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1/*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21#include <linux/mm.h>
22#include <linux/module.h>
23#include <linux/slab.h>
24#include <linux/sysctl.h>
25#include <linux/workqueue.h>
26#include <linux/static_key.h>
27#include <net/tcp.h>
28#include <net/inet_common.h>
29#include <net/xfrm.h>
30#include <net/busy_poll.h>
31
32static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
33{
34 if (seq == s_win)
35 return true;
36 if (after(end_seq, s_win) && before(seq, e_win))
37 return true;
38 return seq == e_win && seq == end_seq;
39}
40
41static enum tcp_tw_status
42tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
43 const struct sk_buff *skb, int mib_idx)
44{
45 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
46
47 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
48 &tcptw->tw_last_oow_ack_time)) {
49 /* Send ACK. Note, we do not put the bucket,
50 * it will be released by caller.
51 */
52 return TCP_TW_ACK;
53 }
54
55 /* We are rate-limiting, so just release the tw sock and drop skb. */
56 inet_twsk_put(tw);
57 return TCP_TW_SUCCESS;
58}
59
60/*
61 * * Main purpose of TIME-WAIT state is to close connection gracefully,
62 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
63 * (and, probably, tail of data) and one or more our ACKs are lost.
64 * * What is TIME-WAIT timeout? It is associated with maximal packet
65 * lifetime in the internet, which results in wrong conclusion, that
66 * it is set to catch "old duplicate segments" wandering out of their path.
67 * It is not quite correct. This timeout is calculated so that it exceeds
68 * maximal retransmission timeout enough to allow to lose one (or more)
69 * segments sent by peer and our ACKs. This time may be calculated from RTO.
70 * * When TIME-WAIT socket receives RST, it means that another end
71 * finally closed and we are allowed to kill TIME-WAIT too.
72 * * Second purpose of TIME-WAIT is catching old duplicate segments.
73 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
74 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
75 * * If we invented some more clever way to catch duplicates
76 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
77 *
78 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
79 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
80 * from the very beginning.
81 *
82 * NOTE. With recycling (and later with fin-wait-2) TW bucket
83 * is _not_ stateless. It means, that strictly speaking we must
84 * spinlock it. I do not want! Well, probability of misbehaviour
85 * is ridiculously low and, seems, we could use some mb() tricks
86 * to avoid misread sequence numbers, states etc. --ANK
87 *
88 * We don't need to initialize tmp_out.sack_ok as we don't use the results
89 */
90enum tcp_tw_status
91tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
92 const struct tcphdr *th)
93{
94 struct tcp_options_received tmp_opt;
95 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
96 bool paws_reject = false;
97
98 tmp_opt.saw_tstamp = 0;
99 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
100 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);
101
102 if (tmp_opt.saw_tstamp) {
103 if (tmp_opt.rcv_tsecr)
104 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
105 tmp_opt.ts_recent = tcptw->tw_ts_recent;
106 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
107 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
108 }
109 }
110
111 if (tw->tw_substate == TCP_FIN_WAIT2) {
112 /* Just repeat all the checks of tcp_rcv_state_process() */
113
114 /* Out of window, send ACK */
115 if (paws_reject ||
116 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
117 tcptw->tw_rcv_nxt,
118 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
119 return tcp_timewait_check_oow_rate_limit(
120 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
121
122 if (th->rst)
123 goto kill;
124
125 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
126 return TCP_TW_RST;
127
128 /* Dup ACK? */
129 if (!th->ack ||
130 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
131 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
132 inet_twsk_put(tw);
133 return TCP_TW_SUCCESS;
134 }
135
136 /* New data or FIN. If new data arrive after half-duplex close,
137 * reset.
138 */
139 if (!th->fin ||
140 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
141 return TCP_TW_RST;
142
143 /* FIN arrived, enter true time-wait state. */
144 tw->tw_substate = TCP_TIME_WAIT;
145 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
146 if (tmp_opt.saw_tstamp) {
147 tcptw->tw_ts_recent_stamp = get_seconds();
148 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
149 }
150
151 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
152 return TCP_TW_ACK;
153 }
154
155 /*
156 * Now real TIME-WAIT state.
157 *
158 * RFC 1122:
159 * "When a connection is [...] on TIME-WAIT state [...]
160 * [a TCP] MAY accept a new SYN from the remote TCP to
161 * reopen the connection directly, if it:
162 *
163 * (1) assigns its initial sequence number for the new
164 * connection to be larger than the largest sequence
165 * number it used on the previous connection incarnation,
166 * and
167 *
168 * (2) returns to TIME-WAIT state if the SYN turns out
169 * to be an old duplicate".
170 */
171
172 if (!paws_reject &&
173 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
174 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
175 /* In window segment, it may be only reset or bare ack. */
176
177 if (th->rst) {
178 /* This is TIME_WAIT assassination, in two flavors.
179 * Oh well... nobody has a sufficient solution to this
180 * protocol bug yet.
181 */
182 if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
183kill:
184 inet_twsk_deschedule_put(tw);
185 return TCP_TW_SUCCESS;
186 }
187 }
188 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
189
190 if (tmp_opt.saw_tstamp) {
191 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
192 tcptw->tw_ts_recent_stamp = get_seconds();
193 }
194
195 inet_twsk_put(tw);
196 return TCP_TW_SUCCESS;
197 }
198
199 /* Out of window segment.
200
201 All the segments are ACKed immediately.
202
203 The only exception is new SYN. We accept it, if it is
204 not old duplicate and we are not in danger to be killed
205 by delayed old duplicates. RFC check is that it has
206 newer sequence number works at rates <40Mbit/sec.
207 However, if paws works, it is reliable AND even more,
208 we even may relax silly seq space cutoff.
209
210 RED-PEN: we violate main RFC requirement, if this SYN will appear
211 old duplicate (i.e. we receive RST in reply to SYN-ACK),
212 we must return socket to time-wait state. It is not good,
213 but not fatal yet.
214 */
215
216 if (th->syn && !th->rst && !th->ack && !paws_reject &&
217 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
218 (tmp_opt.saw_tstamp &&
219 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
220 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
221 if (isn == 0)
222 isn++;
223 TCP_SKB_CB(skb)->tcp_tw_isn = isn;
224 return TCP_TW_SYN;
225 }
226
227 if (paws_reject)
228 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
229
230 if (!th->rst) {
231 /* In this case we must reset the TIMEWAIT timer.
232 *
233 * If it is ACKless SYN it may be both old duplicate
234 * and new good SYN with random sequence number <rcv_nxt.
