1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/hash.h> 43 #include <sys/refcount.h> 44 #include <sys/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_kdtrace.h> 70 #include <netinet/in_systm.h> 71 #include <netinet/ip.h> 72 #include <netinet/in_var.h> 73 #include <netinet/in_pcb.h> 74 #include <netinet/ip_var.h> 75 #include <netinet/ip_options.h> 76 #ifdef INET6 77 #include <netinet/ip6.h> 78 #include <netinet/icmp6.h> 79 #include <netinet6/nd6.h> 80 #include <netinet6/ip6_var.h> 81 #include <netinet6/in6_pcb.h> 82 #endif 83 #include <netinet/tcp.h> 84 #include <netinet/tcp_fastopen.h> 85 #include <netinet/tcp_fsm.h> 86 #include <netinet/tcp_seq.h> 87 #include <netinet/tcp_timer.h> 88 #include <netinet/tcp_var.h> 89 #include <netinet/tcp_syncache.h> 90 #include <netinet/tcp_ecn.h> 91 #ifdef TCP_BLACKBOX 92 #include <netinet/tcp_log_buf.h> 93 #endif 94 #ifdef TCP_OFFLOAD 95 #include <netinet/toecore.h> 96 #endif 97 #include <netinet/udp.h> 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookiesonly), 0, 115 "Use only TCP SYN cookies"); 116 117 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 118 #define V_functions_inherit_listen_socket_stack \ 119 VNET(functions_inherit_listen_socket_stack) 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 121 CTLFLAG_VNET | CTLFLAG_RW, 122 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 123 "Inherit listen socket's stack"); 124 125 #ifdef TCP_OFFLOAD 126 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 127 #endif 128 129 static void syncache_drop(struct syncache *, struct syncache_head *); 130 static void syncache_free(struct syncache *); 131 static void syncache_insert(struct syncache *, struct syncache_head *); 132 static int syncache_respond(struct syncache *, const struct mbuf *, int); 133 static struct socket *syncache_socket(struct syncache *, struct socket *, 134 struct mbuf *m); 135 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 136 int docallout); 137 static void syncache_timer(void *); 138 139 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 140 uint8_t *, uintptr_t); 141 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 142 static struct syncache 143 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 144 struct syncache *, struct tcphdr *, struct tcpopt *, 145 struct socket *, uint16_t); 146 static void syncache_pause(struct in_conninfo *); 147 static void syncache_unpause(void *); 148 static void syncookie_reseed(void *); 149 #ifdef INVARIANTS 150 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 151 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 152 struct socket *lso, uint16_t port); 153 #endif 154 155 /* 156 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 157 * 3 retransmits corresponds to a timeout with default values of 158 * tcp_rexmit_initial * ( 1 + 159 * tcp_backoff[1] + 160 * tcp_backoff[2] + 161 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 162 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 163 * the odds are that the user has given up attempting to connect by then. 164 */ 165 #define SYNCACHE_MAXREXMTS 3 166 167 /* Arbitrary values */ 168 #define TCP_SYNCACHE_HASHSIZE 512 169 #define TCP_SYNCACHE_BUCKETLIMIT 30 170 171 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 172 #define V_tcp_syncache VNET(tcp_syncache) 173 174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 175 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 176 "TCP SYN cache"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.bucket_limit), 0, 180 "Per-bucket hash limit for syncache"); 181 182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 183 &VNET_NAME(tcp_syncache.cache_limit), 0, 184 "Overall entry limit for syncache"); 185 186 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 187 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 188 189 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 190 &VNET_NAME(tcp_syncache.hashsize), 0, 191 "Size of TCP syncache hashtable"); 192 193 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 194 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 195 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 196 "and mac(4) checks"); 197 198 static int 199 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 200 { 201 int error; 202 u_int new; 203 204 new = V_tcp_syncache.rexmt_limit; 205 error = sysctl_handle_int(oidp, &new, 0, req); 206 if ((error == 0) && (req->newptr != NULL)) { 207 if (new > TCP_MAXRXTSHIFT) 208 error = EINVAL; 209 else 210 V_tcp_syncache.rexmt_limit = new; 211 } 212 return (error); 213 } 214 215 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 216 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 217 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 218 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 219 "Limit on SYN/ACK retransmissions"); 220 221 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 222 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 223 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 224 "Send reset on socket allocation failure"); 225 226 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 227 228 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 229 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 230 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 231 232 /* 233 * Requires the syncache entry to be already removed from the bucket list. 234 */ 235 static void 236 syncache_free(struct syncache *sc) 237 { 238 239 if (sc->sc_ipopts) 240 (void) m_free(sc->sc_ipopts); 241 if (sc->sc_cred) 242 crfree(sc->sc_cred); 243 #ifdef MAC 244 mac_syncache_destroy(&sc->sc_label); 245 #endif 246 247 uma_zfree(V_tcp_syncache.zone, sc); 248 } 249 250 void 251 syncache_init(void) 252 { 253 int i; 254 255 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 256 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 257 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 258 V_tcp_syncache.hash_secret = arc4random(); 259 260 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 261 &V_tcp_syncache.hashsize); 262 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 263 &V_tcp_syncache.bucket_limit); 264 if (!powerof2(V_tcp_syncache.hashsize) || 265 V_tcp_syncache.hashsize == 0) { 266 printf("WARNING: syncache hash size is not a power of 2.\n"); 267 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 268 } 269 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 270 271 /* Set limits. */ 272 V_tcp_syncache.cache_limit = 273 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 274 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 275 &V_tcp_syncache.cache_limit); 276 277 /* Allocate the hash table. */ 278 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 279 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 280 281 #ifdef VIMAGE 282 V_tcp_syncache.vnet = curvnet; 283 #endif 284 285 /* Initialize the hash buckets. */ 286 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 287 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 288 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 289 NULL, MTX_DEF); 290 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 291 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 292 V_tcp_syncache.hashbase[i].sch_length = 0; 293 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 294 V_tcp_syncache.hashbase[i].sch_last_overflow = 295 -(SYNCOOKIE_LIFETIME + 1); 296 } 297 298 /* Create the syncache entry zone. */ 299 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 300 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 301 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 302 V_tcp_syncache.cache_limit); 303 304 /* Start the SYN cookie reseeder callout. */ 305 callout_init(&V_tcp_syncache.secret.reseed, 1); 306 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 307 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 308 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 309 syncookie_reseed, &V_tcp_syncache); 310 311 /* Initialize the pause machinery. */ 312 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 313 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 314 0); 315 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 316 V_tcp_syncache.pause_backoff = 0; 317 V_tcp_syncache.paused = false; 318 } 319 320 #ifdef VIMAGE 321 void 322 syncache_destroy(void) 323 { 324 struct syncache_head *sch; 325 struct syncache *sc, *nsc; 326 int i; 327 328 /* 329 * Stop the re-seed timer before freeing resources. No need to 330 * possibly schedule it another time. 331 */ 332 callout_drain(&V_tcp_syncache.secret.reseed); 333 334 /* Stop the SYN cache pause callout. */ 335 mtx_lock(&V_tcp_syncache.pause_mtx); 336 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 337 mtx_unlock(&V_tcp_syncache.pause_mtx); 338 callout_drain(&V_tcp_syncache.pause_co); 339 } else 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 342 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 343 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 344 sch = &V_tcp_syncache.hashbase[i]; 345 callout_drain(&sch->sch_timer); 346 347 SCH_LOCK(sch); 348 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 349 syncache_drop(sc, sch); 350 SCH_UNLOCK(sch); 351 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 352 ("%s: sch->sch_bucket not empty", __func__)); 353 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 354 __func__, sch->sch_length)); 355 mtx_destroy(&sch->sch_mtx); 356 } 357 358 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 359 ("%s: cache_count not 0", __func__)); 360 361 /* Free the allocated global resources. */ 362 uma_zdestroy(V_tcp_syncache.zone); 363 free(V_tcp_syncache.hashbase, M_SYNCACHE); 364 mtx_destroy(&V_tcp_syncache.pause_mtx); 365 } 366 #endif 367 368 /* 369 * Inserts a syncache entry into the specified bucket row. 370 * Locks and unlocks the syncache_head autonomously. 371 */ 372 static void 373 syncache_insert(struct syncache *sc, struct syncache_head *sch) 374 { 375 struct syncache *sc2; 376 377 SCH_LOCK(sch); 378 379 /* 380 * Make sure that we don't overflow the per-bucket limit. 