1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * INET An implementation of the TCP/IP protocol suite for the LINUX
4 * operating system. INET is implemented using the BSD Socket
5 * interface as the means of communication with the user level.
6 *
7 * Implementation of the Transmission Control Protocol(TCP).
8 *
9 * Authors: Ross Biro
10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11 * Mark Evans, <evansmp@uhura.aston.ac.uk>
12 * Corey Minyard <wf-rch!minyard@relay.EU.net>
13 * Florian La Roche, <flla@stud.uni-sb.de>
14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15 * Linus Torvalds, <torvalds@cs.helsinki.fi>
16 * Alan Cox, <gw4pts@gw4pts.ampr.org>
17 * Matthew Dillon, <dillon@apollo.west.oic.com>
18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19 * Jorge Cwik, <jorge@laser.satlink.net>
20 */
21
22 #include <linux/mm.h>
23 #include <linux/module.h>
24 #include <linux/slab.h>
25 #include <linux/sysctl.h>
26 #include <linux/workqueue.h>
27 #include <linux/static_key.h>
28 #include <net/tcp.h>
29 #include <net/inet_common.h>
30 #include <net/xfrm.h>
31 #include <net/busy_poll.h>
32
tcp_in_window(u32 seq,u32 end_seq,u32 s_win,u32 e_win)33 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
34 {
35 if (seq == s_win)
36 return true;
37 if (after(end_seq, s_win) && before(seq, e_win))
38 return true;
39 return seq == e_win && seq == end_seq;
40 }
41
42 static enum tcp_tw_status
tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock * tw,const struct sk_buff * skb,int mib_idx)43 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
44 const struct sk_buff *skb, int mib_idx)
45 {
46 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
47
48 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
49 &tcptw->tw_last_oow_ack_time)) {
50 /* Send ACK. Note, we do not put the bucket,
51 * it will be released by caller.
52 */
53 return TCP_TW_ACK;
54 }
55
56 /* We are rate-limiting, so just release the tw sock and drop skb. */
57 inet_twsk_put(tw);
58 return TCP_TW_SUCCESS;
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 */
91 enum tcp_tw_status
tcp_timewait_state_process(struct inet_timewait_sock * tw,struct sk_buff * skb,const struct tcphdr * th)92 tcp_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(twsk_net(tw), skb, &tmp_opt, 0, NULL);
102
103 if (tmp_opt.saw_tstamp) {
104 if (tmp_opt.rcv_tsecr)
105 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
106 tmp_opt.ts_recent = tcptw->tw_ts_recent;
107 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
108 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
109 }
110 }
111
112 if (tw->tw_substate == TCP_FIN_WAIT2) {
113 /* Just repeat all the checks of tcp_rcv_state_process() */
114
115 /* Out of window, send ACK */
116 if (paws_reject ||
117 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
118 tcptw->tw_rcv_nxt,
119 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
120 return tcp_timewait_check_oow_rate_limit(
121 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
122
123 if (th->rst)
124 goto kill;
125
126 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
127 return TCP_TW_RST;
128
129 /* Dup ACK? */
130 if (!th->ack ||
131 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
132 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
133 inet_twsk_put(tw);
134 return TCP_TW_SUCCESS;
135 }
136
137 /* New data or FIN. If new data arrive after half-duplex close,
138 * reset.
139 */
140 if (!th->fin ||
141 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
142 return TCP_TW_RST;
143
144 /* FIN arrived, enter true time-wait state. */
145 tw->tw_substate = TCP_TIME_WAIT;
146 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
147 if (tmp_opt.saw_tstamp) {
148 tcptw->tw_ts_recent_stamp = ktime_get_seconds();
149 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
150 }
151
152 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
153 return TCP_TW_ACK;
154 }
155
156 /*
157 * Now real TIME-WAIT state.
158 *
159 * RFC 1122:
160 * "When a connection is [...] on TIME-WAIT state [...]
