1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 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 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/hash.h> 45 #include <sys/refcount.h> 46 #include <sys/kernel.h> 47 #include <sys/sysctl.h> 48 #include <sys/limits.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/malloc.h> 52 #include <sys/mbuf.h> 53 #include <sys/proc.h> /* for proc0 declaration */ 54 #include <sys/random.h> 55 #include <sys/socket.h> 56 #include <sys/socketvar.h> 57 #include <sys/syslog.h> 58 #include <sys/ucred.h> 59 60 #include <sys/md5.h> 61 #include <crypto/siphash/siphash.h> 62 63 #include <vm/uma.h> 64 65 #include <net/if.h> 66 #include <net/if_var.h> 67 #include <net/route.h> 68 #include <net/vnet.h> 69 70 #include <netinet/in.h> 71 #include <netinet/in_kdtrace.h> 72 #include <netinet/in_systm.h> 73 #include <netinet/ip.h> 74 #include <netinet/in_var.h> 75 #include <netinet/in_pcb.h> 76 #include <netinet/ip_var.h> 77 #include <netinet/ip_options.h> 78 #ifdef INET6 79 #include <netinet/ip6.h> 80 #include <netinet/icmp6.h> 81 #include <netinet6/nd6.h> 82 #include <netinet6/ip6_var.h> 83 #include <netinet6/in6_pcb.h> 84 #endif 85 #include <netinet/tcp.h> 86 #include <netinet/tcp_fastopen.h> 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #include <netinet/tcp_ecn.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 #include <netinet/udp_var.h> 101 102 #include <netipsec/ipsec_support.h> 103 104 #include <machine/in_cksum.h> 105 106 #include <security/mac/mac_framework.h> 107 108 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 109 #define V_tcp_syncookies VNET(tcp_syncookies) 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 121 #define V_functions_inherit_listen_socket_stack \ 122 VNET(functions_inherit_listen_socket_stack) 123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 124 CTLFLAG_VNET | CTLFLAG_RW, 125 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 126 "Inherit listen socket's stack"); 127 128 #ifdef TCP_OFFLOAD 129 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 130 #endif 131 132 static void syncache_drop(struct syncache *, struct syncache_head *); 133 static void syncache_free(struct syncache *); 134 static void syncache_insert(struct syncache *, struct syncache_head *); 135 static int syncache_respond(struct syncache *, const struct mbuf *, int); 136 static struct socket *syncache_socket(struct syncache *, struct socket *, 137 struct mbuf *m); 138 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 139 int docallout); 140 static void syncache_timer(void *); 141 142 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 143 uint8_t *, uintptr_t); 144 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 145 static struct syncache 146 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 147 struct syncache *, struct tcphdr *, struct tcpopt *, 148 struct socket *, uint16_t); 149 static void syncache_pause(struct in_conninfo *); 150 static void syncache_unpause(void *); 151 static void syncookie_reseed(void *); 152 #ifdef INVARIANTS 153 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 154 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 155 struct socket *lso, uint16_t port); 156 #endif 157 158 /* 159 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 160 * 3 retransmits corresponds to a timeout with default values of 161 * tcp_rexmit_initial * ( 1 + 162 * tcp_backoff[1] + 163 * tcp_backoff[2] + 164 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 165 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 166 * the odds are that the user has given up attempting to connect by then. 167 */ 168 #define SYNCACHE_MAXREXMTS 3 169 170 /* Arbitrary values */ 171 #define TCP_SYNCACHE_HASHSIZE 512 172 #define TCP_SYNCACHE_BUCKETLIMIT 30 173 174 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 175 #define V_tcp_syncache VNET(tcp_syncache) 176 177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 178 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 179 "TCP SYN cache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.bucket_limit), 0, 183 "Per-bucket hash limit for syncache"); 184 185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 186 &VNET_NAME(tcp_syncache.cache_limit), 0, 187 "Overall entry limit for syncache"); 188 189 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 190 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 191 192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 193 &VNET_NAME(tcp_syncache.hashsize), 0, 194 "Size of TCP syncache hashtable"); 195 196 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 197 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 198 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 199 "and mac(4) checks"); 200 201 static int 202 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 203 { 204 int error; 205 u_int new; 206 207 new = V_tcp_syncache.rexmt_limit; 208 error = sysctl_handle_int(oidp, &new, 0, req); 209 if ((error == 0) && (req->newptr != NULL)) { 210 if (new > TCP_MAXRXTSHIFT) 211 error = EINVAL; 212 else 213 V_tcp_syncache.rexmt_limit = new; 214 } 215 return (error); 216 } 217 218 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 219 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 220 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 221 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 222 "Limit on SYN/ACK retransmissions"); 223 224 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 225 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 226 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 227 "Send reset on socket allocation failure"); 228 229 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 230 231 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 232 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 233 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 234 235 /* 236 * Requires the syncache entry to be already removed from the bucket list. 237 */ 238 static void 239 syncache_free(struct syncache *sc) 240 { 241 242 if (sc->sc_ipopts) 243 (void) m_free(sc->sc_ipopts); 244 if (sc->sc_cred) 245 crfree(sc->sc_cred); 246 #ifdef MAC 247 mac_syncache_destroy(&sc->sc_label); 248 #endif 249 250 uma_zfree(V_tcp_syncache.zone, sc); 251 } 252 253 void 254 syncache_init(void) 255 { 256 int i; 257 258 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 259 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 260 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 261 V_tcp_syncache.hash_secret = arc4random(); 262 263 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 264 &V_tcp_syncache.hashsize); 265 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 266 &V_tcp_syncache.bucket_limit); 267 if (!powerof2(V_tcp_syncache.hashsize) || 268 V_tcp_syncache.hashsize == 0) { 269 printf("WARNING: syncache hash size is not a power of 2.\n"); 270 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 271 } 272 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 273 274 /* Set limits. */ 275 V_tcp_syncache.cache_limit = 276 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 277 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 278 &V_tcp_syncache.cache_limit); 279 280 /* Allocate the hash table. */ 281 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 282 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 283 284 #ifdef VIMAGE 285 V_tcp_syncache.vnet = curvnet; 286 #endif 287 288 /* Initialize the hash buckets. */ 289 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 290 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 291 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 292 NULL, MTX_DEF); 293 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 294 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 295 V_tcp_syncache.hashbase[i].sch_length = 0; 296 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 297 V_tcp_syncache.hashbase[i].sch_last_overflow = 298 -(SYNCOOKIE_LIFETIME + 1); 299 } 300 301 /* Create the syncache entry zone. */ 302 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 303 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 304 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 305 V_tcp_syncache.cache_limit); 306 307 /* Start the SYN cookie reseeder callout. */ 308 callout_init(&V_tcp_syncache.secret.reseed, 1); 309 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 310 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 311 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 312 syncookie_reseed, &V_tcp_syncache); 313 314 /* Initialize the pause machinery. */ 315 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 316 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 317 0); 318 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 319 V_tcp_syncache.pause_backoff = 0; 320 V_tcp_syncache.paused = false; 321 } 322 323 #ifdef VIMAGE 324 void 325 syncache_destroy(void) 326 { 327 struct syncache_head *sch; 328 struct syncache *sc, *nsc; 329 int i; 330 331 /* 332 * Stop the re-seed timer before freeing resources. No need to 333 * possibly schedule it another time. 334 */ 335 callout_drain(&V_tcp_syncache.secret.reseed); 336 337 /* Stop the SYN cache pause callout. */ 338 mtx_lock(&V_tcp_syncache.pause_mtx); 339 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 callout_drain(&V_tcp_syncache.pause_co); 342 } else 343 mtx_unlock(&V_tcp_syncache.pause_mtx); 344 345 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 346 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 347 sch = &V_tcp_syncache.hashbase[i]; 348 callout_drain(&sch->sch_timer); 349 350 SCH_LOCK(sch); 351 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 352 syncache_drop(sc, sch); 353 SCH_UNLOCK(sch); 354 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 355 ("%s: sch->sch_bucket not empty", __func__)); 356 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 357 __func__, sch->sch_length)); 358 mtx_destroy(&sch->sch_mtx); 359 } 360 361 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 362 ("%s: cache_count not 0", __func__)); 363 364 /* Free the allocated global resources. */ 365 uma_zdestroy(V_tcp_syncache.zone); 366 free(V_tcp_syncache.hashbase, M_SYNCACHE); 367 mtx_destroy(&V_tcp_syncache.pause_mtx); 368 } 369 #endif 370 371 /* 372 * Inserts a syncache entry into the specified bucket row. 373 * Locks and unlocks the syncache_head autonomously. 