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1/*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21#include <linux/mm.h>
22#include <linux/module.h>
23#include <linux/slab.h>
24#include <linux/sysctl.h>
25#include <linux/workqueue.h>
26#include <net/tcp.h>
27#include <net/inet_common.h>
28#include <net/xfrm.h>
29
30int sysctl_tcp_syncookies __read_mostly = 1;
31EXPORT_SYMBOL(sysctl_tcp_syncookies);
32
33int sysctl_tcp_abort_on_overflow __read_mostly;
34
35struct inet_timewait_death_row tcp_death_row = {
36 .sysctl_max_tw_buckets = NR_FILE * 2,
37 .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
38 .death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
39 .hashinfo = &tcp_hashinfo,
40 .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
41 (unsigned long)&tcp_death_row),
42 .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
43 inet_twdr_twkill_work),
44/* Short-time timewait calendar */
45
46 .twcal_hand = -1,
47 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
48 (unsigned long)&tcp_death_row),
49};
50EXPORT_SYMBOL_GPL(tcp_death_row);
51
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 int 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 1;
76 }
77
78 return 0;
79}
80
81static int 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 1;
98 }
99 return 0;
100}
101
102static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
103{
104 if (seq == s_win)
105 return 1;
106 if (after(end_seq, s_win) && before(seq, e_win))
107 return 1;
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 u8 *hash_location;
145 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
146 int paws_reject = 0;
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 int recycle_ok = 0;
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 defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
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 ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr);
347 ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr);
348 tw->tw_ipv6only = np->ipv6only;
349 }
350#endif
351
352#ifdef CONFIG_TCP_MD5SIG
353 /*
354 * The timewait bucket does not have the key DB from the
355 * sock structure. We just make a quick copy of the
356 * md5 key being used (if indeed we are using one)
357 * so the timewait ack generating code has the key.
358 */
359 do {
360 struct tcp_md5sig_key *key;
361 memset(tcptw->tw_md5_key, 0, sizeof(tcptw->tw_md5_key));
362 tcptw->tw_md5_keylen = 0;
363 key = tp->af_specific->md5_lookup(sk, sk);
364 if (key != NULL) {
365 memcpy(&tcptw->tw_md5_key, key->key, key->keylen);
366 tcptw->tw_md5_keylen = key->keylen;
367 if (tcp_alloc_md5sig_pool(sk) == NULL)
368 BUG();
369 }
370 } while (0);
371#endif
372
373 /* Linkage updates. */
374 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
375
376 /* Get the TIME_WAIT timeout firing. */
377 if (timeo < rto)
378 timeo = rto;
379
380 if (recycle_ok) {
381 tw->tw_timeout = rto;
382 } else {
383 tw->tw_timeout = TCP_TIMEWAIT_LEN;
384 if (state == TCP_TIME_WAIT)
385 timeo = TCP_TIMEWAIT_LEN;
386 }
387
388 inet_twsk_schedule(tw, &tcp_death_row, timeo,
389 TCP_TIMEWAIT_LEN);
390 inet_twsk_put(tw);
391 } else {
392 /* Sorry, if we're out of memory, just CLOSE this
393 * socket up. We've got bigger problems than
394 * non-graceful socket closings.
395 */
396 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
397 }
398
399 tcp_update_metrics(sk);
400 tcp_done(sk);
401}
402
403void tcp_twsk_destructor(struct sock *sk)
404{
405#ifdef CONFIG_TCP_MD5SIG
406 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
407 if (twsk->tw_md5_keylen)
408 tcp_free_md5sig_pool();
409#endif
410}
411EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
412
413static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
414 struct request_sock *req)
415{
416 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
417}
418
419/* This is not only more efficient than what we used to do, it eliminates
420 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
421 *
422 * Actually, we could lots of memory writes here. tp of listening
423 * socket contains all necessary default parameters.
424 */
425struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
426{
427 struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC);
428
429 if (newsk != NULL) {
430 const struct inet_request_sock *ireq = inet_rsk(req);
431 struct tcp_request_sock *treq = tcp_rsk(req);
432 struct inet_connection_sock *newicsk = inet_csk(newsk);
433 struct tcp_sock *newtp = tcp_sk(newsk);
434 struct tcp_sock *oldtp = tcp_sk(sk);
435 struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
436
437 /* TCP Cookie Transactions require space for the cookie pair,
438 * as it differs for each connection. There is no need to
439 * copy any s_data_payload stored at the original socket.
440 * Failure will prevent resuming the connection.
