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 "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 #include "opt_rss.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/in_rss.h> 75 #include <netinet/ip_var.h> 76 #include <netinet/ip_options.h> 77 #ifdef INET6 78 #include <netinet/ip6.h> 79 #include <netinet/icmp6.h> 80 #include <netinet6/nd6.h> 81 #include <netinet6/ip6_var.h> 82 #include <netinet6/in6_pcb.h> 83 #include <netinet6/in6_rss.h> 84 #endif 85 #include <netinet/tcp.h> 86 #include <netinet/tcp_fastopen.h> 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #include <netinet/tcp_ecn.h> 93 #ifdef TCP_BLACKBOX 94 #include <netinet/tcp_log_buf.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 101 #include <netipsec/ipsec_support.h> 102 103 #include <machine/in_cksum.h> 104 105 #include <security/mac/mac_framework.h> 106 107 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true; 108 #define V_tcp_syncookies VNET(tcp_syncookies) 109 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 110 &VNET_NAME(tcp_syncookies), 0, 111 "Use TCP SYN cookies if the syncache overflows"); 112 113 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false; 114 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 115 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 116 &VNET_NAME(tcp_syncookiesonly), 0, 117 "Use only TCP SYN cookies"); 118 119 #ifdef TCP_OFFLOAD 120 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 121 #endif 122 123 static void syncache_drop(struct syncache *, struct syncache_head *); 124 static void syncache_free(struct syncache *); 125 static void syncache_insert(struct syncache *, struct syncache_head *); 126 static int syncache_respond(struct syncache *, int); 127 static void syncache_send_challenge_ack(struct syncache *); 128 static struct socket *syncache_socket(struct syncache *, struct socket *, 129 struct mbuf *m); 130 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 131 int docallout); 132 static void syncache_timer(void *); 133 134 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 135 uint8_t *, uintptr_t); 136 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 137 static bool syncookie_expand(struct in_conninfo *, 138 const struct syncache_head *, struct syncache *, 139 struct tcphdr *, struct tcpopt *, struct socket *, 140 uint16_t); 141 static void syncache_pause(struct in_conninfo *); 142 static void syncache_unpause(void *); 143 static void syncookie_reseed(void *); 144 #ifdef INVARIANTS 145 static void syncookie_cmp(struct in_conninfo *, 146 const struct syncache_head *, struct syncache *, 147 struct tcphdr *, struct tcpopt *, struct socket *, 148 uint16_t); 149 #endif 150 151 /* 152 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 153 * 3 retransmits corresponds to a timeout with default values of 154 * tcp_rexmit_initial * ( 1 + 155 * tcp_backoff[1] + 156 * tcp_backoff[2] + 157 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 158 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 159 * the odds are that the user has given up attempting to connect by then. 160 */ 161 #define SYNCACHE_MAXREXMTS 3 162 163 /* Arbitrary values */ 164 #define TCP_SYNCACHE_HASHSIZE 512 165 #define TCP_SYNCACHE_BUCKETLIMIT 30 166 167 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 168 #define V_tcp_syncache VNET(tcp_syncache) 169 170 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 171 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 172 "TCP SYN cache"); 173 174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 175 &VNET_NAME(tcp_syncache.bucket_limit), 0, 176 "Per-bucket hash limit for syncache"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.cache_limit), 0, 180 "Overall entry limit for syncache"); 181 182 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 183 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 184 185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 186 &VNET_NAME(tcp_syncache.hashsize), 0, 187 "Size of TCP syncache hashtable"); 188 189 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 190 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 191 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 192 "and mac(4) checks"); 193 194 static int 195 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 196 { 197 int error; 198 u_int new; 199 200 new = V_tcp_syncache.rexmt_limit; 201 error = sysctl_handle_int(oidp, &new, 0, req); 202 if ((error == 0) && (req->newptr != NULL)) { 203 if (new > TCP_MAXRXTSHIFT) 204 error = EINVAL; 205 else 206 V_tcp_syncache.rexmt_limit = new; 207 } 208 return (error); 209 } 210 211 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 212 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 213 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 214 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 215 "Limit on SYN/ACK retransmissions"); 216 217 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 219 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 220 "Send reset on socket allocation failure"); 221 222 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 223 224 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 225 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 226 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 227 228 /* 229 * Requires the syncache entry to be already removed from the bucket list. 230 */ 231 static void 232 syncache_free(struct syncache *sc) 233 { 234 235 if (sc->sc_ipopts) 236 (void)m_free(sc->sc_ipopts); 237 if (sc->sc_cred) 238 crfree(sc->sc_cred); 239 #ifdef MAC 240 mac_syncache_destroy(&sc->sc_label); 241 #endif 242 243 uma_zfree(V_tcp_syncache.zone, sc); 244 } 245 246 void 247 syncache_init(void) 248 { 249 int i; 250 251 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 252 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 253 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 254 V_tcp_syncache.hash_secret = arc4random(); 255 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 257 &V_tcp_syncache.hashsize); 258 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 259 &V_tcp_syncache.bucket_limit); 260 if (!powerof2(V_tcp_syncache.hashsize) || 261 V_tcp_syncache.hashsize == 0) { 262 printf("WARNING: syncache hash size is not a power of 2.\n"); 263 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 264 } 265 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 266 267 /* Set limits. */ 268 V_tcp_syncache.cache_limit = 269 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 271 &V_tcp_syncache.cache_limit); 272 273 /* Allocate the hash table. */ 274 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 275 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 276 277 #ifdef VIMAGE 278 V_tcp_syncache.vnet = curvnet; 279 #endif 280 281 /* Initialize the hash buckets. */ 282 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 283 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 284 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 285 NULL, MTX_DEF); 286 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 287 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 288 V_tcp_syncache.hashbase[i].sch_length = 0; 289 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 290 V_tcp_syncache.hashbase[i].sch_last_overflow = 291 -(SYNCOOKIE_LIFETIME + 1); 292 } 293 294 /* Create the syncache entry zone. */ 295 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 296 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 297 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 298 V_tcp_syncache.cache_limit); 299 300 /* Start the SYN cookie reseeder callout. */ 301 callout_init(&V_tcp_syncache.secret.reseed, 1); 302 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 303 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 304 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 305 syncookie_reseed, &V_tcp_syncache); 306 307 /* Initialize the pause machinery. */ 308 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 309 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 310 0); 311 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 312 V_tcp_syncache.pause_backoff = 0; 313 V_tcp_syncache.paused = false; 314 } 315 316 #ifdef VIMAGE 317 void 318 syncache_destroy(void) 319 { 320 struct syncache_head *sch; 321 struct syncache *sc, *nsc; 322 int i; 323 324 /* 325 * Stop the re-seed timer before freeing resources. No need to 326 * possibly schedule it another time. 327 */ 328 callout_drain(&V_tcp_syncache.secret.reseed); 329 330 /* Stop the SYN cache pause callout. */ 331 mtx_lock(&V_tcp_syncache.pause_mtx); 332 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 333 mtx_unlock(&V_tcp_syncache.pause_mtx); 334 callout_drain(&V_tcp_syncache.pause_co); 335 } else 336 mtx_unlock(&V_tcp_syncache.pause_mtx); 337 338 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 339 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 340 sch = &V_tcp_syncache.hashbase[i]; 341 callout_drain(&sch->sch_timer); 342 343 SCH_LOCK(sch); 344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 345 syncache_drop(sc, sch); 346 SCH_UNLOCK(sch); 347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 348 ("%s: sch->sch_bucket not empty", __func__)); 349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 350 __func__, sch->sch_length)); 351 mtx_destroy(&sch->sch_mtx); 352 } 353 354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 355 ("%s: cache_count not 0", __func__)); 356 357 /* Free the allocated global resources. */ 358 uma_zdestroy(V_tcp_syncache.zone); 359 free(V_tcp_syncache.hashbase, M_SYNCACHE); 360 mtx_destroy(&V_tcp_syncache.pause_mtx); 361 } 362 #endif 363 364 /* 365 * Inserts a syncache entry into the specified bucket row. 366 * Locks and unlocks the syncache_head autonomously. 