1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/hash.h> 45 #include <sys/refcount.h> 46 #include <sys/kernel.h> 47 #include <sys/sysctl.h> 48 #include <sys/limits.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/malloc.h> 52 #include <sys/mbuf.h> 53 #include <sys/proc.h> /* for proc0 declaration */ 54 #include <sys/random.h> 55 #include <sys/socket.h> 56 #include <sys/socketvar.h> 57 #include <sys/syslog.h> 58 #include <sys/ucred.h> 59 60 #include <sys/md5.h> 61 #include <crypto/siphash/siphash.h> 62 63 #include <vm/uma.h> 64 65 #include <net/if.h> 66 #include <net/if_var.h> 67 #include <net/route.h> 68 #include <net/vnet.h> 69 70 #include <netinet/in.h> 71 #include <netinet/in_kdtrace.h> 72 #include <netinet/in_systm.h> 73 #include <netinet/ip.h> 74 #include <netinet/in_var.h> 75 #include <netinet/in_pcb.h> 76 #include <netinet/ip_var.h> 77 #include <netinet/ip_options.h> 78 #ifdef INET6 79 #include <netinet/ip6.h> 80 #include <netinet/icmp6.h> 81 #include <netinet6/nd6.h> 82 #include <netinet6/ip6_var.h> 83 #include <netinet6/in6_pcb.h> 84 #endif 85 #include <netinet/tcp.h> 86 #include <netinet/tcp_fastopen.h> 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #include <netinet/tcp_ecn.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 #include <netinet/udp_var.h> 101 102 #include <netipsec/ipsec_support.h> 103 104 #include <machine/in_cksum.h> 105 106 #include <security/mac/mac_framework.h> 107 108 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 109 #define V_tcp_syncookies VNET(tcp_syncookies) 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 121 #define V_functions_inherit_listen_socket_stack \ 122 VNET(functions_inherit_listen_socket_stack) 123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 124 CTLFLAG_VNET | CTLFLAG_RW, 125 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 126 "Inherit listen socket's stack"); 127 128 #ifdef TCP_OFFLOAD 129 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 130 #endif 131 132 static void syncache_drop(struct syncache *, struct syncache_head *); 133 static void syncache_free(struct syncache *); 134 static void syncache_insert(struct syncache *, struct syncache_head *); 135 static int syncache_respond(struct syncache *, const struct mbuf *, int); 136 static struct socket *syncache_socket(struct syncache *, struct socket *, 137 struct mbuf *m); 138 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 139 int docallout); 140 static void syncache_timer(void *); 141 142 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 143 uint8_t *, uintptr_t); 144 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 145 static struct syncache 146 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 147 struct syncache *, struct tcphdr *, struct tcpopt *, 148 struct socket *, uint16_t); 149 static void syncache_pause(struct in_conninfo *); 150 static void syncache_unpause(void *); 151 static void syncookie_reseed(void *); 152 #ifdef INVARIANTS 153 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 154 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 155 struct socket *lso, uint16_t port); 156 #endif 157 158 /* 159 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 160 * 3 retransmits corresponds to a timeout with default values of 161 * tcp_rexmit_initial * ( 1 + 162 * tcp_backoff[1] + 163 * tcp_backoff[2] + 164 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 165 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 166 * the odds are that the user has given up attempting to connect by then. 167 */ 168 #define SYNCACHE_MAXREXMTS 3 169 170 /* Arbitrary values */ 171 #define TCP_SYNCACHE_HASHSIZE 512 172 #define TCP_SYNCACHE_BUCKETLIMIT 30 173 174 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 175 #define V_tcp_syncache VNET(tcp_syncache) 176 177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 178 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 179 "TCP SYN cache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.bucket_limit), 0, 183 "Per-bucket hash limit for syncache"); 184 185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 186 &VNET_NAME(tcp_syncache.cache_limit), 0, 187 "Overall entry limit for syncache"); 188 189 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 190 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 191 192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 193 &VNET_NAME(tcp_syncache.hashsize), 0, 194 "Size of TCP syncache hashtable"); 195 196 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 197 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 198 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 199 "and mac(4) checks"); 200 201 static int 202 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 203 { 204 int error; 205 u_int new; 206 207 new = V_tcp_syncache.rexmt_limit; 208 error = sysctl_handle_int(oidp, &new, 0, req); 209 if ((error == 0) && (req->newptr != NULL)) { 210 if (new > TCP_MAXRXTSHIFT) 211 error = EINVAL; 212 else 213 V_tcp_syncache.rexmt_limit = new; 214 } 215 return (error); 216 } 217 218 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 219 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 220 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 221 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 222 "Limit on SYN/ACK retransmissions"); 223 224 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 225 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 226 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 227 "Send reset on socket allocation failure"); 228 229 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 230 231 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 232 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 233 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 234 235 /* 236 * Requires the syncache entry to be already removed from the bucket list. 237 */ 238 static void 239 syncache_free(struct syncache *sc) 240 { 241 242 if (sc->sc_ipopts) 243 (void) m_free(sc->sc_ipopts); 244 if (sc->sc_cred) 245 crfree(sc->sc_cred); 246 #ifdef MAC 247 mac_syncache_destroy(&sc->sc_label); 248 #endif 249 250 uma_zfree(V_tcp_syncache.zone, sc); 251 } 252 253 void 254 syncache_init(void) 255 { 256 int i; 257 258 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 259 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 260 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 261 V_tcp_syncache.hash_secret = arc4random(); 262 263 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 264 &V_tcp_syncache.hashsize); 265 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 266 &V_tcp_syncache.bucket_limit); 267 if (!powerof2(V_tcp_syncache.hashsize) || 268 V_tcp_syncache.hashsize == 0) { 269 printf("WARNING: syncache hash size is not a power of 2.\n"); 270 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 271 } 272 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 273 274 /* Set limits. */ 275 V_tcp_syncache.cache_limit = 276 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 277 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 278 &V_tcp_syncache.cache_limit); 279 280 /* Allocate the hash table. */ 281 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 282 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 283 284 #ifdef VIMAGE 285 V_tcp_syncache.vnet = curvnet; 286 #endif 287 288 /* Initialize the hash buckets. */ 289 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 290 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 291 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 292 NULL, MTX_DEF); 293 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 294 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 295 V_tcp_syncache.hashbase[i].sch_length = 0; 296 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 297 V_tcp_syncache.hashbase[i].sch_last_overflow = 298 -(SYNCOOKIE_LIFETIME + 1); 299 } 300 301 /* Create the syncache entry zone. */ 302 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 303 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 304 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 305 V_tcp_syncache.cache_limit); 306 307 /* Start the SYN cookie reseeder callout. */ 308 callout_init(&V_tcp_syncache.secret.reseed, 1); 309 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 310 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 311 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 312 syncookie_reseed, &V_tcp_syncache); 313 314 /* Initialize the pause machinery. */ 315 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 316 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 317 0); 318 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 319 V_tcp_syncache.pause_backoff = 0; 320 V_tcp_syncache.paused = false; 321 } 322 323 #ifdef VIMAGE 324 void 325 syncache_destroy(void) 326 { 327 struct syncache_head *sch; 328 struct syncache *sc, *nsc; 329 int i; 330 331 /* 332 * Stop the re-seed timer before freeing resources. No need to 333 * possibly schedule it another time. 334 */ 335 callout_drain(&V_tcp_syncache.secret.reseed); 336 337 /* Stop the SYN cache pause callout. */ 338 mtx_lock(&V_tcp_syncache.pause_mtx); 339 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 callout_drain(&V_tcp_syncache.pause_co); 342 } else 343 mtx_unlock(&V_tcp_syncache.pause_mtx); 344 345 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 346 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 347 sch = &V_tcp_syncache.hashbase[i]; 348 callout_drain(&sch->sch_timer); 349 350 SCH_LOCK(sch); 351 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 352 syncache_drop(sc, sch); 353 SCH_UNLOCK(sch); 354 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 355 ("%s: sch->sch_bucket not empty", __func__)); 356 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 357 __func__, sch->sch_length)); 358 mtx_destroy(&sch->sch_mtx); 359 } 360 361 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 362 ("%s: cache_count not 0", __func__)); 363 364 /* Free the allocated global resources. */ 365 uma_zdestroy(V_tcp_syncache.zone); 366 free(V_tcp_syncache.hashbase, M_SYNCACHE); 367 mtx_destroy(&V_tcp_syncache.pause_mtx); 368 } 369 #endif 370 371 /* 372 * Inserts a syncache entry into the specified bucket row. 373 * Locks and unlocks the syncache_head autonomously. 