381 * If the bucket is full, toss the oldest element. 382 */ 383 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 384 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 385 ("sch->sch_length incorrect")); 386 syncache_pause(&sc->sc_inc); 387 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 388 sch->sch_last_overflow = time_uptime; 389 syncache_drop(sc2, sch); 390 } 391 392 /* Put it into the bucket. */ 393 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 394 sch->sch_length++; 395 396 #ifdef TCP_OFFLOAD 397 if (ADDED_BY_TOE(sc)) { 398 struct toedev *tod = sc->sc_tod; 399 400 tod->tod_syncache_added(tod, sc->sc_todctx); 401 } 402 #endif 403 404 /* Reinitialize the bucket row's timer. */ 405 if (sch->sch_length == 1) 406 sch->sch_nextc = ticks + INT_MAX; 407 syncache_timeout(sc, sch, 1); 408 409 SCH_UNLOCK(sch); 410 411 TCPSTATES_INC(TCPS_SYN_RECEIVED); 412 TCPSTAT_INC(tcps_sc_added); 413 } 414 415 /* 416 * Remove and free entry from syncache bucket row. 417 * Expects locked syncache head. 418 */ 419 static void 420 syncache_drop(struct syncache *sc, struct syncache_head *sch) 421 { 422 423 SCH_LOCK_ASSERT(sch); 424 425 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 426 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 427 sch->sch_length--; 428 429 #ifdef TCP_OFFLOAD 430 if (ADDED_BY_TOE(sc)) { 431 struct toedev *tod = sc->sc_tod; 432 433 tod->tod_syncache_removed(tod, sc->sc_todctx); 434 } 435 #endif 436 437 syncache_free(sc); 438 } 439 440 /* 441 * Engage/reengage time on bucket row. 442 */ 443 static void 444 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 445 { 446 int rexmt; 447 448 if (sc->sc_rxmits == 0) 449 rexmt = tcp_rexmit_initial; 450 else 451 TCPT_RANGESET(rexmt, 452 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 453 tcp_rexmit_min, TCPTV_REXMTMAX); 454 sc->sc_rxttime = ticks + rexmt; 455 sc->sc_rxmits++; 456 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 457 sch->sch_nextc = sc->sc_rxttime; 458 if (docallout) 459 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 460 syncache_timer, (void *)sch); 461 } 462 } 463 464 /* 465 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 466 * If we have retransmitted an entry the maximum number of times, expire it. 467 * One separate timer for each bucket row. 468 */ 469 static void 470 syncache_timer(void *xsch) 471 { 472 struct syncache_head *sch = (struct syncache_head *)xsch; 473 struct syncache *sc, *nsc; 474 struct epoch_tracker et; 475 int tick = ticks; 476 char *s; 477 bool paused; 478 479 CURVNET_SET(sch->sch_sc->vnet); 480 481 /* NB: syncache_head has already been locked by the callout. */ 482 SCH_LOCK_ASSERT(sch); 483 484 /* 485 * In the following cycle we may remove some entries and/or 486 * advance some timeouts, so re-initialize the bucket timer. 487 */ 488 sch->sch_nextc = tick + INT_MAX; 489 490 /* 491 * If we have paused processing, unconditionally remove 492 * all syncache entries. 493 */ 494 mtx_lock(&V_tcp_syncache.pause_mtx); 495 paused = V_tcp_syncache.paused; 496 mtx_unlock(&V_tcp_syncache.pause_mtx); 497 498 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 499 if (paused) { 500 syncache_drop(sc, sch); 501 continue; 502 } 503 /* 504 * We do not check if the listen socket still exists 505 * and accept the case where the listen socket may be 506 * gone by the time we resend the SYN/ACK. We do 507 * not expect this to happens often. If it does, 508 * then the RST will be sent by the time the remote 509 * host does the SYN/ACK->ACK. 510 */ 511 if (TSTMP_GT(sc->sc_rxttime, tick)) { 512 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 513 sch->sch_nextc = sc->sc_rxttime; 514 continue; 515 } 516 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 517 sc->sc_flags &= ~SCF_ECN_MASK; 518 } 519 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 520 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 521 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 522 "giving up and removing syncache entry\n", 523 s, __func__); 524 free(s, M_TCPLOG); 525 } 526 syncache_drop(sc, sch); 527 TCPSTAT_INC(tcps_sc_stale); 528 continue; 529 } 530 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 531 log(LOG_DEBUG, "%s; %s: Response timeout, " 532 "retransmitting (%u) SYN|ACK\n", 533 s, __func__, sc->sc_rxmits); 534 free(s, M_TCPLOG); 535 } 536 537 NET_EPOCH_ENTER(et); 538 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 539 NET_EPOCH_EXIT(et); 540 TCPSTAT_INC(tcps_sc_retransmitted); 541 syncache_timeout(sc, sch, 0); 542 } 543 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 544 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 545 syncache_timer, (void *)(sch)); 546 CURVNET_RESTORE(); 547 } 548 549 /* 550 * Returns true if the system is only using cookies at the moment. 551 * This could be due to a sysadmin decision to only use cookies, or it 552 * could be due to the system detecting an attack. 553 */ 554 static inline bool 555 syncache_cookiesonly(void) 556 { 557 558 return (V_tcp_syncookies && (V_tcp_syncache.paused || 559 V_tcp_syncookiesonly)); 560 } 561 562 /* 563 * Find the hash bucket for the given connection. 564 */ 565 static struct syncache_head * 566 syncache_hashbucket(struct in_conninfo *inc) 567 { 568 uint32_t hash; 569 570 /* 571 * The hash is built on foreign port + local port + foreign address. 572 * We rely on the fact that struct in_conninfo starts with 16 bits 573 * of foreign port, then 16 bits of local port then followed by 128 574 * bits of foreign address. In case of IPv4 address, the first 3 575 * 32-bit words of the address always are zeroes. 576 */ 577 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 578 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 579 580 return (&V_tcp_syncache.hashbase[hash]); 581 } 582 583 /* 584 * Find an entry in the syncache. 585 * Returns always with locked syncache_head plus a matching entry or NULL. 586 */ 587 static struct syncache * 588 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 589 { 590 struct syncache *sc; 591 struct syncache_head *sch; 592 593 *schp = sch = syncache_hashbucket(inc); 594 SCH_LOCK(sch); 595 596 /* Circle through bucket row to find matching entry. */ 597 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 598 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 599 sizeof(struct in_endpoints)) == 0) 600 break; 601 602 return (sc); /* Always returns with locked sch. */ 603 } 604 605 /* 606 * This function is called when we get a RST for a 607 * non-existent connection, so that we can see if the 608 * connection is in the syn cache. If it is, zap it. 609 * If required send a challenge ACK. 610 */ 611 void 612 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 613 uint16_t port) 614 { 615 struct syncache *sc; 616 struct syncache_head *sch; 617 char *s = NULL; 618 619 if (syncache_cookiesonly()) 620 return; 621 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 622 SCH_LOCK_ASSERT(sch); 623 624 /* 625 * No corresponding connection was found in syncache. 626 * If syncookies are enabled and possibly exclusively 627 * used, or we are under memory pressure, a valid RST 628 * may not find a syncache entry. In that case we're 629 * done and no SYN|ACK retransmissions will happen. 630 * Otherwise the RST was misdirected or spoofed. 631 */ 632 if (sc == NULL) { 633 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 634 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 635 "syncache entry (possibly syncookie only), " 636 "segment ignored\n", s, __func__); 637 TCPSTAT_INC(tcps_badrst); 638 goto done; 639 } 640 641 /* The remote UDP encaps port does not match. */ 642 if (sc->sc_port != port) { 643 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 644 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 645 "syncache entry but non-matching UDP encaps port, " 646 "segment ignored\n", s, __func__); 647 TCPSTAT_INC(tcps_badrst); 648 goto done; 649 } 650 651 /* 652 * If the RST bit is set, check the sequence number to see 653 * if this is a valid reset segment. 654 * 655 * RFC 793 page 37: 656 * In all states except SYN-SENT, all reset (RST) segments 657 * are validated by checking their SEQ-fields. A reset is 658 * valid if its sequence number is in the window. 659 * 660 * RFC 793 page 69: 661 * There are four cases for the acceptability test for an incoming 662 * segment: 663 * 664 * Segment Receive Test 665 * Length Window 666 * ------- ------- ------------------------------------------- 667 * 0 0 SEG.SEQ = RCV.NXT 668 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 669 * >0 0 not acceptable 670 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 671 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 672 * 673 * Note that when receiving a SYN segment in the LISTEN state, 674 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 675 * described in RFC 793, page 66. 