2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
33 #include "opt_ipfw.h" /* for ipfw_fwd */
35 #include "opt_inet6.h"
36 #include "opt_ipsec.h"
38 #include "opt_tcpdebug.h"
40 #include <sys/param.h>
41 #include <sys/kernel.h>
42 #include <sys/malloc.h>
44 #include <sys/proc.h> /* for proc0 declaration */
45 #include <sys/protosw.h>
46 #include <sys/signalvar.h>
47 #include <sys/socket.h>
48 #include <sys/socketvar.h>
49 #include <sys/sysctl.h>
50 #include <sys/syslog.h>
51 #include <sys/systm.h>
53 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
58 #include <net/route.h>
60 #include <netinet/in.h>
61 #include <netinet/in_pcb.h>
62 #include <netinet/in_systm.h>
63 #include <netinet/in_var.h>
64 #include <netinet/ip.h>
65 #include <netinet/ip_icmp.h> /* required for icmp_var.h */
66 #include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
67 #include <netinet/ip_var.h>
68 #include <netinet/ip_options.h>
69 #include <netinet/ip6.h>
70 #include <netinet/icmp6.h>
71 #include <netinet6/in6_pcb.h>
72 #include <netinet6/ip6_var.h>
73 #include <netinet6/nd6.h>
74 #include <netinet/tcp.h>
75 #include <netinet/tcp_fsm.h>
76 #include <netinet/tcp_seq.h>
77 #include <netinet/tcp_timer.h>
78 #include <netinet/tcp_var.h>
79 #include <netinet6/tcp6_var.h>
80 #include <netinet/tcpip.h>
82 #include <netinet/tcp_debug.h>
86 #include <netipsec/ipsec.h>
87 #include <netipsec/ipsec6.h>
91 #include <netinet6/ipsec.h>
92 #include <netinet6/ipsec6.h>
93 #include <netkey/key.h>
96 #include <machine/in_cksum.h>
98 #include <security/mac/mac_framework.h>
100 static const int tcprexmtthresh = 3;
102 struct tcpstat tcpstat;
103 SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
104 &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
106 static int tcp_log_in_vain = 0;
107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
108 &tcp_log_in_vain, 0, "Log all incoming TCP segments to closed ports");
110 static int blackhole = 0;
111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
112 &blackhole, 0, "Do not send RST on segments to closed ports");
114 int tcp_delack_enabled = 1;
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
116 &tcp_delack_enabled, 0,
117 "Delay ACK to try and piggyback it onto a data packet");
119 static int drop_synfin = 0;
120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
121 &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
123 static int tcp_do_rfc3042 = 1;
124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
125 &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)");
127 static int tcp_do_rfc3390 = 1;
128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
130 "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
132 static int tcp_insecure_rst = 0;
133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
134 &tcp_insecure_rst, 0,
135 "Follow the old (insecure) criteria for accepting RST packets");
137 int tcp_do_autorcvbuf = 1;
138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
139 &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
141 int tcp_autorcvbuf_inc = 16*1024;
142 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
143 &tcp_autorcvbuf_inc, 0,
144 "Incrementor step size of automatic receive buffer");
146 int tcp_autorcvbuf_max = 256*1024;
147 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
148 &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
150 struct inpcbhead tcb;
151 #define tcb6 tcb /* for KAME src sync over BSD*'s */
152 struct inpcbinfo tcbinfo;
154 static void tcp_dooptions(struct tcpopt *, u_char *, int, int);
155 static void tcp_do_segment(struct mbuf *, struct tcphdr *,
156 struct socket *, struct tcpcb *, int, int);
157 static void tcp_dropwithreset(struct mbuf *, struct tcphdr *,
158 struct tcpcb *, int, int);
159 static void tcp_pulloutofband(struct socket *,
160 struct tcphdr *, struct mbuf *, int);
161 static void tcp_xmit_timer(struct tcpcb *, int);
162 static void tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
164 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
166 #define ND6_HINT(tp) \
168 if ((tp) && (tp)->t_inpcb && \
169 ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
170 nd6_nud_hint(NULL, NULL, 0); \
177 * Indicate whether this ack should be delayed. We can delay the ack if
178 * - there is no delayed ack timer in progress and
179 * - our last ack wasn't a 0-sized window. We never want to delay
180 * the ack that opens up a 0-sized window and
181 * - delayed acks are enabled or
182 * - this is a half-synchronized T/TCP connection.
184 #define DELAY_ACK(tp) \
185 ((!tcp_timer_active(tp, TT_DELACK) && \
186 (tp->t_flags & TF_RXWIN0SENT) == 0) && \
187 (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
191 * TCP input handling is split into multiple parts:
192 * tcp6_input is a thin wrapper around tcp_input for the extended
193 * ip6_protox[] call format in ip6_input
194 * tcp_input handles primary segment validation, inpcb lookup and
195 * SYN processing on listen sockets
196 * tcp_do_segment processes the ACK and text of the segment for
197 * establishing, established and closing connections
201 tcp6_input(struct mbuf **mp, int *offp, int proto)
203 struct mbuf *m = *mp;
204 struct in6_ifaddr *ia6;
206 IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
209 * draft-itojun-ipv6-tcp-to-anycast
210 * better place to put this in?