235 * Do not reschedule in the last case.
236 */
237 if (paws_reject || th->ack)
238 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
239
240 return tcp_timewait_check_oow_rate_limit(
241 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
242 }
243 inet_twsk_put(tw);
244 return TCP_TW_SUCCESS;
245}
246EXPORT_SYMBOL(tcp_timewait_state_process);
247
248/*
249 * Move a socket to time-wait or dead fin-wait-2 state.
250 */
251void tcp_time_wait(struct sock *sk, int state, int timeo)
252{
253 const struct inet_connection_sock *icsk = inet_csk(sk);
254 const struct tcp_sock *tp = tcp_sk(sk);
255 struct inet_timewait_sock *tw;
256 struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
257
258 tw = inet_twsk_alloc(sk, tcp_death_row, state);
259
260 if (tw) {
261 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
262 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
263 struct inet_sock *inet = inet_sk(sk);
264
265 tw->tw_transparent = inet->transparent;
266 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
267 tcptw->tw_rcv_nxt = tp->rcv_nxt;
268 tcptw->tw_snd_nxt = tp->snd_nxt;
269 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
270 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
271 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
272 tcptw->tw_ts_offset = tp->tsoffset;
273 tcptw->tw_last_oow_ack_time = 0;
274
275#if IS_ENABLED(CONFIG_IPV6)
276 if (tw->tw_family == PF_INET6) {
277 struct ipv6_pinfo *np = inet6_sk(sk);
278
279 tw->tw_v6_daddr = sk->sk_v6_daddr;
280 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
281 tw->tw_tclass = np->tclass;
282 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
283 tw->tw_ipv6only = sk->sk_ipv6only;
284 }
285#endif
286
287#ifdef CONFIG_TCP_MD5SIG
288 /*
289 * The timewait bucket does not have the key DB from the
290 * sock structure. We just make a quick copy of the
291 * md5 key being used (if indeed we are using one)
292 * so the timewait ack generating code has the key.
293 */
294 do {
295 struct tcp_md5sig_key *key;
296 tcptw->tw_md5_key = NULL;
297 key = tp->af_specific->md5_lookup(sk, sk);
298 if (key) {
299 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
300 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
301 }
302 } while (0);
303#endif
304
305 /* Get the TIME_WAIT timeout firing. */
306 if (timeo < rto)
307 timeo = rto;
308
309 tw->tw_timeout = TCP_TIMEWAIT_LEN;
310 if (state == TCP_TIME_WAIT)
311 timeo = TCP_TIMEWAIT_LEN;
312
313 /* tw_timer is pinned, so we need to make sure BH are disabled
314 * in following section, otherwise timer handler could run before
315 * we complete the initialization.
316 */
317 local_bh_disable();
318 inet_twsk_schedule(tw, timeo);
319 /* Linkage updates.
320 * Note that access to tw after this point is illegal.
321 */
322 inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
323 local_bh_enable();
324 } else {
325 /* Sorry, if we're out of memory, just CLOSE this
326 * socket up. We've got bigger problems than
327 * non-graceful socket closings.
328 */
329 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
330 }
331
332 tcp_update_metrics(sk);
333 tcp_done(sk);
334}
335EXPORT_SYMBOL(tcp_time_wait);
336
337void tcp_twsk_destructor(struct sock *sk)
338{
339#ifdef CONFIG_TCP_MD5SIG
340 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
341
342 if (twsk->tw_md5_key)
343 kfree_rcu(twsk->tw_md5_key, rcu);
344#endif
345}
346EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
347
348/* Warning : This function is called without sk_listener being locked.
349 * Be sure to read socket fields once, as their value could change under us.
350 */
351void tcp_openreq_init_rwin(struct request_sock *req,
352 const struct sock *sk_listener,
353 const struct dst_entry *dst)
354{
355 struct inet_request_sock *ireq = inet_rsk(req);
356 const struct tcp_sock *tp = tcp_sk(sk_listener);
357 int full_space = tcp_full_space(sk_listener);
358 u32 window_clamp;
359 __u8 rcv_wscale;
360 u32 rcv_wnd;
361 int mss;
362
363 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
364 window_clamp = READ_ONCE(tp->window_clamp);
365 /* Set this up on the first call only */
366 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
367
368 /* limit the window selection if the user enforce a smaller rx buffer */
369 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
370 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
371 req->rsk_window_clamp = full_space;
372
373 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
374 if (rcv_wnd == 0)
375 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
376 else if (full_space < rcv_wnd * mss)
377 full_space = rcv_wnd * mss;
378
379 /* tcp_full_space because it is guaranteed to be the first packet */
380 tcp_select_initial_window(sk_listener, full_space,
381 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
382 &req->rsk_rcv_wnd,
383 &req->rsk_window_clamp,
384 ireq->wscale_ok,
385 &rcv_wscale,
386 rcv_wnd);
387 ireq->rcv_wscale = rcv_wscale;
388}
389EXPORT_SYMBOL(tcp_openreq_init_rwin);
390
391static void tcp_ecn_openreq_child(struct tcp_sock *tp,
392 const struct request_sock *req)
393{
394 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
395}
396
397void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
398{
399 struct inet_connection_sock *icsk = inet_csk(sk);
400 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
401 bool ca_got_dst = false;
402
403 if (ca_key != TCP_CA_UNSPEC) {
404 const struct tcp_congestion_ops *ca;
405
406 rcu_read_lock();
407 ca = tcp_ca_find_key(ca_key);
408 if (likely(ca && try_module_get(ca->owner))) {
409 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
410 icsk->icsk_ca_ops = ca;
411 ca_got_dst = true;
412 }
413 rcu_read_unlock();
414 }
415
416 /* If no valid choice made yet, assign current system default ca. */
417 if (!ca_got_dst &&
418 (!icsk->icsk_ca_setsockopt ||
419 !try_module_get(icsk->icsk_ca_ops->owner)))
420 tcp_assign_congestion_control(sk);
421
422 tcp_set_ca_state(sk, TCP_CA_Open);
423}
424EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
425
426static void smc_check_reset_syn_req(struct tcp_sock *oldtp,
427 struct request_sock *req,
428 struct tcp_sock *newtp)
429{
430#if IS_ENABLED(CONFIG_SMC)
431 struct inet_request_sock *ireq;
432
433 if (static_branch_unlikely(&tcp_have_smc)) {
434 ireq = inet_rsk(req);
435 if (oldtp->syn_smc && !ireq->smc_ok)
436 newtp->syn_smc = 0;
437 }
438#endif
439}
440
441/* This is not only more efficient than what we used to do, it eliminates
442 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
443 *
444 * Actually, we could lots of memory writes here. tp of listening
445 * socket contains all necessary default parameters.
