1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006 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. 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 * $FreeBSD$ 33 */ 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 #include "opt_mac.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/kernel.h> 43 #include <sys/sysctl.h> 44 #include <sys/lock.h> 45 #include <sys/mutex.h> 46 #include <sys/malloc.h> 47 #include <sys/mbuf.h> 48 #include <sys/md5.h> 49 #include <sys/proc.h> /* for proc0 declaration */ 50 #include <sys/random.h> 51 #include <sys/socket.h> 52 #include <sys/socketvar.h> 53 #include <sys/syslog.h> 54 55 #include <vm/uma.h> 56 57 #include <net/if.h> 58 #include <net/route.h> 59 60 #include <netinet/in.h> 61 #include <netinet/in_systm.h> 62 #include <netinet/ip.h> 63 #include <netinet/in_var.h> 64 #include <netinet/in_pcb.h> 65 #include <netinet/ip_var.h> 66 #include <netinet/ip_options.h> 67 #ifdef INET6 68 #include <netinet/ip6.h> 69 #include <netinet/icmp6.h> 70 #include <netinet6/nd6.h> 71 #include <netinet6/ip6_var.h> 72 #include <netinet6/in6_pcb.h> 73 #endif 74 #include <netinet/tcp.h> 75 #include <netinet/tcp_fsm.h> 76 #include <netinet/tcp_seq.h> 77 #include <netinet/tcp_timer.h> 78 #include <netinet/tcp_var.h> 79 #ifdef INET6 80 #include <netinet6/tcp6_var.h> 81 #endif 82 83 #ifdef IPSEC 84 #include <netinet6/ipsec.h> 85 #ifdef INET6 86 #include <netinet6/ipsec6.h> 87 #endif 88 #endif /*IPSEC*/ 89 90 #ifdef FAST_IPSEC 91 #include <netipsec/ipsec.h> 92 #ifdef INET6 93 #include <netipsec/ipsec6.h> 94 #endif 95 #include <netipsec/key.h> 96 #endif /*FAST_IPSEC*/ 97 98 #include <machine/in_cksum.h> 99 100 #include <security/mac/mac_framework.h> 101 102 static int tcp_syncookies = 1; 103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 104 &tcp_syncookies, 0, 105 "Use TCP SYN cookies if the syncache overflows"); 106 107 static int tcp_syncookiesonly = 0; 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 109 &tcp_syncookiesonly, 0, 110 "Use only TCP SYN cookies"); 111 112 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 113 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 114 115 struct syncache { 116 TAILQ_ENTRY(syncache) sc_hash; 117 struct in_conninfo sc_inc; /* addresses */ 118 u_long sc_rxttime; /* retransmit time */ 119 u_int16_t sc_rxmits; /* retransmit counter */ 120 121 u_int32_t sc_tsreflect; /* timestamp to reflect */ 122 u_int32_t sc_ts; /* our timestamp to send */ 123 u_int32_t sc_tsoff; /* ts offset w/ syncookies */ 124 u_int32_t sc_flowlabel; /* IPv6 flowlabel */ 125 tcp_seq sc_irs; /* seq from peer */ 126 tcp_seq sc_iss; /* our ISS */ 127 struct mbuf *sc_ipopts; /* source route */ 128 129 u_int16_t sc_peer_mss; /* peer's MSS */ 130 u_int16_t sc_wnd; /* advertised window */ 131 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 132 u_int8_t sc_ip_tos; /* IPv4 TOS */ 133 u_int8_t sc_requested_s_scale:4, 134 sc_requested_r_scale:4; 135 u_int8_t sc_flags; 136 #define SCF_NOOPT 0x01 /* no TCP options */ 137 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 138 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 139 /* MSS is implicit */ 140 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 141 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 142 #define SCF_SACK 0x80 /* send SACK option */ 143 #ifdef MAC 144 struct label *sc_label; /* MAC label reference */ 145 #endif 146 }; 147 148 struct syncache_head { 149 struct mtx sch_mtx; 150 TAILQ_HEAD(sch_head, syncache) sch_bucket; 151 struct callout sch_timer; 152 int sch_nextc; 153 u_int sch_length; 154 u_int sch_oddeven; 155 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 156 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 157 u_int sch_reseed; /* time_uptime, seconds */ 158 }; 159 160 static void syncache_drop(struct syncache *, struct syncache_head *); 161 static void syncache_free(struct syncache *); 162 static void syncache_insert(struct syncache *, struct syncache_head *); 163 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 164 static int syncache_respond(struct syncache *); 165 static struct socket *syncache_socket(struct syncache *, struct socket *, 166 struct mbuf *m); 167 static void syncache_timer(void *); 168 static void syncookie_generate(struct syncache_head *, struct syncache *, 169 u_int32_t *); 170 static struct syncache 171 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 172 struct syncache *, struct tcpopt *, struct tcphdr *, 173 struct socket *); 174 175 /* 176 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 177 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 178 * the odds are that the user has given up attempting to connect by then. 179 */ 180 #define SYNCACHE_MAXREXMTS 3 181 182 /* Arbitrary values */ 183 #define TCP_SYNCACHE_HASHSIZE 512 184 #define TCP_SYNCACHE_BUCKETLIMIT 30 185 186 struct tcp_syncache { 187 struct syncache_head *hashbase; 188 uma_zone_t zone; 189 u_int hashsize; 190 u_int hashmask; 191 u_int bucket_limit; 192 u_int cache_count; /* XXX: unprotected */ 193 u_int cache_limit; 194 u_int rexmt_limit; 195 u_int hash_secret; 196 }; 197 static struct tcp_syncache tcp_syncache; 198 199 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 200 201 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 202 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 203 204 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 205 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 206 207 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 208 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 209 210 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 211 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 212 213 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 214 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 215 216 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 217 218 #define SYNCACHE_HASH(inc, mask) \ 