1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2001 McAfee, Inc.
5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * All rights reserved.
7 *
8 * This software was developed for the FreeBSD Project by Jonathan Lemon
9 * and McAfee Research, the Security Research Division of McAfee, Inc. under
10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
11 * DARPA CHATS research program. [2001 McAfee, Inc.]
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 #include "opt_inet.h"
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38
39 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/hash.h>
42 #include <sys/refcount.h>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
45 #include <sys/limits.h>
46 #include <sys/lock.h>
47 #include <sys/mutex.h>
48 #include <sys/malloc.h>
49 #include <sys/mbuf.h>
50 #include <sys/proc.h> /* for proc0 declaration */
51 #include <sys/random.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55 #include <sys/ucred.h>
56
57 #include <sys/md5.h>
58 #include <crypto/siphash/siphash.h>
59
60 #include <vm/uma.h>
61
62 #include <net/if.h>
63 #include <net/if_var.h>
64 #include <net/route.h>
65 #include <net/vnet.h>
66
67 #include <netinet/in.h>
68 #include <netinet/in_kdtrace.h>
69 #include <netinet/in_systm.h>
70 #include <netinet/ip.h>
71 #include <netinet/in_var.h>
72 #include <netinet/in_pcb.h>
73 #include <netinet/in_rss.h>
74 #include <netinet/ip_var.h>
75 #include <netinet/ip_options.h>
76 #ifdef INET6
77 #include <netinet/ip6.h>
78 #include <netinet/icmp6.h>
79 #include <netinet6/nd6.h>
80 #include <netinet6/ip6_var.h>
81 #include <netinet6/in6_pcb.h>
82 #include <netinet6/in6_rss.h>
83 #endif
84 #include <netinet/tcp.h>
85 #include <netinet/tcp_fastopen.h>
86 #include <netinet/tcp_fsm.h>
87 #include <netinet/tcp_seq.h>
88 #include <netinet/tcp_timer.h>
89 #include <netinet/tcp_var.h>
90 #include <netinet/tcp_syncache.h>
91 #include <netinet/tcp_ecn.h>
92 #ifdef TCP_BLACKBOX
93 #include <netinet/tcp_log_buf.h>
94 #endif
95 #ifdef TCP_OFFLOAD
96 #include <netinet/toecore.h>
97 #endif
98 #include <netinet/udp.h>
99
100 #include <netipsec/ipsec_support.h>
101
102 #include <machine/in_cksum.h>
103
104 #include <security/mac/mac_framework.h>
105
106 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true;
107 #define V_tcp_syncookies VNET(tcp_syncookies)
108 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
109 &VNET_NAME(tcp_syncookies), 0,
110 "Use TCP SYN cookies if the syncache overflows");
111
112 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false;
113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
114 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
115 &VNET_NAME(tcp_syncookiesonly), 0,
116 "Use only TCP SYN cookies");
117
118 #ifdef TCP_OFFLOAD
119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
120 #endif
121
122 static void syncache_drop(struct syncache *, struct syncache_head *);
123 static void syncache_free(struct syncache *);
124 static void syncache_insert(struct syncache *, struct syncache_head *);
125 static int syncache_respond(struct syncache *, int);
126 static void syncache_send_challenge_ack(struct syncache *);
127 static struct socket *syncache_socket(struct syncache *, struct socket *,
128 struct mbuf *m);
129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
130 int docallout);
131 static void syncache_timer(void *);
132
133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
134 uint8_t *, uintptr_t);
135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
136 static bool syncookie_expand(struct in_conninfo *,
137 const struct syncache_head *, struct syncache *,
138 struct tcphdr *, struct tcpopt *, struct socket *,
139 uint16_t);
140 static void syncache_pause(struct in_conninfo *);
141 static void syncache_unpause(void *);
142 static void syncookie_reseed(void *);
143 #ifdef INVARIANTS
144 static void syncookie_cmp(struct in_conninfo *,
145 const struct syncache_head *, struct syncache *,
146 struct tcphdr *, struct tcpopt *, struct socket *,
147 uint16_t);
148 #endif
149
150 /*
151 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
152 * 3 retransmits corresponds to a timeout with default values of
153 * tcp_rexmit_initial * ( 1 +
154 * tcp_backoff[1] +
155 * tcp_backoff[2] +
156 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
157 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
158 * the odds are that the user has given up attempting to connect by then.
159 */
160 #define SYNCACHE_MAXREXMTS 3
161
162 /* Arbitrary values */
163 #define TCP_SYNCACHE_HASHSIZE 512
164 #define TCP_SYNCACHE_BUCKETLIMIT 30
165
166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
167 #define V_tcp_syncache VNET(tcp_syncache)
168
169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
170 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
171 "TCP SYN cache");
172
173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
174 &VNET_NAME(tcp_syncache.bucket_limit), 0,
175 "Per-bucket hash limit for syncache");
176
177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
178 &VNET_NAME(tcp_syncache.cache_limit), 0,
179 "Overall entry limit for syncache");
180
181 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
182 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
183
184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
185 &VNET_NAME(tcp_syncache.hashsize), 0,
186 "Size of TCP syncache hashtable");
187
188 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
189 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
190 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
191 "and mac(4) checks");
192
193 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
195 {
196 int error;
197 u_int new;
198
199 new = V_tcp_syncache.rexmt_limit;
200 error = sysctl_handle_int(oidp, &new, 0, req);
201 if ((error == 0) && (req->newptr != NULL)) {
202 if (new > TCP_MAXRXTSHIFT)
203 error = EINVAL;
204 else
205 V_tcp_syncache.rexmt_limit = new;
206 }
207 return (error);
208 }
209
210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
212 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
214 "Limit on SYN/ACK retransmissions");
215
216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
219 "Send reset on socket allocation failure");
220
221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
222
223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
226
227 /*
228 * Requires the syncache entry to be already removed from the bucket list.
229 */
230 static void
syncache_free(struct syncache * sc)231 syncache_free(struct syncache *sc)
232 {
233
234 if (sc->sc_ipopts)
235 (void)m_free(sc->sc_ipopts);
236 if (sc->sc_cred)
237 crfree(sc->sc_cred);
238 #ifdef MAC
239 mac_syncache_destroy(&sc->sc_label);
240 #endif
241
242 uma_zfree(V_tcp_syncache.zone, sc);
243 }
244
245 void
syncache_init(void)246 syncache_init(void)
247 {
248 int i;
249
250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
251 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
252 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
253 V_tcp_syncache.hash_secret = arc4random();
254
255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
256 &V_tcp_syncache.hashsize);
257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
258 &V_tcp_syncache.bucket_limit);
259 if (!powerof2(V_tcp_syncache.hashsize) ||
260 V_tcp_syncache.hashsize == 0) {
261 printf("WARNING: syncache hash size is not a power of 2.\n");
262 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
263 }
264 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
265
266 /* Set limits. */
267 V_tcp_syncache.cache_limit =
268 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
269 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
270 &V_tcp_syncache.cache_limit);
271
272 /* Allocate the hash table. */
273 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
274 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
275
276 #ifdef VIMAGE
277 V_tcp_syncache.vnet = curvnet;
278 #endif
279
280 /* Initialize the hash buckets. */
281 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
282 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
283 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
284 NULL, MTX_DEF);
285 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
286 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
287 V_tcp_syncache.hashbase[i].sch_length = 0;
288 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
289 V_tcp_syncache.hashbase[i].sch_last_overflow =
290 -(SYNCOOKIE_LIFETIME + 1);
291 }
292
293 /* Create the syncache entry zone. */
294 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
295 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
296 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
297 V_tcp_syncache.cache_limit);
298
299 /* Start the SYN cookie reseeder callout. */
300 callout_init(&V_tcp_syncache.secret.reseed, 1);
301 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
302 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
303 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
304 syncookie_reseed, &V_tcp_syncache);
305
306 /* Initialize the pause machinery. */
307 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
308 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
309 0);
310 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
311 V_tcp_syncache.pause_backoff = 0;
312 V_tcp_syncache.paused = false;
313 }
314
315 #ifdef VIMAGE
316 void
syncache_destroy(void)317 syncache_destroy(void)
318 {
319 struct syncache_head *sch;
320 struct syncache *sc, *nsc;
321 int i;
322
323 /*
324 * Stop the re-seed timer before freeing resources. No need to
325 * possibly schedule it another time.
326 */
327 callout_drain(&V_tcp_syncache.secret.reseed);
328
329 /* Stop the SYN cache pause callout. */
330 mtx_lock(&V_tcp_syncache.pause_mtx);
331 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
332 mtx_unlock(&V_tcp_syncache.pause_mtx);
333 callout_drain(&V_tcp_syncache.pause_co);
334 } else
335 mtx_unlock(&V_tcp_syncache.pause_mtx);
336
337 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
338 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
339 sch = &V_tcp_syncache.hashbase[i];
340 callout_drain(&sch->sch_timer);
341
342 SCH_LOCK(sch);
343 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
344 syncache_drop(sc, sch);
345 SCH_UNLOCK(sch);
346 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
347 ("%s: sch->sch_bucket not empty", __func__));
348 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
349 __func__, sch->sch_length));
350 mtx_destroy(&sch->sch_mtx);
351 }
352
353 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
354 ("%s: cache_count not 0", __func__));
355
356 /* Free the allocated global resources. */
357 uma_zdestroy(V_tcp_syncache.zone);
358 free(V_tcp_syncache.hashbase, M_SYNCACHE);
359 mtx_destroy(&V_tcp_syncache.pause_mtx);
360 }
361 #endif
362
363 /*
364 * Inserts a syncache entry into the specified bucket row.
365 * Locks and unlocks the syncache_head autonomously.
366 */
367 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)368 syncache_insert(struct syncache *sc, struct syncache_head *sch)
369 {
370 struct syncache *sc2;
371
372 SCH_LOCK(sch);
373
374 /*
375 * Make sure that we don't overflow the per-bucket limit.
376 * If the bucket is full, toss the oldest element.