374 */ 375 static void 376 syncache_insert(struct syncache *sc, struct syncache_head *sch) 377 { 378 struct syncache *sc2; 379 380 SCH_LOCK(sch); 381 382 /* 383 * Make sure that we don't overflow the per-bucket limit. 384 * If the bucket is full, toss the oldest element. 385 */ 386 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 387 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 388 ("sch->sch_length incorrect")); 389 syncache_pause(&sc->sc_inc); 390 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 391 sch->sch_last_overflow = time_uptime; 392 syncache_drop(sc2, sch); 393 } 394 395 /* Put it into the bucket. */ 396 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 397 sch->sch_length++; 398 399 #ifdef TCP_OFFLOAD 400 if (ADDED_BY_TOE(sc)) { 401 struct toedev *tod = sc->sc_tod; 402 403 tod->tod_syncache_added(tod, sc->sc_todctx); 404 } 405 #endif 406 407 /* Reinitialize the bucket row's timer. */ 408 if (sch->sch_length == 1) 409 sch->sch_nextc = ticks + INT_MAX; 410 syncache_timeout(sc, sch, 1); 411 412 SCH_UNLOCK(sch); 413 414 TCPSTATES_INC(TCPS_SYN_RECEIVED); 415 TCPSTAT_INC(tcps_sc_added); 416 } 417 418 /* 419 * Remove and free entry from syncache bucket row. 420 * Expects locked syncache head. 421 */ 422 static void 423 syncache_drop(struct syncache *sc, struct syncache_head *sch) 424 { 425 426 SCH_LOCK_ASSERT(sch); 427 428 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 429 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 430 sch->sch_length--; 431 432 #ifdef TCP_OFFLOAD 433 if (ADDED_BY_TOE(sc)) { 434 struct toedev *tod = sc->sc_tod; 435 436 tod->tod_syncache_removed(tod, sc->sc_todctx); 437 } 438 #endif 439 440 syncache_free(sc); 441 } 442 443 /* 444 * Engage/reengage time on bucket row. 445 */ 446 static void 447 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 448 { 449 int rexmt; 450 451 if (sc->sc_rxmits == 0) 452 rexmt = tcp_rexmit_initial; 453 else 454 TCPT_RANGESET(rexmt, 455 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 456 tcp_rexmit_min, TCPTV_REXMTMAX); 457 sc->sc_rxttime = ticks + rexmt; 458 sc->sc_rxmits++; 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 460 sch->sch_nextc = sc->sc_rxttime; 461 if (docallout) 462 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 463 syncache_timer, (void *)sch); 464 } 465 } 466 467 /* 468 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 469 * If we have retransmitted an entry the maximum number of times, expire it. 470 * One separate timer for each bucket row. 471 */ 472 static void 473 syncache_timer(void *xsch) 474 { 475 struct syncache_head *sch = (struct syncache_head *)xsch; 476 struct syncache *sc, *nsc; 477 struct epoch_tracker et; 478 int tick = ticks; 479 char *s; 480 bool paused; 481 482 CURVNET_SET(sch->sch_sc->vnet); 483 484 /* NB: syncache_head has already been locked by the callout. */ 485 SCH_LOCK_ASSERT(sch); 486 487 /* 488 * In the following cycle we may remove some entries and/or 489 * advance some timeouts, so re-initialize the bucket timer. 490 */ 491 sch->sch_nextc = tick + INT_MAX; 492 493 /* 494 * If we have paused processing, unconditionally remove 495 * all syncache entries. 496 */ 497 mtx_lock(&V_tcp_syncache.pause_mtx); 498 paused = V_tcp_syncache.paused; 499 mtx_unlock(&V_tcp_syncache.pause_mtx); 500 501 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 502 if (paused) { 503 syncache_drop(sc, sch); 504 continue; 505 } 506 /* 507 * We do not check if the listen socket still exists 508 * and accept the case where the listen socket may be 509 * gone by the time we resend the SYN/ACK. We do 510 * not expect this to happens often. If it does, 511 * then the RST will be sent by the time the remote 512 * host does the SYN/ACK->ACK. 513 */ 514 if (TSTMP_GT(sc->sc_rxttime, tick)) { 515 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 516 sch->sch_nextc = sc->sc_rxttime; 517 continue; 518 } 519 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 520 sc->sc_flags &= ~SCF_ECN; 521 } 522 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 524 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 525 "giving up and removing syncache entry\n", 526 s, __func__); 527 free(s, M_TCPLOG); 528 } 529 syncache_drop(sc, sch); 530 TCPSTAT_INC(tcps_sc_stale); 531 continue; 532 } 533 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 534 log(LOG_DEBUG, "%s; %s: Response timeout, " 535 "retransmitting (%u) SYN|ACK\n", 536 s, __func__, sc->sc_rxmits); 537 free(s, M_TCPLOG); 538 } 539 540 NET_EPOCH_ENTER(et); 541 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 542 NET_EPOCH_EXIT(et); 543 TCPSTAT_INC(tcps_sc_retransmitted); 544 syncache_timeout(sc, sch, 0); 545 } 546 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 547 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 548 syncache_timer, (void *)(sch)); 549 CURVNET_RESTORE(); 550 } 551 552 /* 553 * Returns true if the system is only using cookies at the moment. 554 * This could be due to a sysadmin decision to only use cookies, or it 555 * could be due to the system detecting an attack. 556 */ 557 static inline bool 558 syncache_cookiesonly(void) 559 { 560 561 return (V_tcp_syncookies && (V_tcp_syncache.paused || 562 V_tcp_syncookiesonly)); 563 } 564 565 /* 566 * Find the hash bucket for the given connection. 567 */ 568 static struct syncache_head * 569 syncache_hashbucket(struct in_conninfo *inc) 570 { 571 uint32_t hash; 572 573 /* 574 * The hash is built on foreign port + local port + foreign address. 575 * We rely on the fact that struct in_conninfo starts with 16 bits 576 * of foreign port, then 16 bits of local port then followed by 128 577 * bits of foreign address. In case of IPv4 address, the first 3 578 * 32-bit words of the address always are zeroes. 579 */ 580 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 581 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 582 583 return (&V_tcp_syncache.hashbase[hash]); 584 } 585 586 /* 587 * Find an entry in the syncache. 588 * Returns always with locked syncache_head plus a matching entry or NULL. 589 */ 590 static struct syncache * 591 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 592 { 593 struct syncache *sc; 594 struct syncache_head *sch; 595 596 *schp = sch = syncache_hashbucket(inc); 597 SCH_LOCK(sch); 598 599 /* Circle through bucket row to find matching entry. */ 600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 601 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 602 sizeof(struct in_endpoints)) == 0) 603 break; 604 605 return (sc); /* Always returns with locked sch. */ 606 } 607 608 /* 609 * This function is called when we get a RST for a 610 * non-existent connection, so that we can see if the 611 * connection is in the syn cache. If it is, zap it. 612 * If required send a challenge ACK. 613 */ 614 void 615 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 616 uint16_t port) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 char *s = NULL; 621 622 if (syncache_cookiesonly()) 623 return; 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 627 /* 628 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 629 * See RFC 793 page 65, section SEGMENT ARRIVES. 630 */ 631 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) { 632 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 633 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 634 "FIN flag set, segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* 640 * No corresponding connection was found in syncache. 641 * If syncookies are enabled and possibly exclusively 642 * used, or we are under memory pressure, a valid RST 643 * may not find a syncache entry. In that case we're 644 * done and no SYN|ACK retransmissions will happen. 645 * Otherwise the RST was misdirected or spoofed. 646 */ 647 if (sc == NULL) { 648 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 649 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 650 "syncache entry (possibly syncookie only), " 651 "segment ignored\n", s, __func__); 652 TCPSTAT_INC(tcps_badrst); 653 goto done; 654 } 655 656 /* The remote UDP encaps port does not match. */ 657 if (sc->sc_port != port) { 658 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 659 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 660 "syncache entry but non-matching UDP encaps port, " 661 "segment ignored\n", s, __func__); 662 TCPSTAT_INC(tcps_badrst); 663 goto done; 664 } 665 666 /* 667 * If the RST bit is set, check the sequence number to see 668 * if this is a valid reset segment. 669 * 670 * RFC 793 page 37: 671 * In all states except SYN-SENT, all reset (RST) segments 672 * are validated by checking their SEQ-fields. A reset is 673 * valid if its sequence number is in the window. 674 * 675 * RFC 793 page 69: 676 * There are four cases for the acceptability test for an incoming 677 * segment: 678 * 679 * Segment Receive Test 680 * Length Window 681 * ------- ------- ------------------------------------------- 682 * 0 0 SEG.SEQ = RCV.NXT 683 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 684 * >0 0 not acceptable 685 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 686 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 687 * 688 * Note that when receiving a SYN segment in the LISTEN state, 689 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 690 * described in RFC 793, page 66. 