xref: /openbmc/linux/net/ipv4/tcp_fastopen.c (revision 08e39c0d)
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 
tcp_fastopen_init_key_once(struct net * net)7 void tcp_fastopen_init_key_once(struct net *net)
8 {
9 	u8 key[TCP_FASTOPEN_KEY_LENGTH];
10 	struct tcp_fastopen_context *ctxt;
11 
12 	rcu_read_lock();
13 	ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
14 	if (ctxt) {
15 		rcu_read_unlock();
16 		return;
17 	}
18 	rcu_read_unlock();
19 
20 	/* tcp_fastopen_reset_cipher publishes the new context
21 	 * atomically, so we allow this race happening here.
22 	 *
23 	 * All call sites of tcp_fastopen_cookie_gen also check
24 	 * for a valid cookie, so this is an acceptable risk.
25 	 */
26 	get_random_bytes(key, sizeof(key));
27 	tcp_fastopen_reset_cipher(net, NULL, key, NULL);
28 }
29 
tcp_fastopen_ctx_free(struct rcu_head * head)30 static void tcp_fastopen_ctx_free(struct rcu_head *head)
31 {
32 	struct tcp_fastopen_context *ctx =
33 	    container_of(head, struct tcp_fastopen_context, rcu);
34 
35 	kfree_sensitive(ctx);
36 }
37 
tcp_fastopen_destroy_cipher(struct sock * sk)38 void tcp_fastopen_destroy_cipher(struct sock *sk)
39 {
40 	struct tcp_fastopen_context *ctx;
41 
42 	ctx = rcu_dereference_protected(
43 			inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
44 	if (ctx)
45 		call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
46 }
47 
tcp_fastopen_ctx_destroy(struct net * net)48 void tcp_fastopen_ctx_destroy(struct net *net)
49 {
50 	struct tcp_fastopen_context *ctxt;
51 
52 	ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
53 
54 	if (ctxt)
55 		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
56 }
57 
tcp_fastopen_reset_cipher(struct net * net,struct sock * sk,void * primary_key,void * backup_key)58 int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
59 			      void *primary_key, void *backup_key)
60 {
61 	struct tcp_fastopen_context *ctx, *octx;
62 	struct fastopen_queue *q;
63 	int err = 0;
64 
65 	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
66 	if (!ctx) {
67 		err = -ENOMEM;
68 		goto out;
69 	}
70 
71 	ctx->key[0].key[0] = get_unaligned_le64(primary_key);
72 	ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
73 	if (backup_key) {
74 		ctx->key[1].key[0] = get_unaligned_le64(backup_key);
75 		ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
76 		ctx->num = 2;
77 	} else {
78 		ctx->num = 1;
79 	}
80 
81 	if (sk) {
82 		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
83 		octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
84 	} else {
85 		octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
86 	}
87 
88 	if (octx)
89 		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
90 out:
91 	return err;
92 }
93 
tcp_fastopen_get_cipher(struct net * net,struct inet_connection_sock * icsk,u64 * key)94 int tcp_fastopen_get_cipher(struct net *net, struct inet_connection_sock *icsk,
95 			    u64 *key)
96 {
97 	struct tcp_fastopen_context *ctx;
98 	int n_keys = 0, i;
99 
100 	rcu_read_lock();
101 	if (icsk)
102 		ctx = rcu_dereference(icsk->icsk_accept_queue.fastopenq.ctx);
103 	else
104 		ctx = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
105 	if (ctx) {
106 		n_keys = tcp_fastopen_context_len(ctx);
107 		for (i = 0; i < n_keys; i++) {
108 			put_unaligned_le64(ctx->key[i].key[0], key + (i * 2));
109 			put_unaligned_le64(ctx->key[i].key[1], key + (i * 2) + 1);
110 		}
111 	}
112 	rcu_read_unlock();
113 
114 	return n_keys;
115 }
116 
__tcp_fastopen_cookie_gen_cipher(struct request_sock * req,struct sk_buff * syn,const siphash_key_t * key,struct tcp_fastopen_cookie * foc)117 static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
118 					     struct sk_buff *syn,
119 					     const siphash_key_t *key,
120 					     struct tcp_fastopen_cookie *foc)
121 {
122 	BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
123 
124 	if (req->rsk_ops->family == AF_INET) {
125 		const struct iphdr *iph = ip_hdr(syn);
126 
127 		foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
128 					  sizeof(iph->saddr) +
129 					  sizeof(iph->daddr),
130 					  key));
131 		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
132 		return true;
133 	}
134 #if IS_ENABLED(CONFIG_IPV6)
135 	if (req->rsk_ops->family == AF_INET6) {
136 		const struct ipv6hdr *ip6h = ipv6_hdr(syn);
137 
138 		foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
139 					  sizeof(ip6h->saddr) +
140 					  sizeof(ip6h->daddr),
141 					  key));
142 		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
143 		return true;
144 	}
145 #endif
146 	return false;
147 }
148 
149 /* Generate the fastopen cookie by applying SipHash to both the source and
150  * destination addresses.
