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v3.15
 
 
 1#include <linux/err.h>
 2#include <linux/init.h>
 3#include <linux/kernel.h>
 4#include <linux/list.h>
 5#include <linux/tcp.h>
 6#include <linux/rcupdate.h>
 7#include <linux/rculist.h>
 8#include <net/inetpeer.h>
 9#include <net/tcp.h>
10
11int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;
12
13struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
14
15static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);
16
17void tcp_fastopen_init_key_once(bool publish)
18{
19	static u8 key[TCP_FASTOPEN_KEY_LENGTH];
 
 
 
 
 
 
 
 
 
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	if (net_get_random_once(key, sizeof(key)) && publish)
28		tcp_fastopen_reset_cipher(key, sizeof(key));
29}
30
31static 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	crypto_free_cipher(ctx->tfm);
36	kfree(ctx);
37}
38
39int tcp_fastopen_reset_cipher(void *key, unsigned int len)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
40{
41	int err;
42	struct tcp_fastopen_context *ctx, *octx;
 
 
43
44	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
45	if (!ctx)
46		return -ENOMEM;
47	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
48
49	if (IS_ERR(ctx->tfm)) {
50		err = PTR_ERR(ctx->tfm);
51error:		kfree(ctx);
52		pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
53		return err;
54	}
55	err = crypto_cipher_setkey(ctx->tfm, key, len);
56	if (err) {
57		pr_err("TCP: TFO cipher key error: %d\n", err);
58		crypto_free_cipher(ctx->tfm);
59		goto error;
60	}
61	memcpy(ctx->key, key, len);
62
63	spin_lock(&tcp_fastopen_ctx_lock);
64
65	octx = rcu_dereference_protected(tcp_fastopen_ctx,
66				lockdep_is_held(&tcp_fastopen_ctx_lock));
67	rcu_assign_pointer(tcp_fastopen_ctx, ctx);
68	spin_unlock(&tcp_fastopen_ctx_lock);
 
 
 
 
 
 
 
 
69
70	if (octx)
71		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
72	return err;
73}
74
75/* Computes the fastopen cookie for the IP path.
76 * The path is a 128 bits long (pad with zeros for IPv4).
77 *
78 * The caller must check foc->len to determine if a valid cookie
79 * has been generated successfully.
80*/
81void tcp_fastopen_cookie_gen(__be32 src, __be32 dst,
82			     struct tcp_fastopen_cookie *foc)
83{
84	__be32 path[4] = { src, dst, 0, 0 };
85	struct tcp_fastopen_context *ctx;
86
87	tcp_fastopen_init_key_once(true);
88
89	rcu_read_lock();
90	ctx = rcu_dereference(tcp_fastopen_ctx);
 
 
 
 
91	if (ctx) {
92		crypto_cipher_encrypt_one(ctx->tfm, foc->val, (__u8 *)path);
93		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
 
94	}
95	rcu_read_unlock();
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
96}
v4.17
  1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/crypto.h>
  3#include <linux/err.h>
  4#include <linux/init.h>
  5#include <linux/kernel.h>
  6#include <linux/list.h>
  7#include <linux/tcp.h>
  8#include <linux/rcupdate.h>
  9#include <linux/rculist.h>
 10#include <net/inetpeer.h>
 11#include <net/tcp.h>
 12
 13void tcp_fastopen_init_key_once(struct net *net)
 
 
 
 
 
