1 /* 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95 34 * $FreeBSD$ 35 */ 36 37 #include "opt_ipfw.h" /* for ipfw_fwd */ 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 #include "opt_mac.h" 42 #include "opt_tcpdebug.h" 43 #include "opt_tcp_input.h" 44 45 #include <sys/param.h> 46 #include <sys/kernel.h> 47 #include <sys/mac.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/protosw.h> 52 #include <sys/signalvar.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/sysctl.h> 56 #include <sys/syslog.h> 57 #include <sys/systm.h> 58 59 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */ 60 61 #include <net/if.h> 62 #include <net/route.h> 63 64 #include <netinet/in.h> 65 #include <netinet/in_pcb.h> 66 #include <netinet/in_systm.h> 67 #include <netinet/in_var.h> 68 #include <netinet/ip.h> 69 #include <netinet/ip_icmp.h> /* for ICMP_BANDLIM */ 70 #include <netinet/icmp_var.h> /* for ICMP_BANDLIM */ 71 #include <netinet/ip_var.h> 72 #include <netinet/ip6.h> 73 #include <netinet/icmp6.h> 74 #include <netinet6/in6_pcb.h> 75 #include <netinet6/ip6_var.h> 76 #include <netinet6/nd6.h> 77 #include <netinet/tcp.h> 78 #include <netinet/tcp_fsm.h> 79 #include <netinet/tcp_seq.h> 80 #include <netinet/tcp_timer.h> 81 #include <netinet/tcp_var.h> 82 #include <netinet6/tcp6_var.h> 83 #include <netinet/tcpip.h> 84 #ifdef TCPDEBUG 85 #include <netinet/tcp_debug.h> 86 #endif /* TCPDEBUG */ 87 88 #ifdef FAST_IPSEC 89 #include <netipsec/ipsec.h> 90 #include <netipsec/ipsec6.h> 91 #endif /*FAST_IPSEC*/ 92 93 #ifdef IPSEC 94 #include <netinet6/ipsec.h> 95 #include <netinet6/ipsec6.h> 96 #include <netkey/key.h> 97 #endif /*IPSEC*/ 98 99 #include <machine/in_cksum.h> 100 101 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry"); 102 103 static const int tcprexmtthresh = 3; 104 tcp_cc tcp_ccgen; 105 106 struct tcpstat tcpstat; 107 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW, 108 &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)"); 109 110 static int log_in_vain = 0; 111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW, 112 &log_in_vain, 0, "Log all incoming TCP connections"); 113 114 static int blackhole = 0; 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW, 116 &blackhole, 0, "Do not send RST when dropping refused connections"); 117 118 int tcp_delack_enabled = 1; 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW, 120 &tcp_delack_enabled, 0, 121 "Delay ACK to try and piggyback it onto a data packet"); 122 123 #ifdef TCP_DROP_SYNFIN 124 static int drop_synfin = 0; 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW, 126 &drop_synfin, 0, "Drop TCP packets with SYN+FIN set"); 127 #endif 128 129 static int tcp_do_rfc3042 = 1; 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW, 131 &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)"); 132 133 static int tcp_do_rfc3390 = 1; 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW, 135 &tcp_do_rfc3390, 0, 136 "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)"); 137 138 struct inpcbhead tcb; 139 #define tcb6 tcb /* for KAME src sync over BSD*'s */ 140 struct inpcbinfo tcbinfo; 141 struct mtx *tcbinfo_mtx; 142 143 static void tcp_dooptions(struct tcpopt *, u_char *, int, int); 144 static void tcp_pulloutofband(struct socket *, 145 struct tcphdr *, struct mbuf *, int); 146 static int tcp_reass(struct tcpcb *, struct tcphdr *, int *, 147 struct mbuf *); 148 static void tcp_xmit_timer(struct tcpcb *, int); 149 static void tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *); 150 static int tcp_timewait(struct tcptw *, struct tcpopt *, 151 struct tcphdr *, struct mbuf *, int); 152 153 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */ 154 #ifdef INET6 155 #define ND6_HINT(tp) \ 156 do { \ 157 if ((tp) && (tp)->t_inpcb && \ 158 ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \ 159 nd6_nud_hint(NULL, NULL, 0); \ 160 } while (0) 161 #else 162 #define ND6_HINT(tp) 163 #endif 164 165 /* 166 * Indicate whether this ack should be delayed. We can delay the ack if 167 * - there is no delayed ack timer in progress and 168 * - our last ack wasn't a 0-sized window. We never want to delay 169 * the ack that opens up a 0-sized window and 170 * - delayed acks are enabled or 171 * - this is a half-synchronized T/TCP connection. 172 */ 173 #define DELAY_ACK(tp) \ 174 ((!callout_active(tp->tt_delack) && \ 175 (tp->t_flags & TF_RXWIN0SENT) == 0) && \ 176 (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN))) 177 178 static int 179 tcp_reass(tp, th, tlenp, m) 180 register struct tcpcb *tp; 181 register struct tcphdr *th; 182 int *tlenp; 183 struct mbuf *m; 184 { 185 struct tseg_qent *q; 186 struct tseg_qent *p = NULL; 187 struct tseg_qent *nq; 188 struct tseg_qent *te; 189 struct socket *so = tp->t_inpcb->inp_socket; 190 int flags; 191 192 /* 193 * Call with th==0 after become established to 194 * force pre-ESTABLISHED data up to user socket. 195 */ 196 if (th == 0) 197 goto present; 198 199 /* Allocate a new queue entry. If we can't, just drop the pkt. XXX */ 200 MALLOC(te, struct tseg_qent *, sizeof (struct tseg_qent), M_TSEGQ, 201 M_NOWAIT); 202 if (te == NULL) { 203 tcpstat.tcps_rcvmemdrop++; 204 m_freem(m); 205 return (0); 206 } 207 208 /* 209 * Find a segment which begins after this one does. 210 */ 211 LIST_FOREACH(q, &tp->t_segq, tqe_q) { 212 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq)) 213 break; 214 p = q; 215 } 216 217 /* 218 * If there is a preceding segment, it may provide some of 219 * our data already. If so, drop the data from the incoming 220 * segment. If it provides all of our data, drop us. 221 */ 222 if (p != NULL) { 223 register int i; 224 /* conversion to int (in i) handles seq wraparound */ 225 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq; 226 if (i > 0) { 227 if (i >= *tlenp) { 228 tcpstat.tcps_rcvduppack++; 229 tcpstat.tcps_rcvdupbyte += *tlenp; 230 m_freem(m); 231 FREE(te, M_TSEGQ); 232 /* 233 * Try to present any queued data 234 * at the left window edge to the user. 235 * This is needed after the 3-WHS 236 * completes. 237 */ 238 goto present; /* ??? */ 239 } 240 m_adj(m, i); 241 *tlenp -= i; 242 th->th_seq += i; 243 } 244 } 245 tcpstat.tcps_rcvoopack++; 246 tcpstat.tcps_rcvoobyte += *tlenp; 247 248 /* 249 * While we overlap succeeding segments trim them or, 250 * if they are completely covered, dequeue them. 251 */ 252 while (q) { 253 register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq; 254 if (i <= 0) 255 break; 256 if (i < q->tqe_len) { 257 q->tqe_th->th_seq += i; 258 q->tqe_len -= i; 259 m_adj(q->tqe_m, i); 260 break; 261 } 262 263 nq = LIST_NEXT(q, tqe_q); 264 LIST_REMOVE(q, tqe_q); 265 m_freem(q->tqe_m); 266 FREE(q, M_TSEGQ); 267 q = nq; 268 } 269 270 /* Insert the new segment queue entry into place. */ 271 te->tqe_m = m; 272 te->tqe_th = th; 273 te->tqe_len = *tlenp; 274 275 if (p == NULL) { 276 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q); 277 } else { 278 LIST_INSERT_AFTER(p, te, tqe_q); 279 } 280 281 present: 282 /* 283 * Present data to user, advancing rcv_nxt through 284 * completed sequence space. 285 */ 286 if (!TCPS_HAVEESTABLISHED(tp->t_state)) 287 return (0); 288 q = LIST_FIRST(&tp->t_segq); 289 if (!q || q->tqe_th->th_seq != tp->rcv_nxt) 290 return (0); 291 do { 292 tp->rcv_nxt += q->tqe_len; 293 flags = q->tqe_th->th_flags & TH_FIN; 294 nq = LIST_NEXT(q, tqe_q); 295 LIST_REMOVE(q, tqe_q); 296 if (so->so_state & SS_CANTRCVMORE) 297 m_freem(q->tqe_m); 298 else 299 sbappendstream(&so->so_rcv, q->tqe_m); 300 FREE(q, M_TSEGQ); 301 q = nq; 302 } while (q && q->tqe_th->th_seq == tp->rcv_nxt); 303 ND6_HINT(tp); 304 sorwakeup(so); 305 return (flags); 306 } 307 308 /* 309 * TCP input routine, follows pages 65-76 of the 310 * protocol specification dated September, 1981 very closely. 311 */ 312 #ifdef INET6 313 int 314 tcp6_input(mp, offp, proto) 315 struct mbuf **mp; 316 int *offp, proto; 317 { 318 register struct mbuf *m = *mp; 319 struct in6_ifaddr *ia6; 320 321 IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE); 322 323 /* 324 * draft-itojun-ipv6-tcp-to-anycast 325 * better place to put this in? 326 */ 327 ia6 = ip6_getdstifaddr(m); 328 if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) { 329 struct ip6_hdr *ip6; 330 331 ip6 = mtod(m, struct ip6_hdr *); 332 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR, 333 (caddr_t)&ip6->ip6_dst - (caddr_t)ip6); 334 return IPPROTO_DONE; 335 } 336 337 tcp_input(m, *offp); 338 return IPPROTO_DONE; 339 } 340 #endif 341 342 void 343 tcp_input(m, off0) 344 register struct mbuf *m; 345 int off0; 346 { 347 register struct tcphdr *th; 348 register struct ip *ip = NULL; 349 register struct ipovly *ipov; 350 register struct inpcb *inp = NULL; 351 u_char *optp = NULL; 352 int optlen = 0; 353 int len, tlen, off; 354 int drop_hdrlen; 355 register struct tcpcb *tp = 0; 356 register int thflags; 357 struct socket *so = 0; 358 int todrop, acked, ourfinisacked, needoutput = 0; 359 u_long tiwin; 360 struct tcpopt to; /* options in this segment */ 361 struct rmxp_tao tao; /* our TAO cache entry */ 362 int headlocked = 0; 363 struct sockaddr_in *next_hop = NULL; 364 int rstreason; /* For badport_bandlim accounting purposes */ 365 366 struct ip6_hdr *ip6 = NULL; 367 #ifdef INET6 368 int isipv6; 369 #else 370 const int isipv6 = 0; 371 #endif 372 373 #ifdef TCPDEBUG 374 /* 375 * The size of tcp_saveipgen must be the size of the max ip header, 376 * now IPv6. 377 */ 378 u_char tcp_saveipgen[40]; 379 struct tcphdr tcp_savetcp; 380 short ostate = 0; 381 #endif 382 383 /* Grab info from MT_TAG mbufs prepended to the chain. */ 384 for (;m && m->m_type == MT_TAG; m = m->m_next) { 385 if (m->_m_tag_id == PACKET_TAG_IPFORWARD) 386 next_hop = (struct sockaddr_in *)m->m_hdr.mh_data; 387 } 388 #ifdef INET6 389 isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0; 390 #endif 391 bzero(&tao, sizeof(tao)); 392 bzero((char *)&to, sizeof(to)); 393 394 tcpstat.tcps_rcvtotal++; 395 396 if (isipv6) { 397 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */ 398 ip6 = mtod(m, struct ip6_hdr *); 399 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0; 400 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) { 401 tcpstat.tcps_rcvbadsum++; 402 goto drop; 403 } 404 th = (struct tcphdr *)((caddr_t)ip6 + off0); 405 406 /* 407 * Be proactive about unspecified IPv6 address in source. 408 * As we use all-zero to indicate unbounded/unconnected pcb, 409 * unspecified IPv6 address can be used to confuse us. 410 * 411 * Note that packets with unspecified IPv6 destination is 412 * already dropped in ip6_input. 