151  */
tcp_fastopen_cookie_gen(struct sock * sk,struct request_sock * req,struct sk_buff * syn,struct tcp_fastopen_cookie * foc)152 static void tcp_fastopen_cookie_gen(struct sock *sk,
153 				    struct request_sock *req,
154 				    struct sk_buff *syn,
155 				    struct tcp_fastopen_cookie *foc)
156 {
157 	struct tcp_fastopen_context *ctx;
158 
159 	rcu_read_lock();
160 	ctx = tcp_fastopen_get_ctx(sk);
161 	if (ctx)
162 		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
163 	rcu_read_unlock();
164 }
165 
166 /* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
167  * queue this additional data / FIN.
168  */
tcp_fastopen_add_skb(struct sock * sk,struct sk_buff * skb)169 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
170 {
171 	struct tcp_sock *tp = tcp_sk(sk);
172 
173 	if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
174 		return;
175 
176 	skb = skb_clone(skb, GFP_ATOMIC);
177 	if (!skb)
178 		return;
179 
180 	skb_dst_drop(skb);
181 	/* segs_in has been initialized to 1 in tcp_create_openreq_child().
182 	 * Hence, reset segs_in to 0 before calling tcp_segs_in()
183 	 * to avoid double counting.  Also, tcp_segs_in() expects
184 	 * skb->len to include the tcp_hdrlen.  Hence, it should
185 	 * be called before __skb_pull().
186 	 */
187 	tp->segs_in = 0;
188 	tcp_segs_in(tp, skb);
189 	__skb_pull(skb, tcp_hdrlen(skb));
190 	sk_forced_mem_schedule(sk, skb->truesize);
191 	skb_set_owner_r(skb, sk);
192 
193 	TCP_SKB_CB(skb)->seq++;
194 	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
195 
196 	tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
197 	__skb_queue_tail(&sk->sk_receive_queue, skb);
198 	tp->syn_data_acked = 1;
199 
200 	/* u64_stats_update_begin(&tp->syncp) not needed here,
201 	 * as we certainly are not changing upper 32bit value (0)
202 	 */
203 	tp->bytes_received = skb->len;
204 
205 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
206 		tcp_fin(sk);
207 }
208 
209 /* 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)210 static int tcp_fastopen_cookie_gen_check(struct sock *sk,
211 					 struct request_sock *req,
212 					 struct sk_buff *syn,
213 					 struct tcp_fastopen_cookie *orig,
214 					 struct tcp_fastopen_cookie *valid_foc)
215 {
216 	struct tcp_fastopen_cookie search_foc = { .len = -1 };
217 	struct tcp_fastopen_cookie *foc = valid_foc;
218 	struct tcp_fastopen_context *ctx;
219 	int i, ret = 0;
220 
221 	rcu_read_lock();
222 	ctx = tcp_fastopen_get_ctx(sk);
223 	if (!ctx)
224 		goto out;
225 	for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
226 		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
227 		if (tcp_fastopen_cookie_match(foc, orig)) {
228 			ret = i + 1;
229 			goto out;
230 		}
231 		foc = &search_foc;
232 	}
233 out:
234 	rcu_read_unlock();
235 	return ret;
236 }
237 
tcp_fastopen_create_child(struct sock * sk,struct sk_buff * skb,struct request_sock * req)238 static struct sock *tcp_fastopen_create_child(struct sock *sk,
239 					      struct sk_buff *skb,
240 					      struct request_sock *req)
241 {
242 	struct tcp_sock *tp;
243 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
244 	struct sock *child;
245 	bool own_req;
246 
247 	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
248 							 NULL, &own_req);
249 	if (!child)
250 		return NULL;
251 
252 	spin_lock(&queue->fastopenq.lock);
253 	queue->fastopenq.qlen++;
254 	spin_unlock(&queue->fastopenq.lock);
255 
256 	/* Initialize the child socket. Have to fix some values to take
257 	 * into account the child is a Fast Open socket and is created
258 	 * only out of the bits carried in the SYN packet.