367 */ 368 static void 369 syncache_insert(struct syncache *sc, struct syncache_head *sch) 370 { 371 struct syncache *sc2; 372 373 SCH_LOCK(sch); 374 375 /* 376 * Make sure that we don't overflow the per-bucket limit. 377 * If the bucket is full, toss the oldest element. 378 */ 379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 381 ("sch->sch_length incorrect")); 382 syncache_pause(&sc->sc_inc); 383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 384 sch->sch_last_overflow = time_uptime; 385 syncache_drop(sc2, sch); 386 } 387 388 /* Put it into the bucket. */ 389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 390 sch->sch_length++; 391 392 #ifdef TCP_OFFLOAD 393 if (ADDED_BY_TOE(sc)) { 394 struct toedev *tod = sc->sc_tod; 395 396 tod->tod_syncache_added(tod, sc->sc_todctx); 397 } 398 #endif 399 400 /* Reinitialize the bucket row's timer. */ 401 if (sch->sch_length == 1) 402 sch->sch_nextc = ticks + INT_MAX; 403 syncache_timeout(sc, sch, 1); 404 405 SCH_UNLOCK(sch); 406 407 TCPSTATES_INC(TCPS_SYN_RECEIVED); 408 TCPSTAT_INC(tcps_sc_added); 409 } 410 411 /* 412 * Remove and free entry from syncache bucket row. 413 * Expects locked syncache head. 414 */ 415 static void 416 syncache_drop(struct syncache *sc, struct syncache_head *sch) 417 { 418 419 SCH_LOCK_ASSERT(sch); 420 421 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 423 sch->sch_length--; 424 425 #ifdef TCP_OFFLOAD 426 if (ADDED_BY_TOE(sc)) { 427 struct toedev *tod = sc->sc_tod; 428 429 tod->tod_syncache_removed(tod, sc->sc_todctx); 430 } 431 #endif 432 433 syncache_free(sc); 434 } 435 436 /* 437 * Engage/reengage time on bucket row. 438 */ 439 static void 440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 441 { 442 int rexmt; 443 444 if (sc->sc_rxmits == 0) 445 rexmt = tcp_rexmit_initial; 446 else 447 TCPT_RANGESET(rexmt, 448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 449 tcp_rexmit_min, tcp_rexmit_max); 450 sc->sc_rxttime = ticks + rexmt; 451 sc->sc_rxmits++; 452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 453 sch->sch_nextc = sc->sc_rxttime; 454 if (docallout) 455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 456 syncache_timer, (void *)sch); 457 } 458 } 459 460 /* 461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 462 * If we have retransmitted an entry the maximum number of times, expire it. 463 * One separate timer for each bucket row. 464 */ 465 static void 466 syncache_timer(void *xsch) 467 { 468 struct syncache_head *sch = (struct syncache_head *)xsch; 469 struct syncache *sc, *nsc; 470 struct epoch_tracker et; 471 int tick = ticks; 472 char *s; 473 bool paused; 474 475 CURVNET_SET(sch->sch_sc->vnet); 476 477 /* NB: syncache_head has already been locked by the callout. */ 478 SCH_LOCK_ASSERT(sch); 479 480 /* 481 * In the following cycle we may remove some entries and/or 482 * advance some timeouts, so re-initialize the bucket timer. 483 */ 484 sch->sch_nextc = tick + INT_MAX; 485 486 /* 487 * If we have paused processing, unconditionally remove 488 * all syncache entries. 489 */ 490 mtx_lock(&V_tcp_syncache.pause_mtx); 491 paused = V_tcp_syncache.paused; 492 mtx_unlock(&V_tcp_syncache.pause_mtx); 493 494 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 495 if (paused) { 496 syncache_drop(sc, sch); 497 continue; 498 } 499 /* 500 * We do not check if the listen socket still exists 501 * and accept the case where the listen socket may be 502 * gone by the time we resend the SYN/ACK. We do 503 * not expect this to happens often. If it does, 504 * then the RST will be sent by the time the remote 505 * host does the SYN/ACK->ACK. 506 */ 507 if (TSTMP_GT(sc->sc_rxttime, tick)) { 508 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 509 sch->sch_nextc = sc->sc_rxttime; 510 continue; 511 } 512 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 513 sc->sc_flags &= ~SCF_ECN_MASK; 514 } 515 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 516 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 517 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 518 "giving up and removing syncache entry\n", 519 s, __func__); 520 free(s, M_TCPLOG); 521 } 522 syncache_drop(sc, sch); 523 TCPSTAT_INC(tcps_sc_stale); 524 continue; 525 } 526 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 527 log(LOG_DEBUG, "%s; %s: Response timeout, " 528 "retransmitting (%u) SYN|ACK\n", 529 s, __func__, sc->sc_rxmits); 530 free(s, M_TCPLOG); 531 } 532 533 NET_EPOCH_ENTER(et); 534 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 535 syncache_timeout(sc, sch, 0); 536 TCPSTAT_INC(tcps_sndacks); 537 TCPSTAT_INC(tcps_sndtotal); 538 TCPSTAT_INC(tcps_sc_retransmitted); 539 } else { 540 /* 541 * Most likely we are memory constrained, so free 542 * resources. 543 */ 544 syncache_drop(sc, sch); 545 TCPSTAT_INC(tcps_sc_dropped); 546 } 547 NET_EPOCH_EXIT(et); 548 } 549 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 550 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 551 syncache_timer, (void *)(sch)); 552 CURVNET_RESTORE(); 553 } 554 555 /* 556 * Returns true if the system is only using cookies at the moment. 557 * This could be due to a sysadmin decision to only use cookies, or it 558 * could be due to the system detecting an attack. 559 */ 560 static inline bool 561 syncache_cookiesonly(void) 562 { 563 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 564 V_tcp_syncookiesonly); 565 } 566 567 /* 568 * Find the hash bucket for the given connection. 569 */ 570 static struct syncache_head * 571 syncache_hashbucket(struct in_conninfo *inc) 572 { 573 uint32_t hash; 574 575 /* 576 * The hash is built on foreign port + local port + foreign address. 577 * We rely on the fact that struct in_conninfo starts with 16 bits 578 * of foreign port, then 16 bits of local port then followed by 128 579 * bits of foreign address. In case of IPv4 address, the first 3 580 * 32-bit words of the address always are zeroes. 581 */ 582 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 583 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 584 585 return (&V_tcp_syncache.hashbase[hash]); 586 } 587 588 /* 589 * Find an entry in the syncache. 590 * Returns always with locked syncache_head plus a matching entry or NULL. 591 */ 592 static struct syncache * 593 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 594 { 595 struct syncache *sc; 596 struct syncache_head *sch; 597 598 *schp = sch = syncache_hashbucket(inc); 599 SCH_LOCK(sch); 600 601 /* Circle through bucket row to find matching entry. */ 602 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 603 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 604 sizeof(struct in_endpoints)) == 0) 605 break; 606 607 return (sc); /* Always returns with locked sch. */ 608 } 609 610 /* 611 * This function is called when we get a RST for a 612 * non-existent connection, so that we can see if the 613 * connection is in the syn cache. If it is, zap it. 614 * If required send a challenge ACK. 615 */ 616 void 617 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, uint16_t port) 618 { 619 struct syncache *sc; 620 struct syncache_head *sch; 621 char *s = NULL; 622 623 if (syncache_cookiesonly()) 624 return; 625 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 626 SCH_LOCK_ASSERT(sch); 627 628 /* 629 * No corresponding connection was found in syncache. 630 * If syncookies are enabled and possibly exclusively 631 * used, or we are under memory pressure, a valid RST 632 * may not find a syncache entry. In that case we're 633 * done and no SYN|ACK retransmissions will happen. 634 * Otherwise the RST was misdirected or spoofed. 635 */ 636 if (sc == NULL) { 637 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 638 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 639 "syncache entry (possibly syncookie only), " 640 "segment ignored\n", s, __func__); 641 TCPSTAT_INC(tcps_badrst); 642 goto done; 643 } 644 645 /* The remote UDP encaps port does not match. */ 646 if (sc->sc_port != port) { 647 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 648 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 649 "syncache entry but non-matching UDP encaps port, " 650 "segment ignored\n", s, __func__); 651 TCPSTAT_INC(tcps_badrst); 652 goto done; 653 } 654 655 /* 656 * If the RST bit is set, check the sequence number to see 657 * if this is a valid reset segment. 658 * 659 * RFC 793 page 37: 660 * In all states except SYN-SENT, all reset (RST) segments 661 * are validated by checking their SEQ-fields. A reset is 662 * valid if its sequence number is in the window. 663 * 664 * RFC 793 page 69: 665 * There are four cases for the acceptability test for an incoming 666 * segment: 667 * 668 * Segment Receive Test 669 * Length Window 670 * ------- ------- ------------------------------------------- 671 * 0 0 SEG.SEQ = RCV.NXT 672 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 673 * >0 0 not acceptable 674 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 675 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 676 * 677 * Note that when receiving a SYN segment in the LISTEN state, 678 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 679 * described in RFC 793, page 66. 