219 ((tcp_syncache.hash_secret ^ \ 220 (inc)->inc_faddr.s_addr ^ \ 221 ((inc)->inc_faddr.s_addr >> 16) ^ \ 222 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 223 224 #define SYNCACHE_HASH6(inc, mask) \ 225 ((tcp_syncache.hash_secret ^ \ 226 (inc)->inc6_faddr.s6_addr32[0] ^ \ 227 (inc)->inc6_faddr.s6_addr32[3] ^ \ 228 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 229 230 #define ENDPTS_EQ(a, b) ( \ 231 (a)->ie_fport == (b)->ie_fport && \ 232 (a)->ie_lport == (b)->ie_lport && \ 233 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 234 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 235 ) 236 237 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 238 239 #define SYNCACHE_TIMEOUT(sc, sch, co) do { \ 240 (sc)->sc_rxmits++; \ 241 (sc)->sc_rxttime = ticks + \ 242 TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \ 243 if ((sch)->sch_nextc > (sc)->sc_rxttime) \ 244 (sch)->sch_nextc = (sc)->sc_rxttime; \ 245 if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \ 246 callout_reset(&(sch)->sch_timer, \ 247 (sch)->sch_nextc - ticks, \ 248 syncache_timer, (void *)(sch)); \ 249 } while (0) 250 251 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 252 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 253 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 254 255 /* 256 * Requires the syncache entry to be already removed from the bucket list. 257 */ 258 static void 259 syncache_free(struct syncache *sc) 260 { 261 if (sc->sc_ipopts) 262 (void) m_free(sc->sc_ipopts); 263 #ifdef MAC 264 mac_destroy_syncache(&sc->sc_label); 265 #endif 266 267 uma_zfree(tcp_syncache.zone, sc); 268 } 269 270 void 271 syncache_init(void) 272 { 273 int i; 274 275 tcp_syncache.cache_count = 0; 276 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 277 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 278 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 279 tcp_syncache.hash_secret = arc4random(); 280 281 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 282 &tcp_syncache.hashsize); 283 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 284 &tcp_syncache.bucket_limit); 285 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 286 printf("WARNING: syncache hash size is not a power of 2.\n"); 287 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 288 } 289 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 290 291 /* Set limits. */ 292 tcp_syncache.cache_limit = 293 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 294 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 295 &tcp_syncache.cache_limit); 296 297 /* Allocate the hash table. */ 298 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 299 tcp_syncache.hashsize * sizeof(struct syncache_head), 300 M_SYNCACHE, M_WAITOK | M_ZERO); 301 302 /* Initialize the hash buckets. */ 303 for (i = 0; i < tcp_syncache.hashsize; i++) { 304 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 305 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 306 NULL, MTX_DEF); 307 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 308 &tcp_syncache.hashbase[i].sch_mtx, 0); 309 tcp_syncache.hashbase[i].sch_length = 0; 310 } 311 312 /* Create the syncache entry zone. */ 313 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 314 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 315 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 316 } 317 318 /* 319 * Inserts a syncache entry into the specified bucket row. 320 * Locks and unlocks the syncache_head autonomously. 321 */ 322 static void 323 syncache_insert(struct syncache *sc, struct syncache_head *sch) 324 { 325 struct syncache *sc2; 326 327 SCH_LOCK(sch); 328 329 /* 330 * Make sure that we don't overflow the per-bucket limit. 331 * If the bucket is full, toss the oldest element. 332 */ 333 if (sch->sch_length >= tcp_syncache.bucket_limit) { 334 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 335 ("sch->sch_length incorrect")); 336 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 337 syncache_drop(sc2, sch); 338 tcpstat.tcps_sc_bucketoverflow++; 339 } 340 341 /* Put it into the bucket. */ 342 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 343 sch->sch_length++; 344 345 /* Reinitialize the bucket row's timer. */ 346 SYNCACHE_TIMEOUT(sc, sch, 1); 347 348 SCH_UNLOCK(sch); 349 350 tcp_syncache.cache_count++; 351 tcpstat.tcps_sc_added++; 352 } 353 354 /* 355 * Remove and free entry from syncache bucket row. 356 * Expects locked syncache head. 357 */ 358 static void 359 syncache_drop(struct syncache *sc, struct syncache_head *sch) 360 { 361 362 SCH_LOCK_ASSERT(sch); 363 364 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 365 sch->sch_length--; 366 367 syncache_free(sc); 368 tcp_syncache.cache_count--; 369 } 370 371 /* 372 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 373 * If we have retransmitted an entry the maximum number of times, expire it. 374 * One separate timer for each bucket row. 375 */ 376 static void 377 syncache_timer(void *xsch) 378 { 379 struct syncache_head *sch = (struct syncache_head *)xsch; 380 struct syncache *sc, *nsc; 381 int tick = ticks; 382 char *s; 383 384 /* NB: syncache_head has already been locked by the callout. */ 385 SCH_LOCK_ASSERT(sch); 386 387 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 388 /* 389 * We do not check if the listen socket still exists 390 * and accept the case where the listen socket may be 391 * gone by the time we resend the SYN/ACK. We do 392 * not expect this to happens often. If it does, 393 * then the RST will be sent by the time the remote 394 * host does the SYN/ACK->ACK. 395 */ 396 if (sc->sc_rxttime >= tick) { 397 if (sc->sc_rxttime < sch->sch_nextc) 398 sch->sch_nextc = sc->sc_rxttime; 399 continue; 400 } 401 402 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 403 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 404 log(LOG_DEBUG, "%s; %s: Response timeout\n", 405 s, __func__); 406 free(s, M_TCPLOG); 407 } 408 syncache_drop(sc, sch); 409 tcpstat.tcps_sc_stale++; 410 continue; 411 } 412 413 (void) syncache_respond(sc); 414 tcpstat.tcps_sc_retransmitted++; 415 SYNCACHE_TIMEOUT(sc, sch, 0); 416 } 417 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 418 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 419 syncache_timer, (void *)(sch)); 420 } 421 422 /* 423 * Find an entry in the syncache. 