446 */
447struct sock *tcp_create_openreq_child(const struct sock *sk,
448 struct request_sock *req,
449 struct sk_buff *skb)
450{
451 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
452
453 if (newsk) {
454 const struct inet_request_sock *ireq = inet_rsk(req);
455 struct tcp_request_sock *treq = tcp_rsk(req);
456 struct inet_connection_sock *newicsk = inet_csk(newsk);
457 struct tcp_sock *newtp = tcp_sk(newsk);
458 struct tcp_sock *oldtp = tcp_sk(sk);
459
460 smc_check_reset_syn_req(oldtp, req, newtp);
461
462 /* Now setup tcp_sock */
463 newtp->pred_flags = 0;
464
465 newtp->rcv_wup = newtp->copied_seq =
466 newtp->rcv_nxt = treq->rcv_isn + 1;
467 newtp->segs_in = 1;
468
469 newtp->snd_sml = newtp->snd_una =
470 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
471
472 INIT_LIST_HEAD(&newtp->tsq_node);
473 INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
474
475 tcp_init_wl(newtp, treq->rcv_isn);
476
477 newtp->srtt_us = 0;
478 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
479 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
480 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
481 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
482
483 newtp->packets_out = 0;
484 newtp->retrans_out = 0;
485 newtp->sacked_out = 0;
486 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
487 newtp->tlp_high_seq = 0;
488 newtp->lsndtime = tcp_jiffies32;
489 newsk->sk_txhash = treq->txhash;
490 newtp->last_oow_ack_time = 0;
491 newtp->total_retrans = req->num_retrans;
492
493 /* So many TCP implementations out there (incorrectly) count the
494 * initial SYN frame in their delayed-ACK and congestion control
495 * algorithms that we must have the following bandaid to talk
496 * efficiently to them. -DaveM
497 */
498 newtp->snd_cwnd = TCP_INIT_CWND;
499 newtp->snd_cwnd_cnt = 0;
500
501 /* There's a bubble in the pipe until at least the first ACK. */
502 newtp->app_limited = ~0U;
503
504 tcp_init_xmit_timers(newsk);
505 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
506
507 newtp->rx_opt.saw_tstamp = 0;
508
509 newtp->rx_opt.dsack = 0;
510 newtp->rx_opt.num_sacks = 0;
511
512 newtp->urg_data = 0;
513
514 if (sock_flag(newsk, SOCK_KEEPOPEN))
515 inet_csk_reset_keepalive_timer(newsk,
516 keepalive_time_when(newtp));
517
518 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
519 newtp->rx_opt.sack_ok = ireq->sack_ok;
520 newtp->window_clamp = req->rsk_window_clamp;
521 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
522 newtp->rcv_wnd = req->rsk_rcv_wnd;
523 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
524 if (newtp->rx_opt.wscale_ok) {
525 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
526 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
527 } else {
528 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
529 newtp->window_clamp = min(newtp->window_clamp, 65535U);
530 }
531 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
532 newtp->rx_opt.snd_wscale);
533 newtp->max_window = newtp->snd_wnd;
534
535 if (newtp->rx_opt.tstamp_ok) {
536 newtp->rx_opt.ts_recent = req->ts_recent;
537 newtp->rx_opt.ts_recent_stamp = get_seconds();
538 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
539 } else {
540 newtp->rx_opt.ts_recent_stamp = 0;
541 newtp->tcp_header_len = sizeof(struct tcphdr);
542 }
543 newtp->tsoffset = treq->ts_off;
544#ifdef CONFIG_TCP_MD5SIG
545 newtp->md5sig_info = NULL; /*XXX*/
546 if (newtp->af_specific->md5_lookup(sk, newsk))
547 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
548#endif
549 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
550 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
551 newtp->rx_opt.mss_clamp = req->mss;
552 tcp_ecn_openreq_child(newtp, req);
553 newtp->fastopen_req = NULL;
554 newtp->fastopen_rsk = NULL;
555 newtp->syn_data_acked = 0;
556 newtp->rack.mstamp = 0;
557 newtp->rack.advanced = 0;
558 newtp->rack.reo_wnd_steps = 1;
559 newtp->rack.last_delivered = 0;
560 newtp->rack.reo_wnd_persist = 0;
561 newtp->rack.dsack_seen = 0;
562
563 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
564 }
565 return newsk;
566}
567EXPORT_SYMBOL(tcp_create_openreq_child);
568
569/*
570 * Process an incoming packet for SYN_RECV sockets represented as a
571 * request_sock. Normally sk is the listener socket but for TFO it
572 * points to the child socket.
573 *
574 * XXX (TFO) - The current impl contains a special check for ack
575 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
576 *
577 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
578 */
579
580struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
581 struct request_sock *req,
582 bool fastopen, bool *req_stolen)
583{
584 struct tcp_options_received tmp_opt;
585 struct sock *child;
586 const struct tcphdr *th = tcp_hdr(skb);
587 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
588 bool paws_reject = false;
589 bool own_req;
590
591 tmp_opt.saw_tstamp = 0;
592 if (th->doff > (sizeof(struct tcphdr)>>2)) {
593 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
594
595 if (tmp_opt.saw_tstamp) {
596 tmp_opt.ts_recent = req->ts_recent;
597 if (tmp_opt.rcv_tsecr)
598 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
599 /* We do not store true stamp, but it is not required,
600 * it can be estimated (approximately)
601 * from another data.
602 */
603 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
604 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
605 }
606 }
607
608 /* Check for pure retransmitted SYN. */
609 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
610 flg == TCP_FLAG_SYN &&
611 !paws_reject) {
612 /*
613 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
614 * this case on figure 6 and figure 8, but formal
615 * protocol description says NOTHING.
616 * To be more exact, it says that we should send ACK,
617 * because this segment (at least, if it has no data)
618 * is out of window.
619 *
620 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
621 * describe SYN-RECV state. All the description
622 * is wrong, we cannot believe to it and should
623 * rely only on common sense and implementation
624 * experience.
625 *
626 * Enforce "SYN-ACK" according to figure 8, figure 6
627 * of RFC793, fixed by RFC1122.
628 *
629 * Note that even if there is new data in the SYN packet
630 * they will be thrown away too.
631 *
632 * Reset timer after retransmitting SYNACK, similar to
633 * the idea of fast retransmit in recovery.