413 */ 414 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) { 415 /* XXX stat */ 416 goto drop; 417 } 418 } else { 419 /* 420 * Get IP and TCP header together in first mbuf. 421 * Note: IP leaves IP header in first mbuf. 422 */ 423 if (off0 > sizeof (struct ip)) { 424 ip_stripoptions(m, (struct mbuf *)0); 425 off0 = sizeof(struct ip); 426 } 427 if (m->m_len < sizeof (struct tcpiphdr)) { 428 if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) { 429 tcpstat.tcps_rcvshort++; 430 return; 431 } 432 } 433 ip = mtod(m, struct ip *); 434 ipov = (struct ipovly *)ip; 435 th = (struct tcphdr *)((caddr_t)ip + off0); 436 tlen = ip->ip_len; 437 438 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) { 439 if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR) 440 th->th_sum = m->m_pkthdr.csum_data; 441 else 442 th->th_sum = in_pseudo(ip->ip_src.s_addr, 443 ip->ip_dst.s_addr, 444 htonl(m->m_pkthdr.csum_data + 445 ip->ip_len + 446 IPPROTO_TCP)); 447 th->th_sum ^= 0xffff; 448 #ifdef TCPDEBUG 449 ipov->ih_len = (u_short)tlen; 450 ipov->ih_len = htons(ipov->ih_len); 451 #endif 452 } else { 453 /* 454 * Checksum extended TCP header and data. 455 */ 456 len = sizeof (struct ip) + tlen; 457 bzero(ipov->ih_x1, sizeof(ipov->ih_x1)); 458 ipov->ih_len = (u_short)tlen; 459 ipov->ih_len = htons(ipov->ih_len); 460 th->th_sum = in_cksum(m, len); 461 } 462 if (th->th_sum) { 463 tcpstat.tcps_rcvbadsum++; 464 goto drop; 465 } 466 #ifdef INET6 467 /* Re-initialization for later version check */ 468 ip->ip_v = IPVERSION; 469 #endif 470 } 471 472 /* 473 * Check that TCP offset makes sense, 474 * pull out TCP options and adjust length. XXX 475 */ 476 off = th->th_off << 2; 477 if (off < sizeof (struct tcphdr) || off > tlen) { 478 tcpstat.tcps_rcvbadoff++; 479 goto drop; 480 } 481 tlen -= off; /* tlen is used instead of ti->ti_len */ 482 if (off > sizeof (struct tcphdr)) { 483 if (isipv6) { 484 IP6_EXTHDR_CHECK(m, off0, off, ); 485 ip6 = mtod(m, struct ip6_hdr *); 486 th = (struct tcphdr *)((caddr_t)ip6 + off0); 487 } else { 488 if (m->m_len < sizeof(struct ip) + off) { 489 if ((m = m_pullup(m, sizeof (struct ip) + off)) 490 == 0) { 491 tcpstat.tcps_rcvshort++; 492 return; 493 } 494 ip = mtod(m, struct ip *); 495 ipov = (struct ipovly *)ip; 496 th = (struct tcphdr *)((caddr_t)ip + off0); 497 } 498 } 499 optlen = off - sizeof (struct tcphdr); 500 optp = (u_char *)(th + 1); 501 } 502 thflags = th->th_flags; 503 504 #ifdef TCP_DROP_SYNFIN 505 /* 506 * If the drop_synfin option is enabled, drop all packets with 507 * both the SYN and FIN bits set. This prevents e.g. nmap from 508 * identifying the TCP/IP stack. 509 * 510 * This is a violation of the TCP specification. 511 */ 512 if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN)) 513 goto drop; 514 #endif 515 516 /* 517 * Convert TCP protocol specific fields to host format. 518 */ 519 th->th_seq = ntohl(th->th_seq); 520 th->th_ack = ntohl(th->th_ack); 521 th->th_win = ntohs(th->th_win); 522 th->th_urp = ntohs(th->th_urp); 523 524 /* 525 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options, 526 * until after ip6_savecontrol() is called and before other functions 527 * which don't want those proto headers. 528 * Because ip6_savecontrol() is going to parse the mbuf to 529 * search for data to be passed up to user-land, it wants mbuf 530 * parameters to be unchanged. 531 * XXX: the call of ip6_savecontrol() has been obsoleted based on 532 * latest version of the advanced API (20020110). 533 */ 534 drop_hdrlen = off0 + off; 535 536 /* 537 * Locate pcb for segment. 538 */ 539 INP_INFO_WLOCK(&tcbinfo); 540 headlocked = 1; 541 findpcb: 542 /* IPFIREWALL_FORWARD section */ 543 if (next_hop != NULL && isipv6 == 0) { /* IPv6 support is not yet */ 544 /* 545 * Transparently forwarded. Pretend to be the destination. 546 * already got one like this? 547 */ 548 inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport, 549 ip->ip_dst, th->th_dport, 550 0, m->m_pkthdr.rcvif); 551 if (!inp) { 552 /* It's new. Try find the ambushing socket. */ 553 inp = in_pcblookup_hash(&tcbinfo, 554 ip->ip_src, th->th_sport, 555 next_hop->sin_addr, 556 next_hop->sin_port ? 557 ntohs(next_hop->sin_port) : 558 th->th_dport, 559 1, m->m_pkthdr.rcvif); 560 } 561 } else { 562 if (isipv6) 563 inp = in6_pcblookup_hash(&tcbinfo, 564 &ip6->ip6_src, th->th_sport, 565 &ip6->ip6_dst, th->th_dport, 566 1, m->m_pkthdr.rcvif); 567 else 568 inp = in_pcblookup_hash(&tcbinfo, 569 ip->ip_src, th->th_sport, 570 ip->ip_dst, th->th_dport, 571 1, m->m_pkthdr.rcvif); 572 } 573 574 #if defined(IPSEC) || defined(FAST_IPSEC) 575 if (isipv6) { 576 if (inp != NULL && ipsec6_in_reject(m, inp)) { 577 #ifdef IPSEC 578 ipsec6stat.in_polvio++; 579 #endif /*IPSEC*/ 580 goto drop; 581 } 582 } else if (inp != NULL && ipsec4_in_reject(m, inp)) { 583 #ifdef IPSEC 584 ipsecstat.in_polvio++; 585 #endif /*IPSEC*/ 586 goto drop; 587 } 588 #endif /*IPSEC || FAST_IPSEC*/ 589 590 /* 591 * If the state is CLOSED (i.e., TCB does not exist) then 592 * all data in the incoming segment is discarded. 593 * If the TCB exists but is in CLOSED state, it is embryonic, 594 * but should either do a listen or a connect soon. 595 */ 596 if (inp == NULL) { 597 if (log_in_vain) { 598 #ifdef INET6 599 char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2]; 600 #else 601 char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"]; 602 #endif 603 604 if (isipv6) { 605 strcpy(dbuf, "["); 606 strcpy(sbuf, "["); 607 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst)); 608 strcat(sbuf, ip6_sprintf(&ip6->ip6_src)); 609 strcat(dbuf, "]"); 610 strcat(sbuf, "]"); 611 } else { 612 strcpy(dbuf, inet_ntoa(ip->ip_dst)); 613 strcpy(sbuf, inet_ntoa(ip->ip_src)); 614 } 615 switch (log_in_vain) { 616 case 1: 617 if ((thflags & TH_SYN) == 0) 618 break; 619 /* FALLTHROUGH */ 620 case 2: 621 log(LOG_INFO, 622 "Connection attempt to TCP %s:%d " 623 "from %s:%d flags:0x%02x\n", 624 dbuf, ntohs(th->th_dport), sbuf, 625 ntohs(th->th_sport), thflags); 626 break; 627 default: 628 break; 629 } 630 } 631 if (blackhole) { 632 switch (blackhole) { 633 case 1: 634 if (thflags & TH_SYN) 635 goto drop; 636 break; 637 case 2: 638 goto drop; 639 default: 640 goto drop; 641 } 642 } 643 rstreason = BANDLIM_RST_CLOSEDPORT; 644 goto dropwithreset; 645 } 646 INP_LOCK(inp); 647 if (inp->inp_vflag & INP_TIMEWAIT) { 648 /* 649 * The only option of relevance is TOF_CC, and only if 650 * present in a SYN segment. See tcp_timewait(). 651 */ 652 if (thflags & TH_SYN) 653 tcp_dooptions(&to, optp, optlen, 1); 654 if (tcp_timewait((struct tcptw *)inp->inp_ppcb, 655 &to, th, m, tlen)) 656 goto findpcb; 657 /* 658 * tcp_timewait unlocks inp. 659 */ 660 INP_INFO_WUNLOCK(&tcbinfo); 661 return; 662 } 663 tp = intotcpcb(inp); 664 if (tp == 0) { 665 INP_UNLOCK(inp); 666 rstreason = BANDLIM_RST_CLOSEDPORT; 667 goto dropwithreset; 668 } 669 if (tp->t_state == TCPS_CLOSED) 670 goto drop; 671 672 /* Unscale the window into a 32-bit value. */ 673 if ((thflags & TH_SYN) == 0) 674 tiwin = th->th_win << tp->snd_scale; 675 else 676 tiwin = th->th_win; 677 678 #ifdef MAC 679 if (mac_check_inpcb_deliver(inp, m)) 680 goto drop; 681 #endif 682 so = inp->inp_socket; 683 #ifdef TCPDEBUG 684 if (so->so_options & SO_DEBUG) { 685 ostate = tp->t_state; 686 if (isipv6) 687 bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6)); 688 else 689 bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip)); 690 tcp_savetcp = *th; 691 } 692 #endif 693 if (so->so_options & SO_ACCEPTCONN) { 694 struct in_conninfo inc; 695 696 #ifdef INET6 697 inc.inc_isipv6 = isipv6; 698 #endif 699 if (isipv6) { 700 inc.inc6_faddr = ip6->ip6_src; 701 inc.inc6_laddr = ip6->ip6_dst; 702 } else { 703 inc.inc_faddr = ip->ip_src; 704 inc.inc_laddr = ip->ip_dst; 705 } 706 inc.inc_fport = th->th_sport; 707 inc.inc_lport = th->th_dport; 708 709 /* 710 * If the state is LISTEN then ignore segment if it contains 711 * a RST. If the segment contains an ACK then it is bad and 712 * send a RST. If it does not contain a SYN then it is not 713 * interesting; drop it. 714 * 715 * If the state is SYN_RECEIVED (syncache) and seg contains 716 * an ACK, but not for our SYN/ACK, send a RST. If the seg 717 * contains a RST, check the sequence number to see if it 718 * is a valid reset segment. 719 */ 720 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) { 721 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) { 722 if (!syncache_expand(&inc, th, &so, m)) { 723 /* 724 * No syncache entry, or ACK was not 725 * for our SYN/ACK. Send a RST. 726 */ 727 tcpstat.tcps_badsyn++; 728 rstreason = BANDLIM_RST_OPENPORT; 729 goto dropwithreset; 730 } 731 if (so == NULL) { 732 /* 733 * Could not complete 3-way handshake, 734 * connection is being closed down, and 735 * syncache will free mbuf. 736 */ 737 INP_UNLOCK(inp); 738 INP_INFO_WUNLOCK(&tcbinfo); 739 return; 740 } 741 /* 742 * Socket is created in state SYN_RECEIVED. 743 * Continue processing segment. 744 */ 745 INP_UNLOCK(inp); 746 inp = sotoinpcb(so); 747 INP_LOCK(inp); 748 tp = intotcpcb(inp); 749 /* 750 * This is what would have happened in 751 * tcp_output() when the SYN,ACK was sent. 752 */ 753 tp->snd_up = tp->snd_una; 754 tp->snd_max = tp->snd_nxt = tp->iss + 1; 755 tp->last_ack_sent = tp->rcv_nxt; 756 /* 757 * RFC1323: The window in SYN & SYN/ACK 758 * segments is never scaled. 759 */ 760 tp->snd_wnd = tiwin; /* unscaled */ 761 goto after_listen; 762 } 763 if (thflags & TH_RST) { 764 syncache_chkrst(&inc, th); 765 goto drop; 766 } 767 if (thflags & TH_ACK) { 768 syncache_badack(&inc); 769 tcpstat.tcps_badsyn++; 770 rstreason = BANDLIM_RST_OPENPORT; 771 goto dropwithreset; 772 } 773 goto drop; 774 } 775 776 /* 777 * Segment's flags are (SYN) or (SYN|FIN). 778 */ 779 #ifdef INET6 780 /* 781 * If deprecated address is forbidden, 782 * we do not accept SYN to deprecated interface 783 * address to prevent any new inbound connection from 784 * getting established. 785 * When we do not accept SYN, we send a TCP RST, 786 * with deprecated source address (instead of dropping 787 * it). We compromise it as it is much better for peer 788 * to send a RST, and RST will be the final packet 789 * for the exchange. 790 * 791 * If we do not forbid deprecated addresses, we accept 792 * the SYN packet. RFC2462 does not suggest dropping 793 * SYN in this case. 794 * If we decipher RFC2462 5.5.4, it says like this: 795 * 1. use of deprecated addr with existing 796 * communication is okay - "SHOULD continue to be 797 * used" 798 * 2. use of it with new communication: 799 * (2a) "SHOULD NOT be used if alternate address 800 * with sufficient scope is available" 801 * (2b) nothing mentioned otherwise. 802 * Here we fall into (2b) case as we have no choice in 803 * our source address selection - we must obey the peer. 804 * 805 * The wording in RFC2462 is confusing, and there are 806 * multiple description text for deprecated address 807 * handling - worse, they are not exactly the same. 808 * I believe 5.5.4 is the best one, so we follow 5.5.4. 809 */ 810 if (isipv6 && !ip6_use_deprecated) { 811 struct in6_ifaddr *ia6; 812 813 if ((ia6 = ip6_getdstifaddr(m)) && 814 (ia6->ia6_flags & IN6_IFF_DEPRECATED)) { 815 INP_UNLOCK(inp); 816 tp = NULL; 817 rstreason = BANDLIM_RST_OPENPORT; 818 goto dropwithreset; 819 } 820 } 821 #endif 822 /* 823 * If it is from this socket, drop it, it must be forged. 824 * Don't bother responding if the destination was a broadcast. 825 */ 826 if (th->th_dport == th->th_sport) { 827 if (isipv6) { 828 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, 829 &ip6->ip6_src)) 830 goto drop; 831 } else { 832 if (ip->ip_dst.s_addr == ip->ip_src.s_addr) 833 goto drop; 834 } 835 } 836 /* 837 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN 838 * 839 * Note that it is quite possible to receive unicast 840 * link-layer packets with a broadcast IP address. Use 841 * in_broadcast() to find them. 842 */ 843 if (m->m_flags & (M_BCAST|M_MCAST)) 844 goto drop; 845 if (isipv6) { 846 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || 847 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) 848 goto drop; 849 } else { 850 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 851 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 852 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || 853 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) 854 goto drop; 855 } 856 /* 857 * SYN appears to be valid; create compressed TCP state 858 * for syncache, or perform t/tcp connection. 859 */ 860 if (so->so_qlen <= so->so_qlimit) { 861 #ifdef TCPDEBUG 862 if (so->so_options & SO_DEBUG) 863 tcp_trace(TA_INPUT, ostate, tp, 864 (void *)tcp_saveipgen, &tcp_savetcp, 0); 865 #endif 866 tcp_dooptions(&to, optp, optlen, 1); 867 if (!syncache_add(&inc, &to, th, &so, m)) 868 goto drop; 869 if (so == NULL) { 870 /* 871 * Entry added to syncache, mbuf used to 872 * send SYN,ACK packet. 873 */ 874 KASSERT(headlocked, ("headlocked")); 875 INP_UNLOCK(inp); 876 INP_INFO_WUNLOCK(&tcbinfo); 877 return; 878 } 879 /* 880 * Segment passed TAO tests. 