259 	 */
260 	tp = tcp_sk(child);
261 
262 	rcu_assign_pointer(tp->fastopen_rsk, req);
263 	tcp_rsk(req)->tfo_listener = true;
264 
265 	/* RFC1323: The window in SYN & SYN/ACK segments is never
266 	 * scaled. So correct it appropriately.
267 	 */
268 	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
269 	tp->max_window = tp->snd_wnd;
270 
271 	/* Activate the retrans timer so that SYNACK can be retransmitted.
272 	 * The request socket is not added to the ehash
273 	 * because it's been added to the accept queue directly.
274 	 */
275 	req->timeout = tcp_timeout_init(child);
276 	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
277 				  req->timeout, TCP_RTO_MAX);
278 
279 	refcount_set(&req->rsk_refcnt, 2);
280 
281 	/* Now finish processing the fastopen child socket. */
282 	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, skb);
283 
284 	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
285 
286 	tcp_fastopen_add_skb(child, skb);
287 
288 	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
289 	tp->rcv_wup = tp->rcv_nxt;
290 	/* tcp_conn_request() is sending the SYNACK,
291 	 * and queues the child into listener accept queue.
292 	 */
293 	return child;
294 }
295 
tcp_fastopen_queue_check(struct sock * sk)296 static bool tcp_fastopen_queue_check(struct sock *sk)
297 {
298 	struct fastopen_queue *fastopenq;
299 	int max_qlen;
300 
301 	/* Make sure the listener has enabled fastopen, and we don't
302 	 * exceed the max # of pending TFO requests allowed before trying
303 	 * to validating the cookie in order to avoid burning CPU cycles
304 	 * unnecessarily.
305 	 *
306 	 * XXX (TFO) - The implication of checking the max_qlen before
307 	 * processing a cookie request is that clients can't differentiate
308 	 * between qlen overflow causing Fast Open to be disabled
309 	 * temporarily vs a server not supporting Fast Open at all.
310 	 */
311 	fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
312 	max_qlen = READ_ONCE(fastopenq->max_qlen);
313 	if (max_qlen == 0)
314 		return false;
315 
316 	if (fastopenq->qlen >= max_qlen) {
317 		struct request_sock *req1;
318 		spin_lock(&fastopenq->lock);
319 		req1 = fastopenq->rskq_rst_head;
320 		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
321 			__NET_INC_STATS(sock_net(sk),
322 					LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
323 			spin_unlock(&fastopenq->lock);
324 			return false;
325 		}
326 		fastopenq->rskq_rst_head = req1->dl_next;
327 		fastopenq->qlen--;
328 		spin_unlock(&fastopenq->lock);
329 		reqsk_put(req1);
330 	}
331 	return true;
332 }
333 
tcp_fastopen_no_cookie(const struct sock * sk,const struct dst_entry * dst,int flag)334 static bool tcp_fastopen_no_cookie(const struct sock *sk,
335 				   const struct dst_entry *dst,
336 				   int flag)
337 {
338 	return (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen) & flag) ||
339 	       tcp_sk(sk)->fastopen_no_cookie ||
340 	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
341 }
342 
343 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
344  * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
345  * cookie request (foc->len == 0).