374 */ 375 static void 376 syncache_insert(struct syncache *sc, struct syncache_head *sch) 377 { 378 struct syncache *sc2; 379 380 SCH_LOCK(sch); 381 382 /* 383 * Make sure that we don't overflow the per-bucket limit. 384 * If the bucket is full, toss the oldest element. 385 */ 386 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 387 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 388 ("sch->sch_length incorrect")); 389 syncache_pause(&sc->sc_inc); 390 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 391 sch->sch_last_overflow = time_uptime; 392 syncache_drop(sc2, sch); 393 } 394 395 /* Put it into the bucket. */ 396 TAILQ_INSERT_HEAD(&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_added(tod, sc->sc_todctx); 404 } 405 #endif 406 407 /* Reinitialize the bucket row's timer. */ 408 if (sch->sch_length == 1) 409 sch->sch_nextc = ticks + INT_MAX; 410 syncache_timeout(sc, sch, 1); 411 412 SCH_UNLOCK(sch); 413 414 TCPSTATES_INC(TCPS_SYN_RECEIVED); 415 TCPSTAT_INC(tcps_sc_added); 416 } 417 418 /* 419 * Remove and free entry from syncache bucket row. 420 * Expects locked syncache head. 421 */ 422 static void 423 syncache_drop(struct syncache *sc, struct syncache_head *sch) 424 { 425 426 SCH_LOCK_ASSERT(sch); 427 428 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 429 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 430 sch->sch_length--; 431 432 #ifdef TCP_OFFLOAD 433 if (ADDED_BY_TOE(sc)) { 434 struct toedev *tod = sc->sc_tod; 435 436 tod->tod_syncache_removed(tod, sc->sc_todctx); 437 } 438 #endif 439 440 syncache_free(sc); 441 } 442 443 /* 444 * Engage/reengage time on bucket row. 445 */ 446 static void 447 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 448 { 449 int rexmt; 450 451 if (sc->sc_rxmits == 0) 452 rexmt = tcp_rexmit_initial; 453 else 454 TCPT_RANGESET(rexmt, 455 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 456 tcp_rexmit_min, TCPTV_REXMTMAX); 457 sc->sc_rxttime = ticks + rexmt; 458 sc->sc_rxmits++; 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 460 sch->sch_nextc = sc->sc_rxttime; 461 if (docallout) 462 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 463 syncache_timer, (void *)sch); 464 } 465 } 466 467 /* 468 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 469 * If we have retransmitted an entry the maximum number of times, expire it. 470 * One separate timer for each bucket row. 471 */ 472 static void 473 syncache_timer(void *xsch) 474 { 475 struct syncache_head *sch = (struct syncache_head *)xsch; 476 struct syncache *sc, *nsc; 477 struct epoch_tracker et; 478 int tick = ticks; 479 char *s; 480 bool paused; 481 482 CURVNET_SET(sch->sch_sc->vnet); 483 484 /* NB: syncache_head has already been locked by the callout. */ 485 SCH_LOCK_ASSERT(sch); 486 487 /* 488 * In the following cycle we may remove some entries and/or 489 * advance some timeouts, so re-initialize the bucket timer. 490 */ 491 sch->sch_nextc = tick + INT_MAX; 492 493 /* 494 * If we have paused processing, unconditionally remove 495 * all syncache entries. 496 */ 497 mtx_lock(&V_tcp_syncache.pause_mtx); 498 paused = V_tcp_syncache.paused; 499 mtx_unlock(&V_tcp_syncache.pause_mtx); 500 501 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 502 if (paused) { 503 syncache_drop(sc, sch); 504 continue; 505 } 506 /* 507 * We do not check if the listen socket still exists 508 * and accept the case where the listen socket may be 509 * gone by the time we resend the SYN/ACK. We do 510 * not expect this to happens often. If it does, 511 * then the RST will be sent by the time the remote 512 * host does the SYN/ACK->ACK. 513 */ 514 if (TSTMP_GT(sc->sc_rxttime, tick)) { 515 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 516 sch->sch_nextc = sc->sc_rxttime; 517 continue; 518 } 519 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 520 sc->sc_flags &= ~SCF_ECN; 521 } 522 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 524 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 525 "giving up and removing syncache entry\n", 526 s, __func__); 527 free(s, M_TCPLOG); 528 } 529 syncache_drop(sc, sch); 530 TCPSTAT_INC(tcps_sc_stale); 531 continue; 532 } 533 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 534 log(LOG_DEBUG, "%s; %s: Response timeout, " 535 "retransmitting (%u) SYN|ACK\n", 536 s, __func__, sc->sc_rxmits); 537 free(s, M_TCPLOG); 538 } 539 540 NET_EPOCH_ENTER(et); 541 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 542 NET_EPOCH_EXIT(et); 543 TCPSTAT_INC(tcps_sc_retransmitted); 544 syncache_timeout(sc, sch, 0); 545 } 546 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 547 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 548 syncache_timer, (void *)(sch)); 549 CURVNET_RESTORE(); 550 } 551 552 /* 553 * Returns true if the system is only using cookies at the moment. 554 * This could be due to a sysadmin decision to only use cookies, or it 555 * could be due to the system detecting an attack. 556 */ 557 static inline bool 558 syncache_cookiesonly(void) 559 { 560 561 return (V_tcp_syncookies && (V_tcp_syncache.paused || 562 V_tcp_syncookiesonly)); 563 } 564 565 /* 566 * Find the hash bucket for the given connection. 567 */ 568 static struct syncache_head * 569 syncache_hashbucket(struct in_conninfo *inc) 570 { 571 uint32_t hash; 572 573 /* 574 * The hash is built on foreign port + local port + foreign address. 575 * We rely on the fact that struct in_conninfo starts with 16 bits 576 * of foreign port, then 16 bits of local port then followed by 128 577 * bits of foreign address. In case of IPv4 address, the first 3 578 * 32-bit words of the address always are zeroes. 579 */ 580 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 581 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 582 583 return (&V_tcp_syncache.hashbase[hash]); 584 } 585 586 /* 587 * Find an entry in the syncache. 588 * Returns always with locked syncache_head plus a matching entry or NULL. 589 */ 590 static struct syncache * 591 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 592 { 593 struct syncache *sc; 594 struct syncache_head *sch; 595 596 *schp = sch = syncache_hashbucket(inc); 597 SCH_LOCK(sch); 598 599 /* Circle through bucket row to find matching entry. */ 600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 601 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 602 sizeof(struct in_endpoints)) == 0) 603 break; 604 605 return (sc); /* Always returns with locked sch. */ 606 } 607 608 /* 609 * This function is called when we get a RST for a 610 * non-existent connection, so that we can see if the 611 * connection is in the syn cache. If it is, zap it. 612 * If required send a challenge ACK. 613 */ 614 void 615 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 616 uint16_t port) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 char *s = NULL; 621 622 if (syncache_cookiesonly()) 623 return; 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 627 /* 628 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 629 * See RFC 793 page 65, section SEGMENT ARRIVES. 630 */ 631 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) { 632 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 633 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 634 "FIN flag set, segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* 640 * No corresponding connection was found in syncache. 641 * If syncookies are enabled and possibly exclusively 642 * used, or we are under memory pressure, a valid RST 643 * may not find a syncache entry. In that case we're 644 * done and no SYN|ACK retransmissions will happen. 645 * Otherwise the RST was misdirected or spoofed. 646 */ 647 if (sc == NULL) { 648 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 649 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 650 "syncache entry (possibly syncookie only), " 651 "segment ignored\n", s, __func__); 652 TCPSTAT_INC(tcps_badrst); 653 goto done; 654 } 655 656 /* The remote UDP encaps port does not match. */ 657 if (sc->sc_port != port) { 658 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 659 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 660 "syncache entry but non-matching UDP encaps port, " 661 "segment ignored\n", s, __func__); 662 TCPSTAT_INC(tcps_badrst); 663 goto done; 664 } 665 666 /* 667 * If the RST bit is set, check the sequence number to see 668 * if this is a valid reset segment. 669 * 670 * RFC 793 page 37: 671 * In all states except SYN-SENT, all reset (RST) segments 672 * are validated by checking their SEQ-fields. A reset is 673 * valid if its sequence number is in the window. 674 * 675 * RFC 793 page 69: 676 * There are four cases for the acceptability test for an incoming 677 * segment: 678 * 679 * Segment Receive Test 680 * Length Window 681 * ------- ------- ------------------------------------------- 682 * 0 0 SEG.SEQ = RCV.NXT 683 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 684 * >0 0 not acceptable 685 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 686 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 687 * 688 * Note that when receiving a SYN segment in the LISTEN state, 689 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 690 * described in RFC 793, page 66. 