441 *
442 * Presumed copied, in order of appearance:
443 * cookie_in_always, cookie_out_never
444 */
445 if (oldcvp != NULL) {
446 struct tcp_cookie_values *newcvp =
447 kzalloc(sizeof(*newtp->cookie_values),
448 GFP_ATOMIC);
449
450 if (newcvp != NULL) {
451 kref_init(&newcvp->kref);
452 newcvp->cookie_desired =
453 oldcvp->cookie_desired;
454 newtp->cookie_values = newcvp;
455 } else {
456 /* Not Yet Implemented */
457 newtp->cookie_values = NULL;
458 }
459 }
460
461 /* Now setup tcp_sock */
462 newtp->pred_flags = 0;
463
464 newtp->rcv_wup = newtp->copied_seq =
465 newtp->rcv_nxt = treq->rcv_isn + 1;
466
467 newtp->snd_sml = newtp->snd_una =
468 newtp->snd_nxt = newtp->snd_up =
469 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
470
471 tcp_prequeue_init(newtp);
472
473 tcp_init_wl(newtp, treq->rcv_isn);
474
475 newtp->srtt = 0;
476 newtp->mdev = TCP_TIMEOUT_INIT;
477 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
478
479 newtp->packets_out = 0;
480 newtp->retrans_out = 0;
481 newtp->sacked_out = 0;
482 newtp->fackets_out = 0;
483 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
484
485 /* So many TCP implementations out there (incorrectly) count the
486 * initial SYN frame in their delayed-ACK and congestion control
487 * algorithms that we must have the following bandaid to talk
488 * efficiently to them. -DaveM
489 */
490 newtp->snd_cwnd = TCP_INIT_CWND;
491 newtp->snd_cwnd_cnt = 0;
492 newtp->bytes_acked = 0;
493
494 newtp->frto_counter = 0;
495 newtp->frto_highmark = 0;
496
497 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
498
499 tcp_set_ca_state(newsk, TCP_CA_Open);
500 tcp_init_xmit_timers(newsk);
501 skb_queue_head_init(&newtp->out_of_order_queue);
502 newtp->write_seq = newtp->pushed_seq =
503 treq->snt_isn + 1 + tcp_s_data_size(oldtp);
504
505 newtp->rx_opt.saw_tstamp = 0;
506
507 newtp->rx_opt.dsack = 0;
508 newtp->rx_opt.num_sacks = 0;
509
510 newtp->urg_data = 0;
511
512 if (sock_flag(newsk, SOCK_KEEPOPEN))
513 inet_csk_reset_keepalive_timer(newsk,
514 keepalive_time_when(newtp));
515
516 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
517 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
518 if (sysctl_tcp_fack)
519 tcp_enable_fack(newtp);
520 }
521 newtp->window_clamp = req->window_clamp;
522 newtp->rcv_ssthresh = req->rcv_wnd;
523 newtp->rcv_wnd = req->rcv_wnd;
524 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
525 if (newtp->rx_opt.wscale_ok) {
526 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
527 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
528 } else {
529 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
530 newtp->window_clamp = min(newtp->window_clamp, 65535U);
531 }
532 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
533 newtp->rx_opt.snd_wscale);
534 newtp->max_window = newtp->snd_wnd;
535
536 if (newtp->rx_opt.tstamp_ok) {
537 newtp->rx_opt.ts_recent = req->ts_recent;
538 newtp->rx_opt.ts_recent_stamp = get_seconds();
539 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
540 } else {
541 newtp->rx_opt.ts_recent_stamp = 0;
542 newtp->tcp_header_len = sizeof(struct tcphdr);
543 }
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
554 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
555 }
556 return newsk;
557}
558EXPORT_SYMBOL(tcp_create_openreq_child);
559
560/*
561 * Process an incoming packet for SYN_RECV sockets represented
562 * as a request_sock.
563 */
564
565struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
566 struct request_sock *req,
567 struct request_sock **prev)
568{
569 struct tcp_options_received tmp_opt;
570 u8 *hash_location;
571 struct sock *child;
572 const struct tcphdr *th = tcp_hdr(skb);
573 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
574 int paws_reject = 0;
575
576 tmp_opt.saw_tstamp = 0;
577 if (th->doff > (sizeof(struct tcphdr)>>2)) {
578 tcp_parse_options(skb, &tmp_opt, &hash_location, 0);
579
580 if (tmp_opt.saw_tstamp) {
581 tmp_opt.ts_recent = req->ts_recent;
582 /* We do not store true stamp, but it is not required,
583 * it can be estimated (approximately)
584 * from another data.
585 */
586 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
587 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
588 }
589 }
590
591 /* Check for pure retransmitted SYN. */
592 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
593 flg == TCP_FLAG_SYN &&
594 !paws_reject) {
595 /*
596 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
597 * this case on figure 6 and figure 8, but formal
598 * protocol description says NOTHING.
599 * To be more exact, it says that we should send ACK,
600 * because this segment (at least, if it has no data)
601 * is out of window.
602 *
603 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
604 * describe SYN-RECV state. All the description
605 * is wrong, we cannot believe to it and should
606 * rely only on common sense and implementation
607 * experience.