346  */
tcp_try_fastopen(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct tcp_fastopen_cookie * foc,const struct dst_entry * dst)347 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
348 			      struct request_sock *req,
349 			      struct tcp_fastopen_cookie *foc,
350 			      const struct dst_entry *dst)
351 {
352 	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
353 	int tcp_fastopen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen);
354 	struct tcp_fastopen_cookie valid_foc = { .len = -1 };
355 	struct sock *child;
356 	int ret = 0;
357 
358 	if (foc->len == 0) /* Client requests a cookie */
359 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
360 
361 	if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
362 	      (syn_data || foc->len >= 0) &&
363 	      tcp_fastopen_queue_check(sk))) {
364 		foc->len = -1;
365 		return NULL;
366 	}
367 
368 	if (tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
369 		goto fastopen;
370 
371 	if (foc->len == 0) {
372 		/* Client requests a cookie. */
373 		tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
374 	} else if (foc->len > 0) {
375 		ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
376 						    &valid_foc);
377 		if (!ret) {
378 			NET_INC_STATS(sock_net(sk),
379 				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
380 		} else {
381 			/* Cookie is valid. Create a (full) child socket to
382 			 * accept the data in SYN before returning a SYN-ACK to
383 			 * ack the data. If we fail to create the socket, fall
384 			 * back and ack the ISN only but includes the same
385 			 * cookie.
386 			 *
387 			 * Note: Data-less SYN with valid cookie is allowed to
388 			 * send data in SYN_RECV state.
389 			 */
390 fastopen:
391 			child = tcp_fastopen_create_child(sk, skb, req);
392 			if (child) {
393 				if (ret == 2) {
394 					valid_foc.exp = foc->exp;
395 					*foc = valid_foc;
396 					NET_INC_STATS(sock_net(sk),
397 						      LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
398 				} else {
399 					foc->len = -1;
400 				}
401 				NET_INC_STATS(sock_net(sk),
402 					      LINUX_MIB_TCPFASTOPENPASSIVE);
403 				return child;
404 			}
405 			NET_INC_STATS(sock_net(sk),
406 				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
407 		}
408 	}
409 	valid_foc.exp = foc->exp;
410 	*foc = valid_foc;
411 	return NULL;
412 }
413 
tcp_fastopen_cookie_check(struct sock * sk,u16 * mss,struct tcp_fastopen_cookie * cookie)414 bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
415 			       struct tcp_fastopen_cookie *cookie)
416 {
417 	const struct dst_entry *dst;
418 
419 	tcp_fastopen_cache_get(sk, mss, cookie);
420 
421 	/* Firewall blackhole issue check */
422 	if (tcp_fastopen_active_should_disable(sk)) {
423 		cookie->len = -1;
424 		return false;
425 	}
426 
427 	dst = __sk_dst_get(sk);
428 
429 	if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
430 		cookie->len = -1;
431 		return true;
432 	}
433 	if (cookie->len > 0)
434 		return true;
435 	tcp_sk(sk)->fastopen_client_fail = TFO_COOKIE_UNAVAILABLE;
436 	return false;
437 }
438 
439 /* This function checks if we want to defer sending SYN until the first
440  * write().  We defer under the following conditions:
441  * 1. fastopen_connect sockopt is set
442  * 2. we have a valid cookie
443  * Return value: return true if we want to defer until application writes data
444  *               return false if we want to send out SYN immediately
445  */
tcp_fastopen_defer_connect(struct sock * sk,int * err)446 bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
447 {
448 	struct tcp_fastopen_cookie cookie = { .len = 0 };
449 	struct tcp_sock *tp = tcp_sk(sk);
450 	u16 mss;
451 
452 	if (tp->fastopen_connect && !tp->fastopen_req) {
453 		if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
454 			inet_set_bit(DEFER_CONNECT, sk);
455 			return true;
456 		}
457 
458 		/* Alloc fastopen_req in order for FO option to be included
459 		 * in SYN
460 		 */
461 		tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
462 					   sk->sk_allocation);
463 		if (tp->fastopen_req)
464 			tp->fastopen_req->cookie = cookie;
465 		else
466 			*err = -ENOBUFS;
467 	}
468 	return false;
469 }
470 EXPORT_SYMBOL(tcp_fastopen_defer_connect);
471 
472 /*
473  * The following code block is to deal with middle box issues with TFO:
474  * Middlebox firewall issues can potentially cause server's data being
475  * blackholed after a successful 3WHS using TFO.