424 * Returns always with locked syncache_head plus a matching entry or NULL. 425 */ 426 struct syncache * 427 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 428 { 429 struct syncache *sc; 430 struct syncache_head *sch; 431 432 #ifdef INET6 433 if (inc->inc_isipv6) { 434 sch = &tcp_syncache.hashbase[ 435 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 436 *schp = sch; 437 438 SCH_LOCK(sch); 439 440 /* Circle through bucket row to find matching entry. */ 441 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 442 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 443 return (sc); 444 } 445 } else 446 #endif 447 { 448 sch = &tcp_syncache.hashbase[ 449 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 450 *schp = sch; 451 452 SCH_LOCK(sch); 453 454 /* Circle through bucket row to find matching entry. */ 455 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 456 #ifdef INET6 457 if (sc->sc_inc.inc_isipv6) 458 continue; 459 #endif 460 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 461 return (sc); 462 } 463 } 464 SCH_LOCK_ASSERT(*schp); 465 return (NULL); /* always returns with locked sch */ 466 } 467 468 /* 469 * This function is called when we get a RST for a 470 * non-existent connection, so that we can see if the 471 * connection is in the syn cache. If it is, zap it. 472 */ 473 void 474 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 475 { 476 struct syncache *sc; 477 struct syncache_head *sch; 478 479 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 480 SCH_LOCK_ASSERT(sch); 481 if (sc == NULL) 482 goto done; 483 484 /* 485 * If the RST bit is set, check the sequence number to see 486 * if this is a valid reset segment. 487 * RFC 793 page 37: 488 * In all states except SYN-SENT, all reset (RST) segments 489 * are validated by checking their SEQ-fields. A reset is 490 * valid if its sequence number is in the window. 491 * 492 * The sequence number in the reset segment is normally an 493 * echo of our outgoing acknowlegement numbers, but some hosts 494 * send a reset with the sequence number at the rightmost edge 495 * of our receive window, and we have to handle this case. 496 */ 497 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 498 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 499 syncache_drop(sc, sch); 500 tcpstat.tcps_sc_reset++; 501 } 502 done: 503 SCH_UNLOCK(sch); 504 } 505 506 void 507 syncache_badack(struct in_conninfo *inc) 508 { 509 struct syncache *sc; 510 struct syncache_head *sch; 511 512 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 513 SCH_LOCK_ASSERT(sch); 514 if (sc != NULL) { 515 syncache_drop(sc, sch); 516 tcpstat.tcps_sc_badack++; 517 } 518 SCH_UNLOCK(sch); 519 } 520 521 void 522 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 523 { 524 struct syncache *sc; 525 struct syncache_head *sch; 526 527 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 528 SCH_LOCK_ASSERT(sch); 529 if (sc == NULL) 530 goto done; 531 532 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 533 if (ntohl(th->th_seq) != sc->sc_iss) 534 goto done; 535 536 /* 537 * If we've rertransmitted 3 times and this is our second error, 538 * we remove the entry. Otherwise, we allow it to continue on. 539 * This prevents us from incorrectly nuking an entry during a 540 * spurious network outage. 541 * 542 * See tcp_notify(). 543 */ 544 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 545 sc->sc_flags |= SCF_UNREACH; 546 goto done; 547 } 548 syncache_drop(sc, sch); 549 tcpstat.tcps_sc_unreach++; 550 done: 551 SCH_UNLOCK(sch); 552 } 553 554 /* 555 * Build a new TCP socket structure from a syncache entry. 556 */ 557 static struct socket * 558 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 559 { 560 struct inpcb *inp = NULL; 561 struct socket *so; 562 struct tcpcb *tp; 563 char *s; 564 565 NET_ASSERT_GIANT(); 566 INP_INFO_WLOCK_ASSERT(&tcbinfo); 567 568 /* 569 * Ok, create the full blown connection, and set things up 570 * as they would have been set up if we had created the 571 * connection when the SYN arrived. If we can't create 572 * the connection, abort it. 573 */ 574 so = sonewconn(lso, SS_ISCONNECTED); 575 if (so == NULL) { 576 /* 577 * Drop the connection; we will either send a RST or 578 * have the peer retransmit its SYN again after its 579 * RTO and try again. 580 */ 581 tcpstat.tcps_listendrop++; 582 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 583 log(LOG_DEBUG, "%s; %s: Socket create failed " 584 "due to limits or memory shortage\n", 585 s, __func__); 586 free(s, M_TCPLOG); 587 } 588 goto abort2; 589 } 590 #ifdef MAC 591 SOCK_LOCK(so); 592 mac_set_socket_peer_from_mbuf(m, so); 593 SOCK_UNLOCK(so); 594 #endif 595 596 inp = sotoinpcb(so); 597 INP_LOCK(inp); 598 599 /* Insert new socket into PCB hash list. */ 600 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 601 #ifdef INET6 602 if (sc->sc_inc.inc_isipv6) { 603 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 604 } else { 605 inp->inp_vflag &= ~INP_IPV6; 606 inp->inp_vflag |= INP_IPV4; 607 #endif 608 inp->inp_laddr = sc->sc_inc.inc_laddr; 609 #ifdef INET6 610 } 611 #endif 612 inp->inp_lport = sc->sc_inc.inc_lport; 613 if (in_pcbinshash(inp) != 0) { 614 /* 615 * Undo the assignments above if we failed to 616 * put the PCB on the hash lists. 