691 */ 692 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 693 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 694 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 695 if (V_tcp_insecure_rst || 696 th->th_seq == sc->sc_irs + 1) { 697 syncache_drop(sc, sch); 698 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 699 log(LOG_DEBUG, 700 "%s; %s: Our SYN|ACK was rejected, " 701 "connection attempt aborted by remote " 702 "endpoint\n", 703 s, __func__); 704 TCPSTAT_INC(tcps_sc_reset); 705 } else { 706 TCPSTAT_INC(tcps_badrst); 707 /* Send challenge ACK. */ 708 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 709 log(LOG_DEBUG, "%s; %s: RST with invalid " 710 " SEQ %u != NXT %u (+WND %u), " 711 "sending challenge ACK\n", 712 s, __func__, 713 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 714 syncache_respond(sc, m, TH_ACK); 715 } 716 } else { 717 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 718 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 719 "NXT %u (+WND %u), segment ignored\n", 720 s, __func__, 721 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 722 TCPSTAT_INC(tcps_badrst); 723 } 724 725 done: 726 if (s != NULL) 727 free(s, M_TCPLOG); 728 SCH_UNLOCK(sch); 729 } 730 731 void 732 syncache_badack(struct in_conninfo *inc, uint16_t port) 733 { 734 struct syncache *sc; 735 struct syncache_head *sch; 736 737 if (syncache_cookiesonly()) 738 return; 739 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 740 SCH_LOCK_ASSERT(sch); 741 if ((sc != NULL) && (sc->sc_port == port)) { 742 syncache_drop(sc, sch); 743 TCPSTAT_INC(tcps_sc_badack); 744 } 745 SCH_UNLOCK(sch); 746 } 747 748 void 749 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 750 { 751 struct syncache *sc; 752 struct syncache_head *sch; 753 754 if (syncache_cookiesonly()) 755 return; 756 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 757 SCH_LOCK_ASSERT(sch); 758 if (sc == NULL) 759 goto done; 760 761 /* If the port != sc_port, then it's a bogus ICMP msg */ 762 if (port != sc->sc_port) 763 goto done; 764 765 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 766 if (ntohl(th_seq) != sc->sc_iss) 767 goto done; 768 769 /* 770 * If we've rertransmitted 3 times and this is our second error, 771 * we remove the entry. Otherwise, we allow it to continue on. 772 * This prevents us from incorrectly nuking an entry during a 773 * spurious network outage. 774 * 775 * See tcp_notify(). 776 */ 777 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 778 sc->sc_flags |= SCF_UNREACH; 779 goto done; 780 } 781 syncache_drop(sc, sch); 782 TCPSTAT_INC(tcps_sc_unreach); 783 done: 784 SCH_UNLOCK(sch); 785 } 786 787 /* 788 * Build a new TCP socket structure from a syncache entry. 789 * 790 * On success return the newly created socket with its underlying inp locked. 791 */ 792 static struct socket * 793 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 794 { 795 struct tcp_function_block *blk; 796 struct inpcb *inp = NULL; 797 struct socket *so; 798 struct tcpcb *tp; 799 int error; 800 char *s; 801 802 NET_EPOCH_ASSERT(); 803 804 /* 805 * Ok, create the full blown connection, and set things up 806 * as they would have been set up if we had created the 807 * connection when the SYN arrived. 808 */ 809 if ((so = solisten_clone(lso)) == NULL) 810 goto allocfail; 811 #ifdef MAC 812 mac_socketpeer_set_from_mbuf(m, so); 813 #endif 814 error = in_pcballoc(so, &V_tcbinfo); 815 if (error) { 816 sodealloc(so); 817 goto allocfail; 818 } 819 inp = sotoinpcb(so); 820 if ((tp = tcp_newtcpcb(inp)) == NULL) { 821 in_pcbdetach(inp); 822 in_pcbfree(inp); 823 sodealloc(so); 824 goto allocfail; 825 } 826 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 827 #ifdef INET6 828 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 829 inp->inp_vflag &= ~INP_IPV4; 830 inp->inp_vflag |= INP_IPV6; 831 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 832 } else { 833 inp->inp_vflag &= ~INP_IPV6; 834 inp->inp_vflag |= INP_IPV4; 835 #endif 836 inp->inp_ip_ttl = sc->sc_ip_ttl; 837 inp->inp_ip_tos = sc->sc_ip_tos; 838 inp->inp_laddr = sc->sc_inc.inc_laddr; 839 #ifdef INET6 840 } 841 #endif 842 843 /* 844 * If there's an mbuf and it has a flowid, then let's initialise the 845 * inp with that particular flowid. 846 */ 847 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 848 inp->inp_flowid = m->m_pkthdr.flowid; 849 inp->inp_flowtype = M_HASHTYPE_GET(m); 850 #ifdef NUMA 851 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 852 #endif 853 } 854 855 inp->inp_lport = sc->sc_inc.inc_lport; 856 #ifdef INET6 857 if (inp->inp_vflag & INP_IPV6PROTO) { 858 struct inpcb *oinp = sotoinpcb(lso); 859 860 /* 861 * Inherit socket options from the listening socket. 862 * Note that in6p_inputopts are not (and should not be) 863 * copied, since it stores previously received options and is 864 * used to detect if each new option is different than the 865 * previous one and hence should be passed to a user. 866 * If we copied in6p_inputopts, a user would not be able to 867 * receive options just after calling the accept system call. 868 */ 869 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 870 if (oinp->in6p_outputopts) 871 inp->in6p_outputopts = 872 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 873 inp->in6p_hops = oinp->in6p_hops; 874 } 875 876 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 877 struct in6_addr laddr6; 878 struct sockaddr_in6 sin6; 879 880 sin6.sin6_family = AF_INET6; 881 sin6.sin6_len = sizeof(sin6); 882 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 883 sin6.sin6_port = sc->sc_inc.inc_fport; 884 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 885 laddr6 = inp->in6p_laddr; 886 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 887 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 888 INP_HASH_WLOCK(&V_tcbinfo); 889 error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 890 thread0.td_ucred, m, false); 891 INP_HASH_WUNLOCK(&V_tcbinfo); 892 if (error != 0) { 893 inp->in6p_laddr = laddr6; 894 goto abort; 895 } 896 /* Override flowlabel from in6_pcbconnect. */ 897 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 898 inp->inp_flow |= sc->sc_flowlabel; 899 } 900 #endif /* INET6 */ 901 #if defined(INET) && defined(INET6) 902 else 903 #endif 904 #ifdef INET 905 { 906 struct in_addr laddr; 907 struct sockaddr_in sin; 908 909 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 910 911 if (inp->inp_options == NULL) { 912 inp->inp_options = sc->sc_ipopts; 913 sc->sc_ipopts = NULL; 914 } 915 916 sin.sin_family = AF_INET; 917 sin.sin_len = sizeof(sin); 918 sin.sin_addr = sc->sc_inc.inc_faddr; 919 sin.sin_port = sc->sc_inc.inc_fport; 920 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 921 laddr = inp->inp_laddr; 922 if (inp->inp_laddr.s_addr == INADDR_ANY) 923 inp->inp_laddr = sc->sc_inc.inc_laddr; 924 INP_HASH_WLOCK(&V_tcbinfo); 925 error = in_pcbconnect(inp, (struct sockaddr *)&sin, 926 thread0.td_ucred, false); 927 INP_HASH_WUNLOCK(&V_tcbinfo); 928 if (error != 0) { 929 inp->inp_laddr = laddr; 930 goto abort; 931 } 932 } 933 #endif /* INET */ 934 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 935 /* Copy old policy into new socket's. */ 936 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 937 printf("syncache_socket: could not copy policy\n"); 938 #endif 939 tp->t_state = TCPS_SYN_RECEIVED; 940 tp->iss = sc->sc_iss; 941 tp->irs = sc->sc_irs; 942 tp->t_port = sc->sc_port; 943 tcp_rcvseqinit(tp); 944 tcp_sendseqinit(tp); 945 blk = sototcpcb(lso)->t_fb; 946 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 947 /* 948 * Our parents t_fb was not the default, 949 * we need to release our ref on tp->t_fb and 950 * pickup one on the new entry. 951 */ 952 struct tcp_function_block *rblk; 953 954 rblk = find_and_ref_tcp_fb(blk); 955 KASSERT(rblk != NULL, 956 ("cannot find blk %p out of syncache?", blk)); 957 if (tp->t_fb->tfb_tcp_fb_fini) 958 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 959 refcount_release(&tp->t_fb->tfb_refcnt); 960 tp->t_fb = rblk; 961 /* 962 * XXXrrs this is quite dangerous, it is possible 963 * for the new function to fail to init. We also 964 * are not asking if the handoff_is_ok though at 965 * the very start thats probalbly ok. 966 */ 967 if (tp->t_fb->tfb_tcp_fb_init) { 968 (*tp->t_fb->tfb_tcp_fb_init)(tp); 969 } 970 } 971 tp->snd_wl1 = sc->sc_irs; 972 tp->snd_max = tp->iss + 1; 973 tp->snd_nxt = tp->iss + 1; 974 tp->rcv_up = sc->sc_irs + 1; 975 tp->rcv_wnd = sc->sc_wnd; 976 tp->rcv_adv += tp->rcv_wnd; 977 tp->last_ack_sent = tp->rcv_nxt; 978 979 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 980 if (sc->sc_flags & SCF_NOOPT) 981 tp->t_flags |= TF_NOOPT; 982 else { 983 if (sc->sc_flags & SCF_WINSCALE) { 984 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 985 tp->snd_scale = sc->sc_requested_s_scale; 986 tp->request_r_scale = sc->sc_requested_r_scale; 987 } 988 if (sc->sc_flags & SCF_TIMESTAMP) { 989 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 990 tp->ts_recent = sc->sc_tsreflect; 991 tp->ts_recent_age = tcp_ts_getticks(); 992 tp->ts_offset = sc->sc_tsoff; 993 } 994 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 995 if (sc->sc_flags & SCF_SIGNATURE) 996 tp->t_flags |= TF_SIGNATURE; 997 #endif 998 if (sc->sc_flags & SCF_SACK) 999 tp->t_flags |= TF_SACK_PERMIT; 1000 } 1001 1002 tcp_ecn_syncache_socket(tp, sc); 1003 1004 /* 1005 * Set up MSS and get cached values from tcp_hostcache. 1006 * This might overwrite some of the defaults we just set. 1007 */ 1008 tcp_mss(tp, sc->sc_peer_mss); 1009 1010 /* 1011 * If the SYN,ACK was retransmitted, indicate that CWND to be 1012 * limited to one segment in cc_conn_init(). 1013 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1014 */ 1015 if (sc->sc_rxmits > 1) 1016 tp->snd_cwnd = 1; 1017 1018 #ifdef TCP_OFFLOAD 1019 /* 1020 * Allow a TOE driver to install its hooks. Note that we hold the 1021 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1022 * new connection before the TOE driver has done its thing. 1023 */ 1024 if (ADDED_BY_TOE(sc)) { 1025 struct toedev *tod = sc->sc_tod; 1026 1027 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1028 } 1029 #endif 1030 /* 1031 * Copy and activate timers. 