Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]
FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_syncache.c
Version:
- FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
SearchContext: - none - 3 - 10
SearchContext: - none - 3 - 10
1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD: releng/10.3/sys/netinet/tcp_syncache.c 293402 2016-01-08 00:46:28Z stas $"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_pcbgroup.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/limits.h> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 #include <sys/ucred.h> 56 57 #include <sys/md5.h> 58 #include <crypto/siphash/siphash.h> 59 60 #include <vm/uma.h> 61 62 #include <net/if.h> 63 #include <net/route.h> 64 #include <net/vnet.h> 65 66 #include <netinet/in.h> 67 #include <netinet/in_systm.h> 68 #include <netinet/ip.h> 69 #include <netinet/in_var.h> 70 #include <netinet/in_pcb.h> 71 #include <netinet/ip_var.h> 72 #include <netinet/ip_options.h> 73 #ifdef INET6 74 #include <netinet/ip6.h> 75 #include <netinet/icmp6.h> 76 #include <netinet6/nd6.h> 77 #include <netinet6/ip6_var.h> 78 #include <netinet6/in6_pcb.h> 79 #endif 80 #include <netinet/tcp.h> 81 #ifdef TCP_RFC7413 82 #include <netinet/tcp_fastopen.h> 83 #endif 84 #include <netinet/tcp_fsm.h> 85 #include <netinet/tcp_seq.h> 86 #include <netinet/tcp_timer.h> 87 #include <netinet/tcp_var.h> 88 #include <netinet/tcp_syncache.h> 89 #ifdef INET6 90 #include <netinet6/tcp6_var.h> 91 #endif 92 #ifdef TCP_OFFLOAD 93 #include <netinet/toecore.h> 94 #endif 95 96 #ifdef IPSEC 97 #include <netipsec/ipsec.h> 98 #ifdef INET6 99 #include <netipsec/ipsec6.h> 100 #endif 101 #include <netipsec/key.h> 102 #endif /*IPSEC*/ 103 104 #include <machine/in_cksum.h> 105 106 #include <security/mac/mac_framework.h> 107 108 static VNET_DEFINE(int, tcp_syncookies) = 1; 109 #define V_tcp_syncookies VNET(tcp_syncookies) 110 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120 #ifdef TCP_OFFLOAD 121 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 122 #endif 123 124 static void syncache_drop(struct syncache *, struct syncache_head *); 125 static void syncache_free(struct syncache *); 126 static void syncache_insert(struct syncache *, struct syncache_head *); 127 static int syncache_respond(struct syncache *); 128 static struct socket *syncache_socket(struct syncache *, struct socket *, 129 struct mbuf *m); 130 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS); 131 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 132 int docallout); 133 static void syncache_timer(void *); 134 135 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 136 uint8_t *, uintptr_t); 137 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 138 static struct syncache 139 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 140 struct syncache *, struct tcphdr *, struct tcpopt *, 141 struct socket *); 142 static void syncookie_reseed(void *); 143 #ifdef INVARIANTS 144 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 145 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 146 struct socket *lso); 147 #endif 148 149 /* 150 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 151 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 152 * the odds are that the user has given up attempting to connect by then. 153 */ 154 #define SYNCACHE_MAXREXMTS 3 155 156 /* Arbitrary values */ 157 #define TCP_SYNCACHE_HASHSIZE 512 158 #define TCP_SYNCACHE_BUCKETLIMIT 30 159 160 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 161 #define V_tcp_syncache VNET(tcp_syncache) 162 163 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 164 "TCP SYN cache"); 165 166 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 167 &VNET_NAME(tcp_syncache.bucket_limit), 0, 168 "Per-bucket hash limit for syncache"); 169 170 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 171 &VNET_NAME(tcp_syncache.cache_limit), 0, 172 "Overall entry limit for syncache"); 173 174 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD), 175 NULL, 0, &syncache_sysctl_count, "IU", 176 "Current number of entries in syncache"); 177 178 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.hashsize), 0, 180 "Size of TCP syncache hashtable"); 181 182 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 183 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 184 "Limit on SYN/ACK retransmissions"); 185 186 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 187 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 188 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 189 "Send reset on socket allocation failure"); 190 191 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 192 193 #define SYNCACHE_HASH(inc, mask) \ 194 ((V_tcp_syncache.hash_secret ^ \ 195 (inc)->inc_faddr.s_addr ^ \ 196 ((inc)->inc_faddr.s_addr >> 16) ^ \ 197 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 198 199 #define SYNCACHE_HASH6(inc, mask) \ 200 ((V_tcp_syncache.hash_secret ^ \ 201 (inc)->inc6_faddr.s6_addr32[0] ^ \ 202 (inc)->inc6_faddr.s6_addr32[3] ^ \ 203 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 204 205 #define ENDPTS_EQ(a, b) ( \ 206 (a)->ie_fport == (b)->ie_fport && \ 207 (a)->ie_lport == (b)->ie_lport && \ 208 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 209 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 210 ) 211 212 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 213 214 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 215 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 216 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 217 218 /* 219 * Requires the syncache entry to be already removed from the bucket list. 220 */ 221 static void 222 syncache_free(struct syncache *sc) 223 { 224 225 if (sc->sc_ipopts) 226 (void) m_free(sc->sc_ipopts); 227 if (sc->sc_cred) 228 crfree(sc->sc_cred); 229 #ifdef MAC 230 mac_syncache_destroy(&sc->sc_label); 231 #endif 232 233 uma_zfree(V_tcp_syncache.zone, sc); 234 } 235 236 void 237 syncache_init(void) 238 { 239 int i; 240 241 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 242 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 243 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 244 V_tcp_syncache.hash_secret = arc4random(); 245 246 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 247 &V_tcp_syncache.hashsize); 248 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 249 &V_tcp_syncache.bucket_limit); 250 if (!powerof2(V_tcp_syncache.hashsize) || 251 V_tcp_syncache.hashsize == 0) { 252 printf("WARNING: syncache hash size is not a power of 2.\n"); 253 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 254 } 255 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 256 257 /* Set limits. */ 258 V_tcp_syncache.cache_limit = 259 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 260 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 261 &V_tcp_syncache.cache_limit); 262 263 /* Allocate the hash table. */ 264 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 265 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 266 267 #ifdef VIMAGE 268 V_tcp_syncache.vnet = curvnet; 269 #endif 270 271 /* Initialize the hash buckets. */ 272 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 273 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 274 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 275 NULL, MTX_DEF); 276 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 277 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 278 V_tcp_syncache.hashbase[i].sch_length = 0; 279 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 280 } 281 282 /* Create the syncache entry zone. */ 283 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 284 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 285 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 286 V_tcp_syncache.cache_limit); 287 288 /* Start the SYN cookie reseeder callout. */ 289 callout_init(&V_tcp_syncache.secret.reseed, 1); 290 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 291 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 292 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 293 syncookie_reseed, &V_tcp_syncache); 294 } 295 296 #ifdef VIMAGE 297 void 298 syncache_destroy(void) 299 { 300 struct syncache_head *sch; 301 