617 */ 618 #ifdef INET6 619 if (sc->sc_inc.inc_isipv6) 620 inp->in6p_laddr = in6addr_any; 621 else 622 #endif 623 inp->inp_laddr.s_addr = INADDR_ANY; 624 inp->inp_lport = 0; 625 goto abort; 626 } 627 #ifdef IPSEC 628 /* Copy old policy into new socket's. */ 629 if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 630 printf("syncache_socket: could not copy policy\n"); 631 #endif 632 #ifdef FAST_IPSEC 633 /* Copy old policy into new socket's. */ 634 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 635 printf("syncache_socket: could not copy policy\n"); 636 #endif 637 #ifdef INET6 638 if (sc->sc_inc.inc_isipv6) { 639 struct inpcb *oinp = sotoinpcb(lso); 640 struct in6_addr laddr6; 641 struct sockaddr_in6 sin6; 642 /* 643 * Inherit socket options from the listening socket. 644 * Note that in6p_inputopts are not (and should not be) 645 * copied, since it stores previously received options and is 646 * used to detect if each new option is different than the 647 * previous one and hence should be passed to a user. 648 * If we copied in6p_inputopts, a user would not be able to 649 * receive options just after calling the accept system call. 650 */ 651 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 652 if (oinp->in6p_outputopts) 653 inp->in6p_outputopts = 654 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 655 656 sin6.sin6_family = AF_INET6; 657 sin6.sin6_len = sizeof(sin6); 658 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 659 sin6.sin6_port = sc->sc_inc.inc_fport; 660 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 661 laddr6 = inp->in6p_laddr; 662 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 663 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 664 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 665 thread0.td_ucred)) { 666 inp->in6p_laddr = laddr6; 667 goto abort; 668 } 669 /* Override flowlabel from in6_pcbconnect. */ 670 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 671 inp->in6p_flowinfo |= sc->sc_flowlabel; 672 } else 673 #endif 674 { 675 struct in_addr laddr; 676 struct sockaddr_in sin; 677 678 inp->inp_options = ip_srcroute(m); 679 if (inp->inp_options == NULL) { 680 inp->inp_options = sc->sc_ipopts; 681 sc->sc_ipopts = NULL; 682 } 683 684 sin.sin_family = AF_INET; 685 sin.sin_len = sizeof(sin); 686 sin.sin_addr = sc->sc_inc.inc_faddr; 687 sin.sin_port = sc->sc_inc.inc_fport; 688 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 689 laddr = inp->inp_laddr; 690 if (inp->inp_laddr.s_addr == INADDR_ANY) 691 inp->inp_laddr = sc->sc_inc.inc_laddr; 692 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 693 thread0.td_ucred)) { 694 inp->inp_laddr = laddr; 695 goto abort; 696 } 697 } 698 tp = intotcpcb(inp); 699 tp->t_state = TCPS_SYN_RECEIVED; 700 tp->iss = sc->sc_iss; 701 tp->irs = sc->sc_irs; 702 tcp_rcvseqinit(tp); 703 tcp_sendseqinit(tp); 704 tp->snd_wl1 = sc->sc_irs; 705 tp->snd_max = tp->iss + 1; 706 tp->snd_nxt = tp->iss + 1; 707 tp->rcv_up = sc->sc_irs + 1; 708 tp->rcv_wnd = sc->sc_wnd; 709 tp->rcv_adv += tp->rcv_wnd; 710 tp->last_ack_sent = tp->rcv_nxt; 711 712 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 713 if (sc->sc_flags & SCF_NOOPT) 714 tp->t_flags |= TF_NOOPT; 715 else { 716 if (sc->sc_flags & SCF_WINSCALE) { 717 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 718 tp->snd_scale = sc->sc_requested_s_scale; 719 tp->request_r_scale = sc->sc_requested_r_scale; 720 } 721 if (sc->sc_flags & SCF_TIMESTAMP) { 722 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 723 tp->ts_recent = sc->sc_tsreflect; 724 tp->ts_recent_age = ticks; 725 tp->ts_offset = sc->sc_tsoff; 726 } 727 #ifdef TCP_SIGNATURE 728 if (sc->sc_flags & SCF_SIGNATURE) 729 tp->t_flags |= TF_SIGNATURE; 730 #endif 731 if (sc->sc_flags & SCF_SACK) 732 tp->t_flags |= TF_SACK_PERMIT; 733 } 734 735 /* 736 * Set up MSS and get cached values from tcp_hostcache. 737 * This might overwrite some of the defaults we just set. 738 */ 739 tcp_mss(tp, sc->sc_peer_mss); 740 741 /* 742 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 743 */ 744 if (sc->sc_rxmits > 1) 745 tp->snd_cwnd = tp->t_maxseg; 746 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); 747 748 INP_UNLOCK(inp); 749 750 tcpstat.tcps_accepts++; 751 return (so); 752 753 abort: 754 INP_UNLOCK(inp); 755 abort2: 756 if (so != NULL) 757 soabort(so); 758 return (NULL); 759 } 760 761 /* 762 * This function gets called when we receive an ACK for a 763 * socket in the LISTEN state. We look up the connection 764 * in the syncache, and if its there, we pull it out of 765 * the cache and turn it into a full-blown connection in 766 * the SYN-RECEIVED state. 767 */ 768 int 769 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 770 struct socket **lsop, struct mbuf *m) 771 { 772 struct syncache *sc; 773 struct syncache_head *sch; 774 struct syncache scs; 775 char *s; 776 777 /* 778 * Global TCP locks are held because we manipulate the PCB lists 779 * and create a new socket. 780 */ 781 INP_INFO_WLOCK_ASSERT(&tcbinfo); 782 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 783 ("%s: can handle only ACK", __func__)); 784 785 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 786 SCH_LOCK_ASSERT(sch); 787 if (sc == NULL) { 788 /* 789 * There is no syncache entry, so see if this ACK is 790 * a returning syncookie. To do this, first: 791 * A. See if this socket has had a syncache entry dropped in 792 * the past. We don't want to accept a bogus syncookie 793 * if we've never received a SYN. 794 * B. check that the syncookie is valid. If it is, then 795 * cobble up a fake syncache entry, and return. 796 */ 797 if (!tcp_syncookies) { 798 SCH_UNLOCK(sch); 799 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 800 log(LOG_DEBUG, "%s; %s: Spurious ACK\n", 801 s, __func__); 802 goto failed; 803 } 804 bzero(&scs, sizeof(scs)); 805 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 806 SCH_UNLOCK(sch); 807 if (sc == NULL) { 808 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 809 log(LOG_DEBUG, "%s; %s: Segment failed " 810 "SYNCOOKIE authentication\n", 811 s, __func__); 812 goto failed; 813 } 814 tcpstat.tcps_sc_recvcookie++; 815 } else { 816 /* Pull out the entry to unlock the bucket row. */ 817 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 818 sch->sch_length--; 819 tcp_syncache.cache_count--; 820 SCH_UNLOCK(sch); 821 } 822 823 /* 824 * Segment validation: 825 * ACK must match our initial sequence number + 1 (the SYN|ACK). 