377 */
378 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
379 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
380 ("sch->sch_length incorrect"));
381 syncache_pause(&sc->sc_inc);
382 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
383 sch->sch_last_overflow = time_uptime;
384 syncache_drop(sc2, sch);
385 }
386
387 /* Put it into the bucket. */
388 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
389 sch->sch_length++;
390
391 #ifdef TCP_OFFLOAD
392 if (ADDED_BY_TOE(sc)) {
393 struct toedev *tod = sc->sc_tod;
394
395 tod->tod_syncache_added(tod, sc->sc_todctx);
396 }
397 #endif
398
399 /* Reinitialize the bucket row's timer. */
400 if (sch->sch_length == 1)
401 sch->sch_nextc = ticks + INT_MAX;
402 syncache_timeout(sc, sch, 1);
403
404 SCH_UNLOCK(sch);
405
406 TCPSTATES_INC(TCPS_SYN_RECEIVED);
407 TCPSTAT_INC(tcps_sc_added);
408 }
409
410 /*
411 * Remove and free entry from syncache bucket row.
412 * Expects locked syncache head.
413 */
414 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)415 syncache_drop(struct syncache *sc, struct syncache_head *sch)
416 {
417
418 SCH_LOCK_ASSERT(sch);
419
420 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
421 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
422 sch->sch_length--;
423
424 #ifdef TCP_OFFLOAD
425 if (ADDED_BY_TOE(sc)) {
426 struct toedev *tod = sc->sc_tod;
427
428 tod->tod_syncache_removed(tod, sc->sc_todctx);
429 }
430 #endif
431
432 syncache_free(sc);
433 }
434
435 /*
436 * Engage/reengage time on bucket row.
437 */
438 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)439 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
440 {
441 int rexmt;
442
443 if (sc->sc_rxmits == 0)
444 rexmt = tcp_rexmit_initial;
445 else
446 TCPT_RANGESET(rexmt,
447 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
448 tcp_rexmit_min, tcp_rexmit_max);
449 sc->sc_rxttime = ticks + rexmt;
450 sc->sc_rxmits++;
451 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
452 sch->sch_nextc = sc->sc_rxttime;
453 if (docallout)
454 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
455 syncache_timer, (void *)sch);
456 }
457 }
458
459 /*
460 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
461 * If we have retransmitted an entry the maximum number of times, expire it.
462 * One separate timer for each bucket row.
463 */
464 static void
syncache_timer(void * xsch)465 syncache_timer(void *xsch)
466 {
467 struct syncache_head *sch = (struct syncache_head *)xsch;
468 struct syncache *sc, *nsc;
469 struct epoch_tracker et;
470 int tick = ticks;
471 char *s;
472 bool paused;
473
474 CURVNET_SET(sch->sch_sc->vnet);
475
476 /* NB: syncache_head has already been locked by the callout. */
477 SCH_LOCK_ASSERT(sch);
478
479 /*
480 * In the following cycle we may remove some entries and/or
481 * advance some timeouts, so re-initialize the bucket timer.
482 */
483 sch->sch_nextc = tick + INT_MAX;
484
485 /*
486 * If we have paused processing, unconditionally remove
487 * all syncache entries.
488 */
489 mtx_lock(&V_tcp_syncache.pause_mtx);
490 paused = V_tcp_syncache.paused;
491 mtx_unlock(&V_tcp_syncache.pause_mtx);
492
493 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
494 if (paused) {
495 syncache_drop(sc, sch);
496 continue;
497 }
498 /*
499 * We do not check if the listen socket still exists
500 * and accept the case where the listen socket may be
501 * gone by the time we resend the SYN/ACK. We do
502 * not expect this to happens often. If it does,
503 * then the RST will be sent by the time the remote
504 * host does the SYN/ACK->ACK.
505 */
506 if (TSTMP_GT(sc->sc_rxttime, tick)) {
507 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
508 sch->sch_nextc = sc->sc_rxttime;
509 continue;
510 }
511 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
512 sc->sc_flags &= ~SCF_ECN_MASK;
513 }
514 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
515 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
516 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
517 "giving up and removing syncache entry\n",
518 s, __func__);
519 free(s, M_TCPLOG);
520 }
521 syncache_drop(sc, sch);
522 TCPSTAT_INC(tcps_sc_stale);
523 continue;
524 }
525 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
526 log(LOG_DEBUG, "%s; %s: Response timeout, "
527 "retransmitting (%u) SYN|ACK\n",
528 s, __func__, sc->sc_rxmits);
529 free(s, M_TCPLOG);
530 }
531
532 NET_EPOCH_ENTER(et);
533 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
534 syncache_timeout(sc, sch, 0);
535 TCPSTAT_INC(tcps_sndacks);
536 TCPSTAT_INC(tcps_sndtotal);
537 TCPSTAT_INC(tcps_sc_retransmitted);
538 } else {
539 /*
540 * Most likely we are memory constrained, so free
541 * resources.
542 */
543 syncache_drop(sc, sch);
544 TCPSTAT_INC(tcps_sc_dropped);
545 }
546 NET_EPOCH_EXIT(et);
547 }
548 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
549 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
550 syncache_timer, (void *)(sch));
551 CURVNET_RESTORE();
552 }
553
554 /*
555 * Returns true if the system is only using cookies at the moment.
556 * This could be due to a sysadmin decision to only use cookies, or it
557 * could be due to the system detecting an attack.
558 */
559 static inline bool
syncache_cookiesonly(void)560 syncache_cookiesonly(void)
561 {
562 return ((V_tcp_syncookies && V_tcp_syncache.paused) ||
563 V_tcp_syncookiesonly);
564 }
565
566 /*
567 * Find the hash bucket for the given connection.
568 */
569 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)570 syncache_hashbucket(struct in_conninfo *inc)
571 {
572 uint32_t hash;
573
574 /*
575 * The hash is built on foreign port + local port + foreign address.
576 * We rely on the fact that struct in_conninfo starts with 16 bits
577 * of foreign port, then 16 bits of local port then followed by 128
578 * bits of foreign address. In case of IPv4 address, the first 3
579 * 32-bit words of the address always are zeroes.
580 */
581 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
582 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
583
584 return (&V_tcp_syncache.hashbase[hash]);
585 }
586
587 /*
588 * Find an entry in the syncache.
589 * Returns always with locked syncache_head plus a matching entry or NULL.
590 */
591 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)592 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
593 {
594 struct syncache *sc;
595 struct syncache_head *sch;
596
597 *schp = sch = syncache_hashbucket(inc);
598 SCH_LOCK(sch);
599
600 /* Circle through bucket row to find matching entry. */
601 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
602 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
603 sizeof(struct in_endpoints)) == 0)
604 break;
605
606 return (sc); /* Always returns with locked sch. */
607 }
608
609 /*
610 * This function is called when we get a RST for a
611 * non-existent connection, so that we can see if the
612 * connection is in the syn cache. If it is, zap it.
613 * If required send a challenge ACK.
614 */
615 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,uint16_t port)616 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, uint16_t port)
617 {
618 struct syncache *sc;
619 struct syncache_head *sch;
620 char *s = NULL;
621
622 if (syncache_cookiesonly())
623 return;
624 sc = syncache_lookup(inc, &sch); /* returns locked sch */
625 SCH_LOCK_ASSERT(sch);
626
627 /*
628 * No corresponding connection was found in syncache.
629 * If syncookies are enabled and possibly exclusively
630 * used, or we are under memory pressure, a valid RST
631 * may not find a syncache entry. In that case we're
632 * done and no SYN|ACK retransmissions will happen.
633 * Otherwise the RST was misdirected or spoofed.
634 */
635 if (sc == NULL) {
636 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
637 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
638 "syncache entry (possibly syncookie only), "
639 "segment ignored\n", s, __func__);
640 TCPSTAT_INC(tcps_badrst);
641 goto done;
642 }
643
644 /* The remote UDP encaps port does not match. */
645 if (sc->sc_port != port) {
646 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
647 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
648 "syncache entry but non-matching UDP encaps port, "
649 "segment ignored\n", s, __func__);
650 TCPSTAT_INC(tcps_badrst);
651 goto done;
652 }
653
654 /*
655 * If the RST bit is set, check the sequence number to see
656 * if this is a valid reset segment.
657 *
658 * RFC 793 page 37:
659 * In all states except SYN-SENT, all reset (RST) segments
660 * are validated by checking their SEQ-fields. A reset is
661 * valid if its sequence number is in the window.
662 *
663 * RFC 793 page 69:
664 * There are four cases for the acceptability test for an incoming
665 * segment:
666 *
667 * Segment Receive Test
668 * Length Window
669 * ------- ------- -------------------------------------------
670 * 0 0 SEG.SEQ = RCV.NXT
671 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
672 * >0 0 not acceptable
673 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
674 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
675 *
676 * Note that when receiving a SYN segment in the LISTEN state,
677 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
678 * described in RFC 793, page 66.
679 */
680 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
681 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
682 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
683 if (V_tcp_insecure_rst ||
684 th->th_seq == sc->sc_irs + 1) {
685 syncache_drop(sc, sch);
686 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
687 log(LOG_DEBUG,
688 "%s; %s: Our SYN|ACK was rejected, "
689 "connection attempt aborted by remote "
690 "endpoint\n",
691 s, __func__);
692 TCPSTAT_INC(tcps_sc_reset);
693 } else {
694 TCPSTAT_INC(tcps_badrst);
695 /* Send challenge ACK. */
696 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
697 log(LOG_DEBUG, "%s; %s: RST with invalid "
698 " SEQ %u != NXT %u (+WND %u), "
699 "sending challenge ACK\n",
700 s, __func__,
701 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
702 syncache_send_challenge_ack(sc);
703 }
704 } else {
705 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
706 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
707 "NXT %u (+WND %u), segment ignored\n",
708 s, __func__,
709 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
710 TCPSTAT_INC(tcps_badrst);
711 }
712
713 done:
714 if (s != NULL)
715 free(s, M_TCPLOG);
716 SCH_UNLOCK(sch);
717 }
718
719 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)720 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
721 {
722 struct syncache *sc;
723 struct syncache_head *sch;
724
725 if (syncache_cookiesonly())
726 return;
727 sc = syncache_lookup(inc, &sch); /* returns locked sch */
728 SCH_LOCK_ASSERT(sch);
729 if (sc == NULL)
730 goto done;
731
732 /* If the port != sc_port, then it's a bogus ICMP msg */
733 if (port != sc->sc_port)
734 goto done;
735
736 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
737 if (ntohl(th_seq) != sc->sc_iss)
738 goto done;
739
740 /*
741 * If we've retransmitted 3 times and this is our second error,
742 * we remove the entry. Otherwise, we allow it to continue on.
743 * This prevents us from incorrectly nuking an entry during a
744 * spurious network outage.
745 *
746 * See tcp_notify().