691 */ 692 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 693 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 694 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 695 if (V_tcp_insecure_rst || 696 th->th_seq == sc->sc_irs + 1) { 697 syncache_drop(sc, sch); 698 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 699 log(LOG_DEBUG, 700 "%s; %s: Our SYN|ACK was rejected, " 701 "connection attempt aborted by remote " 702 "endpoint\n", 703 s, __func__); 704 TCPSTAT_INC(tcps_sc_reset); 705 } else { 706 TCPSTAT_INC(tcps_badrst); 707 /* Send challenge ACK. */ 708 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 709 log(LOG_DEBUG, "%s; %s: RST with invalid " 710 " SEQ %u != NXT %u (+WND %u), " 711 "sending challenge ACK\n", 712 s, __func__, 713 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 714 syncache_respond(sc, m, TH_ACK); 715 } 716 } else { 717 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 718 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 719 "NXT %u (+WND %u), segment ignored\n", 720 s, __func__, 721 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 722 TCPSTAT_INC(tcps_badrst); 723 } 724 725 done: 726 if (s != NULL) 727 free(s, M_TCPLOG); 728 SCH_UNLOCK(sch); 729 } 730 731 void 732 syncache_badack(struct in_conninfo *inc, uint16_t port) 733 { 734 struct syncache *sc; 735 struct syncache_head *sch; 736 737 if (syncache_cookiesonly()) 738 return; 739 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 740 SCH_LOCK_ASSERT(sch); 741 if ((sc != NULL) && (sc->sc_port == port)) { 742 syncache_drop(sc, sch); 743 TCPSTAT_INC(tcps_sc_badack); 744 } 745 SCH_UNLOCK(sch); 746 } 747 748 void 749 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 750 { 751 struct syncache *sc; 752 struct syncache_head *sch; 753 754 if (syncache_cookiesonly()) 755 return; 756 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 757 SCH_LOCK_ASSERT(sch); 758 if (sc == NULL) 759 goto done; 760 761 /* If the port != sc_port, then it's a bogus ICMP msg */ 762 if (port != sc->sc_port) 763 goto done; 764 765 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 766 if (ntohl(th_seq) != sc->sc_iss) 767 goto done; 768 769 /* 770 * If we've rertransmitted 3 times and this is our second error, 771 * we remove the entry. Otherwise, we allow it to continue on. 772 * This prevents us from incorrectly nuking an entry during a 773 * spurious network outage. 774 * 775 * See tcp_notify(). 776 */ 777 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 778 sc->sc_flags |= SCF_UNREACH; 779 goto done; 780 } 781 syncache_drop(sc, sch); 782 TCPSTAT_INC(tcps_sc_unreach); 783 done: 784 SCH_UNLOCK(sch); 785 } 786 787 /* 788 * Build a new TCP socket structure from a syncache entry. 789 * 790 * On success return the newly created socket with its underlying inp locked. 791 */ 792 static struct socket * 793 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 794 { 795 struct tcp_function_block *blk; 796 struct inpcb *inp = NULL; 797 struct socket *so; 798 struct tcpcb *tp; 799 int error; 800 char *s; 801 802 NET_EPOCH_ASSERT(); 803 804 /* 805 * Ok, create the full blown connection, and set things up 806 * as they would have been set up if we had created the 807 * connection when the SYN arrived. 808 */ 809 if ((so = solisten_clone(lso)) == NULL) 810 goto allocfail; 811 #ifdef MAC 812 mac_socketpeer_set_from_mbuf(m, so); 813 #endif 814 error = in_pcballoc(so, &V_tcbinfo); 815 if (error) { 816 sodealloc(so); 817 goto allocfail; 818 } 819 inp = sotoinpcb(so); 820 if ((tp = tcp_newtcpcb(inp)) == NULL) { 821 in_pcbdetach(inp); 822 in_pcbfree(inp); 823 sodealloc(so); 824 goto allocfail; 825 } 826 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 827 #ifdef INET6 828 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 829 inp->inp_vflag &= ~INP_IPV4; 830 inp->inp_vflag |= INP_IPV6; 831 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 832 } else { 833 inp->inp_vflag &= ~INP_IPV6; 834 inp->inp_vflag |= INP_IPV4; 835 #endif 836 inp->inp_ip_ttl = sc->sc_ip_ttl; 837 inp->inp_ip_tos = sc->sc_ip_tos; 838 inp->inp_laddr = sc->sc_inc.inc_laddr; 839 #ifdef INET6 840 } 841 #endif 842 843 /* 844 * If there's an mbuf and it has a flowid, then let's initialise the 845 * inp with that particular flowid. 846 */ 847 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 848 inp->inp_flowid = m->m_pkthdr.flowid; 849 inp->inp_flowtype = M_HASHTYPE_GET(m); 850 #ifdef NUMA 851 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 852 #endif 853 } 854 855 inp->inp_lport = sc->sc_inc.inc_lport; 856 #ifdef INET6 857 if (inp->inp_vflag & INP_IPV6PROTO) { 858 struct inpcb *oinp = sotoinpcb(lso); 859 860 /* 861 * Inherit socket options from the listening socket. 862 * Note that in6p_inputopts are not (and should not be) 863 * copied, since it stores previously received options and is 864 * used to detect if each new option is different than the 865 * previous one and hence should be passed to a user. 866 * If we copied in6p_inputopts, a user would not be able to 867 * receive options just after calling the accept system call. 868 */ 869 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 870 if (oinp->in6p_outputopts) 871 inp->in6p_outputopts = 872 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 873 inp->in6p_hops = oinp->in6p_hops; 874 } 875 876 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 877 struct in6_addr laddr6; 878 struct sockaddr_in6 sin6; 879 880 sin6.sin6_family = AF_INET6; 881 sin6.sin6_len = sizeof(sin6); 882 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 883 sin6.sin6_port = sc->sc_inc.inc_fport; 884 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 885 laddr6 = inp->in6p_laddr; 886 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 887 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 888 INP_HASH_WLOCK(&V_tcbinfo); 889 error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 890 thread0.td_ucred, m, false); 891 INP_HASH_WUNLOCK(&V_tcbinfo); 892 if (error != 0) { 893 inp->in6p_laddr = laddr6; 894 goto abort; 895 } 896 /* Override flowlabel from in6_pcbconnect. */ 897 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 898 inp->inp_flow |= sc->sc_flowlabel; 899 } 900 #endif /* INET6 */ 901 #if defined(INET) && defined(INET6) 902 else 903 #endif 904 #ifdef INET 905 { 906 struct in_addr laddr; 907 struct sockaddr_in sin; 908 909 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 910 911 if (inp->inp_options == NULL) { 912 inp->inp_options = sc->sc_ipopts; 913 sc->sc_ipopts = NULL; 914 } 915 916 sin.sin_family = AF_INET; 917 sin.sin_len = sizeof(sin); 918 sin.sin_addr = sc->sc_inc.inc_faddr; 919 sin.sin_port = sc->sc_inc.inc_fport; 920 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 921 laddr = inp->inp_laddr; 922 if (inp->inp_laddr.s_addr == INADDR_ANY) 923 inp->inp_laddr = sc->sc_inc.inc_laddr; 924 INP_HASH_WLOCK(&V_tcbinfo); 925 error = in_pcbconnect(inp, (struct sockaddr *)&sin, 926 thread0.td_ucred, false); 927 INP_HASH_WUNLOCK(&V_tcbinfo); 928 if (error != 0) { 929 inp->inp_laddr = laddr; 930 goto abort; 931 } 932 } 933 #endif /* INET */ 934 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 935 /* Copy old policy into new socket's. */ 936 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 937 printf("syncache_socket: could not copy policy\n"); 938 #endif 939 tp->t_state = TCPS_SYN_RECEIVED; 940 tp->iss = sc->sc_iss; 941 tp->irs = sc->sc_irs; 942 tp->t_port = sc->sc_port; 943 tcp_rcvseqinit(tp); 944 tcp_sendseqinit(tp); 945 blk = sototcpcb(lso)->t_fb; 946 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 947 /* 948 * Our parents t_fb was not the default, 949 * we need to release our ref on tp->t_fb and 950 * pickup one on the new entry. 951 */ 952 struct tcp_function_block *rblk; 953 954 rblk = find_and_ref_tcp_fb(blk); 955 KASSERT(rblk != NULL, 956 ("cannot find blk %p out of syncache?", blk)); 957 if (tp->t_fb->tfb_tcp_fb_fini) 958 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 959 refcount_release(&tp->t_fb->tfb_refcnt); 960 tp->t_fb = rblk; 961 /* 962 * XXXrrs this is quite dangerous, it is possible 963 * for the new function to fail to init. We also 964 * are not asking if the handoff_is_ok though at 965 * the very start thats probalbly ok. 966 */ 967 if (tp->t_fb->tfb_tcp_fb_init) { 968 (*tp->t_fb->tfb_tcp_fb_init)(tp); 969 } 970 } 971 tp->snd_wl1 = sc->sc_irs; 972 tp->snd_max = tp->iss + 1; 973 tp->snd_nxt = tp->iss + 1; 974 tp->rcv_up = sc->sc_irs + 1; 975 tp->rcv_wnd = sc->sc_wnd; 976 tp->rcv_adv += tp->rcv_wnd; 977 tp->last_ack_sent = tp->rcv_nxt; 978 979 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 980 if (sc->sc_flags & SCF_NOOPT) 981 tp->t_flags |= TF_NOOPT; 982 else { 983 if (sc->sc_flags & SCF_WINSCALE) { 984 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 985 tp->snd_scale = sc->sc_requested_s_scale; 986 tp->request_r_scale = sc->sc_requested_r_scale; 987 } 988 if (sc->sc_flags & SCF_TIMESTAMP) { 989 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 990 tp->ts_recent = sc->sc_tsreflect; 991 tp->ts_recent_age = tcp_ts_getticks(); 992 tp->ts_offset = sc->sc_tsoff; 993 } 994 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 995 if (sc->sc_flags & SCF_SIGNATURE) 996 tp->t_flags |= TF_SIGNATURE; 997 #endif 998 if (sc->sc_flags & SCF_SACK) 999 tp->t_flags |= TF_SACK_PERMIT; 1000 } 1001 1002 tcp_ecn_syncache_socket(tp, sc); 1003 1004 /* 1005 * Set up MSS and get cached values from tcp_hostcache. 1006 * This might overwrite some of the defaults we just set. 1007 */ 1008 tcp_mss(tp, sc->sc_peer_mss); 1009 1010 /* 1011 * If the SYN,ACK was retransmitted, indicate that CWND to be 1012 * limited to one segment in cc_conn_init(). 1013 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1014 */ 1015 if (sc->sc_rxmits > 1) 1016 tp->snd_cwnd = 1; 1017 1018 #ifdef TCP_OFFLOAD 1019 /* 1020 * Allow a TOE driver to install its hooks. Note that we hold the 1021 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1022 * new connection before the TOE driver has done its thing. 1023 */ 1024 if (ADDED_BY_TOE(sc)) { 1025 struct toedev *tod = sc->sc_tod; 1026 1027 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1028 } 1029 #endif 1030 /* 1031 * Copy and activate timers. 