680 */ 681 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 682 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 683 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 684 if (V_tcp_insecure_rst || 685 th->th_seq == sc->sc_irs + 1) { 686 syncache_drop(sc, sch); 687 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 688 log(LOG_DEBUG, 689 "%s; %s: Our SYN|ACK was rejected, " 690 "connection attempt aborted by remote " 691 "endpoint\n", 692 s, __func__); 693 TCPSTAT_INC(tcps_sc_reset); 694 } else { 695 TCPSTAT_INC(tcps_badrst); 696 /* Send challenge ACK. */ 697 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 698 log(LOG_DEBUG, "%s; %s: RST with invalid " 699 " SEQ %u != NXT %u (+WND %u), " 700 "sending challenge ACK\n", 701 s, __func__, 702 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 703 syncache_send_challenge_ack(sc); 704 } 705 } else { 706 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 707 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 708 "NXT %u (+WND %u), segment ignored\n", 709 s, __func__, 710 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 711 TCPSTAT_INC(tcps_badrst); 712 } 713 714 done: 715 if (s != NULL) 716 free(s, M_TCPLOG); 717 SCH_UNLOCK(sch); 718 } 719 720 void 721 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 722 { 723 struct syncache *sc; 724 struct syncache_head *sch; 725 726 if (syncache_cookiesonly()) 727 return; 728 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 729 SCH_LOCK_ASSERT(sch); 730 if (sc == NULL) 731 goto done; 732 733 /* If the port != sc_port, then it's a bogus ICMP msg */ 734 if (port != sc->sc_port) 735 goto done; 736 737 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 738 if (ntohl(th_seq) != sc->sc_iss) 739 goto done; 740 741 /* 742 * If we've retransmitted 3 times and this is our second error, 743 * we remove the entry. Otherwise, we allow it to continue on. 744 * This prevents us from incorrectly nuking an entry during a 745 * spurious network outage. 746 * 747 * See tcp_notify(). 748 */ 749 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 750 sc->sc_flags |= SCF_UNREACH; 751 goto done; 752 } 753 syncache_drop(sc, sch); 754 TCPSTAT_INC(tcps_sc_unreach); 755 done: 756 SCH_UNLOCK(sch); 757 } 758 759 /* 760 * Build a new TCP socket structure from a syncache entry. 761 * 762 * On success return the newly created socket with its underlying inp locked. 763 */ 764 static struct socket * 765 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 766 { 767 struct inpcb *inp = NULL; 768 struct socket *so; 769 struct tcpcb *tp; 770 int error; 771 char *s; 772 773 NET_EPOCH_ASSERT(); 774 775 /* 776 * Ok, create the full blown connection, and set things up 777 * as they would have been set up if we had created the 778 * connection when the SYN arrived. 779 */ 780 if ((so = solisten_clone(lso)) == NULL) 781 goto allocfail; 782 #ifdef MAC 783 mac_socketpeer_set_from_mbuf(m, so); 784 #endif 785 error = in_pcballoc(so, &V_tcbinfo); 786 if (error) { 787 sodealloc(so); 788 goto allocfail; 789 } 790 inp = sotoinpcb(so); 791 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 792 in_pcbfree(inp); 793 sodealloc(so); 794 goto allocfail; 795 } 796 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 797 #ifdef INET6 798 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 799 inp->inp_vflag &= ~INP_IPV4; 800 inp->inp_vflag |= INP_IPV6; 801 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 802 } else { 803 inp->inp_vflag &= ~INP_IPV6; 804 inp->inp_vflag |= INP_IPV4; 805 #endif 806 inp->inp_ip_ttl = sc->sc_ip_ttl; 807 inp->inp_ip_tos = sc->sc_ip_tos; 808 inp->inp_laddr = sc->sc_inc.inc_laddr; 809 #ifdef INET6 810 } 811 #endif 812 inp->inp_lport = sc->sc_inc.inc_lport; 813 #ifdef INET6 814 if (inp->inp_vflag & INP_IPV6PROTO) { 815 struct inpcb *oinp = sotoinpcb(lso); 816 817 /* 818 * Inherit socket options from the listening socket. 819 * Note that in6p_inputopts are not (and should not be) 820 * copied, since it stores previously received options and is 821 * used to detect if each new option is different than the 822 * previous one and hence should be passed to a user. 823 * If we copied in6p_inputopts, a user would not be able to 824 * receive options just after calling the accept system call. 825 */ 826 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 827 if (oinp->in6p_outputopts) 828 inp->in6p_outputopts = 829 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 830 inp->in6p_hops = oinp->in6p_hops; 831 } 832 833 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 834 struct sockaddr_in6 sin6; 835 836 sin6.sin6_family = AF_INET6; 837 sin6.sin6_len = sizeof(sin6); 838 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 839 sin6.sin6_port = sc->sc_inc.inc_fport; 840 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 841 INP_HASH_WLOCK(&V_tcbinfo); 842 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 843 INP_HASH_WUNLOCK(&V_tcbinfo); 844 if (error != 0) 845 goto abort; 846 /* Override flowlabel from in6_pcbconnect. */ 847 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 848 inp->inp_flow |= sc->sc_flowlabel; 849 } 850 #endif /* INET6 */ 851 #if defined(INET) && defined(INET6) 852 else 853 #endif 854 #ifdef INET 855 { 856 struct sockaddr_in sin; 857 858 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 859 860 if (inp->inp_options == NULL) { 861 inp->inp_options = sc->sc_ipopts; 862 sc->sc_ipopts = NULL; 863 } 864 865 sin.sin_family = AF_INET; 866 sin.sin_len = sizeof(sin); 867 sin.sin_addr = sc->sc_inc.inc_faddr; 868 sin.sin_port = sc->sc_inc.inc_fport; 869 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 870 INP_HASH_WLOCK(&V_tcbinfo); 871 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 872 INP_HASH_WUNLOCK(&V_tcbinfo); 873 if (error != 0) 874 goto abort; 875 } 876 #endif /* INET */ 877 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 878 /* Copy old policy into new socket's. */ 879 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 880 printf("syncache_socket: could not copy policy\n"); 881 #endif 882 if (sc->sc_flowtype != M_HASHTYPE_NONE) { 883 inp->inp_flowid = sc->sc_flowid; 884 inp->inp_flowtype = sc->sc_flowtype; 885 #ifdef RSS 886 } else { 887 /* assign flowid by software RSS hash */ 888 #ifdef INET6 889 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 890 rss_proto_software_hash_v6(&inp->in6p_faddr, 891 &inp->in6p_laddr, 892 inp->inp_fport, 893 inp->inp_lport, 894 IPPROTO_TCP, 895 &inp->inp_flowid, 896 &inp->inp_flowtype); 897 } else 898 #endif /* INET6 */ 899 { 900 rss_proto_software_hash_v4(inp->inp_faddr, 901 inp->inp_laddr, 902 inp->inp_fport, 903 inp->inp_lport, 904 IPPROTO_TCP, 905 &inp->inp_flowid, 906 &inp->inp_flowtype); 907 } 908 #endif /* RSS */ 909 } 910 #ifdef NUMA 911 inp->inp_numa_domain = sc->sc_numa_domain; 912 #endif 913 914 tp->t_state = TCPS_SYN_RECEIVED; 915 tp->iss = sc->sc_iss; 916 tp->irs = sc->sc_irs; 917 tp->t_port = sc->sc_port; 918 tcp_rcvseqinit(tp); 919 tcp_sendseqinit(tp); 920 tp->snd_wl1 = sc->sc_irs; 921 tp->snd_max = tp->iss + 1; 922 tp->snd_nxt = tp->iss + 1; 923 tp->rcv_up = sc->sc_irs + 1; 924 tp->rcv_wnd = sc->sc_wnd; 925 tp->rcv_adv += tp->rcv_wnd; 926 tp->last_ack_sent = tp->rcv_nxt; 927 928 tp->t_flags = sototcpcb(lso)->t_flags & 929 (TF_LRD|TF_NOPUSH|TF_NODELAY); 930 if (sc->sc_flags & SCF_NOOPT) 931 tp->t_flags |= TF_NOOPT; 932 else { 933 if (sc->sc_flags & SCF_WINSCALE) { 934 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 935 tp->snd_scale = sc->sc_requested_s_scale; 936 tp->request_r_scale = sc->sc_requested_r_scale; 937 } 938 if (sc->sc_flags & SCF_TIMESTAMP) { 939 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 940 tp->ts_recent = sc->sc_tsreflect; 941 tp->ts_recent_age = tcp_ts_getticks(); 942 tp->ts_offset = sc->sc_tsoff; 943 } 944 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 945 if (sc->sc_flags & SCF_SIGNATURE) 946 tp->t_flags |= TF_SIGNATURE; 947 #endif 948 if (sc->sc_flags & SCF_SACK) 949 tp->t_flags |= TF_SACK_PERMIT; 950 } 951 952 tcp_ecn_syncache_socket(tp, sc); 953 954 /* 955 * Set up MSS and get cached values from tcp_hostcache. 956 * This might overwrite some of the defaults we just set. 957 */ 958 tcp_mss(tp, sc->sc_peer_mss); 959 960 /* 961 * If the SYN,ACK was retransmitted, indicate that CWND to be 962 * limited to one segment in cc_conn_init(). 963 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 964 */ 965 if (sc->sc_rxmits > 1) 966 tp->snd_cwnd = 1; 967 968 /* Copy over the challenge ACK state. */ 969 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 970 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 971 972 #ifdef TCP_OFFLOAD 973 /* 974 * Allow a TOE driver to install its hooks. Note that we hold the 975 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 976 * new connection before the TOE driver has done its thing. 977 */ 978 if (ADDED_BY_TOE(sc)) { 979 struct toedev *tod = sc->sc_tod; 980 981 tod->tod_offload_socket(tod, sc->sc_todctx, so); 982 } 983 #endif 984 #ifdef TCP_BLACKBOX 985 /* 986 * Inherit the log state from the listening socket, if 987 * - the log state of the listening socket is not off and 988 * - the listening socket was not auto selected from all sessions and 989 * - a log id is not set on the listening socket. 990 * This avoids inheriting a log state which was automatically set. 991 */ 992 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 993 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 994 (sototcpcb(lso)->t_lib == NULL)) { 995 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 996 } 997 #endif 998 /* 999 * Copy and activate timers. 1000 */ 1001 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1002 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1003 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1004 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1005 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1006 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1007 1008 TCPSTAT_INC(tcps_accepts); 1009 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1010 1011 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1012 tp->t_flags |= TF_SONOTCONN; 1013 /* Can we inherit anything from the listener? */ 1014 if (tp->t_fb->tfb_inherit != NULL) { 1015 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1016 } 1017 return (so); 1018 1019 allocfail: 1020 /* 1021 * Drop the connection; we will either send a RST or have the peer 1022 * retransmit its SYN again after its RTO and try again. 