747 */
748 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
749 sc->sc_flags |= SCF_UNREACH;
750 goto done;
751 }
752 syncache_drop(sc, sch);
753 TCPSTAT_INC(tcps_sc_unreach);
754 done:
755 SCH_UNLOCK(sch);
756 }
757
758 /*
759 * Build a new TCP socket structure from a syncache entry.
760 *
761 * On success return the newly created socket with its underlying inp locked.
762 */
763 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)764 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
765 {
766 struct inpcb *inp = NULL;
767 struct socket *so;
768 struct tcpcb *tp;
769 int error;
770 char *s;
771
772 NET_EPOCH_ASSERT();
773
774 /*
775 * Creation of a socket via solisten_clone() bypasses call to pr_attach.
776 * That's why there is some pasted code from soattach() and from
777 * tcp_usr_attach() here. This should improve once TCP is PR_SOCKBUF.
778 */
779 if ((so = solisten_clone(lso)) == NULL)
780 goto allocfail;
781 mtx_init(&so->so_snd_mtx, "so_snd", NULL, MTX_DEF);
782 mtx_init(&so->so_rcv_mtx, "so_rcv", NULL, MTX_DEF);
783 so->so_snd.sb_mtx = &so->so_snd_mtx;
784 so->so_rcv.sb_mtx = &so->so_rcv_mtx;
785 error = soreserve(so, lso->sol_sbsnd_hiwat, lso->sol_sbrcv_hiwat);
786 if (error) {
787 sodealloc(so);
788 goto allocfail;
789 }
790 #ifdef MAC
791 mac_socketpeer_set_from_mbuf(m, so);
792 #endif
793 error = in_pcballoc(so, &V_tcbinfo);
794 if (error) {
795 sodealloc(so);
796 goto allocfail;
797 }
798 inp = sotoinpcb(so);
799 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
800 in_pcbfree(inp);
801 sodealloc(so);
802 goto allocfail;
803 }
804 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
805 #ifdef INET6
806 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
807 inp->inp_vflag &= ~INP_IPV4;
808 inp->inp_vflag |= INP_IPV6;
809 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
810 } else {
811 inp->inp_vflag &= ~INP_IPV6;
812 inp->inp_vflag |= INP_IPV4;
813 #endif
814 inp->inp_ip_ttl = sc->sc_ip_ttl;
815 inp->inp_ip_tos = sc->sc_ip_tos;
816 inp->inp_laddr = sc->sc_inc.inc_laddr;
817 #ifdef INET6
818 }
819 #endif
820 inp->inp_lport = sc->sc_inc.inc_lport;
821 #ifdef INET6
822 if (inp->inp_vflag & INP_IPV6PROTO) {
823 struct inpcb *oinp = sotoinpcb(lso);
824
825 /*
826 * Inherit socket options from the listening socket.
827 * Note that in6p_inputopts are not (and should not be)
828 * copied, since it stores previously received options and is
829 * used to detect if each new option is different than the
830 * previous one and hence should be passed to a user.
831 * If we copied in6p_inputopts, a user would not be able to
832 * receive options just after calling the accept system call.
833 */
834 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
835 if (oinp->in6p_outputopts)
836 inp->in6p_outputopts =
837 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
838 inp->in6p_hops = oinp->in6p_hops;
839 }
840
841 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
842 struct sockaddr_in6 sin6;
843
844 sin6.sin6_family = AF_INET6;
845 sin6.sin6_len = sizeof(sin6);
846 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
847 sin6.sin6_port = sc->sc_inc.inc_fport;
848 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
849 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
850 if (error != 0)
851 goto abort;
852 /* Override flowlabel from in6_pcbconnect. */
853 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
854 inp->inp_flow |= sc->sc_flowlabel;
855 }
856 #endif /* INET6 */
857 #if defined(INET) && defined(INET6)
858 else
859 #endif
860 #ifdef INET
861 {
862 struct sockaddr_in sin;
863
864 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
865
866 if (inp->inp_options == NULL) {
867 inp->inp_options = sc->sc_ipopts;
868 sc->sc_ipopts = NULL;
869 }
870
871 sin.sin_family = AF_INET;
872 sin.sin_len = sizeof(sin);
873 sin.sin_addr = sc->sc_inc.inc_faddr;
874 sin.sin_port = sc->sc_inc.inc_fport;
875 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
876 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
877 if (error != 0)
878 goto abort;
879 }
880 #endif /* INET */
881 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
882 /* Copy old policy into new socket's. */
883 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
884 printf("syncache_socket: could not copy policy\n");
885 #endif
886 if (sc->sc_flowtype != M_HASHTYPE_NONE) {
887 inp->inp_flowid = sc->sc_flowid;
888 inp->inp_flowtype = sc->sc_flowtype;
889 } else {
890 /* assign flowid by software RSS hash */
891 #ifdef INET6
892 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
893 rss_proto_software_hash_v6(&inp->in6p_faddr,
894 &inp->in6p_laddr,
895 inp->inp_fport,
896 inp->inp_lport,
897 IPPROTO_TCP,
898 &inp->inp_flowid,
899 &inp->inp_flowtype);
900 } else
901 #endif /* INET6 */
902 {
903 #ifdef INET
904 rss_proto_software_hash_v4(inp->inp_faddr,
905 inp->inp_laddr,
906 inp->inp_fport,
907 inp->inp_lport,
908 IPPROTO_TCP,
909 &inp->inp_flowid,
910 &inp->inp_flowtype);
911 #endif /* INET */
912 }
913 }
914 #ifdef NUMA
915 inp->inp_numa_domain = sc->sc_numa_domain;
916 #endif
917
918 tp->t_state = TCPS_SYN_RECEIVED;
919 tp->iss = sc->sc_iss;
920 tp->irs = sc->sc_irs;
921 tp->t_port = sc->sc_port;
922 tcp_rcvseqinit(tp);
923 tcp_sendseqinit(tp);
924 tp->snd_wl1 = sc->sc_irs;
925 tp->snd_max = tp->iss + 1;
926 tp->snd_nxt = tp->iss + 1;
927 tp->rcv_up = sc->sc_irs + 1;
928 tp->rcv_wnd = sc->sc_wnd;
929 tp->rcv_adv += tp->rcv_wnd;
930 tp->last_ack_sent = tp->rcv_nxt;
931
932 tp->t_flags = sototcpcb(lso)->t_flags &
933 (TF_LRD|TF_NOPUSH|TF_NODELAY);
934 if (sc->sc_flags & SCF_NOOPT)
935 tp->t_flags |= TF_NOOPT;
936 else {
937 if (sc->sc_flags & SCF_WINSCALE) {
938 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
939 tp->snd_scale = sc->sc_requested_s_scale;
940 tp->request_r_scale = sc->sc_requested_r_scale;
941 }
942 if (sc->sc_flags & SCF_TIMESTAMP) {
943 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
944 tp->ts_recent = sc->sc_tsreflect;
945 tp->ts_recent_age = tcp_ts_getticks();
946 tp->ts_offset = sc->sc_tsoff;
947 }
948 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
949 if (sc->sc_flags & SCF_SIGNATURE)
950 tp->t_flags |= TF_SIGNATURE;
951 #endif
952 if (sc->sc_flags & SCF_SACK)
953 tp->t_flags |= TF_SACK_PERMIT;
954 }
955
956 tcp_ecn_syncache_socket(tp, sc);
957
958 /*
959 * Set up MSS and get cached values from tcp_hostcache.
960 * This might overwrite some of the defaults we just set.
961 */
962 tcp_mss(tp, sc->sc_peer_mss);
963
964 /*
965 * If the SYN,ACK was retransmitted, indicate that CWND to be
966 * limited to one segment in cc_conn_init().
967 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
968 */
969 if (sc->sc_rxmits > 1)
970 tp->snd_cwnd = 1;
971
972 /* Copy over the challenge ACK state. */
973 tp->t_challenge_ack_end = sc->sc_challenge_ack_end;
974 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt;
975
976 #ifdef TCP_OFFLOAD
977 /*
978 * Allow a TOE driver to install its hooks. Note that we hold the
979 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
980 * new connection before the TOE driver has done its thing.
981 */
982 if (ADDED_BY_TOE(sc)) {
983 struct toedev *tod = sc->sc_tod;
984
985 tod->tod_offload_socket(tod, sc->sc_todctx, so);
986 }
987 #endif
988 #ifdef TCP_BLACKBOX
989 /*
990 * Inherit the log state from the listening socket, if
991 * - the log state of the listening socket is not off and
992 * - the listening socket was not auto selected from all sessions and
993 * - a log id is not set on the listening socket.
994 * This avoids inheriting a log state which was automatically set.
995 */
996 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
997 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
998 (sototcpcb(lso)->t_lib == NULL)) {
999 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
1000 }
1001 #endif
1002 /*
1003 * Copy and activate timers.
1004 */
1005 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
1006 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
1007 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
1008 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
1009 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
1010 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1011
1012 TCPSTAT_INC(tcps_accepts);
1013 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1014
1015 if (!solisten_enqueue(so, SS_ISCONNECTED))
1016 tp->t_flags |= TF_SONOTCONN;
1017 /* Can we inherit anything from the listener? */
1018 if (tp->t_fb->tfb_inherit != NULL) {
1019 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1020 }
1021 return (so);
1022
1023 allocfail:
1024 /*
1025 * Drop the connection; we will either send a RST or have the peer
1026 * retransmit its SYN again after its RTO and try again.
1027 */
1028 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1029 log(LOG_DEBUG, "%s; %s: Socket create failed "
1030 "due to limits or memory shortage\n",
1031 s, __func__);
1032 free(s, M_TCPLOG);
1033 }
1034 TCPSTAT_INC(tcps_listendrop);
1035 return (NULL);
1036
1037 abort:
1038 tcp_discardcb(tp);
1039 in_pcbfree(inp);
1040 sodealloc(so);
1041 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1042 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1043 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1044 error);
1045 free(s, M_TCPLOG);
1046 }
1047 TCPSTAT_INC(tcps_listendrop);
1048 return (NULL);
1049 }
1050
1051 /*
1052 * This function gets called when we receive an ACK for a
1053 * socket in the LISTEN state. We look up the connection
1054 * in the syncache, and if its there, we pull it out of
1055 * the cache and turn it into a full-blown connection in
1056 * the SYN-RECEIVED state.
1057 *
1058 * On syncache_socket() success the newly created socket
1059 * has its underlying inp locked.
