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 #include "opt_pcbgroup.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/hash.h> 46 #include <sys/refcount.h> 47 #include <sys/kernel.h> 48 #include <sys/sysctl.h> 49 #include <sys/limits.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/malloc.h> 53 #include <sys/mbuf.h> 54 #include <sys/proc.h> /* for proc0 declaration */ 55 #include <sys/random.h> 56 #include <sys/socket.h> 57 #include <sys/socketvar.h> 58 #include <sys/syslog.h> 59 #include <sys/ucred.h> 60 61 #include <sys/md5.h> 62 #include <crypto/siphash/siphash.h> 63 64 #include <vm/uma.h> 65 66 #include <net/if.h> 67 #include <net/if_var.h> 68 #include <net/route.h> 69 #include <net/vnet.h> 70 71 #include <netinet/in.h> 72 #include <netinet/in_kdtrace.h> 73 #include <netinet/in_systm.h> 74 #include <netinet/ip.h> 75 #include <netinet/in_var.h> 76 #include <netinet/in_pcb.h> 77 #include <netinet/ip_var.h> 78 #include <netinet/ip_options.h> 79 #ifdef INET6 80 #include <netinet/ip6.h> 81 #include <netinet/icmp6.h> 82 #include <netinet6/nd6.h> 83 #include <netinet6/ip6_var.h> 84 #include <netinet6/in6_pcb.h> 85 #endif 86 #include <netinet/tcp.h> 87 #include <netinet/tcp_fastopen.h> 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 119 #define V_functions_inherit_listen_socket_stack \ 120 VNET(functions_inherit_listen_socket_stack) 121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 122 CTLFLAG_VNET | CTLFLAG_RW, 123 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 124 "Inherit listen socket's stack"); 125 126 #ifdef TCP_OFFLOAD 127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 128 #endif 129 130 static void syncache_drop(struct syncache *, struct syncache_head *); 131 static void syncache_free(struct syncache *); 132 static void syncache_insert(struct syncache *, struct syncache_head *); 133 static int syncache_respond(struct syncache *, const struct mbuf *, int); 134 static struct socket *syncache_socket(struct syncache *, struct socket *, 135 struct mbuf *m); 136 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 137 int docallout); 138 static void syncache_timer(void *); 139 140 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 141 uint8_t *, uintptr_t); 142 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 143 static struct syncache 144 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 145 struct syncache *, struct tcphdr *, struct tcpopt *, 146 struct socket *); 147 static void syncache_pause(struct in_conninfo *); 148 static void syncache_unpause(void *); 149 static void syncookie_reseed(void *); 150 #ifdef INVARIANTS 151 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 152 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 153 struct socket *lso); 154 #endif 155 156 /* 157 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 158 * 3 retransmits corresponds to a timeout with default values of 159 * tcp_rexmit_initial * ( 1 + 160 * tcp_backoff[1] + 161 * tcp_backoff[2] + 162 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 163 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 164 * the odds are that the user has given up attempting to connect by then. 165 */ 166 #define SYNCACHE_MAXREXMTS 3 167 168 /* Arbitrary values */ 169 #define TCP_SYNCACHE_HASHSIZE 512 170 #define TCP_SYNCACHE_BUCKETLIMIT 30 171 172 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 173 #define V_tcp_syncache VNET(tcp_syncache) 174 175 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 176 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 177 "TCP SYN cache"); 178 179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 180 &VNET_NAME(tcp_syncache.bucket_limit), 0, 181 "Per-bucket hash limit for syncache"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 184 &VNET_NAME(tcp_syncache.cache_limit), 0, 185 "Overall entry limit for syncache"); 186 187 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 188 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 189 190 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 191 &VNET_NAME(tcp_syncache.hashsize), 0, 192 "Size of TCP syncache hashtable"); 193 194 static int 195 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 196 { 197 int error; 198 u_int new; 199 200 new = V_tcp_syncache.rexmt_limit; 201 error = sysctl_handle_int(oidp, &new, 0, req); 202 if ((error == 0) && (req->newptr != NULL)) { 203 if (new > TCP_MAXRXTSHIFT) 204 error = EINVAL; 205 else 206 V_tcp_syncache.rexmt_limit = new; 207 } 208 return (error); 209 } 210 211 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 212 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 213 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 214 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 215 "Limit on SYN/ACK retransmissions"); 216 217 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 219 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 220 "Send reset on socket allocation failure"); 221 222 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 223 224 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 225 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 226 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 227 228 /* 229 * Requires the syncache entry to be already removed from the bucket list. 230 */ 231 static void 232 syncache_free(struct syncache *sc) 233 { 234 235 if (sc->sc_ipopts) 236 (void) m_free(sc->sc_ipopts); 237 if (sc->sc_cred) 238 crfree(sc->sc_cred); 239 #ifdef MAC 240 mac_syncache_destroy(&sc->sc_label); 241 #endif 242 243 uma_zfree(V_tcp_syncache.zone, sc); 244 } 245 246 void 247 syncache_init(void) 248 { 249 int i; 250 251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 252 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 253 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 254 V_tcp_syncache.hash_secret = arc4random(); 255 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 257 &V_tcp_syncache.hashsize); 258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 259 &V_tcp_syncache.bucket_limit); 260 if (!powerof2(V_tcp_syncache.hashsize) || 261 V_tcp_syncache.hashsize == 0) { 262 printf("WARNING: syncache hash size is not a power of 2.\n"); 263 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 264 } 265 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 266 267 /* Set limits. */ 268 V_tcp_syncache.cache_limit = 269 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 271 &V_tcp_syncache.cache_limit); 272 273 /* Allocate the hash table. */ 274 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 275 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 276 277 #ifdef VIMAGE 278 V_tcp_syncache.vnet = curvnet; 279 #endif 280 281 /* Initialize the hash buckets. */ 282 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 283 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 284 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 285 NULL, MTX_DEF); 286 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 287 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 288 V_tcp_syncache.hashbase[i].sch_length = 0; 289 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 290 V_tcp_syncache.hashbase[i].sch_last_overflow = 291 -(SYNCOOKIE_LIFETIME + 1); 292 } 293 294 /* Create the syncache entry zone. */ 295 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 296 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 297 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 298 V_tcp_syncache.cache_limit); 299 300 /* Start the SYN cookie reseeder callout. */ 301 callout_init(&V_tcp_syncache.secret.reseed, 1); 302 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 303 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 304 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 305 syncookie_reseed, &V_tcp_syncache); 306 307 /* Initialize the pause machinery. */ 308 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 309 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 310 0); 311 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 312 V_tcp_syncache.pause_backoff = 0; 313 V_tcp_syncache.paused = false; 314 } 315 316 #ifdef VIMAGE 317 void 318 syncache_destroy(void) 319 { 320 struct syncache_head *sch; 321 struct syncache *sc, *nsc; 322 int i; 323 324 /* 325 * Stop the re-seed timer before freeing resources. No need to 326 * possibly schedule it another time. 327 */ 328 callout_drain(&V_tcp_syncache.secret.reseed); 329 330 /* Stop the SYN cache pause callout. */ 331 mtx_lock(&V_tcp_syncache.pause_mtx); 332 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 333 mtx_unlock(&V_tcp_syncache.pause_mtx); 334 callout_drain(&V_tcp_syncache.pause_co); 335 } else 336 mtx_unlock(&V_tcp_syncache.pause_mtx); 337 338 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 339 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 340 sch = &V_tcp_syncache.hashbase[i]; 341 callout_drain(&sch->sch_timer); 342 343 SCH_LOCK(sch); 344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 345 syncache_drop(sc, sch); 346 SCH_UNLOCK(sch); 347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 348 ("%s: sch->sch_bucket not empty", __func__)); 349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 350 __func__, sch->sch_length)); 351 mtx_destroy(&sch->sch_mtx); 352 } 353 354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 355 ("%s: cache_count not 0", __func__)); 356 357 /* Free the allocated global resources. */ 358 uma_zdestroy(V_tcp_syncache.zone); 359 free(V_tcp_syncache.hashbase, M_SYNCACHE); 360 mtx_destroy(&V_tcp_syncache.pause_mtx); 361 } 362 #endif 363 364 /* 365 * Inserts a syncache entry into the specified bucket row. 366 * Locks and unlocks the syncache_head autonomously. 