881 */ 882 INP_UNLOCK(inp); 883 inp = sotoinpcb(so); 884 INP_LOCK(inp); 885 tp = intotcpcb(inp); 886 tp->snd_wnd = tiwin; 887 tp->t_starttime = ticks; 888 tp->t_state = TCPS_ESTABLISHED; 889 890 /* 891 * T/TCP logic: 892 * If there is a FIN or if there is data, then 893 * delay SYN,ACK(SYN) in the hope of piggy-backing 894 * it on a response segment. Otherwise must send 895 * ACK now in case the other side is slow starting. 896 */ 897 if (thflags & TH_FIN || tlen != 0) 898 tp->t_flags |= (TF_DELACK | TF_NEEDSYN); 899 else 900 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN); 901 tcpstat.tcps_connects++; 902 soisconnected(so); 903 goto trimthenstep6; 904 } 905 goto drop; 906 } 907 after_listen: 908 909 /* XXX temp debugging */ 910 /* should not happen - syncache should pick up these connections */ 911 if (tp->t_state == TCPS_LISTEN) 912 panic("tcp_input: TCPS_LISTEN"); 913 914 /* 915 * This is the second part of the MSS DoS prevention code (after 916 * minmss on the sending side) and it deals with too many too small 917 * tcp packets in a too short timeframe (1 second). 918 * 919 * For every full second we count the number of received packets 920 * and bytes. If we get a lot of packets per second for this connection 921 * (tcp_minmssoverload) we take a closer look at it and compute the 922 * average packet size for the past second. If that is less than 923 * tcp_minmss we get too many packets with very small payload which 924 * is not good and burdens our system (and every packet generates 925 * a wakeup to the process connected to our socket). We can reasonable 926 * expect this to be small packet DoS attack to exhaust our CPU 927 * cycles. 928 * 929 * Care has to be taken for the minimum packet overload value. This 930 * value defines the minimum number of packets per second before we 931 * start to worry. This must not be too low to avoid killing for 932 * example interactive connections with many small packets like 933 * telnet or SSH. 934 * 935 * Setting either tcp_minmssoverload or tcp_minmss to "0" disables 936 * this check. 937 * 938 * Account for packet if payload packet, skip over ACK, etc. 939 */ 940 if (tcp_minmss && tcp_minmssoverload && 941 tp->t_state == TCPS_ESTABLISHED && tlen > 0) { 942 if (tp->rcv_second > ticks) { 943 tp->rcv_pps++; 944 tp->rcv_byps += tlen + off; 945 if (tp->rcv_pps > tcp_minmssoverload) { 946 if ((tp->rcv_byps / tp->rcv_pps) < tcp_minmss) { 947 printf("too many small tcp packets from " 948 "%s:%u, av. %lubyte/packet, " 949 "dropping connection\n", 950 #ifdef INET6 951 isipv6 ? 952 ip6_sprintf(&inp->inp_inc.inc6_faddr) : 953 #endif 954 inet_ntoa(inp->inp_inc.inc_faddr), 955 inp->inp_inc.inc_fport, 956 tp->rcv_byps / tp->rcv_pps); 957 tp = tcp_drop(tp, ECONNRESET); 958 tcpstat.tcps_minmssdrops++; 959 goto drop; 960 } 961 } 962 } else { 963 tp->rcv_second = ticks + hz; 964 tp->rcv_pps = 1; 965 tp->rcv_byps = tlen + off; 966 } 967 } 968 969 /* 970 * Segment received on connection. 971 * Reset idle time and keep-alive timer. 972 */ 973 tp->t_rcvtime = ticks; 974 if (TCPS_HAVEESTABLISHED(tp->t_state)) 975 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); 976 977 /* 978 * Process options only when we get SYN/ACK back. The SYN case 979 * for incoming connections is handled in tcp_syncache. 980 * XXX this is traditional behavior, may need to be cleaned up. 981 */ 982 tcp_dooptions(&to, optp, optlen, thflags & TH_SYN); 983 if (thflags & TH_SYN) { 984 if (to.to_flags & TOF_SCALE) { 985 tp->t_flags |= TF_RCVD_SCALE; 986 tp->requested_s_scale = to.to_requested_s_scale; 987 } 988 if (to.to_flags & TOF_TS) { 989 tp->t_flags |= TF_RCVD_TSTMP; 990 tp->ts_recent = to.to_tsval; 991 tp->ts_recent_age = ticks; 992 } 993 if (to.to_flags & (TOF_CC|TOF_CCNEW)) 994 tp->t_flags |= TF_RCVD_CC; 995 if (to.to_flags & TOF_MSS) 996 tcp_mss(tp, to.to_mss); 997 } 998 999 /* 1000 * Header prediction: check for the two common cases 1001 * of a uni-directional data xfer. If the packet has 1002 * no control flags, is in-sequence, the window didn't 1003 * change and we're not retransmitting, it's a 1004 * candidate. If the length is zero and the ack moved 1005 * forward, we're the sender side of the xfer. Just 1006 * free the data acked & wake any higher level process 1007 * that was blocked waiting for space. If the length 1008 * is non-zero and the ack didn't move, we're the 1009 * receiver side. If we're getting packets in-order 1010 * (the reassembly queue is empty), add the data to 1011 * the socket buffer and note that we need a delayed ack. 1012 * Make sure that the hidden state-flags are also off. 1013 * Since we check for TCPS_ESTABLISHED above, it can only 1014 * be TH_NEEDSYN. 1015 */ 1016 if (tp->t_state == TCPS_ESTABLISHED && 1017 (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK && 1018 ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) && 1019 ((to.to_flags & TOF_TS) == 0 || 1020 TSTMP_GEQ(to.to_tsval, tp->ts_recent)) && 1021 /* 1022 * Using the CC option is compulsory if once started: 1023 * the segment is OK if no T/TCP was negotiated or 1024 * if the segment has a CC option equal to CCrecv 1025 */ 1026 ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) || 1027 ((to.to_flags & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) && 1028 th->th_seq == tp->rcv_nxt && 1029 tiwin && tiwin == tp->snd_wnd && 1030 tp->snd_nxt == tp->snd_max) { 1031 1032 /* 1033 * If last ACK falls within this segment's sequence numbers, 1034 * record the timestamp. 1035 * NOTE that the test is modified according to the latest 1036 * proposal of the tcplw@cray.com list (Braden 1993/04/26). 1037 */ 1038 if ((to.to_flags & TOF_TS) != 0 && 1039 SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { 1040 tp->ts_recent_age = ticks; 1041 tp->ts_recent = to.to_tsval; 1042 } 1043 1044 if (tlen == 0) { 1045 if (SEQ_GT(th->th_ack, tp->snd_una) && 1046 SEQ_LEQ(th->th_ack, tp->snd_max) && 1047 tp->snd_cwnd >= tp->snd_wnd && 1048 ((!tcp_do_newreno && 1049 tp->t_dupacks < tcprexmtthresh) || 1050 (tcp_do_newreno && !IN_FASTRECOVERY(tp)))) { 1051 KASSERT(headlocked, ("headlocked")); 1052 INP_INFO_WUNLOCK(&tcbinfo); 1053 /* 1054 * this is a pure ack for outstanding data. 1055 */ 1056 ++tcpstat.tcps_predack; 1057 /* 1058 * "bad retransmit" recovery 1059 */ 1060 if (tp->t_rxtshift == 1 && 1061 ticks < tp->t_badrxtwin) { 1062 ++tcpstat.tcps_sndrexmitbad; 1063 tp->snd_cwnd = tp->snd_cwnd_prev; 1064 tp->snd_ssthresh = 1065 tp->snd_ssthresh_prev; 1066 tp->snd_recover = tp->snd_recover_prev; 1067 if (tp->t_flags & TF_WASFRECOVERY) 1068 ENTER_FASTRECOVERY(tp); 1069 tp->snd_nxt = tp->snd_max; 1070 tp->t_badrxtwin = 0; 1071 } 1072 1073 /* 1074 * Recalculate the transmit timer / rtt. 1075 * 1076 * Some boxes send broken timestamp replies 1077 * during the SYN+ACK phase, ignore 1078 * timestamps of 0 or we could calculate a 1079 * huge RTT and blow up the retransmit timer. 1080 */ 1081 if ((to.to_flags & TOF_TS) != 0 && 1082 to.to_tsecr) { 1083 tcp_xmit_timer(tp, 1084 ticks - to.to_tsecr + 1); 1085 } else if (tp->t_rtttime && 1086 SEQ_GT(th->th_ack, tp->t_rtseq)) { 1087 tcp_xmit_timer(tp, 1088 ticks - tp->t_rtttime); 1089 } 1090 tcp_xmit_bandwidth_limit(tp, th->th_ack); 1091 acked = th->th_ack - tp->snd_una; 1092 tcpstat.tcps_rcvackpack++; 1093 tcpstat.tcps_rcvackbyte += acked; 1094 sbdrop(&so->so_snd, acked); 1095 if (SEQ_GT(tp->snd_una, tp->snd_recover) && 1096 SEQ_LEQ(th->th_ack, tp->snd_recover)) 1097 tp->snd_recover = th->th_ack - 1; 1098 tp->snd_una = th->th_ack; 1099 /* 1100 * pull snd_wl2 up to prevent seq wrap relative 1101 * to th_ack. 1102 */ 1103 tp->snd_wl2 = th->th_ack; 1104 tp->t_dupacks = 0; 1105 m_freem(m); 1106 ND6_HINT(tp); /* some progress has been done */ 1107 1108 /* 1109 * If all outstanding data are acked, stop 1110 * retransmit timer, otherwise restart timer 1111 * using current (possibly backed-off) value. 1112 * If process is waiting for space, 1113 * wakeup/selwakeup/signal. If data 1114 * are ready to send, let tcp_output 1115 * decide between more output or persist. 1116 1117 #ifdef TCPDEBUG 1118 if (so->so_options & SO_DEBUG) 1119 tcp_trace(TA_INPUT, ostate, tp, 1120 (void *)tcp_saveipgen, 1121 &tcp_savetcp, 0); 1122 #endif 1123 */ 1124 if (tp->snd_una == tp->snd_max) 1125 callout_stop(tp->tt_rexmt); 1126 else if (!callout_active(tp->tt_persist)) 1127 callout_reset(tp->tt_rexmt, 1128 tp->t_rxtcur, 1129 tcp_timer_rexmt, tp); 1130 1131 sowwakeup(so); 1132 if (so->so_snd.sb_cc) 1133 (void) tcp_output(tp); 1134 goto check_delack; 1135 } 1136 } else if (th->th_ack == tp->snd_una && 1137 LIST_EMPTY(&tp->t_segq) && 1138 tlen <= sbspace(&so->so_rcv)) { 1139 KASSERT(headlocked, ("headlocked")); 1140 INP_INFO_WUNLOCK(&tcbinfo); 1141 /* 1142 * this is a pure, in-sequence data packet 1143 * with nothing on the reassembly queue and 1144 * we have enough buffer space to take it. 1145 */ 1146 ++tcpstat.tcps_preddat; 1147 tp->rcv_nxt += tlen; 1148 /* 1149 * Pull snd_wl1 up to prevent seq wrap relative to 1150 * th_seq. 1151 */ 1152 tp->snd_wl1 = th->th_seq; 1153 /* 1154 * Pull rcv_up up to prevent seq wrap relative to 1155 * rcv_nxt. 1156 */ 1157 tp->rcv_up = tp->rcv_nxt; 1158 tcpstat.tcps_rcvpack++; 1159 tcpstat.tcps_rcvbyte += tlen; 1160 ND6_HINT(tp); /* some progress has been done */ 1161 /* 1162 #ifdef TCPDEBUG 1163 if (so->so_options & SO_DEBUG) 1164 tcp_trace(TA_INPUT, ostate, tp, 1165 (void *)tcp_saveipgen, &tcp_savetcp, 0); 1166 #endif 1167 * Add data to socket buffer. 1168 */ 1169 if (so->so_state & SS_CANTRCVMORE) { 1170 m_freem(m); 1171 } else { 1172 m_adj(m, drop_hdrlen); /* delayed header drop */ 1173 sbappendstream(&so->so_rcv, m); 1174 } 1175 sorwakeup(so); 1176 if (DELAY_ACK(tp)) { 1177 tp->t_flags |= TF_DELACK; 1178 } else { 1179 tp->t_flags |= TF_ACKNOW; 1180 tcp_output(tp); 1181 } 1182 goto check_delack; 1183 } 1184 } 1185 1186 /* 1187 * Calculate amount of space in receive window, 1188 * and then do TCP input processing. 1189 * Receive window is amount of space in rcv queue, 1190 * but not less than advertised window. 1191 */ 1192 { int win; 1193 1194 win = sbspace(&so->so_rcv); 1195 if (win < 0) 1196 win = 0; 1197 tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt)); 1198 } 1199 1200 switch (tp->t_state) { 1201 1202 /* 1203 * If the state is SYN_RECEIVED: 1204 * if seg contains an ACK, but not for our SYN/ACK, send a RST. 1205 */ 1206 case TCPS_SYN_RECEIVED: 1207 if ((thflags & TH_ACK) && 1208 (SEQ_LEQ(th->th_ack, tp->snd_una) || 1209 SEQ_GT(th->th_ack, tp->snd_max))) { 1210 rstreason = BANDLIM_RST_OPENPORT; 1211 goto dropwithreset; 1212 } 1213 break; 1214 1215 /* 1216 * If the state is SYN_SENT: 1217 * if seg contains an ACK, but not for our SYN, drop the input. 1218 * if seg contains a RST, then drop the connection. 