1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/kernel.h>
3 #include <linux/tcp.h>
4 #include <linux/rcupdate.h>
5 #include <net/tcp.h>
6 #include <net/busy_poll.h>
7
tcp_fastopen_init_key_once(struct net * net)8 void tcp_fastopen_init_key_once(struct net *net)
9 {
10 u8 key[TCP_FASTOPEN_KEY_LENGTH];
11 struct tcp_fastopen_context *ctxt;
12
13 rcu_read_lock();
14 ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
15 if (ctxt) {
16 rcu_read_unlock();
17 return;
18 }
19 rcu_read_unlock();
20
21 /* tcp_fastopen_reset_cipher publishes the new context
22 * atomically, so we allow this race happening here.
23 *
24 * All call sites of tcp_fastopen_cookie_gen also check
25 * for a valid cookie, so this is an acceptable risk.
26 */
27 get_random_bytes(key, sizeof(key));
28 tcp_fastopen_reset_cipher(net, NULL, key, NULL);
29 }
30
tcp_fastopen_ctx_free(struct rcu_head * head)31 static void tcp_fastopen_ctx_free(struct rcu_head *head)
32 {
33 struct tcp_fastopen_context *ctx =
34 container_of(head, struct tcp_fastopen_context, rcu);
35
36 kfree_sensitive(ctx);
37 }
38
tcp_fastopen_destroy_cipher(struct sock * sk)39 void tcp_fastopen_destroy_cipher(struct sock *sk)
40 {
41 struct tcp_fastopen_context *ctx;
42
43 ctx = rcu_dereference_protected(
44 inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
45 if (ctx)
46 call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
47 }
48
tcp_fastopen_ctx_destroy(struct net * net)49 void tcp_fastopen_ctx_destroy(struct net *net)
50 {
51 struct tcp_fastopen_context *ctxt;
52
53 ctxt = unrcu_pointer(xchg(&net->ipv4.tcp_fastopen_ctx, NULL));
54
55 if (ctxt)
56 call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
57 }
58
tcp_fastopen_reset_cipher(struct net * net,struct sock * sk,void * primary_key,void * backup_key)59 int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
60 void *primary_key, void *backup_key)
61 {
62 struct tcp_fastopen_context *ctx, *octx;
63 struct fastopen_queue *q;
64 int err = 0;
65
66 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
67 if (!ctx) {
68 err = -ENOMEM;
69 goto out;
70 }
71
72 ctx->key[0].key[0] = get_unaligned_le64(primary_key);
73 ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
74 if (backup_key) {
75 ctx->key[1].key[0] = get_unaligned_le64(backup_key);
76 ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
77 ctx->num = 2;
78 } else {
79 ctx->num = 1;
80 }
81
82 if (sk) {
83 q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
84 octx = unrcu_pointer(xchg(&q->ctx, RCU_INITIALIZER(ctx)));
85 } else {
86 octx = unrcu_pointer(xchg(&net->ipv4.tcp_fastopen_ctx,
87 RCU_INITIALIZER(ctx)));
88 }
89
90 if (octx)
91 call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
92 out:
93 return err;
94 }
95
tcp_fastopen_get_cipher(struct net * net,struct inet_connection_sock * icsk,u64 * key)96 int tcp_fastopen_get_cipher(struct net *net, struct inet_connection_sock *icsk,
97 u64 *key)
98 {
99 struct tcp_fastopen_context *ctx;
100 int n_keys = 0, i;
101
102 rcu_read_lock();
103 if (icsk)
104 ctx = rcu_dereference(icsk->icsk_accept_queue.fastopenq.ctx);
105 else
106 ctx = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
107 if (ctx) {
108 n_keys = tcp_fastopen_context_len(ctx);
109 for (i = 0; i < n_keys; i++) {
110 put_unaligned_le64(ctx->key[i].key[0], key + (i * 2));
111 put_unaligned_le64(ctx->key[i].key[1], key + (i * 2) + 1);
112 }
113 }
114 rcu_read_unlock();
115
116 return n_keys;
117 }
118
__tcp_fastopen_cookie_gen_cipher(struct request_sock * req,struct sk_buff * syn,const siphash_key_t * key,struct tcp_fastopen_cookie * foc)119 static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
120 struct sk_buff *syn,
121 const siphash_key_t *key,
122 struct tcp_fastopen_cookie *foc)
123 {
124 BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
125
126 if (req->rsk_ops->family == AF_INET) {
127 const struct iphdr *iph = ip_hdr(syn);
128
129 foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
130 sizeof(iph->saddr) +
131 sizeof(iph->daddr),
132 key));
133 foc->len = TCP_FASTOPEN_COOKIE_SIZE;
134 return true;
135 }
136 #if IS_ENABLED(CONFIG_IPV6)
137 if (req->rsk_ops->family == AF_INET6) {
138 const struct ipv6hdr *ip6h = ipv6_hdr(syn);
139
140 foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
141 sizeof(ip6h->saddr) +
142 sizeof(ip6h->daddr),
143 key));
144 foc->len = TCP_FASTOPEN_COOKIE_SIZE;
145 return true;
146 }
147 #endif
148 return false;
149 }
150
151 /* Generate the fastopen cookie by applying SipHash to both the source and
152 * destination addresses.