367 */ 368 static void 369 syncache_insert(struct syncache *sc, struct syncache_head *sch) 370 { 371 struct syncache *sc2; 372 373 SCH_LOCK(sch); 374 375 /* 376 * Make sure that we don't overflow the per-bucket limit. 377 * If the bucket is full, toss the oldest element. 378 */ 379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 381 ("sch->sch_length incorrect")); 382 syncache_pause(&sc->sc_inc); 383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 384 sch->sch_last_overflow = time_uptime; 385 syncache_drop(sc2, sch); 386 } 387 388 /* Put it into the bucket. */ 389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 390 sch->sch_length++; 391 392 #ifdef TCP_OFFLOAD 393 if (ADDED_BY_TOE(sc)) { 394 struct toedev *tod = sc->sc_tod; 395 396 tod->tod_syncache_added(tod, sc->sc_todctx); 397 } 398 #endif 399 400 /* Reinitialize the bucket row's timer. */ 401 if (sch->sch_length == 1) 402 sch->sch_nextc = ticks + INT_MAX; 403 syncache_timeout(sc, sch, 1); 404 405 SCH_UNLOCK(sch); 406 407 TCPSTATES_INC(TCPS_SYN_RECEIVED); 408 TCPSTAT_INC(tcps_sc_added); 409 } 410 411 /* 412 * Remove and free entry from syncache bucket row. 413 * Expects locked syncache head. 414 */ 415 static void 416 syncache_drop(struct syncache *sc, struct syncache_head *sch) 417 { 418 419 SCH_LOCK_ASSERT(sch); 420 421 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 423 sch->sch_length--; 424 425 #ifdef TCP_OFFLOAD 426 if (ADDED_BY_TOE(sc)) { 427 struct toedev *tod = sc->sc_tod; 428 429 tod->tod_syncache_removed(tod, sc->sc_todctx); 430 } 431 #endif 432 433 syncache_free(sc); 434 } 435 436 /* 437 * Engage/reengage time on bucket row. 438 */ 439 static void 440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 441 { 442 int rexmt; 443 444 if (sc->sc_rxmits == 0) 445 rexmt = tcp_rexmit_initial; 446 else 447 TCPT_RANGESET(rexmt, 448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 449 tcp_rexmit_min, TCPTV_REXMTMAX); 450 sc->sc_rxttime = ticks + rexmt; 451 sc->sc_rxmits++; 452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 453 sch->sch_nextc = sc->sc_rxttime; 454 if (docallout) 455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 456 syncache_timer, (void *)sch); 457 } 458 } 459 460 /* 461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 462 * If we have retransmitted an entry the maximum number of times, expire it. 463 * One separate timer for each bucket row. 464 */ 465 static void 466 syncache_timer(void *xsch) 467 { 468 struct syncache_head *sch = (struct syncache_head *)xsch; 469 struct syncache *sc, *nsc; 470 struct epoch_tracker et; 471 int tick = ticks; 472 char *s; 473 bool paused; 474 475 CURVNET_SET(sch->sch_sc->vnet); 476 477 /* NB: syncache_head has already been locked by the callout. */ 478 SCH_LOCK_ASSERT(sch); 479 480 /* 481 * In the following cycle we may remove some entries and/or 482 * advance some timeouts, so re-initialize the bucket timer. 483 */ 484 sch->sch_nextc = tick + INT_MAX; 485 486 /* 487 * If we have paused processing, unconditionally remove 488 * all syncache entries. 489 */ 490 mtx_lock(&V_tcp_syncache.pause_mtx); 491 paused = V_tcp_syncache.paused; 492 mtx_unlock(&V_tcp_syncache.pause_mtx); 493 494 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 495 if (paused) { 496 syncache_drop(sc, sch); 497 continue; 498 } 499 /* 500 * We do not check if the listen socket still exists 501 * and accept the case where the listen socket may be 502 * gone by the time we resend the SYN/ACK. We do 503 * not expect this to happens often. If it does, 504 * then the RST will be sent by the time the remote 505 * host does the SYN/ACK->ACK. 506 */ 507 if (TSTMP_GT(sc->sc_rxttime, tick)) { 508 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 509 sch->sch_nextc = sc->sc_rxttime; 510 continue; 511 } 512 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 513 sc->sc_flags &= ~SCF_ECN; 514 } 515 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 516 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 517 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 518 "giving up and removing syncache entry\n", 519 s, __func__); 520 free(s, M_TCPLOG); 521 } 522 syncache_drop(sc, sch); 523 TCPSTAT_INC(tcps_sc_stale); 524 continue; 525 } 526 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 527 log(LOG_DEBUG, "%s; %s: Response timeout, " 528 "retransmitting (%u) SYN|ACK\n", 529 s, __func__, sc->sc_rxmits); 530 free(s, M_TCPLOG); 531 } 532 533 NET_EPOCH_ENTER(et); 534 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 535 NET_EPOCH_EXIT(et); 536 TCPSTAT_INC(tcps_sc_retransmitted); 537 syncache_timeout(sc, sch, 0); 538 } 539 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 540 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 541 syncache_timer, (void *)(sch)); 542 CURVNET_RESTORE(); 543 } 544 545 /* 546 * Returns true if the system is only using cookies at the moment. 547 * This could be due to a sysadmin decision to only use cookies, or it 548 * could be due to the system detecting an attack. 549 */ 550 static inline bool 551 syncache_cookiesonly(void) 552 { 553 554 return (V_tcp_syncookies && (V_tcp_syncache.paused || 555 V_tcp_syncookiesonly)); 556 } 557 558 /* 559 * Find the hash bucket for the given connection. 560 */ 561 static struct syncache_head * 562 syncache_hashbucket(struct in_conninfo *inc) 563 { 564 uint32_t hash; 565 566 /* 567 * The hash is built on foreign port + local port + foreign address. 568 * We rely on the fact that struct in_conninfo starts with 16 bits 569 * of foreign port, then 16 bits of local port then followed by 128 570 * bits of foreign address. In case of IPv4 address, the first 3 571 * 32-bit words of the address always are zeroes. 572 */ 573 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 574 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 575 576 return (&V_tcp_syncache.hashbase[hash]); 577 } 578 579 /* 580 * Find an entry in the syncache. 581 * Returns always with locked syncache_head plus a matching entry or NULL. 582 */ 583 static struct syncache * 584 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 585 { 586 struct syncache *sc; 587 struct syncache_head *sch; 588 589 *schp = sch = syncache_hashbucket(inc); 590 SCH_LOCK(sch); 591 592 /* Circle through bucket row to find matching entry. */ 593 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 594 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 595 sizeof(struct in_endpoints)) == 0) 596 break; 597 598 return (sc); /* Always returns with locked sch. */ 599 } 600 601 /* 602 * This function is called when we get a RST for a 603 * non-existent connection, so that we can see if the 604 * connection is in the syn cache. If it is, zap it. 605 * If required send a challenge ACK. 606 */ 607 void 608 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m) 609 { 610 struct syncache *sc; 611 struct syncache_head *sch; 612 char *s = NULL; 613 614 if (syncache_cookiesonly()) 615 return; 616 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 617 SCH_LOCK_ASSERT(sch); 618 619 /* 620 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 621 * See RFC 793 page 65, section SEGMENT ARRIVES. 622 */ 623 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 624 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 625 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 626 "FIN flag set, segment ignored\n", s, __func__); 627 TCPSTAT_INC(tcps_badrst); 628 goto done; 629 } 630 631 /* 632 * No corresponding connection was found in syncache. 633 * If syncookies are enabled and possibly exclusively 634 * used, or we are under memory pressure, a valid RST 635 * may not find a syncache entry. In that case we're 636 * done and no SYN|ACK retransmissions will happen. 637 * Otherwise the RST was misdirected or spoofed. 638 */ 639 if (sc == NULL) { 640 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 641 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 642 "syncache entry (possibly syncookie only), " 643 "segment ignored\n", s, __func__); 644 TCPSTAT_INC(tcps_badrst); 645 goto done; 646 } 647 648 /* 649 * If the RST bit is set, check the sequence number to see 650 * if this is a valid reset segment. 651 * 652 * RFC 793 page 37: 653 * In all states except SYN-SENT, all reset (RST) segments 654 * are validated by checking their SEQ-fields. A reset is 655 * valid if its sequence number is in the window. 656 * 657 * RFC 793 page 69: 658 * There are four cases for the acceptability test for an incoming 659 * segment: 660 * 661 * Segment Receive Test 662 * Length Window 663 * ------- ------- ------------------------------------------- 664 * 0 0 SEG.SEQ = RCV.NXT 665 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 666 * >0 0 not acceptable 667 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 668 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 669 * 670 * Note that when receiving a SYN segment in the LISTEN state, 671 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 672 * described in RFC 793, page 66. 