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 <sys/cdefs.h>
36 #include "opt_inet.h"
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/hash.h>
43 #include <sys/refcount.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/limits.h>
47 #include <sys/lock.h>
48 #include <sys/mutex.h>
49 #include <sys/malloc.h>
50 #include <sys/mbuf.h>
51 #include <sys/proc.h> /* for proc0 declaration */
52 #include <sys/random.h>
53 #include <sys/socket.h>
54 #include <sys/socketvar.h>
55 #include <sys/syslog.h>
56 #include <sys/ucred.h>
57
58 #include <sys/md5.h>
59 #include <crypto/siphash/siphash.h>
60
61 #include <vm/uma.h>
62
63 #include <net/if.h>
64 #include <net/if_var.h>
65 #include <net/route.h>
66 #include <net/vnet.h>
67
68 #include <netinet/in.h>
69 #include <netinet/in_kdtrace.h>
70 #include <netinet/in_systm.h>
71 #include <netinet/ip.h>
72 #include <netinet/in_var.h>
73 #include <netinet/in_pcb.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 #endif
83 #include <netinet/tcp.h>
84 #include <netinet/tcp_fastopen.h>
85 #include <netinet/tcp_fsm.h>
86 #include <netinet/tcp_seq.h>
87 #include <netinet/tcp_timer.h>
88 #include <netinet/tcp_var.h>
89 #include <netinet/tcp_syncache.h>
90 #include <netinet/tcp_ecn.h>
91 #ifdef TCP_BLACKBOX
92 #include <netinet/tcp_log_buf.h>
93 #endif
94 #ifdef TCP_OFFLOAD
95 #include <netinet/toecore.h>
96 #endif
97 #include <netinet/udp.h>
98
99 #include <netipsec/ipsec_support.h>
100
101 #include <machine/in_cksum.h>
102
103 #include <security/mac/mac_framework.h>
104
105 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true;
106 #define V_tcp_syncookies VNET(tcp_syncookies)
107 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
108 &VNET_NAME(tcp_syncookies), 0,
109 "Use TCP SYN cookies if the syncache overflows");
110
111 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false;
112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
113 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookiesonly), 0,
115 "Use only TCP SYN cookies");
116
117 #ifdef TCP_OFFLOAD
118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
119 #endif
120
121 static void syncache_drop(struct syncache *, struct syncache_head *);
122 static void syncache_free(struct syncache *);
123 static void syncache_insert(struct syncache *, struct syncache_head *);
124 static int syncache_respond(struct syncache *, const struct mbuf *, int);
125 static void syncache_send_challenge_ack(struct syncache *, struct mbuf *);
126 static struct socket *syncache_socket(struct syncache *, struct socket *,
127 struct mbuf *m);
128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
129 int docallout);
130 static void syncache_timer(void *);
131
132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
133 uint8_t *, uintptr_t);
134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
135 static bool syncookie_expand(struct in_conninfo *,
136 const struct syncache_head *, struct syncache *,
137 struct tcphdr *, struct tcpopt *, struct socket *,
138 uint16_t);
139 static void syncache_pause(struct in_conninfo *);
140 static void syncache_unpause(void *);
141 static void syncookie_reseed(void *);
142 #ifdef INVARIANTS
143 static void syncookie_cmp(struct in_conninfo *,
144 const struct syncache_head *, struct syncache *,
145 struct tcphdr *, struct tcpopt *, struct socket *,
146 uint16_t);
147 #endif
148
149 /*
150 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
151 * 3 retransmits corresponds to a timeout with default values of
152 * tcp_rexmit_initial * ( 1 +
153 * tcp_backoff[1] +
154 * tcp_backoff[2] +
155 * tcp_backoff[3]) + 3 * tcp_rexmit_slop,
156 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms,
157 * the odds are that the user has given up attempting to connect by then.
158 */
159 #define SYNCACHE_MAXREXMTS 3
160
161 /* Arbitrary values */
162 #define TCP_SYNCACHE_HASHSIZE 512
163 #define TCP_SYNCACHE_BUCKETLIMIT 30
164
165 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache);
166 #define V_tcp_syncache VNET(tcp_syncache)
167
168 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache,
169 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
170 "TCP SYN cache");
171
172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
173 &VNET_NAME(tcp_syncache.bucket_limit), 0,
174 "Per-bucket hash limit for syncache");
175
176 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
177 &VNET_NAME(tcp_syncache.cache_limit), 0,
178 "Overall entry limit for syncache");
179
180 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
181 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
182
183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
184 &VNET_NAME(tcp_syncache.hashsize), 0,
185 "Size of TCP syncache hashtable");
186
187 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET |
188 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0,
189 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) "
190 "and mac(4) checks");
191
192 static int
sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)193 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS)
194 {
195 int error;
196 u_int new;
197
198 new = V_tcp_syncache.rexmt_limit;
199 error = sysctl_handle_int(oidp, &new, 0, req);
200 if ((error == 0) && (req->newptr != NULL)) {
201 if (new > TCP_MAXRXTSHIFT)
202 error = EINVAL;
203 else
204 V_tcp_syncache.rexmt_limit = new;
205 }
206 return (error);
207 }
208
209 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit,
210 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
211 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
212 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU",
213 "Limit on SYN/ACK retransmissions");
214
215 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
216 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
217 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
218 "Send reset on socket allocation failure");
219
220 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
221
222 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
223 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
224 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
225
226 /*
227 * Requires the syncache entry to be already removed from the bucket list.
228 */
229 static void
syncache_free(struct syncache * sc)230 syncache_free(struct syncache *sc)
231 {
232
233 if (sc->sc_ipopts)
234 (void)m_free(sc->sc_ipopts);
235 if (sc->sc_cred)
236 crfree(sc->sc_cred);
237 #ifdef MAC
238 mac_syncache_destroy(&sc->sc_label);
239 #endif
240
241 uma_zfree(V_tcp_syncache.zone, sc);
242 }
243
244 void
syncache_init(void)245 syncache_init(void)
246 {
247 int i;
248
249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
250 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
251 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
252 V_tcp_syncache.hash_secret = arc4random();
253
254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
255 &V_tcp_syncache.hashsize);
256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
257 &V_tcp_syncache.bucket_limit);
258 if (!powerof2(V_tcp_syncache.hashsize) ||
259 V_tcp_syncache.hashsize == 0) {
260 printf("WARNING: syncache hash size is not a power of 2.\n");
261 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
262 }
263 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
264
265 /* Set limits. */
266 V_tcp_syncache.cache_limit =
267 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
268 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
269 &V_tcp_syncache.cache_limit);
270
271 /* Allocate the hash table. */
272 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
273 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
274
275 #ifdef VIMAGE
276 V_tcp_syncache.vnet = curvnet;
277 #endif
278
279 /* Initialize the hash buckets. */
280 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
281 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
282 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
283 NULL, MTX_DEF);
284 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
285 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
286 V_tcp_syncache.hashbase[i].sch_length = 0;
287 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
288 V_tcp_syncache.hashbase[i].sch_last_overflow =
289 -(SYNCOOKIE_LIFETIME + 1);
290 }
291
292 /* Create the syncache entry zone. */
293 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
294 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
295 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
296 V_tcp_syncache.cache_limit);
297
298 /* Start the SYN cookie reseeder callout. */
299 callout_init(&V_tcp_syncache.secret.reseed, 1);
300 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
301 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
302 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
303 syncookie_reseed, &V_tcp_syncache);
304
305 /* Initialize the pause machinery. */
306 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF);
307 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx,
308 0);
309 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME;
310 V_tcp_syncache.pause_backoff = 0;
311 V_tcp_syncache.paused = false;
312 }
313
314 #ifdef VIMAGE
315 void
syncache_destroy(void)316 syncache_destroy(void)
317 {
318 struct syncache_head *sch;
319 struct syncache *sc, *nsc;
320 int i;
321
322 /*
323 * Stop the re-seed timer before freeing resources. No need to
324 * possibly schedule it another time.
325 */
326 callout_drain(&V_tcp_syncache.secret.reseed);
327
328 /* Stop the SYN cache pause callout. */
329 mtx_lock(&V_tcp_syncache.pause_mtx);
330 if (callout_stop(&V_tcp_syncache.pause_co) == 0) {
331 mtx_unlock(&V_tcp_syncache.pause_mtx);
332 callout_drain(&V_tcp_syncache.pause_co);
333 } else
334 mtx_unlock(&V_tcp_syncache.pause_mtx);
335
336 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
337 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
338 sch = &V_tcp_syncache.hashbase[i];
339 callout_drain(&sch->sch_timer);
340
341 SCH_LOCK(sch);
342 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
343 syncache_drop(sc, sch);
344 SCH_UNLOCK(sch);
345 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
346 ("%s: sch->sch_bucket not empty", __func__));
347 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
348 __func__, sch->sch_length));
349 mtx_destroy(&sch->sch_mtx);
350 }
351
352 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
353 ("%s: cache_count not 0", __func__));
354
355 /* Free the allocated global resources. */
356 uma_zdestroy(V_tcp_syncache.zone);
357 free(V_tcp_syncache.hashbase, M_SYNCACHE);
358 mtx_destroy(&V_tcp_syncache.pause_mtx);
359 }
360 #endif
361
362 /*
363 * Inserts a syncache entry into the specified bucket row.
364 * Locks and unlocks the syncache_head autonomously.
365 */
366 static void
syncache_insert(struct syncache * sc,struct syncache_head * sch)367 syncache_insert(struct syncache *sc, struct syncache_head *sch)
368 {
369 struct syncache *sc2;
370
371 SCH_LOCK(sch);
372
373 /*
374 * Make sure that we don't overflow the per-bucket limit.
375 * If the bucket is full, toss the oldest element.
376 */
377 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
378 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
379 ("sch->sch_length incorrect"));
380 syncache_pause(&sc->sc_inc);
381 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
382 sch->sch_last_overflow = time_uptime;
383 syncache_drop(sc2, sch);
384 }
385
386 /* Put it into the bucket. */
387 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
388 sch->sch_length++;
389
390 #ifdef TCP_OFFLOAD
391 if (ADDED_BY_TOE(sc)) {
392 struct toedev *tod = sc->sc_tod;
393
394 tod->tod_syncache_added(tod, sc->sc_todctx);
395 }
396 #endif
397
398 /* Reinitialize the bucket row's timer. */
399 if (sch->sch_length == 1)
400 sch->sch_nextc = ticks + INT_MAX;
401 syncache_timeout(sc, sch, 1);
402
403 SCH_UNLOCK(sch);
404
405 TCPSTATES_INC(TCPS_SYN_RECEIVED);
406 TCPSTAT_INC(tcps_sc_added);
407 }
408
409 /*
410 * Remove and free entry from syncache bucket row.