634 */
635 if (!tcp_oow_rate_limited(sock_net(sk), skb,
636 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
637 &tcp_rsk(req)->last_oow_ack_time) &&
638
639 !inet_rtx_syn_ack(sk, req)) {
640 unsigned long expires = jiffies;
641
642 expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
643 TCP_RTO_MAX);
644 if (!fastopen)
645 mod_timer_pending(&req->rsk_timer, expires);
646 else
647 req->rsk_timer.expires = expires;
648 }
649 return NULL;
650 }
651
652 /* Further reproduces section "SEGMENT ARRIVES"
653 for state SYN-RECEIVED of RFC793.
654 It is broken, however, it does not work only
655 when SYNs are crossed.
656
657 You would think that SYN crossing is impossible here, since
658 we should have a SYN_SENT socket (from connect()) on our end,
659 but this is not true if the crossed SYNs were sent to both
660 ends by a malicious third party. We must defend against this,
661 and to do that we first verify the ACK (as per RFC793, page
662 36) and reset if it is invalid. Is this a true full defense?
663 To convince ourselves, let us consider a way in which the ACK
664 test can still pass in this 'malicious crossed SYNs' case.
665 Malicious sender sends identical SYNs (and thus identical sequence
666 numbers) to both A and B:
667
668 A: gets SYN, seq=7
669 B: gets SYN, seq=7
670
671 By our good fortune, both A and B select the same initial
672 send sequence number of seven :-)
673
674 A: sends SYN|ACK, seq=7, ack_seq=8
675 B: sends SYN|ACK, seq=7, ack_seq=8
676
677 So we are now A eating this SYN|ACK, ACK test passes. So
678 does sequence test, SYN is truncated, and thus we consider
679 it a bare ACK.
680
681 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
682 bare ACK. Otherwise, we create an established connection. Both
683 ends (listening sockets) accept the new incoming connection and try
684 to talk to each other. 8-)
685
686 Note: This case is both harmless, and rare. Possibility is about the
687 same as us discovering intelligent life on another plant tomorrow.
688
689 But generally, we should (RFC lies!) to accept ACK
690 from SYNACK both here and in tcp_rcv_state_process().
691 tcp_rcv_state_process() does not, hence, we do not too.
692
693 Note that the case is absolutely generic:
694 we cannot optimize anything here without
695 violating protocol. All the checks must be made
696 before attempt to create socket.
697 */
698
699 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
700 * and the incoming segment acknowledges something not yet
701 * sent (the segment carries an unacceptable ACK) ...
702 * a reset is sent."
703 *
704 * Invalid ACK: reset will be sent by listening socket.
705 * Note that the ACK validity check for a Fast Open socket is done
706 * elsewhere and is checked directly against the child socket rather
707 * than req because user data may have been sent out.
708 */
709 if ((flg & TCP_FLAG_ACK) && !fastopen &&
710 (TCP_SKB_CB(skb)->ack_seq !=
711 tcp_rsk(req)->snt_isn + 1))
712 return sk;
713
714 /* Also, it would be not so bad idea to check rcv_tsecr, which
715 * is essentially ACK extension and too early or too late values
716 * should cause reset in unsynchronized states.
717 */
718
719 /* RFC793: "first check sequence number". */
720
721 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
722 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
723 /* Out of window: send ACK and drop. */
724 if (!(flg & TCP_FLAG_RST) &&
725 !tcp_oow_rate_limited(sock_net(sk), skb,
726 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
727 &tcp_rsk(req)->last_oow_ack_time))
728 req->rsk_ops->send_ack(sk, skb, req);
729 if (paws_reject)
730 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
731 return NULL;
732 }
733
734 /* In sequence, PAWS is OK. */
735
736 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
737 req->ts_recent = tmp_opt.rcv_tsval;
738
739 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
740 /* Truncate SYN, it is out of window starting
741 at tcp_rsk(req)->rcv_isn + 1. */
742 flg &= ~TCP_FLAG_SYN;
743 }
744
745 /* RFC793: "second check the RST bit" and
746 * "fourth, check the SYN bit"
747 */
748 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
749 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
750 goto embryonic_reset;
751 }
752
753 /* ACK sequence verified above, just make sure ACK is
754 * set. If ACK not set, just silently drop the packet.
755 *
756 * XXX (TFO) - if we ever allow "data after SYN", the
757 * following check needs to be removed.
758 */
759 if (!(flg & TCP_FLAG_ACK))
760 return NULL;
761
762 /* For Fast Open no more processing is needed (sk is the
763 * child socket).
764 */
765 if (fastopen)
766 return sk;
767
768 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
769 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
770 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
771 inet_rsk(req)->acked = 1;
772 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
773 return NULL;
774 }
775
776 /* OK, ACK is valid, create big socket and
777 * feed this segment to it. It will repeat all
778 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
779 * ESTABLISHED STATE. If it will be dropped after
780 * socket is created, wait for troubles.
781 */
782 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
783 req, &own_req);
784 if (!child)
785 goto listen_overflow;
786
787 sock_rps_save_rxhash(child, skb);
788 tcp_synack_rtt_meas(child, req);
789 *req_stolen = !own_req;
790 return inet_csk_complete_hashdance(sk, child, req, own_req);
791
792listen_overflow:
793 if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
794 inet_rsk(req)->acked = 1;
795 return NULL;
796 }
797
798embryonic_reset:
799 if (!(flg & TCP_FLAG_RST)) {
800 /* Received a bad SYN pkt - for TFO We try not to reset
801 * the local connection unless it's really necessary to
802 * avoid becoming vulnerable to outside attack aiming at
803 * resetting legit local connections.
804 */
805 req->rsk_ops->send_reset(sk, skb);
806 } else if (fastopen) { /* received a valid RST pkt */
807 reqsk_fastopen_remove(sk, req, true);
808 tcp_reset(sk);
809 }
810 if (!fastopen) {
811 inet_csk_reqsk_queue_drop(sk, req);
812 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
813 }
814 return NULL;
815}
816EXPORT_SYMBOL(tcp_check_req);
817
818/*
819 * Queue segment on the new socket if the new socket is active,
820 * otherwise we just shortcircuit this and continue with
821 * the new socket.
822 *
823 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
824 * when entering. But other states are possible due to a race condition
825 * where after __inet_lookup_established() fails but before the listener
826 * locked is obtained, other packets cause the same connection to
827 * be created.