676 */ 677 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 678 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 679 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 680 if (V_tcp_insecure_rst || 681 th->th_seq == sc->sc_irs + 1) { 682 syncache_drop(sc, sch); 683 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 684 log(LOG_DEBUG, 685 "%s; %s: Our SYN|ACK was rejected, " 686 "connection attempt aborted by remote " 687 "endpoint\n", 688 s, __func__); 689 TCPSTAT_INC(tcps_sc_reset); 690 } else { 691 TCPSTAT_INC(tcps_badrst); 692 /* Send challenge ACK. */ 693 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 694 log(LOG_DEBUG, "%s; %s: RST with invalid " 695 " SEQ %u != NXT %u (+WND %u), " 696 "sending challenge ACK\n", 697 s, __func__, 698 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 699 syncache_respond(sc, m, TH_ACK); 700 } 701 } else { 702 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 703 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 704 "NXT %u (+WND %u), segment ignored\n", 705 s, __func__, 706 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 707 TCPSTAT_INC(tcps_badrst); 708 } 709 710 done: 711 if (s != NULL) 712 free(s, M_TCPLOG); 713 SCH_UNLOCK(sch); 714 } 715 716 void 717 syncache_badack(struct in_conninfo *inc, uint16_t port) 718 { 719 struct syncache *sc; 720 struct syncache_head *sch; 721 722 if (syncache_cookiesonly()) 723 return; 724 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 725 SCH_LOCK_ASSERT(sch); 726 if ((sc != NULL) && (sc->sc_port == port)) { 727 syncache_drop(sc, sch); 728 TCPSTAT_INC(tcps_sc_badack); 729 } 730 SCH_UNLOCK(sch); 731 } 732 733 void 734 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 735 { 736 struct syncache *sc; 737 struct syncache_head *sch; 738 739 if (syncache_cookiesonly()) 740 return; 741 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 742 SCH_LOCK_ASSERT(sch); 743 if (sc == NULL) 744 goto done; 745 746 /* If the port != sc_port, then it's a bogus ICMP msg */ 747 if (port != sc->sc_port) 748 goto done; 749 750 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 751 if (ntohl(th_seq) != sc->sc_iss) 752 goto done; 753 754 /* 755 * If we've rertransmitted 3 times and this is our second error, 756 * we remove the entry. Otherwise, we allow it to continue on. 757 * This prevents us from incorrectly nuking an entry during a 758 * spurious network outage. 759 * 760 * See tcp_notify(). 761 */ 762 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 763 sc->sc_flags |= SCF_UNREACH; 764 goto done; 765 } 766 syncache_drop(sc, sch); 767 TCPSTAT_INC(tcps_sc_unreach); 768 done: 769 SCH_UNLOCK(sch); 770 } 771 772 /* 773 * Build a new TCP socket structure from a syncache entry. 774 * 775 * On success return the newly created socket with its underlying inp locked. 776 */ 777 static struct socket * 778 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 779 { 780 struct tcp_function_block *blk; 781 struct inpcb *inp = NULL; 782 struct socket *so; 783 struct tcpcb *tp; 784 int error; 785 char *s; 786 787 NET_EPOCH_ASSERT(); 788 789 /* 790 * Ok, create the full blown connection, and set things up 791 * as they would have been set up if we had created the 792 * connection when the SYN arrived. 793 */ 794 if ((so = solisten_clone(lso)) == NULL) 795 goto allocfail; 796 #ifdef MAC 797 mac_socketpeer_set_from_mbuf(m, so); 798 #endif 799 error = in_pcballoc(so, &V_tcbinfo); 800 if (error) { 801 sodealloc(so); 802 goto allocfail; 803 } 804 inp = sotoinpcb(so); 805 if ((tp = tcp_newtcpcb(inp)) == NULL) { 806 in_pcbfree(inp); 807 sodealloc(so); 808 goto allocfail; 809 } 810 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 811 #ifdef INET6 812 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 813 inp->inp_vflag &= ~INP_IPV4; 814 inp->inp_vflag |= INP_IPV6; 815 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 816 } else { 817 inp->inp_vflag &= ~INP_IPV6; 818 inp->inp_vflag |= INP_IPV4; 819 #endif 820 inp->inp_ip_ttl = sc->sc_ip_ttl; 821 inp->inp_ip_tos = sc->sc_ip_tos; 822 inp->inp_laddr = sc->sc_inc.inc_laddr; 823 #ifdef INET6 824 } 825 #endif 826 827 /* 828 * If there's an mbuf and it has a flowid, then let's initialise the 829 * inp with that particular flowid. 830 */ 831 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 832 inp->inp_flowid = m->m_pkthdr.flowid; 833 inp->inp_flowtype = M_HASHTYPE_GET(m); 834 #ifdef NUMA 835 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 836 #endif 837 } 838 839 inp->inp_lport = sc->sc_inc.inc_lport; 840 #ifdef INET6 841 if (inp->inp_vflag & INP_IPV6PROTO) { 842 struct inpcb *oinp = sotoinpcb(lso); 843 844 /* 845 * Inherit socket options from the listening socket. 846 * Note that in6p_inputopts are not (and should not be) 847 * copied, since it stores previously received options and is 848 * used to detect if each new option is different than the 849 * previous one and hence should be passed to a user. 850 * If we copied in6p_inputopts, a user would not be able to 851 * receive options just after calling the accept system call. 852 */ 853 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 854 if (oinp->in6p_outputopts) 855 inp->in6p_outputopts = 856 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 857 inp->in6p_hops = oinp->in6p_hops; 858 } 859 860 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 861 struct sockaddr_in6 sin6; 862 863 sin6.sin6_family = AF_INET6; 864 sin6.sin6_len = sizeof(sin6); 865 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 866 sin6.sin6_port = sc->sc_inc.inc_fport; 867 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 868 INP_HASH_WLOCK(&V_tcbinfo); 869 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 870 INP_HASH_WUNLOCK(&V_tcbinfo); 871 if (error != 0) 872 goto abort; 873 /* Override flowlabel from in6_pcbconnect. */ 874 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 875 inp->inp_flow |= sc->sc_flowlabel; 876 } 877 #endif /* INET6 */ 878 #if defined(INET) && defined(INET6) 879 else 880 #endif 881 #ifdef INET 882 { 883 struct sockaddr_in sin; 884 885 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 886 887 if (inp->inp_options == NULL) { 888 inp->inp_options = sc->sc_ipopts; 889 sc->sc_ipopts = NULL; 890 } 891 892 sin.sin_family = AF_INET; 893 sin.sin_len = sizeof(sin); 894 sin.sin_addr = sc->sc_inc.inc_faddr; 895 sin.sin_port = sc->sc_inc.inc_fport; 896 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 897 INP_HASH_WLOCK(&V_tcbinfo); 898 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false); 899 INP_HASH_WUNLOCK(&V_tcbinfo); 900 if (error != 0) 901 goto abort; 902 } 903 #endif /* INET */ 904 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 905 /* Copy old policy into new socket's. */ 906 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 907 printf("syncache_socket: could not copy policy\n"); 908 #endif 909 tp->t_state = TCPS_SYN_RECEIVED; 910 tp->iss = sc->sc_iss; 911 tp->irs = sc->sc_irs; 912 tp->t_port = sc->sc_port; 913 tcp_rcvseqinit(tp); 914 tcp_sendseqinit(tp); 915 blk = sototcpcb(lso)->t_fb; 916 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 917 /* 918 * Our parents t_fb was not the default, 919 * we need to release our ref on tp->t_fb and 920 * pickup one on the new entry. 921 */ 922 struct tcp_function_block *rblk; 923 void *ptr = NULL; 924 925 rblk = find_and_ref_tcp_fb(blk); 926 KASSERT(rblk != NULL, 927 ("cannot find blk %p out of syncache?", blk)); 928 929 if (rblk->tfb_tcp_fb_init == NULL || 930 (*rblk->tfb_tcp_fb_init)(tp, &ptr) == 0) { 931 /* Release the old stack */ 932 if (tp->t_fb->tfb_tcp_fb_fini != NULL) 933 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 934 refcount_release(&tp->t_fb->tfb_refcnt); 935 /* Now set in all the pointers */ 936 tp->t_fb = rblk; 937 tp->t_fb_ptr = ptr; 938 } else { 939 /* 940 * Initialization failed. Release the reference count on 941 * the looked up default stack. 942 */ 943 refcount_release(&rblk->tfb_refcnt); 944 } 945 } 946 tp->snd_wl1 = sc->sc_irs; 947 tp->snd_max = tp->iss + 1; 948 tp->snd_nxt = tp->iss + 1; 949 tp->rcv_up = sc->sc_irs + 1; 950 tp->rcv_wnd = sc->sc_wnd; 951 tp->rcv_adv += tp->rcv_wnd; 952 tp->last_ack_sent = tp->rcv_nxt; 953 954 tp->t_flags = sototcpcb(lso)->t_flags & 955 (TF_LRD|TF_NOPUSH|TF_NODELAY); 956 if (sc->sc_flags & SCF_NOOPT) 957 tp->t_flags |= TF_NOOPT; 958 else { 959 if (sc->sc_flags & SCF_WINSCALE) { 960 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 961 tp->snd_scale = sc->sc_requested_s_scale; 962 tp->request_r_scale = sc->sc_requested_r_scale; 963 } 964 if (sc->sc_flags & SCF_TIMESTAMP) { 965 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 966 tp->ts_recent = sc->sc_tsreflect; 967 tp->ts_recent_age = tcp_ts_getticks(); 968 tp->ts_offset = sc->sc_tsoff; 969 } 970 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 971 if (sc->sc_flags & SCF_SIGNATURE) 972 tp->t_flags |= TF_SIGNATURE; 973 #endif 974 if (sc->sc_flags & SCF_SACK) 975 tp->t_flags |= TF_SACK_PERMIT; 976 } 977 978 tcp_ecn_syncache_socket(tp, sc); 979 980 /* 981 * Set up MSS and get cached values from tcp_hostcache. 982 * This might overwrite some of the defaults we just set. 983 */ 984 tcp_mss(tp, sc->sc_peer_mss); 985 986 /* 987 * If the SYN,ACK was retransmitted, indicate that CWND to be 988 * limited to one segment in cc_conn_init(). 989 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 990 */ 991 if (sc->sc_rxmits > 1) 992 tp->snd_cwnd = 1; 993 994 #ifdef TCP_OFFLOAD 995 /* 996 * Allow a TOE driver to install its hooks. Note that we hold the 997 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 998 * new connection before the TOE driver has done its thing. 999 */ 1000 if (ADDED_BY_TOE(sc)) { 1001 struct toedev *tod = sc->sc_tod; 1002 1003 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1004 } 1005 #endif 1006 #ifdef TCP_BLACKBOX 1007 /* 1008 * Inherit the log state from the listening socket, if 1009 * - the log state of the listening socket is not off and 1010 * - the listening socket was not auto selected from all sessions and 1011 * - a log id is not set on the listening socket. 1012 * This avoids inheriting a log state which was automatically set. 1013 */ 1014 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 1015 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 1016 (sototcpcb(lso)->t_lib == NULL)) { 1017 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 1018 } 1019 #endif 1020 /* 1021 * Copy and activate timers. 1022 */ 1023 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1024 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1025 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1026 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1027 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1028 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1029 1030 TCPSTAT_INC(tcps_accepts); 1031 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1032 1033 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1034 tp->t_flags |= TF_SONOTCONN; 1035 /* Can we inherit anything from the listener? */ 1036 if (tp->t_fb->tfb_inherit != NULL) { 1037 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1038 } 1039 return (so); 1040 1041 allocfail: 1042 /* 1043 * Drop the connection; we will either send a RST or have the peer 1044 * retransmit its SYN again after its RTO and try again. 