161 * [a TCP] MAY accept a new SYN from the remote TCP to
162 * reopen the connection directly, if it:
163 *
164 * (1) assigns its initial sequence number for the new
165 * connection to be larger than the largest sequence
166 * number it used on the previous connection incarnation,
167 * and
168 *
169 * (2) returns to TIME-WAIT state if the SYN turns out
170 * to be an old duplicate".
171 */
172
173 if (!paws_reject &&
174 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
175 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
176 /* In window segment, it may be only reset or bare ack. */
177
178 if (th->rst) {
179 /* This is TIME_WAIT assassination, in two flavors.
180 * Oh well... nobody has a sufficient solution to this
181 * protocol bug yet.
182 */
183 if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
184 kill:
185 inet_twsk_deschedule_put(tw);
186 return TCP_TW_SUCCESS;
187 }
188 } else {
189 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
190 }
191
192 if (tmp_opt.saw_tstamp) {
193 tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
194 tcptw->tw_ts_recent_stamp = ktime_get_seconds();
195 }
196
197 inet_twsk_put(tw);
198 return TCP_TW_SUCCESS;
199 }
200
201 /* Out of window segment.
202
203 All the segments are ACKed immediately.
204
205 The only exception is new SYN. We accept it, if it is
206 not old duplicate and we are not in danger to be killed
207 by delayed old duplicates. RFC check is that it has
208 newer sequence number works at rates <40Mbit/sec.
209 However, if paws works, it is reliable AND even more,
210 we even may relax silly seq space cutoff.
211
212 RED-PEN: we violate main RFC requirement, if this SYN will appear
213 old duplicate (i.e. we receive RST in reply to SYN-ACK),
214 we must return socket to time-wait state. It is not good,
215 but not fatal yet.
216 */
217
218 if (th->syn && !th->rst && !th->ack && !paws_reject &&
219 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
220 (tmp_opt.saw_tstamp &&
221 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
222 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
223 if (isn == 0)
224 isn++;
225 TCP_SKB_CB(skb)->tcp_tw_isn = isn;
226 return TCP_TW_SYN;
227 }
228
229 if (paws_reject)
230 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
231
232 if (!th->rst) {
233 /* In this case we must reset the TIMEWAIT timer.
234 *
235 * If it is ACKless SYN it may be both old duplicate
236 * and new good SYN with random sequence number <rcv_nxt.
237 * Do not reschedule in the last case.
238 */
239 if (paws_reject || th->ack)
240 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
241
242 return tcp_timewait_check_oow_rate_limit(
243 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
244 }
245 inet_twsk_put(tw);
246 return TCP_TW_SUCCESS;
247 }
248 EXPORT_SYMBOL(tcp_timewait_state_process);
249
250 /*
251 * Move a socket to time-wait or dead fin-wait-2 state.
252 */
tcp_time_wait(struct sock * sk,int state,int timeo)253 void tcp_time_wait(struct sock *sk, int state, int timeo)
254 {
255 const struct inet_connection_sock *icsk = inet_csk(sk);
256 const struct tcp_sock *tp = tcp_sk(sk);
257 struct inet_timewait_sock *tw;
258 struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
259
260 tw = inet_twsk_alloc(sk, tcp_death_row, state);
261
262 if (tw) {
263 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
264 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
265 struct inet_sock *inet = inet_sk(sk);
266
267 tw->tw_transparent = inet->transparent;
268 tw->tw_mark = sk->sk_mark;
269 tw->tw_priority = sk->sk_priority;
270 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
271 tcptw->tw_rcv_nxt = tp->rcv_nxt;
272 tcptw->tw_snd_nxt = tp->snd_nxt;
273 tcptw->tw_rcv_wnd = tcp_receive_window(tp);
274 tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
275 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
276 tcptw->tw_ts_offset = tp->tsoffset;
277 tcptw->tw_last_oow_ack_time = 0;
278 tcptw->tw_tx_delay = tp->tcp_tx_delay;
279 #if IS_ENABLED(CONFIG_IPV6)
280 if (tw->tw_family == PF_INET6) {
281 struct ipv6_pinfo *np = inet6_sk(sk);
282
283 tw->tw_v6_daddr = sk->sk_v6_daddr;
284 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
285 tw->tw_tclass = np->tclass;
286 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
287 tw->tw_txhash = sk->sk_txhash;
288 tw->tw_ipv6only = sk->sk_ipv6only;
289 }
290 #endif
291
292 #ifdef CONFIG_TCP_MD5SIG
293 /*
294 * The timewait bucket does not have the key DB from the
295 * sock structure. We just make a quick copy of the
296 * md5 key being used (if indeed we are using one)
297 * so the timewait ack generating code has the key.