673 */ 674 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 675 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 676 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 677 if (V_tcp_insecure_rst || 678 th->th_seq == sc->sc_irs + 1) { 679 syncache_drop(sc, sch); 680 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 681 log(LOG_DEBUG, 682 "%s; %s: Our SYN|ACK was rejected, " 683 "connection attempt aborted by remote " 684 "endpoint\n", 685 s, __func__); 686 TCPSTAT_INC(tcps_sc_reset); 687 } else { 688 TCPSTAT_INC(tcps_badrst); 689 /* Send challenge ACK. */ 690 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 691 log(LOG_DEBUG, "%s; %s: RST with invalid " 692 " SEQ %u != NXT %u (+WND %u), " 693 "sending challenge ACK\n", 694 s, __func__, 695 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 696 syncache_respond(sc, m, TH_ACK); 697 } 698 } else { 699 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 700 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 701 "NXT %u (+WND %u), segment ignored\n", 702 s, __func__, 703 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 704 TCPSTAT_INC(tcps_badrst); 705 } 706 707 done: 708 if (s != NULL) 709 free(s, M_TCPLOG); 710 SCH_UNLOCK(sch); 711 } 712 713 void 714 syncache_badack(struct in_conninfo *inc) 715 { 716 struct syncache *sc; 717 struct syncache_head *sch; 718 719 if (syncache_cookiesonly()) 720 return; 721 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 722 SCH_LOCK_ASSERT(sch); 723 if (sc != NULL) { 724 syncache_drop(sc, sch); 725 TCPSTAT_INC(tcps_sc_badack); 726 } 727 SCH_UNLOCK(sch); 728 } 729 730 void 731 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 732 { 733 struct syncache *sc; 734 struct syncache_head *sch; 735 736 if (syncache_cookiesonly()) 737 return; 738 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 739 SCH_LOCK_ASSERT(sch); 740 if (sc == NULL) 741 goto done; 742 743 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 744 if (ntohl(th_seq) != sc->sc_iss) 745 goto done; 746 747 /* 748 * If we've rertransmitted 3 times and this is our second error, 749 * we remove the entry. Otherwise, we allow it to continue on. 750 * This prevents us from incorrectly nuking an entry during a 751 * spurious network outage. 752 * 753 * See tcp_notify(). 754 */ 755 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 756 sc->sc_flags |= SCF_UNREACH; 757 goto done; 758 } 759 syncache_drop(sc, sch); 760 TCPSTAT_INC(tcps_sc_unreach); 761 done: 762 SCH_UNLOCK(sch); 763 } 764 765 /* 766 * Build a new TCP socket structure from a syncache entry. 767 * 768 * On success return the newly created socket with its underlying inp locked. 769 */ 770 static struct socket * 771 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 772 { 773 struct tcp_function_block *blk; 774 struct inpcb *inp = NULL; 775 struct socket *so; 776 struct tcpcb *tp; 777 int error; 778 char *s; 779 780 NET_EPOCH_ASSERT(); 781 782 /* 783 * Ok, create the full blown connection, and set things up 784 * as they would have been set up if we had created the 785 * connection when the SYN arrived. If we can't create 786 * the connection, abort it. 787 */ 788 so = sonewconn(lso, 0); 789 if (so == NULL) { 790 /* 791 * Drop the connection; we will either send a RST or 792 * have the peer retransmit its SYN again after its 793 * RTO and try again. 794 */ 795 TCPSTAT_INC(tcps_listendrop); 796 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 797 log(LOG_DEBUG, "%s; %s: Socket create failed " 798 "due to limits or memory shortage\n", 799 s, __func__); 800 free(s, M_TCPLOG); 801 } 802 goto abort2; 803 } 804 #ifdef MAC 805 mac_socketpeer_set_from_mbuf(m, so); 806 #endif 807 808 inp = sotoinpcb(so); 809 inp->inp_inc.inc_fibnum = so->so_fibnum; 810 INP_WLOCK(inp); 811 /* 812 * Exclusive pcbinfo lock is not required in syncache socket case even 813 * if two inpcb locks can be acquired simultaneously: 814 * - the inpcb in LISTEN state, 815 * - the newly created inp. 816 * 817 * In this case, an inp cannot be at same time in LISTEN state and 818 * just created by an accept() call. 819 */ 820 INP_HASH_WLOCK(&V_tcbinfo); 821 822 /* Insert new socket into PCB hash list. */ 823 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 824 #ifdef INET6 825 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 826 inp->inp_vflag &= ~INP_IPV4; 827 inp->inp_vflag |= INP_IPV6; 828 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 829 } else { 830 inp->inp_vflag &= ~INP_IPV6; 831 inp->inp_vflag |= INP_IPV4; 832 #endif 833 inp->inp_ip_ttl = sc->sc_ip_ttl; 834 inp->inp_ip_tos = sc->sc_ip_tos; 835 inp->inp_laddr = sc->sc_inc.inc_laddr; 836 #ifdef INET6 837 } 838 #endif 839 840 /* 841 * If there's an mbuf and it has a flowid, then let's initialise the 842 * inp with that particular flowid. 843 */ 844 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 845 inp->inp_flowid = m->m_pkthdr.flowid; 846 inp->inp_flowtype = M_HASHTYPE_GET(m); 847 #ifdef NUMA 848 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 849 #endif 850 } 851 852 inp->inp_lport = sc->sc_inc.inc_lport; 853 #ifdef INET6 854 if (inp->inp_vflag & INP_IPV6PROTO) { 855 struct inpcb *oinp = sotoinpcb(lso); 856 857 /* 858 * Inherit socket options from the listening socket. 859 * Note that in6p_inputopts are not (and should not be) 860 * copied, since it stores previously received options and is 861 * used to detect if each new option is different than the 862 * previous one and hence should be passed to a user. 863 * If we copied in6p_inputopts, a user would not be able to 864 * receive options just after calling the accept system call. 865 */ 866 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 867 if (oinp->in6p_outputopts) 868 inp->in6p_outputopts = 869 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 870 inp->in6p_hops = oinp->in6p_hops; 871 } 872 873 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 874 struct in6_addr laddr6; 875 struct sockaddr_in6 sin6; 876 877 sin6.sin6_family = AF_INET6; 878 sin6.sin6_len = sizeof(sin6); 879 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 880 sin6.sin6_port = sc->sc_inc.inc_fport; 881 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 882 laddr6 = inp->in6p_laddr; 883 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 884 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 885 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 886 thread0.td_ucred, m, false)) != 0) { 887 inp->in6p_laddr = laddr6; 888 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 889 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 890 "with error %i\n", 891 s, __func__, error); 892 free(s, M_TCPLOG); 893 } 894 INP_HASH_WUNLOCK(&V_tcbinfo); 895 goto abort; 896 } 897 /* Override flowlabel from in6_pcbconnect. */ 898 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 899 inp->inp_flow |= sc->sc_flowlabel; 900 } 901 #endif /* INET6 */ 902 #if defined(INET) && defined(INET6) 903 else 904 #endif 905 #ifdef INET 906 { 907 struct in_addr laddr; 908 struct sockaddr_in sin; 909 910 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 911 912 if (inp->inp_options == NULL) { 913 inp->inp_options = sc->sc_ipopts; 914 sc->sc_ipopts = NULL; 915 } 916 917 sin.sin_family = AF_INET; 918 sin.sin_len = sizeof(sin); 919 sin.sin_addr = sc->sc_inc.inc_faddr; 920 sin.sin_port = sc->sc_inc.inc_fport; 921 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 922 laddr = inp->inp_laddr; 923 if (inp->inp_laddr.s_addr == INADDR_ANY) 924 inp->inp_laddr = sc->sc_inc.inc_laddr; 925 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 926 thread0.td_ucred, m, false)) != 0) { 927 inp->inp_laddr = laddr; 928 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 929 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 930 "with error %i\n", 931 s, __func__, error); 932 free(s, M_TCPLOG); 933 } 934 INP_HASH_WUNLOCK(&V_tcbinfo); 935 goto abort; 936 } 937 } 938 #endif /* INET */ 939 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 940 /* Copy old policy into new socket's. */ 941 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 942 printf("syncache_socket: could not copy policy\n"); 943 #endif 944 INP_HASH_WUNLOCK(&V_tcbinfo); 945 tp = intotcpcb(inp); 946 tcp_state_change(tp, TCPS_SYN_RECEIVED); 947 tp->iss = sc->sc_iss; 948 tp->irs = sc->sc_irs; 949 tcp_rcvseqinit(tp); 950 tcp_sendseqinit(tp); 951 blk = sototcpcb(lso)->t_fb; 952 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 953 /* 954 * Our parents t_fb was not the default, 955 * we need to release our ref on tp->t_fb and 956 * pickup one on the new entry. 957 */ 958 struct tcp_function_block *rblk; 959 960 rblk = find_and_ref_tcp_fb(blk); 961 KASSERT(rblk != NULL, 962 ("cannot find blk %p out of syncache?", blk)); 963 if (tp->t_fb->tfb_tcp_fb_fini) 964 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 965 refcount_release(&tp->t_fb->tfb_refcnt); 966 tp->t_fb = rblk; 967 /* 968 * XXXrrs this is quite dangerous, it is possible 969 * for the new function to fail to init. We also 970 * are not asking if the handoff_is_ok though at 971 * the very start thats probalbly ok. 972 */ 973 if (tp->t_fb->tfb_tcp_fb_init) { 974 (*tp->t_fb->tfb_tcp_fb_init)(tp); 975 } 976 } 977 tp->snd_wl1 = sc->sc_irs; 978 tp->snd_max = tp->iss + 1; 979 tp->snd_nxt = tp->iss + 1; 980 tp->rcv_up = sc->sc_irs + 1; 981 tp->rcv_wnd = sc->sc_wnd; 982 tp->rcv_adv += tp->rcv_wnd; 983 tp->last_ack_sent = tp->rcv_nxt; 984 985 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 986 if (sc->sc_flags & SCF_NOOPT) 987 tp->t_flags |= TF_NOOPT; 988 else { 989 if (sc->sc_flags & SCF_WINSCALE) { 990 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 991 tp->snd_scale = sc->sc_requested_s_scale; 992 tp->request_r_scale = sc->sc_requested_r_scale; 993 } 994 if (sc->sc_flags & SCF_TIMESTAMP) { 995 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 996 tp->ts_recent = sc->sc_tsreflect; 997 tp->ts_recent_age = tcp_ts_getticks(); 998 tp->ts_offset = sc->sc_tsoff; 999 } 1000 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1001 if (sc->sc_flags & SCF_SIGNATURE) 1002 tp->t_flags |= TF_SIGNATURE; 1003 #endif 1004 if (sc->sc_flags & SCF_SACK) 1005 tp->t_flags |= TF_SACK_PERMIT; 1006 } 1007 1008 if (sc->sc_flags & SCF_ECN) 1009 tp->t_flags2 |= TF2_ECN_PERMIT; 1010 1011 /* 1012 * Set up MSS and get cached values from tcp_hostcache. 