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 tcpcb *listening_tcb; 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 (V_functions_inherit_listen_socket_stack) 806 listening_tcb = sototcpcb(lso); 807 else 808 listening_tcb = NULL; 809 if ((tp = tcp_newtcpcb(inp, listening_tcb)) == NULL) { 810 in_pcbfree(inp); 811 sodealloc(so); 812 goto allocfail; 813 } 814 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 815 #ifdef INET6 816 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 817 inp->inp_vflag &= ~INP_IPV4; 818 inp->inp_vflag |= INP_IPV6; 819 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 820 } else { 821 inp->inp_vflag &= ~INP_IPV6; 822 inp->inp_vflag |= INP_IPV4; 823 #endif 824 inp->inp_ip_ttl = sc->sc_ip_ttl; 825 inp->inp_ip_tos = sc->sc_ip_tos; 826 inp->inp_laddr = sc->sc_inc.inc_laddr; 827 #ifdef INET6 828 } 829 #endif 830 831 /* 832 * If there's an mbuf and it has a flowid, then let's initialise the 833 * inp with that particular flowid. 834 */ 835 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 836 inp->inp_flowid = m->m_pkthdr.flowid; 837 inp->inp_flowtype = M_HASHTYPE_GET(m); 838 #ifdef NUMA 839 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 840 #endif 841 } 842 843 inp->inp_lport = sc->sc_inc.inc_lport; 844 #ifdef INET6 845 if (inp->inp_vflag & INP_IPV6PROTO) { 846 struct inpcb *oinp = sotoinpcb(lso); 847 848 /* 849 * Inherit socket options from the listening socket. 850 * Note that in6p_inputopts are not (and should not be) 851 * copied, since it stores previously received options and is 852 * used to detect if each new option is different than the 853 * previous one and hence should be passed to a user. 854 * If we copied in6p_inputopts, a user would not be able to 855 * receive options just after calling the accept system call. 856 */ 857 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 858 if (oinp->in6p_outputopts) 859 inp->in6p_outputopts = 860 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 861 inp->in6p_hops = oinp->in6p_hops; 862 } 863 864 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 865 struct sockaddr_in6 sin6; 866 867 sin6.sin6_family = AF_INET6; 868 sin6.sin6_len = sizeof(sin6); 869 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 870 sin6.sin6_port = sc->sc_inc.inc_fport; 871 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 872 INP_HASH_WLOCK(&V_tcbinfo); 873 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 874 INP_HASH_WUNLOCK(&V_tcbinfo); 875 if (error != 0) 876 goto abort; 877 /* Override flowlabel from in6_pcbconnect. */ 878 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 879 inp->inp_flow |= sc->sc_flowlabel; 880 } 881 #endif /* INET6 */ 882 #if defined(INET) && defined(INET6) 883 else 884 #endif 885 #ifdef INET 886 { 887 struct sockaddr_in sin; 888 889 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 890 891 if (inp->inp_options == NULL) { 892 inp->inp_options = sc->sc_ipopts; 893 sc->sc_ipopts = NULL; 894 } 895 896 sin.sin_family = AF_INET; 897 sin.sin_len = sizeof(sin); 898 sin.sin_addr = sc->sc_inc.inc_faddr; 899 sin.sin_port = sc->sc_inc.inc_fport; 900 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 901 INP_HASH_WLOCK(&V_tcbinfo); 902 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false); 903 INP_HASH_WUNLOCK(&V_tcbinfo); 904 if (error != 0) 905 goto abort; 906 } 907 #endif /* INET */ 908 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 909 /* Copy old policy into new socket's. */ 910 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 911 printf("syncache_socket: could not copy policy\n"); 912 #endif 913 tp->t_state = TCPS_SYN_RECEIVED; 914 tp->iss = sc->sc_iss; 915 tp->irs = sc->sc_irs; 916 tp->t_port = sc->sc_port; 917 tcp_rcvseqinit(tp); 918 tcp_sendseqinit(tp); 919 tp->snd_wl1 = sc->sc_irs; 920 tp->snd_max = tp->iss + 1; 921 tp->snd_nxt = tp->iss + 1; 922 tp->rcv_up = sc->sc_irs + 1; 923 tp->rcv_wnd = sc->sc_wnd; 924 tp->rcv_adv += tp->rcv_wnd; 925 tp->last_ack_sent = tp->rcv_nxt; 926 927 tp->t_flags = sototcpcb(lso)->t_flags & 928 (TF_LRD|TF_NOPUSH|TF_NODELAY); 929 if (sc->sc_flags & SCF_NOOPT) 930 tp->t_flags |= TF_NOOPT; 931 else { 932 if (sc->sc_flags & SCF_WINSCALE) { 933 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 934 tp->snd_scale = sc->sc_requested_s_scale; 935 tp->request_r_scale = sc->sc_requested_r_scale; 936 } 937 if (sc->sc_flags & SCF_TIMESTAMP) { 938 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 939 tp->ts_recent = sc->sc_tsreflect; 940 tp->ts_recent_age = tcp_ts_getticks(); 941 tp->ts_offset = sc->sc_tsoff; 942 } 943 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 944 if (sc->sc_flags & SCF_SIGNATURE) 945 tp->t_flags |= TF_SIGNATURE; 946 #endif 947 if (sc->sc_flags & SCF_SACK) 948 tp->t_flags |= TF_SACK_PERMIT; 949 } 950 951 tcp_ecn_syncache_socket(tp, sc); 952 953 /* 954 * Set up MSS and get cached values from tcp_hostcache. 955 * This might overwrite some of the defaults we just set. 956 */ 957 tcp_mss(tp, sc->sc_peer_mss); 958 959 /* 960 * If the SYN,ACK was retransmitted, indicate that CWND to be 961 * limited to one segment in cc_conn_init(). 962 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 963 */ 964 if (sc->sc_rxmits > 1) 965 tp->snd_cwnd = 1; 966 967 #ifdef TCP_OFFLOAD 968 /* 969 * Allow a TOE driver to install its hooks. Note that we hold the 970 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 971 * new connection before the TOE driver has done its thing. 972 */ 973 if (ADDED_BY_TOE(sc)) { 974 struct toedev *tod = sc->sc_tod; 975 976 tod->tod_offload_socket(tod, sc->sc_todctx, so); 977 } 978 #endif 979 #ifdef TCP_BLACKBOX 980 /* 981 * Inherit the log state from the listening socket, if 982 * - the log state of the listening socket is not off and 983 * - the listening socket was not auto selected from all sessions and 984 * - a log id is not set on the listening socket. 985 * This avoids inheriting a log state which was automatically set. 986 */ 987 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 988 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 989 (sototcpcb(lso)->t_lib == NULL)) { 990 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 991 } 992 #endif 993 /* 994 * Copy and activate timers. 995 */ 996 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 997 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 998 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 999 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1000 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1001 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1002 1003 TCPSTAT_INC(tcps_accepts); 1004 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1005 1006 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1007 tp->t_flags |= TF_SONOTCONN; 1008 /* Can we inherit anything from the listener? */ 1009 if (tp->t_fb->tfb_inherit != NULL) { 1010 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1011 } 1012 return (so); 1013 1014 allocfail: 1015 /* 1016 * Drop the connection; we will either send a RST or have the peer 1017 * retransmit its SYN again after its RTO and try again. 