 
 14{
 15	u8 key[TCP_FASTOPEN_KEY_LENGTH];
 16	struct tcp_fastopen_context *ctxt;
 17
 18	rcu_read_lock();
 19	ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
 20	if (ctxt) {
 21		rcu_read_unlock();
 22		return;
 23	}
 24	rcu_read_unlock();
 25
 26	/* tcp_fastopen_reset_cipher publishes the new context
 27	 * atomically, so we allow this race happening here.
 28	 *
 29	 * All call sites of tcp_fastopen_cookie_gen also check
 30	 * for a valid cookie, so this is an acceptable risk.
 31	 */
 32	get_random_bytes(key, sizeof(key));
 33	tcp_fastopen_reset_cipher(net, NULL, key, sizeof(key));
 34}
 35
 36static void tcp_fastopen_ctx_free(struct rcu_head *head)
 37{
 38	struct tcp_fastopen_context *ctx =
 39	    container_of(head, struct tcp_fastopen_context, rcu);
 40	crypto_free_cipher(ctx->tfm);
 41	kfree(ctx);
 42}
 43
 44void tcp_fastopen_destroy_cipher(struct sock *sk)
 45{
 46	struct tcp_fastopen_context *ctx;
 47
 48	ctx = rcu_dereference_protected(
 49			inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
 50	if (ctx)
 51		call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
 52}
 53
 54void tcp_fastopen_ctx_destroy(struct net *net)
 55{
 56	struct tcp_fastopen_context *ctxt;
 57
 58	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
 59
 60	ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
 61				lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
 62	rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
 63	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
 64
 65	if (ctxt)
 66		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
 67}
 68
 69int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
 70			      void *key, unsigned int len)
 71{
 
 72	struct tcp_fastopen_context *ctx, *octx;
 73	struct fastopen_queue *q;
 74	int err;
 75
 76	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 77	if (!ctx)
 78		return -ENOMEM;
 79	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 80
 81	if (IS_ERR(ctx->tfm)) {
 82		err = PTR_ERR(ctx->tfm);
 83error:		kfree(ctx);
 84		pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
 85		return err;
 86	}
 87	err = crypto_cipher_setkey(ctx->tfm, key, len);
 88	if (err) {
 89		pr_err("TCP: TFO cipher key error: %d\n", err);
 90		crypto_free_cipher(ctx->tfm);
 91		goto error;
 92	}
 93	memcpy(ctx->key, key, len);
 94
 
 95
 96	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
 97	if (sk) {
 98		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
 99		octx = rcu_dereference_protected(q->ctx,
100			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
101		rcu_assign_pointer(q->ctx, ctx);
102	} else {
103		octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
104			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
105		rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
106	}
107	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
108
109	if (octx)
110		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
111	return err;
112}
113
114static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
115				      struct tcp_fastopen_cookie *foc)
 
 
 
 
 
 
116{
 
117	struct tcp_fastopen_context *ctx;
118	bool ok = false;
 