1032 */ 1033 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1034 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1035 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1036 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1037 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1038 1039 TCPSTAT_INC(tcps_accepts); 1040 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1041 1042 solisten_enqueue(so, SS_ISCONNECTED); 1043 1044 return (so); 1045 1046 allocfail: 1047 /* 1048 * Drop the connection; we will either send a RST or have the peer 1049 * retransmit its SYN again after its RTO and try again. 1050 */ 1051 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1052 log(LOG_DEBUG, "%s; %s: Socket create failed " 1053 "due to limits or memory shortage\n", 1054 s, __func__); 1055 free(s, M_TCPLOG); 1056 } 1057 TCPSTAT_INC(tcps_listendrop); 1058 return (NULL); 1059 1060 abort: 1061 in_pcbdetach(inp); 1062 in_pcbfree(inp); 1063 sodealloc(so); 1064 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1065 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1066 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1067 error); 1068 free(s, M_TCPLOG); 1069 } 1070 TCPSTAT_INC(tcps_listendrop); 1071 return (NULL); 1072 } 1073 1074 /* 1075 * This function gets called when we receive an ACK for a 1076 * socket in the LISTEN state. We look up the connection 1077 * in the syncache, and if its there, we pull it out of 1078 * the cache and turn it into a full-blown connection in 1079 * the SYN-RECEIVED state. 1080 * 1081 * On syncache_socket() success the newly created socket 1082 * has its underlying inp locked. 1083 */ 1084 int 1085 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1086 struct socket **lsop, struct mbuf *m, uint16_t port) 1087 { 1088 struct syncache *sc; 1089 struct syncache_head *sch; 1090 struct syncache scs; 1091 char *s; 1092 bool locked; 1093 1094 NET_EPOCH_ASSERT(); 1095 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1096 ("%s: can handle only ACK", __func__)); 1097 1098 if (syncache_cookiesonly()) { 1099 sc = NULL; 1100 sch = syncache_hashbucket(inc); 1101 locked = false; 1102 } else { 1103 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1104 locked = true; 1105 SCH_LOCK_ASSERT(sch); 1106 } 1107 1108 #ifdef INVARIANTS 1109 /* 1110 * Test code for syncookies comparing the syncache stored 1111 * values with the reconstructed values from the cookie. 1112 */ 1113 if (sc != NULL) 1114 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1115 #endif 1116 1117 if (sc == NULL) { 1118 /* 1119 * There is no syncache entry, so see if this ACK is 1120 * a returning syncookie. To do this, first: 1121 * A. Check if syncookies are used in case of syncache 1122 * overflows 1123 * B. See if this socket has had a syncache entry dropped in 1124 * the recent past. We don't want to accept a bogus 1125 * syncookie if we've never received a SYN or accept it 1126 * twice. 1127 * C. check that the syncookie is valid. If it is, then 1128 * cobble up a fake syncache entry, and return. 1129 */ 1130 if (locked && !V_tcp_syncookies) { 1131 SCH_UNLOCK(sch); 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1133 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1134 "segment rejected (syncookies disabled)\n", 1135 s, __func__); 1136 goto failed; 1137 } 1138 if (locked && !V_tcp_syncookiesonly && 1139 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1140 SCH_UNLOCK(sch); 1141 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1142 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1143 "segment rejected (no syncache entry)\n", 1144 s, __func__); 1145 goto failed; 1146 } 1147 bzero(&scs, sizeof(scs)); 1148 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1149 if (locked) 1150 SCH_UNLOCK(sch); 1151 if (sc == NULL) { 1152 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1153 log(LOG_DEBUG, "%s; %s: Segment failed " 1154 "SYNCOOKIE authentication, segment rejected " 1155 "(probably spoofed)\n", s, __func__); 1156 goto failed; 1157 } 1158 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1159 /* If received ACK has MD5 signature, check it. */ 1160 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1161 (!TCPMD5_ENABLED() || 1162 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1163 /* Drop the ACK. */ 1164 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1165 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1166 "MD5 signature doesn't match.\n", 1167 s, __func__); 1168 free(s, M_TCPLOG); 1169 } 1170 TCPSTAT_INC(tcps_sig_err_sigopt); 1171 return (-1); /* Do not send RST */ 1172 } 1173 #endif /* TCP_SIGNATURE */ 1174 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1175 } else { 1176 if (sc->sc_port != port) { 1177 SCH_UNLOCK(sch); 1178 return (0); 1179 } 1180 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1181 /* 1182 * If listening socket requested TCP digests, check that 1183 * received ACK has signature and it is correct. 1184 * If not, drop the ACK and leave sc entry in th cache, 1185 * because SYN was received with correct signature. 1186 */ 1187 if (sc->sc_flags & SCF_SIGNATURE) { 1188 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1189 /* No signature */ 1190 TCPSTAT_INC(tcps_sig_err_nosigopt); 1191 SCH_UNLOCK(sch); 1192 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1193 log(LOG_DEBUG, "%s; %s: Segment " 1194 "rejected, MD5 signature wasn't " 1195 "provided.\n", s, __func__); 1196 free(s, M_TCPLOG); 1197 } 1198 return (-1); /* Do not send RST */ 1199 } 1200 if (!TCPMD5_ENABLED() || 1201 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1202 /* Doesn't match or no SA */ 1203 SCH_UNLOCK(sch); 1204 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1205 log(LOG_DEBUG, "%s; %s: Segment " 1206 "rejected, MD5 signature doesn't " 1207 "match.\n", s, __func__); 1208 free(s, M_TCPLOG); 1209 } 1210 return (-1); /* Do not send RST */ 1211 } 1212 } 1213 #endif /* TCP_SIGNATURE */ 1214 1215 /* 1216 * RFC 7323 PAWS: If we have a timestamp on this segment and 1217 * it's less than ts_recent, drop it. 1218 * XXXMT: RFC 7323 also requires to send an ACK. 1219 * In tcp_input.c this is only done for TCP segments 1220 * with user data, so be consistent here and just drop 1221 * the segment. 1222 */ 1223 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1224 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1225 SCH_UNLOCK(sch); 1226 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1227 log(LOG_DEBUG, 1228 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1229 "segment dropped\n", s, __func__, 1230 to->to_tsval, sc->sc_tsreflect); 1231 free(s, M_TCPLOG); 1232 } 1233 return (-1); /* Do not send RST */ 1234 } 1235 1236 /* 1237 * If timestamps were not negotiated during SYN/ACK and a 1238 * segment with a timestamp is received, ignore the 1239 * timestamp and process the packet normally. 1240 * See section 3.2 of RFC 7323. 1241 */ 1242 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1243 (to->to_flags & TOF_TS)) { 1244 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1245 log(LOG_DEBUG, "%s; %s: Timestamp not " 1246 "expected, segment processed normally\n", 1247 s, __func__); 1248 free(s, M_TCPLOG); 1249 s = NULL; 1250 } 1251 } 1252 1253 /* 1254 * If timestamps were negotiated during SYN/ACK and a 1255 * segment without a timestamp is received, silently drop 1256 * the segment, unless the missing timestamps are tolerated. 1257 * See section 3.2 of RFC 7323. 1258 */ 1259 if ((sc->sc_flags & SCF_TIMESTAMP) && 1260 !(to->to_flags & TOF_TS)) { 1261 if (V_tcp_tolerate_missing_ts) { 1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1263 log(LOG_DEBUG, 1264 "%s; %s: Timestamp missing, " 1265 "segment processed normally\n", 1266 s, __func__); 1267 free(s, M_TCPLOG); 1268 } 1269 } else { 1270 SCH_UNLOCK(sch); 1271 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1272 log(LOG_DEBUG, 1273 "%s; %s: Timestamp missing, " 1274 "segment silently dropped\n", 1275 s, __func__); 1276 free(s, M_TCPLOG); 1277 } 1278 return (-1); /* Do not send RST */ 1279 } 1280 } 1281 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1282 sch->sch_length--; 1283 #ifdef TCP_OFFLOAD 1284 if (ADDED_BY_TOE(sc)) { 1285 struct toedev *tod = sc->sc_tod; 1286 1287 tod->tod_syncache_removed(tod, sc->sc_todctx); 1288 } 1289 #endif 1290 SCH_UNLOCK(sch); 1291 } 1292 1293 /* 1294 * Segment validation: 1295 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1296 */ 1297 if (th->th_ack != sc->sc_iss + 1) { 1298 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1299 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1300 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1301 goto failed; 1302 } 1303 1304 /* 1305 * The SEQ must fall in the window starting at the received 1306 * initial receive sequence number + 1 (the SYN). 1307 */ 1308 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1309 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1310 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1311 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1312 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1313 goto failed; 1314 } 1315 1316 *lsop = syncache_socket(sc, *lsop, m); 1317 1318 if (*lsop == NULL) 1319 TCPSTAT_INC(tcps_sc_aborted); 1320 else 1321 TCPSTAT_INC(tcps_sc_completed); 1322 1323 /* how do we find the inp for the new socket? */ 1324 if (sc != &scs) 1325 syncache_free(sc); 1326 return (1); 1327 failed: 1328 if (sc != NULL) { 1329 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1330 if (sc != &scs) 1331 syncache_free(sc); 1332 } 1333 if (s != NULL) 1334 free(s, M_TCPLOG); 1335 *lsop = NULL; 1336 return (0); 1337 } 1338 1339 static struct socket * 1340 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1341 uint64_t response_cookie) 1342 { 1343 struct inpcb *inp; 1344 struct tcpcb *tp; 1345 unsigned int *pending_counter; 1346 struct socket *so; 1347 1348 NET_EPOCH_ASSERT(); 1349 1350 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1351 so = syncache_socket(sc, lso, m); 1352 if (so == NULL) { 1353 TCPSTAT_INC(tcps_sc_aborted); 1354 atomic_subtract_int(pending_counter, 1); 1355 } else { 1356 soisconnected(so); 1357 inp = sotoinpcb(so); 1358 tp = intotcpcb(inp); 1359 tp->t_flags |= TF_FASTOPEN; 1360 tp->t_tfo_cookie.server = response_cookie; 1361 tp->snd_max = tp->iss; 1362 tp->snd_nxt = tp->iss; 1363 tp->t_tfo_pending = pending_counter; 1364 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1365 TCPSTAT_INC(tcps_sc_completed); 1366 } 1367 1368 return (so); 1369 } 1370 1371 /* 1372 * Given a LISTEN socket and an inbound SYN request, add 1373 * this to the syn cache, and send back a segment: 1374 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1375 * to the source. 