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sys/netinet/tcp_syncache.c
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1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD$"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_pcbgroup.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/hash.h> 44 #include <sys/refcount.h> 45 #include <sys/kernel.h> 46 #include <sys/sysctl.h> 47 #include <sys/limits.h> 48 #include <sys/lock.h> 49 #include <sys/mutex.h> 50 #include <sys/malloc.h> 51 #include <sys/mbuf.h> 52 #include <sys/proc.h> /* for proc0 declaration */ 53 #include <sys/random.h> 54 #include <sys/socket.h> 55 #include <sys/socketvar.h> 56 #include <sys/syslog.h> 57 #include <sys/ucred.h> 58 59 #include <sys/md5.h> 60 #include <crypto/siphash/siphash.h> 61 62 #include <vm/uma.h> 63 64 #include <net/if.h> 65 #include <net/if_var.h> 66 #include <net/route.h> 67 #include <net/vnet.h> 68 69 #include <netinet/in.h> 70 #include <netinet/in_kdtrace.h> 71 #include <netinet/in_systm.h> 72 #include <netinet/ip.h> 73 #include <netinet/in_var.h> 74 #include <netinet/in_pcb.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 #endif 84 #include <netinet/tcp.h> 85 #ifdef TCP_RFC7413 86 #include <netinet/tcp_fastopen.h> 87 #endif 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 static VNET_DEFINE(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 #ifdef TCP_OFFLOAD 119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 120 #endif 121 122 static void syncache_drop(struct syncache *, struct syncache_head *); 123 static void syncache_free(struct syncache *); 124 static void syncache_insert(struct syncache *, struct syncache_head *); 125 static int syncache_respond(struct syncache *, struct syncache_head *, int, 126 const struct mbuf *); 127 static struct socket *syncache_socket(struct syncache *, struct socket *, 128 struct mbuf *m); 129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 130 int docallout); 131 static void syncache_timer(void *); 132 133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 134 uint8_t *, uintptr_t); 135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 136 static struct syncache 137 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 138 struct syncache *, struct tcphdr *, struct tcpopt *, 139 struct socket *); 140 static void syncookie_reseed(void *); 141 #ifdef INVARIANTS 142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 144 struct socket *lso); 145 #endif 146 147 /* 148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 149 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 150 * the odds are that the user has given up attempting to connect by then. 151 */ 152 #define SYNCACHE_MAXREXMTS 3 153 154 /* Arbitrary values */ 155 #define TCP_SYNCACHE_HASHSIZE 512 156 #define TCP_SYNCACHE_BUCKETLIMIT 30 157 158 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 159 #define V_tcp_syncache VNET(tcp_syncache) 160 161 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 162 "TCP SYN cache"); 163 164 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 165 &VNET_NAME(tcp_syncache.bucket_limit), 0, 166 "Per-bucket hash limit for syncache"); 167 168 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 169 &VNET_NAME(tcp_syncache.cache_limit), 0, 170 "Overall entry limit for syncache"); 171 172 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 173 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 174 175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 176 &VNET_NAME(tcp_syncache.hashsize), 0, 177 "Size of TCP syncache hashtable"); 178 179 static int 180 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 181 { 182 int error; 183 u_int new; 184 185 new = V_tcp_syncache.rexmt_limit; 186 error = sysctl_handle_int(oidp, &new, 0, req); 187 if ((error == 0) && (req->newptr != NULL)) { 188 if (new > TCP_MAXRXTSHIFT) 189 error = EINVAL; 190 else 191 V_tcp_syncache.rexmt_limit = new; 192 } 193 return (error); 194 } 195 196 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 197 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW, 198 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 199 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 200 "Limit on SYN/ACK retransmissions"); 201 202 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 203 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 204 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 205 "Send reset on socket allocation failure"); 206 207 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 208 209 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 210 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 211 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 212 213 /* 214 * Requires the syncache entry to be already removed from the bucket list. 215 */ 216 static void 217 syncache_free(struct syncache *sc) 218 { 219 220 if (sc->sc_ipopts) 221 (void) m_free(sc->sc_ipopts); 222 if (sc->sc_cred) 223 crfree(sc->sc_cred); 224 #ifdef MAC 225 mac_syncache_destroy(&sc->sc_label); 226 #endif 227 228 uma_zfree(V_tcp_syncache.zone, sc); 229 } 230 231 void 232 syncache_init(void) 233 { 234 int i; 235 236 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 237 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 238 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 239 V_tcp_syncache.hash_secret = arc4random(); 240 241 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 242 &V_tcp_syncache.hashsize); 243 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 244 &V_tcp_syncache.bucket_limit); 245 if (!powerof2(V_tcp_syncache.hashsize) || 246 V_tcp_syncache.hashsize == 0) { 247 printf("WARNING: syncache hash size is not a power of 2.\n"); 248 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 249 } 250 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 251 252 /* Set limits. */ 253 V_tcp_syncache.cache_limit = 254 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 256 &V_tcp_syncache.cache_limit); 257 258 /* Allocate the hash table. */ 259 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 260 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 261 262 #ifdef VIMAGE 263 V_tcp_syncache.vnet = curvnet; 264 #endif 265 266 /* Initialize the hash buckets. */ 267 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 268 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 269 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 270 NULL, MTX_DEF); 271 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 272 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 273 V_tcp_syncache.hashbase[i].sch_length = 0; 274 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 275 V_tcp_syncache.hashbase[i].sch_last_overflow = 276 -(SYNCOOKIE_LIFETIME + 1); 277 } 278 279 /* Create the syncache entry zone. */ 280 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 281 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 282 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 283 V_tcp_syncache.cache_limit); 284 285 /* Start the SYN cookie reseeder callout. */ 286 callout_init(&V_tcp_syncache.secret.reseed, 1); 287 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 288 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 289 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 290 syncookie_reseed, &V_tcp_syncache); 291 } 292 293 #ifdef VIMAGE 294 void 295 syncache_destroy(void) 296 { 297 struct syncache_head *sch; 298 struct syncache *sc, *nsc; 299 int i; 300 301 /* 302 * Stop the re-seed timer before freeing resources. No need to 303 * possibly schedule it another time. 304 */ 305 callout_drain(&V_tcp_syncache.secret.reseed); 306 307 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 308 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 309 310 sch = &V_tcp_syncache.hashbase[i]; 311 callout_drain(&sch->sch_timer); 312 313 SCH_LOCK(sch); 314 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 315 syncache_drop(sc, sch); 316 SCH_UNLOCK(sch); 317 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 318 ("%s: sch->sch_bucket not empty", __func__)); 319 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 320 __func__, sch->sch_length)); 321 mtx_destroy(&sch->sch_mtx); 322 } 323 324 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 325 ("%s: cache_count not 0", __func__)); 326 327 /* Free the allocated global resources. */ 328 uma_zdestroy(V_tcp_syncache.zone); 329 free(V_tcp_syncache.hashbase, M_SYNCACHE); 330 } 331 #endif 332 333 /* 334 * Inserts a syncache entry into the specified bucket row. 335 * Locks and unlocks the syncache_head autonomously. 336 */ 337 static void 338 syncache_insert(struct syncache *sc, struct syncache_head *sch) 339 { 340 struct syncache *sc2; 341 342 SCH_LOCK(sch); 343 344 /* 345 * Make sure that we don't overflow the per-bucket limit. 