Line data Source code
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 :
33 4 : static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
34 : {
35 4 : if (seq == s_win)
36 : return true;
37 0 : if (after(end_seq, s_win) && before(seq, e_win))
38 : return true;
39 0 : return seq == e_win && seq == end_seq;
40 : }
41 :
42 : static enum tcp_tw_status
43 0 : tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
44 : const struct sk_buff *skb, int mib_idx)
45 : {
46 0 : struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
47 :
48 0 : 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 0 : inet_twsk_put(tw);
58 0 : 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
92 0 : tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
93 : const struct tcphdr *th)
94 : {
95 0 : struct tcp_options_received tmp_opt;
96 0 : struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
97 0 : bool paws_reject = false;
98 :
99 0 : tmp_opt.saw_tstamp = 0;
100 0 : if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
101 0 : tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);
102 :
103 0 : if (tmp_opt.saw_tstamp) {
104 0 : if (tmp_opt.rcv_tsecr)
105 0 : tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
106 0 : tmp_opt.ts_recent = tcptw->tw_ts_recent;
107 0 : tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
108 0 : paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
109 : }
110 : }
111 :
112 0 : 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 0 : if (paws_reject ||
117 0 : !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
118 : tcptw->tw_rcv_nxt,
119 0 : tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
120 0 : return tcp_timewait_check_oow_rate_limit(
121 : tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
122 :
123 0 : if (th->rst)
124 0 : goto kill;
125 :
126 0 : if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
127 : return TCP_TW_RST;
128 :
129 : /* Dup ACK? */
130 0 : if (!th->ack ||
131 0 : !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
132 : TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
133 0 : inet_twsk_put(tw);
134 0 : return TCP_TW_SUCCESS;
135 : }
136 :
137 : /* New data or FIN. If new data arrive after half-duplex close,
138 : * reset.
139 : */
140 0 : if (!th->fin ||
141 0 : 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 0 : tw->tw_substate = TCP_TIME_WAIT;
146 0 : tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
147 0 : if (tmp_opt.saw_tstamp) {
148 0 : tcptw->tw_ts_recent_stamp = ktime_get_seconds();
149 0 : tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
150 : }
151 :
152 0 : inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
153 0 : 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 0 : if (!paws_reject &&
174 0 : (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
175 0 : (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 0 : 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 0 : if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
184 0 : kill:
185 0 : inet_twsk_deschedule_put(tw);
186 0 : return TCP_TW_SUCCESS;
187 : }
188 : } else {
189 0 : inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
190 : }
191 :
192 0 : if (tmp_opt.saw_tstamp) {
193 0 : tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
194 0 : tcptw->tw_ts_recent_stamp = ktime_get_seconds();
195 : }
196 :
197 0 : inet_twsk_put(tw);
198 0 : 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 0 : if (th->syn && !th->rst && !th->ack && !paws_reject &&
219 0 : (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
220 0 : (tmp_opt.saw_tstamp &&
221 0 : (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
222 0 : u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
223 0 : if (isn == 0)
224 : isn++;
225 0 : TCP_SKB_CB(skb)->tcp_tw_isn = isn;
226 0 : return TCP_TW_SYN;
227 : }
228 :
229 0 : if (paws_reject)
230 0 : __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
231 :
232 0 : 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 0 : if (paws_reject || th->ack)
240 0 : inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
241 :
242 0 : return tcp_timewait_check_oow_rate_limit(
243 : tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
244 : }
245 0 : inet_twsk_put(tw);
246 0 : 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 : */
253 0 : void tcp_time_wait(struct sock *sk, int state, int timeo)
254 : {
255 0 : const struct inet_connection_sock *icsk = inet_csk(sk);
256 0 : const struct tcp_sock *tp = tcp_sk(sk);
257 0 : struct inet_timewait_sock *tw;
258 0 : struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
259 :
260 0 : tw = inet_twsk_alloc(sk, tcp_death_row, state);
261 :
262 0 : if (tw) {
263 0 : struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
264 0 : const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
265 0 : struct inet_sock *inet = inet_sk(sk);
266 :
267 0 : tw->tw_transparent = inet->transparent;
268 0 : tw->tw_mark = sk->sk_mark;
269 0 : tw->tw_priority = sk->sk_priority;
270 0 : tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
271 0 : tcptw->tw_rcv_nxt = tp->rcv_nxt;
272 0 : tcptw->tw_snd_nxt = tp->snd_nxt;
273 0 : tcptw->tw_rcv_wnd = tcp_receive_window(tp);
274 0 : tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
275 0 : tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
276 0 : tcptw->tw_ts_offset = tp->tsoffset;
277 0 : tcptw->tw_last_oow_ack_time = 0;
278 0 : 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 0 : if (timeo < rto)
315 : timeo = rto;
316 :
317 0 : if (state == TCP_TIME_WAIT)
318 0 : 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 0 : local_bh_disable();
325 0 : inet_twsk_schedule(tw, timeo);
326 : /* Linkage updates.