1013 * This might overwrite some of the defaults we just set. 1014 */ 1015 tcp_mss(tp, sc->sc_peer_mss); 1016 1017 /* 1018 * If the SYN,ACK was retransmitted, indicate that CWND to be 1019 * limited to one segment in cc_conn_init(). 1020 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1021 */ 1022 if (sc->sc_rxmits > 1) 1023 tp->snd_cwnd = 1; 1024 1025 #ifdef TCP_OFFLOAD 1026 /* 1027 * Allow a TOE driver to install its hooks. Note that we hold the 1028 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1029 * new connection before the TOE driver has done its thing. 1030 */ 1031 if (ADDED_BY_TOE(sc)) { 1032 struct toedev *tod = sc->sc_tod; 1033 1034 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1035 } 1036 #endif 1037 /* 1038 * Copy and activate timers. 1039 */ 1040 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1041 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1042 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1043 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1044 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1045 1046 TCPSTAT_INC(tcps_accepts); 1047 return (so); 1048 1049 abort: 1050 INP_WUNLOCK(inp); 1051 abort2: 1052 if (so != NULL) 1053 soabort(so); 1054 return (NULL); 1055 } 1056 1057 /* 1058 * This function gets called when we receive an ACK for a 1059 * socket in the LISTEN state. We look up the connection 1060 * in the syncache, and if its there, we pull it out of 1061 * the cache and turn it into a full-blown connection in 1062 * the SYN-RECEIVED state. 1063 * 1064 * On syncache_socket() success the newly created socket 1065 * has its underlying inp locked. 1066 */ 1067 int 1068 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1069 struct socket **lsop, struct mbuf *m) 1070 { 1071 struct syncache *sc; 1072 struct syncache_head *sch; 1073 struct syncache scs; 1074 char *s; 1075 bool locked; 1076 1077 NET_EPOCH_ASSERT(); 1078 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1079 ("%s: can handle only ACK", __func__)); 1080 1081 if (syncache_cookiesonly()) { 1082 sc = NULL; 1083 sch = syncache_hashbucket(inc); 1084 locked = false; 1085 } else { 1086 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1087 locked = true; 1088 SCH_LOCK_ASSERT(sch); 1089 } 1090 1091 #ifdef INVARIANTS 1092 /* 1093 * Test code for syncookies comparing the syncache stored 1094 * values with the reconstructed values from the cookie. 1095 */ 1096 if (sc != NULL) 1097 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1098 #endif 1099 1100 if (sc == NULL) { 1101 /* 1102 * There is no syncache entry, so see if this ACK is 1103 * a returning syncookie. To do this, first: 1104 * A. Check if syncookies are used in case of syncache 1105 * overflows 1106 * B. See if this socket has had a syncache entry dropped in 1107 * the recent past. We don't want to accept a bogus 1108 * syncookie if we've never received a SYN or accept it 1109 * twice. 1110 * C. check that the syncookie is valid. If it is, then 1111 * cobble up a fake syncache entry, and return. 1112 */ 1113 if (locked && !V_tcp_syncookies) { 1114 SCH_UNLOCK(sch); 1115 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1116 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1117 "segment rejected (syncookies disabled)\n", 1118 s, __func__); 1119 goto failed; 1120 } 1121 if (locked && !V_tcp_syncookiesonly && 1122 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1123 SCH_UNLOCK(sch); 1124 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1125 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1126 "segment rejected (no syncache entry)\n", 1127 s, __func__); 1128 goto failed; 1129 } 1130 bzero(&scs, sizeof(scs)); 1131 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1132 if (locked) 1133 SCH_UNLOCK(sch); 1134 if (sc == NULL) { 1135 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1136 log(LOG_DEBUG, "%s; %s: Segment failed " 1137 "SYNCOOKIE authentication, segment rejected " 1138 "(probably spoofed)\n", s, __func__); 1139 goto failed; 1140 } 1141 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1142 /* If received ACK has MD5 signature, check it. */ 1143 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1144 (!TCPMD5_ENABLED() || 1145 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1146 /* Drop the ACK. */ 1147 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1148 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1149 "MD5 signature doesn't match.\n", 1150 s, __func__); 1151 free(s, M_TCPLOG); 1152 } 1153 TCPSTAT_INC(tcps_sig_err_sigopt); 1154 return (-1); /* Do not send RST */ 1155 } 1156 #endif /* TCP_SIGNATURE */ 1157 } else { 1158 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1159 /* 1160 * If listening socket requested TCP digests, check that 1161 * received ACK has signature and it is correct. 1162 * If not, drop the ACK and leave sc entry in th cache, 1163 * because SYN was received with correct signature. 1164 */ 1165 if (sc->sc_flags & SCF_SIGNATURE) { 1166 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1167 /* No signature */ 1168 TCPSTAT_INC(tcps_sig_err_nosigopt); 1169 SCH_UNLOCK(sch); 1170 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1171 log(LOG_DEBUG, "%s; %s: Segment " 1172 "rejected, MD5 signature wasn't " 1173 "provided.\n", s, __func__); 1174 free(s, M_TCPLOG); 1175 } 1176 return (-1); /* Do not send RST */ 1177 } 1178 if (!TCPMD5_ENABLED() || 1179 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1180 /* Doesn't match or no SA */ 1181 SCH_UNLOCK(sch); 1182 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1183 log(LOG_DEBUG, "%s; %s: Segment " 1184 "rejected, MD5 signature doesn't " 1185 "match.\n", s, __func__); 1186 free(s, M_TCPLOG); 1187 } 1188 return (-1); /* Do not send RST */ 1189 } 1190 } 1191 #endif /* TCP_SIGNATURE */ 1192 1193 /* 1194 * RFC 7323 PAWS: If we have a timestamp on this segment and 1195 * it's less than ts_recent, drop it. 1196 * XXXMT: RFC 7323 also requires to send an ACK. 1197 * In tcp_input.c this is only done for TCP segments 1198 * with user data, so be consistent here and just drop 1199 * the segment. 1200 */ 1201 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1202 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1203 SCH_UNLOCK(sch); 1204 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1205 log(LOG_DEBUG, 1206 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1207 "segment dropped\n", s, __func__, 1208 to->to_tsval, sc->sc_tsreflect); 1209 free(s, M_TCPLOG); 1210 } 1211 return (-1); /* Do not send RST */ 1212 } 1213 1214 /* 1215 * If timestamps were not negotiated during SYN/ACK and a 1216 * segment with a timestamp is received, ignore the 1217 * timestamp and process the packet normally. 1218 * See section 3.2 of RFC 7323. 1219 */ 1220 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1221 (to->to_flags & TOF_TS)) { 1222 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1223 log(LOG_DEBUG, "%s; %s: Timestamp not " 1224 "expected, segment processed normally\n", 1225 s, __func__); 1226 free(s, M_TCPLOG); 1227 s = NULL; 1228 } 1229 } 1230 1231 /* 1232 * If timestamps were negotiated during SYN/ACK and a 1233 * segment without a timestamp is received, silently drop 1234 * the segment, unless the missing timestamps are tolerated. 1235 * See section 3.2 of RFC 7323. 1236 */ 1237 if ((sc->sc_flags & SCF_TIMESTAMP) && 1238 !(to->to_flags & TOF_TS)) { 1239 if (V_tcp_tolerate_missing_ts) { 1240 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1241 log(LOG_DEBUG, 1242 "%s; %s: Timestamp missing, " 1243 "segment processed normally\n", 1244 s, __func__); 1245 free(s, M_TCPLOG); 1246 } 1247 } else { 1248 SCH_UNLOCK(sch); 1249 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1250 log(LOG_DEBUG, 1251 "%s; %s: Timestamp missing, " 1252 "segment silently dropped\n", 1253 s, __func__); 1254 free(s, M_TCPLOG); 1255 } 1256 return (-1); /* Do not send RST */ 1257 } 1258 } 1259 1260 /* 1261 * Pull out the entry to unlock the bucket row. 1262 * 1263 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1264 * tcp_state_change(). The tcpcb is not existent at this 1265 * moment. A new one will be allocated via syncache_socket-> 1266 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1267 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1268 */ 1269 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 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 (*lsop == NULL) 1308 TCPSTAT_INC(tcps_sc_aborted); 1309 else 1310 TCPSTAT_INC(tcps_sc_completed); 1311 1312 /* how do we find the inp for the new socket? */ 1313 if (sc != &scs) 1314 syncache_free(sc); 1315 return (1); 1316 failed: 1317 if (sc != NULL && sc != &scs) 1318 syncache_free(sc); 1319 if (s != NULL) 1320 free(s, M_TCPLOG); 1321 *lsop = NULL; 1322 return (0); 1323 } 1324 1325 static struct socket * 1326 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1327 uint64_t response_cookie) 1328 { 1329 struct inpcb *inp; 1330 struct tcpcb *tp; 1331 unsigned int *pending_counter; 1332 struct socket *so; 1333 1334 NET_EPOCH_ASSERT(); 1335 1336 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1337 so = syncache_socket(sc, lso, m); 1338 if (so == NULL) { 1339 TCPSTAT_INC(tcps_sc_aborted); 1340 atomic_subtract_int(pending_counter, 1); 1341 } else { 1342 soisconnected(so); 1343 inp = sotoinpcb(so); 1344 tp = intotcpcb(inp); 1345 tp->t_flags |= TF_FASTOPEN; 1346 tp->t_tfo_cookie.server = response_cookie; 1347 tp->snd_max = tp->iss; 1348 tp->snd_nxt = tp->iss; 1349 tp->t_tfo_pending = pending_counter; 1350 TCPSTAT_INC(tcps_sc_completed); 1351 } 1352 1353 return (so); 1354 } 1355 1356 /* 1357 * Given a LISTEN socket and an inbound SYN request, add 1358 * this to the syn cache, and send back a segment: 1359 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1360 * to the source. 