212 ia6 = ip6_getdstifaddr(m);
213 if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
216 ip6 = mtod(m, struct ip6_hdr *);
217 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
218 (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
228 tcp_input(struct mbuf *m, int off0)
231 struct ip *ip = NULL;
233 struct inpcb *inp = NULL;
234 struct tcpcb *tp = NULL;
235 struct socket *so = NULL;
241 int rstreason = 0; /* For badport_bandlim accounting purposes */
242 #ifdef IPFIREWALL_FORWARD
243 struct m_tag *fwd_tag;
246 struct ip6_hdr *ip6 = NULL;
249 const void *ip6 = NULL;
250 const int isipv6 = 0;
252 struct tcpopt to; /* options in this segment */
253 char *s = NULL; /* address and port logging */
257 * The size of tcp_saveipgen must be the size of the max ip header,
260 u_char tcp_saveipgen[IP6_HDR_LEN];
261 struct tcphdr tcp_savetcp;
266 isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
270 tcpstat.tcps_rcvtotal++;
274 /* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
275 ip6 = mtod(m, struct ip6_hdr *);
276 tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
277 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
278 tcpstat.tcps_rcvbadsum++;
281 th = (struct tcphdr *)((caddr_t)ip6 + off0);
284 * Be proactive about unspecified IPv6 address in source.
285 * As we use all-zero to indicate unbounded/unconnected pcb,
286 * unspecified IPv6 address can be used to confuse us.
288 * Note that packets with unspecified IPv6 destination is
289 * already dropped in ip6_input.
291 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
296 th = NULL; /* XXX: Avoid compiler warning. */
300 * Get IP and TCP header together in first mbuf.
301 * Note: IP leaves IP header in first mbuf.
303 if (off0 > sizeof (struct ip)) {
304 ip_stripoptions(m, (struct mbuf *)0);
305 off0 = sizeof(struct ip);
307 if (m->m_len < sizeof (struct tcpiphdr)) {
308 if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
310 tcpstat.tcps_rcvshort++;
314 ip = mtod(m, struct ip *);
315 ipov = (struct ipovly *)ip;
316 th = (struct tcphdr *)((caddr_t)ip + off0);
319 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
320 if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
321 th->th_sum = m->m_pkthdr.csum_data;
323 th->th_sum = in_pseudo(ip->ip_src.s_addr,
325 htonl(m->m_pkthdr.csum_data +
328 th->th_sum ^= 0xffff;
330 ipov->ih_len = (u_short)tlen;
331 ipov->ih_len = htons(ipov->ih_len);
335 * Checksum extended TCP header and data.
337 len = sizeof (struct ip) + tlen;
338 bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
339 ipov->ih_len = (u_short)tlen;
340 ipov->ih_len = htons(ipov->ih_len);
341 th->th_sum = in_cksum(m, len);
344 tcpstat.tcps_rcvbadsum++;
347 /* Re-initialization for later version check */
348 ip->ip_v = IPVERSION;
352 * Check that TCP offset makes sense,
353 * pull out TCP options and adjust length. XXX
355 off = th->th_off << 2;
356 if (off < sizeof (struct tcphdr) || off > tlen) {
357 tcpstat.tcps_rcvbadoff++;
360 tlen -= off; /* tlen is used instead of ti->ti_len */
361 if (off > sizeof (struct tcphdr)) {
364 IP6_EXTHDR_CHECK(m, off0, off, );
365 ip6 = mtod(m, struct ip6_hdr *);
366 th = (struct tcphdr *)((caddr_t)ip6 + off0);
369 if (m->m_len < sizeof(struct ip) + off) {
370 if ((m = m_pullup(m, sizeof (struct ip) + off))
372 tcpstat.tcps_rcvshort++;
375 ip = mtod(m, struct ip *);
376 ipov = (struct ipovly *)ip;
377 th = (struct tcphdr *)((caddr_t)ip + off0);
380 optlen = off - sizeof (struct tcphdr);
381 optp = (u_char *)(th + 1);
383 thflags = th->th_flags;
386 * Convert TCP protocol specific fields to host format.
388 th->th_seq = ntohl(th->th_seq);
389 th->th_ack = ntohl(th->th_ack);
390 th->th_win = ntohs(th->th_win);
391 th->th_urp = ntohs(th->th_urp);
394 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
396 drop_hdrlen = off0 + off;
399 * Locate pcb for segment.
401 INP_INFO_WLOCK(&tcbinfo);
403 INP_INFO_WLOCK_ASSERT(&tcbinfo);
404 #ifdef IPFIREWALL_FORWARD
406 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
408 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
410 if (fwd_tag != NULL && isipv6 == 0) { /* IPv6 support is not yet */
411 struct sockaddr_in *next_hop;
413 next_hop = (struct sockaddr_in *)(fwd_tag+1);
415 * Transparently forwarded. Pretend to be the destination.
416 * already got one like this?