826 */ 827 if (th->th_ack != sc->sc_iss + 1) { 828 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 829 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u\n", 830 s, __func__, th->th_ack, sc->sc_iss); 831 goto failed; 832 } 833 /* 834 * The SEQ must match the received initial receive sequence 835 * number + 1 (the SYN) because we didn't ACK any data that 836 * may have come with the SYN. 837 */ 838 if (th->th_seq != sc->sc_irs + 1) { 839 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 840 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u\n", 841 s, __func__, th->th_ack, sc->sc_iss); 842 goto failed; 843 } 844 /* 845 * If timestamps were present in the SYN and we accepted 846 * them in our SYN|ACK we require them to be present from 847 * now on. And vice versa. 848 */ 849 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 850 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 851 log(LOG_DEBUG, "%s; %s: Timestamp missing\n", 852 s, __func__); 853 goto failed; 854 } 855 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 856 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 857 log(LOG_DEBUG, "%s; %s: Timestamp not expected\n", 858 s, __func__); 859 goto failed; 860 } 861 /* 862 * If timestamps were negotiated the reflected timestamp 863 * must be equal to what we actually sent in the SYN|ACK. 864 */ 865 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 866 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 867 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u\n", 868 s, __func__, to->to_tsecr, sc->sc_ts); 869 goto failed; 870 } 871 872 *lsop = syncache_socket(sc, *lsop, m); 873 874 if (*lsop == NULL) 875 tcpstat.tcps_sc_aborted++; 876 else 877 tcpstat.tcps_sc_completed++; 878 879 if (sc != &scs) 880 syncache_free(sc); 881 return (1); 882 failed: 883 if (sc != NULL && sc != &scs) 884 syncache_free(sc); 885 if (s != NULL) 886 free(s, M_TCPLOG); 887 *lsop = NULL; 888 return (0); 889 } 890 891 /* 892 * Given a LISTEN socket and an inbound SYN request, add 893 * this to the syn cache, and send back a segment: 894 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 895 * to the source. 896 * 897 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 898 * Doing so would require that we hold onto the data and deliver it 899 * to the application. However, if we are the target of a SYN-flood 900 * DoS attack, an attacker could send data which would eventually 901 * consume all available buffer space if it were ACKed. By not ACKing 902 * the data, we avoid this DoS scenario. 903 */ 904 void 905 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 906 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 907 { 908 struct tcpcb *tp; 909 struct socket *so; 910 struct syncache *sc = NULL; 911 struct syncache_head *sch; 912 struct mbuf *ipopts = NULL; 913 u_int32_t flowtmp; 914 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 915 #ifdef INET6 916 int autoflowlabel = 0; 917 #endif 918 #ifdef MAC 919 struct label *maclabel; 920 #endif 921 struct syncache scs; 922 923 INP_INFO_WLOCK_ASSERT(&tcbinfo); 924 INP_LOCK_ASSERT(inp); /* listen socket */ 925 926 /* 927 * Combine all so/tp operations very early to drop the INP lock as 928 * soon as possible. 929 */ 930 so = *lsop; 931 tp = sototcpcb(so); 932 933 #ifdef INET6 934 if (inc->inc_isipv6 && 935 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 936 autoflowlabel = 1; 937 #endif 938 ip_ttl = inp->inp_ip_ttl; 939 ip_tos = inp->inp_ip_tos; 940 win = sbspace(&so->so_rcv); 941 sb_hiwat = so->so_rcv.sb_hiwat; 942 noopt = (tp->t_flags & TF_NOOPT); 943 944 so = NULL; 945 tp = NULL; 946 947 #ifdef MAC 948 if (mac_init_syncache(&maclabel) != 0) { 949 INP_UNLOCK(inp); 950 INP_INFO_WUNLOCK(&tcbinfo); 951 goto done; 952 } else 953 mac_init_syncache_from_inpcb(maclabel, inp); 954 #endif 955 INP_UNLOCK(inp); 956 INP_INFO_WUNLOCK(&tcbinfo); 957 958 /* 959 * Remember the IP options, if any. 960 */ 961 #ifdef INET6 962 if (!inc->inc_isipv6) 963 #endif 964 ipopts = ip_srcroute(m); 965 966 /* 967 * See if we already have an entry for this connection. 968 * If we do, resend the SYN,ACK, and reset the retransmit timer. 969 * 970 * XXX: should the syncache be re-initialized with the contents 971 * of the new SYN here (which may have different options?) 972 */ 973 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 974 SCH_LOCK_ASSERT(sch); 975 if (sc != NULL) { 976 tcpstat.tcps_sc_dupsyn++; 977 if (ipopts) { 978 /* 979 * If we were remembering a previous source route, 980 * forget it and use the new one we've been given. 981 */ 982 if (sc->sc_ipopts) 983 (void) m_free(sc->sc_ipopts); 984 sc->sc_ipopts = ipopts; 985 } 986 /* 987 * Update timestamp if present. 988 */ 989 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 990 sc->sc_tsreflect = to->to_tsval; 991 else 992 sc->sc_flags &= ~SCF_TIMESTAMP; 993 #ifdef MAC 994 /* 995 * Since we have already unconditionally allocated label 996 * storage, free it up. The syncache entry will already 997 * have an initialized label we can use. 998 */ 999 mac_destroy_syncache(&maclabel); 1000 KASSERT(sc->sc_label != NULL, 1001 ("%s: label not initialized", __func__)); 1002 #endif 1003 if (syncache_respond(sc) == 0) { 1004 SYNCACHE_TIMEOUT(sc, sch, 1); 1005 tcpstat.tcps_sndacks++; 1006 tcpstat.tcps_sndtotal++; 1007 } 1008 SCH_UNLOCK(sch); 1009 goto done; 1010 } 1011 1012 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1013 if (sc == NULL) { 1014 /* 1015 * The zone allocator couldn't provide more entries. 