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