1023 */ 1024 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1025 log(LOG_DEBUG, "%s; %s: Socket create failed " 1026 "due to limits or memory shortage\n", 1027 s, __func__); 1028 free(s, M_TCPLOG); 1029 } 1030 TCPSTAT_INC(tcps_listendrop); 1031 return (NULL); 1032 1033 abort: 1034 tcp_discardcb(tp); 1035 in_pcbfree(inp); 1036 sodealloc(so); 1037 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1038 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1039 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1040 error); 1041 free(s, M_TCPLOG); 1042 } 1043 TCPSTAT_INC(tcps_listendrop); 1044 return (NULL); 1045 } 1046 1047 /* 1048 * This function gets called when we receive an ACK for a 1049 * socket in the LISTEN state. We look up the connection 1050 * in the syncache, and if its there, we pull it out of 1051 * the cache and turn it into a full-blown connection in 1052 * the SYN-RECEIVED state. 1053 * 1054 * On syncache_socket() success the newly created socket 1055 * has its underlying inp locked. 1056 * 1057 * *lsop is updated, if and only if 1 is returned. 1058 */ 1059 int 1060 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1061 struct socket **lsop, struct mbuf *m, uint16_t port) 1062 { 1063 struct syncache *sc; 1064 struct syncache_head *sch; 1065 struct syncache scs; 1066 char *s; 1067 bool locked; 1068 1069 NET_EPOCH_ASSERT(); 1070 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1071 ("%s: can handle only ACK", __func__)); 1072 1073 if (syncache_cookiesonly()) { 1074 sc = NULL; 1075 sch = syncache_hashbucket(inc); 1076 locked = false; 1077 } else { 1078 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1079 locked = true; 1080 SCH_LOCK_ASSERT(sch); 1081 } 1082 1083 #ifdef INVARIANTS 1084 /* 1085 * Test code for syncookies comparing the syncache stored 1086 * values with the reconstructed values from the cookie. 1087 */ 1088 if (sc != NULL) 1089 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1090 #endif 1091 1092 if (sc == NULL) { 1093 if (locked) { 1094 /* 1095 * The syncache is currently in use (neither disabled, 1096 * nor paused), but no entry was found. 1097 */ 1098 if (!V_tcp_syncookies) { 1099 /* 1100 * Since no syncookies are used in case of 1101 * a bucket overflow, don't even check for 1102 * a valid syncookie. 1103 */ 1104 SCH_UNLOCK(sch); 1105 TCPSTAT_INC(tcps_sc_spurcookie); 1106 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1107 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1108 "segment rejected " 1109 "(syncookies disabled)\n", 1110 s, __func__); 1111 free(s, M_TCPLOG); 1112 } 1113 return (0); 1114 } 1115 if (sch->sch_last_overflow < 1116 time_uptime - SYNCOOKIE_LIFETIME) { 1117 /* 1118 * Since the bucket did not overflow recently, 1119 * don't even check for a valid syncookie. 1120 */ 1121 SCH_UNLOCK(sch); 1122 TCPSTAT_INC(tcps_sc_spurcookie); 1123 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1124 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1125 "segment rejected " 1126 "(no syncache entry)\n", 1127 s, __func__); 1128 free(s, M_TCPLOG); 1129 } 1130 return (0); 1131 } 1132 SCH_UNLOCK(sch); 1133 } 1134 bzero(&scs, sizeof(scs)); 1135 /* 1136 * Now check, if the syncookie is valid. If it is, create an on 1137 * stack syncache entry. 1138 */ 1139 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1140 sc = &scs; 1141 TCPSTAT_INC(tcps_sc_recvcookie); 1142 } else { 1143 TCPSTAT_INC(tcps_sc_failcookie); 1144 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1145 log(LOG_DEBUG, "%s; %s: Segment failed " 1146 "SYNCOOKIE authentication, segment rejected " 1147 "(probably spoofed)\n", s, __func__); 1148 free(s, M_TCPLOG); 1149 } 1150 return (0); 1151 } 1152 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1153 /* If received ACK has MD5 signature, check it. */ 1154 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1155 (!TCPMD5_ENABLED() || 1156 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1157 /* Drop the ACK. */ 1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1159 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1160 "MD5 signature doesn't match.\n", 1161 s, __func__); 1162 free(s, M_TCPLOG); 1163 } 1164 TCPSTAT_INC(tcps_sig_err_sigopt); 1165 return (-1); /* Do not send RST */ 1166 } 1167 #endif /* TCP_SIGNATURE */ 1168 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 1169 sc->sc_flowid = m->m_pkthdr.flowid; 1170 sc->sc_flowtype = M_HASHTYPE_GET(m); 1171 } 1172 #ifdef NUMA 1173 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1174 #endif 1175 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1176 } else { 1177 if (sc->sc_port != port) { 1178 SCH_UNLOCK(sch); 1179 return (0); 1180 } 1181 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1182 /* 1183 * If listening socket requested TCP digests, check that 1184 * received ACK has signature and it is correct. 1185 * If not, drop the ACK and leave sc entry in the cache, 1186 * because SYN was received with correct signature. 1187 */ 1188 if (sc->sc_flags & SCF_SIGNATURE) { 1189 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1190 /* No signature */ 1191 TCPSTAT_INC(tcps_sig_err_nosigopt); 1192 SCH_UNLOCK(sch); 1193 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1194 log(LOG_DEBUG, "%s; %s: Segment " 1195 "rejected, MD5 signature wasn't " 1196 "provided.\n", s, __func__); 1197 free(s, M_TCPLOG); 1198 } 1199 return (-1); /* Do not send RST */ 1200 } 1201 if (!TCPMD5_ENABLED() || 1202 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1203 /* Doesn't match or no SA */ 1204 SCH_UNLOCK(sch); 1205 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1206 log(LOG_DEBUG, "%s; %s: Segment " 1207 "rejected, MD5 signature doesn't " 1208 "match.\n", s, __func__); 1209 free(s, M_TCPLOG); 1210 } 1211 return (-1); /* Do not send RST */ 1212 } 1213 } 1214 #endif /* TCP_SIGNATURE */ 1215 1216 /* 1217 * RFC 7323 PAWS: If we have a timestamp on this segment and 1218 * it's less than ts_recent, drop it. 1219 * XXXMT: RFC 7323 also requires to send an ACK. 1220 * In tcp_input.c this is only done for TCP segments 1221 * with user data, so be consistent here and just drop 1222 * the segment. 1223 */ 1224 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1225 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 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 } 1232 SCH_UNLOCK(sch); 1233 free(s, M_TCPLOG); 1234 return (-1); /* Do not send RST */ 1235 } 1236 1237 /* 1238 * If timestamps were not negotiated during SYN/ACK and a 1239 * segment with a timestamp is received, ignore the 1240 * timestamp and process the packet normally. 1241 * See section 3.2 of RFC 7323. 1242 */ 1243 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1244 (to->to_flags & TOF_TS)) { 1245 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1246 log(LOG_DEBUG, "%s; %s: Timestamp not " 1247 "expected, segment processed normally\n", 1248 s, __func__); 1249 free(s, M_TCPLOG); 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 1282 /* 1283 * SEG.SEQ validation: 1284 * The SEG.SEQ must be in the window starting at our 1285 * initial receive sequence number + 1. 1286 */ 1287 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1288 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1289 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1290 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1291 "sending challenge ACK\n", 1292 s, __func__, th->th_seq, sc->sc_irs + 1); 1293 syncache_send_challenge_ack(sc); 1294 SCH_UNLOCK(sch); 1295 free(s, M_TCPLOG); 1296 return (-1); /* Do not send RST */ 1297 } 1298 1299 /* 1300 * SEG.ACK validation: 1301 * SEG.ACK must match our initial send sequence number + 1. 1302 */ 1303 if (th->th_ack != sc->sc_iss + 1) { 1304 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1305 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1306 "segment rejected\n", 1307 s, __func__, th->th_ack, sc->sc_iss + 1); 1308 SCH_UNLOCK(sch); 1309 free(s, M_TCPLOG); 1310 return (0); /* Do send RST, do not free sc. */ 1311 } 1312 1313 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1314 sch->sch_length--; 1315 #ifdef TCP_OFFLOAD 1316 if (ADDED_BY_TOE(sc)) { 1317 struct toedev *tod = sc->sc_tod; 1318 1319 tod->tod_syncache_removed(tod, sc->sc_todctx); 1320 } 1321 #endif 1322 SCH_UNLOCK(sch); 1323 } 1324 1325 *lsop = syncache_socket(sc, *lsop, m); 1326 1327 if (__predict_false(*lsop == NULL)) { 1328 TCPSTAT_INC(tcps_sc_aborted); 1329 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1330 } else if (sc != &scs) 1331 TCPSTAT_INC(tcps_sc_completed); 1332 1333 if (sc != &scs) 1334 syncache_free(sc); 1335 return (1); 1336 } 1337 1338 static struct socket * 1339 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1340 uint64_t response_cookie) 1341 { 1342 struct inpcb *inp; 1343 struct tcpcb *tp; 1344 unsigned int *pending_counter; 1345 struct socket *so; 1346 1347 NET_EPOCH_ASSERT(); 1348 1349 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1350 so = syncache_socket(sc, lso, m); 1351 if (so == NULL) { 1352 TCPSTAT_INC(tcps_sc_aborted); 1353 atomic_subtract_int(pending_counter, 1); 1354 } else { 1355 soisconnected(so); 1356 inp = sotoinpcb(so); 1357 tp = intotcpcb(inp); 1358 tp->t_flags |= TF_FASTOPEN; 1359 tp->t_tfo_cookie.server = response_cookie; 1360 tp->snd_max = tp->iss; 1361 tp->snd_nxt = tp->iss; 1362 tp->t_tfo_pending = pending_counter; 1363 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1364 TCPSTAT_INC(tcps_sc_completed); 1365 } 1366 1367 return (so); 1368 } 1369 1370 /* 1371 * Given a LISTEN socket and an inbound SYN request, add 1372 * this to the syn cache, and send back a segment: 1373 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1374 * to the source. 1375 * 1376 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1377 * Doing so would require that we hold onto the data and deliver it 1378 * to the application. However, if we are the target of a SYN-flood 1379 * DoS attack, an attacker could send data which would eventually 1380 * consume all available buffer space if it were ACKed. By not ACKing 1381 * the data, we avoid this DoS scenario. 