1032 */ 1033 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1034 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1035 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1036 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1037 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1038 1039 TCPSTAT_INC(tcps_accepts); 1040 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1041 1042 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1043 tp->t_flags |= TF_INCQUEUE; 1044 1045 return (so); 1046 1047 allocfail: 1048 /* 1049 * Drop the connection; we will either send a RST or have the peer 1050 * retransmit its SYN again after its RTO and try again. 1051 */ 1052 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1053 log(LOG_DEBUG, "%s; %s: Socket create failed " 1054 "due to limits or memory shortage\n", 1055 s, __func__); 1056 free(s, M_TCPLOG); 1057 } 1058 TCPSTAT_INC(tcps_listendrop); 1059 return (NULL); 1060 1061 abort: 1062 in_pcbdetach(inp); 1063 in_pcbfree(inp); 1064 sodealloc(so); 1065 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1066 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1067 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1068 error); 1069 free(s, M_TCPLOG); 1070 } 1071 TCPSTAT_INC(tcps_listendrop); 1072 return (NULL); 1073 } 1074 1075 /* 1076 * This function gets called when we receive an ACK for a 1077 * socket in the LISTEN state. We look up the connection 1078 * in the syncache, and if its there, we pull it out of 1079 * the cache and turn it into a full-blown connection in 1080 * the SYN-RECEIVED state. 1081 * 1082 * On syncache_socket() success the newly created socket 1083 * has its underlying inp locked. 1084 */ 1085 int 1086 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1087 struct socket **lsop, struct mbuf *m, uint16_t port) 1088 { 1089 struct syncache *sc; 1090 struct syncache_head *sch; 1091 struct syncache scs; 1092 char *s; 1093 bool locked; 1094 1095 NET_EPOCH_ASSERT(); 1096 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1097 ("%s: can handle only ACK", __func__)); 1098 1099 if (syncache_cookiesonly()) { 1100 sc = NULL; 1101 sch = syncache_hashbucket(inc); 1102 locked = false; 1103 } else { 1104 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1105 locked = true; 1106 SCH_LOCK_ASSERT(sch); 1107 } 1108 1109 #ifdef INVARIANTS 1110 /* 1111 * Test code for syncookies comparing the syncache stored 1112 * values with the reconstructed values from the cookie. 1113 */ 1114 if (sc != NULL) 1115 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1116 #endif 1117 1118 if (sc == NULL) { 1119 /* 1120 * There is no syncache entry, so see if this ACK is 1121 * a returning syncookie. To do this, first: 1122 * A. Check if syncookies are used in case of syncache 1123 * overflows 1124 * B. See if this socket has had a syncache entry dropped in 1125 * the recent past. We don't want to accept a bogus 1126 * syncookie if we've never received a SYN or accept it 1127 * twice. 1128 * C. check that the syncookie is valid. If it is, then 1129 * cobble up a fake syncache entry, and return. 1130 */ 1131 if (locked && !V_tcp_syncookies) { 1132 SCH_UNLOCK(sch); 1133 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1134 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1135 "segment rejected (syncookies disabled)\n", 1136 s, __func__); 1137 goto failed; 1138 } 1139 if (locked && !V_tcp_syncookiesonly && 1140 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1141 SCH_UNLOCK(sch); 1142 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1143 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1144 "segment rejected (no syncache entry)\n", 1145 s, __func__); 1146 goto failed; 1147 } 1148 bzero(&scs, sizeof(scs)); 1149 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1150 if (locked) 1151 SCH_UNLOCK(sch); 1152 if (sc == NULL) { 1153 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1154 log(LOG_DEBUG, "%s; %s: Segment failed " 1155 "SYNCOOKIE authentication, segment rejected " 1156 "(probably spoofed)\n", s, __func__); 1157 goto failed; 1158 } 1159 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1160 /* If received ACK has MD5 signature, check it. */ 1161 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1162 (!TCPMD5_ENABLED() || 1163 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1164 /* Drop the ACK. */ 1165 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1166 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1167 "MD5 signature doesn't match.\n", 1168 s, __func__); 1169 free(s, M_TCPLOG); 1170 } 1171 TCPSTAT_INC(tcps_sig_err_sigopt); 1172 return (-1); /* Do not send RST */ 1173 } 1174 #endif /* TCP_SIGNATURE */ 1175 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1176 } else { 1177 if (sc->sc_port != port) { 1178 SCH_UNLOCK(sch); 1179 return (0); 1180 } 1181 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1182 /* 1183 * If listening socket requested TCP digests, check that 1184 * received ACK has signature and it is correct. 1185 * If not, drop the ACK and leave sc entry in th cache, 1186 * because SYN was received with correct signature. 1187 */ 1188 if (sc->sc_flags & SCF_SIGNATURE) { 1189 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1190 /* No signature */ 1191 TCPSTAT_INC(tcps_sig_err_nosigopt); 1192 SCH_UNLOCK(sch); 1193 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1194 log(LOG_DEBUG, "%s; %s: Segment " 1195 "rejected, MD5 signature wasn't " 1196 "provided.\n", s, __func__); 1197 free(s, M_TCPLOG); 1198 } 1199 return (-1); /* Do not send RST */ 1200 } 1201 if (!TCPMD5_ENABLED() || 1202 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1203 /* Doesn't match or no SA */ 1204 SCH_UNLOCK(sch); 1205 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1206 log(LOG_DEBUG, "%s; %s: Segment " 1207 "rejected, MD5 signature doesn't " 1208 "match.\n", s, __func__); 1209 free(s, M_TCPLOG); 1210 } 1211 return (-1); /* Do not send RST */ 1212 } 1213 } 1214 #endif /* TCP_SIGNATURE */ 1215 1216 /* 1217 * RFC 7323 PAWS: If we have a timestamp on this segment and 1218 * it's less than ts_recent, drop it. 1219 * XXXMT: RFC 7323 also requires to send an ACK. 1220 * In tcp_input.c this is only done for TCP segments 1221 * with user data, so be consistent here and just drop 1222 * the segment. 1223 */ 1224 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1225 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1226 SCH_UNLOCK(sch); 1227 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1228 log(LOG_DEBUG, 1229 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1230 "segment dropped\n", s, __func__, 1231 to->to_tsval, sc->sc_tsreflect); 1232 free(s, M_TCPLOG); 1233 } 1234 return (-1); /* Do not send RST */ 1235 } 1236 1237 /* 1238 * If timestamps were not negotiated during SYN/ACK and a 1239 * segment with a timestamp is received, ignore the 1240 * timestamp and process the packet normally. 1241 * See section 3.2 of RFC 7323. 1242 */ 1243 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1244 (to->to_flags & TOF_TS)) { 1245 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1246 log(LOG_DEBUG, "%s; %s: Timestamp not " 1247 "expected, segment processed normally\n", 1248 s, __func__); 1249 free(s, M_TCPLOG); 1250 s = NULL; 1251 } 1252 } 1253 1254 /* 1255 * If timestamps were negotiated during SYN/ACK and a 1256 * segment without a timestamp is received, silently drop 1257 * the segment, unless the missing timestamps are tolerated. 1258 * See section 3.2 of RFC 7323. 1259 */ 1260 if ((sc->sc_flags & SCF_TIMESTAMP) && 1261 !(to->to_flags & TOF_TS)) { 1262 if (V_tcp_tolerate_missing_ts) { 1263 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1264 log(LOG_DEBUG, 1265 "%s; %s: Timestamp missing, " 1266 "segment processed normally\n", 1267 s, __func__); 1268 free(s, M_TCPLOG); 1269 } 1270 } else { 1271 SCH_UNLOCK(sch); 1272 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1273 log(LOG_DEBUG, 1274 "%s; %s: Timestamp missing, " 1275 "segment silently dropped\n", 1276 s, __func__); 1277 free(s, M_TCPLOG); 1278 } 1279 return (-1); /* Do not send RST */ 1280 } 1281 } 1282 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1283 sch->sch_length--; 1284 #ifdef TCP_OFFLOAD 1285 if (ADDED_BY_TOE(sc)) { 1286 struct toedev *tod = sc->sc_tod; 1287 1288 tod->tod_syncache_removed(tod, sc->sc_todctx); 1289 } 1290 #endif 1291 SCH_UNLOCK(sch); 1292 } 1293 1294 /* 1295 * Segment validation: 1296 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1297 */ 1298 if (th->th_ack != sc->sc_iss + 1) { 1299 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1300 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1301 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1302 goto failed; 1303 } 1304 1305 /* 1306 * The SEQ must fall in the window starting at the received 1307 * initial receive sequence number + 1 (the SYN). 1308 */ 1309 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1310 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1311 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1312 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1313 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1314 goto failed; 1315 } 1316 1317 *lsop = syncache_socket(sc, *lsop, m); 1318 1319 if (*lsop == NULL) 1320 TCPSTAT_INC(tcps_sc_aborted); 1321 else 1322 TCPSTAT_INC(tcps_sc_completed); 1323 1324 /* how do we find the inp for the new socket? */ 1325 if (sc != &scs) 1326 syncache_free(sc); 1327 return (1); 1328 failed: 1329 if (sc != NULL) { 1330 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1331 if (sc != &scs) 1332 syncache_free(sc); 1333 } 1334 if (s != NULL) 1335 free(s, M_TCPLOG); 1336 *lsop = NULL; 1337 return (0); 1338 } 1339 1340 static struct socket * 1341 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1342 uint64_t response_cookie) 1343 { 1344 struct inpcb *inp; 1345 struct tcpcb *tp; 1346 unsigned int *pending_counter; 1347 struct socket *so; 1348 1349 NET_EPOCH_ASSERT(); 1350 1351 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1352 so = syncache_socket(sc, lso, m); 1353 if (so == NULL) { 1354 TCPSTAT_INC(tcps_sc_aborted); 1355 atomic_subtract_int(pending_counter, 1); 1356 } else { 1357 soisconnected(so); 1358 inp = sotoinpcb(so); 1359 tp = intotcpcb(inp); 1360 tp->t_flags |= TF_FASTOPEN; 1361 tp->t_tfo_cookie.server = response_cookie; 1362 tp->snd_max = tp->iss; 1363 tp->snd_nxt = tp->iss; 1364 tp->t_tfo_pending = pending_counter; 1365 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1366 TCPSTAT_INC(tcps_sc_completed); 1367 } 1368 1369 return (so); 1370 } 1371 1372 /* 1373 * Given a LISTEN socket and an inbound SYN request, add 1374 * this to the syn cache, and send back a segment: 1375 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1376 * to the source. 