298 */
299 do {
300 tcptw->tw_md5_key = NULL;
301 if (static_branch_unlikely(&tcp_md5_needed)) {
302 struct tcp_md5sig_key *key;
303
304 key = tp->af_specific->md5_lookup(sk, sk);
305 if (key) {
306 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
307 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
308 }
309 }
310 } while (0);
311 #endif
312
313 /* Get the TIME_WAIT timeout firing. */
314 if (timeo < rto)
315 timeo = rto;
316
317 if (state == TCP_TIME_WAIT)
318 timeo = TCP_TIMEWAIT_LEN;
319
320 /* tw_timer is pinned, so we need to make sure BH are disabled
321 * in following section, otherwise timer handler could run before
322 * we complete the initialization.
323 */
324 local_bh_disable();
325 inet_twsk_schedule(tw, timeo);
326 /* Linkage updates.
327 * Note that access to tw after this point is illegal.
328 */
329 inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
330 local_bh_enable();
331 } else {
332 /* Sorry, if we're out of memory, just CLOSE this
333 * socket up. We've got bigger problems than
334 * non-graceful socket closings.
335 */
336 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
337 }
338
339 tcp_update_metrics(sk);
340 tcp_done(sk);
341 }
342 EXPORT_SYMBOL(tcp_time_wait);
343
tcp_twsk_destructor(struct sock * sk)344 void tcp_twsk_destructor(struct sock *sk)
345 {
346 #ifdef CONFIG_TCP_MD5SIG
347 if (static_branch_unlikely(&tcp_md5_needed)) {
348 struct tcp_timewait_sock *twsk = tcp_twsk(sk);
349
350 if (twsk->tw_md5_key)
351 kfree_rcu(twsk->tw_md5_key, rcu);
352 }
353 #endif
354 }
355 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
356
357 /* Warning : This function is called without sk_listener being locked.
358 * Be sure to read socket fields once, as their value could change under us.
359 */
tcp_openreq_init_rwin(struct request_sock * req,const struct sock * sk_listener,const struct dst_entry * dst)360 void tcp_openreq_init_rwin(struct request_sock *req,
361 const struct sock *sk_listener,
362 const struct dst_entry *dst)
363 {
364 struct inet_request_sock *ireq = inet_rsk(req);
365 const struct tcp_sock *tp = tcp_sk(sk_listener);
366 int full_space = tcp_full_space(sk_listener);
367 u32 window_clamp;
368 __u8 rcv_wscale;
369 u32 rcv_wnd;
370 int mss;
371
372 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
373 window_clamp = READ_ONCE(tp->window_clamp);
374 /* Set this up on the first call only */
375 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
376
377 /* limit the window selection if the user enforce a smaller rx buffer */
378 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
379 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
380 req->rsk_window_clamp = full_space;
381
382 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
383 if (rcv_wnd == 0)
384 rcv_wnd = dst_metric(dst, RTAX_INITRWND);
385 else if (full_space < rcv_wnd * mss)
386 full_space = rcv_wnd * mss;
387
388 /* tcp_full_space because it is guaranteed to be the first packet */
389 tcp_select_initial_window(sk_listener, full_space,
390 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
391 &req->rsk_rcv_wnd,
392 &req->rsk_window_clamp,
393 ireq->wscale_ok,
394 &rcv_wscale,
395 rcv_wnd);
396 ireq->rcv_wscale = rcv_wscale;
397 }
398 EXPORT_SYMBOL(tcp_openreq_init_rwin);
399
tcp_ecn_openreq_child(struct tcp_sock * tp,const struct request_sock * req)400 static void tcp_ecn_openreq_child(struct tcp_sock *tp,
401 const struct request_sock *req)
402 {
403 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
404 }
405
tcp_ca_openreq_child(struct sock * sk,const struct dst_entry * dst)406 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