1382 * 1383 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1384 * cookie is processed and a new socket is created. In this case, any data 1385 * accompanying the SYN will be queued to the socket by tcp_input() and will 1386 * be ACKed either when the application sends response data or the delayed 1387 * ACK timer expires, whichever comes first. 1388 */ 1389 struct socket * 1390 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1391 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1392 void *todctx, uint8_t iptos, uint16_t port) 1393 { 1394 struct tcpcb *tp; 1395 struct socket *rv = NULL; 1396 struct syncache *sc = NULL; 1397 struct ucred *cred; 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 = NULL; 1408 #endif 1409 struct syncache scs; 1410 uint64_t tfo_response_cookie; 1411 unsigned int *tfo_pending = NULL; 1412 int tfo_cookie_valid = 0; 1413 int tfo_response_cookie_valid = 0; 1414 bool locked; 1415 1416 INP_RLOCK_ASSERT(inp); /* listen socket */ 1417 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1418 ("%s: unexpected tcp flags", __func__)); 1419 1420 /* 1421 * Combine all so/tp operations very early to drop the INP lock as 1422 * soon as possible. 1423 */ 1424 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1425 tp = sototcpcb(so); 1426 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1427 1428 #ifdef INET6 1429 if (inc->inc_flags & INC_ISIPV6) { 1430 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1431 autoflowlabel = 1; 1432 } 1433 ip_ttl = in6_selecthlim(inp, NULL); 1434 if ((inp->in6p_outputopts == NULL) || 1435 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1436 ip_tos = 0; 1437 } else { 1438 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1439 } 1440 } 1441 #endif 1442 #if defined(INET6) && defined(INET) 1443 else 1444 #endif 1445 #ifdef INET 1446 { 1447 ip_ttl = inp->inp_ip_ttl; 1448 ip_tos = inp->inp_ip_tos; 1449 } 1450 #endif 1451 win = so->sol_sbrcv_hiwat; 1452 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1453 1454 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1455 (tp->t_tfo_pending != NULL) && 1456 (to->to_flags & TOF_FASTOPEN)) { 1457 /* 1458 * Limit the number of pending TFO connections to 1459 * approximately half of the queue limit. This prevents TFO 1460 * SYN floods from starving the service by filling the 1461 * listen queue with bogus TFO connections. 1462 */ 1463 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1464 (so->sol_qlimit / 2)) { 1465 int result; 1466 1467 result = tcp_fastopen_check_cookie(inc, 1468 to->to_tfo_cookie, to->to_tfo_len, 1469 &tfo_response_cookie); 1470 tfo_cookie_valid = (result > 0); 1471 tfo_response_cookie_valid = (result >= 0); 1472 } 1473 1474 /* 1475 * Remember the TFO pending counter as it will have to be 1476 * decremented below if we don't make it to syncache_tfo_expand(). 1477 */ 1478 tfo_pending = tp->t_tfo_pending; 1479 } 1480 1481 #ifdef MAC 1482 if (mac_syncache_init(&maclabel) != 0) { 1483 INP_RUNLOCK(inp); 1484 goto done; 1485 } else 1486 mac_syncache_create(maclabel, inp); 1487 #endif 1488 if (!tfo_cookie_valid) 1489 INP_RUNLOCK(inp); 1490 1491 /* 1492 * Remember the IP options, if any. 1493 */ 1494 #ifdef INET6 1495 if (!(inc->inc_flags & INC_ISIPV6)) 1496 #endif 1497 #ifdef INET 1498 ipopts = (m) ? ip_srcroute(m) : NULL; 1499 #else 1500 ipopts = NULL; 1501 #endif 1502 1503 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1504 /* 1505 * When the socket is TCP-MD5 enabled check that, 1506 * - a signed packet is valid 1507 * - a non-signed packet does not have a security association 1508 * 1509 * If a signed packet fails validation or a non-signed packet has a 1510 * security association, the packet will be dropped. 1511 */ 1512 if (ltflags & TF_SIGNATURE) { 1513 if (to->to_flags & TOF_SIGNATURE) { 1514 if (!TCPMD5_ENABLED() || 1515 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1516 goto done; 1517 } else { 1518 if (TCPMD5_ENABLED() && 1519 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1520 goto done; 1521 } 1522 } else if (to->to_flags & TOF_SIGNATURE) 1523 goto done; 1524 #endif /* TCP_SIGNATURE */ 1525 /* 1526 * See if we already have an entry for this connection. 1527 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1528 * 1529 * XXX: should the syncache be re-initialized with the contents 1530 * of the new SYN here (which may have different options?) 1531 * 1532 * XXX: We do not check the sequence number to see if this is a 1533 * real retransmit or a new connection attempt. The question is 1534 * how to handle such a case; either ignore it as spoofed, or 1535 * drop the current entry and create a new one? 1536 */ 1537 if (syncache_cookiesonly()) { 1538 sc = NULL; 1539 sch = syncache_hashbucket(inc); 1540 locked = false; 1541 } else { 1542 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1543 locked = true; 1544 SCH_LOCK_ASSERT(sch); 1545 } 1546 if (sc != NULL) { 1547 if (tfo_cookie_valid) 1548 INP_RUNLOCK(inp); 1549 TCPSTAT_INC(tcps_sc_dupsyn); 1550 if (ipopts) { 1551 /* 1552 * If we were remembering a previous source route, 1553 * forget it and use the new one we've been given. 1554 */ 1555 if (sc->sc_ipopts) 1556 (void)m_free(sc->sc_ipopts); 1557 sc->sc_ipopts = ipopts; 1558 } 1559 /* 1560 * Update timestamp if present. 1561 */ 1562 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1563 sc->sc_tsreflect = to->to_tsval; 1564 else 1565 sc->sc_flags &= ~SCF_TIMESTAMP; 1566 /* 1567 * Adjust ECN response if needed, e.g. different 1568 * IP ECN field, or a fallback by the remote host. 1569 */ 1570 if (sc->sc_flags & SCF_ECN_MASK) { 1571 sc->sc_flags &= ~SCF_ECN_MASK; 1572 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 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, 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 } else { 1596 /* 1597 * Most likely we are memory constrained, so free 1598 * resources. 1599 */ 1600 syncache_drop(sc, sch); 1601 TCPSTAT_INC(tcps_sc_dropped); 1602 } 1603 SCH_UNLOCK(sch); 1604 goto donenoprobe; 1605 } 1606 1607 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1608 /* 1609 * Skip allocating a syncache entry if we are just going to discard 1610 * it later. 1611 */ 1612 if (!locked || tfo_cookie_valid) { 1613 bzero(&scs, sizeof(scs)); 1614 sc = &scs; 1615 } else { 1616 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1617 if (sc == NULL) { 1618 /* 1619 * The zone allocator couldn't provide more entries. 1620 * Treat this as if the cache was full; drop the oldest 1621 * entry and insert the new one. 1622 */ 1623 TCPSTAT_INC(tcps_sc_zonefail); 1624 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1625 if (sc != NULL) { 1626 sch->sch_last_overflow = time_uptime; 1627 syncache_drop(sc, sch); 1628 syncache_pause(inc); 1629 } 1630 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1631 if (sc == NULL) { 1632 if (V_tcp_syncookies) { 1633 bzero(&scs, sizeof(scs)); 1634 sc = &scs; 1635 } else { 1636 KASSERT(locked, 1637 ("%s: bucket unexpectedly unlocked", 1638 __func__)); 1639 SCH_UNLOCK(sch); 1640 goto done; 1641 } 1642 } 1643 } 1644 } 1645 1646 KASSERT(sc != NULL, ("sc == NULL")); 1647 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1648 sc->sc_tfo_cookie = &tfo_response_cookie; 1649 1650 /* 1651 * Fill in the syncache values. 1652 */ 1653 #ifdef MAC 1654 sc->sc_label = maclabel; 1655 #endif 1656 /* 1657 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1658 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1659 * Therefore, store the credentials only when needed: 1660 * - sc is allocated from the zone and not using the on stack instance. 1661 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1662 * The reference count is decremented when a zone allocated sc is 1663 * freed in syncache_free(). 1664 */ 1665 if (sc != &scs && !V_tcp_syncache.see_other) { 1666 sc->sc_cred = cred; 1667 cred = NULL; 1668 } else 1669 sc->sc_cred = NULL; 1670 sc->sc_port = port; 1671 sc->sc_ipopts = ipopts; 1672 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1673 sc->sc_ip_tos = ip_tos; 1674 sc->sc_ip_ttl = ip_ttl; 1675 #ifdef TCP_OFFLOAD 1676 sc->sc_tod = tod; 1677 sc->sc_todctx = todctx; 1678 #endif 1679 sc->sc_irs = th->th_seq; 1680 sc->sc_flags = 0; 1681 sc->sc_flowlabel = 0; 1682 1683 /* 1684 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1685 * win was derived from socket earlier in the function. 1686 */ 1687 win = imax(win, 0); 1688 win = imin(win, TCP_MAXWIN); 1689 sc->sc_wnd = win; 1690 1691 if (V_tcp_do_rfc1323 && 1692 !(ltflags & TF_NOOPT)) { 1693 /* 1694 * A timestamp received in a SYN makes 1695 * it ok to send timestamp requests and replies. 1696 */ 1697 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1698 sc->sc_tsreflect = to->to_tsval; 1699 sc->sc_flags |= SCF_TIMESTAMP; 1700 sc->sc_tsoff = tcp_new_ts_offset(inc); 1701 } 1702 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1703 u_int wscale = 0; 1704 1705 /* 1706 * Pick the smallest possible scaling factor that 1707 * will still allow us to scale up to sb_max, aka 1708 * kern.ipc.maxsockbuf. 1709 * 1710 * We do this because there are broken firewalls that 1711 * will corrupt the window scale option, leading to 1712 * the other endpoint believing that our advertised 1713 * window is unscaled. At scale factors larger than 1714 * 5 the unscaled window will drop below 1500 bytes, 1715 * leading to serious problems when traversing these 1716 * broken firewalls. 1717 * 1718 * With the default maxsockbuf of 256K, a scale factor 1719 * of 3 will be chosen by this algorithm. Those who 1720 * choose a larger maxsockbuf should watch out 1721 * for the compatibility problems mentioned above. 1722 * 1723 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1724 * or <SYN,ACK>) segment itself is never scaled. 