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}
537