1045 */ 1046 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1047 log(LOG_DEBUG, "%s; %s: Socket create failed " 1048 "due to limits or memory shortage\n", 1049 s, __func__); 1050 free(s, M_TCPLOG); 1051 } 1052 TCPSTAT_INC(tcps_listendrop); 1053 return (NULL); 1054 1055 abort: 1056 in_pcbfree(inp); 1057 sodealloc(so); 1058 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1059 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1060 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1061 error); 1062 free(s, M_TCPLOG); 1063 } 1064 TCPSTAT_INC(tcps_listendrop); 1065 return (NULL); 1066 } 1067 1068 /* 1069 * This function gets called when we receive an ACK for a 1070 * socket in the LISTEN state. We look up the connection 1071 * in the syncache, and if its there, we pull it out of 1072 * the cache and turn it into a full-blown connection in 1073 * the SYN-RECEIVED state. 1074 * 1075 * On syncache_socket() success the newly created socket 1076 * has its underlying inp locked. 1077 */ 1078 int 1079 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1080 struct socket **lsop, struct mbuf *m, uint16_t port) 1081 { 1082 struct syncache *sc; 1083 struct syncache_head *sch; 1084 struct syncache scs; 1085 char *s; 1086 bool locked; 1087 1088 NET_EPOCH_ASSERT(); 1089 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1090 ("%s: can handle only ACK", __func__)); 1091 1092 if (syncache_cookiesonly()) { 1093 sc = NULL; 1094 sch = syncache_hashbucket(inc); 1095 locked = false; 1096 } else { 1097 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1098 locked = true; 1099 SCH_LOCK_ASSERT(sch); 1100 } 1101 1102 #ifdef INVARIANTS 1103 /* 1104 * Test code for syncookies comparing the syncache stored 1105 * values with the reconstructed values from the cookie. 1106 */ 1107 if (sc != NULL) 1108 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1109 #endif 1110 1111 if (sc == NULL) { 1112 /* 1113 * There is no syncache entry, so see if this ACK is 1114 * a returning syncookie. To do this, first: 1115 * A. Check if syncookies are used in case of syncache 1116 * overflows 1117 * B. See if this socket has had a syncache entry dropped in 1118 * the recent past. We don't want to accept a bogus 1119 * syncookie if we've never received a SYN or accept it 1120 * twice. 1121 * C. check that the syncookie is valid. If it is, then 1122 * cobble up a fake syncache entry, and return. 1123 */ 1124 if (locked && !V_tcp_syncookies) { 1125 SCH_UNLOCK(sch); 1126 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1127 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1128 "segment rejected (syncookies disabled)\n", 1129 s, __func__); 1130 goto failed; 1131 } 1132 if (locked && !V_tcp_syncookiesonly && 1133 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1134 SCH_UNLOCK(sch); 1135 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1136 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1137 "segment rejected (no syncache entry)\n", 1138 s, __func__); 1139 goto failed; 1140 } 1141 bzero(&scs, sizeof(scs)); 1142 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1143 if (locked) 1144 SCH_UNLOCK(sch); 1145 if (sc == NULL) { 1146 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1147 log(LOG_DEBUG, "%s; %s: Segment failed " 1148 "SYNCOOKIE authentication, segment rejected " 1149 "(probably spoofed)\n", s, __func__); 1150 goto failed; 1151 } 1152 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1153 /* If received ACK has MD5 signature, check it. */ 1154 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1155 (!TCPMD5_ENABLED() || 1156 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1157 /* Drop the ACK. */ 1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1159 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1160 "MD5 signature doesn't match.\n", 1161 s, __func__); 1162 free(s, M_TCPLOG); 1163 } 1164 TCPSTAT_INC(tcps_sig_err_sigopt); 1165 return (-1); /* Do not send RST */ 1166 } 1167 #endif /* TCP_SIGNATURE */ 1168 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1169 } else { 1170 if (sc->sc_port != port) { 1171 SCH_UNLOCK(sch); 1172 return (0); 1173 } 1174 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1175 /* 1176 * If listening socket requested TCP digests, check that 1177 * received ACK has signature and it is correct. 1178 * If not, drop the ACK and leave sc entry in th cache, 1179 * because SYN was received with correct signature. 1180 */ 1181 if (sc->sc_flags & SCF_SIGNATURE) { 1182 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1183 /* No signature */ 1184 TCPSTAT_INC(tcps_sig_err_nosigopt); 1185 SCH_UNLOCK(sch); 1186 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1187 log(LOG_DEBUG, "%s; %s: Segment " 1188 "rejected, MD5 signature wasn't " 1189 "provided.\n", s, __func__); 1190 free(s, M_TCPLOG); 1191 } 1192 return (-1); /* Do not send RST */ 1193 } 1194 if (!TCPMD5_ENABLED() || 1195 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1196 /* Doesn't match or no SA */ 1197 SCH_UNLOCK(sch); 1198 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1199 log(LOG_DEBUG, "%s; %s: Segment " 1200 "rejected, MD5 signature doesn't " 1201 "match.\n", s, __func__); 1202 free(s, M_TCPLOG); 1203 } 1204 return (-1); /* Do not send RST */ 1205 } 1206 } 1207 #endif /* TCP_SIGNATURE */ 1208 1209 /* 1210 * RFC 7323 PAWS: If we have a timestamp on this segment and 1211 * it's less than ts_recent, drop it. 1212 * XXXMT: RFC 7323 also requires to send an ACK. 1213 * In tcp_input.c this is only done for TCP segments 1214 * with user data, so be consistent here and just drop 1215 * the segment. 1216 */ 1217 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1218 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1219 SCH_UNLOCK(sch); 1220 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1221 log(LOG_DEBUG, 1222 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1223 "segment dropped\n", s, __func__, 1224 to->to_tsval, sc->sc_tsreflect); 1225 free(s, M_TCPLOG); 1226 } 1227 return (-1); /* Do not send RST */ 1228 } 1229 1230 /* 1231 * If timestamps were not negotiated during SYN/ACK and a 1232 * segment with a timestamp is received, ignore the 1233 * timestamp and process the packet normally. 1234 * See section 3.2 of RFC 7323. 1235 */ 1236 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1237 (to->to_flags & TOF_TS)) { 1238 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1239 log(LOG_DEBUG, "%s; %s: Timestamp not " 1240 "expected, segment processed normally\n", 1241 s, __func__); 1242 free(s, M_TCPLOG); 1243 s = NULL; 1244 } 1245 } 1246 1247 /* 1248 * If timestamps were negotiated during SYN/ACK and a 1249 * segment without a timestamp is received, silently drop 1250 * the segment, unless the missing timestamps are tolerated. 1251 * See section 3.2 of RFC 7323. 1252 */ 1253 if ((sc->sc_flags & SCF_TIMESTAMP) && 1254 !(to->to_flags & TOF_TS)) { 1255 if (V_tcp_tolerate_missing_ts) { 1256 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1257 log(LOG_DEBUG, 1258 "%s; %s: Timestamp missing, " 1259 "segment processed normally\n", 1260 s, __func__); 1261 free(s, M_TCPLOG); 1262 } 1263 } else { 1264 SCH_UNLOCK(sch); 1265 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1266 log(LOG_DEBUG, 1267 "%s; %s: Timestamp missing, " 1268 "segment silently dropped\n", 1269 s, __func__); 1270 free(s, M_TCPLOG); 1271 } 1272 return (-1); /* Do not send RST */ 1273 } 1274 } 1275 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1276 sch->sch_length--; 1277 #ifdef TCP_OFFLOAD 1278 if (ADDED_BY_TOE(sc)) { 1279 struct toedev *tod = sc->sc_tod; 1280 1281 tod->tod_syncache_removed(tod, sc->sc_todctx); 1282 } 1283 #endif 1284 SCH_UNLOCK(sch); 1285 } 1286 1287 /* 1288 * Segment validation: 1289 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1290 */ 1291 if (th->th_ack != sc->sc_iss + 1) { 1292 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1293 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1294 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1295 goto failed; 1296 } 1297 1298 /* 1299 * The SEQ must fall in the window starting at the received 1300 * initial receive sequence number + 1 (the SYN). 1301 */ 1302 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1303 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1304 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1305 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1306 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1307 goto failed; 1308 } 1309 1310 *lsop = syncache_socket(sc, *lsop, m); 1311 1312 if (__predict_false(*lsop == NULL)) { 1313 TCPSTAT_INC(tcps_sc_aborted); 1314 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1315 } else 1316 TCPSTAT_INC(tcps_sc_completed); 1317 1318 /* how do we find the inp for the new socket? */ 1319 if (sc != &scs) 1320 syncache_free(sc); 1321 return (1); 1322 failed: 1323 if (sc != NULL) { 1324 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1325 if (sc != &scs) 1326 syncache_free(sc); 1327 } 1328 if (s != NULL) 1329 free(s, M_TCPLOG); 1330 *lsop = NULL; 1331 return (0); 1332 } 1333 1334 static struct socket * 1335 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1336 uint64_t response_cookie) 1337 { 1338 struct inpcb *inp; 1339 struct tcpcb *tp; 1340 unsigned int *pending_counter; 1341 struct socket *so; 1342 1343 NET_EPOCH_ASSERT(); 1344 1345 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1346 so = syncache_socket(sc, lso, m); 1347 if (so == NULL) { 1348 TCPSTAT_INC(tcps_sc_aborted); 1349 atomic_subtract_int(pending_counter, 1); 1350 } else { 1351 soisconnected(so); 1352 inp = sotoinpcb(so); 1353 tp = intotcpcb(inp); 1354 tp->t_flags |= TF_FASTOPEN; 1355 tp->t_tfo_cookie.server = response_cookie; 1356 tp->snd_max = tp->iss; 1357 tp->snd_nxt = tp->iss; 1358 tp->t_tfo_pending = pending_counter; 1359 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1360 TCPSTAT_INC(tcps_sc_completed); 1361 } 1362 1363 return (so); 1364 } 1365 1366 /* 1367 * Given a LISTEN socket and an inbound SYN request, add 1368 * this to the syn cache, and send back a segment: 1369 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1370 * to the source. 