411 * Expects locked syncache head.
412 */
413 static void
syncache_drop(struct syncache * sc,struct syncache_head * sch)414 syncache_drop(struct syncache *sc, struct syncache_head *sch)
415 {
416
417 SCH_LOCK_ASSERT(sch);
418
419 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
420 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
421 sch->sch_length--;
422
423 #ifdef TCP_OFFLOAD
424 if (ADDED_BY_TOE(sc)) {
425 struct toedev *tod = sc->sc_tod;
426
427 tod->tod_syncache_removed(tod, sc->sc_todctx);
428 }
429 #endif
430
431 syncache_free(sc);
432 }
433
434 /*
435 * Engage/reengage time on bucket row.
436 */
437 static void
syncache_timeout(struct syncache * sc,struct syncache_head * sch,int docallout)438 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
439 {
440 int rexmt;
441
442 if (sc->sc_rxmits == 0)
443 rexmt = tcp_rexmit_initial;
444 else
445 TCPT_RANGESET(rexmt,
446 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
447 tcp_rexmit_min, tcp_rexmit_max);
448 sc->sc_rxttime = ticks + rexmt;
449 sc->sc_rxmits++;
450 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
451 sch->sch_nextc = sc->sc_rxttime;
452 if (docallout)
453 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
454 syncache_timer, (void *)sch);
455 }
456 }
457
458 /*
459 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
460 * If we have retransmitted an entry the maximum number of times, expire it.
461 * One separate timer for each bucket row.
462 */
463 static void
syncache_timer(void * xsch)464 syncache_timer(void *xsch)
465 {
466 struct syncache_head *sch = (struct syncache_head *)xsch;
467 struct syncache *sc, *nsc;
468 struct epoch_tracker et;
469 int tick = ticks;
470 char *s;
471 bool paused;
472
473 CURVNET_SET(sch->sch_sc->vnet);
474
475 /* NB: syncache_head has already been locked by the callout. */
476 SCH_LOCK_ASSERT(sch);
477
478 /*
479 * In the following cycle we may remove some entries and/or
480 * advance some timeouts, so re-initialize the bucket timer.
481 */
482 sch->sch_nextc = tick + INT_MAX;
483
484 /*
485 * If we have paused processing, unconditionally remove
486 * all syncache entries.
487 */
488 mtx_lock(&V_tcp_syncache.pause_mtx);
489 paused = V_tcp_syncache.paused;
490 mtx_unlock(&V_tcp_syncache.pause_mtx);
491
492 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
493 if (paused) {
494 syncache_drop(sc, sch);
495 continue;
496 }
497 /*
498 * We do not check if the listen socket still exists
499 * and accept the case where the listen socket may be
500 * gone by the time we resend the SYN/ACK. We do
501 * not expect this to happens often. If it does,
502 * then the RST will be sent by the time the remote
503 * host does the SYN/ACK->ACK.
504 */
505 if (TSTMP_GT(sc->sc_rxttime, tick)) {
506 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
507 sch->sch_nextc = sc->sc_rxttime;
508 continue;
509 }
510 if (sc->sc_rxmits > V_tcp_ecn_maxretries) {
511 sc->sc_flags &= ~SCF_ECN_MASK;
512 }
513 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
514 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
515 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
516 "giving up and removing syncache entry\n",
517 s, __func__);
518 free(s, M_TCPLOG);
519 }
520 syncache_drop(sc, sch);
521 TCPSTAT_INC(tcps_sc_stale);
522 continue;
523 }
524 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
525 log(LOG_DEBUG, "%s; %s: Response timeout, "
526 "retransmitting (%u) SYN|ACK\n",
527 s, __func__, sc->sc_rxmits);
528 free(s, M_TCPLOG);
529 }
530
531 NET_EPOCH_ENTER(et);
532 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) {
533 syncache_timeout(sc, sch, 0);
534 TCPSTAT_INC(tcps_sndacks);
535 TCPSTAT_INC(tcps_sndtotal);
536 TCPSTAT_INC(tcps_sc_retransmitted);
537 } else {
538 syncache_drop(sc, sch);
539 TCPSTAT_INC(tcps_sc_dropped);
540 }
541 NET_EPOCH_EXIT(et);
542 }
543 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
544 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
545 syncache_timer, (void *)(sch));
546 CURVNET_RESTORE();
547 }
548
549 /*
550 * Returns true if the system is only using cookies at the moment.
551 * This could be due to a sysadmin decision to only use cookies, or it
552 * could be due to the system detecting an attack.
553 */
554 static inline bool
syncache_cookiesonly(void)555 syncache_cookiesonly(void)
556 {
557 return ((V_tcp_syncookies && V_tcp_syncache.paused) ||
558 V_tcp_syncookiesonly);
559 }
560
561 /*
562 * Find the hash bucket for the given connection.
563 */
564 static struct syncache_head *
syncache_hashbucket(struct in_conninfo * inc)565 syncache_hashbucket(struct in_conninfo *inc)
566 {
567 uint32_t hash;
568
569 /*
570 * The hash is built on foreign port + local port + foreign address.
571 * We rely on the fact that struct in_conninfo starts with 16 bits
572 * of foreign port, then 16 bits of local port then followed by 128
573 * bits of foreign address. In case of IPv4 address, the first 3
574 * 32-bit words of the address always are zeroes.
575 */
576 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
577 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
578
579 return (&V_tcp_syncache.hashbase[hash]);
580 }
581
582 /*
583 * Find an entry in the syncache.
584 * Returns always with locked syncache_head plus a matching entry or NULL.
585 */
586 static struct syncache *
syncache_lookup(struct in_conninfo * inc,struct syncache_head ** schp)587 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
588 {
589 struct syncache *sc;
590 struct syncache_head *sch;
591
592 *schp = sch = syncache_hashbucket(inc);
593 SCH_LOCK(sch);
594
595 /* Circle through bucket row to find matching entry. */
596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
597 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
598 sizeof(struct in_endpoints)) == 0)
599 break;
600
601 return (sc); /* Always returns with locked sch. */
602 }
603
604 /*
605 * This function is called when we get a RST for a
606 * non-existent connection, so that we can see if the
607 * connection is in the syn cache. If it is, zap it.
608 * If required send a challenge ACK.
609 */
610 void
syncache_chkrst(struct in_conninfo * inc,struct tcphdr * th,struct mbuf * m,uint16_t port)611 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m,
612 uint16_t port)
613 {
614 struct syncache *sc;
615 struct syncache_head *sch;
616 char *s = NULL;
617
618 if (syncache_cookiesonly())
619 return;
620 sc = syncache_lookup(inc, &sch); /* returns locked sch */
621 SCH_LOCK_ASSERT(sch);
622
623 /*
624 * No corresponding connection was found in syncache.
625 * If syncookies are enabled and possibly exclusively
626 * used, or we are under memory pressure, a valid RST
627 * may not find a syncache entry. In that case we're
628 * done and no SYN|ACK retransmissions will happen.
629 * Otherwise the RST was misdirected or spoofed.
630 */
631 if (sc == NULL) {
632 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
633 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
634 "syncache entry (possibly syncookie only), "
635 "segment ignored\n", s, __func__);
636 TCPSTAT_INC(tcps_badrst);
637 goto done;
638 }
639
640 /* The remote UDP encaps port does not match. */
641 if (sc->sc_port != port) {
642 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
643 log(LOG_DEBUG, "%s; %s: Spurious RST with matching "
644 "syncache entry but non-matching UDP encaps port, "
645 "segment ignored\n", s, __func__);
646 TCPSTAT_INC(tcps_badrst);
647 goto done;
648 }
649
650 /*
651 * If the RST bit is set, check the sequence number to see
652 * if this is a valid reset segment.
653 *
654 * RFC 793 page 37:
655 * In all states except SYN-SENT, all reset (RST) segments
656 * are validated by checking their SEQ-fields. A reset is
657 * valid if its sequence number is in the window.
658 *
659 * RFC 793 page 69:
660 * There are four cases for the acceptability test for an incoming
661 * segment:
662 *
663 * Segment Receive Test
664 * Length Window
665 * ------- ------- -------------------------------------------
666 * 0 0 SEG.SEQ = RCV.NXT
667 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
668 * >0 0 not acceptable
669 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
670 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
671 *
672 * Note that when receiving a SYN segment in the LISTEN state,
673 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
674 * described in RFC 793, page 66.
675 */
676 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
677 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
678 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) {
679 if (V_tcp_insecure_rst ||
680 th->th_seq == sc->sc_irs + 1) {
681 syncache_drop(sc, sch);
682 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
683 log(LOG_DEBUG,
684 "%s; %s: Our SYN|ACK was rejected, "
685 "connection attempt aborted by remote "
686 "endpoint\n",
687 s, __func__);
688 TCPSTAT_INC(tcps_sc_reset);
689 } else {
690 TCPSTAT_INC(tcps_badrst);
691 /* Send challenge ACK. */
692 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
693 log(LOG_DEBUG, "%s; %s: RST with invalid "
694 " SEQ %u != NXT %u (+WND %u), "
695 "sending challenge ACK\n",
696 s, __func__,
697 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
698 syncache_send_challenge_ack(sc, m);
699 }
700 } else {
701 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
702 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
703 "NXT %u (+WND %u), segment ignored\n",
704 s, __func__,
705 th->th_seq, sc->sc_irs + 1, sc->sc_wnd);
706 TCPSTAT_INC(tcps_badrst);
707 }
708
709 done:
710 if (s != NULL)
711 free(s, M_TCPLOG);
712 SCH_UNLOCK(sch);
713 }
714
715 void
syncache_badack(struct in_conninfo * inc,uint16_t port)716 syncache_badack(struct in_conninfo *inc, uint16_t port)
717 {
718 struct syncache *sc;
719 struct syncache_head *sch;
720
721 if (syncache_cookiesonly())
722 return;
723 sc = syncache_lookup(inc, &sch); /* returns locked sch */
724 SCH_LOCK_ASSERT(sch);
725 if ((sc != NULL) && (sc->sc_port == port)) {
726 syncache_drop(sc, sch);
727 TCPSTAT_INC(tcps_sc_badack);
728 }
729 SCH_UNLOCK(sch);
730 }
731
732 void
syncache_unreach(struct in_conninfo * inc,tcp_seq th_seq,uint16_t port)733 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port)
734 {
735 struct syncache *sc;
736 struct syncache_head *sch;
737
738 if (syncache_cookiesonly())
739 return;
740 sc = syncache_lookup(inc, &sch); /* returns locked sch */
741 SCH_LOCK_ASSERT(sch);
742 if (sc == NULL)
743 goto done;
744
745 /* If the port != sc_port, then it's a bogus ICMP msg */
746 if (port != sc->sc_port)
747 goto done;
748
749 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
750 if (ntohl(th_seq) != sc->sc_iss)
751 goto done;
752
753 /*
754 * If we've rertransmitted 3 times and this is our second error,
755 * we remove the entry. Otherwise, we allow it to continue on.