1016 * Treat this as if the cache was full; drop the oldest 1017 * entry and insert the new one. 1018 */ 1019 tcpstat.tcps_sc_zonefail++; 1020 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1021 syncache_drop(sc, sch); 1022 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1023 if (sc == NULL) { 1024 if (tcp_syncookies) { 1025 bzero(&scs, sizeof(scs)); 1026 sc = &scs; 1027 } else { 1028 SCH_UNLOCK(sch); 1029 if (ipopts) 1030 (void) m_free(ipopts); 1031 goto done; 1032 } 1033 } 1034 } 1035 1036 /* 1037 * Fill in the syncache values. 1038 */ 1039 #ifdef MAC 1040 sc->sc_label = maclabel; 1041 #endif 1042 sc->sc_ipopts = ipopts; 1043 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1044 #ifdef INET6 1045 if (!inc->inc_isipv6) 1046 #endif 1047 { 1048 sc->sc_ip_tos = ip_tos; 1049 sc->sc_ip_ttl = ip_ttl; 1050 } 1051 1052 sc->sc_irs = th->th_seq; 1053 sc->sc_iss = arc4random(); 1054 sc->sc_flags = 0; 1055 sc->sc_flowlabel = 0; 1056 1057 /* 1058 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1059 * win was derived from socket earlier in the function. 1060 */ 1061 win = imax(win, 0); 1062 win = imin(win, TCP_MAXWIN); 1063 sc->sc_wnd = win; 1064 1065 if (tcp_do_rfc1323) { 1066 /* 1067 * A timestamp received in a SYN makes 1068 * it ok to send timestamp requests and replies. 1069 */ 1070 if (to->to_flags & TOF_TS) { 1071 sc->sc_tsreflect = to->to_tsval; 1072 sc->sc_ts = ticks; 1073 sc->sc_flags |= SCF_TIMESTAMP; 1074 } 1075 if (to->to_flags & TOF_SCALE) { 1076 int wscale = 0; 1077 1078 /* 1079 * Compute proper scaling value from buffer space. 1080 * Leave enough room for the socket buffer to grow 1081 * with auto sizing. This allows us to scale the 1082 * receive buffer over a wide range while not losing 1083 * any efficiency or fine granularity. 1084 * 1085 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1086 * or <SYN,ACK>) segment itself is never scaled. 1087 */ 1088 while (wscale < TCP_MAX_WINSHIFT && 1089 (0x1 << wscale) < tcp_minmss) 1090 wscale++; 1091 sc->sc_requested_r_scale = wscale; 1092 sc->sc_requested_s_scale = to->to_wscale; 1093 sc->sc_flags |= SCF_WINSCALE; 1094 } 1095 } 1096 #ifdef TCP_SIGNATURE 1097 /* 1098 * If listening socket requested TCP digests, and received SYN 1099 * contains the option, flag this in the syncache so that 1100 * syncache_respond() will do the right thing with the SYN+ACK. 1101 * XXX: Currently we always record the option by default and will 1102 * attempt to use it in syncache_respond(). 1103 */ 1104 if (to->to_flags & TOF_SIGNATURE) 1105 sc->sc_flags |= SCF_SIGNATURE; 1106 #endif 1107 if (to->to_flags & TOF_SACK) 1108 sc->sc_flags |= SCF_SACK; 1109 if (to->to_flags & TOF_MSS) 1110 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1111 if (noopt) 1112 sc->sc_flags |= SCF_NOOPT; 1113 1114 if (tcp_syncookies) { 1115 syncookie_generate(sch, sc, &flowtmp); 1116 #ifdef INET6 1117 if (autoflowlabel) 1118 sc->sc_flowlabel = flowtmp; 1119 #endif 1120 } else { 1121 #ifdef INET6 1122 if (autoflowlabel) 1123 sc->sc_flowlabel = 1124 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1125 #endif 1126 } 1127 SCH_UNLOCK(sch); 1128 1129 /* 1130 * Do a standard 3-way handshake. 1131 */ 1132 if (syncache_respond(sc) == 0) { 1133 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1134 syncache_free(sc); 1135 else if (sc != &scs) 1136 syncache_insert(sc, sch); /* locks and unlocks sch */ 1137 tcpstat.tcps_sndacks++; 1138 tcpstat.tcps_sndtotal++; 1139 } else { 1140 if (sc != &scs) 1141 syncache_free(sc); 1142 tcpstat.tcps_sc_dropped++; 1143 } 1144 1145 done: 1146 #ifdef MAC 1147 if (sc == &scs) 1148 mac_destroy_syncache(&maclabel); 1149 #endif 1150 *lsop = NULL; 1151 m_freem(m); 1152 return; 1153 } 1154 1155 static int 1156 syncache_respond(struct syncache *sc) 1157 { 1158 struct ip *ip = NULL; 1159 struct mbuf *m; 1160 struct tcphdr *th; 1161 int optlen, error; 1162 u_int16_t hlen, tlen, mssopt; 1163 struct tcpopt to; 1164 #ifdef INET6 1165 struct ip6_hdr *ip6 = NULL; 1166 #endif 1167 1168 hlen = 1169 #ifdef INET6 1170 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1171 #endif 1172 sizeof(struct ip); 1173 tlen = hlen + sizeof(struct tcphdr); 1174 1175 /* Determine MSS we advertize to other end of connection. */ 1176 mssopt = tcp_mssopt(&sc->sc_inc); 1177 if (sc->sc_peer_mss) 1178 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1179 1180 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1181 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1182 ("syncache: mbuf too small")); 1183 1184 /* Create the IP+TCP header from scratch. */ 1185 m = m_gethdr(M_DONTWAIT, MT_DATA); 1186 if (m == NULL) 1187 return (ENOBUFS); 1188 #ifdef MAC 1189 mac_create_mbuf_from_syncache(sc->sc_label, m); 1190 #endif 1191 m->m_data += max_linkhdr; 1192 m->m_len = tlen; 1193 m->m_pkthdr.len = tlen; 1194 m->m_pkthdr.rcvif = NULL; 1195 1196 #ifdef INET6 1197 if (sc->sc_inc.inc_isipv6) { 1198 ip6 = mtod(m, struct ip6_hdr *); 1199 ip6->ip6_vfc = IPV6_VERSION; 1200 ip6->ip6_nxt = IPPROTO_TCP; 1201 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1202 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1203 ip6->ip6_plen = htons(tlen - hlen); 1204 /* ip6_hlim is set after checksum */ 1205 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1206 ip6->ip6_flow |= sc->sc_flowlabel; 1207 1208 th = (struct tcphdr *)(ip6 + 1); 1209 } else 1210 #endif 1211 { 1212 ip = mtod(m, struct ip *); 1213 ip->ip_v = IPVERSION; 1214 ip->ip_hl = sizeof(struct ip) >> 2; 1215 ip->ip_len = tlen; 1216 ip->ip_id = 0; 1217 ip->ip_off = 0; 1218 ip->ip_sum = 0; 1219 ip->ip_p = IPPROTO_TCP; 1220 ip->ip_src = sc->sc_inc.inc_laddr; 1221 ip->ip_dst = sc->sc_inc.inc_faddr; 1222 ip->ip_ttl = sc->sc_ip_ttl; 1223 ip->ip_tos = sc->sc_ip_tos; 1224 1225 /* 1226 * See if we should do MTU discovery. Route lookups are 1227 * expensive, so we will only unset the DF bit if: 1228 * 1229 * 1) path_mtu_discovery is disabled 1230 * 2) the SCF_UNREACH flag has been set 1231 */ 1232 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1233 