828 */
829
830int tcp_child_process(struct sock *parent, struct sock *child,
831 struct sk_buff *skb)
832{
833 int ret = 0;
834 int state = child->sk_state;
835
836 /* record NAPI ID of child */
837 sk_mark_napi_id(child, skb);
838
839 tcp_segs_in(tcp_sk(child), skb);
840 if (!sock_owned_by_user(child)) {
841 ret = tcp_rcv_state_process(child, skb);
842 /* Wakeup parent, send SIGIO */
843 if (state == TCP_SYN_RECV && child->sk_state != state)
844 parent->sk_data_ready(parent);
845 } else {
846 /* Alas, it is possible again, because we do lookup
847 * in main socket hash table and lock on listening
848 * socket does not protect us more.
849 */
850 __sk_add_backlog(child, skb);
851 }
852
853 bh_unlock_sock(child);
854 sock_put(child);
855 return ret;
856}
857EXPORT_SYMBOL(tcp_child_process);
1/*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21#include <linux/mm.h>
22#include <linux/module.h>
23#include <linux/slab.h>
24#include <linux/sysctl.h>
25#include <linux/workqueue.h>
26#include <net/tcp.h>
27#include <net/inet_common.h>
28#include <net/xfrm.h>
29
30int sysctl_tcp_syncookies __read_mostly = 1;
31EXPORT_SYMBOL(sysctl_tcp_syncookies);
32
33int sysctl_tcp_abort_on_overflow __read_mostly;
34
35struct inet_timewait_death_row tcp_death_row = {
36 .sysctl_max_tw_buckets = NR_FILE * 2,
37 .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
38 .death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
39 .hashinfo = &tcp_hashinfo,
40 .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
41 (unsigned long)&tcp_death_row),
42 .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
43 inet_twdr_twkill_work),
44/* Short-time timewait calendar */
45
46 .twcal_hand = -1,
47 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
48 (unsigned long)&tcp_death_row),
49};
50EXPORT_SYMBOL_GPL(tcp_death_row);
51
52/* VJ's idea. Save last timestamp seen from this destination
53 * and hold it at least for normal timewait interval to use for duplicate
54 * segment detection in subsequent connections, before they enter synchronized
55 * state.
56 */
57
58static bool tcp_remember_stamp(struct sock *sk)
59{
60 const struct inet_connection_sock *icsk = inet_csk(sk);
61 struct tcp_sock *tp = tcp_sk(sk);
62 struct inet_peer *peer;
63 bool release_it;
64
65 peer = icsk->icsk_af_ops->get_peer(sk, &release_it);
66 if (peer) {
67 if ((s32)(peer->tcp_ts - tp->rx_opt.ts_recent) <= 0 ||
68 ((u32)get_seconds() - peer->tcp_ts_stamp > TCP_PAWS_MSL &&
69 peer->tcp_ts_stamp <= (u32)tp->rx_opt.ts_recent_stamp)) {
70 peer->tcp_ts_stamp = (u32)tp->rx_opt.ts_recent_stamp;
71 peer->tcp_ts = tp->rx_opt.ts_recent;
72 }
73 if (release_it)
74 inet_putpeer(peer);
75 return true;
76 }
77
78 return false;
79}
80
81static bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw)
82{
83 struct sock *sk = (struct sock *) tw;
84 struct inet_peer *peer;
85
86 peer = twsk_getpeer(sk);
87 if (peer) {
88 const struct tcp_timewait_sock *tcptw = tcp_twsk(sk);
89
90 if ((s32)(peer->tcp_ts - tcptw->tw_ts_recent) <= 0 ||
91 ((u32)get_seconds() - peer->tcp_ts_stamp > TCP_PAWS_MSL &&
92 peer->tcp_ts_stamp <= (u32)tcptw->tw_ts_recent_stamp)) {
93 peer->tcp_ts_stamp = (u32)tcptw->tw_ts_recent_stamp;
94 peer->tcp_ts = tcptw->tw_ts_recent;
95 }
96 inet_putpeer(peer);
97 return true;
98 }
99 return false;
100}
101
102static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
103{
104 if (seq == s_win)
105 return true;
106 if (after(end_seq, s_win) && before(seq, e_win))
107 return true;
108 return seq == e_win && seq == end_seq;
109}
110
111/*
112 * * Main purpose of TIME-WAIT state is to close connection gracefully,
113 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
114 * (and, probably, tail of data) and one or more our ACKs are lost.
115 * * What is TIME-WAIT timeout? It is associated with maximal packet
116 * lifetime in the internet, which results in wrong conclusion, that
117 * it is set to catch "old duplicate segments" wandering out of their path.
118 * It is not quite correct. This timeout is calculated so that it exceeds
119 * maximal retransmission timeout enough to allow to lose one (or more)
120 * segments sent by peer and our ACKs. This time may be calculated from RTO.
121 * * When TIME-WAIT socket receives RST, it means that another end
122 * finally closed and we are allowed to kill TIME-WAIT too.
123 * * Second purpose of TIME-WAIT is catching old duplicate segments.
124 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
125 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
126 * * If we invented some more clever way to catch duplicates
127 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
128 *
129 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
130 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
131 * from the very beginning.
132 *
133 * NOTE. With recycling (and later with fin-wait-2) TW bucket
134 * is _not_ stateless. It means, that strictly speaking we must
135 * spinlock it. I do not want! Well, probability of misbehaviour
136 * is ridiculously low and, seems, we could use some mb() tricks
137 * to avoid misread sequence numbers, states etc. --ANK
138 */
139enum tcp_tw_status
140tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
141 const struct tcphdr *th)
142{
143 struct tcp_options_received tmp_opt;
144 const u8 *hash_location;
145 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
146 bool paws_reject = false;
147
148 tmp_opt.saw_tstamp = 0;
149 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
150 tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
151
152 if (tmp_opt.saw_tstamp) {
153 tmp_opt.ts_recent = tcptw->tw_ts_recent;
154 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
155 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
156 }
157 }
158
159 if (tw->tw_substate == TCP_FIN_WAIT2) {
160 /* Just repeat all the checks of tcp_rcv_state_process() */
161
162 /* Out of window, send ACK */
163 if (paws_reject ||
164 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
165 tcptw->tw_rcv_nxt,
166 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
167 return TCP_TW_ACK;
168
169 if (th->rst)
170 goto kill;
171
172 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
173 goto kill_with_rst;
174
175 /* Dup ACK? */
176 if (!th->ack ||
177 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
178 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
179 inet_twsk_put(tw);
180 return TCP_TW_SUCCESS;
181 }
182
183 /* New data or FIN. If new data arrive after half-duplex close,
184 * reset.