1725 */ 1726 while (wscale < TCP_MAX_WINSHIFT && 1727 (TCP_MAXWIN << wscale) < sb_max) 1728 wscale++; 1729 sc->sc_requested_r_scale = wscale; 1730 sc->sc_requested_s_scale = to->to_wscale; 1731 sc->sc_flags |= SCF_WINSCALE; 1732 } 1733 } 1734 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1735 /* 1736 * If incoming packet has an MD5 signature, flag this in the 1737 * syncache so that syncache_respond() will do the right thing 1738 * with the SYN+ACK. 1739 */ 1740 if (to->to_flags & TOF_SIGNATURE) 1741 sc->sc_flags |= SCF_SIGNATURE; 1742 #endif /* TCP_SIGNATURE */ 1743 if (to->to_flags & TOF_SACKPERM) 1744 sc->sc_flags |= SCF_SACK; 1745 if (to->to_flags & TOF_MSS) 1746 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1747 if (ltflags & TF_NOOPT) 1748 sc->sc_flags |= SCF_NOOPT; 1749 /* ECN Handshake */ 1750 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1751 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1752 1753 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1754 sc->sc_iss = syncookie_generate(sch, sc); 1755 else 1756 sc->sc_iss = arc4random(); 1757 #ifdef INET6 1758 if (autoflowlabel) { 1759 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1760 sc->sc_flowlabel = sc->sc_iss; 1761 else 1762 sc->sc_flowlabel = ip6_randomflowlabel(); 1763 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1764 } 1765 #endif 1766 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 1767 sc->sc_flowid = m->m_pkthdr.flowid; 1768 sc->sc_flowtype = M_HASHTYPE_GET(m); 1769 } 1770 #ifdef NUMA 1771 sc->sc_numa_domain = m ? m->m_pkthdr.numa_domain : M_NODOM; 1772 #endif 1773 if (locked) 1774 SCH_UNLOCK(sch); 1775 1776 if (tfo_cookie_valid) { 1777 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1778 /* INP_RUNLOCK(inp) will be performed by the caller */ 1779 goto tfo_expanded; 1780 } 1781 1782 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1783 /* 1784 * Do a standard 3-way handshake. 1785 */ 1786 if (syncache_respond(sc, TH_SYN|TH_ACK) == 0) { 1787 if (sc != &scs) 1788 syncache_insert(sc, sch); /* locks and unlocks sch */ 1789 TCPSTAT_INC(tcps_sndacks); 1790 TCPSTAT_INC(tcps_sndtotal); 1791 } else { 1792 /* 1793 * Most likely we are memory constrained, so free resources. 1794 */ 1795 if (sc != &scs) 1796 syncache_free(sc); 1797 TCPSTAT_INC(tcps_sc_dropped); 1798 } 1799 goto donenoprobe; 1800 1801 done: 1802 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1803 donenoprobe: 1804 if (m) 1805 m_freem(m); 1806 /* 1807 * If tfo_pending is not NULL here, then a TFO SYN that did not 1808 * result in a new socket was processed and the associated pending 1809 * counter has not yet been decremented. All such TFO processing paths 1810 * transit this point. 1811 */ 1812 if (tfo_pending != NULL) 1813 tcp_fastopen_decrement_counter(tfo_pending); 1814 1815 tfo_expanded: 1816 if (cred != NULL) 1817 crfree(cred); 1818 if (sc == NULL || sc == &scs) { 1819 #ifdef MAC 1820 mac_syncache_destroy(&maclabel); 1821 #endif 1822 if (ipopts) 1823 (void)m_free(ipopts); 1824 } 1825 return (rv); 1826 } 1827 1828 /* 1829 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment 1830 * or upon 3WHS ACK timeout. 1831 */ 1832 static int 1833 syncache_respond(struct syncache *sc, int flags) 1834 { 1835 struct ip *ip = NULL; 1836 struct mbuf *m; 1837 struct tcphdr *th = NULL; 1838 struct udphdr *udp = NULL; 1839 int optlen, error = 0; /* Make compiler happy */ 1840 u_int16_t hlen, tlen, mssopt, ulen; 1841 struct tcpopt to; 1842 #ifdef INET6 1843 struct ip6_hdr *ip6 = NULL; 1844 #endif 1845 1846 NET_EPOCH_ASSERT(); 1847 1848 hlen = 1849 #ifdef INET6 1850 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1851 #endif 1852 sizeof(struct ip); 1853 tlen = hlen + sizeof(struct tcphdr); 1854 if (sc->sc_port) { 1855 tlen += sizeof(struct udphdr); 1856 } 1857 /* Determine MSS we advertize to other end of connection. */ 1858 mssopt = tcp_mssopt(&sc->sc_inc); 1859 if (sc->sc_port) 1860 mssopt -= V_tcp_udp_tunneling_overhead; 1861 mssopt = max(mssopt, V_tcp_minmss); 1862 1863 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1864 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1865 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1866 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1867 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1868 1869 /* Create the IP+TCP header from scratch. */ 1870 m = m_gethdr(M_NOWAIT, MT_DATA); 1871 if (m == NULL) 1872 return (ENOBUFS); 1873 #ifdef MAC 1874 mac_syncache_create_mbuf(sc->sc_label, m); 1875 #endif 1876 m->m_data += max_linkhdr; 1877 m->m_len = tlen; 1878 m->m_pkthdr.len = tlen; 1879 m->m_pkthdr.rcvif = NULL; 1880 1881 #ifdef INET6 1882 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1883 ip6 = mtod(m, struct ip6_hdr *); 1884 ip6->ip6_vfc = IPV6_VERSION; 1885 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1886 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1887 ip6->ip6_plen = htons(tlen - hlen); 1888 /* ip6_hlim is set after checksum */ 1889 /* Zero out traffic class and flow label. */ 1890 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1891 ip6->ip6_flow |= sc->sc_flowlabel; 1892 if (sc->sc_port != 0) { 1893 ip6->ip6_nxt = IPPROTO_UDP; 1894 udp = (struct udphdr *)(ip6 + 1); 1895 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1896 udp->uh_dport = sc->sc_port; 1897 ulen = (tlen - sizeof(struct ip6_hdr)); 1898 th = (struct tcphdr *)(udp + 1); 1899 } else { 1900 ip6->ip6_nxt = IPPROTO_TCP; 1901 th = (struct tcphdr *)(ip6 + 1); 1902 } 1903 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1904 } 1905 #endif 1906 #if defined(INET6) && defined(INET) 1907 else 1908 #endif 1909 #ifdef INET 1910 { 1911 ip = mtod(m, struct ip *); 1912 ip->ip_v = IPVERSION; 1913 ip->ip_hl = sizeof(struct ip) >> 2; 1914 ip->ip_len = htons(tlen); 1915 ip->ip_id = 0; 1916 ip->ip_off = 0; 1917 ip->ip_sum = 0; 1918 ip->ip_src = sc->sc_inc.inc_laddr; 1919 ip->ip_dst = sc->sc_inc.inc_faddr; 1920 ip->ip_ttl = sc->sc_ip_ttl; 1921 ip->ip_tos = sc->sc_ip_tos; 1922 1923 /* 1924 * See if we should do MTU discovery. Route lookups are 1925 * expensive, so we will only unset the DF bit if: 1926 * 1927 * 1) path_mtu_discovery is disabled 1928 * 2) the SCF_UNREACH flag has been set 1929 */ 1930 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1931 ip->ip_off |= htons(IP_DF); 1932 if (sc->sc_port == 0) { 1933 ip->ip_p = IPPROTO_TCP; 1934 th = (struct tcphdr *)(ip + 1); 1935 } else { 1936 ip->ip_p = IPPROTO_UDP; 1937 udp = (struct udphdr *)(ip + 1); 1938 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1939 udp->uh_dport = sc->sc_port; 1940 ulen = (tlen - sizeof(struct ip)); 1941 th = (struct tcphdr *)(udp + 1); 1942 } 1943 } 1944 #endif /* INET */ 1945 th->th_sport = sc->sc_inc.inc_lport; 1946 th->th_dport = sc->sc_inc.inc_fport; 1947 1948 if (flags & TH_SYN) 1949 th->th_seq = htonl(sc->sc_iss); 1950 else 1951 th->th_seq = htonl(sc->sc_iss + 1); 1952 th->th_ack = htonl(sc->sc_irs + 1); 1953 th->th_off = sizeof(struct tcphdr) >> 2; 1954 th->th_win = htons(sc->sc_wnd); 1955 th->th_urp = 0; 1956 1957 flags = tcp_ecn_syncache_respond(flags, sc); 1958 tcp_set_flags(th, flags); 1959 1960 /* Tack on the TCP options. */ 1961 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1962 to.to_flags = 0; 1963 1964 if (flags & TH_SYN) { 1965 to.to_mss = mssopt; 1966 to.to_flags = TOF_MSS; 1967 if (sc->sc_flags & SCF_WINSCALE) { 1968 to.to_wscale = sc->sc_requested_r_scale; 1969 to.to_flags |= TOF_SCALE; 1970 } 1971 if (sc->sc_flags & SCF_SACK) 1972 to.to_flags |= TOF_SACKPERM; 1973 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1974 if (sc->sc_flags & SCF_SIGNATURE) 1975 to.to_flags |= TOF_SIGNATURE; 1976 #endif 1977 if (sc->sc_tfo_cookie) { 1978 to.to_flags |= TOF_FASTOPEN; 1979 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1980 to.to_tfo_cookie = sc->sc_tfo_cookie; 1981 /* don't send cookie again when retransmitting response */ 1982 sc->sc_tfo_cookie = NULL; 1983 } 1984 } 1985 if (sc->sc_flags & SCF_TIMESTAMP) { 1986 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1987 to.to_tsecr = sc->sc_tsreflect; 1988 to.to_flags |= TOF_TS; 1989 } 1990 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1991 1992 /* Adjust headers by option size. */ 1993 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1994 m->m_len += optlen; 1995 m->m_pkthdr.len += optlen; 1996 #ifdef INET6 1997 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1998 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1999 else 2000 #endif 2001 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 2002 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 2003 if (sc->sc_flags & SCF_SIGNATURE) { 2004 KASSERT(to.to_flags & TOF_SIGNATURE, 2005 ("tcp_addoptions() didn't set tcp_signature")); 2006 2007 /* NOTE: to.to_signature is inside of mbuf */ 2008 if (!TCPMD5_ENABLED() || 2009 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 2010 m_freem(m); 2011 return (EACCES); 2012 } 2013 } 2014 #endif 2015 } else 2016 optlen = 0; 2017 2018 if (udp) { 2019 ulen += optlen; 2020 udp->uh_ulen = htons(ulen); 2021 } 2022 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2023 m->m_pkthdr.flowid = sc->sc_flowid; 2024 M_HASHTYPE_SET(m, sc->sc_flowtype); 2025 #ifdef NUMA 2026 m->m_pkthdr.numa_domain = sc->sc_numa_domain; 2027 #endif 2028 #ifdef INET6 2029 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2030 if (sc->sc_port) { 2031 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2032 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2033 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2034 IPPROTO_UDP, 0); 2035 th->th_sum = htons(0); 2036 } else { 2037 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2038 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2039 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2040 IPPROTO_TCP, 0); 2041 } 2042 ip6->ip6_hlim = sc->sc_ip_ttl; 2043 #ifdef TCP_OFFLOAD 2044 if (ADDED_BY_TOE(sc)) { 2045 struct toedev *tod = sc->sc_tod; 