346 * If the bucket is full, toss the oldest element. 347 */ 348 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 349 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 350 ("sch->sch_length incorrect")); 351 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 352 sch->sch_last_overflow = time_uptime; 353 syncache_drop(sc2, sch); 354 TCPSTAT_INC(tcps_sc_bucketoverflow); 355 } 356 357 /* Put it into the bucket. */ 358 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 359 sch->sch_length++; 360 361 #ifdef TCP_OFFLOAD 362 if (ADDED_BY_TOE(sc)) { 363 struct toedev *tod = sc->sc_tod; 364 365 tod->tod_syncache_added(tod, sc->sc_todctx); 366 } 367 #endif 368 369 /* Reinitialize the bucket row's timer. */ 370 if (sch->sch_length == 1) 371 sch->sch_nextc = ticks + INT_MAX; 372 syncache_timeout(sc, sch, 1); 373 374 SCH_UNLOCK(sch); 375 376 TCPSTATES_INC(TCPS_SYN_RECEIVED); 377 TCPSTAT_INC(tcps_sc_added); 378 } 379 380 /* 381 * Remove and free entry from syncache bucket row. 382 * Expects locked syncache head. 383 */ 384 static void 385 syncache_drop(struct syncache *sc, struct syncache_head *sch) 386 { 387 388 SCH_LOCK_ASSERT(sch); 389 390 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 391 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 392 sch->sch_length--; 393 394 #ifdef TCP_OFFLOAD 395 if (ADDED_BY_TOE(sc)) { 396 struct toedev *tod = sc->sc_tod; 397 398 tod->tod_syncache_removed(tod, sc->sc_todctx); 399 } 400 #endif 401 402 syncache_free(sc); 403 } 404 405 /* 406 * Engage/reengage time on bucket row. 407 */ 408 static void 409 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 410 { 411 int rexmt; 412 413 if (sc->sc_rxmits == 0) 414 rexmt = TCPTV_RTOBASE; 415 else 416 TCPT_RANGESET(rexmt, TCPTV_RTOBASE * tcp_syn_backoff[sc->sc_rxmits], 417 tcp_rexmit_min, TCPTV_REXMTMAX); 418 sc->sc_rxttime = ticks + rexmt; 419 sc->sc_rxmits++; 420 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 421 sch->sch_nextc = sc->sc_rxttime; 422 if (docallout) 423 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 424 syncache_timer, (void *)sch); 425 } 426 } 427 428 /* 429 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 430 * If we have retransmitted an entry the maximum number of times, expire it. 431 * One separate timer for each bucket row. 432 */ 433 static void 434 syncache_timer(void *xsch) 435 { 436 struct syncache_head *sch = (struct syncache_head *)xsch; 437 struct syncache *sc, *nsc; 438 int tick = ticks; 439 char *s; 440 441 CURVNET_SET(sch->sch_sc->vnet); 442 443 /* NB: syncache_head has already been locked by the callout. */ 444 SCH_LOCK_ASSERT(sch); 445 446 /* 447 * In the following cycle we may remove some entries and/or 448 * advance some timeouts, so re-initialize the bucket timer. 449 */ 450 sch->sch_nextc = tick + INT_MAX; 451 452 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 453 /* 454 * We do not check if the listen socket still exists 455 * and accept the case where the listen socket may be 456 * gone by the time we resend the SYN/ACK. We do 457 * not expect this to happens often. If it does, 458 * then the RST will be sent by the time the remote 459 * host does the SYN/ACK->ACK. 460 */ 461 if (TSTMP_GT(sc->sc_rxttime, tick)) { 462 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 463 sch->sch_nextc = sc->sc_rxttime; 464 continue; 465 } 466 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 467 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 468 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 469 "giving up and removing syncache entry\n", 470 s, __func__); 471 free(s, M_TCPLOG); 472 } 473 syncache_drop(sc, sch); 474 TCPSTAT_INC(tcps_sc_stale); 475 continue; 476 } 477 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 478 log(LOG_DEBUG, "%s; %s: Response timeout, " 479 "retransmitting (%u) SYN|ACK\n", 480 s, __func__, sc->sc_rxmits); 481 free(s, M_TCPLOG); 482 } 483 484 syncache_respond(sc, sch, 1, NULL); 485 TCPSTAT_INC(tcps_sc_retransmitted); 486 syncache_timeout(sc, sch, 0); 487 } 488 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 489 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 490 syncache_timer, (void *)(sch)); 491 CURVNET_RESTORE(); 492 } 493 494 /* 495 * Find an entry in the syncache. 496 * Returns always with locked syncache_head plus a matching entry or NULL. 497 */ 498 static struct syncache * 499 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 500 { 501 struct syncache *sc; 502 struct syncache_head *sch; 503 uint32_t hash; 504 505 /* 506 * The hash is built on foreign port + local port + foreign address. 507 * We rely on the fact that struct in_conninfo starts with 16 bits 508 * of foreign port, then 16 bits of local port then followed by 128 509 * bits of foreign address. In case of IPv4 address, the first 3 510 * 32-bit words of the address always are zeroes. 511 */ 512 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 513 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 514 515 sch = &V_tcp_syncache.hashbase[hash]; 516 *schp = sch; 517 SCH_LOCK(sch); 518 519 /* Circle through bucket row to find matching entry. */ 520 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 521 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 522 sizeof(struct in_endpoints)) == 0) 523 break; 524 525 return (sc); /* Always returns with locked sch. */ 526 } 527 528 /* 529 * This function is called when we get a RST for a 530 * non-existent connection, so that we can see if the 531 * connection is in the syn cache. If it is, zap it. 532 */ 533 void 534 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 535 { 536 struct syncache *sc; 537 struct syncache_head *sch; 538 char *s = NULL; 539 540 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 541 SCH_LOCK_ASSERT(sch); 542 543 /* 544 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 545 * See RFC 793 page 65, section SEGMENT ARRIVES. 546 */ 547 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 548 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 549 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 550 "FIN flag set, segment ignored\n", s, __func__); 551 TCPSTAT_INC(tcps_badrst); 552 goto done; 553 } 554 555 /* 556 * No corresponding connection was found in syncache. 557 * If syncookies are enabled and possibly exclusively 558 * used, or we are under memory pressure, a valid RST 559 * may not find a syncache entry. In that case we're 560 * done and no SYN|ACK retransmissions will happen. 561 * Otherwise the RST was misdirected or spoofed. 562 */ 563 if (sc == NULL) { 564 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 565 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 566 "syncache entry (possibly syncookie only), " 567 "segment ignored\n", s, __func__); 568 TCPSTAT_INC(tcps_badrst); 569 goto done; 570 } 571 572 /* 573 * If the RST bit is set, check the sequence number to see 574 * if this is a valid reset segment. 575 * RFC 793 page 37: 576 * In all states except SYN-SENT, all reset (RST) segments 577 * are validated by checking their SEQ-fields. A reset is 578 * valid if its sequence number is in the window. 579 * 580 * The sequence number in the reset segment is normally an 581 * echo of our outgoing acknowlegement numbers, but some hosts 582 * send a reset with the sequence number at the rightmost edge 583 * of our receive window, and we have to handle this case. 584 */ 585 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 586 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 587 syncache_drop(sc, sch); 588 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 589 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 590 "connection attempt aborted by remote endpoint\n", 591 s, __func__); 592 TCPSTAT_INC(tcps_sc_reset); 593 } else { 594 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 595 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 596 "IRS %u (+WND %u), segment ignored\n", 597 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 598 TCPSTAT_INC(tcps_badrst); 599 } 600 601 done: 602 if (s != NULL) 603 free(s, M_TCPLOG); 604 SCH_UNLOCK(sch); 605 } 606 607 void 608 syncache_badack(struct in_conninfo *inc) 609 { 610 struct syncache *sc; 611 struct syncache_head *sch; 612 613 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 614 SCH_LOCK_ASSERT(sch); 615 if (sc != NULL) { 616 syncache_drop(sc, sch); 617 TCPSTAT_INC(tcps_sc_badack); 618 } 619 SCH_UNLOCK(sch); 620 } 621 622 void 623 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 624 { 625 struct syncache *sc; 626 struct syncache_head *sch; 627 628 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 629 SCH_LOCK_ASSERT(sch); 630 if (sc == NULL) 631 goto done; 632 633 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 634 if (ntohl(th_seq) != sc->sc_iss) 635 goto done; 636 637 /* 638 * If we've rertransmitted 3 times and this is our second error, 639 * we remove the entry. Otherwise, we allow it to continue on. 640 * This prevents us from incorrectly nuking an entry during a 641 * spurious network outage. 