ip->ip_off |= IP_DF; 1234 1235 th = (struct tcphdr *)(ip + 1); 1236 } 1237 th->th_sport = sc->sc_inc.inc_lport; 1238 th->th_dport = sc->sc_inc.inc_fport; 1239 1240 th->th_seq = htonl(sc->sc_iss); 1241 th->th_ack = htonl(sc->sc_irs + 1); 1242 th->th_off = sizeof(struct tcphdr) >> 2; 1243 th->th_x2 = 0; 1244 th->th_flags = TH_SYN|TH_ACK; 1245 th->th_win = htons(sc->sc_wnd); 1246 th->th_urp = 0; 1247 1248 /* Tack on the TCP options. */ 1249 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1250 to.to_flags = 0; 1251 1252 to.to_mss = mssopt; 1253 to.to_flags = TOF_MSS; 1254 if (sc->sc_flags & SCF_WINSCALE) { 1255 to.to_wscale = sc->sc_requested_r_scale; 1256 to.to_flags |= TOF_SCALE; 1257 } 1258 if (sc->sc_flags & SCF_TIMESTAMP) { 1259 /* Virgin timestamp or TCP cookie enhanced one. */ 1260 to.to_tsval = sc->sc_ts; 1261 to.to_tsecr = sc->sc_tsreflect; 1262 to.to_flags |= TOF_TS; 1263 } 1264 if (sc->sc_flags & SCF_SACK) 1265 to.to_flags |= TOF_SACKPERM; 1266 #ifdef TCP_SIGNATURE 1267 if (sc->sc_flags & SCF_SIGNATURE) 1268 to.to_flags |= TOF_SIGNATURE; 1269 #endif 1270 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1271 1272 #ifdef TCP_SIGNATURE 1273 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1274 to.to_signature, IPSEC_DIR_OUTBOUND); 1275 #endif 1276 1277 /* Adjust headers by option size. */ 1278 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1279 m->m_len += optlen; 1280 m->m_pkthdr.len += optlen; 1281 #ifdef INET6 1282 if (sc->sc_inc.inc_isipv6) 1283 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1284 else 1285 #endif 1286 ip->ip_len += optlen; 1287 } else 1288 optlen = 0; 1289 1290 #ifdef INET6 1291 if (sc->sc_inc.inc_isipv6) { 1292 th->th_sum = 0; 1293 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, 1294 tlen + optlen - hlen); 1295 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1296 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1297 } else 1298 #endif 1299 { 1300 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1301 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1302 m->m_pkthdr.csum_flags = CSUM_TCP; 1303 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1304 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1305 } 1306 return (error); 1307 } 1308 1309 /* 1310 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1311 * receive and to be able to handle SYN floods from bogus source addresses 1312 * (where we will never receive any reply). SYN floods try to exhaust all 1313 * our memory and available slots in the SYN cache table to cause a denial 1314 * of service to legitimate users of the local host. 1315 * 1316 * The idea of SYN cookies is to encode and include all necessary information 1317 * about the connection setup state within the SYN-ACK we send back and thus 1318 * to get along without keeping any local state until the ACK to the SYN-ACK 1319 * arrives (if ever). Everything we need to know should be available from 1320 * the information we encoded in the SYN-ACK. 1321 * 1322 * More information about the theory behind SYN cookies and its first 1323 * discussion and specification can be found at: 1324 * http://cr.yp.to/syncookies.html (overview) 1325 * http://cr.yp.to/syncookies/archive (gory details) 1326 * 1327 * This implementation extends the orginal idea and first implementation 1328 * of FreeBSD by using not only the initial sequence number field to store 1329 * information but also the timestamp field if present. This way we can 1330 * keep track of the entire state we need to know to recreate the session in 1331 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1332 * these days. For those that do not we still have to live with the known 1333 * shortcomings of the ISN only SYN cookies. 1334 * 1335 * Cookie layers: 1336 * 1337 * Initial sequence number we send: 1338 * 31|................................|0 1339 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1340 * D = MD5 Digest (first dword) 1341 * M = MSS index 1342 * R = Rotation of secret 1343 * P = Odd or Even secret 1344 * 1345 * The MD5 Digest is computed with over following parameters: 1346 * a) randomly rotated secret 1347 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1348 * c) the received initial sequence number from remote host 1349 * d) the rotation offset and odd/even bit 1350 * 1351 * Timestamp we send: 1352 * 31|................................|0 1353 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1354 * D = MD5 Digest (third dword) (only as filler) 1355 * S = Requested send window scale 1356 * R = Requested receive window scale 1357 * A = SACK allowed 1358 * 5 = TCP-MD5 enabled (not implemented yet) 1359 * XORed with MD5 Digest (forth dword) 1360 * 1361 * The timestamp isn't cryptographically secure and doesn't need to be. 1362 * The double use of the MD5 digest dwords ties it to a specific remote/ 1363 * local host/port, remote initial sequence number and our local time 1364 * limited secret. A received timestamp is reverted (XORed) and then 1365 * the contained MD5 dword is compared to the computed one to ensure the 1366 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1367 * have been tampered with but this isn't different from supplying bogus 1368 * values in the SYN in the first place. 1369 * 1370 * Some problems with SYN cookies remain however: 1371 * Consider the problem of a recreated (and retransmitted) cookie. If the 1372 * original SYN was accepted, the connection is established. The second 1373 * SYN is inflight, and if it arrives with an ISN that falls within the 1374 * receive window, the connection is killed. 1375 * 1376 * Notes: 1377 * A heuristic to determine when to accept syn cookies is not necessary. 