153 */
tcp_fastopen_cookie_gen(struct sock * sk,struct request_sock * req,struct sk_buff * syn,struct tcp_fastopen_cookie * foc)154 static void tcp_fastopen_cookie_gen(struct sock *sk,
155 struct request_sock *req,
156 struct sk_buff *syn,
157 struct tcp_fastopen_cookie *foc)
158 {
159 struct tcp_fastopen_context *ctx;
160
161 rcu_read_lock();
162 ctx = tcp_fastopen_get_ctx(sk);
163 if (ctx)
164 __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
165 rcu_read_unlock();
166 }
167
168 /* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
169 * queue this additional data / FIN.
170 */
tcp_fastopen_add_skb(struct sock * sk,struct sk_buff * skb)171 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
172 {
173 struct tcp_sock *tp = tcp_sk(sk);
174
175 if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
176 return;
177
178 skb = skb_clone(skb, GFP_ATOMIC);
179 if (!skb)
180 return;
181
182 tcp_cleanup_skb(skb);
183 /* segs_in has been initialized to 1 in tcp_create_openreq_child().
184 * Hence, reset segs_in to 0 before calling tcp_segs_in()
185 * to avoid double counting. Also, tcp_segs_in() expects
186 * skb->len to include the tcp_hdrlen. Hence, it should
187 * be called before __skb_pull().
188 */
189 tp->segs_in = 0;
190 tcp_segs_in(tp, skb);
191 __skb_pull(skb, tcp_hdrlen(skb));
192 sk_forced_mem_schedule(sk, skb->truesize);
193 skb_set_owner_r(skb, sk);
194
195 TCP_SKB_CB(skb)->seq++;
196 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
197
198 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
199 tcp_add_receive_queue(sk, skb);
200 tp->syn_data_acked = 1;
201
202 /* u64_stats_update_begin(&tp->syncp) not needed here,
203 * as we certainly are not changing upper 32bit value (0)
204 */
205 tp->bytes_received = skb->len;
206
207 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
208 tcp_fin(sk);
209 }
210
211 /* returns 0 - no key match, 1 for primary, 2 for backup */
tcp_fastopen_cookie_gen_check(struct sock * sk,struct request_sock * req,struct sk_buff * syn,struct tcp_fastopen_cookie * orig,struct tcp_fastopen_cookie * valid_foc)212 static int tcp_fastopen_cookie_gen_check(struct sock *sk,
213 struct request_sock *req,
214 struct sk_buff *syn,
215 struct tcp_fastopen_cookie *orig,
216 struct tcp_fastopen_cookie *valid_foc)
217 {
218 struct tcp_fastopen_cookie search_foc = { .len = -1 };
219 struct tcp_fastopen_cookie *foc = valid_foc;
220 struct tcp_fastopen_context *ctx;
221 int i, ret = 0;
222
223 rcu_read_lock();
224 ctx = tcp_fastopen_get_ctx(sk);
225 if (!ctx)
226 goto out;
227 for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
228 __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
229 if (tcp_fastopen_cookie_match(foc, orig)) {
230 ret = i + 1;
231 goto out;
232 }
233 foc = &search_foc;
234 }
235 out:
236 rcu_read_unlock();
237 return ret;
238 }
239
tcp_fastopen_create_child(struct sock * sk,struct sk_buff * skb,struct request_sock * req)240 static struct sock *tcp_fastopen_create_child(struct sock *sk,
241 struct sk_buff *skb,
242 struct request_sock *req)
243 {
244 struct tcp_sock *tp;
245 struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
246 struct sock *child;
247 bool own_req;
248
249 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
250 NULL, &own_req);
251 if (!child)
252 return NULL;
253
254 spin_lock(&queue->fastopenq.lock);
255 queue->fastopenq.qlen++;
256 spin_unlock(&queue->fastopenq.lock);
257
258 /* Initialize the child socket. Have to fix some values to take
259 * into account the child is a Fast Open socket and is created
260 * only out of the bits carried in the SYN packet.