642 * 643 * See tcp_notify(). 644 */ 645 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 646 sc->sc_flags |= SCF_UNREACH; 647 goto done; 648 } 649 syncache_drop(sc, sch); 650 TCPSTAT_INC(tcps_sc_unreach); 651 done: 652 SCH_UNLOCK(sch); 653 } 654 655 /* 656 * Build a new TCP socket structure from a syncache entry. 657 * 658 * On success return the newly created socket with its underlying inp locked. 659 */ 660 static struct socket * 661 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 662 { 663 struct tcp_function_block *blk; 664 struct inpcb *inp = NULL; 665 struct socket *so; 666 struct tcpcb *tp; 667 int error; 668 char *s; 669 670 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 671 672 /* 673 * Ok, create the full blown connection, and set things up 674 * as they would have been set up if we had created the 675 * connection when the SYN arrived. If we can't create 676 * the connection, abort it. 677 */ 678 so = sonewconn(lso, 0); 679 if (so == NULL) { 680 /* 681 * Drop the connection; we will either send a RST or 682 * have the peer retransmit its SYN again after its 683 * RTO and try again. 684 */ 685 TCPSTAT_INC(tcps_listendrop); 686 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 687 log(LOG_DEBUG, "%s; %s: Socket create failed " 688 "due to limits or memory shortage\n", 689 s, __func__); 690 free(s, M_TCPLOG); 691 } 692 goto abort2; 693 } 694 #ifdef MAC 695 mac_socketpeer_set_from_mbuf(m, so); 696 #endif 697 698 inp = sotoinpcb(so); 699 inp->inp_inc.inc_fibnum = so->so_fibnum; 700 INP_WLOCK(inp); 701 /* 702 * Exclusive pcbinfo lock is not required in syncache socket case even 703 * if two inpcb locks can be acquired simultaneously: 704 * - the inpcb in LISTEN state, 705 * - the newly created inp. 706 * 707 * In this case, an inp cannot be at same time in LISTEN state and 708 * just created by an accept() call. 709 */ 710 INP_HASH_WLOCK(&V_tcbinfo); 711 712 /* Insert new socket into PCB hash list. */ 713 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 714 #ifdef INET6 715 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 716 inp->inp_vflag &= ~INP_IPV4; 717 inp->inp_vflag |= INP_IPV6; 718 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 719 } else { 720 inp->inp_vflag &= ~INP_IPV6; 721 inp->inp_vflag |= INP_IPV4; 722 #endif 723 inp->inp_laddr = sc->sc_inc.inc_laddr; 724 #ifdef INET6 725 } 726 #endif 727 728 /* 729 * If there's an mbuf and it has a flowid, then let's initialise the 730 * inp with that particular flowid. 731 */ 732 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 733 inp->inp_flowid = m->m_pkthdr.flowid; 734 inp->inp_flowtype = M_HASHTYPE_GET(m); 735 } 736 737 /* 738 * Install in the reservation hash table for now, but don't yet 739 * install a connection group since the full 4-tuple isn't yet 740 * configured. 741 */ 742 inp->inp_lport = sc->sc_inc.inc_lport; 743 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 744 /* 745 * Undo the assignments above if we failed to 746 * put the PCB on the hash lists. 747 */ 748 #ifdef INET6 749 if (sc->sc_inc.inc_flags & INC_ISIPV6) 750 inp->in6p_laddr = in6addr_any; 751 else 752 #endif 753 inp->inp_laddr.s_addr = INADDR_ANY; 754 inp->inp_lport = 0; 755 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 756 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 757 "with error %i\n", 758 s, __func__, error); 759 free(s, M_TCPLOG); 760 } 761 INP_HASH_WUNLOCK(&V_tcbinfo); 762 goto abort; 763 } 764 #ifdef INET6 765 if (inp->inp_vflag & INP_IPV6PROTO) { 766 struct inpcb *oinp = sotoinpcb(lso); 767 768 /* 769 * Inherit socket options from the listening socket. 770 * Note that in6p_inputopts are not (and should not be) 771 * copied, since it stores previously received options and is 772 * used to detect if each new option is different than the 773 * previous one and hence should be passed to a user. 774 * If we copied in6p_inputopts, a user would not be able to 775 * receive options just after calling the accept system call. 776 */ 777 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 778 if (oinp->in6p_outputopts) 779 inp->in6p_outputopts = 780 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 781 } 782 783 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 784 struct in6_addr laddr6; 785 struct sockaddr_in6 sin6; 786 787 sin6.sin6_family = AF_INET6; 788 sin6.sin6_len = sizeof(sin6); 789 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 790 sin6.sin6_port = sc->sc_inc.inc_fport; 791 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 792 laddr6 = inp->in6p_laddr; 793 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 794 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 795 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 796 thread0.td_ucred, m)) != 0) { 797 inp->in6p_laddr = laddr6; 798 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 799 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 800 "with error %i\n", 801 s, __func__, error); 802 free(s, M_TCPLOG); 803 } 804 INP_HASH_WUNLOCK(&V_tcbinfo); 805 goto abort; 806 } 807 /* Override flowlabel from in6_pcbconnect. */ 808 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 809 inp->inp_flow |= sc->sc_flowlabel; 810 } 811 #endif /* INET6 */ 812 #if defined(INET) && defined(INET6) 813 else 814 #endif 815 #ifdef INET 816 { 817 struct in_addr laddr; 818 struct sockaddr_in sin; 819 820 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 821 822 if (inp->inp_options == NULL) { 823 inp->inp_options = sc->sc_ipopts; 824 sc->sc_ipopts = NULL; 825 } 826 827 sin.sin_family = AF_INET; 828 sin.sin_len = sizeof(sin); 829 sin.sin_addr = sc->sc_inc.inc_faddr; 830 sin.sin_port = sc->sc_inc.inc_fport; 831 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 832 laddr = inp->inp_laddr; 833 if (inp->inp_laddr.s_addr == INADDR_ANY) 834 inp->inp_laddr = sc->sc_inc.inc_laddr; 835 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 836 thread0.td_ucred, m)) != 0) { 837 inp->inp_laddr = laddr; 838 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 839 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 840 "with error %i\n", 841 s, __func__, error); 842 free(s, M_TCPLOG); 843 } 844 INP_HASH_WUNLOCK(&V_tcbinfo); 845 goto abort; 846 } 847 } 848 #endif /* INET */ 849 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 850 /* Copy old policy into new socket's. */ 851 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 852 printf("syncache_socket: could not copy policy\n"); 853 #endif 854 INP_HASH_WUNLOCK(&V_tcbinfo); 855 tp = intotcpcb(inp); 856 tcp_state_change(tp, TCPS_SYN_RECEIVED); 857 tp->iss = sc->sc_iss; 858 tp->irs = sc->sc_irs; 859 tcp_rcvseqinit(tp); 860 tcp_sendseqinit(tp); 861 blk = sototcpcb(lso)->t_fb; 862 if (blk != tp->t_fb) { 863 /* 864 * Our parents t_fb was not the default, 865 * we need to release our ref on tp->t_fb and 866 * pickup one on the new entry. 867 */ 868 struct tcp_function_block *rblk; 869 870 rblk = find_and_ref_tcp_fb(blk); 871 KASSERT(rblk != NULL, 872 ("cannot find blk %p out of syncache?", blk)); 873 if (tp->t_fb->tfb_tcp_fb_fini) 874 (*tp->t_fb->tfb_tcp_fb_fini)(tp); 875 refcount_release(&tp->t_fb->tfb_refcnt); 876 tp->t_fb = rblk; 877 if (tp->t_fb->tfb_tcp_fb_init) { 878 (*tp->t_fb->tfb_tcp_fb_init)(tp); 879 } 880 } 881 tp->snd_wl1 = sc->sc_irs; 882 tp->snd_max = tp->iss + 1; 883 tp->snd_nxt = tp->iss + 1; 884 tp->rcv_up = sc->sc_irs + 1; 885 tp->rcv_wnd = sc->sc_wnd; 886 tp->rcv_adv += tp->rcv_wnd; 887 tp->last_ack_sent = tp->rcv_nxt; 888 889 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 890 if (sc->sc_flags & SCF_NOOPT) 891 tp->t_flags |= TF_NOOPT; 892 else { 893 if (sc->sc_flags & SCF_WINSCALE) { 894 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 895 tp->snd_scale = sc->sc_requested_s_scale; 896 tp->request_r_scale = sc->sc_requested_r_scale; 897 } 898 if (sc->sc_flags & SCF_TIMESTAMP) { 899 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 900 tp->ts_recent = sc->sc_tsreflect; 901 tp->ts_recent_age = tcp_ts_getticks(); 902 tp->ts_offset = sc->sc_tsoff; 903 } 904 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 905 if (sc->sc_flags & SCF_SIGNATURE) 906 tp->t_flags |= TF_SIGNATURE; 907 #endif 908 if (sc->sc_flags & SCF_SACK) 909 tp->t_flags |= TF_SACK_PERMIT; 910 } 911 912 if (sc->sc_flags & SCF_ECN) 913 tp->t_flags |= TF_ECN_PERMIT; 914 915 /* 916 * Set up MSS and get cached values from tcp_hostcache. 917 * This might overwrite some of the defaults we just set. 918 */ 919 tcp_mss(tp, sc->sc_peer_mss); 920 921 /* 922 * If the SYN,ACK was retransmitted, indicate that CWND to be 923 * limited to one segment in cc_conn_init(). 