756 * This prevents us from incorrectly nuking an entry during a
757 * spurious network outage.
758 *
759 * See tcp_notify().
760 */
761 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
762 sc->sc_flags |= SCF_UNREACH;
763 goto done;
764 }
765 syncache_drop(sc, sch);
766 TCPSTAT_INC(tcps_sc_unreach);
767 done:
768 SCH_UNLOCK(sch);
769 }
770
771 /*
772 * Build a new TCP socket structure from a syncache entry.
773 *
774 * On success return the newly created socket with its underlying inp locked.
775 */
776 static struct socket *
syncache_socket(struct syncache * sc,struct socket * lso,struct mbuf * m)777 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
778 {
779 struct inpcb *inp = NULL;
780 struct socket *so;
781 struct tcpcb *tp;
782 int error;
783 char *s;
784
785 NET_EPOCH_ASSERT();
786
787 /*
788 * Ok, create the full blown connection, and set things up
789 * as they would have been set up if we had created the
790 * connection when the SYN arrived.
791 */
792 if ((so = solisten_clone(lso)) == NULL)
793 goto allocfail;
794 #ifdef MAC
795 mac_socketpeer_set_from_mbuf(m, so);
796 #endif
797 error = in_pcballoc(so, &V_tcbinfo);
798 if (error) {
799 sodealloc(so);
800 goto allocfail;
801 }
802 inp = sotoinpcb(so);
803 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) {
804 in_pcbfree(inp);
805 sodealloc(so);
806 goto allocfail;
807 }
808 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
809 #ifdef INET6
810 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
811 inp->inp_vflag &= ~INP_IPV4;
812 inp->inp_vflag |= INP_IPV6;
813 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
814 } else {
815 inp->inp_vflag &= ~INP_IPV6;
816 inp->inp_vflag |= INP_IPV4;
817 #endif
818 inp->inp_ip_ttl = sc->sc_ip_ttl;
819 inp->inp_ip_tos = sc->sc_ip_tos;
820 inp->inp_laddr = sc->sc_inc.inc_laddr;
821 #ifdef INET6
822 }
823 #endif
824
825 /*
826 * If there's an mbuf and it has a flowid, then let's initialise the
827 * inp with that particular flowid.
828 */
829 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
830 inp->inp_flowid = m->m_pkthdr.flowid;
831 inp->inp_flowtype = M_HASHTYPE_GET(m);
832 #ifdef NUMA
833 inp->inp_numa_domain = m->m_pkthdr.numa_domain;
834 #endif
835 }
836
837 inp->inp_lport = sc->sc_inc.inc_lport;
838 #ifdef INET6
839 if (inp->inp_vflag & INP_IPV6PROTO) {
840 struct inpcb *oinp = sotoinpcb(lso);
841
842 /*
843 * Inherit socket options from the listening socket.
844 * Note that in6p_inputopts are not (and should not be)
845 * copied, since it stores previously received options and is
846 * used to detect if each new option is different than the
847 * previous one and hence should be passed to a user.
848 * If we copied in6p_inputopts, a user would not be able to
849 * receive options just after calling the accept system call.
850 */
851 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
852 if (oinp->in6p_outputopts)
853 inp->in6p_outputopts =
854 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
855 inp->in6p_hops = oinp->in6p_hops;
856 }
857
858 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
859 struct sockaddr_in6 sin6;
860
861 sin6.sin6_family = AF_INET6;
862 sin6.sin6_len = sizeof(sin6);
863 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
864 sin6.sin6_port = sc->sc_inc.inc_fport;
865 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
866 INP_HASH_WLOCK(&V_tcbinfo);
867 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false);
868 INP_HASH_WUNLOCK(&V_tcbinfo);
869 if (error != 0)
870 goto abort;
871 /* Override flowlabel from in6_pcbconnect. */
872 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
873 inp->inp_flow |= sc->sc_flowlabel;
874 }
875 #endif /* INET6 */
876 #if defined(INET) && defined(INET6)
877 else
878 #endif
879 #ifdef INET
880 {
881 struct sockaddr_in sin;
882
883 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
884
885 if (inp->inp_options == NULL) {
886 inp->inp_options = sc->sc_ipopts;
887 sc->sc_ipopts = NULL;
888 }
889
890 sin.sin_family = AF_INET;
891 sin.sin_len = sizeof(sin);
892 sin.sin_addr = sc->sc_inc.inc_faddr;
893 sin.sin_port = sc->sc_inc.inc_fport;
894 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
895 INP_HASH_WLOCK(&V_tcbinfo);
896 error = in_pcbconnect(inp, &sin, thread0.td_ucred);
897 INP_HASH_WUNLOCK(&V_tcbinfo);
898 if (error != 0)
899 goto abort;
900 }
901 #endif /* INET */
902 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
903 /* Copy old policy into new socket's. */
904 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
905 printf("syncache_socket: could not copy policy\n");
906 #endif
907 tp->t_state = TCPS_SYN_RECEIVED;
908 tp->iss = sc->sc_iss;
909 tp->irs = sc->sc_irs;
910 tp->t_port = sc->sc_port;
911 tcp_rcvseqinit(tp);
912 tcp_sendseqinit(tp);
913 tp->snd_wl1 = sc->sc_irs;
914 tp->snd_max = tp->iss + 1;
915 tp->snd_nxt = tp->iss + 1;
916 tp->rcv_up = sc->sc_irs + 1;
917 tp->rcv_wnd = sc->sc_wnd;
918 tp->rcv_adv += tp->rcv_wnd;
919 tp->last_ack_sent = tp->rcv_nxt;
920
921 tp->t_flags = sototcpcb(lso)->t_flags &
922 (TF_LRD|TF_NOPUSH|TF_NODELAY);
923 if (sc->sc_flags & SCF_NOOPT)
924 tp->t_flags |= TF_NOOPT;
925 else {
926 if (sc->sc_flags & SCF_WINSCALE) {
927 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
928 tp->snd_scale = sc->sc_requested_s_scale;
929 tp->request_r_scale = sc->sc_requested_r_scale;
930 }
931 if (sc->sc_flags & SCF_TIMESTAMP) {
932 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
933 tp->ts_recent = sc->sc_tsreflect;
934 tp->ts_recent_age = tcp_ts_getticks();
935 tp->ts_offset = sc->sc_tsoff;
936 }
937 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
938 if (sc->sc_flags & SCF_SIGNATURE)
939 tp->t_flags |= TF_SIGNATURE;
940 #endif
941 if (sc->sc_flags & SCF_SACK)
942 tp->t_flags |= TF_SACK_PERMIT;
943 }
944
945 tcp_ecn_syncache_socket(tp, sc);
946
947 /*
948 * Set up MSS and get cached values from tcp_hostcache.
949 * This might overwrite some of the defaults we just set.
950 */
951 tcp_mss(tp, sc->sc_peer_mss);
952
953 /*
954 * If the SYN,ACK was retransmitted, indicate that CWND to be
955 * limited to one segment in cc_conn_init().
956 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
957 */
958 if (sc->sc_rxmits > 1)
959 tp->snd_cwnd = 1;
960
961 /* Copy over the challenge ACK state. */
962 tp->t_challenge_ack_end = sc->sc_challenge_ack_end;
963 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt;
964
965 #ifdef TCP_OFFLOAD
966 /*
967 * Allow a TOE driver to install its hooks. Note that we hold the
968 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
969 * new connection before the TOE driver has done its thing.
970 */
971 if (ADDED_BY_TOE(sc)) {
972 struct toedev *tod = sc->sc_tod;
973
974 tod->tod_offload_socket(tod, sc->sc_todctx, so);
975 }
976 #endif
977 #ifdef TCP_BLACKBOX
978 /*
979 * Inherit the log state from the listening socket, if
980 * - the log state of the listening socket is not off and
981 * - the listening socket was not auto selected from all sessions and
982 * - a log id is not set on the listening socket.
983 * This avoids inheriting a log state which was automatically set.
984 */
985 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) &&
986 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) &&
987 (sototcpcb(lso)->t_lib == NULL)) {
988 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso)));
989 }
990 #endif
991 /*
992 * Copy and activate timers.
993 */
994 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime;
995 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
996 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
997 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
998 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
999 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
1000
1001 TCPSTAT_INC(tcps_accepts);
1002 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN);
1003
1004 if (!solisten_enqueue(so, SS_ISCONNECTED))
1005 tp->t_flags |= TF_SONOTCONN;
1006 /* Can we inherit anything from the listener? */
1007 if (tp->t_fb->tfb_inherit != NULL) {
1008 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso));
1009 }
1010 return (so);
1011
1012 allocfail:
1013 /*
1014 * Drop the connection; we will either send a RST or have the peer
1015 * retransmit its SYN again after its RTO and try again.
1016 */
1017 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1018 log(LOG_DEBUG, "%s; %s: Socket create failed "
1019 "due to limits or memory shortage\n",
1020 s, __func__);
1021 free(s, M_TCPLOG);
1022 }
1023 TCPSTAT_INC(tcps_listendrop);
1024 return (NULL);
1025
1026 abort:
1027 tcp_discardcb(tp);
1028 in_pcbfree(inp);
1029 sodealloc(so);
1030 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
1031 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n",
1032 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "",
1033 error);
1034 free(s, M_TCPLOG);
1035 }
1036 TCPSTAT_INC(tcps_listendrop);
1037 return (NULL);
1038 }
1039
1040 /*
1041 * This function gets called when we receive an ACK for a
1042 * socket in the LISTEN state. We look up the connection
1043 * in the syncache, and if its there, we pull it out of
1044 * the cache and turn it into a full-blown connection in
1045 * the SYN-RECEIVED state.
1046 *
1047 * On syncache_socket() success the newly created socket
1048 * has its underlying inp locked.