608 *
609 * Enforce "SYN-ACK" according to figure 8, figure 6
610 * of RFC793, fixed by RFC1122.
611 */
612 req->rsk_ops->rtx_syn_ack(sk, req, NULL);
613 return NULL;
614 }
615
616 /* Further reproduces section "SEGMENT ARRIVES"
617 for state SYN-RECEIVED of RFC793.
618 It is broken, however, it does not work only
619 when SYNs are crossed.
620
621 You would think that SYN crossing is impossible here, since
622 we should have a SYN_SENT socket (from connect()) on our end,
623 but this is not true if the crossed SYNs were sent to both
624 ends by a malicious third party. We must defend against this,
625 and to do that we first verify the ACK (as per RFC793, page
626 36) and reset if it is invalid. Is this a true full defense?
627 To convince ourselves, let us consider a way in which the ACK
628 test can still pass in this 'malicious crossed SYNs' case.
629 Malicious sender sends identical SYNs (and thus identical sequence
630 numbers) to both A and B:
631
632 A: gets SYN, seq=7
633 B: gets SYN, seq=7
634
635 By our good fortune, both A and B select the same initial
636 send sequence number of seven :-)
637
638 A: sends SYN|ACK, seq=7, ack_seq=8
639 B: sends SYN|ACK, seq=7, ack_seq=8
640
641 So we are now A eating this SYN|ACK, ACK test passes. So
642 does sequence test, SYN is truncated, and thus we consider
643 it a bare ACK.
644
645 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
646 bare ACK. Otherwise, we create an established connection. Both
647 ends (listening sockets) accept the new incoming connection and try
648 to talk to each other. 8-)
649
650 Note: This case is both harmless, and rare. Possibility is about the
651 same as us discovering intelligent life on another plant tomorrow.
652
653 But generally, we should (RFC lies!) to accept ACK
654 from SYNACK both here and in tcp_rcv_state_process().
655 tcp_rcv_state_process() does not, hence, we do not too.
656
657 Note that the case is absolutely generic:
658 we cannot optimize anything here without
659 violating protocol. All the checks must be made
660 before attempt to create socket.
661 */
662
663 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
664 * and the incoming segment acknowledges something not yet
665 * sent (the segment carries an unacceptable ACK) ...
666 * a reset is sent."
667 *
668 * Invalid ACK: reset will be sent by listening socket
669 */
670 if ((flg & TCP_FLAG_ACK) &&
671 (TCP_SKB_CB(skb)->ack_seq !=
672 tcp_rsk(req)->snt_isn + 1 + tcp_s_data_size(tcp_sk(sk))))
673 return sk;
674
675 /* Also, it would be not so bad idea to check rcv_tsecr, which
676 * is essentially ACK extension and too early or too late values
677 * should cause reset in unsynchronized states.
678 */
679
680 /* RFC793: "first check sequence number". */
681
682 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
683 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) {
684 /* Out of window: send ACK and drop. */
685 if (!(flg & TCP_FLAG_RST))
686 req->rsk_ops->send_ack(sk, skb, req);
687 if (paws_reject)
688 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
689 return NULL;
690 }
691
692 /* In sequence, PAWS is OK. */
693
694 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1))
695 req->ts_recent = tmp_opt.rcv_tsval;
696
697 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
698 /* Truncate SYN, it is out of window starting
699 at tcp_rsk(req)->rcv_isn + 1. */
700 flg &= ~TCP_FLAG_SYN;
701 }
702
703 /* RFC793: "second check the RST bit" and
704 * "fourth, check the SYN bit"
705 */
706 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
707 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
708 goto embryonic_reset;
709 }
710
711 /* ACK sequence verified above, just make sure ACK is
712 * set. If ACK not set, just silently drop the packet.
713 */
714 if (!(flg & TCP_FLAG_ACK))
715 return NULL;
716
717 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
718 if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
719 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
720 inet_rsk(req)->acked = 1;
721 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
722 return NULL;
723 }
724 if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
725 tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
726 else if (req->retrans) /* don't take RTT sample if retrans && ~TS */
727 tcp_rsk(req)->snt_synack = 0;
728
729 /* OK, ACK is valid, create big socket and
730 * feed this segment to it. It will repeat all
731 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
732 * ESTABLISHED STATE. If it will be dropped after
733 * socket is created, wait for troubles.
734 */
735 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
736 if (child == NULL)
737 goto listen_overflow;
738
739 inet_csk_reqsk_queue_unlink(sk, req, prev);
740 inet_csk_reqsk_queue_removed(sk, req);
741
742 inet_csk_reqsk_queue_add(sk, req, child);
743 return child;
744
745listen_overflow:
746 if (!sysctl_tcp_abort_on_overflow) {
747 inet_rsk(req)->acked = 1;
748 return NULL;
749 }
750
751embryonic_reset:
752 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
753 if (!(flg & TCP_FLAG_RST))
754 req->rsk_ops->send_reset(sk, skb);
755
756 inet_csk_reqsk_queue_drop(sk, req, prev);
757 return NULL;
758}
759EXPORT_SYMBOL(tcp_check_req);
760
761/*
762 * Queue segment on the new socket if the new socket is active,
763 * otherwise we just shortcircuit this and continue with
764 * the new socket.