924 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 925 */ 926 if (sc->sc_rxmits > 1) 927 tp->snd_cwnd = 1; 928 929 #ifdef TCP_OFFLOAD 930 /* 931 * Allow a TOE driver to install its hooks. Note that we hold the 932 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 933 * new connection before the TOE driver has done its thing. 934 */ 935 if (ADDED_BY_TOE(sc)) { 936 struct toedev *tod = sc->sc_tod; 937 938 tod->tod_offload_socket(tod, sc->sc_todctx, so); 939 } 940 #endif 941 /* 942 * Copy and activate timers. 943 */ 944 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 945 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 946 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 947 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 948 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 949 950 TCPSTAT_INC(tcps_accepts); 951 return (so); 952 953 abort: 954 INP_WUNLOCK(inp); 955 abort2: 956 if (so != NULL) 957 soabort(so); 958 return (NULL); 959 } 960 961 /* 962 * This function gets called when we receive an ACK for a 963 * socket in the LISTEN state. We look up the connection 964 * in the syncache, and if its there, we pull it out of 965 * the cache and turn it into a full-blown connection in 966 * the SYN-RECEIVED state. 967 * 968 * On syncache_socket() success the newly created socket 969 * has its underlying inp locked. 970 */ 971 int 972 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 973 struct socket **lsop, struct mbuf *m) 974 { 975 struct syncache *sc; 976 struct syncache_head *sch; 977 struct syncache scs; 978 char *s; 979 980 /* 981 * Global TCP locks are held because we manipulate the PCB lists 982 * and create a new socket. 983 */ 984 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 985 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 986 ("%s: can handle only ACK", __func__)); 987 988 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 989 SCH_LOCK_ASSERT(sch); 990 991 #ifdef INVARIANTS 992 /* 993 * Test code for syncookies comparing the syncache stored 994 * values with the reconstructed values from the cookie. 995 */ 996 if (sc != NULL) 997 syncookie_cmp(inc, sch, sc, th, to, *lsop); 998 #endif 999 1000 if (sc == NULL) { 1001 /* 1002 * There is no syncache entry, so see if this ACK is 1003 * a returning syncookie. To do this, first: 1004 * A. Check if syncookies are used in case of syncache 1005 * overflows 1006 * B. See if this socket has had a syncache entry dropped in 1007 * the recent past. We don't want to accept a bogus 1008 * syncookie if we've never received a SYN or accept it 1009 * twice. 1010 * C. check that the syncookie is valid. If it is, then 1011 * cobble up a fake syncache entry, and return. 1012 */ 1013 if (!V_tcp_syncookies) { 1014 SCH_UNLOCK(sch); 1015 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1016 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1017 "segment rejected (syncookies disabled)\n", 1018 s, __func__); 1019 goto failed; 1020 } 1021 if (!V_tcp_syncookiesonly && 1022 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1023 SCH_UNLOCK(sch); 1024 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1025 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1026 "segment rejected (no syncache entry)\n", 1027 s, __func__); 1028 goto failed; 1029 } 1030 bzero(&scs, sizeof(scs)); 1031 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1032 SCH_UNLOCK(sch); 1033 if (sc == NULL) { 1034 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1035 log(LOG_DEBUG, "%s; %s: Segment failed " 1036 "SYNCOOKIE authentication, segment rejected " 1037 "(probably spoofed)\n", s, __func__); 1038 goto failed; 1039 } 1040 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1041 /* If received ACK has MD5 signature, check it. */ 1042 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1043 (!TCPMD5_ENABLED() || 1044 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1045 /* Drop the ACK. */ 1046 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1047 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1048 "MD5 signature doesn't match.\n", 1049 s, __func__); 1050 free(s, M_TCPLOG); 1051 } 1052 TCPSTAT_INC(tcps_sig_err_sigopt); 1053 return (-1); /* Do not send RST */ 1054 } 1055 #endif /* TCP_SIGNATURE */ 1056 } else { 1057 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1058 /* 1059 * If listening socket requested TCP digests, check that 1060 * received ACK has signature and it is correct. 1061 * If not, drop the ACK and leave sc entry in th cache, 1062 * because SYN was received with correct signature. 1063 */ 1064 if (sc->sc_flags & SCF_SIGNATURE) { 1065 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1066 /* No signature */ 1067 TCPSTAT_INC(tcps_sig_err_nosigopt); 1068 SCH_UNLOCK(sch); 1069 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1070 log(LOG_DEBUG, "%s; %s: Segment " 1071 "rejected, MD5 signature wasn't " 1072 "provided.\n", s, __func__); 1073 free(s, M_TCPLOG); 1074 } 1075 return (-1); /* Do not send RST */ 1076 } 1077 if (!TCPMD5_ENABLED() || 1078 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1079 /* Doesn't match or no SA */ 1080 SCH_UNLOCK(sch); 1081 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1082 log(LOG_DEBUG, "%s; %s: Segment " 1083 "rejected, MD5 signature doesn't " 1084 "match.\n", s, __func__); 1085 free(s, M_TCPLOG); 1086 } 1087 return (-1); /* Do not send RST */ 1088 } 1089 } 1090 #endif /* TCP_SIGNATURE */ 1091 1092 /* 1093 * RFC 7323 PAWS: If we have a timestamp on this segment and 1094 * it's less than ts_recent, drop it. 1095 * XXXMT: RFC 7323 also requires to send an ACK. 1096 * In tcp_input.c this is only done for TCP segments 1097 * with user data, so be consistent here and just drop 1098 * the segment. 1099 */ 1100 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1101 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1102 SCH_UNLOCK(sch); 1103 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1104 log(LOG_DEBUG, 1105 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1106 "segment dropped\n", s, __func__, 1107 to->to_tsval, sc->sc_tsreflect); 1108 free(s, M_TCPLOG); 1109 } 1110 return (-1); /* Do not send RST */ 1111 } 1112 1113 /* 1114 * If timestamps were not negotiated during SYN/ACK and a 1115 * segment with a timestamp is received, ignore the 1116 * timestamp and process the packet normally. 1117 * See section 3.2 of RFC 7323. 1118 */ 1119 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1120 (to->to_flags & TOF_TS)) { 1121 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1122 log(LOG_DEBUG, "%s; %s: Timestamp not " 1123 "expected, segment processed normally\n", 1124 s, __func__); 1125 free(s, M_TCPLOG); 1126 s = NULL; 1127 } 1128 } 1129 1130 /* 1131 * If timestamps were negotiated during SYN/ACK and a 1132 * segment without a timestamp is received, silently drop 1133 * the segment. 1134 * See section 3.2 of RFC 7323. 1135 */ 1136 if ((sc->sc_flags & SCF_TIMESTAMP) && 1137 !(to->to_flags & TOF_TS)) { 1138 SCH_UNLOCK(sch); 1139 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1140 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1141 "segment silently dropped\n", s, __func__); 1142 free(s, M_TCPLOG); 1143 } 1144 return (-1); /* Do not send RST */ 1145 } 1146 1147 /* 1148 * Pull out the entry to unlock the bucket row. 1149 * 1150 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1151 * tcp_state_change(). The tcpcb is not existent at this 1152 * moment. A new one will be allocated via syncache_socket-> 1153 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1154 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1155 */ 1156 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1157 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1158 sch->sch_length--; 1159 #ifdef TCP_OFFLOAD 1160 if (ADDED_BY_TOE(sc)) { 1161 struct toedev *tod = sc->sc_tod; 1162 1163 tod->tod_syncache_removed(tod, sc->sc_todctx); 1164 } 1165 #endif 1166 SCH_UNLOCK(sch); 1167 } 1168 1169 /* 1170 * Segment validation: 1171 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1172 */ 1173 if (th->th_ack != sc->sc_iss + 1) { 1174 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1175 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1176 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1177 goto failed; 1178 } 1179 1180 /* 1181 * The SEQ must fall in the window starting at the received 1182 * initial receive sequence number + 1 (the SYN). 