407 {
408 struct inet_connection_sock *icsk = inet_csk(sk);
409 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
410 bool ca_got_dst = false;
411
412 if (ca_key != TCP_CA_UNSPEC) {
413 const struct tcp_congestion_ops *ca;
414
415 rcu_read_lock();
416 ca = tcp_ca_find_key(ca_key);
417 if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
418 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
419 icsk->icsk_ca_ops = ca;
420 ca_got_dst = true;
421 }
422 rcu_read_unlock();
423 }
424
425 /* If no valid choice made yet, assign current system default ca. */
426 if (!ca_got_dst &&
427 (!icsk->icsk_ca_setsockopt ||
428 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner)))
429 tcp_assign_congestion_control(sk);
430
431 tcp_set_ca_state(sk, TCP_CA_Open);
432 }
433 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
434
smc_check_reset_syn_req(struct tcp_sock * oldtp,struct request_sock * req,struct tcp_sock * newtp)435 static void smc_check_reset_syn_req(struct tcp_sock *oldtp,
436 struct request_sock *req,
437 struct tcp_sock *newtp)
438 {
439 #if IS_ENABLED(CONFIG_SMC)
440 struct inet_request_sock *ireq;
441
442 if (static_branch_unlikely(&tcp_have_smc)) {
443 ireq = inet_rsk(req);
444 if (oldtp->syn_smc && !ireq->smc_ok)
445 newtp->syn_smc = 0;
446 }
447 #endif
448 }
449
450 /* This is not only more efficient than what we used to do, it eliminates
451 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
452 *
453 * Actually, we could lots of memory writes here. tp of listening
454 * socket contains all necessary default parameters.
455 */
tcp_create_openreq_child(const struct sock * sk,struct request_sock * req,struct sk_buff * skb)456 struct sock *tcp_create_openreq_child(const struct sock *sk,
457 struct request_sock *req,
458 struct sk_buff *skb)
459 {
460 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
461 const struct inet_request_sock *ireq = inet_rsk(req);
462 struct tcp_request_sock *treq = tcp_rsk(req);
463 struct inet_connection_sock *newicsk;
464 struct tcp_sock *oldtp, *newtp;
465 u32 seq;
466
467 if (!newsk)
468 return NULL;
469
470 newicsk = inet_csk(newsk);
471 newtp = tcp_sk(newsk);
472 oldtp = tcp_sk(sk);
473
474 smc_check_reset_syn_req(oldtp, req, newtp);
475
476 /* Now setup tcp_sock */
477 newtp->pred_flags = 0;
478
479 seq = treq->rcv_isn + 1;
480 newtp->rcv_wup = seq;
481 WRITE_ONCE(newtp->copied_seq, seq);
482 WRITE_ONCE(newtp->rcv_nxt, seq);
483 newtp->segs_in = 1;
484
485 seq = treq->snt_isn + 1;
486 newtp->snd_sml = newtp->snd_una = seq;
487 WRITE_ONCE(newtp->snd_nxt, seq);
488 newtp->snd_up = seq;
489
490 INIT_LIST_HEAD(&newtp->tsq_node);
491 INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
492
493 tcp_init_wl(newtp, treq->rcv_isn);
494
495 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
496 newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
497
498 newtp->lsndtime = tcp_jiffies32;
499 newsk->sk_txhash = treq->txhash;
500 newtp->total_retrans = req->num_retrans;
501
502 tcp_init_xmit_timers(newsk);
503 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
504
505 if (sock_flag(newsk, SOCK_KEEPOPEN))
506 inet_csk_reset_keepalive_timer(newsk,
507 keepalive_time_when(newtp));
508
509 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
510 newtp->rx_opt.sack_ok = ireq->sack_ok;
511 newtp->window_clamp = req->rsk_window_clamp;
512 newtp->rcv_ssthresh = req->rsk_rcv_wnd;
513 newtp->rcv_wnd = req->rsk_rcv_wnd;
514 newtp->rx_opt.wscale_ok = ireq->wscale_ok;
515 if (newtp->rx_opt.wscale_ok) {
516 newtp->rx_opt.snd_wscale = ireq->snd_wscale;
517 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