765 */
766
767int tcp_child_process(struct sock *parent, struct sock *child,
768 struct sk_buff *skb)
769{
770 int ret = 0;
771 int state = child->sk_state;
772
773 if (!sock_owned_by_user(child)) {
774 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
775 skb->len);
776 /* Wakeup parent, send SIGIO */
777 if (state == TCP_SYN_RECV && child->sk_state != state)
778 parent->sk_data_ready(parent, 0);
779 } else {
780 /* Alas, it is possible again, because we do lookup
781 * in main socket hash table and lock on listening
782 * socket does not protect us more.
783 */
784 __sk_add_backlog(child, skb);
785 }
786
787 bh_unlock_sock(child);
788 sock_put(child);
789 return ret;
790}
791EXPORT_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
52static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
53{
54 if (seq == s_win)
55 return true;
56 if (after(end_seq, s_win) && before(seq, e_win))
57 return true;
58 return seq == e_win && seq == end_seq;
59}
60
61/*
62 * * Main purpose of TIME-WAIT state is to close connection gracefully,
63 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
64 * (and, probably, tail of data) and one or more our ACKs are lost.
65 * * What is TIME-WAIT timeout? It is associated with maximal packet
66 * lifetime in the internet, which results in wrong conclusion, that
67 * it is set to catch "old duplicate segments" wandering out of their path.
68 * It is not quite correct. This timeout is calculated so that it exceeds
69 * maximal retransmission timeout enough to allow to lose one (or more)
70 * segments sent by peer and our ACKs. This time may be calculated from RTO.
71 * * When TIME-WAIT socket receives RST, it means that another end
72 * finally closed and we are allowed to kill TIME-WAIT too.
73 * * Second purpose of TIME-WAIT is catching old duplicate segments.
74 * Well, certainly it is pure paranoia, but if we load TIME-WAIT
75 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
76 * * If we invented some more clever way to catch duplicates
77 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
78 *
79 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
80 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
81 * from the very beginning.
82 *
83 * NOTE. With recycling (and later with fin-wait-2) TW bucket
84 * is _not_ stateless. It means, that strictly speaking we must
85 * spinlock it. I do not want! Well, probability of misbehaviour
86 * is ridiculously low and, seems, we could use some mb() tricks
87 * to avoid misread sequence numbers, states etc. --ANK
88 *
89 * We don't need to initialize tmp_out.sack_ok as we don't use the results
90 */
91enum tcp_tw_status
92tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
93 const struct tcphdr *th)
94{
95 struct tcp_options_received tmp_opt;
96 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
97 bool paws_reject = false;
98
99 tmp_opt.saw_tstamp = 0;
100 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
101 tcp_parse_options(skb, &tmp_opt, 0, NULL);
102
103 if (tmp_opt.saw_tstamp) {
104 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
105 tmp_opt.ts_recent = tcptw->tw_ts_recent;
106 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
107 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
108 }
109 }
110
111 if (tw->tw_substate == TCP_FIN_WAIT2) {
112 /* Just repeat all the checks of tcp_rcv_state_process() */
113
114 /* Out of window, send ACK */
115 if (paws_reject ||
116 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
117 tcptw->tw_rcv_nxt,
118 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
119 return TCP_TW_ACK;
120
121 if (th->rst)
122 goto kill;
123
124 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
125 goto kill_with_rst;
126
127 /* Dup ACK? */
128 if (!th->ack ||
129 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
130 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
131 inet_twsk_put(tw);
132 return TCP_TW_SUCCESS;
133 }
134
135 /* New data or FIN. If new data arrive after half-duplex close,
136 * reset.
137 */
138 if (!th->fin ||
139 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
140kill_with_rst:
141 inet_twsk_deschedule(tw, &tcp_death_row);
142 inet_twsk_put(tw);
143 return TCP_TW_RST;
144 }
145
146 /* FIN arrived, enter true time-wait state. */
147 tw->tw_substate = TCP_TIME_WAIT;
148 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
149 if (tmp_opt.saw_tstamp) {
150 tcptw->tw_ts_recent_stamp = get_seconds();
151 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
152 }
153
154 if (tcp_death_row.sysctl_tw_recycle &&
155 tcptw->tw_ts_recent_stamp &&
156 tcp_tw_remember_stamp(tw))
157 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
158 TCP_TIMEWAIT_LEN);
159 else
160 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
161 TCP_TIMEWAIT_LEN);
162 return TCP_TW_ACK;
163 }
164
165 /*
166 * Now real TIME-WAIT state.