struct syncache *sc, *nsc; 302 int i; 303 304 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 305 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 306 307 sch = &V_tcp_syncache.hashbase[i]; 308 callout_drain(&sch->sch_timer); 309 310 SCH_LOCK(sch); 311 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 312 syncache_drop(sc, sch); 313 SCH_UNLOCK(sch); 314 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 315 ("%s: sch->sch_bucket not empty", __func__)); 316 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 317 __func__, sch->sch_length)); 318 mtx_destroy(&sch->sch_mtx); 319 } 320 321 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 322 ("%s: cache_count not 0", __func__)); 323 324 /* Free the allocated global resources. */ 325 uma_zdestroy(V_tcp_syncache.zone); 326 free(V_tcp_syncache.hashbase, M_SYNCACHE); 327 328 callout_drain(&V_tcp_syncache.secret.reseed); 329 } 330 #endif 331 332 static int 333 syncache_sysctl_count(SYSCTL_HANDLER_ARGS) 334 { 335 int count; 336 337 count = uma_zone_get_cur(V_tcp_syncache.zone); 338 return (sysctl_handle_int(oidp, &count, 0, req)); 339 } 340 341 /* 342 * Inserts a syncache entry into the specified bucket row. 343 * Locks and unlocks the syncache_head autonomously. 344 */ 345 static void 346 syncache_insert(struct syncache *sc, struct syncache_head *sch) 347 { 348 struct syncache *sc2; 349 350 SCH_LOCK(sch); 351 352 /* 353 * Make sure that we don't overflow the per-bucket limit. 354 * If the bucket is full, toss the oldest element. 355 */ 356 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 357 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 358 ("sch->sch_length incorrect")); 359 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 360 syncache_drop(sc2, sch); 361 TCPSTAT_INC(tcps_sc_bucketoverflow); 362 } 363 364 /* Put it into the bucket. */ 365 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 366 sch->sch_length++; 367 368 #ifdef TCP_OFFLOAD 369 if (ADDED_BY_TOE(sc)) { 370 struct toedev *tod = sc->sc_tod; 371 372 tod->tod_syncache_added(tod, sc->sc_todctx); 373 } 374 #endif 375 376 /* Reinitialize the bucket row's timer. */ 377 if (sch->sch_length == 1) 378 sch->sch_nextc = ticks + INT_MAX; 379 syncache_timeout(sc, sch, 1); 380 381 SCH_UNLOCK(sch); 382 383 TCPSTAT_INC(tcps_sc_added); 384 } 385 386 /* 387 * Remove and free entry from syncache bucket row. 388 * Expects locked syncache head. 389 */ 390 static void 391 syncache_drop(struct syncache *sc, struct syncache_head *sch) 392 { 393 394 SCH_LOCK_ASSERT(sch); 395 396 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 397 sch->sch_length--; 398 399 #ifdef TCP_OFFLOAD 400 if (ADDED_BY_TOE(sc)) { 401 struct toedev *tod = sc->sc_tod; 402 403 tod->tod_syncache_removed(tod, sc->sc_todctx); 404 } 405 #endif 406 407 syncache_free(sc); 408 } 409 410 /* 411 * Engage/reengage time on bucket row. 412 */ 413 static void 414 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 415 { 416 sc->sc_rxttime = ticks + 417 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 418 sc->sc_rxmits++; 419 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 420 sch->sch_nextc = sc->sc_rxttime; 421 if (docallout) 422 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 423 syncache_timer, (void *)sch); 424 } 425 } 426 427 /* 428 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 429 * If we have retransmitted an entry the maximum number of times, expire it. 430 * One separate timer for each bucket row. 431 */ 432 static void 433 syncache_timer(void *xsch) 434 { 435 struct syncache_head *sch = (struct syncache_head *)xsch; 436 struct syncache *sc, *nsc; 437 int tick = ticks; 438 char *s; 439 440 CURVNET_SET(sch->sch_sc->vnet); 441 442 /* NB: syncache_head has already been locked by the callout. */ 443 SCH_LOCK_ASSERT(sch); 444 445 /* 446 * In the following cycle we may remove some entries and/or 447 * advance some timeouts, so re-initialize the bucket timer. 448 */ 449 sch->sch_nextc = tick + INT_MAX; 450 451 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 452 /* 453 * We do not check if the listen socket still exists 454 * and accept the case where the listen socket may be 455 * gone by the time we resend the SYN/ACK. We do 456 * not expect this to happens often. If it does, 457 * then the RST will be sent by the time the remote 458 * host does the SYN/ACK->ACK. 459 */ 460 if (TSTMP_GT(sc->sc_rxttime, tick)) { 461 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 462 sch->sch_nextc = sc->sc_rxttime; 463 continue; 464 } 465 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 466 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 467 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 468 "giving up and removing syncache entry\n", 469 s, __func__); 470 free(s, M_TCPLOG); 471 } 472 syncache_drop(sc, sch); 473 TCPSTAT_INC(tcps_sc_stale); 474 continue; 475 } 476 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 477 log(LOG_DEBUG, "%s; %s: Response timeout, " 478 "retransmitting (%u) SYN|ACK\n", 479 s, __func__, sc->sc_rxmits); 480 free(s, M_TCPLOG); 481 } 482 483 (void) syncache_respond(sc); 484 TCPSTAT_INC(tcps_sc_retransmitted); 485 syncache_timeout(sc, sch, 0); 486 } 487 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 488 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 489 syncache_timer, (void *)(sch)); 490 CURVNET_RESTORE(); 491 } 492 493 /* 494 * Find an entry in the syncache. 495 * Returns always with locked syncache_head plus a matching entry or NULL. 496 */ 497 static struct syncache * 498 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 499 { 500 struct syncache *sc; 501 struct syncache_head *sch; 502 503 #ifdef INET6 504 if (inc->inc_flags & INC_ISIPV6) { 505 sch = &V_tcp_syncache.hashbase[ 506 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 507 *schp = sch; 508 509 SCH_LOCK(sch); 510 511 /* Circle through bucket row to find matching entry. */ 512 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 513 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 514 return (sc); 515 } 516 } else 517 #endif 518 { 519 sch = &V_tcp_syncache.hashbase[ 520 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 521 *schp = sch; 522 523 SCH_LOCK(sch); 524 525 /* Circle through bucket row to find matching entry. */ 526 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 527 #ifdef INET6 528 if (sc->sc_inc.inc_flags & INC_ISIPV6) 529 continue; 530 #endif 531 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 532 return (sc); 533 } 534 } 535 SCH_LOCK_ASSERT(*schp); 536 return (NULL); /* always returns with locked sch */ 537 } 538 539 /* 540 * This function is called when we get a RST for a 541 * non-existent connection, so that we can see if the 542 * connection is in the syn cache. If it is, zap it. 543 */ 544 void 545 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 546 { 547 struct syncache *sc; 548 struct syncache_head *sch; 549 char *s = NULL; 550 551 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 552 SCH_LOCK_ASSERT(sch); 553 554 /* 555 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 556 * See RFC 793 page 65, section SEGMENT ARRIVES. 557 */ 558 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 559 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 560 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 561 "FIN flag set, segment ignored\n", s, __func__); 562 TCPSTAT_INC(tcps_badrst); 563 goto done; 564 } 565 566 /* 567 * No corresponding connection was found in syncache. 568 * If syncookies are enabled and possibly exclusively 569 * used, or we are under memory pressure, a valid RST 570 * may not find a syncache entry. In that case we're 571 * done and no SYN|ACK retransmissions will happen. 572 * Otherwise the RST was misdirected or spoofed. 573 */ 574 if (sc == NULL) { 575 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 576 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 577 "syncache entry (possibly syncookie only), " 578 "segment ignored\n", s, __func__); 579 TCPSTAT_INC(tcps_badrst); 580 goto done; 581 } 582 583 /* 584 * If the RST bit is set, check the sequence number to see 585 * if this is a valid reset segment. 