1376 * 1377 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1378 * Doing so would require that we hold onto the data and deliver it 1379 * to the application. However, if we are the target of a SYN-flood 1380 * DoS attack, an attacker could send data which would eventually 1381 * consume all available buffer space if it were ACKed. By not ACKing 1382 * the data, we avoid this DoS scenario. 1383 * 1384 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1385 * cookie is processed and a new socket is created. In this case, any data 1386 * accompanying the SYN will be queued to the socket by tcp_input() and will 1387 * be ACKed either when the application sends response data or the delayed 1388 * ACK timer expires, whichever comes first. 1389 */ 1390 struct socket * 1391 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1392 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1393 void *todctx, uint8_t iptos, uint16_t port) 1394 { 1395 struct tcpcb *tp; 1396 struct socket *rv = NULL; 1397 struct syncache *sc = NULL; 1398 struct syncache_head *sch; 1399 struct mbuf *ipopts = NULL; 1400 u_int ltflags; 1401 int win, ip_ttl, ip_tos; 1402 char *s; 1403 #ifdef INET6 1404 int autoflowlabel = 0; 1405 #endif 1406 #ifdef MAC 1407 struct label *maclabel; 1408 #endif 1409 struct syncache scs; 1410 struct ucred *cred; 1411 uint64_t tfo_response_cookie; 1412 unsigned int *tfo_pending = NULL; 1413 int tfo_cookie_valid = 0; 1414 int tfo_response_cookie_valid = 0; 1415 bool locked; 1416 1417 INP_RLOCK_ASSERT(inp); /* listen socket */ 1418 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1419 ("%s: unexpected tcp flags", __func__)); 1420 1421 /* 1422 * Combine all so/tp operations very early to drop the INP lock as 1423 * soon as possible. 1424 */ 1425 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1426 tp = sototcpcb(so); 1427 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1428 1429 #ifdef INET6 1430 if (inc->inc_flags & INC_ISIPV6) { 1431 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1432 autoflowlabel = 1; 1433 } 1434 ip_ttl = in6_selecthlim(inp, NULL); 1435 if ((inp->in6p_outputopts == NULL) || 1436 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1437 ip_tos = 0; 1438 } else { 1439 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1440 } 1441 } 1442 #endif 1443 #if defined(INET6) && defined(INET) 1444 else 1445 #endif 1446 #ifdef INET 1447 { 1448 ip_ttl = inp->inp_ip_ttl; 1449 ip_tos = inp->inp_ip_tos; 1450 } 1451 #endif 1452 win = so->sol_sbrcv_hiwat; 1453 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1454 1455 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1456 (tp->t_tfo_pending != NULL) && 1457 (to->to_flags & TOF_FASTOPEN)) { 1458 /* 1459 * Limit the number of pending TFO connections to 1460 * approximately half of the queue limit. This prevents TFO 1461 * SYN floods from starving the service by filling the 1462 * listen queue with bogus TFO connections. 1463 */ 1464 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1465 (so->sol_qlimit / 2)) { 1466 int result; 1467 1468 result = tcp_fastopen_check_cookie(inc, 1469 to->to_tfo_cookie, to->to_tfo_len, 1470 &tfo_response_cookie); 1471 tfo_cookie_valid = (result > 0); 1472 tfo_response_cookie_valid = (result >= 0); 1473 } 1474 1475 /* 1476 * Remember the TFO pending counter as it will have to be 1477 * decremented below if we don't make it to syncache_tfo_expand(). 1478 */ 1479 tfo_pending = tp->t_tfo_pending; 1480 } 1481 1482 #ifdef MAC 1483 if (mac_syncache_init(&maclabel) != 0) { 1484 INP_RUNLOCK(inp); 1485 goto done; 1486 } else 1487 mac_syncache_create(maclabel, inp); 1488 #endif 1489 if (!tfo_cookie_valid) 1490 INP_RUNLOCK(inp); 1491 1492 /* 1493 * Remember the IP options, if any. 1494 */ 1495 #ifdef INET6 1496 if (!(inc->inc_flags & INC_ISIPV6)) 1497 #endif 1498 #ifdef INET 1499 ipopts = (m) ? ip_srcroute(m) : NULL; 1500 #else 1501 ipopts = NULL; 1502 #endif 1503 1504 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1505 /* 1506 * When the socket is TCP-MD5 enabled check that, 1507 * - a signed packet is valid 1508 * - a non-signed packet does not have a security association 1509 * 1510 * If a signed packet fails validation or a non-signed packet has a 1511 * security association, the packet will be dropped. 1512 */ 1513 if (ltflags & TF_SIGNATURE) { 1514 if (to->to_flags & TOF_SIGNATURE) { 1515 if (!TCPMD5_ENABLED() || 1516 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1517 goto done; 1518 } else { 1519 if (TCPMD5_ENABLED() && 1520 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1521 goto done; 1522 } 1523 } else if (to->to_flags & TOF_SIGNATURE) 1524 goto done; 1525 #endif /* TCP_SIGNATURE */ 1526 /* 1527 * See if we already have an entry for this connection. 1528 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1529 * 1530 * XXX: should the syncache be re-initialized with the contents 1531 * of the new SYN here (which may have different options?) 1532 * 1533 * XXX: We do not check the sequence number to see if this is a 1534 * real retransmit or a new connection attempt. The question is 1535 * how to handle such a case; either ignore it as spoofed, or 1536 * drop the current entry and create a new one? 1537 */ 1538 if (syncache_cookiesonly()) { 1539 sc = NULL; 1540 sch = syncache_hashbucket(inc); 1541 locked = false; 1542 } else { 1543 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1544 locked = true; 1545 SCH_LOCK_ASSERT(sch); 1546 } 1547 if (sc != NULL) { 1548 if (tfo_cookie_valid) 1549 INP_RUNLOCK(inp); 1550 TCPSTAT_INC(tcps_sc_dupsyn); 1551 if (ipopts) { 1552 /* 1553 * If we were remembering a previous source route, 1554 * forget it and use the new one we've been given. 1555 */ 1556 if (sc->sc_ipopts) 1557 (void) m_free(sc->sc_ipopts); 1558 sc->sc_ipopts = ipopts; 1559 } 1560 /* 1561 * Update timestamp if present. 1562 */ 1563 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1564 sc->sc_tsreflect = to->to_tsval; 1565 else 1566 sc->sc_flags &= ~SCF_TIMESTAMP; 1567 /* 1568 * Disable ECN if needed. 1569 */ 1570 if ((sc->sc_flags & SCF_ECN) && 1571 ((tcp_get_flags(th) & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1572 sc->sc_flags &= ~SCF_ECN; 1573 } 1574 #ifdef MAC 1575 /* 1576 * Since we have already unconditionally allocated label 1577 * storage, free it up. The syncache entry will already 1578 * have an initialized label we can use. 1579 */ 1580 mac_syncache_destroy(&maclabel); 1581 #endif 1582 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1583 /* Retransmit SYN|ACK and reset retransmit count. */ 1584 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1585 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1586 "resetting timer and retransmitting SYN|ACK\n", 1587 s, __func__); 1588 free(s, M_TCPLOG); 1589 } 1590 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1591 sc->sc_rxmits = 0; 1592 syncache_timeout(sc, sch, 1); 1593 TCPSTAT_INC(tcps_sndacks); 1594 TCPSTAT_INC(tcps_sndtotal); 1595 } 1596 SCH_UNLOCK(sch); 1597 goto donenoprobe; 1598 } 1599 1600 if (tfo_cookie_valid) { 1601 bzero(&scs, sizeof(scs)); 1602 sc = &scs; 1603 goto skip_alloc; 1604 } 1605 1606 /* 1607 * Skip allocating a syncache entry if we are just going to discard 1608 * it later. 1609 */ 1610 if (!locked) { 1611 bzero(&scs, sizeof(scs)); 1612 sc = &scs; 1613 } else 1614 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1615 if (sc == NULL) { 1616 /* 1617 * The zone allocator couldn't provide more entries. 1618 * Treat this as if the cache was full; drop the oldest 1619 * entry and insert the new one. 1620 */ 1621 TCPSTAT_INC(tcps_sc_zonefail); 1622 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1623 sch->sch_last_overflow = time_uptime; 1624 syncache_drop(sc, sch); 1625 syncache_pause(inc); 1626 } 1627 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1628 if (sc == NULL) { 1629 if (V_tcp_syncookies) { 1630 bzero(&scs, sizeof(scs)); 1631 sc = &scs; 1632 } else { 1633 KASSERT(locked, 1634 ("%s: bucket unexpectedly unlocked", 1635 __func__)); 1636 SCH_UNLOCK(sch); 1637 if (ipopts) 1638 (void) m_free(ipopts); 1639 goto done; 1640 } 1641 } 1642 } 1643 1644 skip_alloc: 1645 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1646 sc->sc_tfo_cookie = &tfo_response_cookie; 1647 1648 /* 1649 * Fill in the syncache values. 1650 */ 1651 #ifdef MAC 1652 sc->sc_label = maclabel; 1653 #endif 1654 sc->sc_cred = cred; 1655 sc->sc_port = port; 1656 cred = NULL; 1657 sc->sc_ipopts = ipopts; 1658 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1659 sc->sc_ip_tos = ip_tos; 1660 sc->sc_ip_ttl = ip_ttl; 1661 #ifdef TCP_OFFLOAD 1662 sc->sc_tod = tod; 1663 sc->sc_todctx = todctx; 1664 #endif 1665 sc->sc_irs = th->th_seq; 1666 sc->sc_flags = 0; 1667 sc->sc_flowlabel = 0; 1668 1669 /* 1670 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1671 * win was derived from socket earlier in the function. 1672 */ 1673 win = imax(win, 0); 1674 win = imin(win, TCP_MAXWIN); 1675 sc->sc_wnd = win; 1676 1677 if (V_tcp_do_rfc1323 && 1678 !(ltflags & TF_NOOPT)) { 1679 /* 1680 * A timestamp received in a SYN makes 1681 * it ok to send timestamp requests and replies. 