518 } else {
519 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
520 newtp->window_clamp = min(newtp->window_clamp, 65535U);
521 }
522 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
523 newtp->max_window = newtp->snd_wnd;
524
525 if (newtp->rx_opt.tstamp_ok) {
526 newtp->rx_opt.ts_recent = req->ts_recent;
527 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
528 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
529 } else {
530 newtp->rx_opt.ts_recent_stamp = 0;
531 newtp->tcp_header_len = sizeof(struct tcphdr);
532 }
533 if (req->num_timeout) {
534 newtp->undo_marker = treq->snt_isn;
535 newtp->retrans_stamp = div_u64(treq->snt_synack,
536 USEC_PER_SEC / TCP_TS_HZ);
537 }
538 newtp->tsoffset = treq->ts_off;
539 #ifdef CONFIG_TCP_MD5SIG
540 newtp->md5sig_info = NULL; /*XXX*/
541 if (newtp->af_specific->md5_lookup(sk, newsk))
542 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
543 #endif
544 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
545 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
546 newtp->rx_opt.mss_clamp = req->mss;
547 tcp_ecn_openreq_child(newtp, req);
548 newtp->fastopen_req = NULL;
549 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
550
551 tcp_bpf_clone(sk, newsk);
552
553 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
554
555 return newsk;
556 }
557 EXPORT_SYMBOL(tcp_create_openreq_child);
558
559 /*
560 * Process an incoming packet for SYN_RECV sockets represented as a
561 * request_sock. Normally sk is the listener socket but for TFO it
562 * points to the child socket.
563 *
564 * XXX (TFO) - The current impl contains a special check for ack
565 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
566 *
567 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
568 */
569
tcp_check_req(struct sock * sk,struct sk_buff * skb,struct request_sock * req,bool fastopen,bool * req_stolen)570 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
571 struct request_sock *req,
572 bool fastopen, bool *req_stolen)
573 {
574 struct tcp_options_received tmp_opt;
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 bool own_req;
580
581 tmp_opt.saw_tstamp = 0;
582 if (th->doff > (sizeof(struct tcphdr)>>2)) {
583 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
584
585 if (tmp_opt.saw_tstamp) {
586 tmp_opt.ts_recent = req->ts_recent;
587 if (tmp_opt.rcv_tsecr)
588 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
589 /* We do not store true stamp, but it is not required,
590 * it can be estimated (approximately)
591 * from another data.
592 */
593 tmp_opt.ts_recent_stamp = ktime_get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
594 paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
595 }
596 }
597
598 /* Check for pure retransmitted SYN. */
599 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
600 flg == TCP_FLAG_SYN &&
601 !paws_reject) {
602 /*
603 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
604 * this case on figure 6 and figure 8, but formal
605 * protocol description says NOTHING.
606 * To be more exact, it says that we should send ACK,
607 * because this segment (at least, if it has no data)
608 * is out of window.
609 *
610 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
611 * describe SYN-RECV state. All the description
612 * is wrong, we cannot believe to it and should
613 * rely only on common sense and implementation
614 * experience.
615 *
616 * Enforce "SYN-ACK" according to figure 8, figure 6
617 * of RFC793, fixed by RFC1122.
618 *
619 * Note that even if there is new data in the SYN packet
620 * they will be thrown away too.