185 */
186 if (!th->fin ||
187 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
188kill_with_rst:
189 inet_twsk_deschedule(tw, &tcp_death_row);
190 inet_twsk_put(tw);
191 return TCP_TW_RST;
192 }
193
194 /* FIN arrived, enter true time-wait state. */
195 tw->tw_substate = TCP_TIME_WAIT;
196 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
197 if (tmp_opt.saw_tstamp) {
198 tcptw->tw_ts_recent_stamp = get_seconds();
199 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
200 }
201
202 if (tcp_death_row.sysctl_tw_recycle &&
203 tcptw->tw_ts_recent_stamp &&
204 tcp_tw_remember_stamp(tw))
205 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
206 TCP_TIMEWAIT_LEN);
207 else
208 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
209 TCP_TIMEWAIT_LEN);
210 return TCP_TW_ACK;
211 }
212
213 /*
214 * Now real TIME-WAIT state.
215 *
216 * RFC 1122:
217 * "When a connection is [...] on TIME-WAIT state [...]
218 * [a TCP] MAY accept a new SYN from the remote TCP to
219 * reopen the connection directly, if it:
220 *
221 * (1) assigns its initial sequence number for the new
222 * connection to be larger than the largest sequence
223 * number it used on the previous connection incarnation,
224 * and
225 *
226 * (2) returns to TIME-WAIT state if the SYN turns out
227 * to be an old duplicate".
228 */
229
230 if (!paws_reject &&
231 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
232 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
233 /* In window segment, it may be only reset or bare ack. */
234
235 if (th->rst) {
236 /* This is TIME_WAIT assassination, in two flavors.
237 * Oh well... nobody has a sufficient solution to this
238 * protocol bug yet.
239 */
240 if (sysctl_tcp_rfc1337 == 0) {
241kill:
242 inet_twsk_deschedule(tw, &tcp_death_row);
243 inet_twsk_put(tw);
244 return TCP_TW_SUCCESS;
245 }
246 }
247 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
248 TCP_TIMEWAIT_LEN);
249
250 if (tmp_opt.saw_tstamp) {
251 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
252 tcptw->tw_ts_recent_stamp = get_seconds();
253 }
254
255 inet_twsk_put(tw);
256 return TCP_TW_SUCCESS;
257 }
258
259 /* Out of window segment.
260
261 All the segments are ACKed immediately.
262
263 The only exception is new SYN. We accept it, if it is
264 not old duplicate and we are not in danger to be killed
265 by delayed old duplicates. RFC check is that it has
266 newer sequence number works at rates <40Mbit/sec.
267 However, if paws works, it is reliable AND even more,
268 we even may relax silly seq space cutoff.
269
270 RED-PEN: we violate main RFC requirement, if this SYN will appear
271 old duplicate (i.e. we receive RST in reply to SYN-ACK),
272 we must return socket to time-wait state. It is not good,
273 but not fatal yet.
274 */
275
276 if (th->syn && !th->rst && !th->ack && !paws_reject &&
277 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
278 (tmp_opt.saw_tstamp &&
279 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
280 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
281 if (isn == 0)
282 isn++;
283 TCP_SKB_CB(skb)->when = isn;
284 return TCP_TW_SYN;
285 }
286
287 if (paws_reject)
288 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
289
290 if (!th->rst) {
291 /* In this case we must reset the TIMEWAIT timer.
292 *
293 * If it is ACKless SYN it may be both old duplicate
294 * and new good SYN with random sequence number <rcv_nxt.
295 * Do not reschedule in the last case.
296 */
297 if (paws_reject || th->ack)
298 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
299 TCP_TIMEWAIT_LEN);
300
301 /* Send ACK. Note, we do not put the bucket,
302 * it will be released by caller.
303 */
304 return TCP_TW_ACK;
305 }
306 inet_twsk_put(tw);
307 return TCP_TW_SUCCESS;
308}
309EXPORT_SYMBOL(tcp_timewait_state_process);
310
311/*
312 * Move a socket to time-wait or dead fin-wait-2 state.
313 */
314void tcp_time_wait(struct sock *sk, int state, int timeo)
315{
316 struct inet_timewait_sock *tw = NULL;
317 const struct inet_connection_sock *icsk = inet_csk(sk);
318 const struct tcp_sock *tp = tcp_sk(sk);
319 bool recycle_ok = false;
320
321 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
322 recycle_ok = tcp_remember_stamp(sk);
323
324 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
325 tw = inet_twsk_alloc(sk, state);
326
327 if (tw != NULL) {
328 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
329 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
330
331 tw->tw_transparent = inet_sk(sk)->transparent;
332 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
333 tcptw->tw_rcv_nxt = tp->rcv_nxt;
334 tcptw->tw_snd_nxt = tp->snd_nxt;
335 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
336 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
337 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
338
339#if IS_ENABLED(CONFIG_IPV6)
340 if (tw->tw_family == PF_INET6) {
341 struct ipv6_pinfo *np = inet6_sk(sk);
342 struct inet6_timewait_sock *tw6;
343
344 tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
345 tw6 = inet6_twsk((struct sock *)tw);
346 tw6->tw_v6_daddr = np->daddr;
347 tw6->tw_v6_rcv_saddr = np->rcv_saddr;
348 tw->tw_tclass = np->tclass;
349 tw->tw_ipv6only = np->ipv6only;
350 }
351#endif
352
353#ifdef CONFIG_TCP_MD5SIG
354 /*
355 * The timewait bucket does not have the key DB from the
356 * sock structure. We just make a quick copy of the
357 * md5 key being used (if indeed we are using one)
358 * so the timewait ack generating code has the key.
359 */
360 do {
361 struct tcp_md5sig_key *key;
362 tcptw->tw_md5_key = NULL;
363 key = tp->af_specific->md5_lookup(sk, sk);
364 if (key != NULL) {
365 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
366 if (tcptw->tw_md5_key && tcp_alloc_md5sig_pool(sk) == NULL)
367 BUG();
368 }
369 } while (0);
370#endif
371
372 /* Linkage updates. */
373 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
374
375 /* Get the TIME_WAIT timeout firing. */
376 if (timeo < rto)
377 timeo = rto;
378
379 if (recycle_ok) {
380 tw->tw_timeout = rto;
381 } else {
382 tw->tw_timeout = TCP_TIMEWAIT_LEN;
383 if (state == TCP_TIME_WAIT)
384 timeo = TCP_TIMEWAIT_LEN;
385 }
386
387 inet_twsk_schedule(tw, &tcp_death_row, timeo,
388 TCP_TIMEWAIT_LEN);
389 inet_twsk_put(tw);
390 } else {
391 /* Sorry, if we're out of memory, just CLOSE this
392 * socket up. We've got bigger problems than
393 * non-graceful socket closings.