1682 */ 1683 if (to->to_flags & TOF_TS) { 1684 sc->sc_tsreflect = to->to_tsval; 1685 sc->sc_flags |= SCF_TIMESTAMP; 1686 sc->sc_tsoff = tcp_new_ts_offset(inc); 1687 } 1688 if (to->to_flags & TOF_SCALE) { 1689 int wscale = 0; 1690 1691 /* 1692 * Pick the smallest possible scaling factor that 1693 * will still allow us to scale up to sb_max, aka 1694 * kern.ipc.maxsockbuf. 1695 * 1696 * We do this because there are broken firewalls that 1697 * will corrupt the window scale option, leading to 1698 * the other endpoint believing that our advertised 1699 * window is unscaled. At scale factors larger than 1700 * 5 the unscaled window will drop below 1500 bytes, 1701 * leading to serious problems when traversing these 1702 * broken firewalls. 1703 * 1704 * With the default maxsockbuf of 256K, a scale factor 1705 * of 3 will be chosen by this algorithm. Those who 1706 * choose a larger maxsockbuf should watch out 1707 * for the compatibility problems mentioned above. 1708 * 1709 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1710 * or <SYN,ACK>) segment itself is never scaled. 1711 */ 1712 while (wscale < TCP_MAX_WINSHIFT && 1713 (TCP_MAXWIN << wscale) < sb_max) 1714 wscale++; 1715 sc->sc_requested_r_scale = wscale; 1716 sc->sc_requested_s_scale = to->to_wscale; 1717 sc->sc_flags |= SCF_WINSCALE; 1718 } 1719 } 1720 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1721 /* 1722 * If incoming packet has an MD5 signature, flag this in the 1723 * syncache so that syncache_respond() will do the right thing 1724 * with the SYN+ACK. 1725 */ 1726 if (to->to_flags & TOF_SIGNATURE) 1727 sc->sc_flags |= SCF_SIGNATURE; 1728 #endif /* TCP_SIGNATURE */ 1729 if (to->to_flags & TOF_SACKPERM) 1730 sc->sc_flags |= SCF_SACK; 1731 if (to->to_flags & TOF_MSS) 1732 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1733 if (ltflags & TF_NOOPT) 1734 sc->sc_flags |= SCF_NOOPT; 1735 /* ECN Handshake */ 1736 if (V_tcp_do_ecn) 1737 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1738 1739 if (V_tcp_syncookies) 1740 sc->sc_iss = syncookie_generate(sch, sc); 1741 else 1742 sc->sc_iss = arc4random(); 1743 #ifdef INET6 1744 if (autoflowlabel) { 1745 if (V_tcp_syncookies) 1746 sc->sc_flowlabel = sc->sc_iss; 1747 else 1748 sc->sc_flowlabel = ip6_randomflowlabel(); 1749 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1750 } 1751 #endif 1752 if (locked) 1753 SCH_UNLOCK(sch); 1754 1755 if (tfo_cookie_valid) { 1756 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1757 /* INP_RUNLOCK(inp) will be performed by the caller */ 1758 goto tfo_expanded; 1759 } 1760 1761 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1762 /* 1763 * Do a standard 3-way handshake. 1764 */ 1765 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1766 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1767 syncache_free(sc); 1768 else if (sc != &scs) 1769 syncache_insert(sc, sch); /* locks and unlocks sch */ 1770 TCPSTAT_INC(tcps_sndacks); 1771 TCPSTAT_INC(tcps_sndtotal); 1772 } else { 1773 if (sc != &scs) 1774 syncache_free(sc); 1775 TCPSTAT_INC(tcps_sc_dropped); 1776 } 1777 goto donenoprobe; 1778 1779 done: 1780 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1781 donenoprobe: 1782 if (m) 1783 m_freem(m); 1784 /* 1785 * If tfo_pending is not NULL here, then a TFO SYN that did not 1786 * result in a new socket was processed and the associated pending 1787 * counter has not yet been decremented. All such TFO processing paths 1788 * transit this point. 1789 */ 1790 if (tfo_pending != NULL) 1791 tcp_fastopen_decrement_counter(tfo_pending); 1792 1793 tfo_expanded: 1794 if (cred != NULL) 1795 crfree(cred); 1796 #ifdef MAC 1797 if (sc == &scs) 1798 mac_syncache_destroy(&maclabel); 1799 #endif 1800 return (rv); 1801 } 1802 1803 /* 1804 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1805 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1806 */ 1807 static int 1808 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1809 { 1810 struct ip *ip = NULL; 1811 struct mbuf *m; 1812 struct tcphdr *th = NULL; 1813 struct udphdr *udp = NULL; 1814 int optlen, error = 0; /* Make compiler happy */ 1815 u_int16_t hlen, tlen, mssopt, ulen; 1816 struct tcpopt to; 1817 #ifdef INET6 1818 struct ip6_hdr *ip6 = NULL; 1819 #endif 1820 1821 NET_EPOCH_ASSERT(); 1822 1823 hlen = 1824 #ifdef INET6 1825 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1826 #endif 1827 sizeof(struct ip); 1828 tlen = hlen + sizeof(struct tcphdr); 1829 if (sc->sc_port) { 1830 tlen += sizeof(struct udphdr); 1831 } 1832 /* Determine MSS we advertize to other end of connection. */ 1833 mssopt = tcp_mssopt(&sc->sc_inc); 1834 if (sc->sc_port) 1835 mssopt -= V_tcp_udp_tunneling_overhead; 1836 mssopt = max(mssopt, V_tcp_minmss); 1837 1838 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1839 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1840 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1841 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1842 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1843 1844 /* Create the IP+TCP header from scratch. */ 1845 m = m_gethdr(M_NOWAIT, MT_DATA); 1846 if (m == NULL) 1847 return (ENOBUFS); 1848 #ifdef MAC 1849 mac_syncache_create_mbuf(sc->sc_label, m); 1850 #endif 1851 m->m_data += max_linkhdr; 1852 m->m_len = tlen; 1853 m->m_pkthdr.len = tlen; 1854 m->m_pkthdr.rcvif = NULL; 1855 1856 #ifdef INET6 1857 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1858 ip6 = mtod(m, struct ip6_hdr *); 1859 ip6->ip6_vfc = IPV6_VERSION; 1860 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1861 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1862 ip6->ip6_plen = htons(tlen - hlen); 1863 /* ip6_hlim is set after checksum */ 1864 /* Zero out traffic class and flow label. */ 1865 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1866 ip6->ip6_flow |= sc->sc_flowlabel; 1867 if (sc->sc_port != 0) { 1868 ip6->ip6_nxt = IPPROTO_UDP; 1869 udp = (struct udphdr *)(ip6 + 1); 1870 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1871 udp->uh_dport = sc->sc_port; 1872 ulen = (tlen - sizeof(struct ip6_hdr)); 1873 th = (struct tcphdr *)(udp + 1); 1874 } else { 1875 ip6->ip6_nxt = IPPROTO_TCP; 1876 th = (struct tcphdr *)(ip6 + 1); 1877 } 1878 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1879 } 1880 #endif 1881 #if defined(INET6) && defined(INET) 1882 else 1883 #endif 1884 #ifdef INET 1885 { 1886 ip = mtod(m, struct ip *); 1887 ip->ip_v = IPVERSION; 1888 ip->ip_hl = sizeof(struct ip) >> 2; 1889 ip->ip_len = htons(tlen); 1890 ip->ip_id = 0; 1891 ip->ip_off = 0; 1892 ip->ip_sum = 0; 1893 ip->ip_src = sc->sc_inc.inc_laddr; 1894 ip->ip_dst = sc->sc_inc.inc_faddr; 1895 ip->ip_ttl = sc->sc_ip_ttl; 1896 ip->ip_tos = sc->sc_ip_tos; 1897 1898 /* 1899 * See if we should do MTU discovery. Route lookups are 1900 * expensive, so we will only unset the DF bit if: 1901 * 1902 * 1) path_mtu_discovery is disabled 1903 * 2) the SCF_UNREACH flag has been set 1904 */ 1905 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1906 ip->ip_off |= htons(IP_DF); 1907 if (sc->sc_port == 0) { 1908 ip->ip_p = IPPROTO_TCP; 1909 th = (struct tcphdr *)(ip + 1); 1910 } else { 1911 ip->ip_p = IPPROTO_UDP; 1912 udp = (struct udphdr *)(ip + 1); 1913 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1914 udp->uh_dport = sc->sc_port; 1915 ulen = (tlen - sizeof(struct ip)); 1916 th = (struct tcphdr *)(udp + 1); 1917 } 1918 } 1919 #endif /* INET */ 1920 th->th_sport = sc->sc_inc.inc_lport; 1921 th->th_dport = sc->sc_inc.inc_fport; 1922 1923 if (flags & TH_SYN) 1924 th->th_seq = htonl(sc->sc_iss); 1925 else 1926 th->th_seq = htonl(sc->sc_iss + 1); 1927 th->th_ack = htonl(sc->sc_irs + 1); 1928 th->th_off = sizeof(struct tcphdr) >> 2; 1929 th->th_win = htons(sc->sc_wnd); 1930 th->th_urp = 0; 1931 1932 flags = tcp_ecn_syncache_respond(flags, sc); 1933 tcp_set_flags(th, flags); 1934 1935 /* Tack on the TCP options. */ 1936 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1937 to.to_flags = 0; 1938 1939 if (flags & TH_SYN) { 1940 to.to_mss = mssopt; 1941 to.to_flags = TOF_MSS; 1942 if (sc->sc_flags & SCF_WINSCALE) { 1943 to.to_wscale = sc->sc_requested_r_scale; 1944 to.to_flags |= TOF_SCALE; 1945 } 1946 if (sc->sc_flags & SCF_SACK) 1947 to.to_flags |= TOF_SACKPERM; 1948 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1949 if (sc->sc_flags & SCF_SIGNATURE) 1950 to.to_flags |= TOF_SIGNATURE; 1951 #endif 1952 if (sc->sc_tfo_cookie) { 1953 to.to_flags |= TOF_FASTOPEN; 1954 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1955 to.to_tfo_cookie = sc->sc_tfo_cookie; 1956 /* don't send cookie again when retransmitting response */ 1957 sc->sc_tfo_cookie = NULL; 1958 } 1959 } 1960 if (sc->sc_flags & SCF_TIMESTAMP) { 1961 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1962 to.to_tsecr = sc->sc_tsreflect; 1963 to.to_flags |= TOF_TS; 1964 } 1965 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1966 1967 /* Adjust headers by option size. */ 1968 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1969 m->m_len += optlen; 1970 m->m_pkthdr.len += optlen; 1971 #ifdef INET6 1972 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1973 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1974 else 1975 #endif 1976 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1977 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1978 if (sc->sc_flags & SCF_SIGNATURE) { 1979 KASSERT(to.to_flags & TOF_SIGNATURE, 1980 ("tcp_addoptions() didn't set tcp_signature")); 1981 1982 /* NOTE: to.to_signature is inside of mbuf */ 1983 if (!TCPMD5_ENABLED() || 1984 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1985 m_freem(m); 1986 return (EACCES); 1987 } 1988 } 1989 #endif 1990 } else 1991 optlen = 0; 1992 1993 if (udp) { 1994 ulen += optlen; 1995 udp->uh_ulen = htons(ulen); 1996 } 1997 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1998 /* 1999 * If we have peer's SYN and it has a flowid, then let's assign it to 2000 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2001 * to SYN|ACK due to lack of inp here. 2002 */ 2003 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2004 