1183 */ 1184 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1185 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1186 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1187 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1188 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1189 goto failed; 1190 } 1191 1192 *lsop = syncache_socket(sc, *lsop, m); 1193 1194 if (*lsop == NULL) 1195 TCPSTAT_INC(tcps_sc_aborted); 1196 else 1197 TCPSTAT_INC(tcps_sc_completed); 1198 1199 /* how do we find the inp for the new socket? */ 1200 if (sc != &scs) 1201 syncache_free(sc); 1202 return (1); 1203 failed: 1204 if (sc != NULL && sc != &scs) 1205 syncache_free(sc); 1206 if (s != NULL) 1207 free(s, M_TCPLOG); 1208 *lsop = NULL; 1209 return (0); 1210 } 1211 1212 #ifdef TCP_RFC7413 1213 static void 1214 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1215 uint64_t response_cookie) 1216 { 1217 struct inpcb *inp; 1218 struct tcpcb *tp; 1219 unsigned int *pending_counter; 1220 1221 /* 1222 * Global TCP locks are held because we manipulate the PCB lists 1223 * and create a new socket. 1224 */ 1225 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1226 1227 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1228 *lsop = syncache_socket(sc, *lsop, m); 1229 if (*lsop == NULL) { 1230 TCPSTAT_INC(tcps_sc_aborted); 1231 atomic_subtract_int(pending_counter, 1); 1232 } else { 1233 inp = sotoinpcb(*lsop); 1234 tp = intotcpcb(inp); 1235 tp->t_flags |= TF_FASTOPEN; 1236 tp->t_tfo_cookie = response_cookie; 1237 tp->snd_max = tp->iss; 1238 tp->snd_nxt = tp->iss; 1239 tp->t_tfo_pending = pending_counter; 1240 TCPSTAT_INC(tcps_sc_completed); 1241 } 1242 } 1243 #endif /* TCP_RFC7413 */ 1244 1245 /* 1246 * Given a LISTEN socket and an inbound SYN request, add 1247 * this to the syn cache, and send back a segment: 1248 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1249 * to the source. 1250 * 1251 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1252 * Doing so would require that we hold onto the data and deliver it 1253 * to the application. However, if we are the target of a SYN-flood 1254 * DoS attack, an attacker could send data which would eventually 1255 * consume all available buffer space if it were ACKed. By not ACKing 1256 * the data, we avoid this DoS scenario. 1257 * 1258 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1259 * cookie is processed, V_tcp_fastopen_enabled set to true, and the 1260 * TCP_FASTOPEN socket option is set. In this case, a new socket is created 1261 * and returned via lsop, the mbuf is not freed so that tcp_input() can 1262 * queue its data to the socket, and 1 is returned to indicate the 1263 * TFO-socket-creation path was taken. 1264 */ 1265 int 1266 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1267 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1268 void *todctx) 1269 { 1270 struct tcpcb *tp; 1271 struct socket *so; 1272 struct syncache *sc = NULL; 1273 struct syncache_head *sch; 1274 struct mbuf *ipopts = NULL; 1275 u_int ltflags; 1276 int win, sb_hiwat, ip_ttl, ip_tos; 1277 char *s; 1278 int rv = 0; 1279 #ifdef INET6 1280 int autoflowlabel = 0; 1281 #endif 1282 #ifdef MAC 1283 struct label *maclabel; 1284 #endif 1285 struct syncache scs; 1286 struct ucred *cred; 1287 #ifdef TCP_RFC7413 1288 uint64_t tfo_response_cookie; 1289 int tfo_cookie_valid = 0; 1290 int tfo_response_cookie_valid = 0; 1291 #endif 1292 1293 INP_WLOCK_ASSERT(inp); /* listen socket */ 1294 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1295 ("%s: unexpected tcp flags", __func__)); 1296 1297 /* 1298 * Combine all so/tp operations very early to drop the INP lock as 1299 * soon as possible. 1300 */ 1301 so = *lsop; 1302 tp = sototcpcb(so); 1303 cred = crhold(so->so_cred); 1304 1305 #ifdef INET6 1306 if ((inc->inc_flags & INC_ISIPV6) && 1307 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1308 autoflowlabel = 1; 1309 #endif 1310 ip_ttl = inp->inp_ip_ttl; 1311 ip_tos = inp->inp_ip_tos; 1312 win = sbspace(&so->so_rcv); 1313 sb_hiwat = so->so_rcv.sb_hiwat; 1314 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1315 1316 #ifdef TCP_RFC7413 1317 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) && 1318 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1319 /* 1320 * Limit the number of pending TFO connections to 1321 * approximately half of the queue limit. This prevents TFO 1322 * SYN floods from starving the service by filling the 1323 * listen queue with bogus TFO connections. 1324 */ 1325 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1326 (so->so_qlimit / 2)) { 1327 int result; 1328 1329 result = tcp_fastopen_check_cookie(inc, 1330 to->to_tfo_cookie, to->to_tfo_len, 1331 &tfo_response_cookie); 1332 tfo_cookie_valid = (result > 0); 1333 tfo_response_cookie_valid = (result >= 0); 1334 } else 1335 atomic_subtract_int(tp->t_tfo_pending, 1); 1336 } 1337 #endif 1338 1339 /* By the time we drop the lock these should no longer be used. */ 1340 so = NULL; 1341 tp = NULL; 1342 1343 #ifdef MAC 1344 if (mac_syncache_init(&maclabel) != 0) { 1345 INP_WUNLOCK(inp); 1346 goto done; 1347 } else 1348 mac_syncache_create(maclabel, inp); 1349 #endif 1350 #ifdef TCP_RFC7413 1351 if (!tfo_cookie_valid) 1352 #endif 1353 INP_WUNLOCK(inp); 1354 1355 /* 1356 * Remember the IP options, if any. 1357 */ 1358 #ifdef INET6 1359 if (!(inc->inc_flags & INC_ISIPV6)) 1360 #endif 1361 #ifdef INET 1362 ipopts = (m) ? ip_srcroute(m) : NULL; 1363 #else 1364 ipopts = NULL; 1365 #endif 1366 1367 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1368 /* 1369 * If listening socket requested TCP digests, check that received 1370 * SYN has signature and it is correct. If signature doesn't match 1371 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1372 */ 1373 if (ltflags & TF_SIGNATURE) { 1374 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1375 TCPSTAT_INC(tcps_sig_err_nosigopt); 1376 goto done; 1377 } 1378 if (!TCPMD5_ENABLED() || 1379 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1380 goto done; 1381 } 1382 #endif /* TCP_SIGNATURE */ 1383 /* 1384 * See if we already have an entry for this connection. 1385 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1386 * 1387 * XXX: should the syncache be re-initialized with the contents 1388 * of the new SYN here (which may have different options?) 1389 * 1390 * XXX: We do not check the sequence number to see if this is a 1391 * real retransmit or a new connection attempt. The question is 1392 * how to handle such a case; either ignore it as spoofed, or 1393 * drop the current entry and create a new one? 1394 */ 1395 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1396 SCH_LOCK_ASSERT(sch); 1397 if (sc != NULL) { 1398 #ifdef TCP_RFC7413 1399 if (tfo_cookie_valid) 1400 INP_WUNLOCK(inp); 1401 #endif 1402 TCPSTAT_INC(tcps_sc_dupsyn); 1403 if (ipopts) { 1404 /* 1405 * If we were remembering a previous source route, 1406 * forget it and use the new one we've been given. 1407 */ 1408 if (sc->sc_ipopts) 1409 (void) m_free(sc->sc_ipopts); 1410 sc->sc_ipopts = ipopts; 1411 } 1412 /* 1413 * Update timestamp if present. 1414 */ 1415 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1416 sc->sc_tsreflect = to->to_tsval; 1417 else 1418 sc->sc_flags &= ~SCF_TIMESTAMP; 1419 #ifdef MAC 1420 /* 1421 * Since we have already unconditionally allocated label 1422 * storage, free it up. The syncache entry will already 1423 * have an initialized label we can use. 1424 */ 1425 mac_syncache_destroy(&maclabel); 1426 #endif 1427 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1428 /* Retransmit SYN|ACK and reset retransmit count. */ 1429 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1430 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1431 "resetting timer and retransmitting SYN|ACK\n", 1432 s, __func__); 1433 free(s, M_TCPLOG); 1434 } 1435 if (syncache_respond(sc, sch, 1, m) == 0) { 1436 sc->sc_rxmits = 0; 1437 syncache_timeout(sc, sch, 1); 1438 TCPSTAT_INC(tcps_sndacks); 1439 TCPSTAT_INC(tcps_sndtotal); 1440 } 1441 SCH_UNLOCK(sch); 1442 goto donenoprobe; 1443 } 1444 1445 #ifdef TCP_RFC7413 1446 if (tfo_cookie_valid) { 1447 bzero(&scs, sizeof(scs)); 1448 sc = &scs; 1449 goto skip_alloc; 1450 } 1451 #endif 1452 1453 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1454 if (sc == NULL) { 1455 /* 1456 * The zone allocator couldn't provide more entries. 1457 * Treat this as if the cache was full; drop the oldest 1458 * entry and insert the new one. 1459 */ 1460 TCPSTAT_INC(tcps_sc_zonefail); 1461 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1462 sch->sch_last_overflow = time_uptime; 1463 syncache_drop(sc, sch); 1464 } 1465 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1466 if (sc == NULL) { 1467 if (V_tcp_syncookies) { 1468 bzero(&scs, sizeof(scs)); 1469 sc = &scs; 1470 } else { 1471 SCH_UNLOCK(sch); 1472 if (ipopts) 1473 (void) m_free(ipopts); 1474 goto done; 1475 } 1476 } 1477 } 1478 1479 #ifdef TCP_RFC7413 1480 skip_alloc: 1481 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1482 sc->sc_tfo_cookie = &tfo_response_cookie; 1483 #endif 1484 1485 /* 1486 * Fill in the syncache values. 