1219 * if seg does not contain SYN, then drop it. 1220 * Otherwise this is an acceptable SYN segment 1221 * initialize tp->rcv_nxt and tp->irs 1222 * if seg contains ack then advance tp->snd_una 1223 * if SYN has been acked change to ESTABLISHED else SYN_RCVD state 1224 * arrange for segment to be acked (eventually) 1225 * continue processing rest of data/controls, beginning with URG 1226 */ 1227 case TCPS_SYN_SENT: 1228 if (tcp_do_rfc1644) 1229 tcp_hc_gettao(&inp->inp_inc, &tao); 1230 1231 if ((thflags & TH_ACK) && 1232 (SEQ_LEQ(th->th_ack, tp->iss) || 1233 SEQ_GT(th->th_ack, tp->snd_max))) { 1234 /* 1235 * If we have a cached CCsent for the remote host, 1236 * hence we haven't just crashed and restarted, 1237 * do not send a RST. This may be a retransmission 1238 * from the other side after our earlier ACK was lost. 1239 * Our new SYN, when it arrives, will serve as the 1240 * needed ACK. 1241 */ 1242 if (tao.tao_ccsent != 0) 1243 goto drop; 1244 else { 1245 rstreason = BANDLIM_UNLIMITED; 1246 goto dropwithreset; 1247 } 1248 } 1249 if (thflags & TH_RST) { 1250 if (thflags & TH_ACK) 1251 tp = tcp_drop(tp, ECONNREFUSED); 1252 goto drop; 1253 } 1254 if ((thflags & TH_SYN) == 0) 1255 goto drop; 1256 tp->snd_wnd = th->th_win; /* initial send window */ 1257 tp->cc_recv = to.to_cc; /* foreign CC */ 1258 1259 tp->irs = th->th_seq; 1260 tcp_rcvseqinit(tp); 1261 if (thflags & TH_ACK) { 1262 /* 1263 * Our SYN was acked. If segment contains CC.ECHO 1264 * option, check it to make sure this segment really 1265 * matches our SYN. If not, just drop it as old 1266 * duplicate, but send an RST if we're still playing 1267 * by the old rules. If no CC.ECHO option, make sure 1268 * we don't get fooled into using T/TCP. 1269 */ 1270 if (to.to_flags & TOF_CCECHO) { 1271 if (tp->cc_send != to.to_ccecho) { 1272 if (tao.tao_ccsent != 0) 1273 goto drop; 1274 else { 1275 rstreason = BANDLIM_UNLIMITED; 1276 goto dropwithreset; 1277 } 1278 } 1279 } else 1280 tp->t_flags &= ~TF_RCVD_CC; 1281 tcpstat.tcps_connects++; 1282 soisconnected(so); 1283 #ifdef MAC 1284 mac_set_socket_peer_from_mbuf(m, so); 1285 #endif 1286 /* Do window scaling on this connection? */ 1287 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == 1288 (TF_RCVD_SCALE|TF_REQ_SCALE)) { 1289 tp->snd_scale = tp->requested_s_scale; 1290 tp->rcv_scale = tp->request_r_scale; 1291 } 1292 /* Segment is acceptable, update cache if undefined. */ 1293 if (tao.tao_ccsent == 0 && tcp_do_rfc1644) 1294 tcp_hc_updatetao(&inp->inp_inc, TCP_HC_TAO_CCSENT, to.to_ccecho, 0); 1295 1296 tp->rcv_adv += tp->rcv_wnd; 1297 tp->snd_una++; /* SYN is acked */ 1298 /* 1299 * If there's data, delay ACK; if there's also a FIN 1300 * ACKNOW will be turned on later. 1301 */ 1302 if (DELAY_ACK(tp) && tlen != 0) 1303 callout_reset(tp->tt_delack, tcp_delacktime, 1304 tcp_timer_delack, tp); 1305 else 1306 tp->t_flags |= TF_ACKNOW; 1307 /* 1308 * Received <SYN,ACK> in SYN_SENT[*] state. 1309 * Transitions: 1310 * SYN_SENT --> ESTABLISHED 1311 * SYN_SENT* --> FIN_WAIT_1 1312 */ 1313 tp->t_starttime = ticks; 1314 if (tp->t_flags & TF_NEEDFIN) { 1315 tp->t_state = TCPS_FIN_WAIT_1; 1316 tp->t_flags &= ~TF_NEEDFIN; 1317 thflags &= ~TH_SYN; 1318 } else { 1319 tp->t_state = TCPS_ESTABLISHED; 1320 callout_reset(tp->tt_keep, tcp_keepidle, 1321 tcp_timer_keep, tp); 1322 } 1323 } else { 1324 /* 1325 * Received initial SYN in SYN-SENT[*] state => 1326 * simultaneous open. If segment contains CC option 1327 * and there is a cached CC, apply TAO test. 1328 * If it succeeds, connection is * half-synchronized. 1329 * Otherwise, do 3-way handshake: 1330 * SYN-SENT -> SYN-RECEIVED 1331 * SYN-SENT* -> SYN-RECEIVED* 1332 * If there was no CC option, clear cached CC value. 1333 */ 1334 tp->t_flags |= TF_ACKNOW; 1335 callout_stop(tp->tt_rexmt); 1336 if (to.to_flags & TOF_CC) { 1337 if (tao.tao_cc != 0 && 1338 CC_GT(to.to_cc, tao.tao_cc)) { 1339 /* 1340 * update cache and make transition: 1341 * SYN-SENT -> ESTABLISHED* 1342 * SYN-SENT* -> FIN-WAIT-1* 1343 */ 1344 tao.tao_cc = to.to_cc; 1345 tcp_hc_updatetao(&inp->inp_inc, 1346 TCP_HC_TAO_CC, to.to_cc, 0); 1347 tp->t_starttime = ticks; 1348 if (tp->t_flags & TF_NEEDFIN) { 1349 tp->t_state = TCPS_FIN_WAIT_1; 1350 tp->t_flags &= ~TF_NEEDFIN; 1351 } else { 1352 tp->t_state = TCPS_ESTABLISHED; 1353 callout_reset(tp->tt_keep, 1354 tcp_keepidle, 1355 tcp_timer_keep, 1356 tp); 1357 } 1358 tp->t_flags |= TF_NEEDSYN; 1359 } else 1360 tp->t_state = TCPS_SYN_RECEIVED; 1361 } else { 1362 if (tcp_do_rfc1644) { 1363 /* CC.NEW or no option => invalidate cache */ 1364 tao.tao_cc = 0; 1365 tcp_hc_updatetao(&inp->inp_inc, 1366 TCP_HC_TAO_CC, to.to_cc, 0); 1367 } 1368 tp->t_state = TCPS_SYN_RECEIVED; 1369 } 1370 } 1371 1372 trimthenstep6: 1373 /* 1374 * Advance th->th_seq to correspond to first data byte. 1375 * If data, trim to stay within window, 1376 * dropping FIN if necessary. 1377 */ 1378 th->th_seq++; 1379 if (tlen > tp->rcv_wnd) { 1380 todrop = tlen - tp->rcv_wnd; 1381 m_adj(m, -todrop); 1382 tlen = tp->rcv_wnd; 1383 thflags &= ~TH_FIN; 1384 tcpstat.tcps_rcvpackafterwin++; 1385 tcpstat.tcps_rcvbyteafterwin += todrop; 1386 } 1387 tp->snd_wl1 = th->th_seq - 1; 1388 tp->rcv_up = th->th_seq; 1389 /* 1390 * Client side of transaction: already sent SYN and data. 1391 * If the remote host used T/TCP to validate the SYN, 1392 * our data will be ACK'd; if so, enter normal data segment 1393 * processing in the middle of step 5, ack processing. 1394 * Otherwise, goto step 6. 1395 */ 1396 if (thflags & TH_ACK) 1397 goto process_ACK; 1398 1399 goto step6; 1400 1401 /* 1402 * If the state is LAST_ACK or CLOSING or TIME_WAIT: 1403 * if segment contains a SYN and CC [not CC.NEW] option: 1404 * if state == TIME_WAIT and connection duration > MSL, 1405 * drop packet and send RST; 1406 * 1407 * if SEG.CC > CCrecv then is new SYN, and can implicitly 1408 * ack the FIN (and data) in retransmission queue. 1409 * Complete close and delete TCPCB. Then reprocess 1410 * segment, hoping to find new TCPCB in LISTEN state; 1411 * 1412 * else must be old SYN; drop it. 1413 * else do normal processing. 1414 */ 1415 case TCPS_LAST_ACK: 1416 case TCPS_CLOSING: 1417 case TCPS_TIME_WAIT: 1418 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); 1419 if ((thflags & TH_SYN) && 1420 (to.to_flags & TOF_CC) && tp->cc_recv != 0) { 1421 if (tp->t_state == TCPS_TIME_WAIT && 1422 (ticks - tp->t_starttime) > tcp_msl) { 1423 rstreason = BANDLIM_UNLIMITED; 1424 goto dropwithreset; 1425 } 1426 if (CC_GT(to.to_cc, tp->cc_recv)) { 1427 tp = tcp_close(tp); 1428 goto findpcb; 1429 } 1430 else 1431 goto drop; 1432 } 1433 break; /* continue normal processing */ 1434 } 1435 1436 /* 1437 * States other than LISTEN or SYN_SENT. 1438 * First check the RST flag and sequence number since reset segments 1439 * are exempt from the timestamp and connection count tests. This 1440 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix 1441 * below which allowed reset segments in half the sequence space 1442 * to fall though and be processed (which gives forged reset 1443 * segments with a random sequence number a 50 percent chance of 1444 * killing a connection). 1445 * Then check timestamp, if present. 1446 * Then check the connection count, if present. 1447 * Then check that at least some bytes of segment are within 1448 * receive window. If segment begins before rcv_nxt, 1449 * drop leading data (and SYN); if nothing left, just ack. 1450 * 1451 * 1452 * If the RST bit is set, check the sequence number to see 1453 * if this is a valid reset segment. 1454 * RFC 793 page 37: 1455 * In all states except SYN-SENT, all reset (RST) segments 1456 * are validated by checking their SEQ-fields. A reset is 1457 * valid if its sequence number is in the window. 1458 * Note: this does not take into account delayed ACKs, so 1459 * we should test against last_ack_sent instead of rcv_nxt. 1460 * The sequence number in the reset segment is normally an 1461 * echo of our outgoing acknowlegement numbers, but some hosts 1462 * send a reset with the sequence number at the rightmost edge 1463 * of our receive window, and we have to handle this case. 1464 * If we have multiple segments in flight, the intial reset 1465 * segment sequence numbers will be to the left of last_ack_sent, 1466 * but they will eventually catch up. 1467 * In any case, it never made sense to trim reset segments to 1468 * fit the receive window since RFC 1122 says: 1469 * 4.2.2.12 RST Segment: RFC-793 Section 3.4 1470 * 1471 * A TCP SHOULD allow a received RST segment to include data. 1472 * 1473 * DISCUSSION 1474 * It has been suggested that a RST segment could contain 1475 * ASCII text that encoded and explained the cause of the 1476 * RST. No standard has yet been established for such 1477 * data. 1478 * 1479 * If the reset segment passes the sequence number test examine 1480 * the state: 1481 * SYN_RECEIVED STATE: 1482 * If passive open, return to LISTEN state. 1483 * If active open, inform user that connection was refused. 1484 * ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES: 1485 * Inform user that connection was reset, and close tcb. 1486 * CLOSING, LAST_ACK STATES: 1487 * Close the tcb. 1488 * TIME_WAIT STATE: 1489 * Drop the segment - see Stevens, vol. 2, p. 964 and 1490 * RFC 1337. 1491 */ 1492 if (thflags & TH_RST) { 1493 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) && 1494 SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) { 1495 switch (tp->t_state) { 1496 1497 case TCPS_SYN_RECEIVED: 1498 so->so_error = ECONNREFUSED; 1499 goto close; 1500 1501 case TCPS_ESTABLISHED: 1502 case TCPS_FIN_WAIT_1: 1503 case TCPS_FIN_WAIT_2: 1504 case TCPS_CLOSE_WAIT: 1505 so->so_error = ECONNRESET; 1506 close: 1507 tp->t_state = TCPS_CLOSED; 1508 tcpstat.tcps_drops++; 1509 tp = tcp_close(tp); 1510 break; 1511 1512 case TCPS_CLOSING: 1513 case TCPS_LAST_ACK: 1514 tp = tcp_close(tp); 1515 break; 1516 1517 case TCPS_TIME_WAIT: 1518 KASSERT(tp->t_state != TCPS_TIME_WAIT, 1519 ("timewait")); 1520 break; 1521 } 1522 } 1523 goto drop; 1524 } 1525 1526 /* 1527 * RFC 1323 PAWS: If we have a timestamp reply on this segment 1528 * and it's less than ts_recent, drop it. 1529 */ 1530 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && 1531 TSTMP_LT(to.to_tsval, tp->ts_recent)) { 1532 1533 /* Check to see if ts_recent is over 24 days old. */ 1534 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) { 1535 /* 1536 * Invalidate ts_recent. If this segment updates 1537 * ts_recent, the age will be reset later and ts_recent 1538 * will get a valid value. If it does not, setting 1539 * ts_recent to zero will at least satisfy the 1540 * requirement that zero be placed in the timestamp 1541 * echo reply when ts_recent isn't valid. The 1542 * age isn't reset until we get a valid ts_recent 1543 * because we don't want out-of-order segments to be 1544 * dropped when ts_recent is old. 1545 */ 1546 tp->ts_recent = 0; 1547 } else { 1548 tcpstat.tcps_rcvduppack++; 1549 tcpstat.tcps_rcvdupbyte += tlen; 1550 tcpstat.tcps_pawsdrop++; 1551 if (tlen) 1552 goto dropafterack; 1553 goto drop; 1554 } 1555 } 1556 1557 /* 1558 * T/TCP mechanism 1559 * If T/TCP was negotiated and the segment doesn't have CC, 1560 * or if its CC is wrong then drop the segment. 1561 * RST segments do not have to comply with this. 1562 */ 1563 if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) && 1564 ((to.to_flags & TOF_CC) == 0 || tp->cc_recv != to.to_cc)) 1565 goto dropafterack; 1566 1567 /* 1568 * In the SYN-RECEIVED state, validate that the packet belongs to 1569 * this connection before trimming the data to fit the receive 1570 * window. Check the sequence number versus IRS since we know 1571 * the sequence numbers haven't wrapped. This is a partial fix 1572 * for the "LAND" DoS attack. 1573 */ 1574 if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) { 1575 rstreason = BANDLIM_RST_OPENPORT; 1576 goto dropwithreset; 1577 } 1578 1579 todrop = tp->rcv_nxt - th->th_seq; 1580 if (todrop > 0) { 1581 if (thflags & TH_SYN) { 1582 thflags &= ~TH_SYN; 1583 th->th_seq++; 1584 if (th->th_urp > 1) 1585 th->th_urp--; 1586 else 1587 thflags &= ~TH_URG; 1588 todrop--; 1589 } 1590 /* 1591 * Following if statement from Stevens, vol. 2, p. 960. 1592 */ 1593 if (todrop > tlen 1594 || (todrop == tlen && (thflags & TH_FIN) == 0)) { 1595 /* 1596 * Any valid FIN must be to the left of the window. 