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2005 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2006 } 2007 #ifdef INET6 2008 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2009 if (sc->sc_port) { 2010 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2011 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2012 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2013 IPPROTO_UDP, 0); 2014 th->th_sum = htons(0); 2015 } else { 2016 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2017 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2018 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2019 IPPROTO_TCP, 0); 2020 } 2021 ip6->ip6_hlim = sc->sc_ip_ttl; 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, ip6, NULL, th); 2032 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2033 } 2034 #endif 2035 #if defined(INET6) && defined(INET) 2036 else 2037 #endif 2038 #ifdef INET 2039 { 2040 if (sc->sc_port) { 2041 m->m_pkthdr.csum_flags = CSUM_UDP; 2042 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2043 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2044 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2045 th->th_sum = htons(0); 2046 } else { 2047 m->m_pkthdr.csum_flags = CSUM_TCP; 2048 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2049 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2050 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2051 } 2052 #ifdef TCP_OFFLOAD 2053 if (ADDED_BY_TOE(sc)) { 2054 struct toedev *tod = sc->sc_tod; 2055 2056 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2057 2058 return (error); 2059 } 2060 #endif 2061 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2062 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2063 } 2064 #endif 2065 return (error); 2066 } 2067 2068 /* 2069 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2070 * that exceed the capacity of the syncache by avoiding the storage of any 2071 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2072 * attacks where the attacker does not have access to our responses. 2073 * 2074 * Syncookies encode and include all necessary information about the 2075 * connection setup within the SYN|ACK that we send back. That way we 2076 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2077 * (if ever). Normally the syncache and syncookies are running in parallel 2078 * with the latter taking over when the former is exhausted. When matching 2079 * syncache entry is found the syncookie is ignored. 2080 * 2081 * The only reliable information persisting the 3WHS is our initial sequence 2082 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2083 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2084 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2085 * returns and signifies a legitimate connection if it matches the ACK. 2086 * 2087 * The available space of 32 bits to store the hash and to encode the SYN 2088 * option information is very tight and we should have at least 24 bits for 2089 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2090 * 2091 * SYN option information we have to encode to fully restore a connection: 2092 * MSS: is imporant to chose an optimal segment size to avoid IP level 2093 * fragmentation along the path. The common MSS values can be encoded 2094 * in a 3-bit table. Uncommon values are captured by the next lower value 2095 * in the table leading to a slight increase in packetization overhead. 2096 * WSCALE: is necessary to allow large windows to be used for high delay- 2097 * bandwidth product links. Not scaling the window when it was initially 2098 * negotiated is bad for performance as lack of scaling further decreases 2099 * the apparent available send window. We only need to encode the WSCALE 2100 * we received from the remote end. Our end can be recalculated at any 2101 * time. The common WSCALE values can be encoded in a 3-bit table. 2102 * Uncommon values are captured by the next lower value in the table 2103 * making us under-estimate the available window size halving our 2104 * theoretically possible maximum throughput for that connection. 2105 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2106 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2107 * that are included in all segments on a connection. We enable them when 2108 * the ACK has them. 2109 * 2110 * Security of syncookies and attack vectors: 2111 * 2112 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2113 * together with the gloabl secret to make it unique per connection attempt. 2114 * Thus any change of any of those parameters results in a different MAC output 2115 * in an unpredictable way unless a collision is encountered. 24 bits of the 2116 * MAC are embedded into the ISS. 2117 * 2118 * To prevent replay attacks two rotating global secrets are updated with a 2119 * new random value every 15 seconds. The life-time of a syncookie is thus 2120 * 15-30 seconds. 2121 * 2122 * Vector 1: Attacking the secret. This requires finding a weakness in the 2123 * MAC itself or the way it is used here. The attacker can do a chosen plain 2124 * text attack by varying and testing the all parameters under his control. 2125 * The strength depends on the size and randomness of the secret, and the 2126 * cryptographic security of the MAC function. Due to the constant updating 2127 * of the secret the attacker has at most 29.999 seconds to find the secret 2128 * and launch spoofed connections. After that he has to start all over again. 2129 * 2130 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2131 * size an average of 4,823 attempts are required for a 50% chance of success 2132 * to spoof a single syncookie (birthday collision paradox). However the 2133 * attacker is blind and doesn't know if one of his attempts succeeded unless 2134 * he has a side channel to interfere success from. A single connection setup 2135 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2136 * This many attempts are required for each one blind spoofed connection. For 2137 * every additional spoofed connection he has to launch another N attempts. 2138 * Thus for a sustained rate 100 spoofed connections per second approximately 2139 * 1,800,000 packets per second would have to be sent. 2140 * 2141 * NB: The MAC function should be fast so that it doesn't become a CPU 2142 * exhaustion attack vector itself. 2143 * 2144 * References: 2145 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2146 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2147 * http://cr.yp.to/syncookies.html (overview) 2148 * http://cr.yp.to/syncookies/archive (details) 2149 * 2150 * 2151 * Schematic construction of a syncookie enabled Initial Sequence Number: 2152 * 0 1 2 3 2153 * 12345678901234567890123456789012 2154 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2155 * 2156 * x 24 MAC (truncated) 2157 * W 3 Send Window Scale index 2158 * M 3 MSS index 2159 * S 1 SACK permitted 2160 * P 1 Odd/even secret 2161 */ 2162 2163 /* 2164 * Distribution and probability of certain MSS values. Those in between are 2165 * rounded down to the next lower one. 2166 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2167 * .2% .3% 5% 7% 7% 20% 15% 45% 2168 */ 2169 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2170 2171 /* 2172 * Distribution and probability of certain WSCALE values. We have to map the 2173 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2174 * bits based on prevalence of certain values. Where we don't have an exact 2175 * match for are rounded down to the next lower one letting us under-estimate 2176 * the true available window. At the moment this would happen only for the 2177 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2178 * and window size). The absence of the WSCALE option (no scaling in either 2179 * direction) is encoded with index zero. 2180 * [WSCALE values histograms, Allman, 2012] 2181 * X 10 10 35 5 6 14 10% by host 2182 * X 11 4 5 5 18 49 3% by connections 2183 */ 2184 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2185 2186 /* 2187 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2188 * and good cryptographic properties. 2189 */ 2190 static uint32_t 2191 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2192 uint8_t *secbits, uintptr_t secmod) 2193 { 2194 SIPHASH_CTX ctx; 2195 uint32_t siphash[2]; 2196 2197 SipHash24_Init(&ctx); 2198 SipHash_SetKey(&ctx, secbits); 2199 switch (inc->inc_flags & INC_ISIPV6) { 2200 #ifdef INET 2201 case 0: 2202 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2203 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2204 break; 2205 #endif 2206 #ifdef INET6 2207 case INC_ISIPV6: 2208 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2209 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2210 break; 2211 #endif 2212 } 2213 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2214 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2215 SipHash_Update(&ctx, &irs, sizeof(irs)); 2216 SipHash_Update(&ctx, &flags, sizeof(flags)); 2217 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2218 SipHash_Final((u_int8_t *)&siphash, &ctx); 2219 2220 return (siphash[0] ^ siphash[1]); 2221 } 2222 2223 static tcp_seq 2224 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2225 { 2226 u_int i, secbit, wscale; 2227 uint32_t iss, hash; 2228 uint8_t *secbits; 2229 union syncookie cookie; 2230 2231 cookie.cookie = 0; 2232 2233 /* Map our computed MSS into the 3-bit index. */ 2234 for (i = nitems(tcp_sc_msstab) - 1; 2235 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2236 i--) 2237 ; 2238 cookie.flags.mss_idx = i; 2239 2240 /* 2241 * Map the send window scale into the 3-bit index but only if 2242 * the wscale option was received. 