327 : * Note that access to tw after this point is illegal.
328 : */
329 0 : inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
330 0 : 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 0 : NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
337 : }
338 :
339 0 : tcp_update_metrics(sk);
340 0 : tcp_done(sk);
341 0 : }
342 : EXPORT_SYMBOL(tcp_time_wait);
343 :
344 0 : 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 0 : }
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 : */
360 4 : void tcp_openreq_init_rwin(struct request_sock *req,
361 : const struct sock *sk_listener,
362 : const struct dst_entry *dst)
363 : {
364 4 : struct inet_request_sock *ireq = inet_rsk(req);
365 4 : const struct tcp_sock *tp = tcp_sk(sk_listener);
366 4 : int full_space = tcp_full_space(sk_listener);
367 4 : u32 window_clamp;
368 4 : __u8 rcv_wscale;
369 4 : u32 rcv_wnd;
370 4 : int mss;
371 :
372 4 : mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
373 4 : window_clamp = READ_ONCE(tp->window_clamp);
374 : /* Set this up on the first call only */
375 4 : 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 4 : if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
379 0 : (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
380 0 : req->rsk_window_clamp = full_space;
381 :
382 4 : rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
383 4 : if (rcv_wnd == 0)
384 4 : rcv_wnd = dst_metric(dst, RTAX_INITRWND);
385 0 : else if (full_space < rcv_wnd * mss)
386 0 : full_space = rcv_wnd * mss;
387 :
388 : /* tcp_full_space because it is guaranteed to be the first packet */
389 8 : tcp_select_initial_window(sk_listener, full_space,
390 4 : mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
391 4 : &req->rsk_rcv_wnd,
392 4 : &req->rsk_window_clamp,
393 4 : ireq->wscale_ok,
394 : &rcv_wscale,
395 : rcv_wnd);
396 4 : ireq->rcv_wscale = rcv_wscale;
397 4 : }
398 : EXPORT_SYMBOL(tcp_openreq_init_rwin);
399 :
400 4 : static void tcp_ecn_openreq_child(struct tcp_sock *tp,
401 : const struct request_sock *req)
402 : {
403 4 : tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
404 : }
405 :
406 4 : void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
407 : {
408 4 : struct inet_connection_sock *icsk = inet_csk(sk);
409 4 : u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
410 4 : bool ca_got_dst = false;
411 :
412 4 : if (ca_key != TCP_CA_UNSPEC) {
413 0 : const struct tcp_congestion_ops *ca;
414 :
415 0 : rcu_read_lock();
416 0 : ca = tcp_ca_find_key(ca_key);
417 0 : if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
418 0 : icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
419 0 : icsk->icsk_ca_ops = ca;
420 0 : ca_got_dst = true;
421 : }
422 0 : rcu_read_unlock();
423 : }
424 :
425 : /* If no valid choice made yet, assign current system default ca. */
426 0 : if (!ca_got_dst &&
427 4 : (!icsk->icsk_ca_setsockopt ||
428 4 : !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner)))
429 4 : tcp_assign_congestion_control(sk);
430 :
431 4 : tcp_set_ca_state(sk, TCP_CA_Open);
432 4 : }
433 : EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
434 :
435 4 : 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 4 : }
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 : */
456 4 : struct sock *tcp_create_openreq_child(const struct sock *sk,
457 : struct request_sock *req,
458 : struct sk_buff *skb)
459 : {
460 4 : struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
461 4 : const struct inet_request_sock *ireq = inet_rsk(req);
462 4 : struct tcp_request_sock *treq = tcp_rsk(req);
463 4 : struct inet_connection_sock *newicsk;
464 4 : struct tcp_sock *oldtp, *newtp;
465 4 : u32 seq;
466 :
467 4 : if (!newsk)
468 : return NULL;
469 :
470 4 : newicsk = inet_csk(newsk);
471 4 : newtp = tcp_sk(newsk);
472 4 : oldtp = tcp_sk(sk);
473 :
474 4 : smc_check_reset_syn_req(oldtp, req, newtp);
475 :