1371 * 1372 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1373 * Doing so would require that we hold onto the data and deliver it 1374 * to the application. However, if we are the target of a SYN-flood 1375 * DoS attack, an attacker could send data which would eventually 1376 * consume all available buffer space if it were ACKed. By not ACKing 1377 * the data, we avoid this DoS scenario. 1378 * 1379 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1380 * cookie is processed and a new socket is created. In this case, any data 1381 * accompanying the SYN will be queued to the socket by tcp_input() and will 1382 * be ACKed either when the application sends response data or the delayed 1383 * ACK timer expires, whichever comes first. 1384 */ 1385 struct socket * 1386 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1387 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1388 void *todctx, uint8_t iptos, uint16_t port) 1389 { 1390 struct tcpcb *tp; 1391 struct socket *rv = NULL; 1392 struct syncache *sc = NULL; 1393 struct syncache_head *sch; 1394 struct mbuf *ipopts = NULL; 1395 u_int ltflags; 1396 int win, ip_ttl, ip_tos; 1397 char *s; 1398 #ifdef INET6 1399 int autoflowlabel = 0; 1400 #endif 1401 #ifdef MAC 1402 struct label *maclabel; 1403 #endif 1404 struct syncache scs; 1405 struct ucred *cred; 1406 uint64_t tfo_response_cookie; 1407 unsigned int *tfo_pending = NULL; 1408 int tfo_cookie_valid = 0; 1409 int tfo_response_cookie_valid = 0; 1410 bool locked; 1411 1412 INP_RLOCK_ASSERT(inp); /* listen socket */ 1413 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1414 ("%s: unexpected tcp flags", __func__)); 1415 1416 /* 1417 * Combine all so/tp operations very early to drop the INP lock as 1418 * soon as possible. 1419 */ 1420 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1421 tp = sototcpcb(so); 1422 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1423 1424 #ifdef INET6 1425 if (inc->inc_flags & INC_ISIPV6) { 1426 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1427 autoflowlabel = 1; 1428 } 1429 ip_ttl = in6_selecthlim(inp, NULL); 1430 if ((inp->in6p_outputopts == NULL) || 1431 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1432 ip_tos = 0; 1433 } else { 1434 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1435 } 1436 } 1437 #endif 1438 #if defined(INET6) && defined(INET) 1439 else 1440 #endif 1441 #ifdef INET 1442 { 1443 ip_ttl = inp->inp_ip_ttl; 1444 ip_tos = inp->inp_ip_tos; 1445 } 1446 #endif 1447 win = so->sol_sbrcv_hiwat; 1448 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1449 1450 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1451 (tp->t_tfo_pending != NULL) && 1452 (to->to_flags & TOF_FASTOPEN)) { 1453 /* 1454 * Limit the number of pending TFO connections to 1455 * approximately half of the queue limit. This prevents TFO 1456 * SYN floods from starving the service by filling the 1457 * listen queue with bogus TFO connections. 1458 */ 1459 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1460 (so->sol_qlimit / 2)) { 1461 int result; 1462 1463 result = tcp_fastopen_check_cookie(inc, 1464 to->to_tfo_cookie, to->to_tfo_len, 1465 &tfo_response_cookie); 1466 tfo_cookie_valid = (result > 0); 1467 tfo_response_cookie_valid = (result >= 0); 1468 } 1469 1470 /* 1471 * Remember the TFO pending counter as it will have to be 1472 * decremented below if we don't make it to syncache_tfo_expand(). 1473 */ 1474 tfo_pending = tp->t_tfo_pending; 1475 } 1476 1477 #ifdef MAC 1478 if (mac_syncache_init(&maclabel) != 0) { 1479 INP_RUNLOCK(inp); 1480 goto done; 1481 } else 1482 mac_syncache_create(maclabel, inp); 1483 #endif 1484 if (!tfo_cookie_valid) 1485 INP_RUNLOCK(inp); 1486 1487 /* 1488 * Remember the IP options, if any. 1489 */ 1490 #ifdef INET6 1491 if (!(inc->inc_flags & INC_ISIPV6)) 1492 #endif 1493 #ifdef INET 1494 ipopts = (m) ? ip_srcroute(m) : NULL; 1495 #else 1496 ipopts = NULL; 1497 #endif 1498 1499 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1500 /* 1501 * When the socket is TCP-MD5 enabled check that, 1502 * - a signed packet is valid 1503 * - a non-signed packet does not have a security association 1504 * 1505 * If a signed packet fails validation or a non-signed packet has a 1506 * security association, the packet will be dropped. 1507 */ 1508 if (ltflags & TF_SIGNATURE) { 1509 if (to->to_flags & TOF_SIGNATURE) { 1510 if (!TCPMD5_ENABLED() || 1511 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1512 goto done; 1513 } else { 1514 if (TCPMD5_ENABLED() && 1515 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1516 goto done; 1517 } 1518 } else if (to->to_flags & TOF_SIGNATURE) 1519 goto done; 1520 #endif /* TCP_SIGNATURE */ 1521 /* 1522 * See if we already have an entry for this connection. 1523 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1524 * 1525 * XXX: should the syncache be re-initialized with the contents 1526 * of the new SYN here (which may have different options?) 1527 * 1528 * XXX: We do not check the sequence number to see if this is a 1529 * real retransmit or a new connection attempt. The question is 1530 * how to handle such a case; either ignore it as spoofed, or 1531 * drop the current entry and create a new one? 1532 */ 1533 if (syncache_cookiesonly()) { 1534 sc = NULL; 1535 sch = syncache_hashbucket(inc); 1536 locked = false; 1537 } else { 1538 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1539 locked = true; 1540 SCH_LOCK_ASSERT(sch); 1541 } 1542 if (sc != NULL) { 1543 if (tfo_cookie_valid) 1544 INP_RUNLOCK(inp); 1545 TCPSTAT_INC(tcps_sc_dupsyn); 1546 if (ipopts) { 1547 /* 1548 * If we were remembering a previous source route, 1549 * forget it and use the new one we've been given. 1550 */ 1551 if (sc->sc_ipopts) 1552 (void) m_free(sc->sc_ipopts); 1553 sc->sc_ipopts = ipopts; 1554 } 1555 /* 1556 * Update timestamp if present. 1557 */ 1558 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1559 sc->sc_tsreflect = to->to_tsval; 1560 else 1561 sc->sc_flags &= ~SCF_TIMESTAMP; 1562 /* 1563 * Adjust ECN response if needed, e.g. different 1564 * IP ECN field, or a fallback by the remote host. 1565 */ 1566 if (sc->sc_flags & SCF_ECN_MASK) { 1567 sc->sc_flags &= ~SCF_ECN_MASK; 1568 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1569 } 1570 #ifdef MAC 1571 /* 1572 * Since we have already unconditionally allocated label 1573 * storage, free it up. The syncache entry will already 1574 * have an initialized label we can use. 1575 */ 1576 mac_syncache_destroy(&maclabel); 1577 #endif 1578 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1579 /* Retransmit SYN|ACK and reset retransmit count. */ 1580 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1581 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1582 "resetting timer and retransmitting SYN|ACK\n", 1583 s, __func__); 1584 free(s, M_TCPLOG); 1585 } 1586 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1587 sc->sc_rxmits = 0; 1588 syncache_timeout(sc, sch, 1); 1589 TCPSTAT_INC(tcps_sndacks); 1590 TCPSTAT_INC(tcps_sndtotal); 1591 } 1592 SCH_UNLOCK(sch); 1593 goto donenoprobe; 1594 } 1595 1596 if (tfo_cookie_valid) { 1597 bzero(&scs, sizeof(scs)); 1598 sc = &scs; 1599 goto skip_alloc; 1600 } 1601 1602 /* 1603 * Skip allocating a syncache entry if we are just going to discard 1604 * it later. 1605 */ 1606 if (!locked) { 1607 bzero(&scs, sizeof(scs)); 1608 sc = &scs; 1609 } else 1610 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1611 if (sc == NULL) { 1612 /* 1613 * The zone allocator couldn't provide more entries. 1614 * Treat this as if the cache was full; drop the oldest 1615 * entry and insert the new one. 1616 */ 1617 TCPSTAT_INC(tcps_sc_zonefail); 1618 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1619 sch->sch_last_overflow = time_uptime; 1620 syncache_drop(sc, sch); 1621 syncache_pause(inc); 1622 } 1623 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1624 if (sc == NULL) { 1625 if (V_tcp_syncookies) { 1626 bzero(&scs, sizeof(scs)); 1627 sc = &scs; 1628 } else { 1629 KASSERT(locked, 1630 ("%s: bucket unexpectedly unlocked", 1631 __func__)); 1632 SCH_UNLOCK(sch); 1633 if (ipopts) 1634 (void) m_free(ipopts); 1635 goto done; 1636 } 1637 } 1638 } 1639 1640 skip_alloc: 1641 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1642 sc->sc_tfo_cookie = &tfo_response_cookie; 1643 1644 /* 1645 * Fill in the syncache values. 1646 */ 1647 #ifdef MAC 1648 sc->sc_label = maclabel; 1649 #endif 1650 sc->sc_cred = cred; 1651 sc->sc_port = port; 1652 cred = NULL; 1653 sc->sc_ipopts = ipopts; 1654 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1655 sc->sc_ip_tos = ip_tos; 1656 sc->sc_ip_ttl = ip_ttl; 1657 #ifdef TCP_OFFLOAD 1658 sc->sc_tod = tod; 1659 sc->sc_todctx = todctx; 1660 #endif 1661 sc->sc_irs = th->th_seq; 1662 sc->sc_flags = 0; 1663 sc->sc_flowlabel = 0; 1664 1665 /* 1666 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1667 * win was derived from socket earlier in the function. 1668 */ 1669 win = imax(win, 0); 1670 win = imin(win, TCP_MAXWIN); 1671 sc->sc_wnd = win; 1672 1673 if (V_tcp_do_rfc1323 && 1674 !(ltflags & TF_NOOPT)) { 1675 /* 1676 * A timestamp received in a SYN makes 1677 * it ok to send timestamp requests and replies. 1678 */ 1679 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1680 sc->sc_tsreflect = to->to_tsval; 1681 sc->sc_flags |= SCF_TIMESTAMP; 1682 sc->sc_tsoff = tcp_new_ts_offset(inc); 1683 } 1684 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1685 int wscale = 0; 1686 1687 /* 1688 * Pick the smallest possible scaling factor that 1689 * will still allow us to scale up to sb_max, aka 1690 * kern.ipc.maxsockbuf. 