1049 */
1050 int
syncache_expand(struct in_conninfo * inc,struct tcpopt * to,struct tcphdr * th,struct socket ** lsop,struct mbuf * m,uint16_t port)1051 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1052 struct socket **lsop, struct mbuf *m, uint16_t port)
1053 {
1054 struct syncache *sc;
1055 struct syncache_head *sch;
1056 struct syncache scs;
1057 char *s;
1058 bool locked;
1059
1060 NET_EPOCH_ASSERT();
1061 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
1062 ("%s: can handle only ACK", __func__));
1063
1064 if (syncache_cookiesonly()) {
1065 sc = NULL;
1066 sch = syncache_hashbucket(inc);
1067 locked = false;
1068 } else {
1069 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1070 locked = true;
1071 SCH_LOCK_ASSERT(sch);
1072 }
1073
1074 #ifdef INVARIANTS
1075 /*
1076 * Test code for syncookies comparing the syncache stored
1077 * values with the reconstructed values from the cookie.
1078 */
1079 if (sc != NULL)
1080 syncookie_cmp(inc, sch, sc, th, to, *lsop, port);
1081 #endif
1082
1083 if (sc == NULL) {
1084 if (locked) {
1085 /*
1086 * The syncache is currently in use (neither disabled,
1087 * nor paused), but no entry was found.
1088 */
1089 if (!V_tcp_syncookies) {
1090 /*
1091 * Since no syncookies are used in case of
1092 * a bucket overflow, don't even check for
1093 * a valid syncookie.
1094 */
1095 SCH_UNLOCK(sch);
1096 TCPSTAT_INC(tcps_sc_spurcookie);
1097 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1098 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1099 "segment rejected "
1100 "(syncookies disabled)\n",
1101 s, __func__);
1102 goto failed;
1103 }
1104 if (sch->sch_last_overflow <
1105 time_uptime - SYNCOOKIE_LIFETIME) {
1106 /*
1107 * Since the bucket did not overflow recently,
1108 * don't even check for a valid syncookie.
1109 */
1110 SCH_UNLOCK(sch);
1111 TCPSTAT_INC(tcps_sc_spurcookie);
1112 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1113 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
1114 "segment rejected "
1115 "(no syncache entry)\n",
1116 s, __func__);
1117 goto failed;
1118 }
1119 SCH_UNLOCK(sch);
1120 }
1121 bzero(&scs, sizeof(scs));
1122 /*
1123 * Now check, if the syncookie is valid. If it is, create an on
1124 * stack syncache entry.
1125 */
1126 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) {
1127 sc = &scs;
1128 TCPSTAT_INC(tcps_sc_recvcookie);
1129 } else {
1130 TCPSTAT_INC(tcps_sc_failcookie);
1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1132 log(LOG_DEBUG, "%s; %s: Segment failed "
1133 "SYNCOOKIE authentication, segment rejected "
1134 "(probably spoofed)\n", s, __func__);
1135 goto failed;
1136 }
1137 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1138 /* If received ACK has MD5 signature, check it. */
1139 if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1140 (!TCPMD5_ENABLED() ||
1141 TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1142 /* Drop the ACK. */
1143 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1144 log(LOG_DEBUG, "%s; %s: Segment rejected, "
1145 "MD5 signature doesn't match.\n",
1146 s, __func__);
1147 free(s, M_TCPLOG);
1148 }
1149 TCPSTAT_INC(tcps_sig_err_sigopt);
1150 return (-1); /* Do not send RST */
1151 }
1152 #endif /* TCP_SIGNATURE */
1153 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1154 } else {
1155 if (sc->sc_port != port) {
1156 SCH_UNLOCK(sch);
1157 return (0);
1158 }
1159 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1160 /*
1161 * If listening socket requested TCP digests, check that
1162 * received ACK has signature and it is correct.
1163 * If not, drop the ACK and leave sc entry in th cache,
1164 * because SYN was received with correct signature.
1165 */
1166 if (sc->sc_flags & SCF_SIGNATURE) {
1167 if ((to->to_flags & TOF_SIGNATURE) == 0) {
1168 /* No signature */
1169 TCPSTAT_INC(tcps_sig_err_nosigopt);
1170 SCH_UNLOCK(sch);
1171 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1172 log(LOG_DEBUG, "%s; %s: Segment "
1173 "rejected, MD5 signature wasn't "
1174 "provided.\n", s, __func__);
1175 free(s, M_TCPLOG);
1176 }
1177 return (-1); /* Do not send RST */
1178 }
1179 if (!TCPMD5_ENABLED() ||
1180 TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1181 /* Doesn't match or no SA */
1182 SCH_UNLOCK(sch);
1183 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1184 log(LOG_DEBUG, "%s; %s: Segment "
1185 "rejected, MD5 signature doesn't "
1186 "match.\n", s, __func__);
1187 free(s, M_TCPLOG);
1188 }
1189 return (-1); /* Do not send RST */
1190 }
1191 }
1192 #endif /* TCP_SIGNATURE */
1193
1194 /*
1195 * RFC 7323 PAWS: If we have a timestamp on this segment and
1196 * it's less than ts_recent, drop it.
1197 * XXXMT: RFC 7323 also requires to send an ACK.
1198 * In tcp_input.c this is only done for TCP segments
1199 * with user data, so be consistent here and just drop
1200 * the segment.
1201 */
1202 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS &&
1203 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) {
1204 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1205 log(LOG_DEBUG,
1206 "%s; %s: SEG.TSval %u < TS.Recent %u, "
1207 "segment dropped\n", s, __func__,
1208 to->to_tsval, sc->sc_tsreflect);
1209 free(s, M_TCPLOG);
1210 }
1211 SCH_UNLOCK(sch);
1212 return (-1); /* Do not send RST */
1213 }
1214
1215 /*
1216 * If timestamps were not negotiated during SYN/ACK and a
1217 * segment with a timestamp is received, ignore the
1218 * timestamp and process the packet normally.
1219 * See section 3.2 of RFC 7323.
1220 */
1221 if (!(sc->sc_flags & SCF_TIMESTAMP) &&
1222 (to->to_flags & TOF_TS)) {
1223 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1224 log(LOG_DEBUG, "%s; %s: Timestamp not "
1225 "expected, segment processed normally\n",
1226 s, __func__);
1227 free(s, M_TCPLOG);
1228 s = NULL;
1229 }
1230 }
1231
1232 /*
1233 * If timestamps were negotiated during SYN/ACK and a
1234 * segment without a timestamp is received, silently drop
1235 * the segment, unless the missing timestamps are tolerated.
1236 * See section 3.2 of RFC 7323.
1237 */
1238 if ((sc->sc_flags & SCF_TIMESTAMP) &&
1239 !(to->to_flags & TOF_TS)) {
1240 if (V_tcp_tolerate_missing_ts) {
1241 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1242 log(LOG_DEBUG,
1243 "%s; %s: Timestamp missing, "
1244 "segment processed normally\n",
1245 s, __func__);
1246 free(s, M_TCPLOG);
1247 }
1248 } else {
1249 SCH_UNLOCK(sch);
1250 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1251 log(LOG_DEBUG,
1252 "%s; %s: Timestamp missing, "
1253 "segment silently dropped\n",
1254 s, __func__);
1255 free(s, M_TCPLOG);
1256 }
1257 return (-1); /* Do not send RST */
1258 }
1259 }
1260
1261 /*
1262 * SEG.SEQ validation:
1263 * The SEG.SEQ must be in the window starting at our
1264 * initial receive sequence number + 1.
1265 */
1266 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1267 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1268 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1269 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, "
1270 "sending challenge ACK\n",
1271 s, __func__, th->th_seq, sc->sc_irs + 1);
1272 syncache_send_challenge_ack(sc, m);
1273 SCH_UNLOCK(sch);
1274 free(s, M_TCPLOG);
1275 return (-1); /* Do not send RST */
1276 }
1277
1278 /*
1279 * SEG.ACK validation:
1280 * SEG.ACK must match our initial send sequence number + 1.
1281 */
1282 if (th->th_ack != sc->sc_iss + 1) {
1283 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1284 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, "
1285 "segment rejected\n",
1286 s, __func__, th->th_ack, sc->sc_iss + 1);
1287 SCH_UNLOCK(sch);
1288 free(s, M_TCPLOG);
1289 return (0); /* Do send RST, do not free sc. */
1290 }
1291
1292 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1293 sch->sch_length--;
1294 #ifdef TCP_OFFLOAD
1295 if (ADDED_BY_TOE(sc)) {
1296 struct toedev *tod = sc->sc_tod;
1297
1298 tod->tod_syncache_removed(tod, sc->sc_todctx);
1299 }
1300 #endif
1301 SCH_UNLOCK(sch);
1302 }
1303
1304 *lsop = syncache_socket(sc, *lsop, m);
1305
1306 if (__predict_false(*lsop == NULL)) {
1307 TCPSTAT_INC(tcps_sc_aborted);
1308 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1309 } else if (sc != &scs)
1310 TCPSTAT_INC(tcps_sc_completed);
1311
1312 if (sc != &scs)
1313 syncache_free(sc);
1314 return (1);
1315 failed:
1316 if (sc != NULL) {
1317 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1318 if (sc != &scs)
1319 syncache_free(sc);
1320 }
1321 if (s != NULL)
1322 free(s, M_TCPLOG);
1323 *lsop = NULL;
1324 return (0);
1325 }
1326
1327 static struct socket *
syncache_tfo_expand(struct syncache * sc,struct socket * lso,struct mbuf * m,uint64_t response_cookie)1328 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m,
1329 uint64_t response_cookie)
1330 {
1331 struct inpcb *inp;
1332 struct tcpcb *tp;
1333 unsigned int *pending_counter;
1334 struct socket *so;
1335
1336 NET_EPOCH_ASSERT();
1337
1338 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending;
1339 so = syncache_socket(sc, lso, m);
1340 if (so == NULL) {
1341 TCPSTAT_INC(tcps_sc_aborted);
1342 atomic_subtract_int(pending_counter, 1);
1343 } else {
1344 soisconnected(so);
1345 inp = sotoinpcb(so);
1346 tp = intotcpcb(inp);
1347 tp->t_flags |= TF_FASTOPEN;
1348 tp->t_tfo_cookie.server = response_cookie;
1349 tp->snd_max = tp->iss;
1350 tp->snd_nxt = tp->iss;
1351 tp->t_tfo_pending = pending_counter;
1352 TCPSTATES_INC(TCPS_SYN_RECEIVED);
1353 TCPSTAT_INC(tcps_sc_completed);
1354 }
1355
1356 return (so);
1357 }
1358
1359 /*
1360 * Given a LISTEN socket and an inbound SYN request, add
1361 * this to the syn cache, and send back a segment:
1362 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1363 * to the source.