2046 2047 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2048 2049 return (error); 2050 } 2051 #endif 2052 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2053 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2054 } 2055 #endif 2056 #if defined(INET6) && defined(INET) 2057 else 2058 #endif 2059 #ifdef INET 2060 { 2061 if (sc->sc_port) { 2062 m->m_pkthdr.csum_flags = CSUM_UDP; 2063 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2064 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2065 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2066 th->th_sum = htons(0); 2067 } else { 2068 m->m_pkthdr.csum_flags = CSUM_TCP; 2069 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2070 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2071 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2072 } 2073 #ifdef TCP_OFFLOAD 2074 if (ADDED_BY_TOE(sc)) { 2075 struct toedev *tod = sc->sc_tod; 2076 2077 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2078 2079 return (error); 2080 } 2081 #endif 2082 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2083 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2084 } 2085 #endif 2086 return (error); 2087 } 2088 2089 static void 2090 syncache_send_challenge_ack(struct syncache *sc) 2091 { 2092 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2093 &sc->sc_challenge_ack_cnt)) { 2094 if (syncache_respond(sc, TH_ACK) == 0) { 2095 TCPSTAT_INC(tcps_sndacks); 2096 TCPSTAT_INC(tcps_sndtotal); 2097 } 2098 } 2099 } 2100 2101 /* 2102 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2103 * that exceed the capacity of the syncache by avoiding the storage of any 2104 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2105 * attacks where the attacker does not have access to our responses. 2106 * 2107 * Syncookies encode and include all necessary information about the 2108 * connection setup within the SYN|ACK that we send back. That way we 2109 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2110 * (if ever). Normally the syncache and syncookies are running in parallel 2111 * with the latter taking over when the former is exhausted. When matching 2112 * syncache entry is found the syncookie is ignored. 2113 * 2114 * The only reliable information persisting the 3WHS is our initial sequence 2115 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2116 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2117 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2118 * returns and signifies a legitimate connection if it matches the ACK. 2119 * 2120 * The available space of 32 bits to store the hash and to encode the SYN 2121 * option information is very tight and we should have at least 24 bits for 2122 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2123 * 2124 * SYN option information we have to encode to fully restore a connection: 2125 * MSS: is imporant to chose an optimal segment size to avoid IP level 2126 * fragmentation along the path. The common MSS values can be encoded 2127 * in a 3-bit table. Uncommon values are captured by the next lower value 2128 * in the table leading to a slight increase in packetization overhead. 2129 * WSCALE: is necessary to allow large windows to be used for high delay- 2130 * bandwidth product links. Not scaling the window when it was initially 2131 * negotiated is bad for performance as lack of scaling further decreases 2132 * the apparent available send window. We only need to encode the WSCALE 2133 * we received from the remote end. Our end can be recalculated at any 2134 * time. The common WSCALE values can be encoded in a 3-bit table. 2135 * Uncommon values are captured by the next lower value in the table 2136 * making us under-estimate the available window size halving our 2137 * theoretically possible maximum throughput for that connection. 2138 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2139 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2140 * that are included in all segments on a connection. We enable them when 2141 * the ACK has them. 2142 * 2143 * Security of syncookies and attack vectors: 2144 * 2145 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2146 * together with the gloabl secret to make it unique per connection attempt. 2147 * Thus any change of any of those parameters results in a different MAC output 2148 * in an unpredictable way unless a collision is encountered. 24 bits of the 2149 * MAC are embedded into the ISS. 2150 * 2151 * To prevent replay attacks two rotating global secrets are updated with a 2152 * new random value every 15 seconds. The life-time of a syncookie is thus 2153 * 15-30 seconds. 2154 * 2155 * Vector 1: Attacking the secret. This requires finding a weakness in the 2156 * MAC itself or the way it is used here. The attacker can do a chosen plain 2157 * text attack by varying and testing the all parameters under his control. 2158 * The strength depends on the size and randomness of the secret, and the 2159 * cryptographic security of the MAC function. Due to the constant updating 2160 * of the secret the attacker has at most 29.999 seconds to find the secret 2161 * and launch spoofed connections. After that he has to start all over again. 2162 * 2163 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2164 * size an average of 4,823 attempts are required for a 50% chance of success 2165 * to spoof a single syncookie (birthday collision paradox). However the 2166 * attacker is blind and doesn't know if one of his attempts succeeded unless 2167 * he has a side channel to interfere success from. A single connection setup 2168 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2169 * This many attempts are required for each one blind spoofed connection. For 2170 * every additional spoofed connection he has to launch another N attempts. 2171 * Thus for a sustained rate 100 spoofed connections per second approximately 2172 * 1,800,000 packets per second would have to be sent. 2173 * 2174 * NB: The MAC function should be fast so that it doesn't become a CPU 2175 * exhaustion attack vector itself. 2176 * 2177 * References: 2178 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2179 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2180 * http://cr.yp.to/syncookies.html (overview) 2181 * http://cr.yp.to/syncookies/archive (details) 2182 * 2183 * 2184 * Schematic construction of a syncookie enabled Initial Sequence Number: 2185 * 0 1 2 3 2186 * 12345678901234567890123456789012 2187 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2188 * 2189 * x 24 MAC (truncated) 2190 * W 3 Send Window Scale index 2191 * M 3 MSS index 2192 * S 1 SACK permitted 2193 * P 1 Odd/even secret 2194 */ 2195 2196 /* 2197 * Distribution and probability of certain MSS values. Those in between are 2198 * rounded down to the next lower one. 2199 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2200 * .2% .3% 5% 7% 7% 20% 15% 45% 2201 */ 2202 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2203 2204 /* 2205 * Distribution and probability of certain WSCALE values. We have to map the 2206 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2207 * bits based on prevalence of certain values. Where we don't have an exact 2208 * match for are rounded down to the next lower one letting us under-estimate 2209 * the true available window. At the moment this would happen only for the 2210 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2211 * and window size). The absence of the WSCALE option (no scaling in either 2212 * direction) is encoded with index zero. 2213 * [WSCALE values histograms, Allman, 2012] 2214 * X 10 10 35 5 6 14 10% by host 2215 * X 11 4 5 5 18 49 3% by connections 2216 */ 2217 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2218 2219 /* 2220 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2221 * and good cryptographic properties. 2222 */ 2223 static uint32_t 2224 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2225 uint8_t *secbits, uintptr_t secmod) 2226 { 2227 SIPHASH_CTX ctx; 2228 uint32_t siphash[2]; 2229 2230 SipHash24_Init(&ctx); 2231 SipHash_SetKey(&ctx, secbits); 2232 switch (inc->inc_flags & INC_ISIPV6) { 2233 #ifdef INET 2234 case 0: 2235 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2236 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2237 break; 2238 #endif 2239 #ifdef INET6 2240 case INC_ISIPV6: 2241 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2242 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2243 break; 2244 #endif 2245 } 2246 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2247 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2248 SipHash_Update(&ctx, &irs, sizeof(irs)); 2249 SipHash_Update(&ctx, &flags, sizeof(flags)); 2250 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2251 SipHash_Final((u_int8_t *)&siphash, &ctx); 2252 2253 return (siphash[0] ^ siphash[1]); 2254 } 2255 2256 static tcp_seq 2257 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2258 { 2259 u_int i, secbit, wscale; 2260 uint32_t iss, hash; 2261 uint8_t *secbits; 2262 union syncookie cookie; 2263 2264 cookie.cookie = 0; 2265 2266 /* Map our computed MSS into the 3-bit index. */ 2267 for (i = nitems(tcp_sc_msstab) - 1; 2268 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2269 i--) 2270 ; 2271 cookie.flags.mss_idx = i; 2272 2273 /* 2274 * Map the send window scale into the 3-bit index but only if 2275 * the wscale option was received. 