1597 * At this point the FIN must be a duplicate or out 1598 * of sequence; drop it. 1599 */ 1600 thflags &= ~TH_FIN; 1601 1602 /* 1603 * Send an ACK to resynchronize and drop any data. 1604 * But keep on processing for RST or ACK. 1605 */ 1606 tp->t_flags |= TF_ACKNOW; 1607 todrop = tlen; 1608 tcpstat.tcps_rcvduppack++; 1609 tcpstat.tcps_rcvdupbyte += todrop; 1610 } else { 1611 tcpstat.tcps_rcvpartduppack++; 1612 tcpstat.tcps_rcvpartdupbyte += todrop; 1613 } 1614 drop_hdrlen += todrop; /* drop from the top afterwards */ 1615 th->th_seq += todrop; 1616 tlen -= todrop; 1617 if (th->th_urp > todrop) 1618 th->th_urp -= todrop; 1619 else { 1620 thflags &= ~TH_URG; 1621 th->th_urp = 0; 1622 } 1623 } 1624 1625 /* 1626 * If new data are received on a connection after the 1627 * user processes are gone, then RST the other end. 1628 */ 1629 if ((so->so_state & SS_NOFDREF) && 1630 tp->t_state > TCPS_CLOSE_WAIT && tlen) { 1631 tp = tcp_close(tp); 1632 tcpstat.tcps_rcvafterclose++; 1633 rstreason = BANDLIM_UNLIMITED; 1634 goto dropwithreset; 1635 } 1636 1637 /* 1638 * If segment ends after window, drop trailing data 1639 * (and PUSH and FIN); if nothing left, just ACK. 1640 */ 1641 todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd); 1642 if (todrop > 0) { 1643 tcpstat.tcps_rcvpackafterwin++; 1644 if (todrop >= tlen) { 1645 tcpstat.tcps_rcvbyteafterwin += tlen; 1646 /* 1647 * If a new connection request is received 1648 * while in TIME_WAIT, drop the old connection 1649 * and start over if the sequence numbers 1650 * are above the previous ones. 1651 */ 1652 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); 1653 if (thflags & TH_SYN && 1654 tp->t_state == TCPS_TIME_WAIT && 1655 SEQ_GT(th->th_seq, tp->rcv_nxt)) { 1656 tp = tcp_close(tp); 1657 goto findpcb; 1658 } 1659 /* 1660 * If window is closed can only take segments at 1661 * window edge, and have to drop data and PUSH from 1662 * incoming segments. Continue processing, but 1663 * remember to ack. Otherwise, drop segment 1664 * and ack. 1665 */ 1666 if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) { 1667 tp->t_flags |= TF_ACKNOW; 1668 tcpstat.tcps_rcvwinprobe++; 1669 } else 1670 goto dropafterack; 1671 } else 1672 tcpstat.tcps_rcvbyteafterwin += todrop; 1673 m_adj(m, -todrop); 1674 tlen -= todrop; 1675 thflags &= ~(TH_PUSH|TH_FIN); 1676 } 1677 1678 /* 1679 * If last ACK falls within this segment's sequence numbers, 1680 * record its timestamp. 1681 * NOTE that the test is modified according to the latest 1682 * proposal of the tcplw@cray.com list (Braden 1993/04/26). 1683 */ 1684 if ((to.to_flags & TOF_TS) != 0 && 1685 SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { 1686 tp->ts_recent_age = ticks; 1687 tp->ts_recent = to.to_tsval; 1688 } 1689 1690 /* 1691 * If a SYN is in the window, then this is an 1692 * error and we send an RST and drop the connection. 1693 */ 1694 if (thflags & TH_SYN) { 1695 tp = tcp_drop(tp, ECONNRESET); 1696 rstreason = BANDLIM_UNLIMITED; 1697 goto drop; 1698 } 1699 1700 /* 1701 * If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN 1702 * flag is on (half-synchronized state), then queue data for 1703 * later processing; else drop segment and return. 1704 */ 1705 if ((thflags & TH_ACK) == 0) { 1706 if (tp->t_state == TCPS_SYN_RECEIVED || 1707 (tp->t_flags & TF_NEEDSYN)) 1708 goto step6; 1709 else 1710 goto drop; 1711 } 1712 1713 /* 1714 * Ack processing. 1715 */ 1716 switch (tp->t_state) { 1717 1718 /* 1719 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter 1720 * ESTABLISHED state and continue processing. 1721 * The ACK was checked above. 1722 */ 1723 case TCPS_SYN_RECEIVED: 1724 1725 tcpstat.tcps_connects++; 1726 soisconnected(so); 1727 /* Do window scaling? */ 1728 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == 1729 (TF_RCVD_SCALE|TF_REQ_SCALE)) { 1730 tp->snd_scale = tp->requested_s_scale; 1731 tp->rcv_scale = tp->request_r_scale; 1732 } 1733 /* 1734 * Upon successful completion of 3-way handshake, 1735 * update cache.CC, pass any queued data to the user, 1736 * and advance state appropriately. 1737 */ 1738 if (tcp_do_rfc1644) { 1739 tao.tao_cc = tp->cc_recv; 1740 tcp_hc_updatetao(&inp->inp_inc, TCP_HC_TAO_CC, 1741 tp->cc_recv, 0); 1742 } 1743 /* 1744 * Make transitions: 1745 * SYN-RECEIVED -> ESTABLISHED 1746 * SYN-RECEIVED* -> FIN-WAIT-1 1747 */ 1748 tp->t_starttime = ticks; 1749 if (tp->t_flags & TF_NEEDFIN) { 1750 tp->t_state = TCPS_FIN_WAIT_1; 1751 tp->t_flags &= ~TF_NEEDFIN; 1752 } else { 1753 tp->t_state = TCPS_ESTABLISHED; 1754 callout_reset(tp->tt_keep, tcp_keepidle, 1755 tcp_timer_keep, tp); 1756 } 1757 /* 1758 * If segment contains data or ACK, will call tcp_reass() 1759 * later; if not, do so now to pass queued data to user. 1760 */ 1761 if (tlen == 0 && (thflags & TH_FIN) == 0) 1762 (void) tcp_reass(tp, (struct tcphdr *)0, 0, 1763 (struct mbuf *)0); 1764 tp->snd_wl1 = th->th_seq - 1; 1765 /* FALLTHROUGH */ 1766 1767 /* 1768 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range 1769 * ACKs. If the ack is in the range 1770 * tp->snd_una < th->th_ack <= tp->snd_max 1771 * then advance tp->snd_una to th->th_ack and drop 1772 * data from the retransmission queue. If this ACK reflects 1773 * more up to date window information we update our window information. 1774 */ 1775 case TCPS_ESTABLISHED: 1776 case TCPS_FIN_WAIT_1: 1777 case TCPS_FIN_WAIT_2: 1778 case TCPS_CLOSE_WAIT: 1779 case TCPS_CLOSING: 1780 case TCPS_LAST_ACK: 1781 case TCPS_TIME_WAIT: 1782 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); 1783 if (SEQ_LEQ(th->th_ack, tp->snd_una)) { 1784 if (tlen == 0 && tiwin == tp->snd_wnd) { 1785 tcpstat.tcps_rcvdupack++; 1786 /* 1787 * If we have outstanding data (other than 1788 * a window probe), this is a completely 1789 * duplicate ack (ie, window info didn't 1790 * change), the ack is the biggest we've 1791 * seen and we've seen exactly our rexmt 1792 * threshhold of them, assume a packet 1793 * has been dropped and retransmit it. 1794 * Kludge snd_nxt & the congestion 1795 * window so we send only this one 1796 * packet. 1797 * 1798 * We know we're losing at the current 1799 * window size so do congestion avoidance 1800 * (set ssthresh to half the current window 1801 * and pull our congestion window back to 1802 * the new ssthresh). 1803 * 1804 * Dup acks mean that packets have left the 1805 * network (they're now cached at the receiver) 1806 * so bump cwnd by the amount in the receiver 1807 * to keep a constant cwnd packets in the 1808 * network. 1809 */ 1810 if (!callout_active(tp->tt_rexmt) || 1811 th->th_ack != tp->snd_una) 1812 tp->t_dupacks = 0; 1813 else if (++tp->t_dupacks > tcprexmtthresh || 1814 (tcp_do_newreno && 1815 IN_FASTRECOVERY(tp))) { 1816 tp->snd_cwnd += tp->t_maxseg; 1817 (void) tcp_output(tp); 1818 goto drop; 1819 } else if (tp->t_dupacks == tcprexmtthresh) { 1820 tcp_seq onxt = tp->snd_nxt; 1821 u_int win; 1822 if (tcp_do_newreno && 1823 SEQ_LEQ(th->th_ack, 1824 tp->snd_recover)) { 1825 tp->t_dupacks = 0; 1826 break; 1827 } 1828 win = min(tp->snd_wnd, tp->snd_cwnd) / 1829 2 / tp->t_maxseg; 1830 if (win < 2) 1831 win = 2; 1832 tp->snd_ssthresh = win * tp->t_maxseg; 1833 ENTER_FASTRECOVERY(tp); 1834 tp->snd_recover = tp->snd_max; 1835 callout_stop(tp->tt_rexmt); 1836 tp->t_rtttime = 0; 1837 tp->snd_nxt = th->th_ack; 1838 tp->snd_cwnd = tp->t_maxseg; 1839 (void) tcp_output(tp); 1840 KASSERT(tp->snd_limited <= 2, 1841 ("tp->snd_limited too big")); 1842 tp->snd_cwnd = tp->snd_ssthresh + 1843 tp->t_maxseg * 1844 (tp->t_dupacks - tp->snd_limited); 1845 if (SEQ_GT(onxt, tp->snd_nxt)) 1846 tp->snd_nxt = onxt; 1847 goto drop; 1848 } else if (tcp_do_rfc3042) { 1849 u_long oldcwnd = tp->snd_cwnd; 1850 tcp_seq oldsndmax = tp->snd_max; 1851 u_int sent; 1852 KASSERT(tp->t_dupacks == 1 || 1853 tp->t_dupacks == 2, 1854 ("dupacks not 1 or 2")); 1855 if (tp->t_dupacks == 1) 1856 tp->snd_limited = 0; 1857 tp->snd_cwnd = 1858 (tp->snd_nxt - tp->snd_una) + 1859 (tp->t_dupacks - tp->snd_limited) * 1860 tp->t_maxseg; 1861 (void) tcp_output(tp); 1862 sent = tp->snd_max - oldsndmax; 1863 if (sent > tp->t_maxseg) { 1864 KASSERT(tp->snd_limited == 0 && 1865 tp->t_dupacks == 2, 1866 ("sent too much")); 1867 tp->snd_limited = 2; 1868 } else if (sent > 0) 1869 ++tp->snd_limited; 1870 tp->snd_cwnd = oldcwnd; 1871 goto drop; 1872 } 1873 } else 1874 tp->t_dupacks = 0; 1875 break; 1876 } 1877 1878 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una")); 1879 1880 /* 1881 * If the congestion window was inflated to account 1882 * for the other side's cached packets, retract it. 1883 */ 1884 if (tcp_do_newreno) { 1885 if (IN_FASTRECOVERY(tp)) { 1886 if (SEQ_LT(th->th_ack, tp->snd_recover)) { 1887 tcp_newreno_partial_ack(tp, th); 1888 } else { 1889 /* 1890 * Window inflation should have left us 1891 * with approximately snd_ssthresh 1892 * outstanding data. 1893 * But in case we would be inclined to 1894 * send a burst, better to do it via 1895 * the slow start mechanism. 1896 */ 1897 if (SEQ_GT(th->th_ack + 1898 tp->snd_ssthresh, 1899 tp->snd_max)) 1900 tp->snd_cwnd = tp->snd_max - 1901 th->th_ack + 1902 tp->t_maxseg; 1903 else 1904 tp->snd_cwnd = tp->snd_ssthresh; 1905 } 1906 } 1907 } else { 1908 if (tp->t_dupacks >= tcprexmtthresh && 1909 tp->snd_cwnd > tp->snd_ssthresh) 1910 tp->snd_cwnd = tp->snd_ssthresh; 1911 } 1912 tp->t_dupacks = 0; 1913 if (SEQ_GT(th->th_ack, tp->snd_max)) { 1914 tcpstat.tcps_rcvacktoomuch++; 1915 goto dropafterack; 1916 } 1917 /* 1918 * If we reach this point, ACK is not a duplicate, 1919 * i.e., it ACKs something we sent. 1920 */ 1921 if (tp->t_flags & TF_NEEDSYN) { 1922 /* 1923 * T/TCP: Connection was half-synchronized, and our 1924 * SYN has been ACK'd (so connection is now fully 1925 * synchronized). Go to non-starred state, 1926 * increment snd_una for ACK of SYN, and check if 1927 * we can do window scaling. 1928 */ 1929 tp->t_flags &= ~TF_NEEDSYN; 1930 tp->snd_una++; 1931 /* Do window scaling? */ 1932 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == 1933 (TF_RCVD_SCALE|TF_REQ_SCALE)) { 1934 tp->snd_scale = tp->requested_s_scale; 1935 tp->rcv_scale = tp->request_r_scale; 1936 } 1937 } 1938 1939 process_ACK: 1940 acked = th->th_ack - tp->snd_una; 1941 tcpstat.tcps_rcvackpack++; 1942 tcpstat.tcps_rcvackbyte += acked; 1943 1944 /* 1945 * If we just performed our first retransmit, and the ACK 1946 * arrives within our recovery window, then it was a mistake 1947 * to do the retransmit in the first place. Recover our 1948 * original cwnd and ssthresh, and proceed to transmit where 1949 * we left off. 1950 */ 1951 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) { 1952 ++tcpstat.tcps_sndrexmitbad; 1953 tp->snd_cwnd = tp->snd_cwnd_prev; 1954 tp->snd_ssthresh = tp->snd_ssthresh_prev; 1955 tp->snd_recover = tp->snd_recover_prev; 1956 if (tp->t_flags & TF_WASFRECOVERY) 1957 ENTER_FASTRECOVERY(tp); 1958 tp->snd_nxt = tp->snd_max; 1959 tp->t_badrxtwin = 0; /* XXX probably not required */ 1960 } 1961 1962 /* 1963 * If we have a timestamp reply, update smoothed 1964 * round trip time. If no timestamp is present but 1965 * transmit timer is running and timed sequence 1966 * number was acked, update smoothed round trip time. 1967 * Since we now have an rtt measurement, cancel the 1968 * timer backoff (cf., Phil Karn's retransmit alg.). 1969 * Recompute the initial retransmit timer. 1970 * 1971 * Some boxes send broken timestamp replies 1972 * during the SYN+ACK phase, ignore 1973 * timestamps of 0 or we could calculate a 1974 * huge RTT and blow up the retransmit timer. 1975 */ 1976 if ((to.to_flags & TOF_TS) != 0 && 1977 to.to_tsecr) { 1978 tcp_xmit_timer(tp, ticks - to.to_tsecr + 1); 1979 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) { 1980 tcp_xmit_timer(tp, ticks - tp->t_rtttime); 1981 } 1982 tcp_xmit_bandwidth_limit(tp, th->th_ack); 1983 1984 /* 1985 * If all outstanding data is acked, stop retransmit 1986 * timer and remember to restart (more output or persist). 1987 * If there is more data to be acked, restart retransmit 1988 * timer, using current (possibly backed-off) value. 