119
120	rcu_read_lock();
121
122	ctx = rcu_dereference(inet_csk(sk)->icsk_accept_queue.fastopenq.ctx);
123	if (!ctx)
124		ctx = rcu_dereference(sock_net(sk)->ipv4.tcp_fastopen_ctx);
125
126	if (ctx) {
127		crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
128		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
129		ok = true;
130	}
131	rcu_read_unlock();
132	return ok;
133}
134
135/* Generate the fastopen cookie by doing aes128 encryption on both
136 * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
137 * addresses. For the longer IPv6 addresses use CBC-MAC.
138 *
139 * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
140 */
141static bool tcp_fastopen_cookie_gen(struct sock *sk,
142				    struct request_sock *req,
143				    struct sk_buff *syn,
144				    struct tcp_fastopen_cookie *foc)
145{
146	if (req->rsk_ops->family == AF_INET) {
147		const struct iphdr *iph = ip_hdr(syn);
148
149		__be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
150		return __tcp_fastopen_cookie_gen(sk, path, foc);
151	}
152
153#if IS_ENABLED(CONFIG_IPV6)
154	if (req->rsk_ops->family == AF_INET6) {
155		const struct ipv6hdr *ip6h = ipv6_hdr(syn);
156		struct tcp_fastopen_cookie tmp;
157
158		if (__tcp_fastopen_cookie_gen(sk, &ip6h->saddr, &tmp)) {
159			struct in6_addr *buf = &tmp.addr;
160			int i;
161
162			for (i = 0; i < 4; i++)
163				buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
164			return __tcp_fastopen_cookie_gen(sk, buf, foc);
165		}
166	}
167#endif
168	return false;
169}
170
171
172/* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
173 * queue this additional data / FIN.
174 */
175void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
176{
177	struct tcp_sock *tp = tcp_sk(sk);
178
179	if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
180		return;
181
182	skb = skb_clone(skb, GFP_ATOMIC);
183	if (!skb)
184		return;
185
186	skb_dst_drop(skb);
187	/* segs_in has been initialized to 1 in tcp_create_openreq_child().
188	 * Hence, reset segs_in to 0 before calling tcp_segs_in()
189	 * to avoid double counting.  Also, tcp_segs_in() expects
190	 * skb->len to include the tcp_hdrlen.  Hence, it should
191	 * be called before __skb_pull().
192	 */
193	tp->segs_in = 0;
194	tcp_segs_in(tp, skb);
195	__skb_pull(skb, tcp_hdrlen(skb));
196	sk_forced_mem_schedule(sk, skb->truesize);
197	skb_set_owner_r(skb, sk);
198
199	TCP_SKB_CB(skb)->seq++;
200	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
201
202	tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
203	__skb_queue_tail(&sk->sk_receive_queue, skb);
204	tp->syn_data_acked = 1;
205
206	/* u64_stats_update_begin(&tp->syncp) not needed here,
207	 * as we certainly are not changing upper 32bit value (0)
208	 */
209	tp->bytes_received = skb->len;
210
211	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
212		tcp_fin(sk);
213}
214
215static struct sock *tcp_fastopen_create_child(struct sock *sk,
216					      struct sk_buff *skb,
217					      struct request_sock *req)
218{
219	struct tcp_sock *tp;
220	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
221	struct sock *child;
222	bool own_req;
223
224	req->num_retrans = 0;
225	req->num_timeout = 0;
226	req->sk = NULL;
227
228	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
229							 NULL, &own_req);
230	if (!child)
231		return NULL;
232
233	spin_lock(&queue->fastopenq.lock);
234	queue->fastopenq.qlen++;
235	spin_unlock(&queue->fastopenq.lock);
236
237	/* Initialize the child socket. Have to fix some values to take
238	 * into account the child is a Fast Open socket and is created
239	 * only out of the bits carried in the SYN packet.
240	 */
241	tp = tcp_sk(child);
242
243	tp->fastopen_rsk = req;
244	tcp_rsk(req)->tfo_listener = true;
245
246	/* RFC1323: The window in SYN & SYN/ACK segments is never
247	 * scaled. So correct it appropriately.
248	 */
249	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
250	tp->max_window = tp->snd_wnd;
251
252	/* Activate the retrans timer so that SYNACK can be retransmitted.
253	 * The request socket is not added to the ehash
254	 * because it's been added to the accept queue directly.
255	 */
256	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
257				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);
258
259	refcount_set(&req->rsk_refcnt, 2);
260
261	/* Now finish processing the fastopen child socket. */
262	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
263
264	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
265
266	tcp_fastopen_add_skb(child, skb);
267
268	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