261 */
262 tp = tcp_sk(child);
263
264 rcu_assign_pointer(tp->fastopen_rsk, req);
265 tcp_rsk(req)->tfo_listener = true;
266
267 /* RFC1323: The window in SYN & SYN/ACK segments is never
268 * scaled. So correct it appropriately.
269 */
270 tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
271 tp->max_window = tp->snd_wnd;
272
273 /* Activate the retrans timer so that SYNACK can be retransmitted.
274 * The request socket is not added to the ehash
275 * because it's been added to the accept queue directly.
276 */
277 req->timeout = tcp_timeout_init(child);
278 tcp_reset_xmit_timer(child, ICSK_TIME_RETRANS,
279 req->timeout, false);
280
281 refcount_set(&req->rsk_refcnt, 2);
282
283 sk_mark_napi_id_set(child, skb);
284
285 /* Now finish processing the fastopen child socket. */
286 tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, skb);
287
288 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
289
290 tcp_fastopen_add_skb(child, skb);
291
292 tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
293 tp->rcv_wup = tp->rcv_nxt;
294 /* tcp_conn_request() is sending the SYNACK,
295 * and queues the child into listener accept queue.
296 */
297 return child;
298 }
299
tcp_fastopen_queue_check(struct sock * sk)300 static bool tcp_fastopen_queue_check(struct sock *sk)
301 {
302 struct fastopen_queue *fastopenq;
303 int max_qlen;
304
305 /* Make sure the listener has enabled fastopen, and we don't
306 * exceed the max # of pending TFO requests allowed before trying
307 * to validating the cookie in order to avoid burning CPU cycles
308 * unnecessarily.
309 *
310 * XXX (TFO) - The implication of checking the max_qlen before
311 * processing a cookie request is that clients can't differentiate
312 * between qlen overflow causing Fast Open to be disabled
313 * temporarily vs a server not supporting Fast Open at all.
314 */
315 fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
316 max_qlen = READ_ONCE(fastopenq->max_qlen);
317 if (max_qlen == 0)
318 return false;
319
320 if (fastopenq->qlen >= max_qlen) {
321 struct request_sock *req1;
322 spin_lock(&fastopenq->lock);
323 req1 = fastopenq->rskq_rst_head;
324 if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
325 __NET_INC_STATS(sock_net(sk),
326 LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
327 spin_unlock(&fastopenq->lock);
328 return false;
329 }
330 fastopenq->rskq_rst_head = req1->dl_next;
331 fastopenq->qlen--;
332 spin_unlock(&fastopenq->lock);
333 reqsk_put(req1);
334 }
335 return true;
336 }
337
tcp_fastopen_no_cookie(const struct sock * sk,const struct dst_entry * dst,int flag)338 static bool tcp_fastopen_no_cookie(const struct sock *sk,
339 const struct dst_entry *dst,
340 int flag)
341 {
342 return (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen) & flag) ||
343 tcp_sk(sk)->fastopen_no_cookie ||
344 (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
345 }
346
347 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
348 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
349 * cookie request (foc->len == 0).