1018 */ 1019 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1020 log(LOG_DEBUG, "%s; %s: Socket create failed " 1021 "due to limits or memory shortage\n", 1022 s, __func__); 1023 free(s, M_TCPLOG); 1024 } 1025 TCPSTAT_INC(tcps_listendrop); 1026 return (NULL); 1027 1028 abort: 1029 tcp_discardcb(tp); 1030 in_pcbfree(inp); 1031 sodealloc(so); 1032 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1033 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1034 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1035 error); 1036 free(s, M_TCPLOG); 1037 } 1038 TCPSTAT_INC(tcps_listendrop); 1039 return (NULL); 1040 } 1041 1042 /* 1043 * This function gets called when we receive an ACK for a 1044 * socket in the LISTEN state. We look up the connection 1045 * in the syncache, and if its there, we pull it out of 1046 * the cache and turn it into a full-blown connection in 1047 * the SYN-RECEIVED state. 1048 * 1049 * On syncache_socket() success the newly created socket 1050 * has its underlying inp locked. 1051 */ 1052 int 1053 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1054 struct socket **lsop, struct mbuf *m, uint16_t port) 1055 { 1056 struct syncache *sc; 1057 struct syncache_head *sch; 1058 struct syncache scs; 1059 char *s; 1060 bool locked; 1061 1062 NET_EPOCH_ASSERT(); 1063 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1064 ("%s: can handle only ACK", __func__)); 1065 1066 if (syncache_cookiesonly()) { 1067 sc = NULL; 1068 sch = syncache_hashbucket(inc); 1069 locked = false; 1070 } else { 1071 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1072 locked = true; 1073 SCH_LOCK_ASSERT(sch); 1074 } 1075 1076 #ifdef INVARIANTS 1077 /* 1078 * Test code for syncookies comparing the syncache stored 1079 * values with the reconstructed values from the cookie. 1080 */ 1081 if (sc != NULL) 1082 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1083 #endif 1084 1085 if (sc == NULL) { 1086 /* 1087 * There is no syncache entry, so see if this ACK is 1088 * a returning syncookie. To do this, first: 1089 * A. Check if syncookies are used in case of syncache 1090 * overflows 1091 * B. See if this socket has had a syncache entry dropped in 1092 * the recent past. We don't want to accept a bogus 1093 * syncookie if we've never received a SYN or accept it 1094 * twice. 1095 * C. check that the syncookie is valid. If it is, then 1096 * cobble up a fake syncache entry, and return. 1097 */ 1098 if (locked && !V_tcp_syncookies) { 1099 SCH_UNLOCK(sch); 1100 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1101 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1102 "segment rejected (syncookies disabled)\n", 1103 s, __func__); 1104 goto failed; 1105 } 1106 if (locked && !V_tcp_syncookiesonly && 1107 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1108 SCH_UNLOCK(sch); 1109 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1110 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1111 "segment rejected (no syncache entry)\n", 1112 s, __func__); 1113 goto failed; 1114 } 1115 bzero(&scs, sizeof(scs)); 1116 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1117 if (locked) 1118 SCH_UNLOCK(sch); 1119 if (sc == NULL) { 1120 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1121 log(LOG_DEBUG, "%s; %s: Segment failed " 1122 "SYNCOOKIE authentication, segment rejected " 1123 "(probably spoofed)\n", s, __func__); 1124 goto failed; 1125 } 1126 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1127 /* If received ACK has MD5 signature, check it. */ 1128 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1129 (!TCPMD5_ENABLED() || 1130 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1131 /* Drop the ACK. */ 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1133 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1134 "MD5 signature doesn't match.\n", 1135 s, __func__); 1136 free(s, M_TCPLOG); 1137 } 1138 TCPSTAT_INC(tcps_sig_err_sigopt); 1139 return (-1); /* Do not send RST */ 1140 } 1141 #endif /* TCP_SIGNATURE */ 1142 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1143 } else { 1144 if (sc->sc_port != port) { 1145 SCH_UNLOCK(sch); 1146 return (0); 1147 } 1148 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1149 /* 1150 * If listening socket requested TCP digests, check that 1151 * received ACK has signature and it is correct. 1152 * If not, drop the ACK and leave sc entry in th cache, 1153 * because SYN was received with correct signature. 1154 */ 1155 if (sc->sc_flags & SCF_SIGNATURE) { 1156 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1157 /* No signature */ 1158 TCPSTAT_INC(tcps_sig_err_nosigopt); 1159 SCH_UNLOCK(sch); 1160 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1161 log(LOG_DEBUG, "%s; %s: Segment " 1162 "rejected, MD5 signature wasn't " 1163 "provided.\n", s, __func__); 1164 free(s, M_TCPLOG); 1165 } 1166 return (-1); /* Do not send RST */ 1167 } 1168 if (!TCPMD5_ENABLED() || 1169 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1170 /* Doesn't match or no SA */ 1171 SCH_UNLOCK(sch); 1172 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1173 log(LOG_DEBUG, "%s; %s: Segment " 1174 "rejected, MD5 signature doesn't " 1175 "match.\n", s, __func__); 1176 free(s, M_TCPLOG); 1177 } 1178 return (-1); /* Do not send RST */ 1179 } 1180 } 1181 #endif /* TCP_SIGNATURE */ 1182 1183 /* 1184 * RFC 7323 PAWS: If we have a timestamp on this segment and 1185 * it's less than ts_recent, drop it. 1186 * XXXMT: RFC 7323 also requires to send an ACK. 1187 * In tcp_input.c this is only done for TCP segments 1188 * with user data, so be consistent here and just drop 1189 * the segment. 1190 */ 1191 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1192 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1193 SCH_UNLOCK(sch); 1194 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1195 log(LOG_DEBUG, 1196 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1197 "segment dropped\n", s, __func__, 1198 to->to_tsval, sc->sc_tsreflect); 1199 free(s, M_TCPLOG); 1200 } 1201 return (-1); /* Do not send RST */ 1202 } 1203 1204 /* 1205 * If timestamps were not negotiated during SYN/ACK and a 1206 * segment with a timestamp is received, ignore the 1207 * timestamp and process the packet normally. 1208 * See section 3.2 of RFC 7323. 1209 */ 1210 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1211 (to->to_flags & TOF_TS)) { 1212 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1213 log(LOG_DEBUG, "%s; %s: Timestamp not " 1214 "expected, segment processed normally\n", 1215 s, __func__); 1216 free(s, M_TCPLOG); 1217 s = NULL; 1218 } 1219 } 1220 1221 /* 1222 * If timestamps were negotiated during SYN/ACK and a 1223 * segment without a timestamp is received, silently drop 1224 * the segment, unless the missing timestamps are tolerated. 1225 * See section 3.2 of RFC 7323. 1226 */ 1227 if ((sc->sc_flags & SCF_TIMESTAMP) && 1228 !