1060 *
1061 * *lsop is updated, if and only if 1 is returned.
1062 */
1063 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1064 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1065 struct socket **lsop, struct mbuf *m, uint16_t port)
1066 {
1067 struct syncache *sc;
1068 struct syncache_head *sch;
1069 struct syncache scs;
1070 char *s;
1071 bool locked;
1072
1073 NET_EPOCH_ASSERT();
1074 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1075 ("%s: can handle only ACK", __func__));
1076
1077 if (syncache_cookiesonly()) {
1078 sc = NULL;
1079 sch = syncache_hashbucket(inc);
1080 locked = false;
1081 } else {
1082 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1083 locked = true;
1084 SCH_LOCK_ASSERT(sch);
1085 }
1086
1087 #ifdef INVARIANTS
1088 /*
1089 * Test code for syncookies comparing the syncache stored
1090 * values with the reconstructed values from the cookie.
1091 */
1092 if (sc != NULL)
1093 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1094 #endif
1095
1096 if (sc == NULL) {
1097 if (locked) {
1098 /*
1099 * The syncache is currently in use (neither disabled,
1100 * nor paused), but no entry was found.
1101 */
1102 if (!V_tcp_syncookies) {
1103 /*
1104 * Since no syncookies are used in case of
1105 * a bucket overflow, don't even check for
1106 * a valid syncookie.
1107 */
1108 SCH_UNLOCK(sch);
1109 TCPSTAT_INC(tcps_sc_spurcookie);
1110 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1111 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1112 "segment rejected "
1113 "(syncookies disabled)\n",
1114 s, __func__);
1115 free(s, M_TCPLOG);
1116 }
1117 return (0);
1118 }
1119 if (sch->sch_last_overflow <
1120 time_uptime - SYNCOOKIE_LIFETIME) {
1121 /*
1122 * Since the bucket did not overflow recently,
1123 * don't even check for a valid syncookie.
1124 */
1125 SCH_UNLOCK(sch);
1126 TCPSTAT_INC(tcps_sc_spurcookie);
1127 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1128 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1129 "segment rejected "
1130 "(no syncache entry)\n",
1131 s, __func__);
1132 free(s, M_TCPLOG);
1133 }
1134 return (0);
1135 }
1136 SCH_UNLOCK(sch);
1137 }
1138 bzero(&scs, sizeof(scs));
1139 /*
1140 * Now check, if the syncookie is valid. If it is, create an on
1141 * stack syncache entry.
1142 */
1143 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) {
1144 sc = &scs;
1145 TCPSTAT_INC(tcps_sc_recvcookie);
1146 } else {
1147 TCPSTAT_INC(tcps_sc_failcookie);
1148 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1149 log(LOG_DEBUG, "%s; %s: Segment failed "
1150 "SYNCOOKIE authentication, segment rejected "
1151 "(probably spoofed)\n", s, __func__);
1152 free(s, M_TCPLOG);
1153 }
1154 return (0);
1155 }
1156 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1157 /* If received ACK has MD5 signature, check it. */
1158 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1159 (!TCPMD5_ENABLED() ||
1160 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1161 /* Drop the ACK. */
1162 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1163 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1164 "MD5 signature doesn't match.\n",
1165 s, __func__);
1166 free(s, M_TCPLOG);
1167 }
1168 TCPSTAT_INC(tcps_sig_err_sigopt);
1169 return (-1); /* Do not send RST */
1170 }
1171 #endif /* TCP_SIGNATURE */
1172 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) {
1173 sc->sc_flowid = m->m_pkthdr.flowid;
1174 sc->sc_flowtype = M_HASHTYPE_GET(m);
1175 }
1176 #ifdef NUMA
1177 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1178 #endif
1179 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1180 } else {
1181 if (sc->sc_port != port) {
1182 SCH_UNLOCK(sch);
1183 return (0);
1184 }
1185 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1186 /*
1187 * If listening socket requested TCP digests, check that
1188 * received ACK has signature and it is correct.
1189 * If not, drop the ACK and leave sc entry in the cache,
1190 * because SYN was received with correct signature.
1191 */
1192 if (sc->sc_flags & SCF_SIGNATURE) {
1193 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1194 /* No signature */
1195 TCPSTAT_INC(tcps_sig_err_nosigopt);
1196 SCH_UNLOCK(sch);
1197 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1198 log(LOG_DEBUG, "%s; %s: Segment "
1199 "rejected, MD5 signature wasn't "
1200 "provided.\n", s, __func__);
1201 free(s, M_TCPLOG);
1202 }
1203 return (-1); /* Do not send RST */
1204 }
1205 if (!TCPMD5_ENABLED() ||
1206 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1207 /* Doesn't match or no SA */
1208 SCH_UNLOCK(sch);
1209 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1210 log(LOG_DEBUG, "%s; %s: Segment "
1211 "rejected, MD5 signature doesn't "
1212 "match.\n", s, __func__);
1213 free(s, M_TCPLOG);
1214 }
1215 return (-1); /* Do not send RST */
1216 }
1217 }
1218 #endif /* TCP_SIGNATURE */
1219
1220 /*
1221 * RFC 7323 PAWS: If we have a timestamp on this segment and
1222 * it's less than ts_recent, drop it.
1223 * XXXMT: RFC 7323 also requires to send an ACK.
1224 * In tcp_input.c this is only done for TCP segments
1225 * with user data, so be consistent here and just drop
1226 * the segment.
1227 */
1228 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1229 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1230 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1231 log(LOG_DEBUG,
1232 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1233 "segment dropped\n", s, __func__,
1234 to->to_tsval, sc->sc_tsreflect);
1235 }
1236 SCH_UNLOCK(sch);
1237 free(s, M_TCPLOG);
1238 return (-1); /* Do not send RST */
1239 }
1240
1241 /*
1242 * If timestamps were not negotiated during SYN/ACK and a
1243 * segment with a timestamp is received, ignore the
1244 * timestamp and process the packet normally.
1245 * See section 3.2 of RFC 7323.
1246 */
1247 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1248 (to->to_flags & TOF_TS)) {
1249 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1250 log(LOG_DEBUG, "%s; %s: Timestamp not "
1251 "expected, segment processed normally\n",
1252 s, __func__);
1253 free(s, M_TCPLOG);
1254 }
1255 }
1256
1257 /*
1258 * If timestamps were negotiated during SYN/ACK and a
1259 * segment without a timestamp is received, silently drop
1260 * the segment, unless the missing timestamps are tolerated.
1261 * See section 3.2 of RFC 7323.
1262 */
1263 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1264 !(to->to_flags & TOF_TS)) {
1265 if (V_tcp_tolerate_missing_ts) {
1266 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1267 log(LOG_DEBUG,
1268 "%s; %s: Timestamp missing, "
1269 "segment processed normally\n",
1270 s, __func__);
1271 free(s, M_TCPLOG);
1272 }
1273 } else {
1274 SCH_UNLOCK(sch);
1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1276 log(LOG_DEBUG,
1277 "%s; %s: Timestamp missing, "
1278 "segment silently dropped\n",
1279 s, __func__);
1280 free(s, M_TCPLOG);
1281 }
1282 return (-1); /* Do not send RST */
1283 }
1284 }
1285
1286 /*
1287 * SEG.SEQ validation:
1288 * The SEG.SEQ must be in the window starting at our
1289 * initial receive sequence number + 1.
1290 */
1291 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1292 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1293 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1294 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, "
1295 "sending challenge ACK\n",
1296 s, __func__, th->th_seq, sc->sc_irs + 1);
1297 syncache_send_challenge_ack(sc);
1298 SCH_UNLOCK(sch);
1299 free(s, M_TCPLOG);
1300 return (-1); /* Do not send RST */
1301 }
1302
1303 /*
1304 * SEG.ACK validation:
1305 * SEG.ACK must match our initial send sequence number + 1.
1306 */
1307 if (th->th_ack != sc->sc_iss + 1) {
1308 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1309 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, "
1310 "segment rejected\n",
1311 s, __func__, th->th_ack, sc->sc_iss + 1);
1312 SCH_UNLOCK(sch);
1313 free(s, M_TCPLOG);
1314 return (0); /* Do send RST, do not free sc. */
1315 }
1316
1317 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1318 sch->sch_length--;
1319 #ifdef TCP_OFFLOAD
1320 if (ADDED_BY_TOE(sc)) {
1321 struct toedev *tod = sc->sc_tod;
1322
1323 tod->tod_syncache_removed(tod, sc->sc_todctx);
1324 }
1325 #endif
1326 SCH_UNLOCK(sch);
1327 }
1328
1329 *lsop = syncache_socket(sc, *lsop, m);
1330
1331 if (__predict_false(*lsop == NULL)) {
1332 TCPSTAT_INC(tcps_sc_aborted);
1333 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1334 } else if (sc != &scs)
1335 TCPSTAT_INC(tcps_sc_completed);
1336
1337 if (sc != &scs)
1338 syncache_free(sc);
1339 return (1);
1340 }
1341
1342 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1343 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1344 uint64_t response_cookie)
1345 {
1346 struct inpcb *inp;
1347 struct tcpcb *tp;
1348 unsigned int *pending_counter;
1349 struct socket *so;
1350
1351 NET_EPOCH_ASSERT();
1352
1353 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1354 so = syncache_socket(sc, lso, m);
1355 if (so == NULL) {
1356 TCPSTAT_INC(tcps_sc_aborted);
1357 atomic_subtract_int(pending_counter, 1);
1358 } else {
1359 soisconnected(so);
1360 inp = sotoinpcb(so);
1361 tp = intotcpcb(inp);
1362 tp->t_flags |= TF_FASTOPEN;
1363 tp->t_tfo_cookie.server = response_cookie;
1364 tp->snd_max = tp->iss;
1365 tp->snd_nxt = tp->iss;
1366 tp->t_tfo_pending = pending_counter;
1367 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1368 TCPSTAT_INC(tcps_sc_completed);
1369 }
1370
1371 return (so);
1372 }
1373
1374 /*
1375 * Given a LISTEN socket and an inbound SYN request, add
1376 * this to the syn cache, and send back a segment:
1377 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1378 * to the source.
1379 *
1380 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1381 * Doing so would require that we hold onto the data and deliver it
1382 * to the application. However, if we are the target of a SYN-flood
1383 * DoS attack, an attacker could send data which would eventually
1384 * consume all available buffer space if it were ACKed. By not ACKing
1385 * the data, we avoid this DoS scenario.