1364 *
1365 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1366 * Doing so would require that we hold onto the data and deliver it
1367 * to the application. However, if we are the target of a SYN-flood
1368 * DoS attack, an attacker could send data which would eventually
1369 * consume all available buffer space if it were ACKed. By not ACKing
1370 * the data, we avoid this DoS scenario.
1371 *
1372 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1373 * cookie is processed and a new socket is created. In this case, any data
1374 * accompanying the SYN will be queued to the socket by tcp_input() and will
1375 * be ACKed either when the application sends response data or the delayed
1376 * ACK timer expires, whichever comes first.
1377 */
1378 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)1379 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1380 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod,
1381 void *todctx, uint8_t iptos, uint16_t port)
1382 {
1383 struct tcpcb *tp;
1384 struct socket *rv = NULL;
1385 struct syncache *sc = NULL;
1386 struct syncache_head *sch;
1387 struct mbuf *ipopts = NULL;
1388 u_int ltflags;
1389 int win, ip_ttl, ip_tos;
1390 char *s;
1391 #ifdef INET6
1392 int autoflowlabel = 0;
1393 #endif
1394 #ifdef MAC
1395 struct label *maclabel = NULL;
1396 #endif
1397 struct syncache scs;
1398 uint64_t tfo_response_cookie;
1399 unsigned int *tfo_pending = NULL;
1400 int tfo_cookie_valid = 0;
1401 int tfo_response_cookie_valid = 0;
1402 bool locked;
1403
1404 INP_RLOCK_ASSERT(inp); /* listen socket */
1405 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1406 ("%s: unexpected tcp flags", __func__));
1407
1408 /*
1409 * Combine all so/tp operations very early to drop the INP lock as
1410 * soon as possible.
1411 */
1412 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so));
1413 tp = sototcpcb(so);
1414
1415 #ifdef INET6
1416 if (inc->inc_flags & INC_ISIPV6) {
1417 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) {
1418 autoflowlabel = 1;
1419 }
1420 ip_ttl = in6_selecthlim(inp, NULL);
1421 if ((inp->in6p_outputopts == NULL) ||
1422 (inp->in6p_outputopts->ip6po_tclass == -1)) {
1423 ip_tos = 0;
1424 } else {
1425 ip_tos = inp->in6p_outputopts->ip6po_tclass;
1426 }
1427 }
1428 #endif
1429 #if defined(INET6) && defined(INET)
1430 else
1431 #endif
1432 #ifdef INET
1433 {
1434 ip_ttl = inp->inp_ip_ttl;
1435 ip_tos = inp->inp_ip_tos;
1436 }
1437 #endif
1438 win = so->sol_sbrcv_hiwat;
1439 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1440
1441 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) &&
1442 (tp->t_tfo_pending != NULL) &&
1443 (to->to_flags & TOF_FASTOPEN)) {
1444 /*
1445 * Limit the number of pending TFO connections to
1446 * approximately half of the queue limit. This prevents TFO
1447 * SYN floods from starving the service by filling the
1448 * listen queue with bogus TFO connections.
1449 */
1450 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1451 (so->sol_qlimit / 2)) {
1452 int result;
1453
1454 result = tcp_fastopen_check_cookie(inc,
1455 to->to_tfo_cookie, to->to_tfo_len,
1456 &tfo_response_cookie);
1457 tfo_cookie_valid = (result > 0);
1458 tfo_response_cookie_valid = (result >= 0);
1459 }
1460
1461 /*
1462 * Remember the TFO pending counter as it will have to be
1463 * decremented below if we don't make it to syncache_tfo_expand().
1464 */
1465 tfo_pending = tp->t_tfo_pending;
1466 }
1467
1468 #ifdef MAC
1469 if (mac_syncache_init(&maclabel) != 0) {
1470 INP_RUNLOCK(inp);
1471 goto done;
1472 } else
1473 mac_syncache_create(maclabel, inp);
1474 #endif
1475 if (!tfo_cookie_valid)
1476 INP_RUNLOCK(inp);
1477
1478 /*
1479 * Remember the IP options, if any.
1480 */
1481 #ifdef INET6
1482 if (!(inc->inc_flags & INC_ISIPV6))
1483 #endif
1484 #ifdef INET
1485 ipopts = (m) ? ip_srcroute(m) : NULL;
1486 #else
1487 ipopts = NULL;
1488 #endif
1489
1490 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1491 /*
1492 * When the socket is TCP-MD5 enabled check that,
1493 * - a signed packet is valid
1494 * - a non-signed packet does not have a security association
1495 *
1496 * If a signed packet fails validation or a non-signed packet has a
1497 * security association, the packet will be dropped.
1498 */
1499 if (ltflags & TF_SIGNATURE) {
1500 if (to->to_flags & TOF_SIGNATURE) {
1501 if (!TCPMD5_ENABLED() ||
1502 TCPMD5_INPUT(m, th, to->to_signature) != 0)
1503 goto done;
1504 } else {
1505 if (TCPMD5_ENABLED() &&
1506 TCPMD5_INPUT(m, NULL, NULL) != ENOENT)
1507 goto done;
1508 }
1509 } else if (to->to_flags & TOF_SIGNATURE)
1510 goto done;
1511 #endif /* TCP_SIGNATURE */
1512 /*
1513 * See if we already have an entry for this connection.
1514 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1515 *
1516 * XXX: should the syncache be re-initialized with the contents
1517 * of the new SYN here (which may have different options?)
1518 *
1519 * XXX: We do not check the sequence number to see if this is a
1520 * real retransmit or a new connection attempt. The question is
1521 * how to handle such a case; either ignore it as spoofed, or
1522 * drop the current entry and create a new one?
1523 */
1524 if (syncache_cookiesonly()) {
1525 sc = NULL;
1526 sch = syncache_hashbucket(inc);
1527 locked = false;
1528 } else {
1529 sc = syncache_lookup(inc, &sch); /* returns locked sch */
1530 locked = true;
1531 SCH_LOCK_ASSERT(sch);
1532 }
1533 if (sc != NULL) {
1534 if (tfo_cookie_valid)
1535 INP_RUNLOCK(inp);
1536 TCPSTAT_INC(tcps_sc_dupsyn);
1537 if (ipopts) {
1538 /*
1539 * If we were remembering a previous source route,
1540 * forget it and use the new one we've been given.
1541 */
1542 if (sc->sc_ipopts)
1543 (void)m_free(sc->sc_ipopts);
1544 sc->sc_ipopts = ipopts;
1545 }
1546 /*
1547 * Update timestamp if present.
1548 */
1549 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1550 sc->sc_tsreflect = to->to_tsval;
1551 else
1552 sc->sc_flags &= ~SCF_TIMESTAMP;
1553 /*
1554 * Adjust ECN response if needed, e.g. different
1555 * IP ECN field, or a fallback by the remote host.
1556 */
1557 if (sc->sc_flags & SCF_ECN_MASK) {
1558 sc->sc_flags &= ~SCF_ECN_MASK;
1559 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1560 }
1561 #ifdef MAC
1562 /*
1563 * Since we have already unconditionally allocated label
1564 * storage, free it up. The syncache entry will already
1565 * have an initialized label we can use.
1566 */
1567 mac_syncache_destroy(&maclabel);
1568 #endif
1569 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1570 /* Retransmit SYN|ACK and reset retransmit count. */
1571 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1572 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1573 "resetting timer and retransmitting SYN|ACK\n",
1574 s, __func__);
1575 free(s, M_TCPLOG);
1576 }
1577 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1578 sc->sc_rxmits = 0;
1579 syncache_timeout(sc, sch, 1);
1580 TCPSTAT_INC(tcps_sndacks);
1581 TCPSTAT_INC(tcps_sndtotal);
1582 } else {
1583 syncache_drop(sc, sch);
1584 TCPSTAT_INC(tcps_sc_dropped);
1585 }
1586 SCH_UNLOCK(sch);
1587 goto donenoprobe;
1588 }
1589
1590 KASSERT(sc == NULL, ("sc(%p) != NULL", sc));
1591 /*
1592 * Skip allocating a syncache entry if we are just going to discard
1593 * it later.
1594 */
1595 if (!locked || tfo_cookie_valid) {
1596 bzero(&scs, sizeof(scs));
1597 sc = &scs;
1598 } else {
1599 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1600 if (sc == NULL) {
1601 /*
1602 * The zone allocator couldn't provide more entries.
1603 * Treat this as if the cache was full; drop the oldest
1604 * entry and insert the new one.
1605 */
1606 TCPSTAT_INC(tcps_sc_zonefail);
1607 sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
1608 if (sc != NULL) {
1609 sch->sch_last_overflow = time_uptime;
1610 syncache_drop(sc, sch);
1611 syncache_pause(inc);
1612 }
1613 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1614 if (sc == NULL) {
1615 if (V_tcp_syncookies) {
1616 bzero(&scs, sizeof(scs));
1617 sc = &scs;
1618 } else {
1619 KASSERT(locked,
1620 ("%s: bucket unexpectedly unlocked",
1621 __func__));
1622 SCH_UNLOCK(sch);
1623 goto done;
1624 }
1625 }
1626 }
1627 }
1628
1629 KASSERT(sc != NULL, ("sc == NULL"));
1630 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1631 sc->sc_tfo_cookie = &tfo_response_cookie;
1632
1633 /*
1634 * Fill in the syncache values.
1635 */
1636 #ifdef MAC
1637 sc->sc_label = maclabel;
1638 #endif
1639 /*
1640 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in
1641 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false.
1642 * Therefore, store the credentials and take a reference count only
1643 * when needed:
1644 * - sc is allocated from the zone and not using the on stack instance.
1645 * - the sysctl variable net.inet.tcp.syncache.see_other is false.
1646 * The reference count is decremented when a zone allocated sc is
1647 * freed in syncache_free().
1648 */
1649 if (sc != &scs && !V_tcp_syncache.see_other)
1650 sc->sc_cred = crhold(so->so_cred);
1651 else
1652 sc->sc_cred = NULL;
1653 sc->sc_port = port;
1654 sc->sc_ipopts = ipopts;
1655 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1656 sc->sc_ip_tos = ip_tos;
1657 sc->sc_ip_ttl = ip_ttl;
1658 #ifdef TCP_OFFLOAD
1659 sc->sc_tod = tod;
1660 sc->sc_todctx = todctx;
1661 #endif
1662 sc->sc_irs = th->th_seq;
1663 sc->sc_flags = 0;
1664 sc->sc_flowlabel = 0;
1665
1666 /*
1667 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1668 * win was derived from socket earlier in the function.