350 */
tcp_try_fastopen(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct tcp_fastopen_cookie * foc,const struct dst_entry * dst)351 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
352 struct request_sock *req,
353 struct tcp_fastopen_cookie *foc,
354 const struct dst_entry *dst)
355 {
356 bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
357 int tcp_fastopen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen);
358 struct tcp_fastopen_cookie valid_foc = { .len = -1 };
359 struct sock *child;
360 int ret = 0;
361
362 if (foc->len == 0) /* Client requests a cookie */
363 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
364
365 if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
366 (syn_data || foc->len >= 0) &&
367 tcp_fastopen_queue_check(sk))) {
368 foc->len = -1;
369 return NULL;
370 }
371
372 if (tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
373 goto fastopen;
374
375 if (foc->len == 0) {
376 /* Client requests a cookie. */
377 tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
378 } else if (foc->len > 0) {
379 ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
380 &valid_foc);
381 if (!ret) {
382 NET_INC_STATS(sock_net(sk),
383 LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
384 } else {
385 /* Cookie is valid. Create a (full) child socket to
386 * accept the data in SYN before returning a SYN-ACK to
387 * ack the data. If we fail to create the socket, fall
388 * back and ack the ISN only but includes the same
389 * cookie.
390 *
391 * Note: Data-less SYN with valid cookie is allowed to
392 * send data in SYN_RECV state.
393 */
394 fastopen:
395 child = tcp_fastopen_create_child(sk, skb, req);
396 if (child) {
397 if (ret == 2) {
398 valid_foc.exp = foc->exp;
399 *foc = valid_foc;
400 NET_INC_STATS(sock_net(sk),
401 LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
402 } else {
403 foc->len = -1;
404 }
405 NET_INC_STATS(sock_net(sk),
406 LINUX_MIB_TCPFASTOPENPASSIVE);
407 tcp_sk(child)->syn_fastopen_child = 1;
408 return child;
409 }
410 NET_INC_STATS(sock_net(sk),
411 LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
412 }
413 }
414 valid_foc.exp = foc->exp;
415 *foc = valid_foc;
416 return NULL;
417 }
418
tcp_fastopen_cookie_check(struct sock * sk,u16 * mss,struct tcp_fastopen_cookie * cookie)419 bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
420 struct tcp_fastopen_cookie *cookie)
421 {
422 const struct dst_entry *dst;
423
424 tcp_fastopen_cache_get(sk, mss, cookie);
425
426 /* Firewall blackhole issue check */
427 if (tcp_fastopen_active_should_disable(sk)) {
428 cookie->len = -1;
429 return false;
430 }
431
432 dst = __sk_dst_get(sk);
433
434 if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
435 cookie->len = -1;
436 return true;
437 }
438 if (cookie->len > 0)
439 return true;
440 tcp_sk(sk)->fastopen_client_fail = TFO_COOKIE_UNAVAILABLE;
441 return false;
442 }
443
444 /* This function checks if we want to defer sending SYN until the first
445 * write(). We defer under the following conditions:
446 * 1. fastopen_connect sockopt is set
447 * 2. we have a valid cookie
448 * Return value: return true if we want to defer until application writes data
449 * return false if we want to send out SYN immediately
450 */
tcp_fastopen_defer_connect(struct sock * sk,int * err)451 bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
452 {
453 struct tcp_fastopen_cookie cookie = { .len = 0 };
454 struct tcp_sock *tp = tcp_sk(sk);
455 u16 mss;
456
457 if (tp->fastopen_connect && !tp->fastopen_req) {
458 if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
459 inet_set_bit(DEFER_CONNECT, sk);
460 return true;
461 }
462
463 /* Alloc fastopen_req in order for FO option to be included
464 * in SYN
465 */
466 tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
467 sk->sk_allocation);
468 if (tp->fastopen_req)
469 tp->fastopen_req->cookie = cookie;
470 else
471 *err = -ENOBUFS;
472 }
473 return false;
474 }
475 EXPORT_IPV6_MOD(tcp_fastopen_defer_connect);
476
477 /*
478 * The following code block is to deal with middle box issues with TFO:
479 * Middlebox firewall issues can potentially cause server's data being
480 * blackholed after a successful 3WHS using TFO.