1361 * 1362 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1363 * Doing so would require that we hold onto the data and deliver it 1364 * to the application. However, if we are the target of a SYN-flood 1365 * DoS attack, an attacker could send data which would eventually 1366 * consume all available buffer space if it were ACKed. By not ACKing 1367 * the data, we avoid this DoS scenario. 1368 * 1369 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1370 * cookie is processed and a new socket is created. In this case, any data 1371 * accompanying the SYN will be queued to the socket by tcp_input() and will 1372 * be ACKed either when the application sends response data or the delayed 1373 * ACK timer expires, whichever comes first. 1374 */ 1375 struct socket * 1376 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1377 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1378 void *todctx, uint8_t iptos) 1379 { 1380 struct tcpcb *tp; 1381 struct socket *rv = NULL; 1382 struct syncache *sc = NULL; 1383 struct syncache_head *sch; 1384 struct mbuf *ipopts = NULL; 1385 u_int ltflags; 1386 int win, ip_ttl, ip_tos; 1387 char *s; 1388 #ifdef INET6 1389 int autoflowlabel = 0; 1390 #endif 1391 #ifdef MAC 1392 struct label *maclabel; 1393 #endif 1394 struct syncache scs; 1395 struct ucred *cred; 1396 uint64_t tfo_response_cookie; 1397 unsigned int *tfo_pending = NULL; 1398 int tfo_cookie_valid = 0; 1399 int tfo_response_cookie_valid = 0; 1400 bool locked; 1401 1402 INP_RLOCK_ASSERT(inp); /* listen socket */ 1403 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1404 ("%s: unexpected tcp flags", __func__)); 1405 1406 /* 1407 * Combine all so/tp operations very early to drop the INP lock as 1408 * soon as possible. 1409 */ 1410 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1411 tp = sototcpcb(so); 1412 cred = crhold(so->so_cred); 1413 1414 #ifdef INET6 1415 if (inc->inc_flags & INC_ISIPV6) { 1416 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1417 autoflowlabel = 1; 1418 } 1419 ip_ttl = in6_selecthlim(inp, NULL); 1420 if ((inp->in6p_outputopts == NULL) || 1421 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1422 ip_tos = 0; 1423 } else { 1424 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1425 } 1426 } 1427 #endif 1428 #if defined(INET6) && defined(INET) 1429 else 1430 #endif 1431 #ifdef INET 1432 { 1433 ip_ttl = inp->inp_ip_ttl; 1434 ip_tos = inp->inp_ip_tos; 1435 } 1436 #endif 1437 win = so->sol_sbrcv_hiwat; 1438 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1439 1440 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1441 (tp->t_tfo_pending != NULL) && 1442 (to->to_flags & TOF_FASTOPEN)) { 1443 /* 1444 * Limit the number of pending TFO connections to 1445 * approximately half of the queue limit. This prevents TFO 1446 * SYN floods from starving the service by filling the 1447 * listen queue with bogus TFO connections. 1448 */ 1449 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1450 (so->sol_qlimit / 2)) { 1451 int result; 1452 1453 result = tcp_fastopen_check_cookie(inc, 1454 to->to_tfo_cookie, to->to_tfo_len, 1455 &tfo_response_cookie); 1456 tfo_cookie_valid = (result > 0); 1457 tfo_response_cookie_valid = (result >= 0); 1458 } 1459 1460 /* 1461 * Remember the TFO pending counter as it will have to be 1462 * decremented below if we don't make it to syncache_tfo_expand(). 1463 */ 1464 tfo_pending = tp->t_tfo_pending; 1465 } 1466 1467 /* By the time we drop the lock these should no longer be used. */ 1468 so = NULL; 1469 tp = NULL; 1470 1471 #ifdef MAC 1472 if (mac_syncache_init(&maclabel) != 0) { 1473 INP_RUNLOCK(inp); 1474 goto done; 1475 } else 1476 mac_syncache_create(maclabel, inp); 1477 #endif 1478 if (!tfo_cookie_valid) 1479 INP_RUNLOCK(inp); 1480 1481 /* 1482 * Remember the IP options, if any. 1483 */ 1484 #ifdef INET6 1485 if (!(inc->inc_flags & INC_ISIPV6)) 1486 #endif 1487 #ifdef INET 1488 ipopts = (m) ? ip_srcroute(m) : NULL; 1489 #else 1490 ipopts = NULL; 1491 #endif 1492 1493 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1494 /* 1495 * If listening socket requested TCP digests, check that received 1496 * SYN has signature and it is correct. If signature doesn't match 1497 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1498 */ 1499 if (ltflags & TF_SIGNATURE) { 1500 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1501 TCPSTAT_INC(tcps_sig_err_nosigopt); 1502 goto done; 1503 } 1504 if (!TCPMD5_ENABLED() || 1505 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1506 goto done; 1507 } 1508 #endif /* TCP_SIGNATURE */ 1509 /* 1510 * See if we already have an entry for this connection. 1511 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1512 * 1513 * XXX: should the syncache be re-initialized with the contents 1514 * of the new SYN here (which may have different options?) 1515 * 1516 * XXX: We do not check the sequence number to see if this is a 1517 * real retransmit or a new connection attempt. The question is 1518 * how to handle such a case; either ignore it as spoofed, or 1519 * drop the current entry and create a new one? 1520 */ 1521 if (syncache_cookiesonly()) { 1522 sc = NULL; 1523 sch = syncache_hashbucket(inc); 1524 locked = false; 1525 } else { 1526 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1527 locked = true; 1528 SCH_LOCK_ASSERT(sch); 1529 } 1530 if (sc != NULL) { 1531 if (tfo_cookie_valid) 1532 INP_RUNLOCK(inp); 1533 TCPSTAT_INC(tcps_sc_dupsyn); 1534 if (ipopts) { 1535 /* 1536 * If we were remembering a previous source route, 1537 * forget it and use the new one we've been given. 1538 */ 1539 if (sc->sc_ipopts) 1540 (void) m_free(sc->sc_ipopts); 1541 sc->sc_ipopts = ipopts; 1542 } 1543 /* 1544 * Update timestamp if present. 1545 */ 1546 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1547 sc->sc_tsreflect = to->to_tsval; 1548 else 1549 sc->sc_flags &= ~SCF_TIMESTAMP; 1550 /* 1551 * Disable ECN if needed. 1552 */ 1553 if ((sc->sc_flags & SCF_ECN) && 1554 ((th->th_flags & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1555 sc->sc_flags &= ~SCF_ECN; 1556 } 1557 #ifdef MAC 1558 /* 1559 * Since we have already unconditionally allocated label 1560 * storage, free it up. The syncache entry will already 1561 * have an initialized label we can use. 1562 */ 1563 mac_syncache_destroy(&maclabel); 1564 #endif 1565 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1566 /* Retransmit SYN|ACK and reset retransmit count. */ 1567 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1568 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1569 "resetting timer and retransmitting SYN|ACK\n", 1570 s, __func__); 1571 free(s, M_TCPLOG); 1572 } 1573 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1574 sc->sc_rxmits = 0; 1575 syncache_timeout(sc, sch, 1); 1576 TCPSTAT_INC(tcps_sndacks); 1577 TCPSTAT_INC(tcps_sndtotal); 1578 } 1579 SCH_UNLOCK(sch); 1580 goto donenoprobe; 1581 } 1582 1583 if (tfo_cookie_valid) { 1584 bzero(&scs, sizeof(scs)); 1585 sc = &scs; 1586 goto skip_alloc; 1587 } 1588 1589 /* 1590 * Skip allocating a syncache entry if we are just going to discard 1591 * it later. 1592 */ 1593 if (!locked) { 1594 bzero(&scs, sizeof(scs)); 1595 sc = &scs; 1596 } else 1597 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1598 if (sc == NULL) { 1599 /* 1600 * The zone allocator couldn't provide more entries. 1601 * Treat this as if the cache was full; drop the oldest 1602 * entry and insert the new one. 1603 */ 1604 TCPSTAT_INC(tcps_sc_zonefail); 1605 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1606 sch->sch_last_overflow = time_uptime; 1607 syncache_drop(sc, sch); 1608 syncache_pause(inc); 1609 } 1610 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1611 if (sc == NULL) { 1612 if (V_tcp_syncookies) { 1613 bzero(&scs, sizeof(scs)); 1614 sc = &scs; 1615 } else { 1616 KASSERT(locked, 1617 ("%s: bucket unexpectedly unlocked", 1618 __func__)); 1619 SCH_UNLOCK(sch); 1620 if (ipopts) 1621 (void) m_free(ipopts); 1622 goto done; 1623 } 1624 } 1625 } 1626 1627 skip_alloc: 1628 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1629 sc->sc_tfo_cookie = &tfo_response_cookie; 1630 1631 /* 1632 * Fill in the syncache values. 1633 */ 1634 #ifdef MAC 1635 sc->sc_label = maclabel; 1636 #endif 1637 sc->sc_cred = cred; 1638 cred = NULL; 1639 sc->sc_ipopts = ipopts; 1640 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1641 sc->sc_ip_tos = ip_tos; 1642 sc->sc_ip_ttl = ip_ttl; 1643 #ifdef TCP_OFFLOAD 1644 sc->sc_tod = tod; 1645 sc->sc_todctx = todctx; 1646 #endif 1647 sc->sc_irs = th->th_seq; 1648 sc->sc_flags = 0; 1649 sc->sc_flowlabel = 0; 1650 1651 /* 1652 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1653 * win was derived from socket earlier in the function. 1654 */ 1655 win = imax(win, 0); 1656 win = imin(win, TCP_MAXWIN); 1657 sc->sc_wnd = win; 1658 1659 if (V_tcp_do_rfc1323 && 1660 !