394 */
395 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
396 }
397
398 tcp_update_metrics(sk);
399 tcp_done(sk);
400}
401
402void tcp_twsk_destructor(struct sock *sk)
403{
404#ifdef CONFIG_TCP_MD5SIG
405 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
406 if (twsk->tw_md5_key) {
407 tcp_free_md5sig_pool();
408 kfree_rcu(twsk->tw_md5_key, rcu);
409 }
410#endif
411}
412EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
413
414static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
415 struct request_sock *req)
416{
417 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
418}
419
420/* This is not only more efficient than what we used to do, it eliminates
421 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
422 *
423 * Actually, we could lots of memory writes here. tp of listening
424 * socket contains all necessary default parameters.
425 */
426struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
427{
428 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
429
430 if (newsk != NULL) {
431 const struct inet_request_sock *ireq = inet_rsk(req);
432 struct tcp_request_sock *treq = tcp_rsk(req);
433 struct inet_connection_sock *newicsk = inet_csk(newsk);
434 struct tcp_sock *newtp = tcp_sk(newsk);
435 struct tcp_sock *oldtp = tcp_sk(sk);
436 struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
437
438 /* TCP Cookie Transactions require space for the cookie pair,
439 * as it differs for each connection. There is no need to
440 * copy any s_data_payload stored at the original socket.
441 * Failure will prevent resuming the connection.
442 *
443 * Presumed copied, in order of appearance:
444 * cookie_in_always, cookie_out_never
445 */
446 if (oldcvp != NULL) {
447 struct tcp_cookie_values *newcvp =
448 kzalloc(sizeof(*newtp->cookie_values),
449 GFP_ATOMIC);
450
451 if (newcvp != NULL) {
452 kref_init(&newcvp->kref);
453 newcvp->cookie_desired =
454 oldcvp->cookie_desired;
455 newtp->cookie_values = newcvp;
456 } else {
457 /* Not Yet Implemented */
458 newtp->cookie_values = NULL;
459 }
460 }
461
462 /* Now setup tcp_sock */
463 newtp->pred_flags = 0;
464
465 newtp->rcv_wup = newtp->copied_seq =
466 newtp->rcv_nxt = treq->rcv_isn + 1;
467
468 newtp->snd_sml = newtp->snd_una =
469 newtp->snd_nxt = newtp->snd_up =
470 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
471
472 tcp_prequeue_init(newtp);
473
474 tcp_init_wl(newtp, treq->rcv_isn);
475
476 newtp->srtt = 0;
477 newtp->mdev = TCP_TIMEOUT_INIT;
478 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
479
480 newtp->packets_out = 0;
481 newtp->retrans_out = 0;
482 newtp->sacked_out = 0;
483 newtp->fackets_out = 0;
484 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
485 tcp_enable_early_retrans(newtp);
486
487 /* So many TCP implementations out there (incorrectly) count the
488 * initial SYN frame in their delayed-ACK and congestion control
489 * algorithms that we must have the following bandaid to talk
490 * efficiently to them. -DaveM
491 */
492 newtp->snd_cwnd = TCP_INIT_CWND;
493 newtp->snd_cwnd_cnt = 0;
494 newtp->bytes_acked = 0;
495
496 newtp->frto_counter = 0;
497 newtp->frto_highmark = 0;
498
499 if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
500 !try_module_get(newicsk->icsk_ca_ops->owner))
501 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
502
503 tcp_set_ca_state(newsk, TCP_CA_Open);
504 tcp_init_xmit_timers(newsk);
505 skb_queue_head_init(&newtp->out_of_order_queue);
506 newtp->write_seq = newtp->pushed_seq =
507 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
508
509 newtp->rx_opt.saw_tstamp = 0;
510
511 newtp->rx_opt.dsack = 0;
512 newtp->rx_opt.num_sacks = 0;
513
514 newtp->urg_data = 0;
515
516 if (sock_flag(newsk, SOCK_KEEPOPEN))
517 inet_csk_reset_keepalive_timer(newsk,
518 keepalive_time_when(newtp));
519
520 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
521 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
522 if (sysctl_tcp_fack)
523 tcp_enable_fack(newtp);
524 }
525 newtp->window_clamp = req->window_clamp;
526 newtp->rcv_ssthresh = req->rcv_wnd;
527 newtp->rcv_wnd = req->rcv_wnd;
528 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
529 if (newtp->rx_opt.wscale_ok) {
530 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
531 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
532 } else {
533 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
534 newtp->window_clamp = min(newtp->window_clamp, 65535U);
535 }
536 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
537 newtp->rx_opt.snd_wscale);
538 newtp->max_window = newtp->snd_wnd;
539
540 if (newtp->rx_opt.tstamp_ok) {
541 newtp->rx_opt.ts_recent = req->ts_recent;
542 newtp->rx_opt.ts_recent_stamp = get_seconds();
543 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
544 } else {
545 newtp->rx_opt.ts_recent_stamp = 0;
546 newtp->tcp_header_len = sizeof(struct tcphdr);
547 }
548#ifdef CONFIG_TCP_MD5SIG
549 newtp->md5sig_info = NULL; /*XXX*/
550 if (newtp->af_specific->md5_lookup(sk, newsk))
551 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
552#endif
553 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
554 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
555 newtp->rx_opt.mss_clamp = req->mss;
556 TCP_ECN_openreq_child(newtp, req);
557
558 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
559 }
560 return newsk;
561}
562EXPORT_SYMBOL(tcp_create_openreq_child);
563
564/*
565 * Process an incoming packet for SYN_RECV sockets represented
566 * as a request_sock.
567 */
568
569struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
570 struct request_sock *req,
571 struct request_sock **prev)
572{
573 struct tcp_options_received tmp_opt;
574 const u8 *hash_location;
575 struct sock *child;
576 const struct tcphdr *th = tcp_hdr(skb);
577 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
578 bool paws_reject = false;
579
580 tmp_opt.saw_tstamp = 0;
581 if (th->doff > (sizeof(struct tcphdr)>>2)) {
582 tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
583
584 if (tmp_opt.saw_tstamp) {
585 tmp_opt.ts_recent = req->ts_recent;
586 /* We do not store true stamp, but it is not required,
587 * it can be estimated (approximately)
588 * from another data.