621 *
622 * Reset timer after retransmitting SYNACK, similar to
623 * the idea of fast retransmit in recovery.
624 */
625 if (!tcp_oow_rate_limited(sock_net(sk), skb,
626 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
627 &tcp_rsk(req)->last_oow_ack_time) &&
628
629 !inet_rtx_syn_ack(sk, req)) {
630 unsigned long expires = jiffies;
631
632 expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
633 TCP_RTO_MAX);
634 if (!fastopen)
635 mod_timer_pending(&req->rsk_timer, expires);
636 else
637 req->rsk_timer.expires = expires;
638 }
639 return NULL;
640 }
641
642 /* Further reproduces section "SEGMENT ARRIVES"
643 for state SYN-RECEIVED of RFC793.
644 It is broken, however, it does not work only
645 when SYNs are crossed.
646
647 You would think that SYN crossing is impossible here, since
648 we should have a SYN_SENT socket (from connect()) on our end,
649 but this is not true if the crossed SYNs were sent to both
650 ends by a malicious third party. We must defend against this,
651 and to do that we first verify the ACK (as per RFC793, page
652 36) and reset if it is invalid. Is this a true full defense?
653 To convince ourselves, let us consider a way in which the ACK
654 test can still pass in this 'malicious crossed SYNs' case.
655 Malicious sender sends identical SYNs (and thus identical sequence
656 numbers) to both A and B:
657
658 A: gets SYN, seq=7
659 B: gets SYN, seq=7
660
661 By our good fortune, both A and B select the same initial
662 send sequence number of seven :-)
663
664 A: sends SYN|ACK, seq=7, ack_seq=8
665 B: sends SYN|ACK, seq=7, ack_seq=8
666
667 So we are now A eating this SYN|ACK, ACK test passes. So
668 does sequence test, SYN is truncated, and thus we consider
669 it a bare ACK.
670
671 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
672 bare ACK. Otherwise, we create an established connection. Both
673 ends (listening sockets) accept the new incoming connection and try
674 to talk to each other. 8-)
675
676 Note: This case is both harmless, and rare. Possibility is about the
677 same as us discovering intelligent life on another plant tomorrow.
678
679 But generally, we should (RFC lies!) to accept ACK
680 from SYNACK both here and in tcp_rcv_state_process().
681 tcp_rcv_state_process() does not, hence, we do not too.
682
683 Note that the case is absolutely generic:
684 we cannot optimize anything here without
685 violating protocol. All the checks must be made
686 before attempt to create socket.
687 */
688
689 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
690 * and the incoming segment acknowledges something not yet
691 * sent (the segment carries an unacceptable ACK) ...
692 * a reset is sent."
693 *
694 * Invalid ACK: reset will be sent by listening socket.
695 * Note that the ACK validity check for a Fast Open socket is done
696 * elsewhere and is checked directly against the child socket rather
697 * than req because user data may have been sent out.
698 */
699 if ((flg & TCP_FLAG_ACK) && !fastopen &&
700 (TCP_SKB_CB(skb)->ack_seq !=
701 tcp_rsk(req)->snt_isn + 1))
702 return sk;
703
704 /* Also, it would be not so bad idea to check rcv_tsecr, which
705 * is essentially ACK extension and too early or too late values
706 * should cause reset in unsynchronized states.
707 */
708
709 /* RFC793: "first check sequence number". */
710
711 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
712 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
713 /* Out of window: send ACK and drop. */
714 if (!(flg & TCP_FLAG_RST) &&
715 !tcp_oow_rate_limited(sock_net(sk), skb,
716 LINUX_MIB_TCPACKSKIPPEDSYNRECV,
717 &tcp_rsk(req)->last_oow_ack_time))
718 req->rsk_ops->send_ack(sk, skb, req);
719 if (paws_reject)
720 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
721 return NULL;
722 }
723
724 /* In sequence, PAWS is OK. */
725
726 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
727 req->ts_recent = tmp_opt.rcv_tsval;
728
729 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
730 /* Truncate SYN, it is out of window starting
731 at tcp_rsk(req)->rcv_isn + 1. */
732 flg &= ~TCP_FLAG_SYN;
733 }
734
735 /* RFC793: "second check the RST bit" and
736 * "fourth, check the SYN bit"
737 */
738 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
739 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
740 goto embryonic_reset;
741 }
742
743 /* ACK sequence verified above, just make sure ACK is
744 * set. If ACK not set, just silently drop the packet.