(ltflags & TF_NOOPT)) { 1661 /* 1662 * A timestamp received in a SYN makes 1663 * it ok to send timestamp requests and replies. 1664 */ 1665 if (to->to_flags & TOF_TS) { 1666 sc->sc_tsreflect = to->to_tsval; 1667 sc->sc_flags |= SCF_TIMESTAMP; 1668 sc->sc_tsoff = tcp_new_ts_offset(inc); 1669 } 1670 if (to->to_flags & TOF_SCALE) { 1671 int wscale = 0; 1672 1673 /* 1674 * Pick the smallest possible scaling factor that 1675 * will still allow us to scale up to sb_max, aka 1676 * kern.ipc.maxsockbuf. 1677 * 1678 * We do this because there are broken firewalls that 1679 * will corrupt the window scale option, leading to 1680 * the other endpoint believing that our advertised 1681 * window is unscaled. At scale factors larger than 1682 * 5 the unscaled window will drop below 1500 bytes, 1683 * leading to serious problems when traversing these 1684 * broken firewalls. 1685 * 1686 * With the default maxsockbuf of 256K, a scale factor 1687 * of 3 will be chosen by this algorithm. Those who 1688 * choose a larger maxsockbuf should watch out 1689 * for the compatibility problems mentioned above. 1690 * 1691 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1692 * or <SYN,ACK>) segment itself is never scaled. 1693 */ 1694 while (wscale < TCP_MAX_WINSHIFT && 1695 (TCP_MAXWIN << wscale) < sb_max) 1696 wscale++; 1697 sc->sc_requested_r_scale = wscale; 1698 sc->sc_requested_s_scale = to->to_wscale; 1699 sc->sc_flags |= SCF_WINSCALE; 1700 } 1701 } 1702 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1703 /* 1704 * If listening socket requested TCP digests, flag this in the 1705 * syncache so that syncache_respond() will do the right thing 1706 * with the SYN+ACK. 1707 */ 1708 if (ltflags & TF_SIGNATURE) 1709 sc->sc_flags |= SCF_SIGNATURE; 1710 #endif /* TCP_SIGNATURE */ 1711 if (to->to_flags & TOF_SACKPERM) 1712 sc->sc_flags |= SCF_SACK; 1713 if (to->to_flags & TOF_MSS) 1714 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1715 if (ltflags & TF_NOOPT) 1716 sc->sc_flags |= SCF_NOOPT; 1717 if (((th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) && 1718 V_tcp_do_ecn) 1719 sc->sc_flags |= SCF_ECN; 1720 1721 if (V_tcp_syncookies) 1722 sc->sc_iss = syncookie_generate(sch, sc); 1723 else 1724 sc->sc_iss = arc4random(); 1725 #ifdef INET6 1726 if (autoflowlabel) { 1727 if (V_tcp_syncookies) 1728 sc->sc_flowlabel = sc->sc_iss; 1729 else 1730 sc->sc_flowlabel = ip6_randomflowlabel(); 1731 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1732 } 1733 #endif 1734 if (locked) 1735 SCH_UNLOCK(sch); 1736 1737 if (tfo_cookie_valid) { 1738 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1739 /* INP_RUNLOCK(inp) will be performed by the caller */ 1740 goto tfo_expanded; 1741 } 1742 1743 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1744 /* 1745 * Do a standard 3-way handshake. 1746 */ 1747 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1748 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1749 syncache_free(sc); 1750 else if (sc != &scs) 1751 syncache_insert(sc, sch); /* locks and unlocks sch */ 1752 TCPSTAT_INC(tcps_sndacks); 1753 TCPSTAT_INC(tcps_sndtotal); 1754 } else { 1755 if (sc != &scs) 1756 syncache_free(sc); 1757 TCPSTAT_INC(tcps_sc_dropped); 1758 } 1759 goto donenoprobe; 1760 1761 done: 1762 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1763 donenoprobe: 1764 if (m) 1765 m_freem(m); 1766 /* 1767 * If tfo_pending is not NULL here, then a TFO SYN that did not 1768 * result in a new socket was processed and the associated pending 1769 * counter has not yet been decremented. All such TFO processing paths 1770 * transit this point. 1771 */ 1772 if (tfo_pending != NULL) 1773 tcp_fastopen_decrement_counter(tfo_pending); 1774 1775 tfo_expanded: 1776 if (cred != NULL) 1777 crfree(cred); 1778 #ifdef MAC 1779 if (sc == &scs) 1780 mac_syncache_destroy(&maclabel); 1781 #endif 1782 return (rv); 1783 } 1784 1785 /* 1786 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1787 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1788 */ 1789 static int 1790 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1791 { 1792 struct ip *ip = NULL; 1793 struct mbuf *m; 1794 struct tcphdr *th = NULL; 1795 int optlen, error = 0; /* Make compiler happy */ 1796 u_int16_t hlen, tlen, mssopt; 1797 struct tcpopt to; 1798 #ifdef INET6 1799 struct ip6_hdr *ip6 = NULL; 1800 #endif 1801 1802 NET_EPOCH_ASSERT(); 1803 1804 hlen = 1805 #ifdef INET6 1806 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1807 #endif 1808 sizeof(struct ip); 1809 tlen = hlen + sizeof(struct tcphdr); 1810 1811 /* Determine MSS we advertize to other end of connection. */ 1812 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1813 1814 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1815 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1816 ("syncache: mbuf too small")); 1817 1818 /* Create the IP+TCP header from scratch. */ 1819 m = m_gethdr(M_NOWAIT, MT_DATA); 1820 if (m == NULL) 1821 return (ENOBUFS); 1822 #ifdef MAC 1823 mac_syncache_create_mbuf(sc->sc_label, m); 1824 #endif 1825 m->m_data += max_linkhdr; 1826 m->m_len = tlen; 1827 m->m_pkthdr.len = tlen; 1828 m->m_pkthdr.rcvif = NULL; 1829 1830 #ifdef INET6 1831 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1832 ip6 = mtod(m, struct ip6_hdr *); 1833 ip6->ip6_vfc = IPV6_VERSION; 1834 ip6->ip6_nxt = IPPROTO_TCP; 1835 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1836 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1837 ip6->ip6_plen = htons(tlen - hlen); 1838 /* ip6_hlim is set after checksum */ 1839 /* Zero out traffic class and flow label. */ 1840 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1841 ip6->ip6_flow |= sc->sc_flowlabel; 1842 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1843 1844 th = (struct tcphdr *)(ip6 + 1); 1845 } 1846 #endif 1847 #if defined(INET6) && defined(INET) 1848 else 1849 #endif 1850 #ifdef INET 1851 { 1852 ip = mtod(m, struct ip *); 1853 ip->ip_v = IPVERSION; 1854 ip->ip_hl = sizeof(struct ip) >> 2; 1855 ip->ip_len = htons(tlen); 1856 ip->ip_id = 0; 1857 ip->ip_off = 0; 1858 ip->ip_sum = 0; 1859 ip->ip_p = IPPROTO_TCP; 1860 ip->ip_src = sc->sc_inc.inc_laddr; 1861 ip->ip_dst = sc->sc_inc.inc_faddr; 1862 ip->ip_ttl = sc->sc_ip_ttl; 1863 ip->ip_tos = sc->sc_ip_tos; 1864 1865 /* 1866 * See if we should do MTU discovery. Route lookups are 1867 * expensive, so we will only unset the DF bit if: 1868 * 1869 * 1) path_mtu_discovery is disabled 1870 * 2) the SCF_UNREACH flag has been set 1871 */ 1872 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1873 ip->ip_off |= htons(IP_DF); 1874 1875 th = (struct tcphdr *)(ip + 1); 1876 } 1877 #endif /* INET */ 1878 th->th_sport = sc->sc_inc.inc_lport; 1879 th->th_dport = sc->sc_inc.inc_fport; 1880 1881 if (flags & TH_SYN) 1882 th->th_seq = htonl(sc->sc_iss); 1883 else 1884 th->th_seq = htonl(sc->sc_iss + 1); 1885 th->th_ack = htonl(sc->sc_irs + 1); 1886 th->th_off = sizeof(struct tcphdr) >> 2; 1887 th->th_x2 = 0; 1888 th->th_flags = flags; 1889 th->th_win = htons(sc->sc_wnd); 1890 th->th_urp = 0; 1891 1892 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1893 th->th_flags |= TH_ECE; 1894 TCPSTAT_INC(tcps_ecn_shs); 1895 } 1896 1897 /* Tack on the TCP options. */ 1898 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1899 to.to_flags = 0; 1900 1901 if (flags & TH_SYN) { 1902 to.to_mss = mssopt; 1903 to.to_flags = TOF_MSS; 1904 if (sc->sc_flags & SCF_WINSCALE) { 1905 to.to_wscale = sc->sc_requested_r_scale; 1906 to.to_flags |= TOF_SCALE; 1907 } 1908 if (sc->sc_flags & SCF_SACK) 1909 to.to_flags |= TOF_SACKPERM; 1910 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1911 if (sc->sc_flags & SCF_SIGNATURE) 1912 to.to_flags |= TOF_SIGNATURE; 1913 #endif 1914 if (sc->sc_tfo_cookie) { 1915 to.to_flags |= TOF_FASTOPEN; 1916 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1917 to.to_tfo_cookie = sc->sc_tfo_cookie; 1918 /* don't send cookie again when retransmitting response */ 1919 sc->sc_tfo_cookie = NULL; 1920 } 1921 } 1922 if (sc->sc_flags & SCF_TIMESTAMP) { 1923 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1924 to.to_tsecr = sc->sc_tsreflect; 1925 to.to_flags |= TOF_TS; 1926 } 1927 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1928 1929 /* Adjust headers by option size. */ 1930 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1931 m->m_len += optlen; 1932 m->m_pkthdr.len += optlen; 1933 #ifdef INET6 1934 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1935 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1936 else 1937 #endif 1938 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1939 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1940 if (sc->sc_flags & SCF_SIGNATURE) { 1941 KASSERT(to.to_flags & TOF_SIGNATURE, 1942 ("tcp_addoptions() didn't set tcp_signature")); 1943 1944 /* NOTE: to.to_signature is inside of mbuf */ 1945 if (!TCPMD5_ENABLED() || 1946 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1947 m_freem(m); 1948 return (EACCES); 1949 } 1950 } 1951 #endif 1952 } else 1953 optlen = 0; 1954 1955 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1956 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1957 /* 1958 * If we have peer's SYN and it has a flowid, then let's assign it to 1959 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1960 * to SYN|ACK due to lack of inp here. 1961 */ 1962 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1963 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1964 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1965 } 1966 #ifdef INET6 1967 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1968 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1969 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1970 IPPROTO_TCP, 0); 1971 ip6->ip6_hlim = sc->sc_ip_ttl; 1972 #ifdef TCP_OFFLOAD 1973 if (ADDED_BY_TOE(sc)) { 1974 struct toedev *tod = sc->sc_tod; 1975 1976 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1977 1978 return (error); 1979 } 1980 #endif 1981 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1982 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1983 } 1984 #endif 1985 #if defined(INET6) && defined(INET) 1986 else 1987 #endif 1988 #ifdef INET 1989 { 1990 m->m_pkthdr.csum_flags = CSUM_TCP; 1991 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1992 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1993 #ifdef TCP_OFFLOAD 1994 if (ADDED_BY_TOE(sc)) { 1995 struct toedev *tod = sc->sc_tod; 1996 1997 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1998 1999 return (error); 2000 } 2001 #endif 2002 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2003 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2004 } 2005 #endif 2006 return (error); 2007 } 2008 2009 /* 2010 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2011 * that exceed the capacity of the syncache by avoiding the storage of any 2012 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2013 * attacks where the attacker does not have access to our responses. 