167 *
168 * RFC 1122:
169 * "When a connection is [...] on TIME-WAIT state [...]
170 * [a TCP] MAY accept a new SYN from the remote TCP to
171 * reopen the connection directly, if it:
172 *
173 * (1) assigns its initial sequence number for the new
174 * connection to be larger than the largest sequence
175 * number it used on the previous connection incarnation,
176 * and
177 *
178 * (2) returns to TIME-WAIT state if the SYN turns out
179 * to be an old duplicate".
180 */
181
182 if (!paws_reject &&
183 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
184 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
185 /* In window segment, it may be only reset or bare ack. */
186
187 if (th->rst) {
188 /* This is TIME_WAIT assassination, in two flavors.
189 * Oh well... nobody has a sufficient solution to this
190 * protocol bug yet.
191 */
192 if (sysctl_tcp_rfc1337 == 0) {
193kill:
194 inet_twsk_deschedule(tw, &tcp_death_row);
195 inet_twsk_put(tw);
196 return TCP_TW_SUCCESS;
197 }
198 }
199 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
200 TCP_TIMEWAIT_LEN);
201
202 if (tmp_opt.saw_tstamp) {
203 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
204 tcptw->tw_ts_recent_stamp = get_seconds();
205 }
206
207 inet_twsk_put(tw);
208 return TCP_TW_SUCCESS;
209 }
210
211 /* Out of window segment.
212
213 All the segments are ACKed immediately.
214
215 The only exception is new SYN. We accept it, if it is
216 not old duplicate and we are not in danger to be killed
217 by delayed old duplicates. RFC check is that it has
218 newer sequence number works at rates <40Mbit/sec.
219 However, if paws works, it is reliable AND even more,
220 we even may relax silly seq space cutoff.
221
222 RED-PEN: we violate main RFC requirement, if this SYN will appear
223 old duplicate (i.e. we receive RST in reply to SYN-ACK),
224 we must return socket to time-wait state. It is not good,
225 but not fatal yet.
226 */
227
228 if (th->syn && !th->rst && !th->ack && !paws_reject &&
229 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
230 (tmp_opt.saw_tstamp &&
231 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
232 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
233 if (isn == 0)
234 isn++;
235 TCP_SKB_CB(skb)->when = isn;
236 return TCP_TW_SYN;
237 }
238
239 if (paws_reject)
240 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
241
242 if (!th->rst) {
243 /* In this case we must reset the TIMEWAIT timer.
244 *
245 * If it is ACKless SYN it may be both old duplicate
246 * and new good SYN with random sequence number <rcv_nxt.
247 * Do not reschedule in the last case.
248 */
249 if (paws_reject || th->ack)
250 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
251 TCP_TIMEWAIT_LEN);
252
253 /* Send ACK. Note, we do not put the bucket,
254 * it will be released by caller.
255 */
256 return TCP_TW_ACK;
257 }
258 inet_twsk_put(tw);
259 return TCP_TW_SUCCESS;
260}
261EXPORT_SYMBOL(tcp_timewait_state_process);
262
263/*
264 * Move a socket to time-wait or dead fin-wait-2 state.
265 */
266void tcp_time_wait(struct sock *sk, int state, int timeo)
267{
268 struct inet_timewait_sock *tw = NULL;
269 const struct inet_connection_sock *icsk = inet_csk(sk);
270 const struct tcp_sock *tp = tcp_sk(sk);
271 bool recycle_ok = false;
272
273 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
274 recycle_ok = tcp_remember_stamp(sk);
275
276 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
277 tw = inet_twsk_alloc(sk, state);
278
279 if (tw != NULL) {
280 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
281 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
282 struct inet_sock *inet = inet_sk(sk);
283
284 tw->tw_transparent = inet->transparent;
285 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
286 tcptw->tw_rcv_nxt = tp->rcv_nxt;
287 tcptw->tw_snd_nxt = tp->snd_nxt;
288 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
289 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
290 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
291 tcptw->tw_ts_offset = tp->tsoffset;
292
293#if IS_ENABLED(CONFIG_IPV6)
294 if (tw->tw_family == PF_INET6) {
295 struct ipv6_pinfo *np = inet6_sk(sk);
296
297 tw->tw_v6_daddr = sk->sk_v6_daddr;
298 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
299 tw->tw_tclass = np->tclass;
300 tw->tw_flowlabel = np->flow_label >> 12;
301 tw->tw_ipv6only = np->ipv6only;
302 }
303#endif
304
305#ifdef CONFIG_TCP_MD5SIG
306 /*
307 * The timewait bucket does not have the key DB from the
308 * sock structure. We just make a quick copy of the
309 * md5 key being used (if indeed we are using one)
310 * so the timewait ack generating code has the key.