1989 */ 1990 if (th->th_ack == tp->snd_max) { 1991 callout_stop(tp->tt_rexmt); 1992 needoutput = 1; 1993 } else if (!callout_active(tp->tt_persist)) 1994 callout_reset(tp->tt_rexmt, tp->t_rxtcur, 1995 tcp_timer_rexmt, tp); 1996 1997 /* 1998 * If no data (only SYN) was ACK'd, 1999 * skip rest of ACK processing. 2000 */ 2001 if (acked == 0) 2002 goto step6; 2003 2004 /* 2005 * When new data is acked, open the congestion window. 2006 * If the window gives us less than ssthresh packets 2007 * in flight, open exponentially (maxseg per packet). 2008 * Otherwise open linearly: maxseg per window 2009 * (maxseg^2 / cwnd per packet). 2010 */ 2011 if (!tcp_do_newreno || !IN_FASTRECOVERY(tp)) { 2012 register u_int cw = tp->snd_cwnd; 2013 register u_int incr = tp->t_maxseg; 2014 if (cw > tp->snd_ssthresh) 2015 incr = incr * incr / cw; 2016 tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale); 2017 } 2018 if (acked > so->so_snd.sb_cc) { 2019 tp->snd_wnd -= so->so_snd.sb_cc; 2020 sbdrop(&so->so_snd, (int)so->so_snd.sb_cc); 2021 ourfinisacked = 1; 2022 } else { 2023 sbdrop(&so->so_snd, acked); 2024 tp->snd_wnd -= acked; 2025 ourfinisacked = 0; 2026 } 2027 sowwakeup(so); 2028 /* detect una wraparound */ 2029 if (tcp_do_newreno && !IN_FASTRECOVERY(tp) && 2030 SEQ_GT(tp->snd_una, tp->snd_recover) && 2031 SEQ_LEQ(th->th_ack, tp->snd_recover)) 2032 tp->snd_recover = th->th_ack - 1; 2033 if (tcp_do_newreno && IN_FASTRECOVERY(tp) && 2034 SEQ_GEQ(th->th_ack, tp->snd_recover)) 2035 EXIT_FASTRECOVERY(tp); 2036 tp->snd_una = th->th_ack; 2037 if (SEQ_LT(tp->snd_nxt, tp->snd_una)) 2038 tp->snd_nxt = tp->snd_una; 2039 2040 switch (tp->t_state) { 2041 2042 /* 2043 * In FIN_WAIT_1 STATE in addition to the processing 2044 * for the ESTABLISHED state if our FIN is now acknowledged 2045 * then enter FIN_WAIT_2. 2046 */ 2047 case TCPS_FIN_WAIT_1: 2048 if (ourfinisacked) { 2049 /* 2050 * If we can't receive any more 2051 * data, then closing user can proceed. 2052 * Starting the timer is contrary to the 2053 * specification, but if we don't get a FIN 2054 * we'll hang forever. 2055 */ 2056 /* XXXjl 2057 * we should release the tp also, and use a 2058 * compressed state. 2059 */ 2060 if (so->so_state & SS_CANTRCVMORE) { 2061 soisdisconnected(so); 2062 callout_reset(tp->tt_2msl, tcp_maxidle, 2063 tcp_timer_2msl, tp); 2064 } 2065 tp->t_state = TCPS_FIN_WAIT_2; 2066 } 2067 break; 2068 2069 /* 2070 * In CLOSING STATE in addition to the processing for 2071 * the ESTABLISHED state if the ACK acknowledges our FIN 2072 * then enter the TIME-WAIT state, otherwise ignore 2073 * the segment. 2074 */ 2075 case TCPS_CLOSING: 2076 if (ourfinisacked) { 2077 KASSERT(headlocked, ("headlocked")); 2078 tcp_twstart(tp); 2079 INP_INFO_WUNLOCK(&tcbinfo); 2080 m_freem(m); 2081 return; 2082 } 2083 break; 2084 2085 /* 2086 * In LAST_ACK, we may still be waiting for data to drain 2087 * and/or to be acked, as well as for the ack of our FIN. 2088 * If our FIN is now acknowledged, delete the TCB, 2089 * enter the closed state and return. 2090 */ 2091 case TCPS_LAST_ACK: 2092 if (ourfinisacked) { 2093 tp = tcp_close(tp); 2094 goto drop; 2095 } 2096 break; 2097 2098 /* 2099 * In TIME_WAIT state the only thing that should arrive 2100 * is a retransmission of the remote FIN. Acknowledge 2101 * it and restart the finack timer. 2102 */ 2103 case TCPS_TIME_WAIT: 2104 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); 2105 callout_reset(tp->tt_2msl, 2 * tcp_msl, 2106 tcp_timer_2msl, tp); 2107 goto dropafterack; 2108 } 2109 } 2110 2111 step6: 2112 /* 2113 * Update window information. 2114 * Don't look at window if no ACK: TAC's send garbage on first SYN. 2115 */ 2116 if ((thflags & TH_ACK) && 2117 (SEQ_LT(tp->snd_wl1, th->th_seq) || 2118 (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) || 2119 (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) { 2120 /* keep track of pure window updates */ 2121 if (tlen == 0 && 2122 tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd) 2123 tcpstat.tcps_rcvwinupd++; 2124 tp->snd_wnd = tiwin; 2125 tp->snd_wl1 = th->th_seq; 2126 tp->snd_wl2 = th->th_ack; 2127 if (tp->snd_wnd > tp->max_sndwnd) 2128 tp->max_sndwnd = tp->snd_wnd; 2129 needoutput = 1; 2130 } 2131 2132 /* 2133 * Process segments with URG. 2134 */ 2135 if ((thflags & TH_URG) && th->th_urp && 2136 TCPS_HAVERCVDFIN(tp->t_state) == 0) { 2137 /* 2138 * This is a kludge, but if we receive and accept 2139 * random urgent pointers, we'll crash in 2140 * soreceive. It's hard to imagine someone 2141 * actually wanting to send this much urgent data. 2142 */ 2143 if (th->th_urp + so->so_rcv.sb_cc > sb_max) { 2144 th->th_urp = 0; /* XXX */ 2145 thflags &= ~TH_URG; /* XXX */ 2146 goto dodata; /* XXX */ 2147 } 2148 /* 2149 * If this segment advances the known urgent pointer, 2150 * then mark the data stream. This should not happen 2151 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since 2152 * a FIN has been received from the remote side. 2153 * In these states we ignore the URG. 2154 * 2155 * According to RFC961 (Assigned Protocols), 2156 * the urgent pointer points to the last octet 2157 * of urgent data. We continue, however, 2158 * to consider it to indicate the first octet 2159 * of data past the urgent section as the original 2160 * spec states (in one of two places). 2161 */ 2162 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) { 2163 tp->rcv_up = th->th_seq + th->th_urp; 2164 so->so_oobmark = so->so_rcv.sb_cc + 2165 (tp->rcv_up - tp->rcv_nxt) - 1; 2166 if (so->so_oobmark == 0) 2167 so->so_state |= SS_RCVATMARK; 2168 sohasoutofband(so); 2169 tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA); 2170 } 2171 /* 2172 * Remove out of band data so doesn't get presented to user. 2173 * This can happen independent of advancing the URG pointer, 2174 * but if two URG's are pending at once, some out-of-band 2175 * data may creep in... ick. 2176 */ 2177 if (th->th_urp <= (u_long)tlen && 2178 !(so->so_options & SO_OOBINLINE)) { 2179 /* hdr drop is delayed */ 2180 tcp_pulloutofband(so, th, m, drop_hdrlen); 2181 } 2182 } else { 2183 /* 2184 * If no out of band data is expected, 2185 * pull receive urgent pointer along 2186 * with the receive window. 2187 */ 2188 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up)) 2189 tp->rcv_up = tp->rcv_nxt; 2190 } 2191 dodata: /* XXX */ 2192 KASSERT(headlocked, ("headlocked")); 2193 /* 2194 * Process the segment text, merging it into the TCP sequencing queue, 2195 * and arranging for acknowledgment of receipt if necessary. 2196 * This process logically involves adjusting tp->rcv_wnd as data 2197 * is presented to the user (this happens in tcp_usrreq.c, 2198 * case PRU_RCVD). If a FIN has already been received on this 2199 * connection then we just ignore the text. 2200 */ 2201 if ((tlen || (thflags & TH_FIN)) && 2202 TCPS_HAVERCVDFIN(tp->t_state) == 0) { 2203 m_adj(m, drop_hdrlen); /* delayed header drop */ 2204 /* 2205 * Insert segment which includes th into TCP reassembly queue 2206 * with control block tp. Set thflags to whether reassembly now 2207 * includes a segment with FIN. This handles the common case 2208 * inline (segment is the next to be received on an established 2209 * connection, and the queue is empty), avoiding linkage into 2210 * and removal from the queue and repetition of various 2211 * conversions. 2212 * Set DELACK for segments received in order, but ack 2213 * immediately when segments are out of order (so 2214 * fast retransmit can work). 2215 */ 2216 if (th->th_seq == tp->rcv_nxt && 2217 LIST_EMPTY(&tp->t_segq) && 2218 TCPS_HAVEESTABLISHED(tp->t_state)) { 2219 if (DELAY_ACK(tp)) 2220 tp->t_flags |= TF_DELACK; 2221 else 2222 tp->t_flags |= TF_ACKNOW; 2223 tp->rcv_nxt += tlen; 2224 thflags = th->th_flags & TH_FIN; 2225 tcpstat.tcps_rcvpack++; 2226 tcpstat.tcps_rcvbyte += tlen; 2227 ND6_HINT(tp); 2228 if (so->so_state & SS_CANTRCVMORE) 2229 m_freem(m); 2230 else 2231 sbappendstream(&so->so_rcv, m); 2232 sorwakeup(so); 2233 } else { 2234 thflags = tcp_reass(tp, th, &tlen, m); 2235 tp->t_flags |= TF_ACKNOW; 2236 } 2237 2238 /* 2239 * Note the amount of data that peer has sent into 2240 * our window, in order to estimate the sender's 2241 * buffer size. 2242 */ 2243 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt); 2244 } else { 2245 m_freem(m); 2246 thflags &= ~TH_FIN; 2247 } 2248 2249 /* 2250 * If FIN is received ACK the FIN and let the user know 2251 * that the connection is closing. 2252 */ 2253 if (thflags & TH_FIN) { 2254 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) { 2255 socantrcvmore(so); 2256 /* 2257 * If connection is half-synchronized 2258 * (ie NEEDSYN flag on) then delay ACK, 2259 * so it may be piggybacked when SYN is sent. 2260 * Otherwise, since we received a FIN then no 2261 * more input can be expected, send ACK now. 2262 */ 2263 if (tp->t_flags & TF_NEEDSYN) 2264 tp->t_flags |= TF_DELACK; 2265 else 2266 tp->t_flags |= TF_ACKNOW; 2267 tp->rcv_nxt++; 2268 } 2269 switch (tp->t_state) { 2270 2271 /* 2272 * In SYN_RECEIVED and ESTABLISHED STATES 2273 * enter the CLOSE_WAIT state. 2274 */ 2275 case TCPS_SYN_RECEIVED: 2276 tp->t_starttime = ticks; 2277 /*FALLTHROUGH*/ 2278 case TCPS_ESTABLISHED: 2279 tp->t_state = TCPS_CLOSE_WAIT; 2280 break; 2281 2282 /* 2283 * If still in FIN_WAIT_1 STATE FIN has not been acked so 2284 * enter the CLOSING state. 2285 */ 2286 case TCPS_FIN_WAIT_1: 2287 tp->t_state = TCPS_CLOSING; 2288 break; 2289 2290 /* 2291 * In FIN_WAIT_2 state enter the TIME_WAIT state, 2292 * starting the time-wait timer, turning off the other 2293 * standard timers. 2294 */ 2295 case TCPS_FIN_WAIT_2: 2296 KASSERT(headlocked == 1, ("headlocked should be 1")); 2297 tcp_twstart(tp); 2298 INP_INFO_WUNLOCK(&tcbinfo); 2299 return; 2300 2301 /* 2302 * In TIME_WAIT state restart the 2 MSL time_wait timer. 2303 */ 2304 case TCPS_TIME_WAIT: 2305 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); 2306 callout_reset(tp->tt_2msl, 2 * tcp_msl, 2307 tcp_timer_2msl, tp); 2308 break; 2309 } 2310 } 2311 INP_INFO_WUNLOCK(&tcbinfo); 2312 #ifdef TCPDEBUG 2313 if (so->so_options & SO_DEBUG) 2314 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen, 2315 &tcp_savetcp, 0); 2316 #endif 2317 2318 /* 2319 * Return any desired output. 2320 */ 2321 if (needoutput || (tp->t_flags & TF_ACKNOW)) 2322 (void) tcp_output(tp); 2323 2324 check_delack: 2325 if (tp->t_flags & TF_DELACK) { 2326 tp->t_flags &= ~TF_DELACK; 2327 callout_reset(tp->tt_delack, tcp_delacktime, 2328 tcp_timer_delack, tp); 2329 } 2330 INP_UNLOCK(inp); 2331 return; 2332 2333 dropafterack: 2334 /* 2335 * Generate an ACK dropping incoming segment if it occupies 2336 * sequence space, where the ACK reflects our state. 2337 * 2338 * We can now skip the test for the RST flag since all 2339 * paths to this code happen after packets containing 2340 * RST have been dropped. 2341 * 2342 * In the SYN-RECEIVED state, don't send an ACK unless the 2343 * segment we received passes the SYN-RECEIVED ACK test. 2344 * If it fails send a RST. This breaks the loop in the 2345 * "LAND" DoS attack, and also prevents an ACK storm 2346 * between two listening ports that have been sent forged 2347 * SYN segments, each with the source address of the other. 2348 */ 2349 if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) && 2350 (SEQ_GT(tp->snd_una, th->th_ack) || 2351 SEQ_GT(th->th_ack, tp->snd_max)) ) { 2352 rstreason = BANDLIM_RST_OPENPORT; 2353 goto dropwithreset; 2354 } 2355 #ifdef TCPDEBUG 2356 if (so->so_options & SO_DEBUG) 2357 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, 2358 &tcp_savetcp, 0); 2359 #endif 2360 KASSERT(headlocked, ("headlocked should be 1")); 2361 INP_INFO_WUNLOCK(&tcbinfo); 2362 m_freem(m); 2363 tp->t_flags |= TF_ACKNOW; 2364 (void) tcp_output(tp); 2365 INP_UNLOCK(inp); 2366 return; 2367 2368 dropwithreset: 2369 /* 2370 * Generate a RST, dropping incoming segment. 2371 * Make ACK acceptable to originator of segment. 