(to->to_flags & TOF_TS)) { 1229 if (V_tcp_tolerate_missing_ts) { 1230 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1231 log(LOG_DEBUG, 1232 "%s; %s: Timestamp missing, " 1233 "segment processed normally\n", 1234 s, __func__); 1235 free(s, M_TCPLOG); 1236 } 1237 } else { 1238 SCH_UNLOCK(sch); 1239 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1240 log(LOG_DEBUG, 1241 "%s; %s: Timestamp missing, " 1242 "segment silently dropped\n", 1243 s, __func__); 1244 free(s, M_TCPLOG); 1245 } 1246 return (-1); /* Do not send RST */ 1247 } 1248 } 1249 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1250 sch->sch_length--; 1251 #ifdef TCP_OFFLOAD 1252 if (ADDED_BY_TOE(sc)) { 1253 struct toedev *tod = sc->sc_tod; 1254 1255 tod->tod_syncache_removed(tod, sc->sc_todctx); 1256 } 1257 #endif 1258 SCH_UNLOCK(sch); 1259 } 1260 1261 /* 1262 * Segment validation: 1263 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1264 */ 1265 if (th->th_ack != sc->sc_iss + 1) { 1266 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1267 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1268 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1269 goto failed; 1270 } 1271 1272 /* 1273 * The SEQ must fall in the window starting at the received 1274 * initial receive sequence number + 1 (the SYN). 1275 */ 1276 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1277 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1278 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1279 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1280 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1281 goto failed; 1282 } 1283 1284 *lsop = syncache_socket(sc, *lsop, m); 1285 1286 if (__predict_false(*lsop == NULL)) { 1287 TCPSTAT_INC(tcps_sc_aborted); 1288 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1289 } else 1290 TCPSTAT_INC(tcps_sc_completed); 1291 1292 /* how do we find the inp for the new socket? */ 1293 if (sc != &scs) 1294 syncache_free(sc); 1295 return (1); 1296 failed: 1297 if (sc != NULL) { 1298 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1299 if (sc != &scs) 1300 syncache_free(sc); 1301 } 1302 if (s != NULL) 1303 free(s, M_TCPLOG); 1304 *lsop = NULL; 1305 return (0); 1306 } 1307 1308 static struct socket * 1309 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1310 uint64_t response_cookie) 1311 { 1312 struct inpcb *inp; 1313 struct tcpcb *tp; 1314 unsigned int *pending_counter; 1315 struct socket *so; 1316 1317 NET_EPOCH_ASSERT(); 1318 1319 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1320 so = syncache_socket(sc, lso, m); 1321 if (so == NULL) { 1322 TCPSTAT_INC(tcps_sc_aborted); 1323 atomic_subtract_int(pending_counter, 1); 1324 } else { 1325 soisconnected(so); 1326 inp = sotoinpcb(so); 1327 tp = intotcpcb(inp); 1328 tp->t_flags |= TF_FASTOPEN; 1329 tp->t_tfo_cookie.server = response_cookie; 1330 tp->snd_max = tp->iss; 1331 tp->snd_nxt = tp->iss; 1332 tp->t_tfo_pending = pending_counter; 1333 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1334 TCPSTAT_INC(tcps_sc_completed); 1335 } 1336 1337 return (so); 1338 } 1339 1340 /* 1341 * Given a LISTEN socket and an inbound SYN request, add 1342 * this to the syn cache, and send back a segment: 1343 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1344 * to the source. 1345 * 1346 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1347 * Doing so would require that we hold onto the data and deliver it 1348 * to the application. However, if we are the target of a SYN-flood 1349 * DoS attack, an attacker could send data which would eventually 1350 * consume all available buffer space if it were ACKed. By not ACKing 1351 * the data, we avoid this DoS scenario. 1352 * 1353 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1354 * cookie is processed and a new socket is created. In this case, any data 1355 * accompanying the SYN will be queued to the socket by tcp_input() and will 1356 * be ACKed either when the application sends response data or the delayed 1357 * ACK timer expires, whichever comes first. 1358 */ 1359 struct socket * 1360 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1361 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1362 void *todctx, uint8_t iptos, uint16_t port) 1363 { 1364 struct tcpcb *tp; 1365 struct socket *rv = NULL; 1366 struct syncache *sc = NULL; 1367 struct syncache_head *sch; 1368 struct mbuf *ipopts = NULL; 1369 u_int ltflags; 1370 int win, ip_ttl, ip_tos; 1371 char *s; 1372 #ifdef INET6 1373 int autoflowlabel = 0; 1374 #endif 1375 #ifdef MAC 1376 struct label *maclabel; 1377 #endif 1378 struct syncache scs; 1379 struct ucred *cred; 1380 uint64_t tfo_response_cookie; 1381 unsigned int *tfo_pending = NULL; 1382 int tfo_cookie_valid = 0; 1383 int tfo_response_cookie_valid = 0; 1384 bool locked; 1385 1386 INP_RLOCK_ASSERT(inp); /* listen socket */ 1387 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1388 ("%s: unexpected tcp flags", __func__)); 1389 1390 /* 1391 * Combine all so/tp operations very early to drop the INP lock as 1392 * soon as possible. 1393 */ 1394 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1395 tp = sototcpcb(so); 1396 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1397 1398 #ifdef INET6 1399 if (inc->inc_flags & INC_ISIPV6) { 1400 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1401 autoflowlabel = 1; 1402 } 1403 ip_ttl = in6_selecthlim(inp, NULL); 1404 if ((inp->in6p_outputopts == NULL) || 1405 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1406 ip_tos = 0; 1407 } else { 1408 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1409 } 1410 } 1411 #endif 1412 #if defined(INET6) && defined(INET) 1413 else 1414 #endif 1415 #ifdef INET 1416 { 1417 ip_ttl = inp->inp_ip_ttl; 1418 ip_tos = inp->inp_ip_tos; 1419 } 1420 #endif 1421 win = so->sol_sbrcv_hiwat; 1422 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1423 1424 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1425 (tp->t_tfo_pending != NULL) && 1426 (to->to_flags & TOF_FASTOPEN)) { 1427 /* 1428 * Limit the number of pending TFO connections to 1429 * approximately half of the queue limit. This prevents TFO 1430 * SYN floods from starving the service by filling the 1431 * listen queue with bogus TFO connections. 1432 */ 1433 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1434 (so->sol_qlimit / 2)) { 1435 int result; 1436 1437 result = tcp_fastopen_check_cookie(inc, 1438 to->to_tfo_cookie, to->to_tfo_len, 1439 &tfo_response_cookie); 1440 tfo_cookie_valid = (result > 0); 1441 tfo_response_cookie_valid = (result >= 0); 1442 } 1443 1444 /* 1445 * Remember the TFO pending counter as it will have to be 1446 * decremented below if we don't make it to syncache_tfo_expand(). 1447 */ 1448 tfo_pending = tp->t_tfo_pending; 1449 } 1450 1451 #ifdef MAC 1452 if (mac_syncache_init(&maclabel) != 0) { 1453 INP_RUNLOCK(inp); 1454 goto done; 1455 } else 1456 mac_syncache_create(maclabel, inp); 1457 #endif 1458 if (!tfo_cookie_valid) 1459 INP_RUNLOCK(inp); 1460 1461 /* 1462 * Remember the IP options, if any. 1463 */ 1464 #ifdef INET6 1465 if (!