1386 *
1387 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1388 * cookie is processed and a new socket is created. In this case, any data
1389 * accompanying the SYN will be queued to the socket by tcp_input() and will
1390 * be ACKed either when the application sends response data or the delayed
1391 * ACK timer expires, whichever comes first.
1392 */
1393 struct socket *
syncache_add(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct inpcb * inp,struct socket * so,struct mbuf * m,void * tod,void * todctx,uint8_t iptos,uint16_t port)1394 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1395 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1396 void *todctx, uint8_t iptos, uint16_t port)
1397 {
1398 struct tcpcb *tp;
1399 struct socket *rv = NULL;
1400 struct syncache *sc = NULL;
1401 struct ucred *cred;
1402 struct syncache_head *sch;
1403 struct mbuf *ipopts = NULL;
1404 u_int ltflags;
1405 int win, ip_ttl, ip_tos;
1406 char *s;
1407 #ifdef INET6
1408 int autoflowlabel = 0;
1409 #endif
1410 #ifdef MAC
1411 struct label *maclabel = NULL;
1412 #endif
1413 struct syncache scs;
1414 uint64_t tfo_response_cookie;
1415 unsigned int *tfo_pending = NULL;
1416 int tfo_cookie_valid = 0;
1417 int tfo_response_cookie_valid = 0;
1418 bool locked;
1419
1420 INP_RLOCK_ASSERT(inp); /* listen socket */
1421 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1422 ("%s: unexpected tcp flags", __func__));
1423
1424 /*
1425 * Combine all so/tp operations very early to drop the INP lock as
1426 * soon as possible.
1427 */
1428 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1429 tp = sototcpcb(so);
1430 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred);
1431
1432 #ifdef INET6
1433 if (inc->inc_flags & INC_ISIPV6) {
1434 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1435 autoflowlabel = 1;
1436 }
1437 ip_ttl = in6_selecthlim(inp, NULL);
1438 if ((inp->in6p_outputopts == NULL) ||
1439 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1440 ip_tos = 0;
1441 } else {
1442 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1443 }
1444 }
1445 #endif
1446 #if defined(INET6) && defined(INET)
1447 else
1448 #endif
1449 #ifdef INET
1450 {
1451 ip_ttl = inp->inp_ip_ttl;
1452 ip_tos = inp->inp_ip_tos;
1453 }
1454 #endif
1455 win = so->sol_sbrcv_hiwat;
1456 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1457
1458 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) &&
1459 (tp->t_tfo_pending != NULL) &&
1460 (to->to_flags & TOF_FASTOPEN)) {
1461 /*
1462 * Limit the number of pending TFO connections to
1463 * approximately half of the queue limit. This prevents TFO
1464 * SYN floods from starving the service by filling the
1465 * listen queue with bogus TFO connections.
1466 */
1467 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1468 (so->sol_qlimit / 2)) {
1469 int result;
1470
1471 result = tcp_fastopen_check_cookie(inc,
1472 to->to_tfo_cookie, to->to_tfo_len,
1473 &tfo_response_cookie);
1474 tfo_cookie_valid = (result > 0);
1475 tfo_response_cookie_valid = (result >= 0);
1476 }
1477
1478 /*
1479 * Remember the TFO pending counter as it will have to be
1480 * decremented below if we don't make it to syncache_tfo_expand().
1481 */
1482 tfo_pending = tp->t_tfo_pending;
1483 }
1484
1485 #ifdef MAC
1486 if (mac_syncache_init(&maclabel) != 0) {
1487 INP_RUNLOCK(inp);
1488 goto done;
1489 } else
1490 mac_syncache_create(maclabel, inp);
1491 #endif
1492 if (!tfo_cookie_valid)
1493 INP_RUNLOCK(inp);
1494
1495 /*
1496 * Remember the IP options, if any.
1497 */
1498 #ifdef INET6
1499 if (!(inc->inc_flags & INC_ISIPV6))
1500 #endif
1501 #ifdef INET
1502 ipopts = (m) ? ip_srcroute(m) : NULL;
1503 #else
1504 ipopts = NULL;
1505 #endif
1506
1507 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1508 /*
1509 * When the socket is TCP-MD5 enabled check that,
1510 * - a signed packet is valid
1511 * - a non-signed packet does not have a security association
1512 *
1513 * If a signed packet fails validation or a non-signed packet has a
1514 * security association, the packet will be dropped.
1515 */
1516 if (ltflags & TF_SIGNATURE) {
1517 if (to->to_flags & TOF_SIGNATURE) {
1518 if (!TCPMD5_ENABLED() ||
1519 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1520 goto done;
1521 } else {
1522 if (TCPMD5_ENABLED() &&
1523 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1524 goto done;
1525 }
1526 } else if (to->to_flags & TOF_SIGNATURE)
1527 goto done;
1528 #endif /* TCP_SIGNATURE */
1529 /*
1530 * See if we already have an entry for this connection.
1531 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1532 *
1533 * XXX: should the syncache be re-initialized with the contents
1534 * of the new SYN here (which may have different options?)
1535 *
1536 * XXX: We do not check the sequence number to see if this is a
1537 * real retransmit or a new connection attempt. The question is
1538 * how to handle such a case; either ignore it as spoofed, or
1539 * drop the current entry and create a new one?
1540 */
1541 if (syncache_cookiesonly()) {
1542 sc = NULL;
1543 sch = syncache_hashbucket(inc);
1544 locked = false;
1545 } else {
1546 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1547 locked = true;
1548 SCH_LOCK_ASSERT(sch);
1549 }
1550 if (sc != NULL) {
1551 if (tfo_cookie_valid)
1552 INP_RUNLOCK(inp);
1553 TCPSTAT_INC(tcps_sc_dupsyn);
1554 if (ipopts) {
1555 /*
1556 * If we were remembering a previous source route,
1557 * forget it and use the new one we've been given.
1558 */
1559 if (sc->sc_ipopts)
1560 (void)m_free(sc->sc_ipopts);
1561 sc->sc_ipopts = ipopts;
1562 }
1563 /*
1564 * Update timestamp if present.
1565 */
1566 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1567 sc->sc_tsreflect = to->to_tsval;
1568 else
1569 sc->sc_flags &= ~SCF_TIMESTAMP;
1570 /*
1571 * Adjust ECN response if needed, e.g. different
1572 * IP ECN field, or a fallback by the remote host.
1573 */
1574 if (sc->sc_flags & SCF_ECN_MASK) {
1575 sc->sc_flags &= ~SCF_ECN_MASK;
1576 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1577 }
1578 #ifdef MAC
1579 /*
1580 * Since we have already unconditionally allocated label
1581 * storage, free it up. The syncache entry will already
1582 * have an initialized label we can use.
1583 */
1584 mac_syncache_destroy(&maclabel);
1585 #endif
1586 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1587 /* Retransmit SYN|ACK and reset retransmit count. */
1588 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1589 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1590 "resetting timer and retransmitting SYN|ACK\n",
1591 s, __func__);
1592 free(s, M_TCPLOG);
1593 }
1594 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
1595 sc->sc_rxmits = 0;
1596 syncache_timeout(sc, sch, 1);
1597 TCPSTAT_INC(tcps_sndacks);
1598 TCPSTAT_INC(tcps_sndtotal);
1599 } else {
1600 /*
1601 * Most likely we are memory constrained, so free
1602 * resources.
1603 */
1604 syncache_drop(sc, sch);
1605 TCPSTAT_INC(tcps_sc_dropped);
1606 }
1607 SCH_UNLOCK(sch);
1608 goto donenoprobe;
1609 }
1610
1611 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1612 /*
1613 * Skip allocating a syncache entry if we are just going to discard
1614 * it later.
1615 */
1616 if (!locked || tfo_cookie_valid) {
1617 bzero(&scs, sizeof(scs));
1618 sc = &scs;
1619 } else {
1620 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1621 if (sc == NULL) {
1622 /*
1623 * The zone allocator couldn't provide more entries.
1624 * Treat this as if the cache was full; drop the oldest
1625 * entry and insert the new one.
1626 */
1627 TCPSTAT_INC(tcps_sc_zonefail);
1628 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1629 if (sc != NULL) {
1630 sch->sch_last_overflow = time_uptime;
1631 syncache_drop(sc, sch);
1632 syncache_pause(inc);
1633 }
1634 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1635 if (sc == NULL) {
1636 if (V_tcp_syncookies) {
1637 bzero(&scs, sizeof(scs));
1638 sc = &scs;
1639 } else {
1640 KASSERT(locked,
1641 ("%s: bucket unexpectedly unlocked",
1642 __func__));
1643 SCH_UNLOCK(sch);
1644 goto done;
1645 }
1646 }
1647 }
1648 }
1649
1650 KASSERT(sc != NULL, ("sc == NULL"));
1651 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1652 sc->sc_tfo_cookie = &tfo_response_cookie;
1653
1654 /*
1655 * Fill in the syncache values.
1656 */
1657 #ifdef MAC
1658 sc->sc_label = maclabel;
1659 #endif
1660 /*
1661 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1662 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1663 * Therefore, store the credentials only when needed:
1664 * - sc is allocated from the zone and not using the on stack instance.
1665 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1666 * The reference count is decremented when a zone allocated sc is
1667 * freed in syncache_free().
1668 */
1669 if (sc != &scs && !V_tcp_syncache.see_other) {
1670 sc->sc_cred = cred;
1671 cred = NULL;
1672 } else
1673 sc->sc_cred = NULL;
1674 sc->sc_port = port;
1675 sc->sc_ipopts = ipopts;
1676 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1677 sc->sc_ip_tos = ip_tos;
1678 sc->sc_ip_ttl = ip_ttl;
1679 #ifdef TCP_OFFLOAD
1680 sc->sc_tod = tod;
1681 sc->sc_todctx = todctx;
1682 #endif
1683 sc->sc_irs = th->th_seq;
1684 sc->sc_flags = 0;
1685 sc->sc_flowlabel = 0;
1686
1687 /*
1688 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1689 * win was derived from socket earlier in the function.
1690 */
1691 win = imax(win, 0);
1692 win = imin(win, TCP_MAXWIN);
1693 sc->sc_wnd = win;
1694
1695 if (V_tcp_do_rfc1323 &&
1696 !(ltflags & TF_NOOPT)) {
1697 /*
1698 * A timestamp received in a SYN makes
1699 * it ok to send timestamp requests and replies.