586 * RFC 793 page 37: 587 * In all states except SYN-SENT, all reset (RST) segments 588 * are validated by checking their SEQ-fields. A reset is 589 * valid if its sequence number is in the window. 590 * 591 * The sequence number in the reset segment is normally an 592 * echo of our outgoing acknowlegement numbers, but some hosts 593 * send a reset with the sequence number at the rightmost edge 594 * of our receive window, and we have to handle this case. 595 */ 596 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 597 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 598 syncache_drop(sc, sch); 599 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 600 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 601 "connection attempt aborted by remote endpoint\n", 602 s, __func__); 603 TCPSTAT_INC(tcps_sc_reset); 604 } else { 605 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 606 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 607 "IRS %u (+WND %u), segment ignored\n", 608 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 609 TCPSTAT_INC(tcps_badrst); 610 } 611 612 done: 613 if (s != NULL) 614 free(s, M_TCPLOG); 615 SCH_UNLOCK(sch); 616 } 617 618 void 619 syncache_badack(struct in_conninfo *inc) 620 { 621 struct syncache *sc; 622 struct syncache_head *sch; 623 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 if (sc != NULL) { 627 syncache_drop(sc, sch); 628 TCPSTAT_INC(tcps_sc_badack); 629 } 630 SCH_UNLOCK(sch); 631 } 632 633 void 634 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 635 { 636 struct syncache *sc; 637 struct syncache_head *sch; 638 639 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 640 SCH_LOCK_ASSERT(sch); 641 if (sc == NULL) 642 goto done; 643 644 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 645 if (ntohl(th->th_seq) != sc->sc_iss) 646 goto done; 647 648 /* 649 * If we've rertransmitted 3 times and this is our second error, 650 * we remove the entry. Otherwise, we allow it to continue on. 651 * This prevents us from incorrectly nuking an entry during a 652 * spurious network outage. 653 * 654 * See tcp_notify(). 655 */ 656 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 657 sc->sc_flags |= SCF_UNREACH; 658 goto done; 659 } 660 syncache_drop(sc, sch); 661 TCPSTAT_INC(tcps_sc_unreach); 662 done: 663 SCH_UNLOCK(sch); 664 } 665 666 /* 667 * Build a new TCP socket structure from a syncache entry. 668 */ 669 static struct socket * 670 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 671 { 672 struct inpcb *inp = NULL; 673 struct socket *so; 674 struct tcpcb *tp; 675 int error; 676 char *s; 677 678 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 679 680 /* 681 * Ok, create the full blown connection, and set things up 682 * as they would have been set up if we had created the 683 * connection when the SYN arrived. If we can't create 684 * the connection, abort it. 685 */ 686 so = sonewconn(lso, SS_ISCONNECTED); 687 if (so == NULL) { 688 /* 689 * Drop the connection; we will either send a RST or 690 * have the peer retransmit its SYN again after its 691 * RTO and try again. 692 */ 693 TCPSTAT_INC(tcps_listendrop); 694 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 695 log(LOG_DEBUG, "%s; %s: Socket create failed " 696 "due to limits or memory shortage\n", 697 s, __func__); 698 free(s, M_TCPLOG); 699 } 700 goto abort2; 701 } 702 #ifdef MAC 703 mac_socketpeer_set_from_mbuf(m, so); 704 #endif 705 706 inp = sotoinpcb(so); 707 inp->inp_inc.inc_fibnum = so->so_fibnum; 708 INP_WLOCK(inp); 709 INP_HASH_WLOCK(&V_tcbinfo); 710 711 /* Insert new socket into PCB hash list. */ 712 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 713 #ifdef INET6 714 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 715 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 716 } else { 717 inp->inp_vflag &= ~INP_IPV6; 718 inp->inp_vflag |= INP_IPV4; 719 #endif 720 inp->inp_laddr = sc->sc_inc.inc_laddr; 721 #ifdef INET6 722 } 723 #endif 724 725 /* 726 * If there's an mbuf and it has a flowid, then let's initialise the 727 * inp with that particular flowid. 728 */ 729 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 730 inp->inp_flowid = m->m_pkthdr.flowid; 731 inp->inp_flowtype = M_HASHTYPE_GET(m); 732 } 733 734 /* 735 * Install in the reservation hash table for now, but don't yet 736 * install a connection group since the full 4-tuple isn't yet 737 * configured. 738 */ 739 inp->inp_lport = sc->sc_inc.inc_lport; 740 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 741 /* 742 * Undo the assignments above if we failed to 743 * put the PCB on the hash lists. 744 */ 745 #ifdef INET6 746 if (sc->sc_inc.inc_flags & INC_ISIPV6) 747 inp->in6p_laddr = in6addr_any; 748 else 749 #endif 750 inp->inp_laddr.s_addr = INADDR_ANY; 751 inp->inp_lport = 0; 752 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 753 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 754 "with error %i\n", 755 s, __func__, error); 756 free(s, M_TCPLOG); 757 } 758 INP_HASH_WUNLOCK(&V_tcbinfo); 759 goto abort; 760 } 761 #ifdef IPSEC 762 /* Copy old policy into new socket's. */ 763 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 764 printf("syncache_socket: could not copy policy\n"); 765 #endif 766 #ifdef INET6 767 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 768 struct inpcb *oinp = sotoinpcb(lso); 769 struct in6_addr laddr6; 770 struct sockaddr_in6 sin6; 771 /* 772 * Inherit socket options from the listening socket. 773 * Note that in6p_inputopts are not (and should not be) 774 * copied, since it stores previously received options and is 775 * used to detect if each new option is different than the 776 * previous one and hence should be passed to a user. 777 * If we copied in6p_inputopts, a user would not be able to 778 * receive options just after calling the accept system call. 779 */ 780 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 781 if (oinp->in6p_outputopts) 782 inp->in6p_outputopts = 783 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 784 785 sin6.sin6_family = AF_INET6; 786 sin6.sin6_len = sizeof(sin6); 787 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 788 sin6.sin6_port = sc->sc_inc.inc_fport; 789 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 790 laddr6 = inp->in6p_laddr; 791 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 792 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 793 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 794 thread0.td_ucred, m)) != 0) { 795 inp->in6p_laddr = laddr6; 796 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 797 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 798 "with error %i\n", 799 s, __func__, error); 800 free(s, M_TCPLOG); 801 } 802 INP_HASH_WUNLOCK(&V_tcbinfo); 803 goto abort; 804 } 805 /* Override flowlabel from in6_pcbconnect. */ 806 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 807 inp->inp_flow |= sc->sc_flowlabel; 808 } 809 #endif /* INET6 */ 810 #if defined(INET) && defined(INET6) 811 else 812 #endif 813 #ifdef INET 814 { 815 struct in_addr laddr; 816 struct sockaddr_in sin; 817 818 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 819 820 if (inp->inp_options == NULL) { 821 inp->inp_options = sc->sc_ipopts; 822 sc->sc_ipopts = NULL; 823 } 824 825 sin.sin_family = AF_INET; 826 sin.sin_len = sizeof(sin); 827 sin.sin_addr = sc->sc_inc.inc_faddr; 828 sin.sin_port = sc->sc_inc.inc_fport; 829 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 830 laddr = inp->inp_laddr; 831 if (inp->inp_laddr.s_addr == INADDR_ANY) 832 inp->inp_laddr = sc->sc_inc.inc_laddr; 833 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 834 thread0.td_ucred, m)) != 0) { 835 inp->inp_laddr = laddr; 836 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 837 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 838 "with error %i\n", 839 s, __func__, error); 840 free(s, M_TCPLOG); 841 } 842 INP_HASH_WUNLOCK(&V_tcbinfo); 843 goto abort; 844 } 845 } 846 #endif /* INET */ 847 INP_HASH_WUNLOCK(&V_tcbinfo); 848 tp = intotcpcb(inp); 849 tcp_state_change(tp, TCPS_SYN_RECEIVED); 850 tp->iss = sc->sc_iss; 851 tp->irs = sc->sc_irs; 852 tcp_rcvseqinit(tp); 853 tcp_sendseqinit(tp); 854 tp->snd_wl1 = sc->sc_irs; 855 tp->snd_max = tp->iss + 1; 856 tp->snd_nxt = tp->iss + 1; 857 tp->rcv_up = sc->sc_irs + 1; 858 tp->rcv_wnd = sc->sc_wnd; 859 tp->rcv_adv += tp->rcv_wnd; 860 tp->last_ack_sent = tp->rcv_nxt; 861 862 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 863 if (sc->sc_flags & SCF_NOOPT) 864 tp->t_flags |= TF_NOOPT; 865 else { 866 if (sc->sc_flags & SCF_WINSCALE) { 867 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 868 tp->snd_scale = sc->sc_requested_s_scale; 869 tp->request_r_scale = sc->sc_requested_r_scale; 870 } 871 if (sc->sc_flags & SCF_TIMESTAMP) { 872 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 873 tp->ts_recent = sc->sc_tsreflect; 874 tp->ts_recent_age = tcp_ts_getticks(); 875 tp->ts_offset = sc->sc_tsoff; 876 } 877 #ifdef TCP_SIGNATURE 878 if (sc->sc_flags & SCF_SIGNATURE) 879 tp->t_flags |= TF_SIGNATURE; 880 #endif 881 if (sc->sc_flags & SCF_SACK) 882 tp->t_flags |= TF_SACK_PERMIT; 883 } 884 885 if (sc->sc_flags & SCF_ECN) 886 tp->t_flags |= TF_ECN_PERMIT; 887 888 /* 889 * Set up MSS and get cached values from tcp_hostcache. 