311 */
312 do {
313 struct tcp_md5sig_key *key;
314 tcptw->tw_md5_key = NULL;
315 key = tp->af_specific->md5_lookup(sk, sk);
316 if (key != NULL) {
317 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
318 if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
319 BUG();
320 }
321 } while (0);
322#endif
323
324 /* Linkage updates. */
325 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
326
327 /* Get the TIME_WAIT timeout firing. */
328 if (timeo < rto)
329 timeo = rto;
330
331 if (recycle_ok) {
332 tw->tw_timeout = rto;
333 } else {
334 tw->tw_timeout = TCP_TIMEWAIT_LEN;
335 if (state == TCP_TIME_WAIT)
336 timeo = TCP_TIMEWAIT_LEN;
337 }
338
339 inet_twsk_schedule(tw, &tcp_death_row, timeo,
340 TCP_TIMEWAIT_LEN);
341 inet_twsk_put(tw);
342 } else {
343 /* Sorry, if we're out of memory, just CLOSE this
344 * socket up. We've got bigger problems than
345 * non-graceful socket closings.
346 */
347 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
348 }
349
350 tcp_update_metrics(sk);
351 tcp_done(sk);
352}
353
354void tcp_twsk_destructor(struct sock *sk)
355{
356#ifdef CONFIG_TCP_MD5SIG
357 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
358
359 if (twsk->tw_md5_key)
360 kfree_rcu(twsk->tw_md5_key, rcu);
361#endif
362}
363EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
364
365static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
366 struct request_sock *req)
367{
368 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
369}
370
371/* This is not only more efficient than what we used to do, it eliminates
372 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
373 *
374 * Actually, we could lots of memory writes here. tp of listening
375 * socket contains all necessary default parameters.
376 */
377struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
378{
379 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
380
381 if (newsk != NULL) {
382 const struct inet_request_sock *ireq = inet_rsk(req);
383 struct tcp_request_sock *treq = tcp_rsk(req);
384 struct inet_connection_sock *newicsk = inet_csk(newsk);
385 struct tcp_sock *newtp = tcp_sk(newsk);
386
387 /* Now setup tcp_sock */
388 newtp->pred_flags = 0;
389
390 newtp->rcv_wup = newtp->copied_seq =
391 newtp->rcv_nxt = treq->rcv_isn + 1;
392
393 newtp->snd_sml = newtp->snd_una =
394 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
395
396 tcp_prequeue_init(newtp);
397 INIT_LIST_HEAD(&newtp->tsq_node);
398
399 tcp_init_wl(newtp, treq->rcv_isn);
400
401 newtp->srtt_us = 0;
402 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
403 newicsk->icsk_rto = TCP_TIMEOUT_INIT;
404
405 newtp->packets_out = 0;
406 newtp->retrans_out = 0;
407 newtp->sacked_out = 0;
408 newtp->fackets_out = 0;
409 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
410 tcp_enable_early_retrans(newtp);
411 newtp->tlp_high_seq = 0;
412 newtp->lsndtime = treq->snt_synack;
413 newtp->total_retrans = req->num_retrans;
414
415 /* So many TCP implementations out there (incorrectly) count the
416 * initial SYN frame in their delayed-ACK and congestion control
417 * algorithms that we must have the following bandaid to talk
418 * efficiently to them. -DaveM
419 */
420 newtp->snd_cwnd = TCP_INIT_CWND;
421 newtp->snd_cwnd_cnt = 0;
422
423 if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
424 !try_module_get(newicsk->icsk_ca_ops->owner))
425 newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
426
427 tcp_set_ca_state(newsk, TCP_CA_Open);
428 tcp_init_xmit_timers(newsk);
429 __skb_queue_head_init(&newtp->out_of_order_queue);
430 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
431
432 newtp->rx_opt.saw_tstamp = 0;
433
434 newtp->rx_opt.dsack = 0;
435 newtp->rx_opt.num_sacks = 0;
436
437 newtp->urg_data = 0;
438
439 if (sock_flag(newsk, SOCK_KEEPOPEN))
440 inet_csk_reset_keepalive_timer(newsk,
441 keepalive_time_when(newtp));
442
443 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
444 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
445 if (sysctl_tcp_fack)
446 tcp_enable_fack(newtp);
447 }
448 newtp->window_clamp = req->window_clamp;
449 newtp->rcv_ssthresh = req->rcv_wnd;
450 newtp->rcv_wnd = req->rcv_wnd;
451 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
452 if (newtp->rx_opt.wscale_ok) {
453 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
454 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
455 } else {
456 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
457 newtp->window_clamp = min(newtp->window_clamp, 65535U);
458 }
459 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
460 newtp->rx_opt.snd_wscale);
461 newtp->max_window = newtp->snd_wnd;
462
463 if (newtp->rx_opt.tstamp_ok) {
464 newtp->rx_opt.ts_recent = req->ts_recent;
465 newtp->rx_opt.ts_recent_stamp = get_seconds();
466 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
467 } else {
468 newtp->rx_opt.ts_recent_stamp = 0;
469 newtp->tcp_header_len = sizeof(struct tcphdr);
470 }
471 newtp->tsoffset = 0;
472#ifdef CONFIG_TCP_MD5SIG
473 newtp->md5sig_info = NULL; /*XXX*/
474 if (newtp->af_specific->md5_lookup(sk, newsk))
475 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
476#endif
477 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
478 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
479 newtp->rx_opt.mss_clamp = req->mss;
480 TCP_ECN_openreq_child(newtp, req);
481 newtp->fastopen_rsk = NULL;
482 newtp->syn_data_acked = 0;
483
484 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
485 }
486 return newsk;
487}
488EXPORT_SYMBOL(tcp_create_openreq_child);
489
490/*
491 * Process an incoming packet for SYN_RECV sockets represented as a
492 * request_sock. Normally sk is the listener socket but for TFO it
493 * points to the child socket.