2014 * 2015 * Syncookies encode and include all necessary information about the 2016 * connection setup within the SYN|ACK that we send back. That way we 2017 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2018 * (if ever). Normally the syncache and syncookies are running in parallel 2019 * with the latter taking over when the former is exhausted. When matching 2020 * syncache entry is found the syncookie is ignored. 2021 * 2022 * The only reliable information persisting the 3WHS is our initial sequence 2023 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2024 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2025 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2026 * returns and signifies a legitimate connection if it matches the ACK. 2027 * 2028 * The available space of 32 bits to store the hash and to encode the SYN 2029 * option information is very tight and we should have at least 24 bits for 2030 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2031 * 2032 * SYN option information we have to encode to fully restore a connection: 2033 * MSS: is imporant to chose an optimal segment size to avoid IP level 2034 * fragmentation along the path. The common MSS values can be encoded 2035 * in a 3-bit table. Uncommon values are captured by the next lower value 2036 * in the table leading to a slight increase in packetization overhead. 2037 * WSCALE: is necessary to allow large windows to be used for high delay- 2038 * bandwidth product links. Not scaling the window when it was initially 2039 * negotiated is bad for performance as lack of scaling further decreases 2040 * the apparent available send window. We only need to encode the WSCALE 2041 * we received from the remote end. Our end can be recalculated at any 2042 * time. The common WSCALE values can be encoded in a 3-bit table. 2043 * Uncommon values are captured by the next lower value in the table 2044 * making us under-estimate the available window size halving our 2045 * theoretically possible maximum throughput for that connection. 2046 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2047 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2048 * that are included in all segments on a connection. We enable them when 2049 * the ACK has them. 2050 * 2051 * Security of syncookies and attack vectors: 2052 * 2053 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2054 * together with the gloabl secret to make it unique per connection attempt. 2055 * Thus any change of any of those parameters results in a different MAC output 2056 * in an unpredictable way unless a collision is encountered. 24 bits of the 2057 * MAC are embedded into the ISS. 2058 * 2059 * To prevent replay attacks two rotating global secrets are updated with a 2060 * new random value every 15 seconds. The life-time of a syncookie is thus 2061 * 15-30 seconds. 2062 * 2063 * Vector 1: Attacking the secret. This requires finding a weakness in the 2064 * MAC itself or the way it is used here. The attacker can do a chosen plain 2065 * text attack by varying and testing the all parameters under his control. 2066 * The strength depends on the size and randomness of the secret, and the 2067 * cryptographic security of the MAC function. Due to the constant updating 2068 * of the secret the attacker has at most 29.999 seconds to find the secret 2069 * and launch spoofed connections. After that he has to start all over again. 2070 * 2071 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2072 * size an average of 4,823 attempts are required for a 50% chance of success 2073 * to spoof a single syncookie (birthday collision paradox). However the 2074 * attacker is blind and doesn't know if one of his attempts succeeded unless 2075 * he has a side channel to interfere success from. A single connection setup 2076 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2077 * This many attempts are required for each one blind spoofed connection. For 2078 * every additional spoofed connection he has to launch another N attempts. 2079 * Thus for a sustained rate 100 spoofed connections per second approximately 2080 * 1,800,000 packets per second would have to be sent. 2081 * 2082 * NB: The MAC function should be fast so that it doesn't become a CPU 2083 * exhaustion attack vector itself. 2084 * 2085 * References: 2086 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2087 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2088 * http://cr.yp.to/syncookies.html (overview) 2089 * http://cr.yp.to/syncookies/archive (details) 2090 * 2091 * 2092 * Schematic construction of a syncookie enabled Initial Sequence Number: 2093 * 0 1 2 3 2094 * 12345678901234567890123456789012 2095 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2096 * 2097 * x 24 MAC (truncated) 2098 * W 3 Send Window Scale index 2099 * M 3 MSS index 2100 * S 1 SACK permitted 2101 * P 1 Odd/even secret 2102 */ 2103 2104 /* 2105 * Distribution and probability of certain MSS values. Those in between are 2106 * rounded down to the next lower one. 2107 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2108 * .2% .3% 5% 7% 7% 20% 15% 45% 2109 */ 2110 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2111 2112 /* 2113 * Distribution and probability of certain WSCALE values. We have to map the 2114 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2115 * bits based on prevalence of certain values. Where we don't have an exact 2116 * match for are rounded down to the next lower one letting us under-estimate 2117 * the true available window. At the moment this would happen only for the 2118 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2119 * and window size). The absence of the WSCALE option (no scaling in either 2120 * direction) is encoded with index zero. 2121 * [WSCALE values histograms, Allman, 2012] 2122 * X 10 10 35 5 6 14 10% by host 2123 * X 11 4 5 5 18 49 3% by connections 2124 */ 2125 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2126 2127 /* 2128 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2129 * and good cryptographic properties. 2130 */ 2131 static uint32_t 2132 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2133 uint8_t *secbits, uintptr_t secmod) 2134 { 2135 SIPHASH_CTX ctx; 2136 uint32_t siphash[2]; 2137 2138 SipHash24_Init(&ctx); 2139 SipHash_SetKey(&ctx, secbits); 2140 switch (inc->inc_flags & INC_ISIPV6) { 2141 #ifdef INET 2142 case 0: 2143 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2144 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2145 break; 2146 #endif 2147 #ifdef INET6 2148 case INC_ISIPV6: 2149 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2150 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2151 break; 2152 #endif 2153 } 2154 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2155 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2156 SipHash_Update(&ctx, &irs, sizeof(irs)); 2157 SipHash_Update(&ctx, &flags, sizeof(flags)); 2158 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2159 SipHash_Final((u_int8_t *)&siphash, &ctx); 2160 2161 return (siphash[0] ^ siphash[1]); 2162 } 2163 2164 static tcp_seq 2165 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2166 { 2167 u_int i, secbit, wscale; 2168 uint32_t iss, hash; 2169 uint8_t *secbits; 2170 union syncookie cookie; 2171 2172 cookie.cookie = 0; 2173 2174 /* Map our computed MSS into the 3-bit index. */ 2175 for (i = nitems(tcp_sc_msstab) - 1; 2176 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2177 i--) 2178 ; 2179 cookie.flags.mss_idx = i; 2180 2181 /* 2182 * Map the send window scale into the 3-bit index but only if 2183 * the wscale option was received. 