890 * This might overwrite some of the defaults we just set. 891 */ 892 tcp_mss(tp, sc->sc_peer_mss); 893 894 /* 895 * If the SYN,ACK was retransmitted, indicate that CWND to be 896 * limited to one segment in cc_conn_init(). 897 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 898 */ 899 if (sc->sc_rxmits > 1) 900 tp->snd_cwnd = 1; 901 902 #ifdef TCP_OFFLOAD 903 /* 904 * Allow a TOE driver to install its hooks. Note that we hold the 905 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 906 * new connection before the TOE driver has done its thing. 907 */ 908 if (ADDED_BY_TOE(sc)) { 909 struct toedev *tod = sc->sc_tod; 910 911 tod->tod_offload_socket(tod, sc->sc_todctx, so); 912 } 913 #endif 914 /* 915 * Copy and activate timers. 916 */ 917 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 918 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 919 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 920 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 921 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 922 923 INP_WUNLOCK(inp); 924 925 TCPSTAT_INC(tcps_accepts); 926 return (so); 927 928 abort: 929 INP_WUNLOCK(inp); 930 abort2: 931 if (so != NULL) 932 soabort(so); 933 return (NULL); 934 } 935 936 /* 937 * This function gets called when we receive an ACK for a 938 * socket in the LISTEN state. We look up the connection 939 * in the syncache, and if its there, we pull it out of 940 * the cache and turn it into a full-blown connection in 941 * the SYN-RECEIVED state. 942 */ 943 int 944 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 945 struct socket **lsop, struct mbuf *m) 946 { 947 struct syncache *sc; 948 struct syncache_head *sch; 949 struct syncache scs; 950 char *s; 951 952 /* 953 * Global TCP locks are held because we manipulate the PCB lists 954 * and create a new socket. 955 */ 956 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 957 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 958 ("%s: can handle only ACK", __func__)); 959 960 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 961 SCH_LOCK_ASSERT(sch); 962 963 #ifdef INVARIANTS 964 /* 965 * Test code for syncookies comparing the syncache stored 966 * values with the reconstructed values from the cookie. 967 */ 968 if (sc != NULL) 969 syncookie_cmp(inc, sch, sc, th, to, *lsop); 970 #endif 971 972 if (sc == NULL) { 973 /* 974 * There is no syncache entry, so see if this ACK is 975 * a returning syncookie. To do this, first: 976 * A. See if this socket has had a syncache entry dropped in 977 * the past. We don't want to accept a bogus syncookie 978 * if we've never received a SYN. 979 * B. check that the syncookie is valid. If it is, then 980 * cobble up a fake syncache entry, and return. 981 */ 982 if (!V_tcp_syncookies) { 983 SCH_UNLOCK(sch); 984 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 985 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 986 "segment rejected (syncookies disabled)\n", 987 s, __func__); 988 goto failed; 989 } 990 bzero(&scs, sizeof(scs)); 991 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 992 SCH_UNLOCK(sch); 993 if (sc == NULL) { 994 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 995 log(LOG_DEBUG, "%s; %s: Segment failed " 996 "SYNCOOKIE authentication, segment rejected " 997 "(probably spoofed)\n", s, __func__); 998 goto failed; 999 } 1000 } else { 1001 /* Pull out the entry to unlock the bucket row. */ 1002 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1003 sch->sch_length--; 1004 #ifdef TCP_OFFLOAD 1005 if (ADDED_BY_TOE(sc)) { 1006 struct toedev *tod = sc->sc_tod; 1007 1008 tod->tod_syncache_removed(tod, sc->sc_todctx); 1009 } 1010 #endif 1011 SCH_UNLOCK(sch); 1012 } 1013 1014 /* 1015 * Segment validation: 1016 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1017 */ 1018 if (th->th_ack != sc->sc_iss + 1) { 1019 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1020 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1021 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1022 goto failed; 1023 } 1024 1025 /* 1026 * The SEQ must fall in the window starting at the received 1027 * initial receive sequence number + 1 (the SYN). 1028 */ 1029 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1030 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1031 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1032 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1033 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1034 goto failed; 1035 } 1036 1037 /* 1038 * If timestamps were not negotiated during SYN/ACK they 1039 * must not appear on any segment during this session. 1040 */ 1041 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1042 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1043 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1044 "segment rejected\n", s, __func__); 1045 goto failed; 1046 } 1047 1048 /* 1049 * If timestamps were negotiated during SYN/ACK they should 1050 * appear on every segment during this session. 1051 * XXXAO: This is only informal as there have been unverified 1052 * reports of non-compliants stacks. 1053 */ 1054 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1055 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1056 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1057 "no action\n", s, __func__); 1058 free(s, M_TCPLOG); 1059 s = NULL; 1060 } 1061 } 1062 1063 /* 1064 * If timestamps were negotiated the reflected timestamp 1065 * must be equal to what we actually sent in the SYN|ACK. 1066 */ 1067 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1068 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1069 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1070 "segment rejected\n", 1071 s, __func__, to->to_tsecr, sc->sc_ts); 1072 goto failed; 1073 } 1074 1075 *lsop = syncache_socket(sc, *lsop, m); 1076 1077 if (*lsop == NULL) 1078 TCPSTAT_INC(tcps_sc_aborted); 1079 else 1080 TCPSTAT_INC(tcps_sc_completed); 1081 1082 /* how do we find the inp for the new socket? */ 1083 if (sc != &scs) 1084 syncache_free(sc); 1085 return (1); 1086 failed: 1087 if (sc != NULL && sc != &scs) 1088 syncache_free(sc); 1089 if (s != NULL) 1090 free(s, M_TCPLOG); 1091 *lsop = NULL; 1092 return (0); 1093 } 1094 1095 #ifdef TCP_RFC7413 1096 static void 1097 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1098 uint64_t response_cookie) 1099 { 1100 struct inpcb *inp; 1101 struct tcpcb *tp; 1102 unsigned int *pending_counter; 1103 1104 /* 1105 * Global TCP locks are held because we manipulate the PCB lists 1106 * and create a new socket. 1107 */ 1108 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1109 1110 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1111 *lsop = syncache_socket(sc, *lsop, m); 1112 if (*lsop == NULL) { 1113 TCPSTAT_INC(tcps_sc_aborted); 1114 atomic_subtract_int(pending_counter, 1); 1115 } else { 1116 inp = sotoinpcb(*lsop); 1117 tp = intotcpcb(inp); 1118 tp->t_flags |= TF_FASTOPEN; 1119 tp->t_tfo_cookie = response_cookie; 1120 tp->snd_max = tp->iss; 1121 tp->snd_nxt = tp->iss; 1122 tp->t_tfo_pending = pending_counter; 1123 TCPSTAT_INC(tcps_sc_completed); 1124 } 1125 } 1126 #endif /* TCP_RFC7413 */ 1127 1128 /* 1129 * Given a LISTEN socket and an inbound SYN request, add 1130 * this to the syn cache, and send back a segment: 1131 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1132 * to the source. 