1378 * An ACK flood would cause the syncookie verification to be attempted, 1379 * but a SYN flood causes syncookies to be generated. Both are of equal 1380 * cost, so there's no point in trying to optimize the ACK flood case. 1381 * Also, if you don't process certain ACKs for some reason, then all someone 1382 * would have to do is launch a SYN and ACK flood at the same time, which 1383 * would stop cookie verification and defeat the entire purpose of syncookies. 1384 */ 1385 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1386 1387 static void 1388 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1389 u_int32_t *flowlabel) 1390 { 1391 MD5_CTX ctx; 1392 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1393 u_int32_t data; 1394 u_int32_t *secbits; 1395 u_int off, pmss, mss; 1396 int i; 1397 1398 SCH_LOCK_ASSERT(sch); 1399 1400 /* Which of the two secrets to use. */ 1401 secbits = sch->sch_oddeven ? 1402 sch->sch_secbits_odd : sch->sch_secbits_even; 1403 1404 /* Reseed secret if too old. */ 1405 if (sch->sch_reseed < time_uptime) { 1406 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1407 secbits = sch->sch_oddeven ? 1408 sch->sch_secbits_odd : sch->sch_secbits_even; 1409 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1410 secbits[i] = arc4random(); 1411 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1412 } 1413 1414 /* Secret rotation offset. */ 1415 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1416 1417 /* Maximum segment size calculation. */ 1418 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1419 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1420 if (tcp_sc_msstab[mss] <= pmss) 1421 break; 1422 1423 /* Fold parameters and MD5 digest into the ISN we will send. */ 1424 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1425 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1426 data |= mss << 4; /* mss, 3 bits */ 1427 1428 MD5Init(&ctx); 1429 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1430 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1431 MD5Update(&ctx, secbits, off); 1432 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1433 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1434 MD5Update(&ctx, &data, sizeof(data)); 1435 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1436 1437 data |= (md5_buffer[0] << 7); 1438 sc->sc_iss = data; 1439 1440 #ifdef INET6 1441 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1442 #endif 1443 1444 /* Additional parameters are stored in the timestamp if present. */ 1445 if (sc->sc_flags & SCF_TIMESTAMP) { 1446 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1447 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1448 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1449 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1450 data |= md5_buffer[2] << 10; /* more digest bits */ 1451 data ^= md5_buffer[3]; 1452 sc->sc_ts = data; 1453 sc->sc_tsoff = data - ticks; /* after XOR */ 1454 } 1455 1456 return; 1457 } 1458 1459 static struct syncache * 1460 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1461 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1462 struct socket *so) 1463 { 1464 MD5_CTX ctx; 1465 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1466 u_int32_t data = 0; 1467 u_int32_t *secbits; 1468 tcp_seq ack, seq; 1469 int off, mss, wnd, flags; 1470 1471 SCH_LOCK_ASSERT(sch); 1472 1473 /* 1474 * Pull information out of SYN-ACK/ACK and 1475 * revert sequence number advances. 1476 */ 1477 ack = th->th_ack - 1; 1478 seq = th->th_seq - 1; 1479 off = (ack >> 1) & 0x7; 1480 mss = (ack >> 4) & 0x7; 1481 flags = ack & 0x7f; 1482 1483 /* Which of the two secrets to use. */ 1484 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1485 1486 /* 1487 * The secret wasn't updated for the lifetime of a syncookie, 1488 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1489 */ 1490 if (sch->sch_reseed < time_uptime) { 1491 return (NULL); 1492 } 1493 1494 /* Recompute the digest so we can compare it. */ 1495 MD5Init(&ctx); 1496 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1497 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1498 MD5Update(&ctx, secbits, off); 1499 MD5Update(&ctx, inc, sizeof(*inc)); 1500 MD5Update(&ctx, &seq, sizeof(seq)); 1501 MD5Update(&ctx, &flags, sizeof(flags)); 1502 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1503 1504 /* Does the digest part of or ACK'ed ISS match? */ 1505 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1506 return (NULL); 1507 1508 /* Does the digest part of our reflected timestamp match? */ 1509 if (to->to_flags & TOF_TS) { 1510 data = md5_buffer[3] ^ to->to_tsecr; 1511 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1512 return (NULL); 1513 } 1514 1515 /* Fill in the syncache values. */ 1516 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1517 sc->sc_ipopts = NULL; 1518 1519 sc->sc_irs = seq; 1520 sc->sc_iss = ack; 1521 1522 #ifdef INET6 1523 if (inc->inc_isipv6) { 1524 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1525 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1526 } else 1527 #endif 1528 { 1529 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1530 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1531 } 1532 1533 /* Additional parameters that were encoded in the timestamp. */ 1534 if (data) { 1535 sc->sc_flags |= SCF_TIMESTAMP; 1536 sc->sc_tsreflect = to->to_tsval; 1537 sc->sc_ts = to->to_tsecr; 1538 sc->sc_tsoff = to->to_tsecr - ticks; 1539 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1540 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1541 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1542 TCP_MAX_WINSHIFT); 1543 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1544 TCP_MAX_WINSHIFT); 1545 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1546 sc->sc_flags |= SCF_WINSCALE; 1547 } else 1548 sc->sc_flags |= SCF_NOOPT; 1549 1550 wnd = sbspace(&so->so_rcv); 1551 wnd = imax(wnd, 0); 1552 wnd = imin(wnd, TCP_MAXWIN); 1553 sc->sc_wnd = wnd; 1554 1555 sc->sc_rxmits = 0; 1556 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1557 1558 return (sc); 1559 } 1560