1377 * 1378 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1379 * Doing so would require that we hold onto the data and deliver it 1380 * to the application. However, if we are the target of a SYN-flood 1381 * DoS attack, an attacker could send data which would eventually 1382 * consume all available buffer space if it were ACKed. By not ACKing 1383 * the data, we avoid this DoS scenario. 1384 * 1385 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1386 * cookie is processed and a new socket is created. In this case, any data 1387 * accompanying the SYN will be queued to the socket by tcp_input() and will 1388 * be ACKed either when the application sends response data or the delayed 1389 * ACK timer expires, whichever comes first. 1390 */ 1391 struct socket * 1392 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1393 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1394 void *todctx, uint8_t iptos, uint16_t port) 1395 { 1396 struct tcpcb *tp; 1397 struct socket *rv = NULL; 1398 struct syncache *sc = NULL; 1399 struct syncache_head *sch; 1400 struct mbuf *ipopts = NULL; 1401 u_int ltflags; 1402 int win, ip_ttl, ip_tos; 1403 char *s; 1404 #ifdef INET6 1405 int autoflowlabel = 0; 1406 #endif 1407 #ifdef MAC 1408 struct label *maclabel; 1409 #endif 1410 struct syncache scs; 1411 struct ucred *cred; 1412 uint64_t tfo_response_cookie; 1413 unsigned int *tfo_pending = NULL; 1414 int tfo_cookie_valid = 0; 1415 int tfo_response_cookie_valid = 0; 1416 bool locked; 1417 1418 INP_RLOCK_ASSERT(inp); /* listen socket */ 1419 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1420 ("%s: unexpected tcp flags", __func__)); 1421 1422 /* 1423 * Combine all so/tp operations very early to drop the INP lock as 1424 * soon as possible. 1425 */ 1426 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1427 tp = sototcpcb(so); 1428 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1429 1430 #ifdef INET6 1431 if (inc->inc_flags & INC_ISIPV6) { 1432 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1433 autoflowlabel = 1; 1434 } 1435 ip_ttl = in6_selecthlim(inp, NULL); 1436 if ((inp->in6p_outputopts == NULL) || 1437 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1438 ip_tos = 0; 1439 } else { 1440 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1441 } 1442 } 1443 #endif 1444 #if defined(INET6) && defined(INET) 1445 else 1446 #endif 1447 #ifdef INET 1448 { 1449 ip_ttl = inp->inp_ip_ttl; 1450 ip_tos = inp->inp_ip_tos; 1451 } 1452 #endif 1453 win = so->sol_sbrcv_hiwat; 1454 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1455 1456 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1457 (tp->t_tfo_pending != NULL) && 1458 (to->to_flags & TOF_FASTOPEN)) { 1459 /* 1460 * Limit the number of pending TFO connections to 1461 * approximately half of the queue limit. This prevents TFO 1462 * SYN floods from starving the service by filling the 1463 * listen queue with bogus TFO connections. 1464 */ 1465 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1466 (so->sol_qlimit / 2)) { 1467 int result; 1468 1469 result = tcp_fastopen_check_cookie(inc, 1470 to->to_tfo_cookie, to->to_tfo_len, 1471 &tfo_response_cookie); 1472 tfo_cookie_valid = (result > 0); 1473 tfo_response_cookie_valid = (result >= 0); 1474 } 1475 1476 /* 1477 * Remember the TFO pending counter as it will have to be 1478 * decremented below if we don't make it to syncache_tfo_expand(). 1479 */ 1480 tfo_pending = tp->t_tfo_pending; 1481 } 1482 1483 #ifdef MAC 1484 if (mac_syncache_init(&maclabel) != 0) { 1485 INP_RUNLOCK(inp); 1486 goto done; 1487 } else 1488 mac_syncache_create(maclabel, inp); 1489 #endif 1490 if (!tfo_cookie_valid) 1491 INP_RUNLOCK(inp); 1492 1493 /* 1494 * Remember the IP options, if any. 1495 */ 1496 #ifdef INET6 1497 if (!(inc->inc_flags & INC_ISIPV6)) 1498 #endif 1499 #ifdef INET 1500 ipopts = (m) ? ip_srcroute(m) : NULL; 1501 #else 1502 ipopts = NULL; 1503 #endif 1504 1505 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1506 /* 1507 * When the socket is TCP-MD5 enabled check that, 1508 * - a signed packet is valid 1509 * - a non-signed packet does not have a security association 1510 * 1511 * If a signed packet fails validation or a non-signed packet has a 1512 * security association, the packet will be dropped. 1513 */ 1514 if (ltflags & TF_SIGNATURE) { 1515 if (to->to_flags & TOF_SIGNATURE) { 1516 if (!TCPMD5_ENABLED() || 1517 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1518 goto done; 1519 } else { 1520 if (TCPMD5_ENABLED() && 1521 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1522 goto done; 1523 } 1524 } else if (to->to_flags & TOF_SIGNATURE) 1525 goto done; 1526 #endif /* TCP_SIGNATURE */ 1527 /* 1528 * See if we already have an entry for this connection. 1529 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1530 * 1531 * XXX: should the syncache be re-initialized with the contents 1532 * of the new SYN here (which may have different options?) 1533 * 1534 * XXX: We do not check the sequence number to see if this is a 1535 * real retransmit or a new connection attempt. The question is 1536 * how to handle such a case; either ignore it as spoofed, or 1537 * drop the current entry and create a new one? 1538 */ 1539 if (syncache_cookiesonly()) { 1540 sc = NULL; 1541 sch = syncache_hashbucket(inc); 1542 locked = false; 1543 } else { 1544 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1545 locked = true; 1546 SCH_LOCK_ASSERT(sch); 1547 } 1548 if (sc != NULL) { 1549 if (tfo_cookie_valid) 1550 INP_RUNLOCK(inp); 1551 TCPSTAT_INC(tcps_sc_dupsyn); 1552 if (ipopts) { 1553 /* 1554 * If we were remembering a previous source route, 1555 * forget it and use the new one we've been given. 1556 */ 1557 if (sc->sc_ipopts) 1558 (void) m_free(sc->sc_ipopts); 1559 sc->sc_ipopts = ipopts; 1560 } 1561 /* 1562 * Update timestamp if present. 1563 */ 1564 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1565 sc->sc_tsreflect = to->to_tsval; 1566 else 1567 sc->sc_flags &= ~SCF_TIMESTAMP; 1568 /* 1569 * Disable ECN if needed. 1570 */ 1571 if ((sc->sc_flags & SCF_ECN) && 1572 ((tcp_get_flags(th) & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1573 sc->sc_flags &= ~SCF_ECN; 1574 } 1575 #ifdef MAC 1576 /* 1577 * Since we have already unconditionally allocated label 1578 * storage, free it up. The syncache entry will already 1579 * have an initialized label we can use. 1580 */ 1581 mac_syncache_destroy(&maclabel); 1582 #endif 1583 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1584 /* Retransmit SYN|ACK and reset retransmit count. */ 1585 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1586 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1587 "resetting timer and retransmitting SYN|ACK\n", 1588 s, __func__); 1589 free(s, M_TCPLOG); 1590 } 1591 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1592 sc->sc_rxmits = 0; 1593 syncache_timeout(sc, sch, 1); 1594 TCPSTAT_INC(tcps_sndacks); 1595 TCPSTAT_INC(tcps_sndtotal); 1596 } 1597 SCH_UNLOCK(sch); 1598 goto donenoprobe; 1599 } 1600 1601 if (tfo_cookie_valid) { 1602 bzero(&scs, sizeof(scs)); 1603 sc = &scs; 1604 goto skip_alloc; 1605 } 1606 1607 /* 1608 * Skip allocating a syncache entry if we are just going to discard 1609 * it later. 1610 */ 1611 if (!locked) { 1612 bzero(&scs, sizeof(scs)); 1613 sc = &scs; 1614 } else 1615 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1616 if (sc == NULL) { 1617 /* 1618 * The zone allocator couldn't provide more entries. 1619 * Treat this as if the cache was full; drop the oldest 1620 * entry and insert the new one. 1621 */ 1622 TCPSTAT_INC(tcps_sc_zonefail); 1623 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1624 sch->sch_last_overflow = time_uptime; 1625 syncache_drop(sc, sch); 1626 syncache_pause(inc); 1627 } 1628 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1629 if (sc == NULL) { 1630 if (V_tcp_syncookies) { 1631 bzero(&scs, sizeof(scs)); 1632 sc = &scs; 1633 } else { 1634 KASSERT(locked, 1635 ("%s: bucket unexpectedly unlocked", 1636 __func__)); 1637 SCH_UNLOCK(sch); 1638 if (ipopts) 1639 (void) m_free(ipopts); 1640 goto done; 1641 } 1642 } 1643 } 1644 1645 skip_alloc: 1646 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1647 sc->sc_tfo_cookie = &tfo_response_cookie; 1648 1649 /* 1650 * Fill in the syncache values. 1651 */ 1652 #ifdef MAC 1653 sc->sc_label = maclabel; 1654 #endif 1655 sc->sc_cred = cred; 1656 sc->sc_port = port; 1657 cred = NULL; 1658 sc->sc_ipopts = ipopts; 1659 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1660 sc->sc_ip_tos = ip_tos; 1661 sc->sc_ip_ttl = ip_ttl; 1662 #ifdef TCP_OFFLOAD 1663 sc->sc_tod = tod; 1664 sc->sc_todctx = todctx; 1665 #endif 1666 sc->sc_irs = th->th_seq; 1667 sc->sc_flags = 0; 1668 sc->sc_flowlabel = 0; 1669 1670 /* 1671 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1672 * win was derived from socket earlier in the function. 1673 */ 1674 win = imax(win, 0); 1675 win = imin(win, TCP_MAXWIN); 1676 sc->sc_wnd = win; 1677 1678 if (V_tcp_do_rfc1323 && 1679 !(ltflags & TF_NOOPT)) { 1680 /* 1681 * A timestamp received in a SYN makes 1682 * it ok to send timestamp requests and replies. 1683 */ 1684 if (to->to_flags & TOF_TS) { 1685 sc->sc_tsreflect = to->to_tsval; 1686 sc->sc_flags |= SCF_TIMESTAMP; 1687 sc->sc_tsoff = tcp_new_ts_offset(inc); 1688 } 1689 if (to->to_flags & TOF_SCALE) { 1690 int wscale = 0; 1691 1692 /* 1693 * Pick the smallest possible scaling factor that 1694 * will still allow us to scale up to sb_max, aka 1695 * kern.ipc.maxsockbuf. 