2372 * Don't bother to respond if destination was broadcast/multicast. 2373 */ 2374 if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST)) 2375 goto drop; 2376 if (isipv6) { 2377 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || 2378 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) 2379 goto drop; 2380 } else { 2381 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 2382 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 2383 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || 2384 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) 2385 goto drop; 2386 } 2387 /* IPv6 anycast check is done at tcp6_input() */ 2388 2389 /* 2390 * Perform bandwidth limiting. 2391 */ 2392 if (badport_bandlim(rstreason) < 0) 2393 goto drop; 2394 2395 #ifdef TCPDEBUG 2396 if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 2397 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, 2398 &tcp_savetcp, 0); 2399 #endif 2400 2401 if (thflags & TH_ACK) 2402 /* mtod() below is safe as long as hdr dropping is delayed */ 2403 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack, 2404 TH_RST); 2405 else { 2406 if (thflags & TH_SYN) 2407 tlen++; 2408 /* mtod() below is safe as long as hdr dropping is delayed */ 2409 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen, 2410 (tcp_seq)0, TH_RST|TH_ACK); 2411 } 2412 2413 if (tp) 2414 INP_UNLOCK(inp); 2415 if (headlocked) 2416 INP_INFO_WUNLOCK(&tcbinfo); 2417 return; 2418 2419 drop: 2420 /* 2421 * Drop space held by incoming segment and return. 2422 */ 2423 #ifdef TCPDEBUG 2424 if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 2425 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, 2426 &tcp_savetcp, 0); 2427 #endif 2428 if (tp) 2429 INP_UNLOCK(inp); 2430 m_freem(m); 2431 if (headlocked) 2432 INP_INFO_WUNLOCK(&tcbinfo); 2433 return; 2434 } 2435 2436 /* 2437 * Parse TCP options and place in tcpopt. 2438 */ 2439 static void 2440 tcp_dooptions(to, cp, cnt, is_syn) 2441 struct tcpopt *to; 2442 u_char *cp; 2443 int cnt; 2444 int is_syn; 2445 { 2446 int opt, optlen; 2447 2448 to->to_flags = 0; 2449 for (; cnt > 0; cnt -= optlen, cp += optlen) { 2450 opt = cp[0]; 2451 if (opt == TCPOPT_EOL) 2452 break; 2453 if (opt == TCPOPT_NOP) 2454 optlen = 1; 2455 else { 2456 if (cnt < 2) 2457 break; 2458 optlen = cp[1]; 2459 if (optlen < 2 || optlen > cnt) 2460 break; 2461 } 2462 switch (opt) { 2463 case TCPOPT_MAXSEG: 2464 if (optlen != TCPOLEN_MAXSEG) 2465 continue; 2466 if (!is_syn) 2467 continue; 2468 to->to_flags |= TOF_MSS; 2469 bcopy((char *)cp + 2, 2470 (char *)&to->to_mss, sizeof(to->to_mss)); 2471 to->to_mss = ntohs(to->to_mss); 2472 break; 2473 case TCPOPT_WINDOW: 2474 if (optlen != TCPOLEN_WINDOW) 2475 continue; 2476 if (! is_syn) 2477 continue; 2478 to->to_flags |= TOF_SCALE; 2479 to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT); 2480 break; 2481 case TCPOPT_TIMESTAMP: 2482 if (optlen != TCPOLEN_TIMESTAMP) 2483 continue; 2484 to->to_flags |= TOF_TS; 2485 bcopy((char *)cp + 2, 2486 (char *)&to->to_tsval, sizeof(to->to_tsval)); 2487 to->to_tsval = ntohl(to->to_tsval); 2488 bcopy((char *)cp + 6, 2489 (char *)&to->to_tsecr, sizeof(to->to_tsecr)); 2490 to->to_tsecr = ntohl(to->to_tsecr); 2491 break; 2492 case TCPOPT_CC: 2493 if (optlen != TCPOLEN_CC) 2494 continue; 2495 to->to_flags |= TOF_CC; 2496 bcopy((char *)cp + 2, 2497 (char *)&to->to_cc, sizeof(to->to_cc)); 2498 to->to_cc = ntohl(to->to_cc); 2499 break; 2500 case TCPOPT_CCNEW: 2501 if (optlen != TCPOLEN_CC) 2502 continue; 2503 if (!is_syn) 2504 continue; 2505 to->to_flags |= TOF_CCNEW; 2506 bcopy((char *)cp + 2, 2507 (char *)&to->to_cc, sizeof(to->to_cc)); 2508 to->to_cc = ntohl(to->to_cc); 2509 break; 2510 case TCPOPT_CCECHO: 2511 if (optlen != TCPOLEN_CC) 2512 continue; 2513 if (!is_syn) 2514 continue; 2515 to->to_flags |= TOF_CCECHO; 2516 bcopy((char *)cp + 2, 2517 (char *)&to->to_ccecho, sizeof(to->to_ccecho)); 2518 to->to_ccecho = ntohl(to->to_ccecho); 2519 break; 2520 #ifdef TCP_SIGNATURE 2521 /* 2522 * XXX In order to reply to a host which has set the 2523 * TCP_SIGNATURE option in its initial SYN, we have to 2524 * record the fact that the option was observed here 2525 * for the syncache code to perform the correct response. 2526 */ 2527 case TCPOPT_SIGNATURE: 2528 if (optlen != TCPOLEN_SIGNATURE) 2529 continue; 2530 to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN); 2531 break; 2532 #endif 2533 default: 2534 continue; 2535 } 2536 } 2537 } 2538 2539 /* 2540 * Pull out of band byte out of a segment so 2541 * it doesn't appear in the user's data queue. 2542 * It is still reflected in the segment length for 2543 * sequencing purposes. 2544 */ 2545 static void 2546 tcp_pulloutofband(so, th, m, off) 2547 struct socket *so; 2548 struct tcphdr *th; 2549 register struct mbuf *m; 2550 int off; /* delayed to be droped hdrlen */ 2551 { 2552 int cnt = off + th->th_urp - 1; 2553 2554 while (cnt >= 0) { 2555 if (m->m_len > cnt) { 2556 char *cp = mtod(m, caddr_t) + cnt; 2557 struct tcpcb *tp = sototcpcb(so); 2558 2559 tp->t_iobc = *cp; 2560 tp->t_oobflags |= TCPOOB_HAVEDATA; 2561 bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1)); 2562 m->m_len--; 2563 if (m->m_flags & M_PKTHDR) 2564 m->m_pkthdr.len--; 2565 return; 2566 } 2567 cnt -= m->m_len; 2568 m = m->m_next; 2569 if (m == 0) 2570 break; 2571 } 2572 panic("tcp_pulloutofband"); 2573 } 2574 2575 /* 2576 * Collect new round-trip time estimate 2577 * and update averages and current timeout. 2578 */ 2579 static void 2580 tcp_xmit_timer(tp, rtt) 2581 register struct tcpcb *tp; 2582 int rtt; 2583 { 2584 register int delta; 2585 2586 tcpstat.tcps_rttupdated++; 2587 tp->t_rttupdated++; 2588 if (tp->t_srtt != 0) { 2589 /* 2590 * srtt is stored as fixed point with 5 bits after the 2591 * binary point (i.e., scaled by 8). The following magic 2592 * is equivalent to the smoothing algorithm in rfc793 with 2593 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed 2594 * point). Adjust rtt to origin 0. 2595 */ 2596 delta = ((rtt - 1) << TCP_DELTA_SHIFT) 2597 - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT)); 2598 2599 if ((tp->t_srtt += delta) <= 0) 2600 tp->t_srtt = 1; 2601 2602 /* 2603 * We accumulate a smoothed rtt variance (actually, a 2604 * smoothed mean difference), then set the retransmit 2605 * timer to smoothed rtt + 4 times the smoothed variance. 2606 * rttvar is stored as fixed point with 4 bits after the 2607 * binary point (scaled by 16). The following is 2608 * equivalent to rfc793 smoothing with an alpha of .75 2609 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces 2610 * rfc793's wired-in beta. 2611 */ 2612 if (delta < 0) 2613 delta = -delta; 2614 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT); 2615 if ((tp->t_rttvar += delta) <= 0) 2616 tp->t_rttvar = 1; 2617 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar) 2618 tp->t_rttbest = tp->t_srtt + tp->t_rttvar; 2619 } else { 2620 /* 2621 * No rtt measurement yet - use the unsmoothed rtt. 2622 * Set the variance to half the rtt (so our first 2623 * retransmit happens at 3*rtt). 2624 */ 2625 tp->t_srtt = rtt << TCP_RTT_SHIFT; 2626 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1); 2627 tp->t_rttbest = tp->t_srtt + tp->t_rttvar; 2628 } 2629 tp->t_rtttime = 0; 2630 tp->t_rxtshift = 0; 2631 2632 /* 2633 * the retransmit should happen at rtt + 4 * rttvar. 2634 * Because of the way we do the smoothing, srtt and rttvar 2635 * will each average +1/2 tick of bias. When we compute 2636 * the retransmit timer, we want 1/2 tick of rounding and 2637 * 1 extra tick because of +-1/2 tick uncertainty in the 2638 * firing of the timer. The bias will give us exactly the 2639 * 1.5 tick we need. But, because the bias is 2640 * statistical, we have to test that we don't drop below 2641 * the minimum feasible timer (which is 2 ticks). 2642 */ 2643 TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), 2644 max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX); 2645 2646 /* 2647 * We received an ack for a packet that wasn't retransmitted; 2648 * it is probably safe to discard any error indications we've 2649 * received recently. This isn't quite right, but close enough 2650 * for now (a route might have failed after we sent a segment, 2651 * and the return path might not be symmetrical). 2652 */ 2653 tp->t_softerror = 0; 2654 } 2655 2656 /* 2657 * Determine a reasonable value for maxseg size. 2658 * If the route is known, check route for mtu. 2659 * If none, use an mss that can be handled on the outgoing 2660 * interface without forcing IP to fragment; if bigger than 2661 * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES 2662 * to utilize large mbufs. If no route is found, route has no mtu, 2663 * or the destination isn't local, use a default, hopefully conservative 2664 * size (usually 512 or the default IP max size, but no more than the mtu 2665 * of the interface), as we can't discover anything about intervening 2666 * gateways or networks. We also initialize the congestion/slow start 2667 * window to be a single segment if the destination isn't local. 2668 * While looking at the routing entry, we also initialize other path-dependent 2669 * parameters from pre-set or cached values in the routing entry. 2670 * 2671 * Also take into account the space needed for options that we 2672 * send regularly. Make maxseg shorter by that amount to assure 2673 * that we can send maxseg amount of data even when the options 2674 * are present. Store the upper limit of the length of options plus 2675 * data in maxopd. 2676 * 2677 * 2678 * In case of T/TCP, we call this routine during implicit connection 2679 * setup as well (offer = -1), to initialize maxseg from the cached 2680 * MSS of our peer. 2681 * 2682 * NOTE that this routine is only called when we process an incoming 2683 * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt(). 2684 */ 2685 void 2686 tcp_mss(tp, offer) 2687 struct tcpcb *tp; 2688 int offer; 2689 { 2690 int rtt, mss; 2691 u_long bufsize; 2692 u_long maxmtu; 2693 struct inpcb *inp = tp->t_inpcb; 2694 struct socket *so; 2695 struct hc_metrics_lite metrics; 2696 struct rmxp_tao tao; 2697 int origoffer = offer; 2698 #ifdef INET6 2699 int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0; 2700 size_t min_protoh = isipv6 ? 2701 sizeof (struct ip6_hdr) + sizeof (struct tcphdr) : 2702 sizeof (struct tcpiphdr); 2703 #else 2704 const size_t min_protoh = sizeof(struct tcpiphdr); 2705 #endif 2706 bzero(&tao, sizeof(tao)); 2707 2708 /* initialize */ 2709 #ifdef INET6 2710 if (isipv6) { 2711 maxmtu = tcp_maxmtu6(&inp->inp_inc); 2712 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt; 2713 } else 2714 #endif 2715 { 2716 maxmtu = tcp_maxmtu(&inp->inp_inc); 2717 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt; 2718 } 2719 so = inp->inp_socket; 2720 2721 /* 2722 * no route to sender, take default mss and return 2723 */ 2724 if (maxmtu == 0) 2725 return; 2726 2727 /* what have we got? */ 2728 switch (offer) { 2729 case 0: 2730 /* 2731 * Offer == 0 means that there was no MSS on the SYN 2732 * segment, in this case we use tcp_mssdflt. 2733 */ 2734 offer = 2735 #ifdef INET6 2736 isipv6 ? tcp_v6mssdflt : 2737 #endif 2738 tcp_mssdflt; 2739 break; 2740 2741 case -1: 2742 /* 2743 * Offer == -1 means that we didn't receive SYN yet, 2744 * use cached value in that case; 2745 */ 2746 if (tcp_do_rfc1644) 2747 tcp_hc_gettao(&inp->inp_inc, &tao); 2748 if (tao.tao_mssopt != 0) 2749 offer = tao.tao_mssopt; 2750 /* FALLTHROUGH */ 2751 2752 default: 2753 /* 2754 * Prevent DoS attack with too small MSS. Round up 2755 * to at least minmss. 2756 */ 2757 offer = max(offer, tcp_minmss); 2758 /* 2759 * Sanity check: make sure that maxopd will be large 2760 * enough to allow some data on segments even if the 2761 * all the option space is used (40bytes). Otherwise 2762 * funny things may happen in tcp_output. 