1700 */
1701 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1702 sc->sc_tsreflect = to->to_tsval;
1703 sc->sc_flags |= SCF_TIMESTAMP;
1704 sc->sc_tsoff = tcp_new_ts_offset(inc);
1705 }
1706 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1707 u_int wscale = 0;
1708
1709 /*
1710 * Pick the smallest possible scaling factor that
1711 * will still allow us to scale up to sb_max, aka
1712 * kern.ipc.maxsockbuf.
1713 *
1714 * We do this because there are broken firewalls that
1715 * will corrupt the window scale option, leading to
1716 * the other endpoint believing that our advertised
1717 * window is unscaled. At scale factors larger than
1718 * 5 the unscaled window will drop below 1500 bytes,
1719 * leading to serious problems when traversing these
1720 * broken firewalls.
1721 *
1722 * With the default maxsockbuf of 256K, a scale factor
1723 * of 3 will be chosen by this algorithm. Those who
1724 * choose a larger maxsockbuf should watch out
1725 * for the compatibility problems mentioned above.
1726 *
1727 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1728 * or <SYN,ACK>) segment itself is never scaled.
1729 */
1730 while (wscale < TCP_MAX_WINSHIFT &&
1731 (TCP_MAXWIN << wscale) < sb_max)
1732 wscale++;
1733 sc->sc_requested_r_scale = wscale;
1734 sc->sc_requested_s_scale = to->to_wscale;
1735 sc->sc_flags |= SCF_WINSCALE;
1736 }
1737 }
1738 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1739 /*
1740 * If incoming packet has an MD5 signature, flag this in the
1741 * syncache so that syncache_respond() will do the right thing
1742 * with the SYN+ACK.
1743 */
1744 if (to->to_flags & TOF_SIGNATURE)
1745 sc->sc_flags |= SCF_SIGNATURE;
1746 #endif /* TCP_SIGNATURE */
1747 if (to->to_flags & TOF_SACKPERM)
1748 sc->sc_flags |= SCF_SACK;
1749 if (to->to_flags & TOF_MSS)
1750 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1751 if (ltflags & TF_NOOPT)
1752 sc->sc_flags |= SCF_NOOPT;
1753 /* ECN Handshake */
1754 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1755 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1756
1757 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1758 sc->sc_iss = syncookie_generate(sch, sc);
1759 else
1760 sc->sc_iss = arc4random();
1761 #ifdef INET6
1762 if (autoflowlabel) {
1763 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1764 sc->sc_flowlabel = sc->sc_iss;
1765 else
1766 sc->sc_flowlabel = ip6_randomflowlabel();
1767 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1768 }
1769 #endif
1770 if (m != NULL && M_HASHTYPE_ISHASH_TCP(m)) {
1771 sc->sc_flowid = m->m_pkthdr.flowid;
1772 sc->sc_flowtype = M_HASHTYPE_GET(m);
1773 }
1774 #ifdef NUMA
1775 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM;
1776 #endif
1777 if (locked)
1778 SCH_UNLOCK(sch);
1779
1780 if (tfo_cookie_valid) {
1781 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1782 /* INP_RUNLOCK(inp) will be performed by the caller */
1783 goto tfo_expanded;
1784 }
1785
1786 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1787 /*
1788 * Do a standard 3-way handshake.
1789 */
1790 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) {
1791 if (sc != &scs)
1792 syncache_insert(sc, sch); /* locks and unlocks sch */
1793 TCPSTAT_INC(tcps_sndacks);
1794 TCPSTAT_INC(tcps_sndtotal);
1795 } else {
1796 /*
1797 * Most likely we are memory constrained, so free resources.
1798 */
1799 if (sc != &scs)
1800 syncache_free(sc);
1801 TCPSTAT_INC(tcps_sc_dropped);
1802 }
1803 goto donenoprobe;
1804
1805 done:
1806 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1807 donenoprobe:
1808 if (m)
1809 m_freem(m);
1810 /*
1811 * If tfo_pending is not NULL here, then a TFO SYN that did not
1812 * result in a new socket was processed and the associated pending
1813 * counter has not yet been decremented. All such TFO processing paths
1814 * transit this point.
1815 */
1816 if (tfo_pending != NULL)
1817 tcp_fastopen_decrement_counter(tfo_pending);
1818
1819 tfo_expanded:
1820 if (cred != NULL)
1821 crfree(cred);
1822 if (sc == NULL || sc == &scs) {
1823 #ifdef MAC
1824 mac_syncache_destroy(&maclabel);
1825 #endif
1826 if (ipopts)
1827 (void)m_free(ipopts);
1828 }
1829 return (rv);
1830 }
1831
1832 /*
1833 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment
1834 * or upon 3WHS ACK timeout.
1835 */
1836 static int
syncache_respond(struct syncache * sc,int flags)1837 syncache_respond(struct syncache *sc, int flags)
1838 {
1839 struct ip *ip = NULL;
1840 struct mbuf *m;
1841 struct tcphdr *th = NULL;
1842 struct udphdr *udp = NULL;
1843 int optlen, error = 0; /* Make compiler happy */
1844 u_int16_t hlen, tlen, mssopt, ulen;
1845 struct tcpopt to;
1846 #ifdef INET6
1847 struct ip6_hdr *ip6 = NULL;
1848 #endif
1849
1850 NET_EPOCH_ASSERT();
1851
1852 hlen =
1853 #ifdef INET6
1854 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1855 #endif
1856 sizeof(struct ip);
1857 tlen = hlen + sizeof(struct tcphdr);
1858 if (sc->sc_port) {
1859 tlen += sizeof(struct udphdr);
1860 }
1861 /* Determine MSS we advertize to other end of connection. */
1862 mssopt = tcp_mssopt(&sc->sc_inc);
1863 if (sc->sc_port)
1864 mssopt -= V_tcp_udp_tunneling_overhead;
1865 mssopt = max(mssopt, V_tcp_minmss);
1866
1867 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1868 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1869 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1870 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1871 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1872
1873 /* Create the IP+TCP header from scratch. */
1874 m = m_gethdr(M_NOWAIT, MT_DATA);
1875 if (m == NULL)
1876 return (ENOBUFS);
1877 #ifdef MAC
1878 mac_syncache_create_mbuf(sc->sc_label, m);
1879 #endif
1880 m->m_data += max_linkhdr;
1881 m->m_len = tlen;
1882 m->m_pkthdr.len = tlen;
1883 m->m_pkthdr.rcvif = NULL;
1884
1885 #ifdef INET6
1886 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1887 ip6 = mtod(m, struct ip6_hdr *);
1888 ip6->ip6_vfc = IPV6_VERSION;
1889 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1890 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1891 ip6->ip6_plen = htons(tlen - hlen);
1892 /* ip6_hlim is set after checksum */
1893 /* Zero out traffic class and flow label. */
1894 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1895 ip6->ip6_flow |= sc->sc_flowlabel;
1896 if (sc->sc_port != 0) {
1897 ip6->ip6_nxt = IPPROTO_UDP;
1898 udp = (struct udphdr *)(ip6 + 1);
1899 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1900 udp->uh_dport = sc->sc_port;
1901 ulen = (tlen - sizeof(struct ip6_hdr));
1902 th = (struct tcphdr *)(udp + 1);
1903 } else {
1904 ip6->ip6_nxt = IPPROTO_TCP;
1905 th = (struct tcphdr *)(ip6 + 1);
1906 }
1907 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1908 }
1909 #endif
1910 #if defined(INET6) && defined(INET)
1911 else
1912 #endif
1913 #ifdef INET
1914 {
1915 ip = mtod(m, struct ip *);
1916 ip->ip_v = IPVERSION;
1917 ip->ip_hl = sizeof(struct ip) >> 2;
1918 ip->ip_len = htons(tlen);
1919 ip->ip_id = 0;
1920 ip->ip_off = 0;
1921 ip->ip_sum = 0;
1922 ip->ip_src = sc->sc_inc.inc_laddr;
1923 ip->ip_dst = sc->sc_inc.inc_faddr;
1924 ip->ip_ttl = sc->sc_ip_ttl;
1925 ip->ip_tos = sc->sc_ip_tos;
1926
1927 /*
1928 * See if we should do MTU discovery. Route lookups are
1929 * expensive, so we will only unset the DF bit if:
1930 *
1931 * 1) path_mtu_discovery is disabled
1932 * 2) the SCF_UNREACH flag has been set
1933 */
1934 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1935 ip->ip_off |= htons(IP_DF);
1936 if (sc->sc_port == 0) {
1937 ip->ip_p = IPPROTO_TCP;
1938 th = (struct tcphdr *)(ip + 1);
1939 } else {
1940 ip->ip_p = IPPROTO_UDP;
1941 udp = (struct udphdr *)(ip + 1);
1942 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1943 udp->uh_dport = sc->sc_port;
1944 ulen = (tlen - sizeof(struct ip));
1945 th = (struct tcphdr *)(udp + 1);
1946 }
1947 }
1948 #endif /* INET */
1949 th->th_sport = sc->sc_inc.inc_lport;
1950 th->th_dport = sc->sc_inc.inc_fport;
1951
1952 if (flags & TH_SYN)
1953 th->th_seq = htonl(sc->sc_iss);
1954 else
1955 th->th_seq = htonl(sc->sc_iss + 1);
1956 th->th_ack = htonl(sc->sc_irs + 1);
1957 th->th_off = sizeof(struct tcphdr) >> 2;
1958 th->th_win = htons(sc->sc_wnd);
1959 th->th_urp = 0;
1960
1961 flags = tcp_ecn_syncache_respond(flags, sc);
1962 tcp_set_flags(th, flags);
1963
1964 /* Tack on the TCP options. */
1965 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1966 to.to_flags = 0;
1967
1968 if (flags & TH_SYN) {
1969 to.to_mss = mssopt;
1970 to.to_flags = TOF_MSS;
1971 if (sc->sc_flags & SCF_WINSCALE) {
1972 to.to_wscale = sc->sc_requested_r_scale;
1973 to.to_flags |= TOF_SCALE;
1974 }
1975 if (sc->sc_flags & SCF_SACK)
1976 to.to_flags |= TOF_SACKPERM;
1977 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1978 if (sc->sc_flags & SCF_SIGNATURE)
1979 to.to_flags |= TOF_SIGNATURE;
1980 #endif
1981 if (sc->sc_tfo_cookie) {
1982 to.to_flags |= TOF_FASTOPEN;
1983 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1984 to.to_tfo_cookie = sc->sc_tfo_cookie;
1985 /* don't send cookie again when retransmitting response */
1986 sc->sc_tfo_cookie = NULL;
1987 }
1988 }
1989 if (sc->sc_flags & SCF_TIMESTAMP) {
1990 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1991 to.to_tsecr = sc->sc_tsreflect;
1992 to.to_flags |= TOF_TS;
1993 }
1994 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1995
1996 /* Adjust headers by option size. */
1997 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1998 m->m_len += optlen;
1999 m->m_pkthdr.len += optlen;
2000 #ifdef INET6
2001 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2002 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
2003 else
2004 #endif
2005 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
2006 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
2007 if (sc->sc_flags & SCF_SIGNATURE) {
2008 KASSERT(to.to_flags & TOF_SIGNATURE,
2009 ("tcp_addoptions() didn't set tcp_signature"));
2010
2011 /* NOTE: to.to_signature is inside of mbuf */
2012 if (!TCPMD5_ENABLED() ||
2013 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
2014 m_freem(m);
2015 return (EACCES);
2016 }
2017 }
2018 #endif
2019 } else
2020 optlen = 0;
2021
2022 if (udp) {
2023 ulen += optlen;
2024 udp->uh_ulen = htons(ulen);
2025 }
2026 M_SETFIB(m, sc->sc_inc.inc_fibnum);
2027 m->m_pkthdr.flowid = sc->sc_flowid;
2028 M_HASHTYPE_SET(m, sc->sc_flowtype);
2029 #ifdef NUMA
2030 m->m_pkthdr.numa_domain = sc->sc_numa_domain;
2031 #endif
2032 #ifdef INET6
2033 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2034 if (sc->sc_port) {
2035 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2036 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2037 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2038 IPPROTO_UDP, 0);
