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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 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);
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);