1669 */
1670 win = imax(win, 0);
1671 win = imin(win, TCP_MAXWIN);
1672 sc->sc_wnd = win;
1673
1674 if (V_tcp_do_rfc1323 &&
1675 !(ltflags & TF_NOOPT)) {
1676 /*
1677 * A timestamp received in a SYN makes
1678 * it ok to send timestamp requests and replies.
1679 */
1680 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) {
1681 sc->sc_tsreflect = to->to_tsval;
1682 sc->sc_flags |= SCF_TIMESTAMP;
1683 sc->sc_tsoff = tcp_new_ts_offset(inc);
1684 }
1685 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) {
1686 u_int wscale = 0;
1687
1688 /*
1689 * Pick the smallest possible scaling factor that
1690 * will still allow us to scale up to sb_max, aka
1691 * kern.ipc.maxsockbuf.
1692 *
1693 * We do this because there are broken firewalls that
1694 * will corrupt the window scale option, leading to
1695 * the other endpoint believing that our advertised
1696 * window is unscaled. At scale factors larger than
1697 * 5 the unscaled window will drop below 1500 bytes,
1698 * leading to serious problems when traversing these
1699 * broken firewalls.
1700 *
1701 * With the default maxsockbuf of 256K, a scale factor
1702 * of 3 will be chosen by this algorithm. Those who
1703 * choose a larger maxsockbuf should watch out
1704 * for the compatibility problems mentioned above.
1705 *
1706 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1707 * or <SYN,ACK>) segment itself is never scaled.
1708 */
1709 while (wscale < TCP_MAX_WINSHIFT &&
1710 (TCP_MAXWIN << wscale) < sb_max)
1711 wscale++;
1712 sc->sc_requested_r_scale = wscale;
1713 sc->sc_requested_s_scale = to->to_wscale;
1714 sc->sc_flags |= SCF_WINSCALE;
1715 }
1716 }
1717 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1718 /*
1719 * If incoming packet has an MD5 signature, flag this in the
1720 * syncache so that syncache_respond() will do the right thing
1721 * with the SYN+ACK.
1722 */
1723 if (to->to_flags & TOF_SIGNATURE)
1724 sc->sc_flags |= SCF_SIGNATURE;
1725 #endif /* TCP_SIGNATURE */
1726 if (to->to_flags & TOF_SACKPERM)
1727 sc->sc_flags |= SCF_SACK;
1728 if (to->to_flags & TOF_MSS)
1729 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1730 if (ltflags & TF_NOOPT)
1731 sc->sc_flags |= SCF_NOOPT;
1732 /* ECN Handshake */
1733 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0)
1734 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos);
1735
1736 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1737 sc->sc_iss = syncookie_generate(sch, sc);
1738 else
1739 sc->sc_iss = arc4random();
1740 #ifdef INET6
1741 if (autoflowlabel) {
1742 if (V_tcp_syncookies || V_tcp_syncookiesonly)
1743 sc->sc_flowlabel = sc->sc_iss;
1744 else
1745 sc->sc_flowlabel = ip6_randomflowlabel();
1746 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1747 }
1748 #endif
1749 if (locked)
1750 SCH_UNLOCK(sch);
1751
1752 if (tfo_cookie_valid) {
1753 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie);
1754 /* INP_RUNLOCK(inp) will be performed by the caller */
1755 goto tfo_expanded;
1756 }
1757
1758 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1759 /*
1760 * Do a standard 3-way handshake.
1761 */
1762 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) {
1763 if (sc != &scs)
1764 syncache_insert(sc, sch); /* locks and unlocks sch */
1765 TCPSTAT_INC(tcps_sndacks);
1766 TCPSTAT_INC(tcps_sndtotal);
1767 } else {
1768 if (sc != &scs)
1769 syncache_free(sc);
1770 TCPSTAT_INC(tcps_sc_dropped);
1771 }
1772 goto donenoprobe;
1773
1774 done:
1775 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
1776 donenoprobe:
1777 if (m)
1778 m_freem(m);
1779 /*
1780 * If tfo_pending is not NULL here, then a TFO SYN that did not
1781 * result in a new socket was processed and the associated pending
1782 * counter has not yet been decremented. All such TFO processing paths
1783 * transit this point.
1784 */
1785 if (tfo_pending != NULL)
1786 tcp_fastopen_decrement_counter(tfo_pending);
1787
1788 tfo_expanded:
1789 if (sc == NULL || sc == &scs) {
1790 #ifdef MAC
1791 mac_syncache_destroy(&maclabel);
1792 #endif
1793 if (ipopts)
1794 (void)m_free(ipopts);
1795 }
1796 return (rv);
1797 }
1798
1799 /*
1800 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment,
1801 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1802 */
1803 static int
syncache_respond(struct syncache * sc,const struct mbuf * m0,int flags)1804 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
1805 {
1806 struct ip *ip = NULL;
1807 struct mbuf *m;
1808 struct tcphdr *th = NULL;
1809 struct udphdr *udp = NULL;
1810 int optlen, error = 0; /* Make compiler happy */
1811 u_int16_t hlen, tlen, mssopt, ulen;
1812 struct tcpopt to;
1813 #ifdef INET6
1814 struct ip6_hdr *ip6 = NULL;
1815 #endif
1816
1817 NET_EPOCH_ASSERT();
1818
1819 hlen =
1820 #ifdef INET6
1821 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1822 #endif
1823 sizeof(struct ip);
1824 tlen = hlen + sizeof(struct tcphdr);
1825 if (sc->sc_port) {
1826 tlen += sizeof(struct udphdr);
1827 }
1828 /* Determine MSS we advertize to other end of connection. */
1829 mssopt = tcp_mssopt(&sc->sc_inc);
1830 if (sc->sc_port)
1831 mssopt -= V_tcp_udp_tunneling_overhead;
1832 mssopt = max(mssopt, V_tcp_minmss);
1833
1834 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1835 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1836 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + "
1837 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port,
1838 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN));
1839
1840 /* Create the IP+TCP header from scratch. */
1841 m = m_gethdr(M_NOWAIT, MT_DATA);
1842 if (m == NULL)
1843 return (ENOBUFS);
1844 #ifdef MAC
1845 mac_syncache_create_mbuf(sc->sc_label, m);
1846 #endif
1847 m->m_data += max_linkhdr;
1848 m->m_len = tlen;
1849 m->m_pkthdr.len = tlen;
1850 m->m_pkthdr.rcvif = NULL;
1851
1852 #ifdef INET6
1853 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1854 ip6 = mtod(m, struct ip6_hdr *);
1855 ip6->ip6_vfc = IPV6_VERSION;
1856 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1857 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1858 ip6->ip6_plen = htons(tlen - hlen);
1859 /* ip6_hlim is set after checksum */
1860 /* Zero out traffic class and flow label. */
1861 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
1862 ip6->ip6_flow |= sc->sc_flowlabel;
1863 if (sc->sc_port != 0) {
1864 ip6->ip6_nxt = IPPROTO_UDP;
1865 udp = (struct udphdr *)(ip6 + 1);
1866 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1867 udp->uh_dport = sc->sc_port;
1868 ulen = (tlen - sizeof(struct ip6_hdr));
1869 th = (struct tcphdr *)(udp + 1);
1870 } else {
1871 ip6->ip6_nxt = IPPROTO_TCP;
1872 th = (struct tcphdr *)(ip6 + 1);
1873 }
1874 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN);
1875 }
1876 #endif
1877 #if defined(INET6) && defined(INET)
1878 else
1879 #endif
1880 #ifdef INET
1881 {
1882 ip = mtod(m, struct ip *);
1883 ip->ip_v = IPVERSION;
1884 ip->ip_hl = sizeof(struct ip) >> 2;
1885 ip->ip_len = htons(tlen);
1886 ip->ip_id = 0;
1887 ip->ip_off = 0;
1888 ip->ip_sum = 0;
1889 ip->ip_src = sc->sc_inc.inc_laddr;
1890 ip->ip_dst = sc->sc_inc.inc_faddr;
1891 ip->ip_ttl = sc->sc_ip_ttl;
1892 ip->ip_tos = sc->sc_ip_tos;
1893
1894 /*
1895 * See if we should do MTU discovery. Route lookups are
1896 * expensive, so we will only unset the DF bit if:
1897 *
1898 * 1) path_mtu_discovery is disabled
1899 * 2) the SCF_UNREACH flag has been set
1900 */
1901 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1902 ip->ip_off |= htons(IP_DF);
1903 if (sc->sc_port == 0) {
1904 ip->ip_p = IPPROTO_TCP;
1905 th = (struct tcphdr *)(ip + 1);
1906 } else {
1907 ip->ip_p = IPPROTO_UDP;
1908 udp = (struct udphdr *)(ip + 1);
1909 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1910 udp->uh_dport = sc->sc_port;
1911 ulen = (tlen - sizeof(struct ip));
1912 th = (struct tcphdr *)(udp + 1);
1913 }
1914 }
1915 #endif /* INET */
1916 th->th_sport = sc->sc_inc.inc_lport;
1917 th->th_dport = sc->sc_inc.inc_fport;
1918
1919 if (flags & TH_SYN)
1920 th->th_seq = htonl(sc->sc_iss);
1921 else
1922 th->th_seq = htonl(sc->sc_iss + 1);
1923 th->th_ack = htonl(sc->sc_irs + 1);
1924 th->th_off = sizeof(struct tcphdr) >> 2;
1925 th->th_win = htons(sc->sc_wnd);
1926 th->th_urp = 0;
1927
1928 flags = tcp_ecn_syncache_respond(flags, sc);
1929 tcp_set_flags(th, flags);
1930
1931 /* Tack on the TCP options. */
1932 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1933 to.to_flags = 0;
1934
1935 if (flags & TH_SYN) {
1936 to.to_mss = mssopt;
1937 to.to_flags = TOF_MSS;
1938 if (sc->sc_flags & SCF_WINSCALE) {
1939 to.to_wscale = sc->sc_requested_r_scale;
1940 to.to_flags |= TOF_SCALE;
1941 }
1942 if (sc->sc_flags & SCF_SACK)
1943 to.to_flags |= TOF_SACKPERM;
1944 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1945 if (sc->sc_flags & SCF_SIGNATURE)
1946 to.to_flags |= TOF_SIGNATURE;
1947 #endif
1948 if (sc->sc_tfo_cookie) {
1949 to.to_flags |= TOF_FASTOPEN;
1950 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1951 to.to_tfo_cookie = sc->sc_tfo_cookie;
1952 /* don't send cookie again when retransmitting response */
1953 sc->sc_tfo_cookie = NULL;
1954 }
1955 }
1956 if (sc->sc_flags & SCF_TIMESTAMP) {
1957 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
1958 to.to_tsecr = sc->sc_tsreflect;
1959 to.to_flags |= TOF_TS;
1960 }
1961 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1962
1963 /* Adjust headers by option size. */
1964 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1965 m->m_len += optlen;
1966 m->m_pkthdr.len += optlen;
1967 #ifdef INET6
1968 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1969 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1970 else
1971 #endif
1972 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1973 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1974 if (sc->sc_flags & SCF_SIGNATURE) {
1975 KASSERT(to.to_flags & TOF_SIGNATURE,
1976 ("tcp_addoptions() didn't set tcp_signature"));
1977
1978 /* NOTE: to.to_signature is inside of mbuf */
1979 if (!TCPMD5_ENABLED() ||
1980 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1981 m_freem(m);
1982 return (EACCES);
1983 }
1984 }
1985 #endif
1986 } else
1987 optlen = 0;
1988
1989 if (udp) {
1990 ulen += optlen;
1991 udp->uh_ulen = htons(ulen);
1992 }
1993 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1994 /*
1995 * If we have peer's SYN and it has a flowid, then let's assign it to
1996 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1997 * to SYN|ACK due to lack of inp here.