1691 * 1692 * We do this because there are broken firewalls that 1693 * will corrupt the window scale option, leading to 1694 * the other endpoint believing that our advertised 1695 * window is unscaled. At scale factors larger than 1696 * 5 the unscaled window will drop below 1500 bytes, 1697 * leading to serious problems when traversing these 1698 * broken firewalls. 1699 * 1700 * With the default maxsockbuf of 256K, a scale factor 1701 * of 3 will be chosen by this algorithm. Those who 1702 * choose a larger maxsockbuf should watch out 1703 * for the compatibility problems mentioned above. 1704 * 1705 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1706 * or <SYN,ACK>) segment itself is never scaled. 1707 */ 1708 while (wscale < TCP_MAX_WINSHIFT && 1709 (TCP_MAXWIN << wscale) < sb_max) 1710 wscale++; 1711 sc->sc_requested_r_scale = wscale; 1712 sc->sc_requested_s_scale = to->to_wscale; 1713 sc->sc_flags |= SCF_WINSCALE; 1714 } 1715 } 1716 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1717 /* 1718 * If incoming packet has an MD5 signature, flag this in the 1719 * syncache so that syncache_respond() will do the right thing 1720 * with the SYN+ACK. 1721 */ 1722 if (to->to_flags & TOF_SIGNATURE) 1723 sc->sc_flags |= SCF_SIGNATURE; 1724 #endif /* TCP_SIGNATURE */ 1725 if (to->to_flags & TOF_SACKPERM) 1726 sc->sc_flags |= SCF_SACK; 1727 if (to->to_flags & TOF_MSS) 1728 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1729 if (ltflags & TF_NOOPT) 1730 sc->sc_flags |= SCF_NOOPT; 1731 /* ECN Handshake */ 1732 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1733 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1734 1735 if (V_tcp_syncookies) 1736 sc->sc_iss = syncookie_generate(sch, sc); 1737 else 1738 sc->sc_iss = arc4random(); 1739 #ifdef INET6 1740 if (autoflowlabel) { 1741 if (V_tcp_syncookies) 1742 sc->sc_flowlabel = sc->sc_iss; 1743 else 1744 sc->sc_flowlabel = ip6_randomflowlabel(); 1745 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1746 } 1747 #endif 1748 if (locked) 1749 SCH_UNLOCK(sch); 1750 1751 if (tfo_cookie_valid) { 1752 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1753 /* INP_RUNLOCK(inp) will be performed by the caller */ 1754 goto tfo_expanded; 1755 } 1756 1757 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1758 /* 1759 * Do a standard 3-way handshake. 1760 */ 1761 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1762 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1763 syncache_free(sc); 1764 else if (sc != &scs) 1765 syncache_insert(sc, sch); /* locks and unlocks sch */ 1766 TCPSTAT_INC(tcps_sndacks); 1767 TCPSTAT_INC(tcps_sndtotal); 1768 } else { 1769 if (sc != &scs) 1770 syncache_free(sc); 1771 TCPSTAT_INC(tcps_sc_dropped); 1772 } 1773 goto donenoprobe; 1774 1775 done: 1776 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1777 donenoprobe: 1778 if (m) 1779 m_freem(m); 1780 /* 1781 * If tfo_pending is not NULL here, then a TFO SYN that did not 1782 * result in a new socket was processed and the associated pending 1783 * counter has not yet been decremented. All such TFO processing paths 1784 * transit this point. 1785 */ 1786 if (tfo_pending != NULL) 1787 tcp_fastopen_decrement_counter(tfo_pending); 1788 1789 tfo_expanded: 1790 if (cred != NULL) 1791 crfree(cred); 1792 #ifdef MAC 1793 if (sc == &scs) 1794 mac_syncache_destroy(&maclabel); 1795 #endif 1796 return (rv); 1797 } 1798 1799 /* 1800 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1801 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1802 */ 1803 static int 1804 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1805 { 1806 struct ip *ip = NULL; 1807 struct mbuf *m; 1808 struct tcphdr *th = NULL; 1809 struct udphdr *udp = NULL; 1810 int optlen, error = 0; /* Make compiler happy */ 1811 u_int16_t hlen, tlen, mssopt, ulen; 1812 struct tcpopt to; 1813 #ifdef INET6 1814 struct ip6_hdr *ip6 = NULL; 1815 #endif 1816 1817 NET_EPOCH_ASSERT(); 1818 1819 hlen = 1820 #ifdef INET6 1821 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1822 #endif 1823 sizeof(struct ip); 1824 tlen = hlen + sizeof(struct tcphdr); 1825 if (sc->sc_port) { 1826 tlen += sizeof(struct udphdr); 1827 } 1828 /* Determine MSS we advertize to other end of connection. */ 1829 mssopt = tcp_mssopt(&sc->sc_inc); 1830 if (sc->sc_port) 1831 mssopt -= V_tcp_udp_tunneling_overhead; 1832 mssopt = max(mssopt, V_tcp_minmss); 1833 1834 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1835 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1836 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1837 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1838 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1839 1840 /* Create the IP+TCP header from scratch. */ 1841 m = m_gethdr(M_NOWAIT, MT_DATA); 1842 if (m == NULL) 1843 return (ENOBUFS); 1844 #ifdef MAC 1845 mac_syncache_create_mbuf(sc->sc_label, m); 1846 #endif 1847 m->m_data += max_linkhdr; 1848 m->m_len = tlen; 1849 m->m_pkthdr.len = tlen; 1850 m->m_pkthdr.rcvif = NULL; 1851 1852 #ifdef INET6 1853 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1854 ip6 = mtod(m, struct ip6_hdr *); 1855 ip6->ip6_vfc = IPV6_VERSION; 1856 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1857 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1858 ip6->ip6_plen = htons(tlen - hlen); 1859 /* ip6_hlim is set after checksum */ 1860 /* Zero out traffic class and flow label. */ 1861 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1862 ip6->ip6_flow |= sc->sc_flowlabel; 1863 if (sc->sc_port != 0) { 1864 ip6->ip6_nxt = IPPROTO_UDP; 1865 udp = (struct udphdr *)(ip6 + 1); 1866 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1867 udp->uh_dport = sc->sc_port; 1868 ulen = (tlen - sizeof(struct ip6_hdr)); 1869 th = (struct tcphdr *)(udp + 1); 1870 } else { 1871 ip6->ip6_nxt = IPPROTO_TCP; 1872 th = (struct tcphdr *)(ip6 + 1); 1873 } 1874 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1875 } 1876 #endif 1877 #if defined(INET6) && defined(INET) 1878 else 1879 #endif 1880 #ifdef INET 1881 { 1882 ip = mtod(m, struct ip *); 1883 ip->ip_v = IPVERSION; 1884 ip->ip_hl = sizeof(struct ip) >> 2; 1885 ip->ip_len = htons(tlen); 1886 ip->ip_id = 0; 1887 ip->ip_off = 0; 1888 ip->ip_sum = 0; 1889 ip->ip_src = sc->sc_inc.inc_laddr; 1890 ip->ip_dst = sc->sc_inc.inc_faddr; 1891 ip->ip_ttl = sc->sc_ip_ttl; 1892 ip->ip_tos = sc->sc_ip_tos; 1893 1894 /* 1895 * See if we should do MTU discovery. Route lookups are 1896 * expensive, so we will only unset the DF bit if: 1897 * 1898 * 1) path_mtu_discovery is disabled 1899 * 2) the SCF_UNREACH flag has been set 1900 */ 1901 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1902 ip->ip_off |= htons(IP_DF); 1903 if (sc->sc_port == 0) { 1904 ip->ip_p = IPPROTO_TCP; 1905 th = (struct tcphdr *)(ip + 1); 1906 } else { 1907 ip->ip_p = IPPROTO_UDP; 1908 udp = (struct udphdr *)(ip + 1); 1909 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1910 udp->uh_dport = sc->sc_port; 1911 ulen = (tlen - sizeof(struct ip)); 1912 th = (struct tcphdr *)(udp + 1); 1913 } 1914 } 1915 #endif /* INET */ 1916 th->th_sport = sc->sc_inc.inc_lport; 1917 th->th_dport = sc->sc_inc.inc_fport; 1918 1919 if (flags & TH_SYN) 1920 th->th_seq = htonl(sc->sc_iss); 1921 else 1922 th->th_seq = htonl(sc->sc_iss + 1); 1923 th->th_ack = htonl(sc->sc_irs + 1); 1924 th->th_off = sizeof(struct tcphdr) >> 2; 1925 th->th_win = htons(sc->sc_wnd); 1926 th->th_urp = 0; 1927 1928 flags = tcp_ecn_syncache_respond(flags, sc); 1929 tcp_set_flags(th, flags); 1930 1931 /* Tack on the TCP options. */ 1932 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1933 to.to_flags = 0; 1934 1935 if (flags & TH_SYN) { 1936 to.to_mss = mssopt; 1937 to.to_flags = TOF_MSS; 1938 if (sc->sc_flags & SCF_WINSCALE) { 1939 to.to_wscale = sc->sc_requested_r_scale; 1940 to.to_flags |= TOF_SCALE; 1941 } 1942 if (sc->sc_flags & SCF_SACK) 1943 to.to_flags |= TOF_SACKPERM; 1944 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1945 if (sc->sc_flags & SCF_SIGNATURE) 1946 to.to_flags |= TOF_SIGNATURE; 1947 #endif 1948 if (sc->sc_tfo_cookie) { 1949 to.to_flags |= TOF_FASTOPEN; 1950 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1951 to.to_tfo_cookie = sc->sc_tfo_cookie; 1952 /* don't send cookie again when retransmitting response */ 1953 sc->sc_tfo_cookie = NULL; 1954 } 1955 } 1956 if (sc->sc_flags & SCF_TIMESTAMP) { 1957 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1958 to.to_tsecr = sc->sc_tsreflect; 1959 to.to_flags |= TOF_TS; 1960 } 1961 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1962 1963 /* Adjust headers by option size. */ 1964 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1965 m->m_len += optlen; 1966 m->m_pkthdr.len += optlen; 1967 #ifdef INET6 1968 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1969 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1970 else 1971 #endif 1972 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1973 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1974 if (sc->sc_flags & SCF_SIGNATURE) { 1975 KASSERT(to.to_flags & TOF_SIGNATURE, 1976 ("tcp_addoptions() didn't set tcp_signature")); 1977 1978 /* NOTE: to.to_signature is inside of mbuf */ 1979 if (!TCPMD5_ENABLED() || 1980 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1981 m_freem(m); 1982 return (EACCES); 1983 } 1984 } 1985 #endif 1986 } else 1987 optlen = 0; 1988 1989 if (udp) { 1990 ulen += optlen; 1991 udp->uh_ulen = htons(ulen); 1992 } 1993 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1994 /* 1995 * If we have peer's SYN and it has a flowid, then let's assign it to 1996 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1997 * to SYN|ACK due to lack of inp here. 1998 */ 1999 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2000 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2001 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2002 } 