476  * The proposed solution is to disable active TFO globally under the
477  * following circumstances:
478  *   1. client side TFO socket receives out of order FIN
479  *   2. client side TFO socket receives out of order RST
480  *   3. client side TFO socket has timed out three times consecutively during
481  *      or after handshake
482  * We disable active side TFO globally for 1hr at first. Then if it
483  * happens again, we disable it for 2h, then 4h, 8h, ...
484  * And we reset the timeout back to 1hr when we see a successful active
485  * TFO connection with data exchanges.
486  */
487 
488 /* Disable active TFO and record current jiffies and
489  * tfo_active_disable_times
490  */
tcp_fastopen_active_disable(struct sock * sk)491 void tcp_fastopen_active_disable(struct sock *sk)
492 {
493 	struct net *net = sock_net(sk);
494 
495 	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout))
496 		return;
497 
498 	/* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
499 	WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
500 
501 	/* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
502 	 * We want net->ipv4.tfo_active_disable_stamp to be updated first.
503 	 */
504 	smp_mb__before_atomic();
505 	atomic_inc(&net->ipv4.tfo_active_disable_times);
506 
507 	NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
508 }
509 
510 /* Calculate timeout for tfo active disable
511  * Return true if we are still in the active TFO disable period
512  * Return false if timeout already expired and we should use active TFO
513  */
tcp_fastopen_active_should_disable(struct sock * sk)514 bool tcp_fastopen_active_should_disable(struct sock *sk)
515 {
516 	unsigned int tfo_bh_timeout =
517 		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout);
518 	unsigned long timeout;
519 	int tfo_da_times;
520 	int multiplier;
521 
522 	if (!tfo_bh_timeout)
523 		return false;
524 
525 	tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
526 	if (!tfo_da_times)
527 		return false;
528 
529 	/* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
530 	smp_rmb();
531 
532 	/* Limit timeout to max: 2^6 * initial timeout */
533 	multiplier = 1 << min(tfo_da_times - 1, 6);
534 
535 	/* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
536 	timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
537 		  multiplier * tfo_bh_timeout * HZ;
538 	if (time_before(jiffies, timeout))
539 		return true;
540 
541 	/* Mark check bit so we can check for successful active TFO
542 	 * condition and reset tfo_active_disable_times
543 	 */
544 	tcp_sk(sk)->syn_fastopen_ch = 1;
545 	return false;
546 }
547 
548 /* Disable active TFO if FIN is the only packet in the ofo queue
549  * and no data is received.
550  * Also check if we can reset tfo_active_disable_times if data is
551  * received successfully on a marked active TFO sockets opened on
552  * a non-loopback interface
553  */
tcp_fastopen_active_disable_ofo_check(struct sock * sk)554 void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
555 {
556 	struct tcp_sock *tp = tcp_sk(sk);
557 	struct dst_entry *dst;
558 	struct sk_buff *skb;
559 
560 	if (!tp->syn_fastopen)
561 		return;
562 
563 	if (!tp->data_segs_in) {
564 		skb = skb_rb_first(&tp->out_of_order_queue);
565 		if (skb && !skb_rb_next(skb)) {
566 			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
567 				tcp_fastopen_active_disable(sk);
568 				return;
569 			}
570 		}
571 	} else if (tp->syn_fastopen_ch &&
572 		   atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
573 		dst = sk_dst_get(sk);
574 		if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
575 			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
576 		dst_release(dst);
577 	}
578 }
579 
tcp_fastopen_active_detect_blackhole(struct sock * sk,bool expired)580 void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
581 {
582 	u32 timeouts = inet_csk(sk)->icsk_retransmits;
583 	struct tcp_sock *tp = tcp_sk(sk);
584 
585 	/* Broken middle-boxes may black-hole Fast Open connection during or
586 	 * even after the handshake. Be extremely conservative and pause
587 	 * Fast Open globally after hitting the third consecutive timeout or
588 	 * exceeding the configured timeout limit.
589 	 */
590 	if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
591 	    (timeouts == 2 || (timeouts < 2 && expired))) {
592 		tcp_fastopen_active_disable(sk);
593 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
594 	}
595 }
596