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