(inc->inc_flags & INC_ISIPV6)) 1466 #endif 1467 #ifdef INET 1468 ipopts = (m) ? ip_srcroute(m) : NULL; 1469 #else 1470 ipopts = NULL; 1471 #endif 1472 1473 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1474 /* 1475 * When the socket is TCP-MD5 enabled check that, 1476 * - a signed packet is valid 1477 * - a non-signed packet does not have a security association 1478 * 1479 * If a signed packet fails validation or a non-signed packet has a 1480 * security association, the packet will be dropped. 1481 */ 1482 if (ltflags & TF_SIGNATURE) { 1483 if (to->to_flags & TOF_SIGNATURE) { 1484 if (!TCPMD5_ENABLED() || 1485 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1486 goto done; 1487 } else { 1488 if (TCPMD5_ENABLED() && 1489 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1490 goto done; 1491 } 1492 } else if (to->to_flags & TOF_SIGNATURE) 1493 goto done; 1494 #endif /* TCP_SIGNATURE */ 1495 /* 1496 * See if we already have an entry for this connection. 1497 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1498 * 1499 * XXX: should the syncache be re-initialized with the contents 1500 * of the new SYN here (which may have different options?) 1501 * 1502 * XXX: We do not check the sequence number to see if this is a 1503 * real retransmit or a new connection attempt. The question is 1504 * how to handle such a case; either ignore it as spoofed, or 1505 * drop the current entry and create a new one? 1506 */ 1507 if (syncache_cookiesonly()) { 1508 sc = NULL; 1509 sch = syncache_hashbucket(inc); 1510 locked = false; 1511 } else { 1512 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1513 locked = true; 1514 SCH_LOCK_ASSERT(sch); 1515 } 1516 if (sc != NULL) { 1517 if (tfo_cookie_valid) 1518 INP_RUNLOCK(inp); 1519 TCPSTAT_INC(tcps_sc_dupsyn); 1520 if (ipopts) { 1521 /* 1522 * If we were remembering a previous source route, 1523 * forget it and use the new one we've been given. 1524 */ 1525 if (sc->sc_ipopts) 1526 (void) m_free(sc->sc_ipopts); 1527 sc->sc_ipopts = ipopts; 1528 } 1529 /* 1530 * Update timestamp if present. 1531 */ 1532 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1533 sc->sc_tsreflect = to->to_tsval; 1534 else 1535 sc->sc_flags &= ~SCF_TIMESTAMP; 1536 /* 1537 * Adjust ECN response if needed, e.g. different 1538 * IP ECN field, or a fallback by the remote host. 1539 */ 1540 if (sc->sc_flags & SCF_ECN_MASK) { 1541 sc->sc_flags &= ~SCF_ECN_MASK; 1542 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1543 } 1544 #ifdef MAC 1545 /* 1546 * Since we have already unconditionally allocated label 1547 * storage, free it up. The syncache entry will already 1548 * have an initialized label we can use. 1549 */ 1550 mac_syncache_destroy(&maclabel); 1551 #endif 1552 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1553 /* Retransmit SYN|ACK and reset retransmit count. */ 1554 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1555 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1556 "resetting timer and retransmitting SYN|ACK\n", 1557 s, __func__); 1558 free(s, M_TCPLOG); 1559 } 1560 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1561 sc->sc_rxmits = 0; 1562 syncache_timeout(sc, sch, 1); 1563 TCPSTAT_INC(tcps_sndacks); 1564 TCPSTAT_INC(tcps_sndtotal); 1565 } 1566 SCH_UNLOCK(sch); 1567 goto donenoprobe; 1568 } 1569 1570 if (tfo_cookie_valid) { 1571 bzero(&scs, sizeof(scs)); 1572 sc = &scs; 1573 goto skip_alloc; 1574 } 1575 1576 /* 1577 * Skip allocating a syncache entry if we are just going to discard 1578 * it later. 1579 */ 1580 if (!locked) { 1581 bzero(&scs, sizeof(scs)); 1582 sc = &scs; 1583 } else 1584 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1585 if (sc == NULL) { 1586 /* 1587 * The zone allocator couldn't provide more entries. 1588 * Treat this as if the cache was full; drop the oldest 1589 * entry and insert the new one. 1590 */ 1591 TCPSTAT_INC(tcps_sc_zonefail); 1592 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1593 sch->sch_last_overflow = time_uptime; 1594 syncache_drop(sc, sch); 1595 syncache_pause(inc); 1596 } 1597 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1598 if (sc == NULL) { 1599 if (V_tcp_syncookies) { 1600 bzero(&scs, sizeof(scs)); 1601 sc = &scs; 1602 } else { 1603 KASSERT(locked, 1604 ("%s: bucket unexpectedly unlocked", 1605 __func__)); 1606 SCH_UNLOCK(sch); 1607 if (ipopts) 1608 (void) m_free(ipopts); 1609 goto done; 1610 } 1611 } 1612 } 1613 1614 skip_alloc: 1615 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1616 sc->sc_tfo_cookie = &tfo_response_cookie; 1617 1618 /* 1619 * Fill in the syncache values. 1620 */ 1621 #ifdef MAC 1622 sc->sc_label = maclabel; 1623 #endif 1624 sc->sc_cred = cred; 1625 sc->sc_port = port; 1626 cred = NULL; 1627 sc->sc_ipopts = ipopts; 1628 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1629 sc->sc_ip_tos = ip_tos; 1630 sc->sc_ip_ttl = ip_ttl; 1631 #ifdef TCP_OFFLOAD 1632 sc->sc_tod = tod; 1633 sc->sc_todctx = todctx; 1634 #endif 1635 sc->sc_irs = th->th_seq; 1636 sc->sc_flags = 0; 1637 sc->sc_flowlabel = 0; 1638 1639 /* 1640 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1641 * win was derived from socket earlier in the function. 1642 */ 1643 win = imax(win, 0); 1644 win = imin(win, TCP_MAXWIN); 1645 sc->sc_wnd = win; 1646 1647 if (V_tcp_do_rfc1323 && 1648 !(ltflags & TF_NOOPT)) { 1649 /* 1650 * A timestamp received in a SYN makes 1651 * it ok to send timestamp requests and replies. 1652 */ 1653 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1654 sc->sc_tsreflect = to->to_tsval; 1655 sc->sc_flags |= SCF_TIMESTAMP; 1656 sc->sc_tsoff = tcp_new_ts_offset(inc); 1657 } 1658 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1659 int wscale = 0; 1660 1661 /* 1662 * Pick the smallest possible scaling factor that 1663 * will still allow us to scale up to sb_max, aka 1664 * kern.ipc.maxsockbuf. 1665 * 1666 * We do this because there are broken firewalls that 1667 * will corrupt the window scale option, leading to 1668 * the other endpoint believing that our advertised 1669 * window is unscaled. At scale factors larger than 1670 * 5 the unscaled window will drop below 1500 bytes, 1671 * leading to serious problems when traversing these 1672 * broken firewalls. 1673 * 1674 * With the default maxsockbuf of 256K, a scale factor 1675 * of 3 will be chosen by this algorithm. Those who 1676 * choose a larger maxsockbuf should watch out 1677 * for the compatibility problems mentioned above. 1678 * 1679 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1680 * or <SYN,ACK>) segment itself is never scaled. 