269	tp->rcv_wup = tp->rcv_nxt;
270	/* tcp_conn_request() is sending the SYNACK,
271	 * and queues the child into listener accept queue.
272	 */
273	return child;
274}
275
276static bool tcp_fastopen_queue_check(struct sock *sk)
277{
278	struct fastopen_queue *fastopenq;
279
280	/* Make sure the listener has enabled fastopen, and we don't
281	 * exceed the max # of pending TFO requests allowed before trying
282	 * to validating the cookie in order to avoid burning CPU cycles
283	 * unnecessarily.
284	 *
285	 * XXX (TFO) - The implication of checking the max_qlen before
286	 * processing a cookie request is that clients can't differentiate
287	 * between qlen overflow causing Fast Open to be disabled
288	 * temporarily vs a server not supporting Fast Open at all.
289	 */
290	fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
291	if (fastopenq->max_qlen == 0)
292		return false;
293
294	if (fastopenq->qlen >= fastopenq->max_qlen) {
295		struct request_sock *req1;
296		spin_lock(&fastopenq->lock);
297		req1 = fastopenq->rskq_rst_head;
298		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
299			__NET_INC_STATS(sock_net(sk),
300					LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
301			spin_unlock(&fastopenq->lock);
302			return false;
303		}
304		fastopenq->rskq_rst_head = req1->dl_next;
305		fastopenq->qlen--;
306		spin_unlock(&fastopenq->lock);
307		reqsk_put(req1);
308	}
309	return true;
310}
311
312static bool tcp_fastopen_no_cookie(const struct sock *sk,
313				   const struct dst_entry *dst,
314				   int flag)
315{
316	return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
317	       tcp_sk(sk)->fastopen_no_cookie ||
318	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
319}
320
321/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
322 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
323 * cookie request (foc->len == 0).
324 */
325struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
326			      struct request_sock *req,
327			      struct tcp_fastopen_cookie *foc,
328			      const struct dst_entry *dst)
329{
330	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
331	int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
332	struct tcp_fastopen_cookie valid_foc = { .len = -1 };
333	struct sock *child;
334
335	if (foc->len == 0) /* Client requests a cookie */
336		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
337
338	if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
339	      (syn_data || foc->len >= 0) &&
340	      tcp_fastopen_queue_check(sk))) {
341		foc->len = -1;
342		return NULL;
343	}
344
345	if (syn_data &&
346	    tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
347		goto fastopen;
348
349	if (foc->len >= 0 &&  /* Client presents or requests a cookie */
350	    tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc) &&
351	    foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
352	    foc->len == valid_foc.len &&
353	    !memcmp(foc->val, valid_foc.val, foc->len)) {
354		/* Cookie is valid. Create a (full) child socket to accept
355		 * the data in SYN before returning a SYN-ACK to ack the
356		 * data. If we fail to create the socket, fall back and
357		 * ack the ISN only but includes the same cookie.
358		 *
359		 * Note: Data-less SYN with valid cookie is allowed to send
360		 * data in SYN_RECV state.
361		 */
362fastopen:
363		child = tcp_fastopen_create_child(sk, skb, req);
364		if (child) {
365			foc->len = -1;
366			NET_INC_STATS(sock_net(sk),
367				      LINUX_MIB_TCPFASTOPENPASSIVE);
368			return child;
369		}
370		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
371	} else if (foc->len > 0) /* Client presents an invalid cookie */
372		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
373
374	valid_foc.exp = foc->exp;
375	*foc = valid_foc;
376	return NULL;
377}
378
379bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
380			       struct tcp_fastopen_cookie *cookie)
381{
382	const struct dst_entry *dst;
383
384	tcp_fastopen_cache_get(sk, mss, cookie);
385
386	/* Firewall blackhole issue check */
387	if (tcp_fastopen_active_should_disable(sk)) {
388		cookie->len = -1;
389		return false;
390	}
391
392	dst = __sk_dst_get(sk);
393
394	if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
395		cookie->len = -1;
396		return true;
397	}
398	return cookie->len > 0;
399}
400
401/* This function checks if we want to defer sending SYN until the first
402 * write().  We defer under the following conditions:
403 * 1. fastopen_connect sockopt is set
404 * 2. we have a valid cookie