481 * The proposed solution is to disable active TFO globally under the
482 * following circumstances:
483 * 1. client side TFO socket receives out of order FIN
484 * 2. client side TFO socket receives out of order RST
485 * 3. client side TFO socket has timed out three times consecutively during
486 * or after handshake
487 * We disable active side TFO globally for 1hr at first. Then if it
488 * happens again, we disable it for 2h, then 4h, 8h, ...
489 * And we reset the timeout back to 1hr when we see a successful active
490 * TFO connection with data exchanges.
491 */
492
493 /* Disable active TFO and record current jiffies and
494 * tfo_active_disable_times
495 */
tcp_fastopen_active_disable(struct sock * sk)496 void tcp_fastopen_active_disable(struct sock *sk)
497 {
498 struct net *net = sock_net(sk);
499
500 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout))
501 return;
502
503 /* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
504 WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
505
506 /* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
507 * We want net->ipv4.tfo_active_disable_stamp to be updated first.
508 */
509 smp_mb__before_atomic();
510 atomic_inc(&net->ipv4.tfo_active_disable_times);
511
512 NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
513 }
514
515 /* Calculate timeout for tfo active disable
516 * Return true if we are still in the active TFO disable period
517 * Return false if timeout already expired and we should use active TFO
518 */
tcp_fastopen_active_should_disable(struct sock * sk)519 bool tcp_fastopen_active_should_disable(struct sock *sk)
520 {
521 unsigned int tfo_bh_timeout =
522 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout);
523 unsigned long timeout;
524 int tfo_da_times;
525 int multiplier;
526
527 if (!tfo_bh_timeout)
528 return false;
529
530 tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
531 if (!tfo_da_times)
532 return false;
533
534 /* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
535 smp_rmb();
536
537 /* Limit timeout to max: 2^6 * initial timeout */
538 multiplier = 1 << min(tfo_da_times - 1, 6);
539
540 /* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
541 timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
542 multiplier * tfo_bh_timeout * HZ;
543 if (time_before(jiffies, timeout))
544 return true;
545
546 /* Mark check bit so we can check for successful active TFO
547 * condition and reset tfo_active_disable_times
548 */
549 tcp_sk(sk)->syn_fastopen_ch = 1;
550 return false;
551 }
552
553 /* Disable active TFO if FIN is the only packet in the ofo queue
554 * and no data is received.
555 * Also check if we can reset tfo_active_disable_times if data is
556 * received successfully on a marked active TFO sockets opened on
557 * a non-loopback interface
558 */
tcp_fastopen_active_disable_ofo_check(struct sock * sk)559 void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
560 {
561 struct tcp_sock *tp = tcp_sk(sk);
562 struct dst_entry *dst;
563 struct sk_buff *skb;
564
565 if (!tp->syn_fastopen)
566 return;
567
568 if (!tp->data_segs_in) {
569 skb = skb_rb_first(&tp->out_of_order_queue);
570 if (skb && !skb_rb_next(skb)) {
571 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
572 tcp_fastopen_active_disable(sk);
573 return;
574 }
575 }
576 } else if (tp->syn_fastopen_ch &&
577 atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
578 dst = sk_dst_get(sk);
579 if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
580 atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
581 dst_release(dst);
582 }
583 }
584
tcp_fastopen_active_detect_blackhole(struct sock * sk,bool expired)585 void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
586 {
587 u32 timeouts = inet_csk(sk)->icsk_retransmits;
588 struct tcp_sock *tp = tcp_sk(sk);
589
590 /* Broken middle-boxes may black-hole Fast Open connection during or
591 * even after the handshake. Be extremely conservative and pause
592 * Fast Open globally after hitting the third consecutive timeout or
593 * exceeding the configured timeout limit.
594 */
595 if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
596 (timeouts == 2 || (timeouts < 2 && expired))) {
597 tcp_fastopen_active_disable(sk);
598 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
599 }
600 }
601