1696 * 1697 * We do this because there are broken firewalls that 1698 * will corrupt the window scale option, leading to 1699 * the other endpoint believing that our advertised 1700 * window is unscaled. At scale factors larger than 1701 * 5 the unscaled window will drop below 1500 bytes, 1702 * leading to serious problems when traversing these 1703 * broken firewalls. 1704 * 1705 * With the default maxsockbuf of 256K, a scale factor 1706 * of 3 will be chosen by this algorithm. Those who 1707 * choose a larger maxsockbuf should watch out 1708 * for the compatibility problems mentioned above. 1709 * 1710 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1711 * or <SYN,ACK>) segment itself is never scaled. 1712 */ 1713 while (wscale < TCP_MAX_WINSHIFT && 1714 (TCP_MAXWIN << wscale) < sb_max) 1715 wscale++; 1716 sc->sc_requested_r_scale = wscale; 1717 sc->sc_requested_s_scale = to->to_wscale; 1718 sc->sc_flags |= SCF_WINSCALE; 1719 } 1720 } 1721 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1722 /* 1723 * If incoming packet has an MD5 signature, flag this in the 1724 * syncache so that syncache_respond() will do the right thing 1725 * with the SYN+ACK. 1726 */ 1727 if (to->to_flags & TOF_SIGNATURE) 1728 sc->sc_flags |= SCF_SIGNATURE; 1729 #endif /* TCP_SIGNATURE */ 1730 if (to->to_flags & TOF_SACKPERM) 1731 sc->sc_flags |= SCF_SACK; 1732 if (to->to_flags & TOF_MSS) 1733 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1734 if (ltflags & TF_NOOPT) 1735 sc->sc_flags |= SCF_NOOPT; 1736 /* ECN Handshake */ 1737 if (V_tcp_do_ecn) 1738 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1739 1740 if (V_tcp_syncookies) 1741 sc->sc_iss = syncookie_generate(sch, sc); 1742 else 1743 sc->sc_iss = arc4random(); 1744 #ifdef INET6 1745 if (autoflowlabel) { 1746 if (V_tcp_syncookies) 1747 sc->sc_flowlabel = sc->sc_iss; 1748 else 1749 sc->sc_flowlabel = ip6_randomflowlabel(); 1750 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1751 } 1752 #endif 1753 if (locked) 1754 SCH_UNLOCK(sch); 1755 1756 if (tfo_cookie_valid) { 1757 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1758 /* INP_RUNLOCK(inp) will be performed by the caller */ 1759 goto tfo_expanded; 1760 } 1761 1762 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1763 /* 1764 * Do a standard 3-way handshake. 1765 */ 1766 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1767 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1768 syncache_free(sc); 1769 else if (sc != &scs) 1770 syncache_insert(sc, sch); /* locks and unlocks sch */ 1771 TCPSTAT_INC(tcps_sndacks); 1772 TCPSTAT_INC(tcps_sndtotal); 1773 } else { 1774 if (sc != &scs) 1775 syncache_free(sc); 1776 TCPSTAT_INC(tcps_sc_dropped); 1777 } 1778 goto donenoprobe; 1779 1780 done: 1781 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1782 donenoprobe: 1783 if (m) 1784 m_freem(m); 1785 /* 1786 * If tfo_pending is not NULL here, then a TFO SYN that did not 1787 * result in a new socket was processed and the associated pending 1788 * counter has not yet been decremented. All such TFO processing paths 1789 * transit this point. 1790 */ 1791 if (tfo_pending != NULL) 1792 tcp_fastopen_decrement_counter(tfo_pending); 1793 1794 tfo_expanded: 1795 if (cred != NULL) 1796 crfree(cred); 1797 #ifdef MAC 1798 if (sc == &scs) 1799 mac_syncache_destroy(&maclabel); 1800 #endif 1801 return (rv); 1802 } 1803 1804 /* 1805 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1806 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1807 */ 1808 static int 1809 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1810 { 1811 struct ip *ip = NULL; 1812 struct mbuf *m; 1813 struct tcphdr *th = NULL; 1814 struct udphdr *udp = NULL; 1815 int optlen, error = 0; /* Make compiler happy */ 1816 u_int16_t hlen, tlen, mssopt, ulen; 1817 struct tcpopt to; 1818 #ifdef INET6 1819 struct ip6_hdr *ip6 = NULL; 1820 #endif 1821 1822 NET_EPOCH_ASSERT(); 1823 1824 hlen = 1825 #ifdef INET6 1826 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1827 #endif 1828 sizeof(struct ip); 1829 tlen = hlen + sizeof(struct tcphdr); 1830 if (sc->sc_port) { 1831 tlen += sizeof(struct udphdr); 1832 } 1833 /* Determine MSS we advertize to other end of connection. */ 1834 mssopt = tcp_mssopt(&sc->sc_inc); 1835 if (sc->sc_port) 1836 mssopt -= V_tcp_udp_tunneling_overhead; 1837 mssopt = max(mssopt, V_tcp_minmss); 1838 1839 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1840 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1841 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1842 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1843 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1844 1845 /* Create the IP+TCP header from scratch. */ 1846 m = m_gethdr(M_NOWAIT, MT_DATA); 1847 if (m == NULL) 1848 return (ENOBUFS); 1849 #ifdef MAC 1850 mac_syncache_create_mbuf(sc->sc_label, m); 1851 #endif 1852 m->m_data += max_linkhdr; 1853 m->m_len = tlen; 1854 m->m_pkthdr.len = tlen; 1855 m->m_pkthdr.rcvif = NULL; 1856 1857 #ifdef INET6 1858 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1859 ip6 = mtod(m, struct ip6_hdr *); 1860 ip6->ip6_vfc = IPV6_VERSION; 1861 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1862 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1863 ip6->ip6_plen = htons(tlen - hlen); 1864 /* ip6_hlim is set after checksum */ 1865 /* Zero out traffic class and flow label. */ 1866 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1867 ip6->ip6_flow |= sc->sc_flowlabel; 1868 if (sc->sc_port != 0) { 1869 ip6->ip6_nxt = IPPROTO_UDP; 1870 udp = (struct udphdr *)(ip6 + 1); 1871 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1872 udp->uh_dport = sc->sc_port; 1873 ulen = (tlen - sizeof(struct ip6_hdr)); 1874 th = (struct tcphdr *)(udp + 1); 1875 } else { 1876 ip6->ip6_nxt = IPPROTO_TCP; 1877 th = (struct tcphdr *)(ip6 + 1); 1878 } 1879 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1880 } 1881 #endif 1882 #if defined(INET6) && defined(INET) 1883 else 1884 #endif 1885 #ifdef INET 1886 { 1887 ip = mtod(m, struct ip *); 1888 ip->ip_v = IPVERSION; 1889 ip->ip_hl = sizeof(struct ip) >> 2; 1890 ip->ip_len = htons(tlen); 1891 ip->ip_id = 0; 1892 ip->ip_off = 0; 1893 ip->ip_sum = 0; 1894 ip->ip_src = sc->sc_inc.inc_laddr; 1895 ip->ip_dst = sc->sc_inc.inc_faddr; 1896 ip->ip_ttl = sc->sc_ip_ttl; 1897 ip->ip_tos = sc->sc_ip_tos; 1898 1899 /* 1900 * See if we should do MTU discovery. Route lookups are 1901 * expensive, so we will only unset the DF bit if: 1902 * 1903 * 1) path_mtu_discovery is disabled 1904 * 2) the SCF_UNREACH flag has been set 1905 */ 1906 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1907 ip->ip_off |= htons(IP_DF); 1908 if (sc->sc_port == 0) { 1909 ip->ip_p = IPPROTO_TCP; 1910 th = (struct tcphdr *)(ip + 1); 1911 } else { 1912 ip->ip_p = IPPROTO_UDP; 1913 udp = (struct udphdr *)(ip + 1); 1914 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1915 udp->uh_dport = sc->sc_port; 1916 ulen = (tlen - sizeof(struct ip)); 1917 th = (struct tcphdr *)(udp + 1); 1918 } 1919 } 1920 #endif /* INET */ 1921 th->th_sport = sc->sc_inc.inc_lport; 1922 th->th_dport = sc->sc_inc.inc_fport; 1923 1924 if (flags & TH_SYN) 1925 th->th_seq = htonl(sc->sc_iss); 1926 else 1927 th->th_seq = htonl(sc->sc_iss + 1); 1928 th->th_ack = htonl(sc->sc_irs + 1); 1929 th->th_off = sizeof(struct tcphdr) >> 2; 1930 th->th_win = htons(sc->sc_wnd); 1931 th->th_urp = 0; 1932 1933 flags = tcp_ecn_syncache_respond(flags, sc); 1934 tcp_set_flags(th, flags); 1935 1936 /* Tack on the TCP options. */ 1937 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1938 to.to_flags = 0; 1939 1940 if (flags & TH_SYN) { 1941 to.to_mss = mssopt; 1942 to.to_flags = TOF_MSS; 1943 if (sc->sc_flags & SCF_WINSCALE) { 1944 to.to_wscale = sc->sc_requested_r_scale; 1945 to.to_flags |= TOF_SCALE; 1946 } 1947 if (sc->sc_flags & SCF_SACK) 1948 to.to_flags |= TOF_SACKPERM; 1949 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1950 if (sc->sc_flags & SCF_SIGNATURE) 1951 to.to_flags |= TOF_SIGNATURE; 1952 #endif 1953 if (sc->sc_tfo_cookie) { 1954 to.to_flags |= TOF_FASTOPEN; 1955 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1956 to.to_tfo_cookie = sc->sc_tfo_cookie; 1957 /* don't send cookie again when retransmitting response */ 1958 sc->sc_tfo_cookie = NULL; 1959 } 1960 } 1961 if (sc->sc_flags & SCF_TIMESTAMP) { 1962 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1963 to.to_tsecr = sc->sc_tsreflect; 1964 to.to_flags |= TOF_TS; 1965 } 1966 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1967 1968 /* Adjust headers by option size. */ 1969 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1970 m->m_len += optlen; 1971 m->m_pkthdr.len += optlen; 1972 #ifdef INET6 1973 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1974 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1975 else 1976 #endif 1977 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1978 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1979 if (sc->sc_flags & SCF_SIGNATURE) { 1980 KASSERT(to.to_flags & TOF_SIGNATURE, 1981 ("tcp_addoptions() didn't set tcp_signature")); 1982 1983 /* NOTE: to.to_signature is inside of mbuf */ 1984 if (!TCPMD5_ENABLED() || 1985 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1986 m_freem(m); 1987 return (EACCES); 1988 } 1989 } 1990 #endif 1991 } else 1992 optlen = 0; 1993 1994 if (udp) { 1995 ulen += optlen; 1996 udp->uh_ulen = htons(ulen); 1997 } 1998 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1999 /* 2000 * If we have peer's SYN and it has a flowid, then let's assign it to 2001 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2002 * to SYN|ACK due to lack of inp here. 2003 */ 2004 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2005 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2006 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2007 } 2008 #ifdef INET6 2009 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2010 if (sc->sc_port) { 2011 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2012 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2013 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2014 IPPROTO_UDP, 0); 2015 th->th_sum = htons(0); 2016 } else { 2017 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2018 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2019 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2020 IPPROTO_TCP, 0); 2021 } 2022 ip6->ip6_hlim = sc->sc_ip_ttl; 2023 #ifdef TCP_OFFLOAD 2024 if (ADDED_BY_TOE(sc)) { 2025 struct toedev *tod = sc->sc_tod; 2026 2027 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2028 2029 return (error); 2030 } 2031 #endif 2032 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2033 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2034 } 2035 #endif 2036 #if defined(INET6) && defined(INET) 2037 else 2038 #endif 2039 #ifdef INET 2040 { 2041 if (sc->sc_port) { 2042 m->m_pkthdr.csum_flags = CSUM_UDP; 2043 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2044 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2045 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2046 th->th_sum = htons(0); 2047 } else { 2048 m->m_pkthdr.csum_flags = CSUM_TCP; 2049 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2050 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2051 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2052 } 2053 #ifdef TCP_OFFLOAD 2054 if (ADDED_BY_TOE(sc)) { 2055 struct toedev *tod = sc->sc_tod; 2056 2057 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2058 2059 return (error); 2060 } 2061 #endif 2062 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2063 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2064 } 2065 #endif 2066 return (error); 2067 } 2068 2069 /* 2070 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2071 * that exceed the capacity of the syncache by avoiding the storage of any 2072 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2073 * attacks where the attacker does not have access to our responses. 2074 * 2075 * Syncookies encode and include all necessary information about the 2076 * connection setup within the SYN|ACK that we send back. That way we 2077 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2078 * (if ever). Normally the syncache and syncookies are running in parallel 2079 * with the latter taking over when the former is exhausted. When matching 2080 * syncache entry is found the syncookie is ignored. 2081 * 2082 * The only reliable information persisting the 3WHS is our initial sequence 2083 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2084 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2085 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2086 * returns and signifies a legitimate connection if it matches the ACK. 2087 * 2088 * The available space of 32 bits to store the hash and to encode the SYN 2089 * option information is very tight and we should have at least 24 bits for 2090 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2091 * 2092 * SYN option information we have to encode to fully restore a connection: 2093 * MSS: is imporant to chose an optimal segment size to avoid IP level 2094 * fragmentation along the path. The common MSS values can be encoded 2095 * in a 3-bit table. Uncommon values are captured by the next lower value 2096 * in the table leading to a slight increase in packetization overhead. 2097 * WSCALE: is necessary to allow large windows to be used for high delay- 2098 * bandwidth product links. Not scaling the window when it was initially 2099 * negotiated is bad for performance as lack of scaling further decreases 2100 * the apparent available send window. We only need to encode the WSCALE 2101 * we received from the remote end. Our end can be recalculated at any 2102 * time. The common WSCALE values can be encoded in a 3-bit table. 2103 * Uncommon values are captured by the next lower value in the table 2104 * making us under-estimate the available window size halving our 2105 * theoretically possible maximum throughput for that connection. 2106 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2107 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2108 * that are included in all segments on a connection. We enable them when 2109 * the ACK has them. 2110 * 2111 * Security of syncookies and attack vectors: 2112 * 2113 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2114 * together with the gloabl secret to make it unique per connection attempt. 2115 * Thus any change of any of those parameters results in a different MAC output 2116 * in an unpredictable way unless a collision is encountered. 24 bits of the 2117 * MAC are embedded into the ISS. 2118 * 2119 * To prevent replay attacks two rotating global secrets are updated with a 2120 * new random value every 15 seconds. The life-time of a syncookie is thus 2121 * 15-30 seconds. 2122 * 2123 * Vector 1: Attacking the secret. This requires finding a weakness in the 2124 * MAC itself or the way it is used here. The attacker can do a chosen plain 2125 * text attack by varying and testing the all parameters under his control. 2126 * The strength depends on the size and randomness of the secret, and the 2127 * cryptographic security of the MAC function. Due to the constant updating 2128 * of the secret the attacker has at most 29.999 seconds to find the secret 2129 * and launch spoofed connections. After that he has to start all over again. 2130 * 2131 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2132 * size an average of 4,823 attempts are required for a 50% chance of success 2133 * to spoof a single syncookie (birthday collision paradox). However the 2134 * attacker is blind and doesn't know if one of his attempts succeeded unless 2135 * he has a side channel to interfere success from. A single connection setup 2136 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2137 * This many attempts are required for each one blind spoofed connection. For 2138 * every additional spoofed connection he has to launch another N attempts. 2139 * Thus for a sustained rate 100 spoofed connections per second approximately 2140 * 1,800,000 packets per second would have to be sent. 2141 * 2142 * NB: The MAC function should be fast so that it doesn't become a CPU 2143 * exhaustion attack vector itself. 2144 * 2145 * References: 2146 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2147 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2148 * http://cr.yp.to/syncookies.html (overview) 2149 * http://cr.yp.to/syncookies/archive (details) 2150 * 2151 * 2152 * Schematic construction of a syncookie enabled Initial Sequence Number: 2153 * 0 1 2 3 2154 * 12345678901234567890123456789012 2155 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2156 * 2157 * x 24 MAC (truncated) 2158 * W 3 Send Window Scale index 2159 * M 3 MSS index 2160 * S 1 SACK permitted 2161 * P 1 Odd/even secret 2162 */ 2163 2164 /* 2165 * Distribution and probability of certain MSS values. Those in between are 2166 * rounded down to the next lower one. 2167 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2168 * .2% .3% 5% 7% 7% 20% 15% 45% 2169 */ 2170 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2171 2172 /* 2173 * Distribution and probability of certain WSCALE values. We have to map the 2174 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2175 * bits based on prevalence of certain values. Where we don't have an exact 2176 * match for are rounded down to the next lower one letting us under-estimate 2177 * the true available window. At the moment this would happen only for the 2178 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2179 * and window size). The absence of the WSCALE option (no scaling in either 2180 * direction) is encoded with index zero. 2181 * [WSCALE values histograms, Allman, 2012] 2182 * X 10 10 35 5 6 14 10% by host 2183 * X 11 4 5 5 18 49 3% by connections 2184 */ 2185 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2186 2187 /* 2188 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2189 * and good cryptographic properties. 2190 */ 2191 static uint32_t 2192 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2193 uint8_t *secbits, uintptr_t secmod) 2194 { 2195 SIPHASH_CTX ctx; 2196 uint32_t siphash[2]; 2197 2198 SipHash24_Init(&ctx); 2199 SipHash_SetKey(&ctx, secbits); 2200 switch (inc->inc_flags & INC_ISIPV6) { 2201 #ifdef INET 2202 case 0: 2203 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2204 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2205 break; 2206 #endif 2207 #ifdef INET6 2208 case INC_ISIPV6: 2209 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2210 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2211 break; 2212 #endif 2213 } 2214 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2215 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2216 SipHash_Update(&ctx, &irs, sizeof(irs)); 2217 SipHash_Update(&ctx, &flags, sizeof(flags)); 2218 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2219 SipHash_Final((u_int8_t *)&siphash, &ctx); 2220 2221 return (siphash[0] ^ siphash[1]); 2222 } 2223 2224 static tcp_seq 2225 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2226 { 2227 u_int i, secbit, wscale; 2228 uint32_t iss, hash; 2229 uint8_t *secbits; 2230 union syncookie cookie; 2231 2232 cookie.cookie = 0; 2233 2234 /* Map our computed MSS into the 3-bit index. */ 2235 for (i = nitems(tcp_sc_msstab) - 1; 2236 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2237 i--) 2238 ; 2239 cookie.flags.mss_idx = i; 2240 2241 /* 2242 * Map the send window scale into the 3-bit index but only if 2243 * the wscale option was received. 