1487 */ 1488 #ifdef MAC 1489 sc->sc_label = maclabel; 1490 #endif 1491 sc->sc_cred = cred; 1492 cred = NULL; 1493 sc->sc_ipopts = ipopts; 1494 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1495 #ifdef INET6 1496 if (!(inc->inc_flags & INC_ISIPV6)) 1497 #endif 1498 { 1499 sc->sc_ip_tos = ip_tos; 1500 sc->sc_ip_ttl = ip_ttl; 1501 } 1502 #ifdef TCP_OFFLOAD 1503 sc->sc_tod = tod; 1504 sc->sc_todctx = todctx; 1505 #endif 1506 sc->sc_irs = th->th_seq; 1507 sc->sc_iss = arc4random(); 1508 sc->sc_flags = 0; 1509 sc->sc_flowlabel = 0; 1510 1511 /* 1512 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1513 * win was derived from socket earlier in the function. 1514 */ 1515 win = imax(win, 0); 1516 win = imin(win, TCP_MAXWIN); 1517 sc->sc_wnd = win; 1518 1519 if (V_tcp_do_rfc1323) { 1520 /* 1521 * A timestamp received in a SYN makes 1522 * it ok to send timestamp requests and replies. 1523 */ 1524 if (to->to_flags & TOF_TS) { 1525 sc->sc_tsreflect = to->to_tsval; 1526 sc->sc_flags |= SCF_TIMESTAMP; 1527 sc->sc_tsoff = tcp_new_ts_offset(inc); 1528 } 1529 if (to->to_flags & TOF_SCALE) { 1530 int wscale = 0; 1531 1532 /* 1533 * Pick the smallest possible scaling factor that 1534 * will still allow us to scale up to sb_max, aka 1535 * kern.ipc.maxsockbuf. 1536 * 1537 * We do this because there are broken firewalls that 1538 * will corrupt the window scale option, leading to 1539 * the other endpoint believing that our advertised 1540 * window is unscaled. At scale factors larger than 1541 * 5 the unscaled window will drop below 1500 bytes, 1542 * leading to serious problems when traversing these 1543 * broken firewalls. 1544 * 1545 * With the default maxsockbuf of 256K, a scale factor 1546 * of 3 will be chosen by this algorithm. Those who 1547 * choose a larger maxsockbuf should watch out 1548 * for the compatibility problems mentioned above. 1549 * 1550 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1551 * or <SYN,ACK>) segment itself is never scaled. 1552 */ 1553 while (wscale < TCP_MAX_WINSHIFT && 1554 (TCP_MAXWIN << wscale) < sb_max) 1555 wscale++; 1556 sc->sc_requested_r_scale = wscale; 1557 sc->sc_requested_s_scale = to->to_wscale; 1558 sc->sc_flags |= SCF_WINSCALE; 1559 } 1560 } 1561 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1562 /* 1563 * If listening socket requested TCP digests, flag this in the 1564 * syncache so that syncache_respond() will do the right thing 1565 * with the SYN+ACK. 1566 */ 1567 if (ltflags & TF_SIGNATURE) 1568 sc->sc_flags |= SCF_SIGNATURE; 1569 #endif /* TCP_SIGNATURE */ 1570 if (to->to_flags & TOF_SACKPERM) 1571 sc->sc_flags |= SCF_SACK; 1572 if (to->to_flags & TOF_MSS) 1573 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1574 if (ltflags & TF_NOOPT) 1575 sc->sc_flags |= SCF_NOOPT; 1576 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1577 sc->sc_flags |= SCF_ECN; 1578 1579 if (V_tcp_syncookies) 1580 sc->sc_iss = syncookie_generate(sch, sc); 1581 #ifdef INET6 1582 if (autoflowlabel) { 1583 if (V_tcp_syncookies) 1584 sc->sc_flowlabel = sc->sc_iss; 1585 else 1586 sc->sc_flowlabel = ip6_randomflowlabel(); 1587 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1588 } 1589 #endif 1590 SCH_UNLOCK(sch); 1591 1592 #ifdef TCP_RFC7413 1593 if (tfo_cookie_valid) { 1594 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1595 /* INP_WUNLOCK(inp) will be performed by the called */ 1596 rv = 1; 1597 goto tfo_done; 1598 } 1599 #endif 1600 1601 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1602 /* 1603 * Do a standard 3-way handshake. 1604 */ 1605 if (syncache_respond(sc, sch, 0, m) == 0) { 1606 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1607 syncache_free(sc); 1608 else if (sc != &scs) 1609 syncache_insert(sc, sch); /* locks and unlocks sch */ 1610 TCPSTAT_INC(tcps_sndacks); 1611 TCPSTAT_INC(tcps_sndtotal); 1612 } else { 1613 if (sc != &scs) 1614 syncache_free(sc); 1615 TCPSTAT_INC(tcps_sc_dropped); 1616 } 1617 goto donenoprobe; 1618 1619 done: 1620 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1621 donenoprobe: 1622 if (m) { 1623 *lsop = NULL; 1624 m_freem(m); 1625 } 1626 #ifdef TCP_RFC7413 1627 tfo_done: 1628 #endif 1629 if (cred != NULL) 1630 crfree(cred); 1631 #ifdef MAC 1632 if (sc == &scs) 1633 mac_syncache_destroy(&maclabel); 1634 #endif 1635 return (rv); 1636 } 1637 1638 /* 1639 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1640 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1641 */ 1642 static int 1643 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1644 const struct mbuf *m0) 1645 { 1646 struct ip *ip = NULL; 1647 struct mbuf *m; 1648 struct tcphdr *th = NULL; 1649 int optlen, error = 0; /* Make compiler happy */ 1650 u_int16_t hlen, tlen, mssopt; 1651 struct tcpopt to; 1652 #ifdef INET6 1653 struct ip6_hdr *ip6 = NULL; 1654 #endif 1655 hlen = 1656 #ifdef INET6 1657 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1658 #endif 1659 sizeof(struct ip); 1660 tlen = hlen + sizeof(struct tcphdr); 1661 1662 /* Determine MSS we advertize to other end of connection. */ 1663 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1664 1665 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1666 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1667 ("syncache: mbuf too small")); 1668 1669 /* Create the IP+TCP header from scratch. */ 1670 m = m_gethdr(M_NOWAIT, MT_DATA); 1671 if (m == NULL) 1672 return (ENOBUFS); 1673 #ifdef MAC 1674 mac_syncache_create_mbuf(sc->sc_label, m); 1675 #endif 1676 m->m_data += max_linkhdr; 1677 m->m_len = tlen; 1678 m->m_pkthdr.len = tlen; 1679 m->m_pkthdr.rcvif = NULL; 1680 1681 #ifdef INET6 1682 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1683 ip6 = mtod(m, struct ip6_hdr *); 1684 ip6->ip6_vfc = IPV6_VERSION; 1685 ip6->ip6_nxt = IPPROTO_TCP; 1686 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1687 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1688 ip6->ip6_plen = htons(tlen - hlen); 1689 /* ip6_hlim is set after checksum */ 1690 /* Zero out traffic class and flow label. */ 1691 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1692 ip6->ip6_flow |= sc->sc_flowlabel; 1693 1694 th = (struct tcphdr *)(ip6 + 1); 1695 } 1696 #endif 1697 #if defined(INET6) && defined(INET) 1698 else 1699 #endif 1700 #ifdef INET 1701 { 1702 ip = mtod(m, struct ip *); 1703 ip->ip_v = IPVERSION; 1704 ip->ip_hl = sizeof(struct ip) >> 2; 1705 ip->ip_len = htons(tlen); 1706 ip->ip_id = 0; 1707 ip->ip_off = 0; 1708 ip->ip_sum = 0; 1709 ip->ip_p = IPPROTO_TCP; 1710 ip->ip_src = sc->sc_inc.inc_laddr; 1711 ip->ip_dst = sc->sc_inc.inc_faddr; 1712 ip->ip_ttl = sc->sc_ip_ttl; 1713 ip->ip_tos = sc->sc_ip_tos; 1714 1715 /* 1716 * See if we should do MTU discovery. Route lookups are 1717 * expensive, so we will only unset the DF bit if: 1718 * 1719 * 1) path_mtu_discovery is disabled 1720 * 2) the SCF_UNREACH flag has been set 1721 */ 1722 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1723 ip->ip_off |= htons(IP_DF); 1724 1725 th = (struct tcphdr *)(ip + 1); 1726 } 1727 #endif /* INET */ 1728 th->th_sport = sc->sc_inc.inc_lport; 1729 th->th_dport = sc->sc_inc.inc_fport; 1730 1731 th->th_seq = htonl(sc->sc_iss); 1732 th->th_ack = htonl(sc->sc_irs + 1); 1733 th->th_off = sizeof(struct tcphdr) >> 2; 1734 th->th_x2 = 0; 1735 th->th_flags = TH_SYN|TH_ACK; 1736 th->th_win = htons(sc->sc_wnd); 1737 th->th_urp = 0; 1738 1739 if (sc->sc_flags & SCF_ECN) { 1740 th->th_flags |= TH_ECE; 1741 TCPSTAT_INC(tcps_ecn_shs); 1742 } 1743 1744 /* Tack on the TCP options. */ 1745 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1746 to.to_flags = 0; 1747 1748 to.to_mss = mssopt; 1749 to.to_flags = TOF_MSS; 1750 if (sc->sc_flags & SCF_WINSCALE) { 1751 to.to_wscale = sc->sc_requested_r_scale; 1752 to.to_flags |= TOF_SCALE; 1753 } 1754 if (sc->sc_flags & SCF_TIMESTAMP) { 1755 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1756 to.to_tsecr = sc->sc_tsreflect; 1757 to.to_flags |= TOF_TS; 1758 } 1759 if (sc->sc_flags & SCF_SACK) 1760 to.to_flags |= TOF_SACKPERM; 1761 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1762 if (sc->sc_flags & SCF_SIGNATURE) 1763 to.to_flags |= TOF_SIGNATURE; 1764 #endif 1765 #ifdef TCP_RFC7413 1766 if (sc->sc_tfo_cookie) { 1767 to.to_flags |= TOF_FASTOPEN; 1768 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1769 to.to_tfo_cookie = sc->sc_tfo_cookie; 1770 /* don't send cookie again when retransmitting response */ 1771 sc->sc_tfo_cookie = NULL; 1772 } 1773 #endif 1774 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1775 1776 /* Adjust headers by option size. */ 1777 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1778 m->m_len += optlen; 1779 m->m_pkthdr.len += optlen; 1780 #ifdef INET6 1781 