2243 */ 2244 if (sc->sc_flags & SCF_WINSCALE) { 2245 wscale = sc->sc_requested_s_scale; 2246 for (i = nitems(tcp_sc_wstab) - 1; 2247 tcp_sc_wstab[i] > wscale && i > 0; 2248 i--) 2249 ; 2250 cookie.flags.wscale_idx = i; 2251 } 2252 2253 /* Can we do SACK? */ 2254 if (sc->sc_flags & SCF_SACK) 2255 cookie.flags.sack_ok = 1; 2256 2257 /* Which of the two secrets to use. */ 2258 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2259 cookie.flags.odd_even = secbit; 2260 2261 secbits = V_tcp_syncache.secret.key[secbit]; 2262 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2263 (uintptr_t)sch); 2264 2265 /* 2266 * Put the flags into the hash and XOR them to get better ISS number 2267 * variance. This doesn't enhance the cryptographic strength and is 2268 * done to prevent the 8 cookie bits from showing up directly on the 2269 * wire. 2270 */ 2271 iss = hash & ~0xff; 2272 iss |= cookie.cookie ^ (hash >> 24); 2273 2274 TCPSTAT_INC(tcps_sc_sendcookie); 2275 return (iss); 2276 } 2277 2278 static struct syncache * 2279 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2280 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2281 struct socket *lso, uint16_t port) 2282 { 2283 uint32_t hash; 2284 uint8_t *secbits; 2285 tcp_seq ack, seq; 2286 int wnd, wscale = 0; 2287 union syncookie cookie; 2288 2289 /* 2290 * Pull information out of SYN-ACK/ACK and revert sequence number 2291 * advances. 2292 */ 2293 ack = th->th_ack - 1; 2294 seq = th->th_seq - 1; 2295 2296 /* 2297 * Unpack the flags containing enough information to restore the 2298 * connection. 2299 */ 2300 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2301 2302 /* Which of the two secrets to use. */ 2303 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2304 2305 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2306 2307 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2308 if ((ack & ~0xff) != (hash & ~0xff)) 2309 return (NULL); 2310 2311 /* Fill in the syncache values. */ 2312 sc->sc_flags = 0; 2313 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2314 sc->sc_ipopts = NULL; 2315 2316 sc->sc_irs = seq; 2317 sc->sc_iss = ack; 2318 2319 switch (inc->inc_flags & INC_ISIPV6) { 2320 #ifdef INET 2321 case 0: 2322 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2323 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2324 break; 2325 #endif 2326 #ifdef INET6 2327 case INC_ISIPV6: 2328 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2329 sc->sc_flowlabel = 2330 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2331 break; 2332 #endif 2333 } 2334 2335 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2336 2337 /* We can simply recompute receive window scale we sent earlier. */ 2338 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2339 wscale++; 2340 2341 /* Only use wscale if it was enabled in the orignal SYN. */ 2342 if (cookie.flags.wscale_idx > 0) { 2343 sc->sc_requested_r_scale = wscale; 2344 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2345 sc->sc_flags |= SCF_WINSCALE; 2346 } 2347 2348 wnd = lso->sol_sbrcv_hiwat; 2349 wnd = imax(wnd, 0); 2350 wnd = imin(wnd, TCP_MAXWIN); 2351 sc->sc_wnd = wnd; 2352 2353 if (cookie.flags.sack_ok) 2354 sc->sc_flags |= SCF_SACK; 2355 2356 if (to->to_flags & TOF_TS) { 2357 sc->sc_flags |= SCF_TIMESTAMP; 2358 sc->sc_tsreflect = to->to_tsval; 2359 sc->sc_tsoff = tcp_new_ts_offset(inc); 2360 } 2361 2362 if (to->to_flags & TOF_SIGNATURE) 2363 sc->sc_flags |= SCF_SIGNATURE; 2364 2365 sc->sc_rxmits = 0; 2366 2367 sc->sc_port = port; 2368 2369 TCPSTAT_INC(tcps_sc_recvcookie); 2370 return (sc); 2371 } 2372 2373 #ifdef INVARIANTS 2374 static int 2375 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2376 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2377 struct socket *lso, uint16_t port) 2378 { 2379 struct syncache scs, *scx; 2380 char *s; 2381 2382 bzero(&scs, sizeof(scs)); 2383 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2384 2385 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2386 return (0); 2387 2388 if (scx != NULL) { 2389 if (sc->sc_peer_mss != scx->sc_peer_mss) 2390 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2391 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2392 2393 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2394 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2395 s, __func__, sc->sc_requested_r_scale, 2396 scx->sc_requested_r_scale); 2397 2398 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2399 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2400 s, __func__, sc->sc_requested_s_scale, 2401 scx->sc_requested_s_scale); 2402 2403 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2404 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2405 } 2406 2407 if (s != NULL) 2408 free(s, M_TCPLOG); 2409 return (0); 2410 } 2411 #endif /* INVARIANTS */ 2412 2413 static void 2414 syncookie_reseed(void *arg) 2415 { 2416 struct tcp_syncache *sc = arg; 2417 uint8_t *secbits; 2418 int secbit; 2419 2420 /* 2421 * Reseeding the secret doesn't have to be protected by a lock. 2422 * It only must be ensured that the new random values are visible 2423 * to all CPUs in a SMP environment. The atomic with release 2424 * semantics ensures that. 2425 */ 2426 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2427 secbits = sc->secret.key[secbit]; 2428 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2429 atomic_add_rel_int(&sc->secret.oddeven, 1); 2430 2431 /* Reschedule ourself. */ 2432 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2433 } 2434 2435 /* 2436 * We have overflowed a bucket. Let's pause dealing with the syncache. 2437 * This function will increment the bucketoverflow statistics appropriately 2438 * (once per pause when pausing is enabled; otherwise, once per overflow). 2439 */ 2440 static void 2441 syncache_pause(struct in_conninfo *inc) 2442 { 2443 time_t delta; 2444 const char *s; 2445 2446 /* XXX: 2447 * 2. Add sysctl read here so we don't get the benefit of this 2448 * change without the new sysctl. 2449 */ 2450 2451 /* 2452 * Try an unlocked read. If we already know that another thread 2453 * has activated the feature, there is no need to proceed. 2454 */ 2455 if (V_tcp_syncache.paused) 2456 return; 2457 2458 /* Are cookied enabled? If not, we can't pause. */ 2459 if (!V_tcp_syncookies) { 2460 TCPSTAT_INC(tcps_sc_bucketoverflow); 2461 return; 2462 } 2463 2464 /* 2465 * We may be the first thread to find an overflow. Get the lock 2466 * and evaluate if we need to take action. 2467 */ 2468 mtx_lock(&V_tcp_syncache.pause_mtx); 2469 if (V_tcp_syncache.paused) { 2470 mtx_unlock(&V_tcp_syncache.pause_mtx); 2471 return; 2472 } 2473 2474 /* Activate protection. */ 2475 V_tcp_syncache.paused = true; 2476 TCPSTAT_INC(tcps_sc_bucketoverflow); 2477 2478 /* 2479 * Determine the last backoff time. If we are seeing a re-newed 2480 * attack within that same time after last reactivating the syncache, 2481 * consider it an extension of the same attack. 2482 */ 2483 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2484 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2485 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2486 delta <<= 1; 2487 V_tcp_syncache.pause_backoff++; 2488 } 2489 } else { 2490 delta = TCP_SYNCACHE_PAUSE_TIME; 2491 V_tcp_syncache.pause_backoff = 0; 2492 } 2493 2494 /* Log a warning, including IP addresses, if able. */ 2495 if (inc != NULL) 2496 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2497 else 2498 s = (const char *)NULL; 2499 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2500 "the next %lld seconds%s%s%s\n", (long long)delta, 2501 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2502 (s != NULL) ? ")" : ""); 2503 free(__DECONST(void *, s), M_TCPLOG); 2504 2505 /* Use the calculated delta to set a new pause time. */ 2506 V_tcp_syncache.pause_until = time_uptime + delta; 2507 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2508 &V_tcp_syncache); 2509 mtx_unlock(&V_tcp_syncache.pause_mtx); 2510 } 2511 2512 /* Evaluate whether we need to unpause. */ 2513 static void 2514 syncache_unpause(void *arg) 2515 { 2516 struct tcp_syncache *sc; 2517 time_t delta; 2518 2519 sc = arg; 2520 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2521 callout_deactivate(&sc->pause_co); 2522 2523 /* 2524 * Check to make sure we are not running early. If the pause 2525 * time has expired, then deactivate the protection. 2526 */ 2527 if ((delta = sc->pause_until - time_uptime) > 0) 2528 callout_schedule(&sc->pause_co, delta * hz); 2529 else 2530 sc->paused = false; 2531 } 2532 2533 /* 2534 * Exports the syncache entries to userland so that netstat can display 2535 * them alongside the other sockets. This function is intended to be 2536 * called only from tcp_pcblist. 2537 * 2538 * Due to concurrency on an active system, the number of pcbs exported 2539 * may have no relation to max_pcbs. max_pcbs merely indicates the 2540 * amount of space the caller allocated for this function to use. 2541 */ 2542 int 2543 syncache_pcblist(struct sysctl_req *req) 2544 { 2545 struct xtcpcb xt; 2546 struct syncache *sc; 2547 struct syncache_head *sch; 2548 int error, i; 2549 2550 bzero(&xt, sizeof(xt)); 2551 xt.xt_len = sizeof(xt); 2552 xt.t_state = TCPS_SYN_RECEIVED; 2553 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2554 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2555 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2556 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2557 2558 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2559 sch = &V_tcp_syncache.hashbase[i]; 2560 SCH_LOCK(sch); 2561 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2562 if (sc->sc_cred != NULL && 2563 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2564 continue; 2565 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2566 xt.xt_inp.inp_vflag = INP_IPV6; 2567 else 2568 xt.xt_inp.inp_vflag = INP_IPV4; 2569 xt.xt_encaps_port = sc->sc_port; 2570 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2571 sizeof (struct in_conninfo)); 2572 error = SYSCTL_OUT(req, &xt, sizeof xt); 2573 if (error) { 2574 SCH_UNLOCK(sch); 2575 return (0); 2576 } 2577 } 2578 SCH_UNLOCK(sch); 2579 } 2580 2581 return (0); 2582 } 2583