2039 th->th_sum = htons(0);
2040 } else {
2041 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2042 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2043 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2044 IPPROTO_TCP, 0);
2045 }
2046 ip6->ip6_hlim = sc->sc_ip_ttl;
2047 #ifdef TCP_OFFLOAD
2048 if (ADDED_BY_TOE(sc)) {
2049 struct toedev *tod = sc->sc_tod;
2050
2051 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2052
2053 return (error);
2054 }
2055 #endif
2056 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2057 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2058 }
2059 #endif
2060 #if defined(INET6) && defined(INET)
2061 else
2062 #endif
2063 #ifdef INET
2064 {
2065 if (sc->sc_port) {
2066 m->m_pkthdr.csum_flags = CSUM_UDP;
2067 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2068 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2069 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2070 th->th_sum = htons(0);
2071 } else {
2072 m->m_pkthdr.csum_flags = CSUM_TCP;
2073 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2074 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2075 htons(tlen + optlen - hlen + IPPROTO_TCP));
2076 }
2077 #ifdef TCP_OFFLOAD
2078 if (ADDED_BY_TOE(sc)) {
2079 struct toedev *tod = sc->sc_tod;
2080
2081 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2082
2083 return (error);
2084 }
2085 #endif
2086 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2087 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2088 }
2089 #endif
2090 return (error);
2091 }
2092
2093 static void
syncache_send_challenge_ack(struct syncache * sc)2094 syncache_send_challenge_ack(struct syncache *sc)
2095 {
2096 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end,
2097 &sc->sc_challenge_ack_cnt)) {
2098 if (syncache_respond(sc, TH_ACK) == 0) {
2099 TCPSTAT_INC(tcps_sndacks);
2100 TCPSTAT_INC(tcps_sndtotal);
2101 }
2102 }
2103 }
2104
2105 /*
2106 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2107 * that exceed the capacity of the syncache by avoiding the storage of any
2108 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2109 * attacks where the attacker does not have access to our responses.
2110 *
2111 * Syncookies encode and include all necessary information about the
2112 * connection setup within the SYN|ACK that we send back. That way we
2113 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2114 * (if ever). Normally the syncache and syncookies are running in parallel
2115 * with the latter taking over when the former is exhausted. When matching
2116 * syncache entry is found the syncookie is ignored.
2117 *
2118 * The only reliable information persisting the 3WHS is our initial sequence
2119 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2120 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2121 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2122 * returns and signifies a legitimate connection if it matches the ACK.
2123 *
2124 * The available space of 32 bits to store the hash and to encode the SYN
2125 * option information is very tight and we should have at least 24 bits for
2126 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2127 *
2128 * SYN option information we have to encode to fully restore a connection:
2129 * MSS: is imporant to chose an optimal segment size to avoid IP level
2130 * fragmentation along the path. The common MSS values can be encoded
2131 * in a 3-bit table. Uncommon values are captured by the next lower value
2132 * in the table leading to a slight increase in packetization overhead.
2133 * WSCALE: is necessary to allow large windows to be used for high delay-
2134 * bandwidth product links. Not scaling the window when it was initially
2135 * negotiated is bad for performance as lack of scaling further decreases
2136 * the apparent available send window. We only need to encode the WSCALE
2137 * we received from the remote end. Our end can be recalculated at any
2138 * time. The common WSCALE values can be encoded in a 3-bit table.
2139 * Uncommon values are captured by the next lower value in the table
2140 * making us under-estimate the available window size halving our
2141 * theoretically possible maximum throughput for that connection.
2142 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2143 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2144 * that are included in all segments on a connection. We enable them when
2145 * the ACK has them.
2146 *
2147 * Security of syncookies and attack vectors:
2148 *
2149 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2150 * together with the gloabl secret to make it unique per connection attempt.
2151 * Thus any change of any of those parameters results in a different MAC output
2152 * in an unpredictable way unless a collision is encountered. 24 bits of the
2153 * MAC are embedded into the ISS.
2154 *
2155 * To prevent replay attacks two rotating global secrets are updated with a
2156 * new random value every 15 seconds. The life-time of a syncookie is thus
2157 * 15-30 seconds.
2158 *
2159 * Vector 1: Attacking the secret. This requires finding a weakness in the
2160 * MAC itself or the way it is used here. The attacker can do a chosen plain
2161 * text attack by varying and testing the all parameters under his control.
2162 * The strength depends on the size and randomness of the secret, and the
2163 * cryptographic security of the MAC function. Due to the constant updating
2164 * of the secret the attacker has at most 29.999 seconds to find the secret
2165 * and launch spoofed connections. After that he has to start all over again.
2166 *
2167 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2168 * size an average of 4,823 attempts are required for a 50% chance of success
2169 * to spoof a single syncookie (birthday collision paradox). However the
2170 * attacker is blind and doesn't know if one of his attempts succeeded unless
2171 * he has a side channel to interfere success from. A single connection setup
2172 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2173 * This many attempts are required for each one blind spoofed connection. For
2174 * every additional spoofed connection he has to launch another N attempts.
2175 * Thus for a sustained rate 100 spoofed connections per second approximately
2176 * 1,800,000 packets per second would have to be sent.
2177 *
2178 * NB: The MAC function should be fast so that it doesn't become a CPU
2179 * exhaustion attack vector itself.
2180 *
2181 * References:
2182 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2183 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2184 * http://cr.yp.to/syncookies.html (overview)
2185 * http://cr.yp.to/syncookies/archive (details)
2186 *
2187 *
2188 * Schematic construction of a syncookie enabled Initial Sequence Number:
2189 * 0 1 2 3
2190 * 12345678901234567890123456789012
2191 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2192 *
2193 * x 24 MAC (truncated)
2194 * W 3 Send Window Scale index
2195 * M 3 MSS index
2196 * S 1 SACK permitted
2197 * P 1 Odd/even secret
2198 */
2199
2200 /*
2201 * Distribution and probability of certain MSS values. Those in between are
2202 * rounded down to the next lower one.
2203 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2204 * .2% .3% 5% 7% 7% 20% 15% 45%
2205 */
2206 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2207
2208 /*
2209 * Distribution and probability of certain WSCALE values. We have to map the
2210 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2211 * bits based on prevalence of certain values. Where we don't have an exact
2212 * match for are rounded down to the next lower one letting us under-estimate
2213 * the true available window. At the moment this would happen only for the
2214 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2215 * and window size). The absence of the WSCALE option (no scaling in either
2216 * direction) is encoded with index zero.
2217 * [WSCALE values histograms, Allman, 2012]
2218 * X 10 10 35 5 6 14 10% by host
2219 * X 11 4 5 5 18 49 3% by connections
2220 */
2221 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2222
2223 /*
2224 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2225 * and good cryptographic properties.
2226 */
2227 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2228 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2229 uint8_t *secbits, uintptr_t secmod)
2230 {
2231 SIPHASH_CTX ctx;
2232 uint32_t siphash[2];
2233
2234 SipHash24_Init(&ctx);
2235 SipHash_SetKey(&ctx, secbits);
2236 switch (inc->inc_flags & INC_ISIPV6) {
2237 #ifdef INET
2238 case 0:
2239 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2240 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2241 break;
2242 #endif
2243 #ifdef INET6
2244 case INC_ISIPV6:
2245 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2246 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2247 break;
2248 #endif
2249 }
2250 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2251 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2252 SipHash_Update(&ctx, &irs, sizeof(irs));
2253 SipHash_Update(&ctx, &flags, sizeof(flags));
2254 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2255 SipHash_Final((u_int8_t *)&siphash, &ctx);
2256
2257 return (siphash[0] ^ siphash[1]);
2258 }
2259
2260 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2261 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2262 {
2263 u_int i, secbit, wscale;
2264 uint32_t iss, hash;
2265 uint8_t *secbits;
2266 union syncookie cookie;
2267
2268 cookie.cookie = 0;
2269
2270 /* Map our computed MSS into the 3-bit index. */
2271 for (i = nitems(tcp_sc_msstab) - 1;
2272 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2273 i--)
2274 ;
2275 cookie.flags.mss_idx = i;
2276
2277 /*
2278 * Map the send window scale into the 3-bit index but only if
2279 * the wscale option was received.
2280 */
2281 if (sc->sc_flags & SCF_WINSCALE) {
2282 wscale = sc->sc_requested_s_scale;
2283 for (i = nitems(tcp_sc_wstab) - 1;
2284 tcp_sc_wstab[i] > wscale && i > 0;
2285 i--)
2286 ;
2287 cookie.flags.wscale_idx = i;
2288 }
2289
2290 /* Can we do SACK? */
2291 if (sc->sc_flags & SCF_SACK)
2292 cookie.flags.sack_ok = 1;
2293
2294 /* Which of the two secrets to use. */
2295 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2296 cookie.flags.odd_even = secbit;
2297
2298 secbits = V_tcp_syncache.secret.key[secbit];
2299 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2300 (uintptr_t)sch);
2301
2302 /*
2303 * Put the flags into the hash and XOR them to get better ISS number
2304 * variance. This doesn't enhance the cryptographic strength and is
2305 * done to prevent the 8 cookie bits from showing up directly on the
2306 * wire.