2003 #ifdef INET6 2004 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2005 if (sc->sc_port) { 2006 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2007 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2008 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2009 IPPROTO_UDP, 0); 2010 th->th_sum = htons(0); 2011 } else { 2012 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2013 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2014 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2015 IPPROTO_TCP, 0); 2016 } 2017 ip6->ip6_hlim = sc->sc_ip_ttl; 2018 #ifdef TCP_OFFLOAD 2019 if (ADDED_BY_TOE(sc)) { 2020 struct toedev *tod = sc->sc_tod; 2021 2022 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2023 2024 return (error); 2025 } 2026 #endif 2027 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2028 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2029 } 2030 #endif 2031 #if defined(INET6) && defined(INET) 2032 else 2033 #endif 2034 #ifdef INET 2035 { 2036 if (sc->sc_port) { 2037 m->m_pkthdr.csum_flags = CSUM_UDP; 2038 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2039 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2040 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2041 th->th_sum = htons(0); 2042 } else { 2043 m->m_pkthdr.csum_flags = CSUM_TCP; 2044 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2045 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2046 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2047 } 2048 #ifdef TCP_OFFLOAD 2049 if (ADDED_BY_TOE(sc)) { 2050 struct toedev *tod = sc->sc_tod; 2051 2052 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2053 2054 return (error); 2055 } 2056 #endif 2057 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2058 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2059 } 2060 #endif 2061 return (error); 2062 } 2063 2064 /* 2065 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2066 * that exceed the capacity of the syncache by avoiding the storage of any 2067 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2068 * attacks where the attacker does not have access to our responses. 2069 * 2070 * Syncookies encode and include all necessary information about the 2071 * connection setup within the SYN|ACK that we send back. That way we 2072 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2073 * (if ever). Normally the syncache and syncookies are running in parallel 2074 * with the latter taking over when the former is exhausted. When matching 2075 * syncache entry is found the syncookie is ignored. 2076 * 2077 * The only reliable information persisting the 3WHS is our initial sequence 2078 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2079 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2080 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2081 * returns and signifies a legitimate connection if it matches the ACK. 2082 * 2083 * The available space of 32 bits to store the hash and to encode the SYN 2084 * option information is very tight and we should have at least 24 bits for 2085 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2086 * 2087 * SYN option information we have to encode to fully restore a connection: 2088 * MSS: is imporant to chose an optimal segment size to avoid IP level 2089 * fragmentation along the path. The common MSS values can be encoded 2090 * in a 3-bit table. Uncommon values are captured by the next lower value 2091 * in the table leading to a slight increase in packetization overhead. 2092 * WSCALE: is necessary to allow large windows to be used for high delay- 2093 * bandwidth product links. Not scaling the window when it was initially 2094 * negotiated is bad for performance as lack of scaling further decreases 2095 * the apparent available send window. We only need to encode the WSCALE 2096 * we received from the remote end. Our end can be recalculated at any 2097 * time. The common WSCALE values can be encoded in a 3-bit table. 2098 * Uncommon values are captured by the next lower value in the table 2099 * making us under-estimate the available window size halving our 2100 * theoretically possible maximum throughput for that connection. 2101 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2102 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2103 * that are included in all segments on a connection. We enable them when 2104 * the ACK has them. 2105 * 2106 * Security of syncookies and attack vectors: 2107 * 2108 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2109 * together with the gloabl secret to make it unique per connection attempt. 2110 * Thus any change of any of those parameters results in a different MAC output 2111 * in an unpredictable way unless a collision is encountered. 24 bits of the 2112 * MAC are embedded into the ISS. 2113 * 2114 * To prevent replay attacks two rotating global secrets are updated with a 2115 * new random value every 15 seconds. The life-time of a syncookie is thus 2116 * 15-30 seconds. 2117 * 2118 * Vector 1: Attacking the secret. This requires finding a weakness in the 2119 * MAC itself or the way it is used here. The attacker can do a chosen plain 2120 * text attack by varying and testing the all parameters under his control. 2121 * The strength depends on the size and randomness of the secret, and the 2122 * cryptographic security of the MAC function. Due to the constant updating 2123 * of the secret the attacker has at most 29.999 seconds to find the secret 2124 * and launch spoofed connections. After that he has to start all over again. 2125 * 2126 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2127 * size an average of 4,823 attempts are required for a 50% chance of success 2128 * to spoof a single syncookie (birthday collision paradox). However the 2129 * attacker is blind and doesn't know if one of his attempts succeeded unless 2130 * he has a side channel to interfere success from. A single connection setup 2131 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2132 * This many attempts are required for each one blind spoofed connection. For 2133 * every additional spoofed connection he has to launch another N attempts. 2134 * Thus for a sustained rate 100 spoofed connections per second approximately 2135 * 1,800,000 packets per second would have to be sent. 2136 * 2137 * NB: The MAC function should be fast so that it doesn't become a CPU 2138 * exhaustion attack vector itself. 2139 * 2140 * References: 2141 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2142 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2143 * http://cr.yp.to/syncookies.html (overview) 2144 * http://cr.yp.to/syncookies/archive (details) 2145 * 2146 * 2147 * Schematic construction of a syncookie enabled Initial Sequence Number: 2148 * 0 1 2 3 2149 * 12345678901234567890123456789012 2150 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2151 * 2152 * x 24 MAC (truncated) 2153 * W 3 Send Window Scale index 2154 * M 3 MSS index 2155 * S 1 SACK permitted 2156 * P 1 Odd/even secret 2157 */ 2158 2159 /* 2160 * Distribution and probability of certain MSS values. Those in between are 2161 * rounded down to the next lower one. 2162 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2163 * .2% .3% 5% 7% 7% 20% 15% 45% 2164 */ 2165 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2166 2167 /* 2168 * Distribution and probability of certain WSCALE values. We have to map the 2169 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2170 * bits based on prevalence of certain values. Where we don't have an exact 2171 * match for are rounded down to the next lower one letting us under-estimate 2172 * the true available window. At the moment this would happen only for the 2173 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2174 * and window size). The absence of the WSCALE option (no scaling in either 2175 * direction) is encoded with index zero. 2176 * [WSCALE values histograms, Allman, 2012] 2177 * X 10 10 35 5 6 14 10% by host 2178 * X 11 4 5 5 18 49 3% by connections 2179 */ 2180 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2181 2182 /* 2183 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2184 * and good cryptographic properties. 2185 */ 2186 static uint32_t 2187 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2188 uint8_t *secbits, uintptr_t secmod) 2189 { 2190 SIPHASH_CTX ctx; 2191 uint32_t siphash[2]; 2192 2193 SipHash24_Init(&ctx); 2194 SipHash_SetKey(&ctx, secbits); 2195 switch (inc->inc_flags & INC_ISIPV6) { 2196 #ifdef INET 2197 case 0: 2198 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2199 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2200 break; 2201 #endif 2202 #ifdef INET6 2203 case INC_ISIPV6: 2204 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2205 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2206 break; 2207 #endif 2208 } 2209 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2210 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2211 SipHash_Update(&ctx, &irs, sizeof(irs)); 2212 SipHash_Update(&ctx, &flags, sizeof(flags)); 2213 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2214 SipHash_Final((u_int8_t *)&siphash, &ctx); 2215 2216 return (siphash[0] ^ siphash[1]); 2217 } 2218 2219 static tcp_seq 2220 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2221 { 2222 u_int i, secbit, wscale; 2223 uint32_t iss, hash; 2224 uint8_t *secbits; 2225 union syncookie cookie; 2226 2227 cookie.cookie = 0; 2228 2229 /* Map our computed MSS into the 3-bit index. */ 2230 for (i = nitems(tcp_sc_msstab) - 1; 2231 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2232 i--) 2233 ; 2234 cookie.flags.mss_idx = i; 2235 2236 /* 2237 * Map the send window scale into the 3-bit index but only if 2238 * the wscale option was received. 