2184 */ 2185 if (sc->sc_flags & SCF_WINSCALE) { 2186 wscale = sc->sc_requested_s_scale; 2187 for (i = nitems(tcp_sc_wstab) - 1; 2188 tcp_sc_wstab[i] > wscale && i > 0; 2189 i--) 2190 ; 2191 cookie.flags.wscale_idx = i; 2192 } 2193 2194 /* Can we do SACK? */ 2195 if (sc->sc_flags & SCF_SACK) 2196 cookie.flags.sack_ok = 1; 2197 2198 /* Which of the two secrets to use. */ 2199 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2200 cookie.flags.odd_even = secbit; 2201 2202 secbits = V_tcp_syncache.secret.key[secbit]; 2203 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2204 (uintptr_t)sch); 2205 2206 /* 2207 * Put the flags into the hash and XOR them to get better ISS number 2208 * variance. This doesn't enhance the cryptographic strength and is 2209 * done to prevent the 8 cookie bits from showing up directly on the 2210 * wire. 2211 */ 2212 iss = hash & ~0xff; 2213 iss |= cookie.cookie ^ (hash >> 24); 2214 2215 TCPSTAT_INC(tcps_sc_sendcookie); 2216 return (iss); 2217 } 2218 2219 static struct syncache * 2220 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2221 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2222 struct socket *lso) 2223 { 2224 uint32_t hash; 2225 uint8_t *secbits; 2226 tcp_seq ack, seq; 2227 int wnd, wscale = 0; 2228 union syncookie cookie; 2229 2230 /* 2231 * Pull information out of SYN-ACK/ACK and revert sequence number 2232 * advances. 2233 */ 2234 ack = th->th_ack - 1; 2235 seq = th->th_seq - 1; 2236 2237 /* 2238 * Unpack the flags containing enough information to restore the 2239 * connection. 2240 */ 2241 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2242 2243 /* Which of the two secrets to use. */ 2244 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2245 2246 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2247 2248 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2249 if ((ack & ~0xff) != (hash & ~0xff)) 2250 return (NULL); 2251 2252 /* Fill in the syncache values. */ 2253 sc->sc_flags = 0; 2254 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2255 sc->sc_ipopts = NULL; 2256 2257 sc->sc_irs = seq; 2258 sc->sc_iss = ack; 2259 2260 switch (inc->inc_flags & INC_ISIPV6) { 2261 #ifdef INET 2262 case 0: 2263 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2264 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2265 break; 2266 #endif 2267 #ifdef INET6 2268 case INC_ISIPV6: 2269 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2270 sc->sc_flowlabel = 2271 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2272 break; 2273 #endif 2274 } 2275 2276 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2277 2278 /* We can simply recompute receive window scale we sent earlier. */ 2279 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2280 wscale++; 2281 2282 /* Only use wscale if it was enabled in the orignal SYN. */ 2283 if (cookie.flags.wscale_idx > 0) { 2284 sc->sc_requested_r_scale = wscale; 2285 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2286 sc->sc_flags |= SCF_WINSCALE; 2287 } 2288 2289 wnd = lso->sol_sbrcv_hiwat; 2290 wnd = imax(wnd, 0); 2291 wnd = imin(wnd, TCP_MAXWIN); 2292 sc->sc_wnd = wnd; 2293 2294 if (cookie.flags.sack_ok) 2295 sc->sc_flags |= SCF_SACK; 2296 2297 if (to->to_flags & TOF_TS) { 2298 sc->sc_flags |= SCF_TIMESTAMP; 2299 sc->sc_tsreflect = to->to_tsval; 2300 sc->sc_tsoff = tcp_new_ts_offset(inc); 2301 } 2302 2303 if (to->to_flags & TOF_SIGNATURE) 2304 sc->sc_flags |= SCF_SIGNATURE; 2305 2306 sc->sc_rxmits = 0; 2307 2308 TCPSTAT_INC(tcps_sc_recvcookie); 2309 return (sc); 2310 } 2311 2312 #ifdef INVARIANTS 2313 static int 2314 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2315 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2316 struct socket *lso) 2317 { 2318 struct syncache scs, *scx; 2319 char *s; 2320 2321 bzero(&scs, sizeof(scs)); 2322 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2323 2324 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2325 return (0); 2326 2327 if (scx != NULL) { 2328 if (sc->sc_peer_mss != scx->sc_peer_mss) 2329 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2330 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2331 2332 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2333 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2334 s, __func__, sc->sc_requested_r_scale, 2335 scx->sc_requested_r_scale); 2336 2337 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2338 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2339 s, __func__, sc->sc_requested_s_scale, 2340 scx->sc_requested_s_scale); 2341 2342 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2343 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2344 } 2345 2346 if (s != NULL) 2347 free(s, M_TCPLOG); 2348 return (0); 2349 } 2350 #endif /* INVARIANTS */ 2351 2352 static void 2353 syncookie_reseed(void *arg) 2354 { 2355 struct tcp_syncache *sc = arg; 2356 uint8_t *secbits; 2357 int secbit; 2358 2359 /* 2360 * Reseeding the secret doesn't have to be protected by a lock. 2361 * It only must be ensured that the new random values are visible 2362 * to all CPUs in a SMP environment. The atomic with release 2363 * semantics ensures that. 2364 */ 2365 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2366 secbits = sc->secret.key[secbit]; 2367 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2368 atomic_add_rel_int(&sc->secret.oddeven, 1); 2369 2370 /* Reschedule ourself. */ 2371 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2372 } 2373 2374 /* 2375 * We have overflowed a bucket. Let's pause dealing with the syncache. 2376 * This function will increment the bucketoverflow statistics appropriately 2377 * (once per pause when pausing is enabled; otherwise, once per overflow). 2378 */ 2379 static void 2380 syncache_pause(struct in_conninfo *inc) 2381 { 2382 time_t delta; 2383 const char *s; 2384 2385 /* XXX: 2386 * 2. Add sysctl read here so we don't get the benefit of this 2387 * change without the new sysctl. 2388 */ 2389 2390 /* 2391 * Try an unlocked read. If we already know that another thread 2392 * has activated the feature, there is no need to proceed. 2393 */ 2394 if (V_tcp_syncache.paused) 2395 return; 2396 2397 /* Are cookied enabled? If not, we can't pause. */ 2398 if (!V_tcp_syncookies) { 2399 TCPSTAT_INC(tcps_sc_bucketoverflow); 2400 return; 2401 } 2402 2403 /* 2404 * We may be the first thread to find an overflow. Get the lock 2405 * and evaluate if we need to take action. 2406 */ 2407 mtx_lock(&V_tcp_syncache.pause_mtx); 2408 if (V_tcp_syncache.paused) { 2409 mtx_unlock(&V_tcp_syncache.pause_mtx); 2410 return; 2411 } 2412 2413 /* Activate protection. */ 2414 V_tcp_syncache.paused = true; 2415 TCPSTAT_INC(tcps_sc_bucketoverflow); 2416 2417 /* 2418 * Determine the last backoff time. If we are seeing a re-newed 2419 * attack within that same time after last reactivating the syncache, 2420 * consider it an extension of the same attack. 2421 */ 2422 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2423 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2424 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2425 delta <<= 1; 2426 V_tcp_syncache.pause_backoff++; 2427 } 2428 } else { 2429 delta = TCP_SYNCACHE_PAUSE_TIME; 2430 V_tcp_syncache.pause_backoff = 0; 2431 } 2432 2433 /* Log a warning, including IP addresses, if able. */ 2434 if (inc != NULL) 2435 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2436 else 2437 s = (const char *)NULL; 2438 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2439 "the next %lld seconds%s%s%s\n", (long long)delta, 2440 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2441 (s != NULL) ? ")" : ""); 2442 free(__DECONST(void *, s), M_TCPLOG); 2443 2444 /* Use the calculated delta to set a new pause time. */ 2445 V_tcp_syncache.pause_until = time_uptime + delta; 2446 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2447 &V_tcp_syncache); 2448 mtx_unlock(&V_tcp_syncache.pause_mtx); 2449 } 2450 2451 /* Evaluate whether we need to unpause. */ 2452 static void 2453 syncache_unpause(void *arg) 2454 { 2455 struct tcp_syncache *sc; 2456 time_t delta; 2457 2458 sc = arg; 2459 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2460 callout_deactivate(&sc->pause_co); 2461 2462 /* 2463 * Check to make sure we are not running early. If the pause 2464 * time has expired, then deactivate the protection. 2465 */ 2466 if ((delta = sc->pause_until - time_uptime) > 0) 2467 callout_schedule(&sc->pause_co, delta * hz); 2468 else 2469 sc->paused = false; 2470 } 2471 2472 /* 2473 * Exports the syncache entries to userland so that netstat can display 2474 * them alongside the other sockets. This function is intended to be 2475 * called only from tcp_pcblist. 2476 * 2477 * Due to concurrency on an active system, the number of pcbs exported 2478 * may have no relation to max_pcbs. max_pcbs merely indicates the 2479 * amount of space the caller allocated for this function to use. 2480 */ 2481 int 2482 syncache_pcblist(struct sysctl_req *req) 2483 { 2484 struct xtcpcb xt; 2485 struct syncache *sc; 2486 struct syncache_head *sch; 2487 int error, i; 2488 2489 bzero(&xt, sizeof(xt)); 2490 xt.xt_len = sizeof(xt); 2491 xt.t_state = TCPS_SYN_RECEIVED; 2492 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2493 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2494 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2495 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2496 2497 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2498 sch = &V_tcp_syncache.hashbase[i]; 2499 SCH_LOCK(sch); 2500 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2501 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2502 continue; 2503 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2504 xt.xt_inp.inp_vflag = INP_IPV6; 2505 else 2506 xt.xt_inp.inp_vflag = INP_IPV4; 2507 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2508 sizeof (struct in_conninfo)); 2509 error = SYSCTL_OUT(req, &xt, sizeof xt); 2510 if (error) { 2511 SCH_UNLOCK(sch); 2512 return (0); 2513 } 2514 } 2515 SCH_UNLOCK(sch); 2516 } 2517 2518 return (0); 2519 } 2520