589 */
590 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
591 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
592 }
593 }
594
595 /* Check for pure retransmitted SYN. */
596 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
597 flg == TCP_FLAG_SYN &&
598 !paws_reject) {
599 /*
600 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
601 * this case on figure 6 and figure 8, but formal
602 * protocol description says NOTHING.
603 * To be more exact, it says that we should send ACK,
604 * because this segment (at least, if it has no data)
605 * is out of window.
606 *
607 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
608 * describe SYN-RECV state. All the description
609 * is wrong, we cannot believe to it and should
610 * rely only on common sense and implementation
611 * experience.
612 *
613 * Enforce "SYN-ACK" according to figure 8, figure 6
614 * of RFC793, fixed by RFC1122.
615 */
616 req->rsk_ops->rtx_syn_ack(sk, req, NULL);
617 return NULL;
618 }
619
620 /* Further reproduces section "SEGMENT ARRIVES"
621 for state SYN-RECEIVED of RFC793.
622 It is broken, however, it does not work only
623 when SYNs are crossed.
624
625 You would think that SYN crossing is impossible here, since
626 we should have a SYN_SENT socket (from connect()) on our end,
627 but this is not true if the crossed SYNs were sent to both
628 ends by a malicious third party. We must defend against this,
629 and to do that we first verify the ACK (as per RFC793, page
630 36) and reset if it is invalid. Is this a true full defense?
631 To convince ourselves, let us consider a way in which the ACK
632 test can still pass in this 'malicious crossed SYNs' case.
633 Malicious sender sends identical SYNs (and thus identical sequence
634 numbers) to both A and B:
635
636 A: gets SYN, seq=7
637 B: gets SYN, seq=7
638
639 By our good fortune, both A and B select the same initial
640 send sequence number of seven :-)
641
642 A: sends SYN|ACK, seq=7, ack_seq=8
643 B: sends SYN|ACK, seq=7, ack_seq=8
644
645 So we are now A eating this SYN|ACK, ACK test passes. So
646 does sequence test, SYN is truncated, and thus we consider
647 it a bare ACK.
648
649 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
650 bare ACK. Otherwise, we create an established connection. Both
651 ends (listening sockets) accept the new incoming connection and try
652 to talk to each other. 8-)
653
654 Note: This case is both harmless, and rare. Possibility is about the
655 same as us discovering intelligent life on another plant tomorrow.
656
657 But generally, we should (RFC lies!) to accept ACK
658 from SYNACK both here and in tcp_rcv_state_process().
659 tcp_rcv_state_process() does not, hence, we do not too.
660
661 Note that the case is absolutely generic:
662 we cannot optimize anything here without
663 violating protocol. All the checks must be made
664 before attempt to create socket.
665 */
666
667 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
668 * and the incoming segment acknowledges something not yet
669 * sent (the segment carries an unacceptable ACK) ...
670 * a reset is sent."
671 *
672 * Invalid ACK: reset will be sent by listening socket
673 */
674 if ((flg & TCP_FLAG_ACK) &&
675 (TCP_SKB_CB(skb)->ack_seq !=
676 tcp_rsk(req)->snt_isn + 1 + tcp_s_data_size(tcp_sk(sk))))
677 return sk;
678
679 /* Also, it would be not so bad idea to check rcv_tsecr, which
680 * is essentially ACK extension and too early or too late values
681 * should cause reset in unsynchronized states.
682 */
683
684 /* RFC793: "first check sequence number". */
685
686 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
687 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) {
688 /* Out of window: send ACK and drop. */
689 if (!(flg & TCP_FLAG_RST))
690 req->rsk_ops->send_ack(sk, skb, req);
691 if (paws_reject)
692 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
693 return NULL;
694 }
695
696 /* In sequence, PAWS is OK. */
697
698 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1))
699 req->ts_recent = tmp_opt.rcv_tsval;
700
701 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
702 /* Truncate SYN, it is out of window starting
703 at tcp_rsk(req)->rcv_isn + 1. */
704 flg &= ~TCP_FLAG_SYN;
705 }
706
707 /* RFC793: "second check the RST bit" and
708 * "fourth, check the SYN bit"
709 */
710 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
711 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
712 goto embryonic_reset;
713 }
714
715 /* ACK sequence verified above, just make sure ACK is
716 * set. If ACK not set, just silently drop the packet.
717 */
718 if (!(flg & TCP_FLAG_ACK))
719 return NULL;
720
721 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
722 if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
723 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
724 inet_rsk(req)->acked = 1;
725 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
726 return NULL;
727 }
728 if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
729 tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
730 else if (req->retrans) /* don't take RTT sample if retrans && ~TS */
731 tcp_rsk(req)->snt_synack = 0;
732
733 /* OK, ACK is valid, create big socket and
734 * feed this segment to it. It will repeat all
735 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
736 * ESTABLISHED STATE. If it will be dropped after
737 * socket is created, wait for troubles.
738 */
739 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
740 if (child == NULL)
741 goto listen_overflow;
742
743 inet_csk_reqsk_queue_unlink(sk, req, prev);
744 inet_csk_reqsk_queue_removed(sk, req);
745
746 inet_csk_reqsk_queue_add(sk, req, child);
747 return child;
748
749listen_overflow:
750 if (!sysctl_tcp_abort_on_overflow) {
751 inet_rsk(req)->acked = 1;
752 return NULL;
753 }
754
755embryonic_reset:
756 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
757 if (!(flg & TCP_FLAG_RST))
758 req->rsk_ops->send_reset(sk, skb);
759
760 inet_csk_reqsk_queue_drop(sk, req, prev);
761 return NULL;
762}
763EXPORT_SYMBOL(tcp_check_req);
764
765/*
766 * Queue segment on the new socket if the new socket is active,
767 * otherwise we just shortcircuit this and continue with
768 * the new socket.
769 */
770
771int tcp_child_process(struct sock *parent, struct sock *child,
772 struct sk_buff *skb)
773{
774 int ret = 0;
775 int state = child->sk_state;
776
777 if (!sock_owned_by_user(child)) {
778 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
779 skb->len);
780 /* Wakeup parent, send SIGIO */
781 if (state == TCP_SYN_RECV && child->sk_state != state)
782 parent->sk_data_ready(parent, 0);
783 } else {
784 /* Alas, it is possible again, because we do lookup
785 * in main socket hash table and lock on listening
786 * socket does not protect us more.
787 */
788 __sk_add_backlog(child, skb);
789 }
790
791 bh_unlock_sock(child);
792 sock_put(child);
793 return ret;
794}
795EXPORT_SYMBOL(tcp_child_process);