1133 * 1134 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1135 * Doing so would require that we hold onto the data and deliver it 1136 * to the application. However, if we are the target of a SYN-flood 1137 * DoS attack, an attacker could send data which would eventually 1138 * consume all available buffer space if it were ACKed. By not ACKing 1139 * the data, we avoid this DoS scenario. 1140 * 1141 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1142 * cookie is processed, V_tcp_fastopen_enabled set to true, and the 1143 * TCP_FASTOPEN socket option is set. In this case, a new socket is created 1144 * and returned via lsop, the mbuf is not freed so that tcp_input() can 1145 * queue its data to the socket, and 1 is returned to indicate the 1146 * TFO-socket-creation path was taken. 1147 */ 1148 int 1149 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1150 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1151 void *todctx) 1152 { 1153 struct tcpcb *tp; 1154 struct socket *so; 1155 struct syncache *sc = NULL; 1156 struct syncache_head *sch; 1157 struct mbuf *ipopts = NULL; 1158 u_int ltflags; 1159 int win, sb_hiwat, ip_ttl, ip_tos; 1160 char *s; 1161 int rv = 0; 1162 #ifdef INET6 1163 int autoflowlabel = 0; 1164 #endif 1165 #ifdef MAC 1166 struct label *maclabel; 1167 #endif 1168 struct syncache scs; 1169 struct ucred *cred; 1170 #ifdef TCP_RFC7413 1171 uint64_t tfo_response_cookie; 1172 int tfo_cookie_valid = 0; 1173 int tfo_response_cookie_valid = 0; 1174 #endif 1175 1176 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 1177 INP_WLOCK_ASSERT(inp); /* listen socket */ 1178 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1179 ("%s: unexpected tcp flags", __func__)); 1180 1181 /* 1182 * Combine all so/tp operations very early to drop the INP lock as 1183 * soon as possible. 1184 */ 1185 so = *lsop; 1186 tp = sototcpcb(so); 1187 cred = crhold(so->so_cred); 1188 1189 #ifdef INET6 1190 if ((inc->inc_flags & INC_ISIPV6) && 1191 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1192 autoflowlabel = 1; 1193 #endif 1194 ip_ttl = inp->inp_ip_ttl; 1195 ip_tos = inp->inp_ip_tos; 1196 win = sbspace(&so->so_rcv); 1197 sb_hiwat = so->so_rcv.sb_hiwat; 1198 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1199 1200 #ifdef TCP_RFC7413 1201 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) && 1202 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1203 /* 1204 * Limit the number of pending TFO connections to 1205 * approximately half of the queue limit. This prevents TFO 1206 * SYN floods from starving the service by filling the 1207 * listen queue with bogus TFO connections. 1208 */ 1209 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1210 (so->so_qlimit / 2)) { 1211 int result; 1212 1213 result = tcp_fastopen_check_cookie(inc, 1214 to->to_tfo_cookie, to->to_tfo_len, 1215 &tfo_response_cookie); 1216 tfo_cookie_valid = (result > 0); 1217 tfo_response_cookie_valid = (result >= 0); 1218 } else 1219 atomic_subtract_int(tp->t_tfo_pending, 1); 1220 } 1221 #endif 1222 1223 /* By the time we drop the lock these should no longer be used. */ 1224 so = NULL; 1225 tp = NULL; 1226 1227 #ifdef MAC 1228 if (mac_syncache_init(&maclabel) != 0) { 1229 INP_WUNLOCK(inp); 1230 INP_INFO_WUNLOCK(&V_tcbinfo); 1231 goto done; 1232 } else 1233 mac_syncache_create(maclabel, inp); 1234 #endif 1235 #ifdef TCP_RFC7413 1236 if (!tfo_cookie_valid) { 1237 INP_WUNLOCK(inp); 1238 INP_INFO_WUNLOCK(&V_tcbinfo); 1239 } 1240 #else 1241 INP_WUNLOCK(inp); 1242 INP_INFO_WUNLOCK(&V_tcbinfo); 1243 #endif 1244 1245 /* 1246 * Remember the IP options, if any. 1247 */ 1248 #ifdef INET6 1249 if (!(inc->inc_flags & INC_ISIPV6)) 1250 #endif 1251 #ifdef INET 1252 ipopts = (m) ? ip_srcroute(m) : NULL; 1253 #else 1254 ipopts = NULL; 1255 #endif 1256 1257 /* 1258 * See if we already have an entry for this connection. 1259 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1260 * 1261 * XXX: should the syncache be re-initialized with the contents 1262 * of the new SYN here (which may have different options?) 1263 * 1264 * XXX: We do not check the sequence number to see if this is a 1265 * real retransmit or a new connection attempt. The question is 1266 * how to handle such a case; either ignore it as spoofed, or 1267 * drop the current entry and create a new one? 1268 */ 1269 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1270 SCH_LOCK_ASSERT(sch); 1271 if (sc != NULL) { 1272 #ifdef TCP_RFC7413 1273 if (tfo_cookie_valid) { 1274 INP_WUNLOCK(inp); 1275 INP_INFO_WUNLOCK(&V_tcbinfo); 1276 } 1277 #endif 1278 TCPSTAT_INC(tcps_sc_dupsyn); 1279 if (ipopts) { 1280 /* 1281 * If we were remembering a previous source route, 1282 * forget it and use the new one we've been given. 1283 */ 1284 if (sc->sc_ipopts) 1285 (void) m_free(sc->sc_ipopts); 1286 sc->sc_ipopts = ipopts; 1287 } 1288 /* 1289 * Update timestamp if present. 1290 */ 1291 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1292 sc->sc_tsreflect = to->to_tsval; 1293 else 1294 sc->sc_flags &= ~SCF_TIMESTAMP; 1295 #ifdef MAC 1296 /* 1297 * Since we have already unconditionally allocated label 1298 * storage, free it up. The syncache entry will already 1299 * have an initialized label we can use. 1300 */ 1301 mac_syncache_destroy(&maclabel); 1302 #endif 1303 /* Retransmit SYN|ACK and reset retransmit count. */ 1304 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1305 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1306 "resetting timer and retransmitting SYN|ACK\n", 1307 s, __func__); 1308 free(s, M_TCPLOG); 1309 } 1310 if (syncache_respond(sc) == 0) { 1311 sc->sc_rxmits = 0; 1312 syncache_timeout(sc, sch, 1); 1313 TCPSTAT_INC(tcps_sndacks); 1314 TCPSTAT_INC(tcps_sndtotal); 1315 } 1316 SCH_UNLOCK(sch); 1317 goto done; 1318 } 1319 1320 #ifdef TCP_RFC7413 1321 if (tfo_cookie_valid) { 1322 bzero(&scs, sizeof(scs)); 1323 sc = &scs; 1324 goto skip_alloc; 1325 } 1326 #endif 1327 1328 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1329 if (sc == NULL) { 1330 /* 1331 * The zone allocator couldn't provide more entries. 1332 * Treat this as if the cache was full; drop the oldest 1333 * entry and insert the new one. 1334 */ 1335 TCPSTAT_INC(tcps_sc_zonefail); 1336 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1337 syncache_drop(sc, sch); 1338 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1339 if (sc == NULL) { 1340 if (V_tcp_syncookies) { 1341 bzero(&scs, sizeof(scs)); 1342 sc = &scs; 1343 } else { 1344 SCH_UNLOCK(sch); 1345 if (ipopts) 1346 (void) m_free(ipopts); 1347 goto done; 1348 } 1349 } 1350 } 1351 1352 #ifdef TCP_RFC7413 1353 skip_alloc: 1354 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1355 sc->sc_tfo_cookie = &tfo_response_cookie; 1356 #endif 1357 1358 /* 1359 * Fill in the syncache values. 1360 */ 1361 #ifdef MAC 1362 sc->sc_label = maclabel; 1363 #endif 1364 sc->sc_cred = cred; 1365 cred = NULL; 1366 sc->sc_ipopts = ipopts; 1367 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1368 #ifdef INET6 1369 if (!(inc->inc_flags & INC_ISIPV6)) 1370 #endif 1371 { 1372 sc->sc_ip_tos = ip_tos; 1373 sc->sc_ip_ttl = ip_ttl; 1374 } 1375 #ifdef TCP_OFFLOAD 1376 sc->sc_tod = tod; 1377 sc->sc_todctx = todctx; 1378 #endif 1379 sc->sc_irs = th->th_seq; 1380 sc->sc_iss = arc4random(); 1381 sc->sc_flags = 0; 1382 sc->sc_flowlabel = 0; 1383 1384 /* 1385 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1386 * win was derived from socket earlier in the function. 1387 */ 1388 win = imax(win, 0); 1389 win = imin(win, TCP_MAXWIN); 1390 sc->sc_wnd = win; 1391 1392 if (V_tcp_do_rfc1323) { 1393 /* 1394 * A timestamp received in a SYN makes 1395 * it ok to send timestamp requests and replies. 1396 */ 1397 if (to->to_flags & TOF_TS) { 1398 sc->sc_tsreflect = to->to_tsval; 1399 sc->sc_ts = tcp_ts_getticks(); 1400 sc->sc_flags |= SCF_TIMESTAMP; 1401 } 1402 if (to->to_flags & TOF_SCALE) { 1403 int wscale = 0; 1404 1405 /* 1406 * Pick the smallest possible scaling factor that 1407 * will still allow us to scale up to sb_max, aka 1408 * kern.ipc.maxsockbuf. 