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1782 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1783 else 1784 #endif 1785 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1786 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1787 if (sc->sc_flags & SCF_SIGNATURE) { 1788 KASSERT(to.to_flags & TOF_SIGNATURE, 1789 ("tcp_addoptions() didn't set tcp_signature")); 1790 1791 /* NOTE: to.to_signature is inside of mbuf */ 1792 if (!TCPMD5_ENABLED() || 1793 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1794 m_freem(m); 1795 return (EACCES); 1796 } 1797 } 1798 #endif 1799 } else 1800 optlen = 0; 1801 1802 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1803 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1804 /* 1805 * If we have peer's SYN and it has a flowid, then let's assign it to 1806 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1807 * to SYN|ACK due to lack of inp here. 1808 */ 1809 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1810 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1811 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1812 } 1813 #ifdef INET6 1814 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1815 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1816 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1817 IPPROTO_TCP, 0); 1818 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1819 #ifdef TCP_OFFLOAD 1820 if (ADDED_BY_TOE(sc)) { 1821 struct toedev *tod = sc->sc_tod; 1822 1823 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1824 1825 return (error); 1826 } 1827 #endif 1828 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1829 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1830 } 1831 #endif 1832 #if defined(INET6) && defined(INET) 1833 else 1834 #endif 1835 #ifdef INET 1836 { 1837 m->m_pkthdr.csum_flags = CSUM_TCP; 1838 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1839 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1840 #ifdef TCP_OFFLOAD 1841 if (ADDED_BY_TOE(sc)) { 1842 struct toedev *tod = sc->sc_tod; 1843 1844 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1845 1846 return (error); 1847 } 1848 #endif 1849 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1850 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1851 } 1852 #endif 1853 return (error); 1854 } 1855 1856 /* 1857 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1858 * that exceed the capacity of the syncache by avoiding the storage of any 1859 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1860 * attacks where the attacker does not have access to our responses. 1861 * 1862 * Syncookies encode and include all necessary information about the 1863 * connection setup within the SYN|ACK that we send back. That way we 1864 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1865 * (if ever). Normally the syncache and syncookies are running in parallel 1866 * with the latter taking over when the former is exhausted. When matching 1867 * syncache entry is found the syncookie is ignored. 1868 * 1869 * The only reliable information persisting the 3WHS is our initial sequence 1870 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1871 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1872 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1873 * returns and signifies a legitimate connection if it matches the ACK. 1874 * 1875 * The available space of 32 bits to store the hash and to encode the SYN 1876 * option information is very tight and we should have at least 24 bits for 1877 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1878 * 1879 * SYN option information we have to encode to fully restore a connection: 1880 * MSS: is imporant to chose an optimal segment size to avoid IP level 1881 * fragmentation along the path. The common MSS values can be encoded 1882 * in a 3-bit table. Uncommon values are captured by the next lower value 1883 * in the table leading to a slight increase in packetization overhead. 1884 * WSCALE: is necessary to allow large windows to be used for high delay- 1885 * bandwidth product links. Not scaling the window when it was initially 1886 * negotiated is bad for performance as lack of scaling further decreases 1887 * the apparent available send window. We only need to encode the WSCALE 1888 * we received from the remote end. Our end can be recalculated at any 1889 * time. The common WSCALE values can be encoded in a 3-bit table. 1890 * Uncommon values are captured by the next lower value in the table 1891 * making us under-estimate the available window size halving our 1892 * theoretically possible maximum throughput for that connection. 1893 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1894 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1895 * that are included in all segments on a connection. We enable them when 1896 * the ACK has them. 1897 * 1898 * Security of syncookies and attack vectors: 1899 * 1900 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1901 * together with the gloabl secret to make it unique per connection attempt. 1902 * Thus any change of any of those parameters results in a different MAC output 1903 * in an unpredictable way unless a collision is encountered. 24 bits of the 1904 * MAC are embedded into the ISS. 1905 * 1906 * To prevent replay attacks two rotating global secrets are updated with a 1907 * new random value every 15 seconds. The life-time of a syncookie is thus 1908 * 15-30 seconds. 1909 * 1910 * Vector 1: Attacking the secret. This requires finding a weakness in the 1911 * MAC itself or the way it is used here. The attacker can do a chosen plain 1912 * text attack by varying and testing the all parameters under his control. 1913 * The strength depends on the size and randomness of the secret, and the 1914 * cryptographic security of the MAC function. Due to the constant updating 1915 * of the secret the attacker has at most 29.999 seconds to find the secret 1916 * and launch spoofed connections. After that he has to start all over again. 1917 * 1918 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1919 * size an average of 4,823 attempts are required for a 50% chance of success 1920 * to spoof a single syncookie (birthday collision paradox). However the 1921 * attacker is blind and doesn't know if one of his attempts succeeded unless 1922 * he has a side channel to interfere success from. A single connection setup 1923 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1924 * This many attempts are required for each one blind spoofed connection. For 1925 * every additional spoofed connection he has to launch another N attempts. 1926 * Thus for a sustained rate 100 spoofed connections per second approximately 1927 * 1,800,000 packets per second would have to be sent. 1928 * 1929 * NB: The MAC function should be fast so that it doesn't become a CPU 1930 * exhaustion attack vector itself. 1931 * 1932 * References: 1933 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1934 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1935 * http://cr.yp.to/syncookies.html (overview) 1936 * http://cr.yp.to/syncookies/archive (details) 1937 * 1938 * 1939 * Schematic construction of a syncookie enabled Initial Sequence Number: 1940 * 0 1 2 3 1941 * 12345678901234567890123456789012 1942 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1943 * 1944 * x 24 MAC (truncated) 1945 * W 3 Send Window Scale index 1946 * M 3 MSS index 1947 * S 1 SACK permitted 1948 * P 1 Odd/even secret 1949 */ 1950 1951 /* 1952 * Distribution and probability of certain MSS values. Those in between are 1953 * rounded down to the next lower one. 1954 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1955 * .2% .3% 5% 7% 7% 20% 15% 45% 1956 */ 1957 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1958 1959 /* 1960 * Distribution and probability of certain WSCALE values. We have to map the 1961 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1962 * bits based on prevalence of certain values. Where we don't have an exact 1963 * match for are rounded down to the next lower one letting us under-estimate 1964 * the true available window. At the moment this would happen only for the 1965 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1966 * and window size). The absence of the WSCALE option (no scaling in either 1967 * direction) is encoded with index zero. 1968 * [WSCALE values histograms, Allman, 2012] 1969 * X 10 10 35 5 6 14 10% by host 1970 * X 11 4 5 5 18 49 3% by connections 1971 */ 1972 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1973 1974 /* 1975 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1976 * and good cryptographic properties. 