405 * Return value: return true if we want to defer until application writes data
406 *               return false if we want to send out SYN immediately
407 */
408bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
409{
410	struct tcp_fastopen_cookie cookie = { .len = 0 };
411	struct tcp_sock *tp = tcp_sk(sk);
412	u16 mss;
413
414	if (tp->fastopen_connect && !tp->fastopen_req) {
415		if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
416			inet_sk(sk)->defer_connect = 1;
417			return true;
418		}
419
420		/* Alloc fastopen_req in order for FO option to be included
421		 * in SYN
422		 */
423		tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
424					   sk->sk_allocation);
425		if (tp->fastopen_req)
426			tp->fastopen_req->cookie = cookie;
427		else
428			*err = -ENOBUFS;
429	}
430	return false;
431}
432EXPORT_SYMBOL(tcp_fastopen_defer_connect);
433
434/*
435 * The following code block is to deal with middle box issues with TFO:
436 * Middlebox firewall issues can potentially cause server's data being
437 * blackholed after a successful 3WHS using TFO.
438 * The proposed solution is to disable active TFO globally under the
439 * following circumstances:
440 *   1. client side TFO socket receives out of order FIN
441 *   2. client side TFO socket receives out of order RST
442 *   3. client side TFO socket has timed out three times consecutively during
443 *      or after handshake
444 * We disable active side TFO globally for 1hr at first. Then if it
445 * happens again, we disable it for 2h, then 4h, 8h, ...
446 * And we reset the timeout back to 1hr when we see a successful active
447 * TFO connection with data exchanges.
448 */
449
450/* Disable active TFO and record current jiffies and
451 * tfo_active_disable_times
452 */
453void tcp_fastopen_active_disable(struct sock *sk)
454{
455	struct net *net = sock_net(sk);
456
457	atomic_inc(&net->ipv4.tfo_active_disable_times);
458	net->ipv4.tfo_active_disable_stamp = jiffies;
459	NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
460}
461
462/* Calculate timeout for tfo active disable
463 * Return true if we are still in the active TFO disable period
464 * Return false if timeout already expired and we should use active TFO
465 */
466bool tcp_fastopen_active_should_disable(struct sock *sk)
467{
468	unsigned int tfo_bh_timeout = sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout;
469	int tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
470	unsigned long timeout;
471	int multiplier;
472
473	if (!tfo_da_times)
474		return false;
475
476	/* Limit timout to max: 2^6 * initial timeout */
477	multiplier = 1 << min(tfo_da_times - 1, 6);
478	timeout = multiplier * tfo_bh_timeout * HZ;
479	if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))
480		return true;
481
482	/* Mark check bit so we can check for successful active TFO
483	 * condition and reset tfo_active_disable_times
484	 */
485	tcp_sk(sk)->syn_fastopen_ch = 1;
486	return false;
487}
488
489/* Disable active TFO if FIN is the only packet in the ofo queue
490 * and no data is received.
491 * Also check if we can reset tfo_active_disable_times if data is
492 * received successfully on a marked active TFO sockets opened on
493 * a non-loopback interface
494 */
495void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
496{
497	struct tcp_sock *tp = tcp_sk(sk);
498	struct dst_entry *dst;
499	struct sk_buff *skb;
500
501	if (!tp->syn_fastopen)
502		return;
503
504	if (!tp->data_segs_in) {
505		skb = skb_rb_first(&tp->out_of_order_queue);
506		if (skb && !skb_rb_next(skb)) {
507			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
508				tcp_fastopen_active_disable(sk);
509				return;
510			}
511		}
512	} else if (tp->syn_fastopen_ch &&
513		   atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
514		dst = sk_dst_get(sk);
515		if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
516			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
517		dst_release(dst);
518	}
519}
520
521void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
522{
523	u32 timeouts = inet_csk(sk)->icsk_retransmits;
524	struct tcp_sock *tp = tcp_sk(sk);
525
526	/* Broken middle-boxes may black-hole Fast Open connection during or
527	 * even after the handshake. Be extremely conservative and pause
528	 * Fast Open globally after hitting the third consecutive timeout or
529	 * exceeding the configured timeout limit.
530	 */
531	if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
532	    (timeouts == 2 || (timeouts < 2 && expired))) {
533		tcp_fastopen_active_disable(sk);
534		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
535	}
536}