1681 */ 1682 while (wscale < TCP_MAX_WINSHIFT && 1683 (TCP_MAXWIN << wscale) < sb_max) 1684 wscale++; 1685 sc->sc_requested_r_scale = wscale; 1686 sc->sc_requested_s_scale = to->to_wscale; 1687 sc->sc_flags |= SCF_WINSCALE; 1688 } 1689 } 1690 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1691 /* 1692 * If incoming packet has an MD5 signature, flag this in the 1693 * syncache so that syncache_respond() will do the right thing 1694 * with the SYN+ACK. 1695 */ 1696 if (to->to_flags & TOF_SIGNATURE) 1697 sc->sc_flags |= SCF_SIGNATURE; 1698 #endif /* TCP_SIGNATURE */ 1699 if (to->to_flags & TOF_SACKPERM) 1700 sc->sc_flags |= SCF_SACK; 1701 if (to->to_flags & TOF_MSS) 1702 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1703 if (ltflags & TF_NOOPT) 1704 sc->sc_flags |= SCF_NOOPT; 1705 /* ECN Handshake */ 1706 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1707 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1708 1709 if (V_tcp_syncookies) 1710 sc->sc_iss = syncookie_generate(sch, sc); 1711 else 1712 sc->sc_iss = arc4random(); 1713 #ifdef INET6 1714 if (autoflowlabel) { 1715 if (V_tcp_syncookies) 1716 sc->sc_flowlabel = sc->sc_iss; 1717 else 1718 sc->sc_flowlabel = ip6_randomflowlabel(); 1719 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1720 } 1721 #endif 1722 if (locked) 1723 SCH_UNLOCK(sch); 1724 1725 if (tfo_cookie_valid) { 1726 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1727 /* INP_RUNLOCK(inp) will be performed by the caller */ 1728 goto tfo_expanded; 1729 } 1730 1731 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1732 /* 1733 * Do a standard 3-way handshake. 1734 */ 1735 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1736 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1737 syncache_free(sc); 1738 else if (sc != &scs) 1739 syncache_insert(sc, sch); /* locks and unlocks sch */ 1740 TCPSTAT_INC(tcps_sndacks); 1741 TCPSTAT_INC(tcps_sndtotal); 1742 } else { 1743 if (sc != &scs) 1744 syncache_free(sc); 1745 TCPSTAT_INC(tcps_sc_dropped); 1746 } 1747 goto donenoprobe; 1748 1749 done: 1750 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1751 donenoprobe: 1752 if (m) 1753 m_freem(m); 1754 /* 1755 * If tfo_pending is not NULL here, then a TFO SYN that did not 1756 * result in a new socket was processed and the associated pending 1757 * counter has not yet been decremented. All such TFO processing paths 1758 * transit this point. 1759 */ 1760 if (tfo_pending != NULL) 1761 tcp_fastopen_decrement_counter(tfo_pending); 1762 1763 tfo_expanded: 1764 if (cred != NULL) 1765 crfree(cred); 1766 #ifdef MAC 1767 if (sc == &scs) 1768 mac_syncache_destroy(&maclabel); 1769 #endif 1770 return (rv); 1771 } 1772 1773 /* 1774 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1775 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1776 */ 1777 static int 1778 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1779 { 1780 struct ip *ip = NULL; 1781 struct mbuf *m; 1782 struct tcphdr *th = NULL; 1783 struct udphdr *udp = NULL; 1784 int optlen, error = 0; /* Make compiler happy */ 1785 u_int16_t hlen, tlen, mssopt, ulen; 1786 struct tcpopt to; 1787 #ifdef INET6 1788 struct ip6_hdr *ip6 = NULL; 1789 #endif 1790 1791 NET_EPOCH_ASSERT(); 1792 1793 hlen = 1794 #ifdef INET6 1795 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1796 #endif 1797 sizeof(struct ip); 1798 tlen = hlen + sizeof(struct tcphdr); 1799 if (sc->sc_port) { 1800 tlen += sizeof(struct udphdr); 1801 } 1802 /* Determine MSS we advertize to other end of connection. */ 1803 mssopt = tcp_mssopt(&sc->sc_inc); 1804 if (sc->sc_port) 1805 mssopt -= V_tcp_udp_tunneling_overhead; 1806 mssopt = max(mssopt, V_tcp_minmss); 1807 1808 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1809 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1810 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1811 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1812 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1813 1814 /* Create the IP+TCP header from scratch. */ 1815 m = m_gethdr(M_NOWAIT, MT_DATA); 1816 if (m == NULL) 1817 return (ENOBUFS); 1818 #ifdef MAC 1819 mac_syncache_create_mbuf(sc->sc_label, m); 1820 #endif 1821 m->m_data += max_linkhdr; 1822 m->m_len = tlen; 1823 m->m_pkthdr.len = tlen; 1824 m->m_pkthdr.rcvif = NULL; 1825 1826 #ifdef INET6 1827 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1828 ip6 = mtod(m, struct ip6_hdr *); 1829 ip6->ip6_vfc = IPV6_VERSION; 1830 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1831 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1832 ip6->ip6_plen = htons(tlen - hlen); 1833 /* ip6_hlim is set after checksum */ 1834 /* Zero out traffic class and flow label. */ 1835 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1836 ip6->ip6_flow |= sc->sc_flowlabel; 1837 if (sc->sc_port != 0) { 1838 ip6->ip6_nxt = IPPROTO_UDP; 1839 udp = (struct udphdr *)(ip6 + 1); 1840 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1841 udp->uh_dport = sc->sc_port; 1842 ulen = (tlen - sizeof(struct ip6_hdr)); 1843 th = (struct tcphdr *)(udp + 1); 1844 } else { 1845 ip6->ip6_nxt = IPPROTO_TCP; 1846 th = (struct tcphdr *)(ip6 + 1); 1847 } 1848 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1849 } 1850 #endif 1851 #if defined(INET6) && defined(INET) 1852 else 1853 #endif 1854 #ifdef INET 1855 { 1856 ip = mtod(m, struct ip *); 1857 ip->ip_v = IPVERSION; 1858 ip->ip_hl = sizeof(struct ip) >> 2; 1859 ip->ip_len = htons(tlen); 1860 ip->ip_id = 0; 1861 ip->ip_off = 0; 1862 ip->ip_sum = 0; 1863 ip->ip_src = sc->sc_inc.inc_laddr; 1864 ip->ip_dst = sc->sc_inc.inc_faddr; 1865 ip->ip_ttl = sc->sc_ip_ttl; 1866 ip->ip_tos = sc->sc_ip_tos; 1867 1868 /* 1869 * See if we should do MTU discovery. Route lookups are 1870 * expensive, so we will only unset the DF bit if: 1871 * 1872 * 1) path_mtu_discovery is disabled 1873 * 2) the SCF_UNREACH flag has been set 1874 */ 1875 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1876 ip->ip_off |= htons(IP_DF); 1877 if (sc->sc_port == 0) { 1878 ip->ip_p = IPPROTO_TCP; 1879 th = (struct tcphdr *)(ip + 1); 1880 } else { 1881 ip->ip_p = IPPROTO_UDP; 1882 udp = (struct udphdr *)(ip + 1); 1883 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1884 udp->uh_dport = sc->sc_port; 1885 ulen = (tlen - sizeof(struct ip)); 1886 th = (struct tcphdr *)(udp + 1); 1887 } 1888 } 1889 #endif /* INET */ 1890 th->th_sport = sc->sc_inc.inc_lport; 1891 th->th_dport = sc->sc_inc.inc_fport; 1892 1893 if (flags & TH_SYN) 1894 th->th_seq = htonl(sc->sc_iss); 1895 else 1896 th->th_seq = htonl(sc->sc_iss + 1); 1897 th->th_ack = htonl(sc->sc_irs + 1); 1898 th->th_off = sizeof(struct tcphdr) >> 2; 1899 th->th_win = htons(sc->sc_wnd); 1900 th->th_urp = 0; 1901 1902 flags = tcp_ecn_syncache_respond(flags, sc); 1903 tcp_set_flags(th, flags); 1904 1905 /* Tack on the TCP options. */ 1906 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1907 to.to_flags = 0; 1908 1909 if (flags & TH_SYN) { 1910 to.to_mss = mssopt; 1911 to.to_flags = TOF_MSS; 1912 if (sc->sc_flags & SCF_WINSCALE) { 1913 to.to_wscale = sc->sc_requested_r_scale; 1914 to.to_flags |= TOF_SCALE; 1915 } 1916 if (sc->sc_flags & SCF_SACK) 1917 to.to_flags |= TOF_SACKPERM; 1918 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1919 if (sc->sc_flags & SCF_SIGNATURE) 1920 to.to_flags |= TOF_SIGNATURE; 1921 #endif 1922 if (sc->sc_tfo_cookie) { 1923 to.to_flags |= TOF_FASTOPEN; 1924 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1925 to.to_tfo_cookie = sc->sc_tfo_cookie; 1926 /* don't send cookie again when retransmitting response */ 1927 sc->sc_tfo_cookie = NULL; 1928 } 1929 } 1930 if (sc->sc_flags & SCF_TIMESTAMP) { 1931 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1932 to.to_tsecr = sc->sc_tsreflect; 1933 to.to_flags |= TOF_TS; 1934 } 1935 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1936 1937 /* Adjust headers by option size. */ 1938 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1939 m->m_len += optlen; 1940 m->m_pkthdr.len += optlen; 1941 #ifdef INET6 1942 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1943 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1944 else 1945 #endif 1946 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1947 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1948 if (sc->sc_flags & SCF_SIGNATURE) { 1949 KASSERT(to.to_flags & TOF_SIGNATURE, 1950 ("tcp_addoptions() didn't set tcp_signature")); 1951 1952 /* NOTE: to.to_signature is inside of mbuf */ 1953 if (!TCPMD5_ENABLED() || 1954 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1955 m_freem(m); 1956 return (EACCES); 1957 } 1958 } 1959 #endif 1960 } else 1961 optlen = 0; 1962 1963 if (udp) { 1964 ulen += optlen; 1965 udp->uh_ulen = htons(ulen); 1966 } 1967 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1968 /* 1969 * If we have peer's SYN and it has a flowid, then let's assign it to 1970 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1971 * to SYN|ACK due to lack of inp here. 1972 */ 1973 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1974 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1975 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1976 } 1977 #ifdef INET6 1978 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1979 if (sc->sc_port) { 1980 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 1981 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 1982 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 1983 IPPROTO_UDP, 0); 1984 th->th_sum = htons(0); 1985 } else { 1986 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1987 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1988 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1989 IPPROTO_TCP, 0); 1990 } 1991 ip6->ip6_hlim = sc->sc_ip_ttl; 1992 #ifdef TCP_OFFLOAD 1993 if (ADDED_BY_TOE(sc)) { 1994 struct toedev *tod = sc->sc_tod; 1995 1996 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1997 1998 return (error); 1999 } 2000 #endif 2001 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2002 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2003 } 2004 #endif 2005 #if defined(INET6) && defined(INET) 2006 else 2007 #endif 2008 #ifdef INET 2009 { 2010 if (sc->sc_port) { 2011 m->m_pkthdr.csum_flags = CSUM_UDP; 2012 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2013 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2014 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2015 th->th_sum = htons(0); 2016 } else { 2017 m->m_pkthdr.csum_flags = CSUM_TCP; 2018 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2019 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2020 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2021 } 2022 #ifdef TCP_OFFLOAD 2023 if (ADDED_BY_TOE(sc)) { 2024 struct toedev *tod = sc->sc_tod; 2025 2026 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2027 2028 return (error); 2029 } 2030 #endif 2031 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2032 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2033 } 2034 #endif 2035 return (error); 2036 } 2037 2038 /* 2039 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2040 * that exceed the capacity of the syncache by avoiding the storage of any 2041 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2042 * attacks where the attacker does not have access to our responses. 2043 * 2044 * Syncookies encode and include all necessary information about the 2045 * connection setup within the SYN|ACK that we send back. That way we 2046 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2047 * (if ever). Normally the syncache and syncookies are running in parallel 2048 * with the latter taking over when the former is exhausted. When matching 2049 * syncache entry is found the syncookie is ignored. 2050 * 2051 * The only reliable information persisting the 3WHS is our initial sequence 2052 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2053 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2054 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2055 * returns and signifies a legitimate connection if it matches the ACK. 2056 * 2057 * The available space of 32 bits to store the hash and to encode the SYN 2058 * option information is very tight and we should have at least 24 bits for 2059 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2060 * 2061 * SYN option information we have to encode to fully restore a connection: 2062 * MSS: is imporant to chose an optimal segment size to avoid IP level 2063 * fragmentation along the path. The common MSS values can be encoded 2064 * in a 3-bit table. Uncommon values are captured by the next lower value 2065 * in the table leading to a slight increase in packetization overhead. 2066 * WSCALE: is necessary to allow large windows to be used for high delay- 2067 * bandwidth product links. Not scaling the window when it was initially 2068 * negotiated is bad for performance as lack of scaling further decreases 2069 * the apparent available send window. We only need to encode the WSCALE 2070 * we received from the remote end. Our end can be recalculated at any 2071 * time. The common WSCALE values can be encoded in a 3-bit table. 2072 * Uncommon values are captured by the next lower value in the table 2073 * making us under-estimate the available window size halving our 2074 * theoretically possible maximum throughput for that connection. 2075 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2076 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2077 * that are included in all segments on a connection. We enable them when 2078 * the ACK has them. 2079 * 2080 * Security of syncookies and attack vectors: 2081 * 2082 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2083 * together with the gloabl secret to make it unique per connection attempt. 2084 * Thus any change of any of those parameters results in a different MAC output 2085 * in an unpredictable way unless a collision is encountered. 24 bits of the 2086 * MAC are embedded into the ISS. 2087 * 2088 * To prevent replay attacks two rotating global secrets are updated with a 2089 * new random value every 15 seconds. The life-time of a syncookie is thus 2090 * 15-30 seconds. 2091 * 2092 * Vector 1: Attacking the secret. This requires finding a weakness in the 2093 * MAC itself or the way it is used here. The attacker can do a chosen plain 2094 * text attack by varying and testing the all parameters under his control. 2095 * The strength depends on the size and randomness of the secret, and the 2096 * cryptographic security of the MAC function. Due to the constant updating 2097 * of the secret the attacker has at most 29.999 seconds to find the secret 2098 * and launch spoofed connections. After that he has to start all over again. 