2763 */ 2764 offer = max(offer, 64); 2765 if (tcp_do_rfc1644) 2766 tcp_hc_updatetao(&inp->inp_inc, 2767 TCP_HC_TAO_MSSOPT, 0, offer); 2768 } 2769 2770 /* 2771 * rmx information is now retrieved from tcp_hostcache 2772 */ 2773 tcp_hc_get(&inp->inp_inc, &metrics); 2774 2775 /* 2776 * if there's a discovered mtu int tcp hostcache, use it 2777 * else, use the link mtu. 2778 */ 2779 if (metrics.rmx_mtu) 2780 mss = metrics.rmx_mtu - min_protoh; 2781 else { 2782 #ifdef INET6 2783 if (isipv6) { 2784 mss = maxmtu - min_protoh; 2785 if (!path_mtu_discovery && 2786 !in6_localaddr(&inp->in6p_faddr)) 2787 mss = min(mss, tcp_v6mssdflt); 2788 } else 2789 #endif 2790 { 2791 mss = maxmtu - min_protoh; 2792 if (!path_mtu_discovery && 2793 !in_localaddr(inp->inp_faddr)) 2794 mss = min(mss, tcp_mssdflt); 2795 } 2796 } 2797 mss = min(mss, offer); 2798 2799 /* 2800 * maxopd stores the maximum length of data AND options 2801 * in a segment; maxseg is the amount of data in a normal 2802 * segment. We need to store this value (maxopd) apart 2803 * from maxseg, because now every segment carries options 2804 * and thus we normally have somewhat less data in segments. 2805 */ 2806 tp->t_maxopd = mss; 2807 2808 /* 2809 * In case of T/TCP, origoffer==-1 indicates, that no segments 2810 * were received yet. In this case we just guess, otherwise 2811 * we do the same as before T/TCP. 2812 */ 2813 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 2814 (origoffer == -1 || 2815 (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)) 2816 mss -= TCPOLEN_TSTAMP_APPA; 2817 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC && 2818 (origoffer == -1 || 2819 (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC)) 2820 mss -= TCPOLEN_CC_APPA; 2821 tp->t_maxseg = mss; 2822 2823 #if (MCLBYTES & (MCLBYTES - 1)) == 0 2824 if (mss > MCLBYTES) 2825 mss &= ~(MCLBYTES-1); 2826 #else 2827 if (mss > MCLBYTES) 2828 mss = mss / MCLBYTES * MCLBYTES; 2829 #endif 2830 tp->t_maxseg = mss; 2831 2832 /* 2833 * If there's a pipesize, change the socket buffer to that size, 2834 * don't change if sb_hiwat is different than default (then it 2835 * has been changed on purpose with setsockopt). 2836 * Make the socket buffers an integral number of mss units; 2837 * if the mss is larger than the socket buffer, decrease the mss. 2838 */ 2839 if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe) 2840 bufsize = metrics.rmx_sendpipe; 2841 else 2842 bufsize = so->so_snd.sb_hiwat; 2843 if (bufsize < mss) 2844 mss = bufsize; 2845 else { 2846 bufsize = roundup(bufsize, mss); 2847 if (bufsize > sb_max) 2848 bufsize = sb_max; 2849 if (bufsize > so->so_snd.sb_hiwat) 2850 (void)sbreserve(&so->so_snd, bufsize, so, NULL); 2851 } 2852 tp->t_maxseg = mss; 2853 2854 if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe) 2855 bufsize = metrics.rmx_recvpipe; 2856 else 2857 bufsize = so->so_rcv.sb_hiwat; 2858 if (bufsize > mss) { 2859 bufsize = roundup(bufsize, mss); 2860 if (bufsize > sb_max) 2861 bufsize = sb_max; 2862 if (bufsize > so->so_rcv.sb_hiwat) 2863 (void)sbreserve(&so->so_rcv, bufsize, so, NULL); 2864 } 2865 /* 2866 * While we're here, check the others too 2867 */ 2868 if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) { 2869 tp->t_srtt = rtt; 2870 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE; 2871 tcpstat.tcps_usedrtt++; 2872 if (metrics.rmx_rttvar) { 2873 tp->t_rttvar = metrics.rmx_rttvar; 2874 tcpstat.tcps_usedrttvar++; 2875 } else { 2876 /* default variation is +- 1 rtt */ 2877 tp->t_rttvar = 2878 tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE; 2879 } 2880 TCPT_RANGESET(tp->t_rxtcur, 2881 ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1, 2882 tp->t_rttmin, TCPTV_REXMTMAX); 2883 } 2884 if (metrics.rmx_ssthresh) { 2885 /* 2886 * There's some sort of gateway or interface 2887 * buffer limit on the path. Use this to set 2888 * the slow start threshhold, but set the 2889 * threshold to no less than 2*mss. 2890 */ 2891 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh); 2892 tcpstat.tcps_usedssthresh++; 2893 } 2894 if (metrics.rmx_bandwidth) 2895 tp->snd_bandwidth = metrics.rmx_bandwidth; 2896 2897 /* 2898 * Set the slow-start flight size depending on whether this 2899 * is a local network or not. 2900 * 2901 * Extend this so we cache the cwnd too and retrieve it here. 2902 * Make cwnd even bigger than RFC3390 suggests but only if we 2903 * have previous experience with the remote host. Be careful 2904 * not make cwnd bigger than remote receive window or our own 2905 * send socket buffer. Maybe put some additional upper bound 2906 * on the retrieved cwnd. Should do incremental updates to 2907 * hostcache when cwnd collapses so next connection doesn't 2908 * overloads the path again. 2909 * 2910 * RFC3390 says only do this if SYN or SYN/ACK didn't got lost. 2911 * We currently check only in syncache_socket for that. 2912 */ 2913 #define TCP_METRICS_CWND 2914 #ifdef TCP_METRICS_CWND 2915 if (metrics.rmx_cwnd) 2916 tp->snd_cwnd = max(mss, 2917 min(metrics.rmx_cwnd / 2, 2918 min(tp->snd_wnd, so->so_snd.sb_hiwat))); 2919 else 2920 #endif 2921 if (tcp_do_rfc3390) 2922 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380)); 2923 #ifdef INET6 2924 else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) || 2925 (!isipv6 && in_localaddr(inp->inp_faddr))) 2926 #else 2927 else if (in_localaddr(inp->inp_faddr)) 2928 #endif 2929 tp->snd_cwnd = mss * ss_fltsz_local; 2930 else 2931 tp->snd_cwnd = mss * ss_fltsz; 2932 } 2933 2934 /* 2935 * Determine the MSS option to send on an outgoing SYN. 2936 */ 2937 int 2938 tcp_mssopt(inc) 2939 struct in_conninfo *inc; 2940 { 2941 int mss = 0; 2942 u_long maxmtu = 0; 2943 u_long thcmtu = 0; 2944 size_t min_protoh; 2945 #ifdef INET6 2946 int isipv6 = inc->inc_isipv6 ? 1 : 0; 2947 #endif 2948 2949 KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer")); 2950 2951 #ifdef INET6 2952 if (isipv6) { 2953 mss = tcp_v6mssdflt; 2954 maxmtu = tcp_maxmtu6(inc); 2955 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */ 2956 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 2957 } else 2958 #endif 2959 { 2960 mss = tcp_mssdflt; 2961 maxmtu = tcp_maxmtu(inc); 2962 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */ 2963 min_protoh = sizeof(struct tcpiphdr); 2964 } 2965 if (maxmtu && thcmtu) 2966 mss = min(maxmtu, thcmtu) - min_protoh; 2967 else if (maxmtu || thcmtu) 2968 mss = max(maxmtu, thcmtu) - min_protoh; 2969 2970 return (mss); 2971 } 2972 2973 2974 /* 2975 * On a partial ack arrives, force the retransmission of the 2976 * next unacknowledged segment. Do not clear tp->t_dupacks. 2977 * By setting snd_nxt to ti_ack, this forces retransmission timer to 2978 * be started again. 2979 */ 2980 static void 2981 tcp_newreno_partial_ack(tp, th) 2982 struct tcpcb *tp; 2983 struct tcphdr *th; 2984 { 2985 tcp_seq onxt = tp->snd_nxt; 2986 u_long ocwnd = tp->snd_cwnd; 2987 2988 callout_stop(tp->tt_rexmt); 2989 tp->t_rtttime = 0; 2990 tp->snd_nxt = th->th_ack; 2991 /* 2992 * Set snd_cwnd to one segment beyond acknowledged offset. 2993 * (tp->snd_una has not yet been updated when this function is called.) 2994 */ 2995 tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una); 2996 tp->t_flags |= TF_ACKNOW; 2997 (void) tcp_output(tp); 2998 tp->snd_cwnd = ocwnd; 2999 if (SEQ_GT(onxt, tp->snd_nxt)) 3000 tp->snd_nxt = onxt; 3001 /* 3002 * Partial window deflation. Relies on fact that tp->snd_una 3003 * not updated yet. 3004 */ 3005 tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg); 3006 } 3007 3008 /* 3009 * Returns 1 if the TIME_WAIT state was killed and we should start over, 3010 * looking for a pcb in the listen state. Returns 0 otherwise. 3011 */ 3012 static int 3013 tcp_timewait(tw, to, th, m, tlen) 3014 struct tcptw *tw; 3015 struct tcpopt *to; 3016 struct tcphdr *th; 3017 struct mbuf *m; 3018 int tlen; 3019 { 3020 int thflags; 3021 tcp_seq seq; 3022 #ifdef INET6 3023 int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0; 3024 #else 3025 const int isipv6 = 0; 3026 #endif 3027 3028 thflags = th->th_flags; 3029 3030 /* 3031 * NOTE: for FIN_WAIT_2 (to be added later), 3032 * must validate sequence number before accepting RST 3033 */ 3034 3035 /* 3036 * If the segment contains RST: 3037 * Drop the segment - see Stevens, vol. 2, p. 964 and 3038 * RFC 1337. 3039 */ 3040 if (thflags & TH_RST) 3041 goto drop; 3042 3043 /* 3044 * If segment contains a SYN and CC [not CC.NEW] option: 3045 * if connection duration > MSL, drop packet and send RST; 3046 * 3047 * if SEG.CC > CCrecv then is new SYN. 3048 * Complete close and delete TCPCB. Then reprocess 3049 * segment, hoping to find new TCPCB in LISTEN state; 3050 * 3051 * else must be old SYN; drop it. 3052 * else do normal processing. 3053 */ 3054 if ((thflags & TH_SYN) && (to->to_flags & TOF_CC) && tw->cc_recv != 0) { 3055 if ((ticks - tw->t_starttime) > tcp_msl) 3056 goto reset; 3057 if (CC_GT(to->to_cc, tw->cc_recv)) { 3058 (void) tcp_twclose(tw, 0); 3059 return (1); 3060 } 3061 goto drop; 3062 } 3063 3064 #if 0 3065 /* PAWS not needed at the moment */ 3066 /* 3067 * RFC 1323 PAWS: If we have a timestamp reply on this segment 3068 * and it's less than ts_recent, drop it. 3069 */ 3070 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && 3071 TSTMP_LT(to.to_tsval, tp->ts_recent)) { 3072 if ((thflags & TH_ACK) == 0) 3073 goto drop; 3074 goto ack; 3075 } 3076 /* 3077 * ts_recent is never updated because we never accept new segments. 3078 */ 3079 #endif 3080 3081 /* 3082 * If a new connection request is received 3083 * while in TIME_WAIT, drop the old connection 3084 * and start over if the sequence numbers 3085 * are above the previous ones. 3086 */ 3087 if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) { 3088 (void) tcp_twclose(tw, 0); 3089 return (1); 3090 } 3091 3092 /* 3093 * Drop the the segment if it does not contain an ACK. 3094 */ 3095 if ((thflags & TH_ACK) == 0) 3096 goto drop; 3097 3098 /* 3099 * Reset the 2MSL timer if this is a duplicate FIN. 3100 */ 3101 if (thflags & TH_FIN) { 3102 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0); 3103 if (seq + 1 == tw->rcv_nxt) 3104 tcp_timer_2msl_reset(tw, 2 * tcp_msl); 3105 } 3106 3107 /* 3108 * Acknowledge the segment if it has data or is not a duplicate ACK. 3109 */ 3110 if (thflags != TH_ACK || tlen != 0 || 3111 th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) 3112 tcp_twrespond(tw, NULL, m, TH_ACK); 3113 goto drop; 3114 3115 reset: 3116 /* 3117 * Generate a RST, dropping incoming segment. 3118 * Make ACK acceptable to originator of segment. 3119 * Don't bother to respond if destination was broadcast/multicast. 3120 */ 3121 if (m->m_flags & (M_BCAST|M_MCAST)) 3122 goto drop; 3123 if (isipv6) { 3124 struct ip6_hdr *ip6; 3125 3126 /* IPv6 anycast check is done at tcp6_input() */ 3127 ip6 = mtod(m, struct ip6_hdr *); 3128 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || 3129 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) 3130 goto drop; 3131 } else { 3132 struct ip *ip; 3133 3134 ip = mtod(m, struct ip *); 3135 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 3136 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 3137 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || 3138 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) 3139 goto drop; 3140 } 3141 if (thflags & TH_ACK) { 3142 tcp_respond(NULL, 3143 mtod(m, void *), th, m, 0, th->th_ack, TH_RST); 3144 } else { 3145 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0); 3146 tcp_respond(NULL, 3147 mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK); 3148 } 3149 INP_UNLOCK(tw->tw_inpcb); 3150 return (0); 3151 3152 drop: 3153 INP_UNLOCK(tw->tw_inpcb); 3154 m_freem(m); 3155 return (0); 3156 } 3157