1409 * 1410 * We do this because there are broken firewalls that 1411 * will corrupt the window scale option, leading to 1412 * the other endpoint believing that our advertised 1413 * window is unscaled. At scale factors larger than 1414 * 5 the unscaled window will drop below 1500 bytes, 1415 * leading to serious problems when traversing these 1416 * broken firewalls. 1417 * 1418 * With the default maxsockbuf of 256K, a scale factor 1419 * of 3 will be chosen by this algorithm. Those who 1420 * choose a larger maxsockbuf should watch out 1421 * for the compatiblity problems mentioned above. 1422 * 1423 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1424 * or <SYN,ACK>) segment itself is never scaled. 1425 */ 1426 while (wscale < TCP_MAX_WINSHIFT && 1427 (TCP_MAXWIN << wscale) < sb_max) 1428 wscale++; 1429 sc->sc_requested_r_scale = wscale; 1430 sc->sc_requested_s_scale = to->to_wscale; 1431 sc->sc_flags |= SCF_WINSCALE; 1432 } 1433 } 1434 #ifdef TCP_SIGNATURE 1435 /* 1436 * If listening socket requested TCP digests, and received SYN 1437 * contains the option, flag this in the syncache so that 1438 * syncache_respond() will do the right thing with the SYN+ACK. 1439 * XXX: Currently we always record the option by default and will 1440 * attempt to use it in syncache_respond(). 1441 */ 1442 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1443 sc->sc_flags |= SCF_SIGNATURE; 1444 #endif 1445 if (to->to_flags & TOF_SACKPERM) 1446 sc->sc_flags |= SCF_SACK; 1447 if (to->to_flags & TOF_MSS) 1448 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1449 if (ltflags & TF_NOOPT) 1450 sc->sc_flags |= SCF_NOOPT; 1451 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1452 sc->sc_flags |= SCF_ECN; 1453 1454 if (V_tcp_syncookies) 1455 sc->sc_iss = syncookie_generate(sch, sc); 1456 #ifdef INET6 1457 if (autoflowlabel) { 1458 if (V_tcp_syncookies) 1459 sc->sc_flowlabel = sc->sc_iss; 1460 else 1461 sc->sc_flowlabel = ip6_randomflowlabel(); 1462 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1463 } 1464 #endif 1465 SCH_UNLOCK(sch); 1466 1467 #ifdef TCP_RFC7413 1468 if (tfo_cookie_valid) { 1469 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1470 /* INP_WUNLOCK(inp) will be performed by the called */ 1471 rv = 1; 1472 goto tfo_done; 1473 } 1474 #endif 1475 1476 /* 1477 * Do a standard 3-way handshake. 1478 */ 1479 if (syncache_respond(sc) == 0) { 1480 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1481 syncache_free(sc); 1482 else if (sc != &scs) 1483 syncache_insert(sc, sch); /* locks and unlocks sch */ 1484 TCPSTAT_INC(tcps_sndacks); 1485 TCPSTAT_INC(tcps_sndtotal); 1486 } else { 1487 if (sc != &scs) 1488 syncache_free(sc); 1489 TCPSTAT_INC(tcps_sc_dropped); 1490 } 1491 1492 done: 1493 if (m) { 1494 *lsop = NULL; 1495 m_freem(m); 1496 } 1497 #ifdef TCP_RFC7413 1498 tfo_done: 1499 #endif 1500 if (cred != NULL) 1501 crfree(cred); 1502 #ifdef MAC 1503 if (sc == &scs) 1504 mac_syncache_destroy(&maclabel); 1505 #endif 1506 return (rv); 1507 } 1508 1509 static int 1510 syncache_respond(struct syncache *sc) 1511 { 1512 struct ip *ip = NULL; 1513 struct mbuf *m; 1514 struct tcphdr *th = NULL; 1515 int optlen, error = 0; /* Make compiler happy */ 1516 u_int16_t hlen, tlen, mssopt; 1517 struct tcpopt to; 1518 #ifdef INET6 1519 struct ip6_hdr *ip6 = NULL; 1520 #endif 1521 1522 hlen = 1523 #ifdef INET6 1524 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1525 #endif 1526 sizeof(struct ip); 1527 tlen = hlen + sizeof(struct tcphdr); 1528 1529 /* Determine MSS we advertize to other end of connection. */ 1530 mssopt = tcp_mssopt(&sc->sc_inc); 1531 if (sc->sc_peer_mss) 1532 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1533 1534 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1535 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1536 ("syncache: mbuf too small")); 1537 1538 /* Create the IP+TCP header from scratch. */ 1539 m = m_gethdr(M_NOWAIT, MT_DATA); 1540 if (m == NULL) 1541 return (ENOBUFS); 1542 #ifdef MAC 1543 mac_syncache_create_mbuf(sc->sc_label, m); 1544 #endif 1545 m->m_data += max_linkhdr; 1546 m->m_len = tlen; 1547 m->m_pkthdr.len = tlen; 1548 m->m_pkthdr.rcvif = NULL; 1549 1550 #ifdef INET6 1551 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1552 ip6 = mtod(m, struct ip6_hdr *); 1553 ip6->ip6_vfc = IPV6_VERSION; 1554 ip6->ip6_nxt = IPPROTO_TCP; 1555 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1556 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1557 ip6->ip6_plen = htons(tlen - hlen); 1558 /* ip6_hlim is set after checksum */ 1559 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1560 ip6->ip6_flow |= sc->sc_flowlabel; 1561 1562 th = (struct tcphdr *)(ip6 + 1); 1563 } 1564 #endif 1565 #if defined(INET6) && defined(INET) 1566 else 1567 #endif 1568 #ifdef INET 1569 { 1570 ip = mtod(m, struct ip *); 1571 ip->ip_v = IPVERSION; 1572 ip->ip_hl = sizeof(struct ip) >> 2; 1573 ip->ip_len = htons(tlen); 1574 ip->ip_id = 0; 1575 ip->ip_off = 0; 1576 ip->ip_sum = 0; 1577 ip->ip_p = IPPROTO_TCP; 1578 ip->ip_src = sc->sc_inc.inc_laddr; 1579 ip->ip_dst = sc->sc_inc.inc_faddr; 1580 ip->ip_ttl = sc->sc_ip_ttl; 1581 ip->ip_tos = sc->sc_ip_tos; 1582 1583 /* 1584 * See if we should do MTU discovery. Route lookups are 1585 * expensive, so we will only unset the DF bit if: 1586 * 1587 * 1) path_mtu_discovery is disabled 1588 * 2) the SCF_UNREACH flag has been set 1589 */ 1590 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1591 ip->ip_off |= htons(IP_DF); 1592 1593 th = (struct tcphdr *)(ip + 1); 1594 } 1595 #endif /* INET */ 1596 th->th_sport = sc->sc_inc.inc_lport; 1597 th->th_dport = sc->sc_inc.inc_fport; 1598 1599 th->th_seq = htonl(sc->sc_iss); 1600 th->th_ack = htonl(sc->sc_irs + 1); 1601 th->th_off = sizeof(struct tcphdr) >> 2; 1602 th->th_x2 = 0; 1603 th->th_flags = TH_SYN|TH_ACK; 1604 th->th_win = htons(sc->sc_wnd); 1605 th->th_urp = 0; 1606 1607 if (sc->sc_flags & SCF_ECN) { 1608 th->th_flags |= TH_ECE; 1609 TCPSTAT_INC(tcps_ecn_shs); 1610 } 1611 1612 /* Tack on the TCP options. */ 1613 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1614 to.to_flags = 0; 1615 1616 to.to_mss = mssopt; 1617 to.to_flags = TOF_MSS; 1618 if (sc->sc_flags & SCF_WINSCALE) { 1619 to.to_wscale = sc->sc_requested_r_scale; 1620 to.to_flags |= TOF_SCALE; 1621 } 1622 if (sc->sc_flags & SCF_TIMESTAMP) { 1623 /* Virgin timestamp or TCP cookie enhanced one. */ 1624 to.to_tsval = sc->sc_ts; 1625 to.to_tsecr = sc->sc_tsreflect; 1626 to.to_flags |= TOF_TS; 1627 } 1628 if (sc->sc_flags & SCF_SACK) 1629 to.to_flags |= TOF_SACKPERM; 1630 #ifdef TCP_SIGNATURE 1631 if (sc->sc_flags & SCF_SIGNATURE) 1632 to.to_flags |= TOF_SIGNATURE; 1633 #endif 1634 1635 #ifdef TCP_RFC7413 1636 if (sc->sc_tfo_cookie) { 1637 to.to_flags |= TOF_FASTOPEN; 1638 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1639 to.to_tfo_cookie = sc->sc_tfo_cookie; 1640 /* don't send cookie again when retransmitting response */ 1641 sc->sc_tfo_cookie = NULL; 1642 } 1643 #endif 1644 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1645 1646 /* Adjust headers by option size. */ 1647 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1648 m->m_len += optlen; 1649 m->m_pkthdr.len += optlen; 1650 1651 #ifdef TCP_SIGNATURE 1652 if (sc->sc_flags & SCF_SIGNATURE) 1653 tcp_signature_compute(m, 0, 0, optlen, 1654 to.to_signature, IPSEC_DIR_OUTBOUND); 1655 #endif 1656 #ifdef INET6 1657 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1658 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1659 else 1660 #endif 1661 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1662 } else 1663 optlen = 0; 1664 1665 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1666 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1667 #ifdef INET6 1668 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1669 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1670 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1671 IPPROTO_TCP, 0); 1672 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1673 #ifdef TCP_OFFLOAD 1674 if (ADDED_BY_TOE(sc)) { 1675 struct toedev *tod = sc->sc_tod; 1676 1677 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1678 1679 return (error); 1680 } 1681 #endif 1682 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1683 } 1684 #endif 1685 #if defined(INET6) && defined(INET) 1686 else 1687 #endif 1688 #ifdef INET 1689 { 1690 m->m_pkthdr.csum_flags = CSUM_TCP; 1691 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1692 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1693 #ifdef TCP_OFFLOAD 1694 if (ADDED_BY_TOE(sc)) { 1695 struct toedev *tod = sc->sc_tod; 1696 1697 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1698 1699 return (error); 1700 } 1701 #endif 1702 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1703 } 1704 #endif 1705 return (error); 1706 } 1707 1708 /* 1709 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1710 * that exceed the capacity of the syncache by avoiding the storage of any 1711 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1712 * attacks where the attacker does not have access to our responses. 