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