1998 */
1999 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
2000 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
2001 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
2002 }
2003 #ifdef INET6
2004 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
2005 if (sc->sc_port) {
2006 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
2007 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2008 udp->uh_sum = in6_cksum_pseudo(ip6, ulen,
2009 IPPROTO_UDP, 0);
2010 th->th_sum = htons(0);
2011 } else {
2012 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
2013 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2014 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
2015 IPPROTO_TCP, 0);
2016 }
2017 ip6->ip6_hlim = sc->sc_ip_ttl;
2018 #ifdef TCP_OFFLOAD
2019 if (ADDED_BY_TOE(sc)) {
2020 struct toedev *tod = sc->sc_tod;
2021
2022 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2023
2024 return (error);
2025 }
2026 #endif
2027 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
2028 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
2029 }
2030 #endif
2031 #if defined(INET6) && defined(INET)
2032 else
2033 #endif
2034 #ifdef INET
2035 {
2036 if (sc->sc_port) {
2037 m->m_pkthdr.csum_flags = CSUM_UDP;
2038 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
2039 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
2040 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
2041 th->th_sum = htons(0);
2042 } else {
2043 m->m_pkthdr.csum_flags = CSUM_TCP;
2044 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
2045 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
2046 htons(tlen + optlen - hlen + IPPROTO_TCP));
2047 }
2048 #ifdef TCP_OFFLOAD
2049 if (ADDED_BY_TOE(sc)) {
2050 struct toedev *tod = sc->sc_tod;
2051
2052 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
2053
2054 return (error);
2055 }
2056 #endif
2057 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
2058 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
2059 }
2060 #endif
2061 return (error);
2062 }
2063
2064 static void
syncache_send_challenge_ack(struct syncache * sc,struct mbuf * m)2065 syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m)
2066 {
2067 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end,
2068 &sc->sc_challenge_ack_cnt)) {
2069 if (syncache_respond(sc, m, TH_ACK) == 0) {
2070 TCPSTAT_INC(tcps_sndacks);
2071 TCPSTAT_INC(tcps_sndtotal);
2072 }
2073 }
2074 }
2075
2076 /*
2077 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
2078 * that exceed the capacity of the syncache by avoiding the storage of any
2079 * of the SYNs we receive. Syncookies defend against blind SYN flooding
2080 * attacks where the attacker does not have access to our responses.
2081 *
2082 * Syncookies encode and include all necessary information about the
2083 * connection setup within the SYN|ACK that we send back. That way we
2084 * can avoid keeping any local state until the ACK to our SYN|ACK returns
2085 * (if ever). Normally the syncache and syncookies are running in parallel
2086 * with the latter taking over when the former is exhausted. When matching
2087 * syncache entry is found the syncookie is ignored.
2088 *
2089 * The only reliable information persisting the 3WHS is our initial sequence
2090 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
2091 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
2092 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
2093 * returns and signifies a legitimate connection if it matches the ACK.
2094 *
2095 * The available space of 32 bits to store the hash and to encode the SYN
2096 * option information is very tight and we should have at least 24 bits for
2097 * the MAC to keep the number of guesses by blind spoofing reasonably high.
2098 *
2099 * SYN option information we have to encode to fully restore a connection:
2100 * MSS: is imporant to chose an optimal segment size to avoid IP level
2101 * fragmentation along the path. The common MSS values can be encoded
2102 * in a 3-bit table. Uncommon values are captured by the next lower value
2103 * in the table leading to a slight increase in packetization overhead.
2104 * WSCALE: is necessary to allow large windows to be used for high delay-
2105 * bandwidth product links. Not scaling the window when it was initially
2106 * negotiated is bad for performance as lack of scaling further decreases
2107 * the apparent available send window. We only need to encode the WSCALE
2108 * we received from the remote end. Our end can be recalculated at any
2109 * time. The common WSCALE values can be encoded in a 3-bit table.
2110 * Uncommon values are captured by the next lower value in the table
2111 * making us under-estimate the available window size halving our
2112 * theoretically possible maximum throughput for that connection.
2113 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
2114 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
2115 * that are included in all segments on a connection. We enable them when
2116 * the ACK has them.
2117 *
2118 * Security of syncookies and attack vectors:
2119 *
2120 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
2121 * together with the gloabl secret to make it unique per connection attempt.
2122 * Thus any change of any of those parameters results in a different MAC output
2123 * in an unpredictable way unless a collision is encountered. 24 bits of the
2124 * MAC are embedded into the ISS.
2125 *
2126 * To prevent replay attacks two rotating global secrets are updated with a
2127 * new random value every 15 seconds. The life-time of a syncookie is thus
2128 * 15-30 seconds.
2129 *
2130 * Vector 1: Attacking the secret. This requires finding a weakness in the
2131 * MAC itself or the way it is used here. The attacker can do a chosen plain
2132 * text attack by varying and testing the all parameters under his control.
2133 * The strength depends on the size and randomness of the secret, and the
2134 * cryptographic security of the MAC function. Due to the constant updating
2135 * of the secret the attacker has at most 29.999 seconds to find the secret
2136 * and launch spoofed connections. After that he has to start all over again.
2137 *
2138 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
2139 * size an average of 4,823 attempts are required for a 50% chance of success
2140 * to spoof a single syncookie (birthday collision paradox). However the
2141 * attacker is blind and doesn't know if one of his attempts succeeded unless
2142 * he has a side channel to interfere success from. A single connection setup
2143 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
2144 * This many attempts are required for each one blind spoofed connection. For
2145 * every additional spoofed connection he has to launch another N attempts.
2146 * Thus for a sustained rate 100 spoofed connections per second approximately
2147 * 1,800,000 packets per second would have to be sent.
2148 *
2149 * NB: The MAC function should be fast so that it doesn't become a CPU
2150 * exhaustion attack vector itself.
2151 *
2152 * References:
2153 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
2154 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
2155 * http://cr.yp.to/syncookies.html (overview)
2156 * http://cr.yp.to/syncookies/archive (details)
2157 *
2158 *
2159 * Schematic construction of a syncookie enabled Initial Sequence Number:
2160 * 0 1 2 3
2161 * 12345678901234567890123456789012
2162 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
2163 *
2164 * x 24 MAC (truncated)
2165 * W 3 Send Window Scale index
2166 * M 3 MSS index
2167 * S 1 SACK permitted
2168 * P 1 Odd/even secret
2169 */
2170
2171 /*
2172 * Distribution and probability of certain MSS values. Those in between are
2173 * rounded down to the next lower one.
2174 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
2175 * .2% .3% 5% 7% 7% 20% 15% 45%
2176 */
2177 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
2178
2179 /*
2180 * Distribution and probability of certain WSCALE values. We have to map the
2181 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
2182 * bits based on prevalence of certain values. Where we don't have an exact
2183 * match for are rounded down to the next lower one letting us under-estimate
2184 * the true available window. At the moment this would happen only for the
2185 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
2186 * and window size). The absence of the WSCALE option (no scaling in either
2187 * direction) is encoded with index zero.
2188 * [WSCALE values histograms, Allman, 2012]
2189 * X 10 10 35 5 6 14 10% by host
2190 * X 11 4 5 5 18 49 3% by connections
2191 */
2192 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
2193
2194 /*
2195 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
2196 * and good cryptographic properties.
2197 */
2198 static uint32_t
syncookie_mac(struct in_conninfo * inc,tcp_seq irs,uint8_t flags,uint8_t * secbits,uintptr_t secmod)2199 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
2200 uint8_t *secbits, uintptr_t secmod)
2201 {
2202 SIPHASH_CTX ctx;
2203 uint32_t siphash[2];
2204
2205 SipHash24_Init(&ctx);
2206 SipHash_SetKey(&ctx, secbits);
2207 switch (inc->inc_flags & INC_ISIPV6) {
2208 #ifdef INET
2209 case 0:
2210 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
2211 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
2212 break;
2213 #endif
2214 #ifdef INET6
2215 case INC_ISIPV6:
2216 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
2217 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
2218 break;
2219 #endif
2220 }
2221 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
2222 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
2223 SipHash_Update(&ctx, &irs, sizeof(irs));
2224 SipHash_Update(&ctx, &flags, sizeof(flags));
2225 SipHash_Update(&ctx, &secmod, sizeof(secmod));
2226 SipHash_Final((u_int8_t *)&siphash, &ctx);
2227
2228 return (siphash[0] ^ siphash[1]);
2229 }
2230
2231 static tcp_seq
syncookie_generate(struct syncache_head * sch,struct syncache * sc)2232 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
2233 {
2234 u_int i, secbit, wscale;
2235 uint32_t iss, hash;
2236 uint8_t *secbits;
2237 union syncookie cookie;
2238
2239 cookie.cookie = 0;
2240
2241 /* Map our computed MSS into the 3-bit index. */
2242 for (i = nitems(tcp_sc_msstab) - 1;
2243 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0;
2244 i--)
2245 ;
2246 cookie.flags.mss_idx = i;
2247
2248 /*
2249 * Map the send window scale into the 3-bit index but only if
2250 * the wscale option was received.