2239 */ 2240 if (sc->sc_flags & SCF_WINSCALE) { 2241 wscale = sc->sc_requested_s_scale; 2242 for (i = nitems(tcp_sc_wstab) - 1; 2243 tcp_sc_wstab[i] > wscale && i > 0; 2244 i--) 2245 ; 2246 cookie.flags.wscale_idx = i; 2247 } 2248 2249 /* Can we do SACK? */ 2250 if (sc->sc_flags & SCF_SACK) 2251 cookie.flags.sack_ok = 1; 2252 2253 /* Which of the two secrets to use. */ 2254 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2255 cookie.flags.odd_even = secbit; 2256 2257 secbits = V_tcp_syncache.secret.key[secbit]; 2258 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2259 (uintptr_t)sch); 2260 2261 /* 2262 * Put the flags into the hash and XOR them to get better ISS number 2263 * variance. This doesn't enhance the cryptographic strength and is 2264 * done to prevent the 8 cookie bits from showing up directly on the 2265 * wire. 2266 */ 2267 iss = hash & ~0xff; 2268 iss |= cookie.cookie ^ (hash >> 24); 2269 2270 TCPSTAT_INC(tcps_sc_sendcookie); 2271 return (iss); 2272 } 2273 2274 static struct syncache * 2275 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2276 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2277 struct socket *lso, uint16_t port) 2278 { 2279 uint32_t hash; 2280 uint8_t *secbits; 2281 tcp_seq ack, seq; 2282 int wnd, wscale = 0; 2283 union syncookie cookie; 2284 2285 /* 2286 * Pull information out of SYN-ACK/ACK and revert sequence number 2287 * advances. 2288 */ 2289 ack = th->th_ack - 1; 2290 seq = th->th_seq - 1; 2291 2292 /* 2293 * Unpack the flags containing enough information to restore the 2294 * connection. 2295 */ 2296 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2297 2298 /* Which of the two secrets to use. */ 2299 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2300 2301 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2302 2303 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2304 if ((ack & ~0xff) != (hash & ~0xff)) 2305 return (NULL); 2306 2307 /* Fill in the syncache values. */ 2308 sc->sc_flags = 0; 2309 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2310 sc->sc_ipopts = NULL; 2311 2312 sc->sc_irs = seq; 2313 sc->sc_iss = ack; 2314 2315 switch (inc->inc_flags & INC_ISIPV6) { 2316 #ifdef INET 2317 case 0: 2318 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2319 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2320 break; 2321 #endif 2322 #ifdef INET6 2323 case INC_ISIPV6: 2324 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2325 sc->sc_flowlabel = 2326 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2327 break; 2328 #endif 2329 } 2330 2331 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2332 2333 /* We can simply recompute receive window scale we sent earlier. */ 2334 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2335 wscale++; 2336 2337 /* Only use wscale if it was enabled in the orignal SYN. */ 2338 if (cookie.flags.wscale_idx > 0) { 2339 sc->sc_requested_r_scale = wscale; 2340 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2341 sc->sc_flags |= SCF_WINSCALE; 2342 } 2343 2344 wnd = lso->sol_sbrcv_hiwat; 2345 wnd = imax(wnd, 0); 2346 wnd = imin(wnd, TCP_MAXWIN); 2347 sc->sc_wnd = wnd; 2348 2349 if (cookie.flags.sack_ok) 2350 sc->sc_flags |= SCF_SACK; 2351 2352 if (to->to_flags & TOF_TS) { 2353 sc->sc_flags |= SCF_TIMESTAMP; 2354 sc->sc_tsreflect = to->to_tsval; 2355 sc->sc_tsoff = tcp_new_ts_offset(inc); 2356 } 2357 2358 if (to->to_flags & TOF_SIGNATURE) 2359 sc->sc_flags |= SCF_SIGNATURE; 2360 2361 sc->sc_rxmits = 0; 2362 2363 sc->sc_port = port; 2364 2365 TCPSTAT_INC(tcps_sc_recvcookie); 2366 return (sc); 2367 } 2368 2369 #ifdef INVARIANTS 2370 static int 2371 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2372 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2373 struct socket *lso, uint16_t port) 2374 { 2375 struct syncache scs, *scx; 2376 char *s; 2377 2378 bzero(&scs, sizeof(scs)); 2379 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2380 2381 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2382 return (0); 2383 2384 if (scx != NULL) { 2385 if (sc->sc_peer_mss != scx->sc_peer_mss) 2386 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2387 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2388 2389 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2390 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2391 s, __func__, sc->sc_requested_r_scale, 2392 scx->sc_requested_r_scale); 2393 2394 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2395 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2396 s, __func__, sc->sc_requested_s_scale, 2397 scx->sc_requested_s_scale); 2398 2399 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2400 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2401 } 2402 2403 if (s != NULL) 2404 free(s, M_TCPLOG); 2405 return (0); 2406 } 2407 #endif /* INVARIANTS */ 2408 2409 static void 2410 syncookie_reseed(void *arg) 2411 { 2412 struct tcp_syncache *sc = arg; 2413 uint8_t *secbits; 2414 int secbit; 2415 2416 /* 2417 * Reseeding the secret doesn't have to be protected by a lock. 2418 * It only must be ensured that the new random values are visible 2419 * to all CPUs in a SMP environment. The atomic with release 2420 * semantics ensures that. 2421 */ 2422 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2423 secbits = sc->secret.key[secbit]; 2424 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2425 atomic_add_rel_int(&sc->secret.oddeven, 1); 2426 2427 /* Reschedule ourself. */ 2428 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2429 } 2430 2431 /* 2432 * We have overflowed a bucket. Let's pause dealing with the syncache. 2433 * This function will increment the bucketoverflow statistics appropriately 2434 * (once per pause when pausing is enabled; otherwise, once per overflow). 2435 */ 2436 static void 2437 syncache_pause(struct in_conninfo *inc) 2438 { 2439 time_t delta; 2440 const char *s; 2441 2442 /* XXX: 2443 * 2. Add sysctl read here so we don't get the benefit of this 2444 * change without the new sysctl. 2445 */ 2446 2447 /* 2448 * Try an unlocked read. If we already know that another thread 2449 * has activated the feature, there is no need to proceed. 2450 */ 2451 if (V_tcp_syncache.paused) 2452 return; 2453 2454 /* Are cookied enabled? If not, we can't pause. */ 2455 if (!V_tcp_syncookies) { 2456 TCPSTAT_INC(tcps_sc_bucketoverflow); 2457 return; 2458 } 2459 2460 /* 2461 * We may be the first thread to find an overflow. Get the lock 2462 * and evaluate if we need to take action. 2463 */ 2464 mtx_lock(&V_tcp_syncache.pause_mtx); 2465 if (V_tcp_syncache.paused) { 2466 mtx_unlock(&V_tcp_syncache.pause_mtx); 2467 return; 2468 } 2469 2470 /* Activate protection. */ 2471 V_tcp_syncache.paused = true; 2472 TCPSTAT_INC(tcps_sc_bucketoverflow); 2473 2474 /* 2475 * Determine the last backoff time. If we are seeing a re-newed 2476 * attack within that same time after last reactivating the syncache, 2477 * consider it an extension of the same attack. 2478 */ 2479 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2480 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2481 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2482 delta <<= 1; 2483 V_tcp_syncache.pause_backoff++; 2484 } 2485 } else { 2486 delta = TCP_SYNCACHE_PAUSE_TIME; 2487 V_tcp_syncache.pause_backoff = 0; 2488 } 2489 2490 /* Log a warning, including IP addresses, if able. */ 2491 if (inc != NULL) 2492 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2493 else 2494 s = (const char *)NULL; 2495 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2496 "the next %lld seconds%s%s%s\n", (long long)delta, 2497 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2498 (s != NULL) ? ")" : ""); 2499 free(__DECONST(void *, s), M_TCPLOG); 2500 2501 /* Use the calculated delta to set a new pause time. */ 2502 V_tcp_syncache.pause_until = time_uptime + delta; 2503 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2504 &V_tcp_syncache); 2505 mtx_unlock(&V_tcp_syncache.pause_mtx); 2506 } 2507 2508 /* Evaluate whether we need to unpause. */ 2509 static void 2510 syncache_unpause(void *arg) 2511 { 2512 struct tcp_syncache *sc; 2513 time_t delta; 2514 2515 sc = arg; 2516 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2517 callout_deactivate(&sc->pause_co); 2518 2519 /* 2520 * Check to make sure we are not running early. If the pause 2521 * time has expired, then deactivate the protection. 2522 */ 2523 if ((delta = sc->pause_until - time_uptime) > 0) 2524 callout_schedule(&sc->pause_co, delta * hz); 2525 else 2526 sc->paused = false; 2527 } 2528 2529 /* 2530 * Exports the syncache entries to userland so that netstat can display 2531 * them alongside the other sockets. This function is intended to be 2532 * called only from tcp_pcblist. 2533 * 2534 * Due to concurrency on an active system, the number of pcbs exported 2535 * may have no relation to max_pcbs. max_pcbs merely indicates the 2536 * amount of space the caller allocated for this function to use. 2537 */ 2538 int 2539 syncache_pcblist(struct sysctl_req *req) 2540 { 2541 struct xtcpcb xt; 2542 struct syncache *sc; 2543 struct syncache_head *sch; 2544 int error, i; 2545 2546 bzero(&xt, sizeof(xt)); 2547 xt.xt_len = sizeof(xt); 2548 xt.t_state = TCPS_SYN_RECEIVED; 2549 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2550 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2551 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2552 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2553 2554 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2555 sch = &V_tcp_syncache.hashbase[i]; 2556 SCH_LOCK(sch); 2557 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2558 if (sc->sc_cred != NULL && 2559 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2560 continue; 2561 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2562 xt.xt_inp.inp_vflag = INP_IPV6; 2563 else 2564 xt.xt_inp.inp_vflag = INP_IPV4; 2565 xt.xt_encaps_port = sc->sc_port; 2566 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2567 sizeof (struct in_conninfo)); 2568 error = SYSCTL_OUT(req, &xt, sizeof xt); 2569 if (error) { 2570 SCH_UNLOCK(sch); 2571 return (0); 2572 } 2573 } 2574 SCH_UNLOCK(sch); 2575 } 2576 2577 return (0); 2578 } 2579