otherwise, we create an established connection. Both
798 ends (listening sockets) accept the new incoming connection and try
799 to talk to each other. 8-)
800
801 Note: This case is both harmless, and rare. Possibility is about the
802 same as us discovering intelligent life on another plant tomorrow.
803
804 But generally, we should (RFC lies!) to accept ACK
805 from SYNACK both here and in tcp_rcv_state_process().
806 tcp_rcv_state_process() does not, hence, we do not too.
807
808 Note that the case is absolutely generic:
809 we cannot optimize anything here without
810 violating protocol. All the checks must be made
811 before attempt to create socket.
812 */
813
814 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
815 * and the incoming segment acknowledges something not yet
816 * sent (the segment carries an unacceptable ACK) ...
817 * a reset is sent."
818 *
819 * Invalid ACK: reset will be sent by listening socket.
820 * Note that the ACK validity check for a Fast Open socket is done
821 * elsewhere and is checked directly against the child socket rather
822 * than req because user data may have been sent out.
823 */
824 if ((flg & TCP_FLAG_ACK) && !fastopen &&
825 (TCP_SKB_CB(skb)->ack_seq !=
826 tcp_rsk(req)->snt_isn + 1))
827 return sk;
828
829 /* RFC793: "first check sequence number". */
830
831 if (paws_reject || tsecr_reject ||
832 !tcp_in_window(TCP_SKB_CB(skb)->seq,
833 TCP_SKB_CB(skb)->end_seq,
834 s_win: tcp_rsk(req)->rcv_nxt,
835 e_win: tcp_rsk(req)->rcv_nxt +
836 tcp_synack_window(req))) {
837 /* Out of window: send ACK and drop. */
838 if (!(flg & TCP_FLAG_RST) &&
839 !tcp_oow_rate_limited(net: sock_net(sk), skb,
840 mib_idx: LINUX_MIB_TCPACKSKIPPEDSYNRECV,
841 last_oow_ack_time: &tcp_rsk(req)->last_oow_ack_time))
842 req->rsk_ops->send_ack(sk, skb, req);
843 if (paws_reject) {
844 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS);
845 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
846 } else if (tsecr_reject) {
847 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR);
848 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED);
849 } else {
850 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW);
851 }
852 return NULL;
853 }
854
855 /* In sequence, PAWS is OK. */
856
857 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
858 /* Truncate SYN, it is out of window starting
859 at tcp_rsk(req)->rcv_isn + 1. */
860 flg &= ~TCP_FLAG_SYN;
861 }
862
863 /* RFC793: "second check the RST bit" and
864 * "fourth, check the SYN bit"
865 */
866 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
867 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
868 goto embryonic_reset;
869 }
870
871 /* ACK sequence verified above, just make sure ACK is
872 * set. If ACK not set, just silently drop the packet.
873 *
874 * XXX (TFO) - if we ever allow "data after SYN", the
875 * following check needs to be removed.
876 */
877 if (!(flg & TCP_FLAG_ACK))
878 return NULL;
879
880 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn &&
881 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
882 u8 saw_opt = tcp_accecn_option_init(skb, opt_offset: tmp_opt.accecn);
883
884 tcp_rsk(req)->saw_accecn_opt = saw_opt;
885 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) {
886 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV;
887
888 tcp_rsk(req)->accecn_fail_mode |= fail_mode;
889 }
890 }
891
892 /* For Fast Open no more processing is needed (sk is the
893 * child socket).
894 */
895 if (fastopen)
896 return sk;
897
898 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
899 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
900 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
901 inet_rsk(sk: req)->acked = 1;
902 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
903 return NULL;
904 }
905
906 /* OK, ACK is valid, create big socket and
907 * feed this segment to it. It will repeat all
908 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
909 * ESTABLISHED STATE. If it will be dropped after
910 * socket is created, wait for troubles.
911 */
912 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
913 req, &own_req);
914 if (!child)
915 goto listen_overflow;
916
917 if (own_req && tmp_opt.saw_tstamp &&
918 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
919 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval;
920
921 if (own_req && rsk_drop_req(req)) {
922 reqsk_queue_removed(queue: &inet_csk(req->rsk_listener)->icsk_accept_queue, req);
923 inet_csk_reqsk_queue_drop_and_put(sk: req->rsk_listener, req);
924 return child;
925 }
926
927 sock_rps_save_rxhash(sk: child, skb);
928 tcp_synack_rtt_meas(sk: child, req);
929 *req_stolen = !own_req;
930 return inet_csk_complete_hashdance(sk, child, req, own_req);
931
932listen_overflow:
933 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW);
934 if (sk != req->rsk_listener)
935 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
936
937 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) {
938 inet_rsk(sk: req)->acked = 1;
939 return NULL;
940 }
941
942embryonic_reset:
943 if (!(flg & TCP_FLAG_RST)) {
944 /* Received a bad SYN pkt - for TFO We try not to reset
945 * the local connection unless it's really necessary to
946 * avoid becoming vulnerable to outside attack aiming at
947 * resetting legit local connections.
948 */
949 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN);
950 } else if (fastopen) { /* received a valid RST pkt */
951 reqsk_fastopen_remove(sk, req, reset: true);
952 tcp_reset(sk, skb);
953 }
954 if (!fastopen) {
955 bool unlinked = inet_csk_reqsk_queue_drop(sk, req);
956
957 if (unlinked)
958 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
959 *req_stolen = !unlinked;
960 }
961 return NULL;
962}
963EXPORT_IPV6_MOD(tcp_check_req);
964
965/*
966 * Queue segment on the new socket if the new socket is active,
967 * otherwise we just shortcircuit this and continue with
968 * the new socket.
969 *
970 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
971 * when entering. But other states are possible due to a race condition
972 * where after __inet_lookup_established() fails but before the listener
973 * locked is obtained, other packets cause the same connection to
974 * be created.
975 */
976
977enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child,
978 struct sk_buff *skb)
979 __releases(&((child)->sk_lock.slock))
980{
981 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET;
982 int state = child->sk_state;
983
984 /* record sk_napi_id and sk_rx_queue_mapping of child. */
985 sk_mark_napi_id_set(sk: child, skb);
986
987 tcp_segs_in(tcp_sk(child), skb);
988 if (!sock_owned_by_user(sk: child)) {
989 reason = tcp_rcv_state_process(sk: child, skb);
990 /* Wakeup parent, send SIGIO */
991 if (state == TCP_SYN_RECV && child->sk_state != state)
992 parent->sk_data_ready(parent);
993 } else {
994 /* Alas, it is possible again, because we do lookup
995 * in main socket hash table and lock on listening
996 * socket does not protect us more.
997 */
998 __sk_add_backlog(sk: child, skb);
999 }
1000
1001 bh_unlock_sock(child);
1002 sock_put(sk: child);
1003 return reason;
1004}
1005EXPORT_IPV6_MOD(tcp_child_process);
1006