2099 * 2100 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2101 * size an average of 4,823 attempts are required for a 50% chance of success 2102 * to spoof a single syncookie (birthday collision paradox). However the 2103 * attacker is blind and doesn't know if one of his attempts succeeded unless 2104 * he has a side channel to interfere success from. A single connection setup 2105 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2106 * This many attempts are required for each one blind spoofed connection. For 2107 * every additional spoofed connection he has to launch another N attempts. 2108 * Thus for a sustained rate 100 spoofed connections per second approximately 2109 * 1,800,000 packets per second would have to be sent. 2110 * 2111 * NB: The MAC function should be fast so that it doesn't become a CPU 2112 * exhaustion attack vector itself. 2113 * 2114 * References: 2115 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2116 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2117 * http://cr.yp.to/syncookies.html (overview) 2118 * http://cr.yp.to/syncookies/archive (details) 2119 * 2120 * 2121 * Schematic construction of a syncookie enabled Initial Sequence Number: 2122 * 0 1 2 3 2123 * 12345678901234567890123456789012 2124 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2125 * 2126 * x 24 MAC (truncated) 2127 * W 3 Send Window Scale index 2128 * M 3 MSS index 2129 * S 1 SACK permitted 2130 * P 1 Odd/even secret 2131 */ 2132 2133 /* 2134 * Distribution and probability of certain MSS values. Those in between are 2135 * rounded down to the next lower one. 2136 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2137 * .2% .3% 5% 7% 7% 20% 15% 45% 2138 */ 2139 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2140 2141 /* 2142 * Distribution and probability of certain WSCALE values. We have to map the 2143 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2144 * bits based on prevalence of certain values. Where we don't have an exact 2145 * match for are rounded down to the next lower one letting us under-estimate 2146 * the true available window. At the moment this would happen only for the 2147 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2148 * and window size). The absence of the WSCALE option (no scaling in either 2149 * direction) is encoded with index zero. 2150 * [WSCALE values histograms, Allman, 2012] 2151 * X 10 10 35 5 6 14 10% by host 2152 * X 11 4 5 5 18 49 3% by connections 2153 */ 2154 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2155 2156 /* 2157 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2158 * and good cryptographic properties. 2159 */ 2160 static uint32_t 2161 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2162 uint8_t *secbits, uintptr_t secmod) 2163 { 2164 SIPHASH_CTX ctx; 2165 uint32_t siphash[2]; 2166 2167 SipHash24_Init(&ctx); 2168 SipHash_SetKey(&ctx, secbits); 2169 switch (inc->inc_flags & INC_ISIPV6) { 2170 #ifdef INET 2171 case 0: 2172 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2173 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2174 break; 2175 #endif 2176 #ifdef INET6 2177 case INC_ISIPV6: 2178 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2179 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2180 break; 2181 #endif 2182 } 2183 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2184 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2185 SipHash_Update(&ctx, &irs, sizeof(irs)); 2186 SipHash_Update(&ctx, &flags, sizeof(flags)); 2187 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2188 SipHash_Final((u_int8_t *)&siphash, &ctx); 2189 2190 return (siphash[0] ^ siphash[1]); 2191 } 2192 2193 static tcp_seq 2194 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2195 { 2196 u_int i, secbit, wscale; 2197 uint32_t iss, hash; 2198 uint8_t *secbits; 2199 union syncookie cookie; 2200 2201 cookie.cookie = 0; 2202 2203 /* Map our computed MSS into the 3-bit index. */ 2204 for (i = nitems(tcp_sc_msstab) - 1; 2205 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2206 i--) 2207 ; 2208 cookie.flags.mss_idx = i; 2209 2210 /* 2211 * Map the send window scale into the 3-bit index but only if 2212 * the wscale option was received. 2213 */ 2214 if (sc->sc_flags & SCF_WINSCALE) { 2215 wscale = sc->sc_requested_s_scale; 2216 for (i = nitems(tcp_sc_wstab) - 1; 2217 tcp_sc_wstab[i] > wscale && i > 0; 2218 i--) 2219 ; 2220 cookie.flags.wscale_idx = i; 2221 } 2222 2223 /* Can we do SACK? */ 2224 if (sc->sc_flags & SCF_SACK) 2225 cookie.flags.sack_ok = 1; 2226 2227 /* Which of the two secrets to use. */ 2228 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2229 cookie.flags.odd_even = secbit; 2230 2231 secbits = V_tcp_syncache.secret.key[secbit]; 2232 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2233 (uintptr_t)sch); 2234 2235 /* 2236 * Put the flags into the hash and XOR them to get better ISS number 2237 * variance. This doesn't enhance the cryptographic strength and is 2238 * done to prevent the 8 cookie bits from showing up directly on the 2239 * wire. 2240 */ 2241 iss = hash & ~0xff; 2242 iss |= cookie.cookie ^ (hash >> 24); 2243 2244 TCPSTAT_INC(tcps_sc_sendcookie); 2245 return (iss); 2246 } 2247 2248 static struct syncache * 2249 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2250 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2251 struct socket *lso, uint16_t port) 2252 { 2253 uint32_t hash; 2254 uint8_t *secbits; 2255 tcp_seq ack, seq; 2256 int wnd, wscale = 0; 2257 union syncookie cookie; 2258 2259 /* 2260 * Pull information out of SYN-ACK/ACK and revert sequence number 2261 * advances. 2262 */ 2263 ack = th->th_ack - 1; 2264 seq = th->th_seq - 1; 2265 2266 /* 2267 * Unpack the flags containing enough information to restore the 2268 * connection. 2269 */ 2270 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2271 2272 /* Which of the two secrets to use. */ 2273 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2274 2275 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2276 2277 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2278 if ((ack & ~0xff) != (hash & ~0xff)) 2279 return (NULL); 2280 2281 /* Fill in the syncache values. */ 2282 sc->sc_flags = 0; 2283 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2284 sc->sc_ipopts = NULL; 2285 2286 sc->sc_irs = seq; 2287 sc->sc_iss = ack; 2288 2289 switch (inc->inc_flags & INC_ISIPV6) { 2290 #ifdef INET 2291 case 0: 2292 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2293 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2294 break; 2295 #endif 2296 #ifdef INET6 2297 case INC_ISIPV6: 2298 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2299 sc->sc_flowlabel = 2300 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2301 break; 2302 #endif 2303 } 2304 2305 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2306 2307 /* We can simply recompute receive window scale we sent earlier. */ 2308 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2309 wscale++; 2310 2311 /* Only use wscale if it was enabled in the orignal SYN. */ 2312 if (cookie.flags.wscale_idx > 0) { 2313 sc->sc_requested_r_scale = wscale; 2314 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2315 sc->sc_flags |= SCF_WINSCALE; 2316 } 2317 2318 wnd = lso->sol_sbrcv_hiwat; 2319 wnd = imax(wnd, 0); 2320 wnd = imin(wnd, TCP_MAXWIN); 2321 sc->sc_wnd = wnd; 2322 2323 if (cookie.flags.sack_ok) 2324 sc->sc_flags |= SCF_SACK; 2325 2326 if (to->to_flags & TOF_TS) { 2327 sc->sc_flags |= SCF_TIMESTAMP; 2328 sc->sc_tsreflect = to->to_tsval; 2329 sc->sc_tsoff = tcp_new_ts_offset(inc); 2330 } 2331 2332 if (to->to_flags & TOF_SIGNATURE) 2333 sc->sc_flags |= SCF_SIGNATURE; 2334 2335 sc->sc_rxmits = 0; 2336 2337 sc->sc_port = port; 2338 2339 TCPSTAT_INC(tcps_sc_recvcookie); 2340 return (sc); 2341 } 2342 2343 #ifdef INVARIANTS 2344 static int 2345 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2346 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2347 struct socket *lso, uint16_t port) 2348 { 2349 struct syncache scs, *scx; 2350 char *s; 2351 2352 bzero(&scs, sizeof(scs)); 2353 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2354 2355 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2356 return (0); 2357 2358 if (scx != NULL) { 2359 if (sc->sc_peer_mss != scx->sc_peer_mss) 2360 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2361 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2362 2363 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2364 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2365 s, __func__, sc->sc_requested_r_scale, 2366 scx->sc_requested_r_scale); 2367 2368 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2369 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2370 s, __func__, sc->sc_requested_s_scale, 2371 scx->sc_requested_s_scale); 2372 2373 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2374 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2375 } 2376 2377 if (s != NULL) 2378 free(s, M_TCPLOG); 2379 return (0); 2380 } 2381 #endif /* INVARIANTS */ 2382 2383 static void 2384 syncookie_reseed(void *arg) 2385 { 2386 struct tcp_syncache *sc = arg; 2387 uint8_t *secbits; 2388 int secbit; 2389 2390 /* 2391 * Reseeding the secret doesn't have to be protected by a lock. 2392 * It only must be ensured that the new random values are visible 2393 * to all CPUs in a SMP environment. The atomic with release 2394 * semantics ensures that. 2395 */ 2396 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2397 secbits = sc->secret.key[secbit]; 2398 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2399 atomic_add_rel_int(&sc->secret.oddeven, 1); 2400 2401 /* Reschedule ourself. */ 2402 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2403 } 2404 2405 /* 2406 * We have overflowed a bucket. Let's pause dealing with the syncache. 2407 * This function will increment the bucketoverflow statistics appropriately 2408 * (once per pause when pausing is enabled; otherwise, once per overflow). 2409 */ 2410 static void 2411 syncache_pause(struct in_conninfo *inc) 2412 { 2413 time_t delta; 2414 const char *s; 2415 2416 /* XXX: 2417 * 2. Add sysctl read here so we don't get the benefit of this 2418 * change without the new sysctl. 2419 */ 2420 2421 /* 2422 * Try an unlocked read. If we already know that another thread 2423 * has activated the feature, there is no need to proceed. 2424 */ 2425 if (V_tcp_syncache.paused) 2426 return; 2427 2428 /* Are cookied enabled? If not, we can't pause. */ 2429 if (!V_tcp_syncookies) { 2430 TCPSTAT_INC(tcps_sc_bucketoverflow); 2431 return; 2432 } 2433 2434 /* 2435 * We may be the first thread to find an overflow. Get the lock 2436 * and evaluate if we need to take action. 2437 */ 2438 mtx_lock(&V_tcp_syncache.pause_mtx); 2439 if (V_tcp_syncache.paused) { 2440 mtx_unlock(&V_tcp_syncache.pause_mtx); 2441 return; 2442 } 2443 2444 /* Activate protection. */ 2445 V_tcp_syncache.paused = true; 2446 TCPSTAT_INC(tcps_sc_bucketoverflow); 2447 2448 /* 2449 * Determine the last backoff time. If we are seeing a re-newed 2450 * attack within that same time after last reactivating the syncache, 2451 * consider it an extension of the same attack. 2452 */ 2453 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2454 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2455 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2456 delta <<= 1; 2457 V_tcp_syncache.pause_backoff++; 2458 } 2459 } else { 2460 delta = TCP_SYNCACHE_PAUSE_TIME; 2461 V_tcp_syncache.pause_backoff = 0; 2462 } 2463 2464 /* Log a warning, including IP addresses, if able. */ 2465 if (inc != NULL) 2466 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2467 else 2468 s = (const char *)NULL; 2469 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2470 "the next %lld seconds%s%s%s\n", (long long)delta, 2471 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2472 (s != NULL) ? ")" : ""); 2473 free(__DECONST(void *, s), M_TCPLOG); 2474 2475 /* Use the calculated delta to set a new pause time. */ 2476 V_tcp_syncache.pause_until = time_uptime + delta; 2477 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2478 &V_tcp_syncache); 2479 mtx_unlock(&V_tcp_syncache.pause_mtx); 2480 } 2481 2482 /* Evaluate whether we need to unpause. */ 2483 static void 2484 syncache_unpause(void *arg) 2485 { 2486 struct tcp_syncache *sc; 2487 time_t delta; 2488 2489 sc = arg; 2490 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2491 callout_deactivate(&sc->pause_co); 2492 2493 /* 2494 * Check to make sure we are not running early. If the pause 2495 * time has expired, then deactivate the protection. 2496 */ 2497 if ((delta = sc->pause_until - time_uptime) > 0) 2498 callout_schedule(&sc->pause_co, delta * hz); 2499 else 2500 sc->paused = false; 2501 } 2502 2503 /* 2504 * Exports the syncache entries to userland so that netstat can display 2505 * them alongside the other sockets. This function is intended to be 2506 * called only from tcp_pcblist. 2507 * 2508 * Due to concurrency on an active system, the number of pcbs exported 2509 * may have no relation to max_pcbs. max_pcbs merely indicates the 2510 * amount of space the caller allocated for this function to use. 2511 */ 2512 int 2513 syncache_pcblist(struct sysctl_req *req) 2514 { 2515 struct xtcpcb xt; 2516 struct syncache *sc; 2517 struct syncache_head *sch; 2518 int error, i; 2519 2520 bzero(&xt, sizeof(xt)); 2521 xt.xt_len = sizeof(xt); 2522 xt.t_state = TCPS_SYN_RECEIVED; 2523 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2524 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2525 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2526 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2527 2528 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2529 sch = &V_tcp_syncache.hashbase[i]; 2530 SCH_LOCK(sch); 2531 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2532 if (sc->sc_cred != NULL && 2533 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2534 continue; 2535 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2536 xt.xt_inp.inp_vflag = INP_IPV6; 2537 else 2538 xt.xt_inp.inp_vflag = INP_IPV4; 2539 xt.xt_encaps_port = sc->sc_port; 2540 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2541 sizeof (struct in_conninfo)); 2542 error = SYSCTL_OUT(req, &xt, sizeof xt); 2543 if (error) { 2544 SCH_UNLOCK(sch); 2545 return (0); 2546 } 2547 } 2548 SCH_UNLOCK(sch); 2549 } 2550 2551 return (0); 2552 } 2553