2307 */
2308 iss = hash & ~0xff;
2309 iss |= cookie.cookie ^ (hash >> 24);
2310
2311 TCPSTAT_INC(tcps_sc_sendcookie);
2312 return (iss);
2313 }
2314
2315 static bool
syncookie_expand(struct in_conninfo * inc,const struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso,uint16_t port)2316 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch,
2317 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2318 struct socket *lso, uint16_t port)
2319 {
2320 uint32_t hash;
2321 uint8_t *secbits;
2322 tcp_seq ack, seq;
2323 int wnd;
2324 union syncookie cookie;
2325
2326 /*
2327 * Pull information out of SYN-ACK/ACK and revert sequence number
2328 * advances.
2329 */
2330 ack = th->th_ack - 1;
2331 seq = th->th_seq - 1;
2332
2333 /*
2334 * Unpack the flags containing enough information to restore the
2335 * connection.
2336 */
2337 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2338
2339 /* Which of the two secrets to use. */
2340 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2341
2342 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2343
2344 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2345 if ((ack & ~0xff) != (hash & ~0xff))
2346 return (false);
2347
2348 /* Fill in the syncache values. */
2349 sc->sc_flags = 0;
2350 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2351 sc->sc_ipopts = NULL;
2352
2353 sc->sc_irs = seq;
2354 sc->sc_iss = ack;
2355
2356 switch (inc->inc_flags & INC_ISIPV6) {
2357 #ifdef INET
2358 case 0:
2359 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2360 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2361 break;
2362 #endif
2363 #ifdef INET6
2364 case INC_ISIPV6:
2365 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2366 sc->sc_flowlabel =
2367 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2368 break;
2369 #endif
2370 }
2371
2372 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2373
2374 /* Only use wscale if it was enabled in the orignal SYN. */
2375 if (cookie.flags.wscale_idx > 0) {
2376 u_int wscale = 0;
2377
2378 /* Recompute the receive window scale that was sent earlier. */
2379 while (wscale < TCP_MAX_WINSHIFT &&
2380 (TCP_MAXWIN << wscale) < sb_max)
2381 wscale++;
2382 sc->sc_requested_r_scale = wscale;
2383 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2384 sc->sc_flags |= SCF_WINSCALE;
2385 }
2386
2387 wnd = lso->sol_sbrcv_hiwat;
2388 wnd = imax(wnd, 0);
2389 wnd = imin(wnd, TCP_MAXWIN);
2390 sc->sc_wnd = wnd;
2391
2392 if (cookie.flags.sack_ok)
2393 sc->sc_flags |= SCF_SACK;
2394
2395 if (to->to_flags & TOF_TS) {
2396 sc->sc_flags |= SCF_TIMESTAMP;
2397 sc->sc_tsreflect = to->to_tsval;
2398 sc->sc_tsoff = tcp_new_ts_offset(inc);
2399 }
2400
2401 if (to->to_flags & TOF_SIGNATURE)
2402 sc->sc_flags |= SCF_SIGNATURE;
2403
2404 sc->sc_rxmits = 0;
2405
2406 sc->sc_port = port;
2407
2408 return (true);
2409 }
2410
2411 #ifdef INVARIANTS
2412 static void
syncookie_cmp(struct in_conninfo * inc,const struct syncache_head * sch,struct syncache * sc,struct tcphdr * th,struct tcpopt * to,struct socket * lso,uint16_t port)2413 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch,
2414 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2415 struct socket *lso, uint16_t port)
2416 {
2417 struct syncache scs;
2418 char *s;
2419
2420 bzero(&scs, sizeof(scs));
2421 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) &&
2422 (sc->sc_peer_mss != scs.sc_peer_mss ||
2423 sc->sc_requested_r_scale != scs.sc_requested_r_scale ||
2424 sc->sc_requested_s_scale != scs.sc_requested_s_scale ||
2425 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) {
2426
2427 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2428 return;
2429
2430 if (sc->sc_peer_mss != scs.sc_peer_mss)
2431 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2432 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss);
2433
2434 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale)
2435 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2436 s, __func__, sc->sc_requested_r_scale,
2437 scs.sc_requested_r_scale);
2438
2439 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale)
2440 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2441 s, __func__, sc->sc_requested_s_scale,
2442 scs.sc_requested_s_scale);
2443
2444 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))
2445 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2446
2447 free(s, M_TCPLOG);
2448 }
2449 }
2450 #endif /* INVARIANTS */
2451
2452 static void
syncookie_reseed(void * arg)2453 syncookie_reseed(void *arg)
2454 {
2455 struct tcp_syncache *sc = arg;
2456 uint8_t *secbits;
2457 int secbit;
2458
2459 /*
2460 * Reseeding the secret doesn't have to be protected by a lock.
2461 * It only must be ensured that the new random values are visible
2462 * to all CPUs in a SMP environment. The atomic with release
2463 * semantics ensures that.
2464 */
2465 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2466 secbits = sc->secret.key[secbit];
2467 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2468 atomic_add_rel_int(&sc->secret.oddeven, 1);
2469
2470 /* Reschedule ourself. */
2471 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2472 }
2473
2474 /*
2475 * We have overflowed a bucket. Let's pause dealing with the syncache.
2476 * This function will increment the bucketoverflow statistics appropriately
2477 * (once per pause when pausing is enabled; otherwise, once per overflow).
2478 */
2479 static void
syncache_pause(struct in_conninfo * inc)2480 syncache_pause(struct in_conninfo *inc)
2481 {
2482 time_t delta;
2483 const char *s;
2484
2485 /* XXX:
2486 * 2. Add sysctl read here so we don't get the benefit of this
2487 * change without the new sysctl.
2488 */
2489
2490 /*
2491 * Try an unlocked read. If we already know that another thread
2492 * has activated the feature, there is no need to proceed.
2493 */
2494 if (V_tcp_syncache.paused)
2495 return;
2496
2497 /* Are cookied enabled? If not, we can't pause. */
2498 if (!V_tcp_syncookies) {
2499 TCPSTAT_INC(tcps_sc_bucketoverflow);
2500 return;
2501 }
2502
2503 /*
2504 * We may be the first thread to find an overflow. Get the lock
2505 * and evaluate if we need to take action.
2506 */
2507 mtx_lock(&V_tcp_syncache.pause_mtx);
2508 if (V_tcp_syncache.paused) {
2509 mtx_unlock(&V_tcp_syncache.pause_mtx);
2510 return;
2511 }
2512
2513 /* Activate protection. */
2514 V_tcp_syncache.paused = true;
2515 TCPSTAT_INC(tcps_sc_bucketoverflow);
2516
2517 /*
2518 * Determine the last backoff time. If we are seeing a re-newed
2519 * attack within that same time after last reactivating the syncache,
2520 * consider it an extension of the same attack.
2521 */
2522 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2523 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2524 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2525 delta <<= 1;
2526 V_tcp_syncache.pause_backoff++;
2527 }
2528 } else {
2529 delta = TCP_SYNCACHE_PAUSE_TIME;
2530 V_tcp_syncache.pause_backoff = 0;
2531 }
2532
2533 /* Log a warning, including IP addresses, if able. */
2534 if (inc != NULL)
2535 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2536 else
2537 s = (const char *)NULL;
2538 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2539 "the next %lld seconds%s%s%s\n", (long long)delta,
2540 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2541 (s != NULL) ? ")" : "");
2542 free(__DECONST(void *, s), M_TCPLOG);
2543
2544 /* Use the calculated delta to set a new pause time. */
2545 V_tcp_syncache.pause_until = time_uptime + delta;
2546 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2547 &V_tcp_syncache);
2548 mtx_unlock(&V_tcp_syncache.pause_mtx);
2549 }
2550
2551 /* Evaluate whether we need to unpause. */
2552 static void
syncache_unpause(void * arg)2553 syncache_unpause(void *arg)
2554 {
2555 struct tcp_syncache *sc;
2556 time_t delta;
2557
2558 sc = arg;
2559 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2560 callout_deactivate(&sc->pause_co);
2561
2562 /*
2563 * Check to make sure we are not running early. If the pause
2564 * time has expired, then deactivate the protection.
2565 */
2566 if ((delta = sc->pause_until - time_uptime) > 0)
2567 callout_schedule(&sc->pause_co, delta * hz);
2568 else
2569 sc->paused = false;
2570 }
2571
2572 /*
2573 * Exports the syncache entries to userland so that netstat can display
2574 * them alongside the other sockets. This function is intended to be
2575 * called only from tcp_pcblist.
2576 *
2577 * Due to concurrency on an active system, the number of pcbs exported
2578 * may have no relation to max_pcbs. max_pcbs merely indicates the
2579 * amount of space the caller allocated for this function to use.
2580 */
2581 int
syncache_pcblist(struct sysctl_req * req)2582 syncache_pcblist(struct sysctl_req *req)
2583 {
2584 struct xtcpcb xt;
2585 struct syncache *sc;
2586 struct syncache_head *sch;
2587 int error, i;
2588
2589 bzero(&xt, sizeof(xt));
2590 xt.xt_len = sizeof(xt);
2591 xt.t_state = TCPS_SYN_RECEIVED;
2592 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2593 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2594 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2595 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2596
2597 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2598 sch = &V_tcp_syncache.hashbase[i];
2599 SCH_LOCK(sch);
2600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2601 if (sc->sc_cred != NULL &&
2602 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2603 continue;
2604 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2605 xt.xt_inp.inp_vflag = INP_IPV6;
2606 else
2607 xt.xt_inp.inp_vflag = INP_IPV4;
2608 xt.xt_encaps_port = sc->sc_port;
2609 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2610 sizeof (struct in_conninfo));
2611 error = SYSCTL_OUT(req, &xt, sizeof xt);
2612 if (error) {
2613 SCH_UNLOCK(sch);
2614 return (0);
2615 }
2616 }
2617 SCH_UNLOCK(sch);
2618 }
2619
2620 return (0);
2621 }
2622