494 *
495 * XXX (TFO) - The current impl contains a special check for ack
496 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
497 *
498 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
499 */
500
501struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
502 struct request_sock *req,
503 struct request_sock **prev,
504 bool fastopen)
505{
506 struct tcp_options_received tmp_opt;
507 struct sock *child;
508 const struct tcphdr *th = tcp_hdr(skb);
509 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
510 bool paws_reject = false;
511
512 BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
513
514 tmp_opt.saw_tstamp = 0;
515 if (th->doff > (sizeof(struct tcphdr)>>2)) {
516 tcp_parse_options(skb, &tmp_opt, 0, NULL);
517
518 if (tmp_opt.saw_tstamp) {
519 tmp_opt.ts_recent = req->ts_recent;
520 /* We do not store true stamp, but it is not required,
521 * it can be estimated (approximately)
522 * from another data.
523 */
524 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
525 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
526 }
527 }
528
529 /* Check for pure retransmitted SYN. */
530 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
531 flg == TCP_FLAG_SYN &&
532 !paws_reject) {
533 /*
534 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
535 * this case on figure 6 and figure 8, but formal
536 * protocol description says NOTHING.
537 * To be more exact, it says that we should send ACK,
538 * because this segment (at least, if it has no data)
539 * is out of window.
540 *
541 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
542 * describe SYN-RECV state. All the description
543 * is wrong, we cannot believe to it and should
544 * rely only on common sense and implementation
545 * experience.
546 *
547 * Enforce "SYN-ACK" according to figure 8, figure 6
548 * of RFC793, fixed by RFC1122.
549 *
550 * Note that even if there is new data in the SYN packet
551 * they will be thrown away too.
552 *
553 * Reset timer after retransmitting SYNACK, similar to
554 * the idea of fast retransmit in recovery.
555 */
556 if (!inet_rtx_syn_ack(sk, req))
557 req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
558 TCP_RTO_MAX) + jiffies;
559 return NULL;
560 }
561
562 /* Further reproduces section "SEGMENT ARRIVES"
563 for state SYN-RECEIVED of RFC793.
564 It is broken, however, it does not work only
565 when SYNs are crossed.
566
567 You would think that SYN crossing is impossible here, since
568 we should have a SYN_SENT socket (from connect()) on our end,
569 but this is not true if the crossed SYNs were sent to both
570 ends by a malicious third party. We must defend against this,
571 and to do that we first verify the ACK (as per RFC793, page
572 36) and reset if it is invalid. Is this a true full defense?
573 To convince ourselves, let us consider a way in which the ACK
574 test can still pass in this 'malicious crossed SYNs' case.
575 Malicious sender sends identical SYNs (and thus identical sequence
576 numbers) to both A and B:
577
578 A: gets SYN, seq=7
579 B: gets SYN, seq=7
580
581 By our good fortune, both A and B select the same initial
582 send sequence number of seven :-)
583
584 A: sends SYN|ACK, seq=7, ack_seq=8
585 B: sends SYN|ACK, seq=7, ack_seq=8
586
587 So we are now A eating this SYN|ACK, ACK test passes. So
588 does sequence test, SYN is truncated, and thus we consider
589 it a bare ACK.
590
591 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
592 bare ACK. Otherwise, we create an established connection. Both
593 ends (listening sockets) accept the new incoming connection and try
594 to talk to each other. 8-)
595
596 Note: This case is both harmless, and rare. Possibility is about the
597 same as us discovering intelligent life on another plant tomorrow.
598
599 But generally, we should (RFC lies!) to accept ACK
600 from SYNACK both here and in tcp_rcv_state_process().
601 tcp_rcv_state_process() does not, hence, we do not too.
602
603 Note that the case is absolutely generic:
604 we cannot optimize anything here without
605 violating protocol. All the checks must be made
606 before attempt to create socket.