745 *
746 * XXX (TFO) - if we ever allow "data after SYN", the
747 * following check needs to be removed.
748 */
749 if (!(flg & TCP_FLAG_ACK))
750 return NULL;
751
752 /* For Fast Open no more processing is needed (sk is the
753 * child socket).
754 */
755 if (fastopen)
756 return sk;
757
758 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
759 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
760 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
761 inet_rsk(req)->acked = 1;
762 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
763 return NULL;
764 }
765
766 /* OK, ACK is valid, create big socket and
767 * feed this segment to it. It will repeat all
768 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
769 * ESTABLISHED STATE. If it will be dropped after
770 * socket is created, wait for troubles.
771 */
772 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
773 req, &own_req);
774 if (!child)
775 goto listen_overflow;
776
777 if (own_req && rsk_drop_req(req)) {
778 reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
779 inet_csk_reqsk_queue_drop_and_put(sk, req);
780 return child;
781 }
782
783 sock_rps_save_rxhash(child, skb);
784 tcp_synack_rtt_meas(child, req);
785 *req_stolen = !own_req;
786 return inet_csk_complete_hashdance(sk, child, req, own_req);
787
788 listen_overflow:
789 if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
790 inet_rsk(req)->acked = 1;
791 return NULL;
792 }
793
794 embryonic_reset:
795 if (!(flg & TCP_FLAG_RST)) {
796 /* Received a bad SYN pkt - for TFO We try not to reset
797 * the local connection unless it's really necessary to
798 * avoid becoming vulnerable to outside attack aiming at
799 * resetting legit local connections.
800 */
801 req->rsk_ops->send_reset(sk, skb);
802 } else if (fastopen) { /* received a valid RST pkt */
803 reqsk_fastopen_remove(sk, req, true);
804 tcp_reset(sk);
805 }
806 if (!fastopen) {
807 inet_csk_reqsk_queue_drop(sk, req);
808 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
809 }
810 return NULL;
811 }
812 EXPORT_SYMBOL(tcp_check_req);
813
814 /*
815 * Queue segment on the new socket if the new socket is active,
816 * otherwise we just shortcircuit this and continue with
817 * the new socket.
818 *
819 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
820 * when entering. But other states are possible due to a race condition
821 * where after __inet_lookup_established() fails but before the listener
822 * locked is obtained, other packets cause the same connection to
823 * be created.
824 */
825
tcp_child_process(struct sock * parent,struct sock * child,struct sk_buff * skb)826 int tcp_child_process(struct sock *parent, struct sock *child,
827 struct sk_buff *skb)
828 __releases(&((child)->sk_lock.slock))
829 {
830 int ret = 0;
831 int state = child->sk_state;
832
833 /* record NAPI ID of child */
834 sk_mark_napi_id(child, skb);
835
836 tcp_segs_in(tcp_sk(child), skb);
837 if (!sock_owned_by_user(child)) {
838 ret = tcp_rcv_state_process(child, skb);
839 /* Wakeup parent, send SIGIO */
840 if (state == TCP_SYN_RECV && child->sk_state != state)
841 parent->sk_data_ready(parent);
842 } else {
843 /* Alas, it is possible again, because we do lookup
844 * in main socket hash table and lock on listening
845 * socket does not protect us more.
846 */
847 __sk_add_backlog(child, skb);
848 }
849
850 bh_unlock_sock(child);
851 sock_put(child);
852 return ret;
853 }
854 EXPORT_SYMBOL(tcp_child_process);
855