2276 */ 2277 if (sc->sc_flags & SCF_WINSCALE) { 2278 wscale = sc->sc_requested_s_scale; 2279 for (i = nitems(tcp_sc_wstab) - 1; 2280 tcp_sc_wstab[i] > wscale && i > 0; 2281 i--) 2282 ; 2283 cookie.flags.wscale_idx = i; 2284 } 2285 2286 /* Can we do SACK? */ 2287 if (sc->sc_flags & SCF_SACK) 2288 cookie.flags.sack_ok = 1; 2289 2290 /* Which of the two secrets to use. */ 2291 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2292 cookie.flags.odd_even = secbit; 2293 2294 secbits = V_tcp_syncache.secret.key[secbit]; 2295 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2296 (uintptr_t)sch); 2297 2298 /* 2299 * Put the flags into the hash and XOR them to get better ISS number 2300 * variance. This doesn't enhance the cryptographic strength and is 2301 * done to prevent the 8 cookie bits from showing up directly on the 2302 * wire. 2303 */ 2304 iss = hash & ~0xff; 2305 iss |= cookie.cookie ^ (hash >> 24); 2306 2307 TCPSTAT_INC(tcps_sc_sendcookie); 2308 return (iss); 2309 } 2310 2311 static bool 2312 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2313 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2314 struct socket *lso, uint16_t port) 2315 { 2316 uint32_t hash; 2317 uint8_t *secbits; 2318 tcp_seq ack, seq; 2319 int wnd; 2320 union syncookie cookie; 2321 2322 /* 2323 * Pull information out of SYN-ACK/ACK and revert sequence number 2324 * advances. 2325 */ 2326 ack = th->th_ack - 1; 2327 seq = th->th_seq - 1; 2328 2329 /* 2330 * Unpack the flags containing enough information to restore the 2331 * connection. 2332 */ 2333 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2334 2335 /* Which of the two secrets to use. */ 2336 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2337 2338 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2339 2340 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2341 if ((ack & ~0xff) != (hash & ~0xff)) 2342 return (false); 2343 2344 /* Fill in the syncache values. */ 2345 sc->sc_flags = 0; 2346 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2347 sc->sc_ipopts = NULL; 2348 2349 sc->sc_irs = seq; 2350 sc->sc_iss = ack; 2351 2352 switch (inc->inc_flags & INC_ISIPV6) { 2353 #ifdef INET 2354 case 0: 2355 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2356 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2357 break; 2358 #endif 2359 #ifdef INET6 2360 case INC_ISIPV6: 2361 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2362 sc->sc_flowlabel = 2363 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2364 break; 2365 #endif 2366 } 2367 2368 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2369 2370 /* Only use wscale if it was enabled in the orignal SYN. */ 2371 if (cookie.flags.wscale_idx > 0) { 2372 u_int wscale = 0; 2373 2374 /* Recompute the receive window scale that was sent earlier. */ 2375 while (wscale < TCP_MAX_WINSHIFT && 2376 (TCP_MAXWIN << wscale) < sb_max) 2377 wscale++; 2378 sc->sc_requested_r_scale = wscale; 2379 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2380 sc->sc_flags |= SCF_WINSCALE; 2381 } 2382 2383 wnd = lso->sol_sbrcv_hiwat; 2384 wnd = imax(wnd, 0); 2385 wnd = imin(wnd, TCP_MAXWIN); 2386 sc->sc_wnd = wnd; 2387 2388 if (cookie.flags.sack_ok) 2389 sc->sc_flags |= SCF_SACK; 2390 2391 if (to->to_flags & TOF_TS) { 2392 sc->sc_flags |= SCF_TIMESTAMP; 2393 sc->sc_tsreflect = to->to_tsval; 2394 sc->sc_tsoff = tcp_new_ts_offset(inc); 2395 } 2396 2397 if (to->to_flags & TOF_SIGNATURE) 2398 sc->sc_flags |= SCF_SIGNATURE; 2399 2400 sc->sc_rxmits = 0; 2401 2402 sc->sc_port = port; 2403 2404 return (true); 2405 } 2406 2407 #ifdef INVARIANTS 2408 static void 2409 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2410 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2411 struct socket *lso, uint16_t port) 2412 { 2413 struct syncache scs; 2414 char *s; 2415 2416 bzero(&scs, sizeof(scs)); 2417 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2418 (sc->sc_peer_mss != scs.sc_peer_mss || 2419 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2420 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2421 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2422 2423 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2424 return; 2425 2426 if (sc->sc_peer_mss != scs.sc_peer_mss) 2427 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2428 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2429 2430 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2431 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2432 s, __func__, sc->sc_requested_r_scale, 2433 scs.sc_requested_r_scale); 2434 2435 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2436 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2437 s, __func__, sc->sc_requested_s_scale, 2438 scs.sc_requested_s_scale); 2439 2440 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2441 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2442 2443 free(s, M_TCPLOG); 2444 } 2445 } 2446 #endif /* INVARIANTS */ 2447 2448 static void 2449 syncookie_reseed(void *arg) 2450 { 2451 struct tcp_syncache *sc = arg; 2452 uint8_t *secbits; 2453 int secbit; 2454 2455 /* 2456 * Reseeding the secret doesn't have to be protected by a lock. 2457 * It only must be ensured that the new random values are visible 2458 * to all CPUs in a SMP environment. The atomic with release 2459 * semantics ensures that. 2460 */ 2461 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2462 secbits = sc->secret.key[secbit]; 2463 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2464 atomic_add_rel_int(&sc->secret.oddeven, 1); 2465 2466 /* Reschedule ourself. */ 2467 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2468 } 2469 2470 /* 2471 * We have overflowed a bucket. Let's pause dealing with the syncache. 2472 * This function will increment the bucketoverflow statistics appropriately 2473 * (once per pause when pausing is enabled; otherwise, once per overflow). 2474 */ 2475 static void 2476 syncache_pause(struct in_conninfo *inc) 2477 { 2478 time_t delta; 2479 const char *s; 2480 2481 /* XXX: 2482 * 2. Add sysctl read here so we don't get the benefit of this 2483 * change without the new sysctl. 2484 */ 2485 2486 /* 2487 * Try an unlocked read. If we already know that another thread 2488 * has activated the feature, there is no need to proceed. 2489 */ 2490 if (V_tcp_syncache.paused) 2491 return; 2492 2493 /* Are cookied enabled? If not, we can't pause. */ 2494 if (!V_tcp_syncookies) { 2495 TCPSTAT_INC(tcps_sc_bucketoverflow); 2496 return; 2497 } 2498 2499 /* 2500 * We may be the first thread to find an overflow. Get the lock 2501 * and evaluate if we need to take action. 2502 */ 2503 mtx_lock(&V_tcp_syncache.pause_mtx); 2504 if (V_tcp_syncache.paused) { 2505 mtx_unlock(&V_tcp_syncache.pause_mtx); 2506 return; 2507 } 2508 2509 /* Activate protection. */ 2510 V_tcp_syncache.paused = true; 2511 TCPSTAT_INC(tcps_sc_bucketoverflow); 2512 2513 /* 2514 * Determine the last backoff time. If we are seeing a re-newed 2515 * attack within that same time after last reactivating the syncache, 2516 * consider it an extension of the same attack. 2517 */ 2518 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2519 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2520 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2521 delta <<= 1; 2522 V_tcp_syncache.pause_backoff++; 2523 } 2524 } else { 2525 delta = TCP_SYNCACHE_PAUSE_TIME; 2526 V_tcp_syncache.pause_backoff = 0; 2527 } 2528 2529 /* Log a warning, including IP addresses, if able. */ 2530 if (inc != NULL) 2531 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2532 else 2533 s = (const char *)NULL; 2534 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2535 "the next %lld seconds%s%s%s\n", (long long)delta, 2536 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2537 (s != NULL) ? ")" : ""); 2538 free(__DECONST(void *, s), M_TCPLOG); 2539 2540 /* Use the calculated delta to set a new pause time. */ 2541 V_tcp_syncache.pause_until = time_uptime + delta; 2542 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2543 &V_tcp_syncache); 2544 mtx_unlock(&V_tcp_syncache.pause_mtx); 2545 } 2546 2547 /* Evaluate whether we need to unpause. */ 2548 static void 2549 syncache_unpause(void *arg) 2550 { 2551 struct tcp_syncache *sc; 2552 time_t delta; 2553 2554 sc = arg; 2555 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2556 callout_deactivate(&sc->pause_co); 2557 2558 /* 2559 * Check to make sure we are not running early. If the pause 2560 * time has expired, then deactivate the protection. 2561 */ 2562 if ((delta = sc->pause_until - time_uptime) > 0) 2563 callout_schedule(&sc->pause_co, delta * hz); 2564 else 2565 sc->paused = false; 2566 } 2567 2568 /* 2569 * Exports the syncache entries to userland so that netstat can display 2570 * them alongside the other sockets. This function is intended to be 2571 * called only from tcp_pcblist. 2572 * 2573 * Due to concurrency on an active system, the number of pcbs exported 2574 * may have no relation to max_pcbs. max_pcbs merely indicates the 2575 * amount of space the caller allocated for this function to use. 2576 */ 2577 int 2578 syncache_pcblist(struct sysctl_req *req) 2579 { 2580 struct xtcpcb xt; 2581 struct syncache *sc; 2582 struct syncache_head *sch; 2583 int error, i; 2584 2585 bzero(&xt, sizeof(xt)); 2586 xt.xt_len = sizeof(xt); 2587 xt.t_state = TCPS_SYN_RECEIVED; 2588 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2589 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2590 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2591 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2592 2593 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2594 sch = &V_tcp_syncache.hashbase[i]; 2595 SCH_LOCK(sch); 2596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2597 if (sc->sc_cred != NULL && 2598 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2599 continue; 2600 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2601 xt.xt_inp.inp_vflag = INP_IPV6; 2602 else 2603 xt.xt_inp.inp_vflag = INP_IPV4; 2604 xt.xt_encaps_port = sc->sc_port; 2605 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2606 sizeof (struct in_conninfo)); 2607 error = SYSCTL_OUT(req, &xt, sizeof xt); 2608 if (error) { 2609 SCH_UNLOCK(sch); 2610 return (0); 2611 } 2612 } 2613 SCH_UNLOCK(sch); 2614 } 2615 2616 return (0); 2617 } 2618