607 */
608
609 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
610 * and the incoming segment acknowledges something not yet
611 * sent (the segment carries an unacceptable ACK) ...
612 * a reset is sent."
613 *
614 * Invalid ACK: reset will be sent by listening socket.
615 * Note that the ACK validity check for a Fast Open socket is done
616 * elsewhere and is checked directly against the child socket rather
617 * than req because user data may have been sent out.
618 */
619 if ((flg & TCP_FLAG_ACK) && !fastopen &&
620 (TCP_SKB_CB(skb)->ack_seq !=
621 tcp_rsk(req)->snt_isn + 1))
622 return sk;
623
624 /* Also, it would be not so bad idea to check rcv_tsecr, which
625 * is essentially ACK extension and too early or too late values
626 * should cause reset in unsynchronized states.
627 */
628
629 /* RFC793: "first check sequence number". */
630
631 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
632 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rcv_wnd)) {
633 /* Out of window: send ACK and drop. */
634 if (!(flg & TCP_FLAG_RST))
635 req->rsk_ops->send_ack(sk, skb, req);
636 if (paws_reject)
637 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
638 return NULL;
639 }
640
641 /* In sequence, PAWS is OK. */
642
643 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
644 req->ts_recent = tmp_opt.rcv_tsval;
645
646 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
647 /* Truncate SYN, it is out of window starting
648 at tcp_rsk(req)->rcv_isn + 1. */
649 flg &= ~TCP_FLAG_SYN;
650 }
651
652 /* RFC793: "second check the RST bit" and
653 * "fourth, check the SYN bit"
654 */
655 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
656 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
657 goto embryonic_reset;
658 }
659
660 /* ACK sequence verified above, just make sure ACK is
661 * set. If ACK not set, just silently drop the packet.
662 *
663 * XXX (TFO) - if we ever allow "data after SYN", the
664 * following check needs to be removed.
665 */
666 if (!(flg & TCP_FLAG_ACK))
667 return NULL;
668
669 /* For Fast Open no more processing is needed (sk is the
670 * child socket).
671 */
672 if (fastopen)
673 return sk;
674
675 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
676 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
677 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
678 inet_rsk(req)->acked = 1;
679 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
680 return NULL;
681 }
682
683 /* OK, ACK is valid, create big socket and
684 * feed this segment to it. It will repeat all
685 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
686 * ESTABLISHED STATE. If it will be dropped after
687 * socket is created, wait for troubles.
688 */
689 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
690 if (child == NULL)
691 goto listen_overflow;
692
693 inet_csk_reqsk_queue_unlink(sk, req, prev);
694 inet_csk_reqsk_queue_removed(sk, req);
695
696 inet_csk_reqsk_queue_add(sk, req, child);
697 return child;
698
699listen_overflow:
700 if (!sysctl_tcp_abort_on_overflow) {
701 inet_rsk(req)->acked = 1;
702 return NULL;
703 }
704
705embryonic_reset:
706 if (!(flg & TCP_FLAG_RST)) {
707 /* Received a bad SYN pkt - for TFO We try not to reset
708 * the local connection unless it's really necessary to
709 * avoid becoming vulnerable to outside attack aiming at
710 * resetting legit local connections.
711 */
712 req->rsk_ops->send_reset(sk, skb);
713 } else if (fastopen) { /* received a valid RST pkt */
714 reqsk_fastopen_remove(sk, req, true);
715 tcp_reset(sk);
716 }
717 if (!fastopen) {
718 inet_csk_reqsk_queue_drop(sk, req, prev);
719 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
720 }
721 return NULL;
722}
723EXPORT_SYMBOL(tcp_check_req);
724
725/*
726 * Queue segment on the new socket if the new socket is active,
727 * otherwise we just shortcircuit this and continue with
728 * the new socket.
729 *
730 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
731 * when entering. But other states are possible due to a race condition
732 * where after __inet_lookup_established() fails but before the listener
733 * locked is obtained, other packets cause the same connection to
734 * be created.
735 */
736
737int tcp_child_process(struct sock *parent, struct sock *child,
738 struct sk_buff *skb)
739{
740 int ret = 0;
741 int state = child->sk_state;
742
743 if (!sock_owned_by_user(child)) {
744 ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
745 skb->len);
746 /* Wakeup parent, send SIGIO */
747 if (state == TCP_SYN_RECV && child->sk_state != state)
748 parent->sk_data_ready(parent);
749 } else {
750 /* Alas, it is possible again, because we do lookup
751 * in main socket hash table and lock on listening
752 * socket does not protect us more.
753 */
754 __sk_add_backlog(child, skb);
755 }
756
757 bh_unlock_sock(child);
758 sock_put(child);
759 return ret;
760}
761EXPORT_SYMBOL(tcp_child_process);