476 : /* Now setup tcp_sock */
477 4 : newtp->pred_flags = 0;
478 :
479 4 : seq = treq->rcv_isn + 1;
480 4 : newtp->rcv_wup = seq;
481 4 : WRITE_ONCE(newtp->copied_seq, seq);
482 4 : WRITE_ONCE(newtp->rcv_nxt, seq);
483 4 : newtp->segs_in = 1;
484 :
485 4 : seq = treq->snt_isn + 1;
486 4 : newtp->snd_sml = newtp->snd_una = seq;
487 4 : WRITE_ONCE(newtp->snd_nxt, seq);
488 4 : newtp->snd_up = seq;
489 :
490 4 : INIT_LIST_HEAD(&newtp->tsq_node);
491 4 : INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
492 :
493 4 : tcp_init_wl(newtp, treq->rcv_isn);
494 :
495 4 : minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
496 4 : newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
497 :
498 4 : newtp->lsndtime = tcp_jiffies32;
499 4 : newsk->sk_txhash = treq->txhash;
500 4 : newtp->total_retrans = req->num_retrans;
501 :
502 4 : tcp_init_xmit_timers(newsk);
503 4 : WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
504 :
505 4 : if (sock_flag(newsk, SOCK_KEEPOPEN))
506 0 : inet_csk_reset_keepalive_timer(newsk,
507 0 : keepalive_time_when(newtp));
508 :
509 4 : newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
510 4 : newtp->rx_opt.sack_ok = ireq->sack_ok;
511 4 : newtp->window_clamp = req->rsk_window_clamp;
512 4 : newtp->rcv_ssthresh = req->rsk_rcv_wnd;
513 4 : newtp->rcv_wnd = req->rsk_rcv_wnd;
514 4 : newtp->rx_opt.wscale_ok = ireq->wscale_ok;
515 4 : if (newtp->rx_opt.wscale_ok) {
516 0 : newtp->rx_opt.snd_wscale = ireq->snd_wscale;
517 0 : newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
518 : } else {
519 4 : newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
520 4 : newtp->window_clamp = min(newtp->window_clamp, 65535U);
521 : }
522 4 : newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
523 4 : newtp->max_window = newtp->snd_wnd;
524 :
525 4 : if (newtp->rx_opt.tstamp_ok) {
526 0 : newtp->rx_opt.ts_recent = req->ts_recent;
527 0 : newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
528 0 : newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
529 : } else {
530 4 : newtp->rx_opt.ts_recent_stamp = 0;
531 4 : newtp->tcp_header_len = sizeof(struct tcphdr);
532 : }
533 4 : if (req->num_timeout) {
534 0 : newtp->undo_marker = treq->snt_isn;
535 0 : newtp->retrans_stamp = div_u64(treq->snt_synack,
536 : USEC_PER_SEC / TCP_TS_HZ);
537 : }
538 4 : 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 4 : if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
545 0 : newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
546 4 : newtp->rx_opt.mss_clamp = req->mss;
547 4 : tcp_ecn_openreq_child(newtp, req);
548 4 : newtp->fastopen_req = NULL;
549 4 : RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
550 :
551 4 : tcp_bpf_clone(sk, newsk);
552 :
553 4 : __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
554 :
555 4 : 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 :
570 4 : 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 4 : struct tcp_options_received tmp_opt;
575 4 : struct sock *child;
576 4 : const struct tcphdr *th = tcp_hdr(skb);
577 4 : __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
578 4 : bool paws_reject = false;
579 4 : bool own_req;
580 :
581 4 : tmp_opt.saw_tstamp = 0;
582 4 : if (th->doff > (sizeof(struct tcphdr)>>2)) {
583 0 : tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
584 :
585 0 : if (tmp_opt.saw_tstamp) {
586 0 : tmp_opt.ts_recent = req->ts_recent;
587 0 : if (tmp_opt.rcv_tsecr)
588 0 : 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 0 : tmp_opt.ts_recent_stamp = ktime_get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
594 0 : paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
595 : }
596 : }
597 :
598 : /* Check for pure retransmitted SYN. */
599 4 : if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
600 0 : flg == TCP_FLAG_SYN &&
601 0 : !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 0 : if (!tcp_oow_rate_limited(sock_net(sk), skb,