1713 * 1714 * Syncookies encode and include all necessary information about the 1715 * connection setup within the SYN|ACK that we send back. That way we 1716 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1717 * (if ever). Normally the syncache and syncookies are running in parallel 1718 * with the latter taking over when the former is exhausted. When matching 1719 * syncache entry is found the syncookie is ignored. 1720 * 1721 * The only reliable information persisting the 3WHS is our inital sequence 1722 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1723 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1724 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1725 * returns and signifies a legitimate connection if it matches the ACK. 1726 * 1727 * The available space of 32 bits to store the hash and to encode the SYN 1728 * option information is very tight and we should have at least 24 bits for 1729 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1730 * 1731 * SYN option information we have to encode to fully restore a connection: 1732 * MSS: is imporant to chose an optimal segment size to avoid IP level 1733 * fragmentation along the path. The common MSS values can be encoded 1734 * in a 3-bit table. Uncommon values are captured by the next lower value 1735 * in the table leading to a slight increase in packetization overhead. 1736 * WSCALE: is necessary to allow large windows to be used for high delay- 1737 * bandwidth product links. Not scaling the window when it was initially 1738 * negotiated is bad for performance as lack of scaling further decreases 1739 * the apparent available send window. We only need to encode the WSCALE 1740 * we received from the remote end. Our end can be recalculated at any 1741 * time. The common WSCALE values can be encoded in a 3-bit table. 1742 * Uncommon values are captured by the next lower value in the table 1743 * making us under-estimate the available window size halving our 1744 * theoretically possible maximum throughput for that connection. 1745 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1746 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1747 * that are included in all segments on a connection. We enable them when 1748 * the ACK has them. 1749 * 1750 * Security of syncookies and attack vectors: 1751 * 1752 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1753 * together with the gloabl secret to make it unique per connection attempt. 1754 * Thus any change of any of those parameters results in a different MAC output 1755 * in an unpredictable way unless a collision is encountered. 24 bits of the 1756 * MAC are embedded into the ISS. 1757 * 1758 * To prevent replay attacks two rotating global secrets are updated with a 1759 * new random value every 15 seconds. The life-time of a syncookie is thus 1760 * 15-30 seconds. 1761 * 1762 * Vector 1: Attacking the secret. This requires finding a weakness in the 1763 * MAC itself or the way it is used here. The attacker can do a chosen plain 1764 * text attack by varying and testing the all parameters under his control. 1765 * The strength depends on the size and randomness of the secret, and the 1766 * cryptographic security of the MAC function. Due to the constant updating 1767 * of the secret the attacker has at most 29.999 seconds to find the secret 1768 * and launch spoofed connections. After that he has to start all over again. 1769 * 1770 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1771 * size an average of 4,823 attempts are required for a 50% chance of success 1772 * to spoof a single syncookie (birthday collision paradox). However the 1773 * attacker is blind and doesn't know if one of his attempts succeeded unless 1774 * he has a side channel to interfere success from. A single connection setup 1775 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1776 * This many attempts are required for each one blind spoofed connection. For 1777 * every additional spoofed connection he has to launch another N attempts. 1778 * Thus for a sustained rate 100 spoofed connections per second approximately 1779 * 1,800,000 packets per second would have to be sent. 1780 * 1781 * NB: The MAC function should be fast so that it doesn't become a CPU 1782 * exhaustion attack vector itself. 1783 * 1784 * References: 1785 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1786 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1787 * http://cr.yp.to/syncookies.html (overview) 1788 * http://cr.yp.to/syncookies/archive (details) 1789 * 1790 * 1791 * Schematic construction of a syncookie enabled Initial Sequence Number: 1792 * 0 1 2 3 1793 * 12345678901234567890123456789012 1794 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1795 * 1796 * x 24 MAC (truncated) 1797 * W 3 Send Window Scale index 1798 * M 3 MSS index 1799 * S 1 SACK permitted 1800 * P 1 Odd/even secret 1801 */ 1802 1803 /* 1804 * Distribution and probability of certain MSS values. Those in between are 1805 * rounded down to the next lower one. 1806 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1807 * .2% .3% 5% 7% 7% 20% 15% 45% 1808 */ 1809 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1810 1811 /* 1812 * Distribution and probability of certain WSCALE values. We have to map the 1813 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1814 * bits based on prevalence of certain values. Where we don't have an exact 1815 * match for are rounded down to the next lower one letting us under-estimate 1816 * the true available window. At the moment this would happen only for the 1817 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1818 * and window size). The absence of the WSCALE option (no scaling in either 1819 * direction) is encoded with index zero. 1820 * [WSCALE values histograms, Allman, 2012] 1821 * X 10 10 35 5 6 14 10% by host 1822 * X 11 4 5 5 18 49 3% by connections 1823 */ 1824 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1825 1826 /* 1827 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1828 * and good cryptographic properties. 1829 */ 1830 static uint32_t 1831 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1832 uint8_t *secbits, uintptr_t secmod) 1833 { 1834 SIPHASH_CTX ctx; 1835 uint32_t siphash[2]; 1836 1837 SipHash24_Init(&ctx); 1838 SipHash_SetKey(&ctx, secbits); 1839 switch (inc->inc_flags & INC_ISIPV6) { 1840 #ifdef INET 1841 case 0: 1842 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1843 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1844 break; 1845 #endif 1846 #ifdef INET6 1847 case INC_ISIPV6: 1848 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1849 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1850 break; 1851 #endif 1852 } 1853 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1854 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1855 SipHash_Update(&ctx, &irs, sizeof(irs)); 1856 SipHash_Update(&ctx, &flags, sizeof(flags)); 1857 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1858 SipHash_Final((u_int8_t *)&siphash, &ctx); 1859 1860 return (siphash[0] ^ siphash[1]); 1861 } 1862 1863 static tcp_seq 1864 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1865 { 1866 u_int i, mss, secbit, wscale; 1867 uint32_t iss, hash; 1868 uint8_t *secbits; 1869 union syncookie cookie; 1870 1871 SCH_LOCK_ASSERT(sch); 1872 1873 cookie.cookie = 0; 1874 1875 /* Map our computed MSS into the 3-bit index. */ 1876 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1877 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1878 tcp_sc_msstab[i] > mss && i > 0; 1879 i--) 1880 ; 1881 cookie.flags.mss_idx = i; 1882 1883 /* 1884 * Map the send window scale into the 3-bit index but only if 1885 * the wscale option was received. 