1977 */ 1978 static uint32_t 1979 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1980 uint8_t *secbits, uintptr_t secmod) 1981 { 1982 SIPHASH_CTX ctx; 1983 uint32_t siphash[2]; 1984 1985 SipHash24_Init(&ctx); 1986 SipHash_SetKey(&ctx, secbits); 1987 switch (inc->inc_flags & INC_ISIPV6) { 1988 #ifdef INET 1989 case 0: 1990 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1991 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1992 break; 1993 #endif 1994 #ifdef INET6 1995 case INC_ISIPV6: 1996 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1997 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1998 break; 1999 #endif 2000 } 2001 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2002 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2003 SipHash_Update(&ctx, &irs, sizeof(irs)); 2004 SipHash_Update(&ctx, &flags, sizeof(flags)); 2005 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2006 SipHash_Final((u_int8_t *)&siphash, &ctx); 2007 2008 return (siphash[0] ^ siphash[1]); 2009 } 2010 2011 static tcp_seq 2012 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2013 { 2014 u_int i, secbit, wscale; 2015 uint32_t iss, hash; 2016 uint8_t *secbits; 2017 union syncookie cookie; 2018 2019 SCH_LOCK_ASSERT(sch); 2020 2021 cookie.cookie = 0; 2022 2023 /* Map our computed MSS into the 3-bit index. */ 2024 for (i = nitems(tcp_sc_msstab) - 1; 2025 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2026 i--) 2027 ; 2028 cookie.flags.mss_idx = i; 2029 2030 /* 2031 * Map the send window scale into the 3-bit index but only if 2032 * the wscale option was received. 2033 */ 2034 if (sc->sc_flags & SCF_WINSCALE) { 2035 wscale = sc->sc_requested_s_scale; 2036 for (i = nitems(tcp_sc_wstab) - 1; 2037 tcp_sc_wstab[i] > wscale && i > 0; 2038 i--) 2039 ; 2040 cookie.flags.wscale_idx = i; 2041 } 2042 2043 /* Can we do SACK? */ 2044 if (sc->sc_flags & SCF_SACK) 2045 cookie.flags.sack_ok = 1; 2046 2047 /* Which of the two secrets to use. */ 2048 secbit = sch->sch_sc->secret.oddeven & 0x1; 2049 cookie.flags.odd_even = secbit; 2050 2051 secbits = sch->sch_sc->secret.key[secbit]; 2052 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2053 (uintptr_t)sch); 2054 2055 /* 2056 * Put the flags into the hash and XOR them to get better ISS number 2057 * variance. This doesn't enhance the cryptographic strength and is 2058 * done to prevent the 8 cookie bits from showing up directly on the 2059 * wire. 2060 */ 2061 iss = hash & ~0xff; 2062 iss |= cookie.cookie ^ (hash >> 24); 2063 2064 TCPSTAT_INC(tcps_sc_sendcookie); 2065 return (iss); 2066 } 2067 2068 static struct syncache * 2069 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2070 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2071 struct socket *lso) 2072 { 2073 uint32_t hash; 2074 uint8_t *secbits; 2075 tcp_seq ack, seq; 2076 int wnd, wscale = 0; 2077 union syncookie cookie; 2078 2079 SCH_LOCK_ASSERT(sch); 2080 2081 /* 2082 * Pull information out of SYN-ACK/ACK and revert sequence number 2083 * advances. 2084 */ 2085 ack = th->th_ack - 1; 2086 seq = th->th_seq - 1; 2087 2088 /* 2089 * Unpack the flags containing enough information to restore the 2090 * connection. 2091 */ 2092 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2093 2094 /* Which of the two secrets to use. */ 2095 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2096 2097 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2098 2099 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2100 if ((ack & ~0xff) != (hash & ~0xff)) 2101 return (NULL); 2102 2103 /* Fill in the syncache values. */ 2104 sc->sc_flags = 0; 2105 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2106 sc->sc_ipopts = NULL; 2107 2108 sc->sc_irs = seq; 2109 sc->sc_iss = ack; 2110 2111 switch (inc->inc_flags & INC_ISIPV6) { 2112 #ifdef INET 2113 case 0: 2114 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2115 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2116 break; 2117 #endif 2118 #ifdef INET6 2119 case INC_ISIPV6: 2120 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2121 sc->sc_flowlabel = 2122 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2123 break; 2124 #endif 2125 } 2126 2127 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2128 2129 /* We can simply recompute receive window scale we sent earlier. */ 2130 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2131 wscale++; 2132 2133 /* Only use wscale if it was enabled in the orignal SYN. */ 2134 if (cookie.flags.wscale_idx > 0) { 2135 sc->sc_requested_r_scale = wscale; 2136 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2137 sc->sc_flags |= SCF_WINSCALE; 2138 } 2139 2140 wnd = sbspace(&lso->so_rcv); 2141 wnd = imax(wnd, 0); 2142 wnd = imin(wnd, TCP_MAXWIN); 2143 sc->sc_wnd = wnd; 2144 2145 if (cookie.flags.sack_ok) 2146 sc->sc_flags |= SCF_SACK; 2147 2148 if (to->to_flags & TOF_TS) { 2149 sc->sc_flags |= SCF_TIMESTAMP; 2150 sc->sc_tsreflect = to->to_tsval; 2151 sc->sc_tsoff = tcp_new_ts_offset(inc); 2152 } 2153 2154 if (to->to_flags & TOF_SIGNATURE) 2155 sc->sc_flags |= SCF_SIGNATURE; 2156 2157 sc->sc_rxmits = 0; 2158 2159 TCPSTAT_INC(tcps_sc_recvcookie); 2160 return (sc); 2161 } 2162 2163 #ifdef INVARIANTS 2164 static int 2165 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2166 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2167 struct socket *lso) 2168 { 2169 struct syncache scs, *scx; 2170 char *s; 2171 2172 bzero(&scs, sizeof(scs)); 2173 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2174 2175 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2176 return (0); 2177 2178 if (scx != NULL) { 2179 if (sc->sc_peer_mss != scx->sc_peer_mss) 2180 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2181 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2182 2183 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2184 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2185 s, __func__, sc->sc_requested_r_scale, 2186 scx->sc_requested_r_scale); 2187 2188 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2189 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2190 s, __func__, sc->sc_requested_s_scale, 2191 scx->sc_requested_s_scale); 2192 2193 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2194 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2195 } 2196 2197 if (s != NULL) 2198 free(s, M_TCPLOG); 2199 return (0); 2200 } 2201 #endif /* INVARIANTS */ 2202 2203 static void 2204 syncookie_reseed(void *arg) 2205 { 2206 struct tcp_syncache *sc = arg; 2207 uint8_t *secbits; 2208 int secbit; 2209 2210 /* 2211 * Reseeding the secret doesn't have to be protected by a lock. 2212 * It only must be ensured that the new random values are visible 2213 * to all CPUs in a SMP environment. The atomic with release 2214 * semantics ensures that. 2215 */ 2216 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2217 secbits = sc->secret.key[secbit]; 2218 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2219 atomic_add_rel_int(&sc->secret.oddeven, 1); 2220 2221 /* Reschedule ourself. */ 2222 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2223 } 2224 2225 /* 2226 * Exports the syncache entries to userland so that netstat can display 2227 * them alongside the other sockets. This function is intended to be 2228 * called only from tcp_pcblist. 2229 * 2230 * Due to concurrency on an active system, the number of pcbs exported 2231 * may have no relation to max_pcbs. max_pcbs merely indicates the 2232 * amount of space the caller allocated for this function to use. 2233 */ 2234 int 2235 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2236 { 2237 struct xtcpcb xt; 2238 struct syncache *sc; 2239 struct syncache_head *sch; 2240 int count, error, i; 2241 2242 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2243 sch = &V_tcp_syncache.hashbase[i]; 2244 SCH_LOCK(sch); 2245 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2246 if (count >= max_pcbs) { 2247 SCH_UNLOCK(sch); 2248 goto exit; 2249 } 2250 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2251 continue; 2252 bzero(&xt, sizeof(xt)); 2253 xt.xt_len = sizeof(xt); 2254 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2255 xt.xt_inp.inp_vflag = INP_IPV6; 2256 else 2257 xt.xt_inp.inp_vflag = INP_IPV4; 2258 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2259 xt.xt_tp.t_inpcb = &xt.xt_inp; 2260 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2261 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2262 xt.xt_socket.xso_len = sizeof (struct xsocket); 2263 xt.xt_socket.so_type = SOCK_STREAM; 2264 xt.xt_socket.so_state = SS_ISCONNECTING; 2265 error = SYSCTL_OUT(req, &xt, sizeof xt); 2266 if (error) { 2267 SCH_UNLOCK(sch); 2268 goto exit; 2269 } 2270 count++; 2271 } 2272 SCH_UNLOCK(sch); 2273 } 2274 exit: 2275 *pcbs_exported = count; 2276 return error; 2277 }
Cache object: 6895f90818cbe2771a5458cfcc463978
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