626 : LINUX_MIB_TCPACKSKIPPEDSYNRECV,
627 0 : &tcp_rsk(req)->last_oow_ack_time) &&
628 :
629 0 : !inet_rtx_syn_ack(sk, req)) {
630 0 : unsigned long expires = jiffies;
631 :
632 0 : expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
633 : TCP_RTO_MAX);
634 0 : if (!fastopen)
635 0 : mod_timer_pending(&req->rsk_timer, expires);
636 : else
637 0 : req->rsk_timer.expires = expires;
638 : }
639 0 : 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 4 : if ((flg & TCP_FLAG_ACK) && !fastopen &&
700 4 : (TCP_SKB_CB(skb)->ack_seq !=
701 4 : 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 4 : if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
712 4 : tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
713 : /* Out of window: send ACK and drop. */
714 0 : if (!(flg & TCP_FLAG_RST) &&
715 0 : !tcp_oow_rate_limited(sock_net(sk), skb,
716 : LINUX_MIB_TCPACKSKIPPEDSYNRECV,
717 0 : &tcp_rsk(req)->last_oow_ack_time))
718 0 : req->rsk_ops->send_ack(sk, skb, req);
719 0 : if (paws_reject)
720 0 : __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
721 0 : return NULL;
722 : }
723 :
724 : /* In sequence, PAWS is OK. */
725 :
726 4 : if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
727 0 : req->ts_recent = tmp_opt.rcv_tsval;
728 :
729 4 : 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 0 : flg &= ~TCP_FLAG_SYN;
733 : }
734 :
735 : /* RFC793: "second check the RST bit" and
736 : * "fourth, check the SYN bit"
737 : */
738 4 : if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
739 0 : __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
740 0 : 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 4 : 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 4 : if (fastopen)
756 : return sk;
757 :
758 : /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
759 4 : if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
760 0 : TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
761 0 : inet_rsk(req)->acked = 1;
762 0 : __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
763 0 : 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 4 : child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
773 : req, &own_req);
774 4 : if (!child)
775 0 : goto listen_overflow;
776 :
777 4 : 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 4 : sock_rps_save_rxhash(child, skb);
784 4 : tcp_synack_rtt_meas(child, req);
785 4 : *req_stolen = !own_req;
786 4 : return inet_csk_complete_hashdance(sk, child, req, own_req);
787 :
788 0 : listen_overflow:
789 0 : if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
790 0 : inet_rsk(req)->acked = 1;
791 0 : return NULL;
792 : }
793 :
794 0 : embryonic_reset:
795 0 : 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 0 : req->rsk_ops->send_reset(sk, skb);
802 0 : } else if (fastopen) { /* received a valid RST pkt */
803 0 : reqsk_fastopen_remove(sk, req, true);
804 0 : tcp_reset(sk, skb);
805 : }
806 0 : if (!fastopen) {
807 0 : inet_csk_reqsk_queue_drop(sk, req);
808 0 : __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 :
826 4 : int tcp_child_process(struct sock *parent, struct sock *child,
827 : struct sk_buff *skb)
828 : __releases(&((child)->sk_lock.slock))
829 : {
830 4 : int ret = 0;
831 4 : int state = child->sk_state;
832 :
833 : /* record NAPI ID of child */
834 4 : sk_mark_napi_id(child, skb);
835 :
836 4 : tcp_segs_in(tcp_sk(child), skb);
837 4 : if (!sock_owned_by_user(child)) {
838 4 : ret = tcp_rcv_state_process(child, skb);
839 : /* Wakeup parent, send SIGIO */
840 4 : if (state == TCP_SYN_RECV && child->sk_state != state)
841 4 : 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 0 : __sk_add_backlog(child, skb);
848 : }
849 :
850 4 : bh_unlock_sock(child);
851 4 : sock_put(child);
852 4 : return ret;
853 : }
854 : EXPORT_SYMBOL(tcp_child_process);
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