1886 */ 1887 if (sc->sc_flags & SCF_WINSCALE) { 1888 wscale = sc->sc_requested_s_scale; 1889 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1890 tcp_sc_wstab[i] > wscale && i > 0; 1891 i--) 1892 ; 1893 cookie.flags.wscale_idx = i; 1894 } 1895 1896 /* Can we do SACK? */ 1897 if (sc->sc_flags & SCF_SACK) 1898 cookie.flags.sack_ok = 1; 1899 1900 /* Which of the two secrets to use. */ 1901 secbit = sch->sch_sc->secret.oddeven & 0x1; 1902 cookie.flags.odd_even = secbit; 1903 1904 secbits = sch->sch_sc->secret.key[secbit]; 1905 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1906 (uintptr_t)sch); 1907 1908 /* 1909 * Put the flags into the hash and XOR them to get better ISS number 1910 * variance. This doesn't enhance the cryptographic strength and is 1911 * done to prevent the 8 cookie bits from showing up directly on the 1912 * wire. 1913 */ 1914 iss = hash & ~0xff; 1915 iss |= cookie.cookie ^ (hash >> 24); 1916 1917 /* Randomize the timestamp. */ 1918 if (sc->sc_flags & SCF_TIMESTAMP) { 1919 sc->sc_ts = arc4random(); 1920 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1921 } 1922 1923 TCPSTAT_INC(tcps_sc_sendcookie); 1924 return (iss); 1925 } 1926 1927 static struct syncache * 1928 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1929 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1930 struct socket *lso) 1931 { 1932 uint32_t hash; 1933 uint8_t *secbits; 1934 tcp_seq ack, seq; 1935 int wnd, wscale = 0; 1936 union syncookie cookie; 1937 1938 SCH_LOCK_ASSERT(sch); 1939 1940 /* 1941 * Pull information out of SYN-ACK/ACK and revert sequence number 1942 * advances. 1943 */ 1944 ack = th->th_ack - 1; 1945 seq = th->th_seq - 1; 1946 1947 /* 1948 * Unpack the flags containing enough information to restore the 1949 * connection. 1950 */ 1951 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1952 1953 /* Which of the two secrets to use. */ 1954 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1955 1956 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1957 1958 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1959 if ((ack & ~0xff) != (hash & ~0xff)) 1960 return (NULL); 1961 1962 /* Fill in the syncache values. */ 1963 sc->sc_flags = 0; 1964 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1965 sc->sc_ipopts = NULL; 1966 1967 sc->sc_irs = seq; 1968 sc->sc_iss = ack; 1969 1970 switch (inc->inc_flags & INC_ISIPV6) { 1971 #ifdef INET 1972 case 0: 1973 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1974 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1975 break; 1976 #endif 1977 #ifdef INET6 1978 case INC_ISIPV6: 1979 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1980 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1981 break; 1982 #endif 1983 } 1984 1985 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1986 1987 /* We can simply recompute receive window scale we sent earlier. */ 1988 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1989 wscale++; 1990 1991 /* Only use wscale if it was enabled in the orignal SYN. */ 1992 if (cookie.flags.wscale_idx > 0) { 1993 sc->sc_requested_r_scale = wscale; 1994 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1995 sc->sc_flags |= SCF_WINSCALE; 1996 } 1997 1998 wnd = sbspace(&lso->so_rcv); 1999 wnd = imax(wnd, 0); 2000 wnd = imin(wnd, TCP_MAXWIN); 2001 sc->sc_wnd = wnd; 2002 2003 if (cookie.flags.sack_ok) 2004 sc->sc_flags |= SCF_SACK; 2005 2006 if (to->to_flags & TOF_TS) { 2007 sc->sc_flags |= SCF_TIMESTAMP; 2008 sc->sc_tsreflect = to->to_tsval; 2009 sc->sc_ts = to->to_tsecr; 2010 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2011 } 2012 2013 if (to->to_flags & TOF_SIGNATURE) 2014 sc->sc_flags |= SCF_SIGNATURE; 2015 2016 sc->sc_rxmits = 0; 2017 2018 TCPSTAT_INC(tcps_sc_recvcookie); 2019 return (sc); 2020 } 2021 2022 #ifdef INVARIANTS 2023 static int 2024 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2025 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2026 struct socket *lso) 2027 { 2028 struct syncache scs, *scx; 2029 char *s; 2030 2031 bzero(&scs, sizeof(scs)); 2032 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2033 2034 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2035 return (0); 2036 2037 if (scx != NULL) { 2038 if (sc->sc_peer_mss != scx->sc_peer_mss) 2039 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2040 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2041 2042 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2043 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2044 s, __func__, sc->sc_requested_r_scale, 2045 scx->sc_requested_r_scale); 2046 2047 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2048 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2049 s, __func__, sc->sc_requested_s_scale, 2050 scx->sc_requested_s_scale); 2051 2052 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2053 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2054 } 2055 2056 if (s != NULL) 2057 free(s, M_TCPLOG); 2058 return (0); 2059 } 2060 #endif /* INVARIANTS */ 2061 2062 static void 2063 syncookie_reseed(void *arg) 2064 { 2065 struct tcp_syncache *sc = arg; 2066 uint8_t *secbits; 2067 int secbit; 2068 2069 /* 2070 * Reseeding the secret doesn't have to be protected by a lock. 2071 * It only must be ensured that the new random values are visible 2072 * to all CPUs in a SMP environment. The atomic with release 2073 * semantics ensures that. 2074 */ 2075 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2076 secbits = sc->secret.key[secbit]; 2077 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2078 atomic_add_rel_int(&sc->secret.oddeven, 1); 2079 2080 /* Reschedule ourself. */ 2081 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2082 } 2083 2084 /* 2085 * Returns the current number of syncache entries. This number 2086 * will probably change before you get around to calling 2087 * syncache_pcblist. 2088 */ 2089 int 2090 syncache_pcbcount(void) 2091 { 2092 struct syncache_head *sch; 2093 int count, i; 2094 2095 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2096 /* No need to lock for a read. */ 2097 sch = &V_tcp_syncache.hashbase[i]; 2098 count += sch->sch_length; 2099 } 2100 return count; 2101 } 2102 2103 /* 2104 * Exports the syncache entries to userland so that netstat can display 2105 * them alongside the other sockets. This function is intended to be 2106 * called only from tcp_pcblist. 2107 * 2108 * Due to concurrency on an active system, the number of pcbs exported 2109 * may have no relation to max_pcbs. max_pcbs merely indicates the 2110 * amount of space the caller allocated for this function to use. 2111 */ 2112 int 2113 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2114 { 2115 struct xtcpcb xt; 2116 struct syncache *sc; 2117 struct syncache_head *sch; 2118 int count, error, i; 2119 2120 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2121 sch = &V_tcp_syncache.hashbase[i]; 2122 SCH_LOCK(sch); 2123 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2124 if (count >= max_pcbs) { 2125 SCH_UNLOCK(sch); 2126 goto exit; 2127 } 2128 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2129 continue; 2130 bzero(&xt, sizeof(xt)); 2131 xt.xt_len = sizeof(xt); 2132 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2133 xt.xt_inp.inp_vflag = INP_IPV6; 2134 else 2135 xt.xt_inp.inp_vflag = INP_IPV4; 2136 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2137 xt.xt_tp.t_inpcb = &xt.xt_inp; 2138 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2139 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2140 xt.xt_socket.xso_len = sizeof (struct xsocket); 2141 xt.xt_socket.so_type = SOCK_STREAM; 2142 xt.xt_socket.so_state = SS_ISCONNECTING; 2143 error = SYSCTL_OUT(req, &xt, sizeof xt); 2144 if (error) { 2145 SCH_UNLOCK(sch); 2146 goto exit; 2147 } 2148 count++; 2149 } 2150 SCH_UNLOCK(sch); 2151 } 2152 exit: 2153 *pcbs_exported = count; 2154 return error; 2155 }
Cache object: 256fad118412d7cbe165a6f43337b98a
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]