2251 */
2252 if (sc->sc_flags & SCF_WINSCALE) {
2253 wscale = sc->sc_requested_s_scale;
2254 for (i = nitems(tcp_sc_wstab) - 1;
2255 tcp_sc_wstab[i] > wscale && i > 0;
2256 i--)
2257 ;
2258 cookie.flags.wscale_idx = i;
2259 }
2260
2261 /* Can we do SACK? */
2262 if (sc->sc_flags & SCF_SACK)
2263 cookie.flags.sack_ok = 1;
2264
2265 /* Which of the two secrets to use. */
2266 secbit = V_tcp_syncache.secret.oddeven & 0x1;
2267 cookie.flags.odd_even = secbit;
2268
2269 secbits = V_tcp_syncache.secret.key[secbit];
2270 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2271 (uintptr_t)sch);
2272
2273 /*
2274 * Put the flags into the hash and XOR them to get better ISS number
2275 * variance. This doesn't enhance the cryptographic strength and is
2276 * done to prevent the 8 cookie bits from showing up directly on the
2277 * wire.
2278 */
2279 iss = hash & ~0xff;
2280 iss |= cookie.cookie ^ (hash >> 24);
2281
2282 TCPSTAT_INC(tcps_sc_sendcookie);
2283 return (iss);
2284 }
2285
2286 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)2287 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch,
2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2289 struct socket *lso, uint16_t port)
2290 {
2291 uint32_t hash;
2292 uint8_t *secbits;
2293 tcp_seq ack, seq;
2294 int wnd;
2295 union syncookie cookie;
2296
2297 /*
2298 * Pull information out of SYN-ACK/ACK and revert sequence number
2299 * advances.
2300 */
2301 ack = th->th_ack - 1;
2302 seq = th->th_seq - 1;
2303
2304 /*
2305 * Unpack the flags containing enough information to restore the
2306 * connection.
2307 */
2308 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2309
2310 /* Which of the two secrets to use. */
2311 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even];
2312
2313 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2314
2315 /* The recomputed hash matches the ACK if this was a genuine cookie. */
2316 if ((ack & ~0xff) != (hash & ~0xff))
2317 return (false);
2318
2319 /* Fill in the syncache values. */
2320 sc->sc_flags = 0;
2321 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2322 sc->sc_ipopts = NULL;
2323
2324 sc->sc_irs = seq;
2325 sc->sc_iss = ack;
2326
2327 switch (inc->inc_flags & INC_ISIPV6) {
2328 #ifdef INET
2329 case 0:
2330 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2331 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2332 break;
2333 #endif
2334 #ifdef INET6
2335 case INC_ISIPV6:
2336 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2337 sc->sc_flowlabel =
2338 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK;
2339 break;
2340 #endif
2341 }
2342
2343 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2344
2345 /* Only use wscale if it was enabled in the orignal SYN. */
2346 if (cookie.flags.wscale_idx > 0) {
2347 u_int wscale = 0;
2348
2349 /* Recompute the receive window scale that was sent earlier. */
2350 while (wscale < TCP_MAX_WINSHIFT &&
2351 (TCP_MAXWIN << wscale) < sb_max)
2352 wscale++;
2353 sc->sc_requested_r_scale = wscale;
2354 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2355 sc->sc_flags |= SCF_WINSCALE;
2356 }
2357
2358 wnd = lso->sol_sbrcv_hiwat;
2359 wnd = imax(wnd, 0);
2360 wnd = imin(wnd, TCP_MAXWIN);
2361 sc->sc_wnd = wnd;
2362
2363 if (cookie.flags.sack_ok)
2364 sc->sc_flags |= SCF_SACK;
2365
2366 if (to->to_flags & TOF_TS) {
2367 sc->sc_flags |= SCF_TIMESTAMP;
2368 sc->sc_tsreflect = to->to_tsval;
2369 sc->sc_tsoff = tcp_new_ts_offset(inc);
2370 }
2371
2372 if (to->to_flags & TOF_SIGNATURE)
2373 sc->sc_flags |= SCF_SIGNATURE;
2374
2375 sc->sc_rxmits = 0;
2376
2377 sc->sc_port = port;
2378
2379 return (true);
2380 }
2381
2382 #ifdef INVARIANTS
2383 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)2384 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch,
2385 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2386 struct socket *lso, uint16_t port)
2387 {
2388 struct syncache scs;
2389 char *s;
2390
2391 bzero(&scs, sizeof(scs));
2392 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) &&
2393 (sc->sc_peer_mss != scs.sc_peer_mss ||
2394 sc->sc_requested_r_scale != scs.sc_requested_r_scale ||
2395 sc->sc_requested_s_scale != scs.sc_requested_s_scale ||
2396 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) {
2397
2398 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2399 return;
2400
2401 if (sc->sc_peer_mss != scs.sc_peer_mss)
2402 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2403 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss);
2404
2405 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale)
2406 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2407 s, __func__, sc->sc_requested_r_scale,
2408 scs.sc_requested_r_scale);
2409
2410 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale)
2411 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2412 s, __func__, sc->sc_requested_s_scale,
2413 scs.sc_requested_s_scale);
2414
2415 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))
2416 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2417
2418 free(s, M_TCPLOG);
2419 }
2420 }
2421 #endif /* INVARIANTS */
2422
2423 static void
syncookie_reseed(void * arg)2424 syncookie_reseed(void *arg)
2425 {
2426 struct tcp_syncache *sc = arg;
2427 uint8_t *secbits;
2428 int secbit;
2429
2430 /*
2431 * Reseeding the secret doesn't have to be protected by a lock.
2432 * It only must be ensured that the new random values are visible
2433 * to all CPUs in a SMP environment. The atomic with release
2434 * semantics ensures that.
2435 */
2436 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2437 secbits = sc->secret.key[secbit];
2438 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2439 atomic_add_rel_int(&sc->secret.oddeven, 1);
2440
2441 /* Reschedule ourself. */
2442 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2443 }
2444
2445 /*
2446 * We have overflowed a bucket. Let's pause dealing with the syncache.
2447 * This function will increment the bucketoverflow statistics appropriately
2448 * (once per pause when pausing is enabled; otherwise, once per overflow).
2449 */
2450 static void
syncache_pause(struct in_conninfo * inc)2451 syncache_pause(struct in_conninfo *inc)
2452 {
2453 time_t delta;
2454 const char *s;
2455
2456 /* XXX:
2457 * 2. Add sysctl read here so we don't get the benefit of this
2458 * change without the new sysctl.
2459 */
2460
2461 /*
2462 * Try an unlocked read. If we already know that another thread
2463 * has activated the feature, there is no need to proceed.
2464 */
2465 if (V_tcp_syncache.paused)
2466 return;
2467
2468 /* Are cookied enabled? If not, we can't pause. */
2469 if (!V_tcp_syncookies) {
2470 TCPSTAT_INC(tcps_sc_bucketoverflow);
2471 return;
2472 }
2473
2474 /*
2475 * We may be the first thread to find an overflow. Get the lock
2476 * and evaluate if we need to take action.
2477 */
2478 mtx_lock(&V_tcp_syncache.pause_mtx);
2479 if (V_tcp_syncache.paused) {
2480 mtx_unlock(&V_tcp_syncache.pause_mtx);
2481 return;
2482 }
2483
2484 /* Activate protection. */
2485 V_tcp_syncache.paused = true;
2486 TCPSTAT_INC(tcps_sc_bucketoverflow);
2487
2488 /*
2489 * Determine the last backoff time. If we are seeing a re-newed
2490 * attack within that same time after last reactivating the syncache,
2491 * consider it an extension of the same attack.
2492 */
2493 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff;
2494 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) {
2495 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) {
2496 delta <<= 1;
2497 V_tcp_syncache.pause_backoff++;
2498 }
2499 } else {
2500 delta = TCP_SYNCACHE_PAUSE_TIME;
2501 V_tcp_syncache.pause_backoff = 0;
2502 }
2503
2504 /* Log a warning, including IP addresses, if able. */
2505 if (inc != NULL)
2506 s = tcp_log_addrs(inc, NULL, NULL, NULL);
2507 else
2508 s = (const char *)NULL;
2509 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for "
2510 "the next %lld seconds%s%s%s\n", (long long)delta,
2511 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "",
2512 (s != NULL) ? ")" : "");
2513 free(__DECONST(void *, s), M_TCPLOG);
2514
2515 /* Use the calculated delta to set a new pause time. */
2516 V_tcp_syncache.pause_until = time_uptime + delta;
2517 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause,
2518 &V_tcp_syncache);
2519 mtx_unlock(&V_tcp_syncache.pause_mtx);
2520 }
2521
2522 /* Evaluate whether we need to unpause. */
2523 static void
syncache_unpause(void * arg)2524 syncache_unpause(void *arg)
2525 {
2526 struct tcp_syncache *sc;
2527 time_t delta;
2528
2529 sc = arg;
2530 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED);
2531 callout_deactivate(&sc->pause_co);
2532
2533 /*
2534 * Check to make sure we are not running early. If the pause
2535 * time has expired, then deactivate the protection.
2536 */
2537 if ((delta = sc->pause_until - time_uptime) > 0)
2538 callout_schedule(&sc->pause_co, delta * hz);
2539 else
2540 sc->paused = false;
2541 }
2542
2543 /*
2544 * Exports the syncache entries to userland so that netstat can display
2545 * them alongside the other sockets. This function is intended to be
2546 * called only from tcp_pcblist.
2547 *
2548 * Due to concurrency on an active system, the number of pcbs exported
2549 * may have no relation to max_pcbs. max_pcbs merely indicates the
2550 * amount of space the caller allocated for this function to use.
2551 */
2552 int
syncache_pcblist(struct sysctl_req * req)2553 syncache_pcblist(struct sysctl_req *req)
2554 {
2555 struct xtcpcb xt;
2556 struct syncache *sc;
2557 struct syncache_head *sch;
2558 int error, i;
2559
2560 bzero(&xt, sizeof(xt));
2561 xt.xt_len = sizeof(xt);
2562 xt.t_state = TCPS_SYN_RECEIVED;
2563 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
2564 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket);
2565 xt.xt_inp.xi_socket.so_type = SOCK_STREAM;
2566 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING;
2567
2568 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
2569 sch = &V_tcp_syncache.hashbase[i];
2570 SCH_LOCK(sch);
2571 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2572 if (sc->sc_cred != NULL &&
2573 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2574 continue;
2575 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2576 xt.xt_inp.inp_vflag = INP_IPV6;
2577 else
2578 xt.xt_inp.inp_vflag = INP_IPV4;
2579 xt.xt_encaps_port = sc->sc_port;
2580 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc,
2581 sizeof (struct in_conninfo));
2582 error = SYSCTL_OUT(req, &xt, sizeof xt);
2583 if (error) {
2584 SCH_UNLOCK(sch);
2585 return (0);
2586 }
2587 }
2588 SCH_UNLOCK(sch);
2589 }
2590
2591 return (0);
2592 }
2593