2244 */ 2245 if (sc->sc_flags & SCF_WINSCALE) { 2246 wscale = sc->sc_requested_s_scale; 2247 for (i = nitems(tcp_sc_wstab) - 1; 2248 tcp_sc_wstab[i] > wscale && i > 0; 2249 i--) 2250 ; 2251 cookie.flags.wscale_idx = i; 2252 } 2253 2254 /* Can we do SACK? */ 2255 if (sc->sc_flags & SCF_SACK) 2256 cookie.flags.sack_ok = 1; 2257 2258 /* Which of the two secrets to use. */ 2259 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2260 cookie.flags.odd_even = secbit; 2261 2262 secbits = V_tcp_syncache.secret.key[secbit]; 2263 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2264 (uintptr_t)sch); 2265 2266 /* 2267 * Put the flags into the hash and XOR them to get better ISS number 2268 * variance. This doesn't enhance the cryptographic strength and is 2269 * done to prevent the 8 cookie bits from showing up directly on the 2270 * wire. 2271 */ 2272 iss = hash & ~0xff; 2273 iss |= cookie.cookie ^ (hash >> 24); 2274 2275 TCPSTAT_INC(tcps_sc_sendcookie); 2276 return (iss); 2277 } 2278 2279 static struct syncache * 2280 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2281 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2282 struct socket *lso, uint16_t port) 2283 { 2284 uint32_t hash; 2285 uint8_t *secbits; 2286 tcp_seq ack, seq; 2287 int wnd, wscale = 0; 2288 union syncookie cookie; 2289 2290 /* 2291 * Pull information out of SYN-ACK/ACK and revert sequence number 2292 * advances. 2293 */ 2294 ack = th->th_ack - 1; 2295 seq = th->th_seq - 1; 2296 2297 /* 2298 * Unpack the flags containing enough information to restore the 2299 * connection. 2300 */ 2301 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2302 2303 /* Which of the two secrets to use. */ 2304 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2305 2306 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2307 2308 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2309 if ((ack & ~0xff) != (hash & ~0xff)) 2310 return (NULL); 2311 2312 /* Fill in the syncache values. */ 2313 sc->sc_flags = 0; 2314 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2315 sc->sc_ipopts = NULL; 2316 2317 sc->sc_irs = seq; 2318 sc->sc_iss = ack; 2319 2320 switch (inc->inc_flags & INC_ISIPV6) { 2321 #ifdef INET 2322 case 0: 2323 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2324 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2325 break; 2326 #endif 2327 #ifdef INET6 2328 case INC_ISIPV6: 2329 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2330 sc->sc_flowlabel = 2331 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2332 break; 2333 #endif 2334 } 2335 2336 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2337 2338 /* We can simply recompute receive window scale we sent earlier. */ 2339 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2340 wscale++; 2341 2342 /* Only use wscale if it was enabled in the orignal SYN. */ 2343 if (cookie.flags.wscale_idx > 0) { 2344 sc->sc_requested_r_scale = wscale; 2345 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2346 sc->sc_flags |= SCF_WINSCALE; 2347 } 2348 2349 wnd = lso->sol_sbrcv_hiwat; 2350 wnd = imax(wnd, 0); 2351 wnd = imin(wnd, TCP_MAXWIN); 2352 sc->sc_wnd = wnd; 2353 2354 if (cookie.flags.sack_ok) 2355 sc->sc_flags |= SCF_SACK; 2356 2357 if (to->to_flags & TOF_TS) { 2358 sc->sc_flags |= SCF_TIMESTAMP; 2359 sc->sc_tsreflect = to->to_tsval; 2360 sc->sc_tsoff = tcp_new_ts_offset(inc); 2361 } 2362 2363 if (to->to_flags & TOF_SIGNATURE) 2364 sc->sc_flags |= SCF_SIGNATURE; 2365 2366 sc->sc_rxmits = 0; 2367 2368 sc->sc_port = port; 2369 2370 TCPSTAT_INC(tcps_sc_recvcookie); 2371 return (sc); 2372 } 2373 2374 #ifdef INVARIANTS 2375 static int 2376 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2377 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2378 struct socket *lso, uint16_t port) 2379 { 2380 struct syncache scs, *scx; 2381 char *s; 2382 2383 bzero(&scs, sizeof(scs)); 2384 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2385 2386 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2387 return (0); 2388 2389 if (scx != NULL) { 2390 if (sc->sc_peer_mss != scx->sc_peer_mss) 2391 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2392 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2393 2394 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2395 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2396 s, __func__, sc->sc_requested_r_scale, 2397 scx->sc_requested_r_scale); 2398 2399 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2400 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2401 s, __func__, sc->sc_requested_s_scale, 2402 scx->sc_requested_s_scale); 2403 2404 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2405 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2406 } 2407 2408 if (s != NULL) 2409 free(s, M_TCPLOG); 2410 return (0); 2411 } 2412 #endif /* INVARIANTS */ 2413 2414 static void 2415 syncookie_reseed(void *arg) 2416 { 2417 struct tcp_syncache *sc = arg; 2418 uint8_t *secbits; 2419 int secbit; 2420 2421 /* 2422 * Reseeding the secret doesn't have to be protected by a lock. 2423 * It only must be ensured that the new random values are visible 2424 * to all CPUs in a SMP environment. The atomic with release 2425 * semantics ensures that. 2426 */ 2427 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2428 secbits = sc->secret.key[secbit]; 2429 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2430 atomic_add_rel_int(&sc->secret.oddeven, 1); 2431 2432 /* Reschedule ourself. */ 2433 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2434 } 2435 2436 /* 2437 * We have overflowed a bucket. Let's pause dealing with the syncache. 2438 * This function will increment the bucketoverflow statistics appropriately 2439 * (once per pause when pausing is enabled; otherwise, once per overflow). 2440 */ 2441 static void 2442 syncache_pause(struct in_conninfo *inc) 2443 { 2444 time_t delta; 2445 const char *s; 2446 2447 /* XXX: 2448 * 2. Add sysctl read here so we don't get the benefit of this 2449 * change without the new sysctl. 2450 */ 2451 2452 /* 2453 * Try an unlocked read. If we already know that another thread 2454 * has activated the feature, there is no need to proceed. 2455 */ 2456 if (V_tcp_syncache.paused) 2457 return; 2458 2459 /* Are cookied enabled? If not, we can't pause. */ 2460 if (!V_tcp_syncookies) { 2461 TCPSTAT_INC(tcps_sc_bucketoverflow); 2462 return; 2463 } 2464 2465 /* 2466 * We may be the first thread to find an overflow. Get the lock 2467 * and evaluate if we need to take action. 2468 */ 2469 mtx_lock(&V_tcp_syncache.pause_mtx); 2470 if (V_tcp_syncache.paused) { 2471 mtx_unlock(&V_tcp_syncache.pause_mtx); 2472 return; 2473 } 2474 2475 /* Activate protection. */ 2476 V_tcp_syncache.paused = true; 2477 TCPSTAT_INC(tcps_sc_bucketoverflow); 2478 2479 /* 2480 * Determine the last backoff time. If we are seeing a re-newed 2481 * attack within that same time after last reactivating the syncache, 2482 * consider it an extension of the same attack. 2483 */ 2484 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2485 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2486 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2487 delta <<= 1; 2488 V_tcp_syncache.pause_backoff++; 2489 } 2490 } else { 2491 delta = TCP_SYNCACHE_PAUSE_TIME; 2492 V_tcp_syncache.pause_backoff = 0; 2493 } 2494 2495 /* Log a warning, including IP addresses, if able. */ 2496 if (inc != NULL) 2497 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2498 else 2499 s = (const char *)NULL; 2500 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2501 "the next %lld seconds%s%s%s\n", (long long)delta, 2502 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2503 (s != NULL) ? ")" : ""); 2504 free(__DECONST(void *, s), M_TCPLOG); 2505 2506 /* Use the calculated delta to set a new pause time. */ 2507 V_tcp_syncache.pause_until = time_uptime + delta; 2508 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2509 &V_tcp_syncache); 2510 mtx_unlock(&V_tcp_syncache.pause_mtx); 2511 } 2512 2513 /* Evaluate whether we need to unpause. */ 2514 static void 2515 syncache_unpause(void *arg) 2516 { 2517 struct tcp_syncache *sc; 2518 time_t delta; 2519 2520 sc = arg; 2521 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2522 callout_deactivate(&sc->pause_co); 2523 2524 /* 2525 * Check to make sure we are not running early. If the pause 2526 * time has expired, then deactivate the protection. 2527 */ 2528 if ((delta = sc->pause_until - time_uptime) > 0) 2529 callout_schedule(&sc->pause_co, delta * hz); 2530 else 2531 sc->paused = false; 2532 } 2533 2534 /* 2535 * Exports the syncache entries to userland so that netstat can display 2536 * them alongside the other sockets. This function is intended to be 2537 * called only from tcp_pcblist. 2538 * 2539 * Due to concurrency on an active system, the number of pcbs exported 2540 * may have no relation to max_pcbs. max_pcbs merely indicates the 2541 * amount of space the caller allocated for this function to use. 2542 */ 2543 int 2544 syncache_pcblist(struct sysctl_req *req) 2545 { 2546 struct xtcpcb xt; 2547 struct syncache *sc; 2548 struct syncache_head *sch; 2549 int error, i; 2550 2551 bzero(&xt, sizeof(xt)); 2552 xt.xt_len = sizeof(xt); 2553 xt.t_state = TCPS_SYN_RECEIVED; 2554 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2555 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2556 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2557 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2558 2559 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2560 sch = &V_tcp_syncache.hashbase[i]; 2561 SCH_LOCK(sch); 2562 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2563 if (sc->sc_cred != NULL && 2564 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2565 continue; 2566 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2567 xt.xt_inp.inp_vflag = INP_IPV6; 2568 else 2569 xt.xt_inp.inp_vflag = INP_IPV4; 2570 xt.xt_encaps_port = sc->sc_port; 2571 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2572 sizeof (struct in_conninfo)); 2573 error = SYSCTL_OUT(req, &xt, sizeof xt); 2574 if (error) { 2575 SCH_UNLOCK(sch); 2576 return (0); 2577 } 2578 } 2579 SCH_UNLOCK(sch); 2580 } 2581 2582 return (0); 2583 } 2584