418 inp = in_pcblookup_hash(&tcbinfo,
419 ip->ip_src, th->th_sport,
420 ip->ip_dst, th->th_dport,
421 0, m->m_pkthdr.rcvif);
423 /* It's new. Try to find the ambushing socket. */
424 inp = in_pcblookup_hash(&tcbinfo,
425 ip->ip_src, th->th_sport,
428 ntohs(next_hop->sin_port) :
433 /* Remove the tag from the packet. We don't need it anymore. */
434 m_tag_delete(m, fwd_tag);
436 #endif /* IPFIREWALL_FORWARD */
440 inp = in6_pcblookup_hash(&tcbinfo,
441 &ip6->ip6_src, th->th_sport,
442 &ip6->ip6_dst, th->th_dport,
447 inp = in_pcblookup_hash(&tcbinfo,
448 ip->ip_src, th->th_sport,
449 ip->ip_dst, th->th_dport,
454 #if defined(IPSEC) || defined(FAST_IPSEC)
456 if (isipv6 && inp != NULL && ipsec6_in_reject(m, inp)) {
458 ipsec6stat.in_polvio++;
463 if (inp != NULL && ipsec4_in_reject(m, inp)) {
465 ipsecstat.in_polvio++;
469 #endif /*IPSEC || FAST_IPSEC*/
472 * If the INPCB does not exist then all data in the incoming
473 * segment is discarded and an appropriate RST is sent back.
477 * Log communication attempts to ports that are not
480 if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
481 tcp_log_in_vain == 2) {
482 if ((s = tcp_log_addrs(NULL, th, (void *)ip,
484 log(LOG_INFO, "%s; %s: Connection attempt "
485 "to closed port\n", s, __func__);
488 * When blackholing do not respond with a RST but
489 * completely ignore the segment and drop it.
491 if ((blackhole == 1 && (thflags & TH_SYN)) ||
495 rstreason = BANDLIM_RST_CLOSEDPORT;
501 * Check the minimum TTL for socket.
503 if (inp->inp_ip_minttl != 0) {
505 if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
509 if (inp->inp_ip_minttl > ip->ip_ttl)
514 * A previous connection in TIMEWAIT state is supposed to catch
515 * stray or duplicate segments arriving late. If this segment
516 * was a legitimate new connection attempt the old INPCB gets
517 * removed and we can try again to find a listening socket.
519 if (inp->inp_vflag & INP_TIMEWAIT) {
520 if (thflags & TH_SYN)
521 tcp_dooptions(&to, optp, optlen, TO_SYN);
523 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
525 if (tcp_twcheck(inp, &to, th, m, tlen))
527 INP_INFO_WUNLOCK(&tcbinfo);
531 * The TCPCB may no longer exist if the connection is winding
532 * down or it is in the CLOSED state. Either way we drop the
533 * segment and send an appropriate response.
536 if (tp == NULL || tp->t_state == TCPS_CLOSED) {
537 rstreason = BANDLIM_RST_CLOSEDPORT;
542 INP_LOCK_ASSERT(inp);
543 if (mac_check_inpcb_deliver(inp, m))
546 so = inp->inp_socket;
547 KASSERT(so != NULL, ("%s: so == NULL", __func__));
549 if (so->so_options & SO_DEBUG) {
550 ostate = tp->t_state;
553 bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
556 bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
561 * When the socket is accepting connections (the INPCB is in LISTEN
562 * state) we look into the SYN cache if this is a new connection
563 * attempt or the completion of a previous one.
565 if (so->so_options & SO_ACCEPTCONN) {
566 struct in_conninfo inc;
568 KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
569 "tp not listening", __func__));
571 bzero(&inc, sizeof(inc));
572 inc.inc_isipv6 = isipv6;
575 inc.inc6_faddr = ip6->ip6_src;
576 inc.inc6_laddr = ip6->ip6_dst;
580 inc.inc_faddr = ip->ip_src;
581 inc.inc_laddr = ip->ip_dst;
583 inc.inc_fport = th->th_sport;
584 inc.inc_lport = th->th_dport;
587 * Check for an existing connection attempt in syncache if
588 * the flag is only ACK. A successful lookup creates a new
589 * socket appended to the listen queue in SYN_RECEIVED state.
591 if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
593 * Parse the TCP options here because
594 * syncookies need access to the reflected
597 tcp_dooptions(&to, optp, optlen, 0);
599 * NB: syncache_expand() doesn't unlock
600 * inp and tcpinfo locks.
602 if (!syncache_expand(&inc, &to, th, &so, m)) {
604 * No syncache entry or ACK was not
605 * for our SYN/ACK. Send a RST.
606 * NB: syncache did its own logging
607 * of the failure cause.
609 rstreason = BANDLIM_RST_OPENPORT;
614 * We completed the 3-way handshake
615 * but could not allocate a socket
616 * either due to memory shortage,
617 * listen queue length limits or
618 * global socket limits. Send RST
619 * or wait and have the remote end
620 * retransmit the ACK for another
623 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
624 log(LOG_DEBUG, "%s; %s: Listen socket: "
625 "Socket allocation failed due to "
626 "limits or memory shortage, %s\n",
627 s, __func__, (tcp_sc_rst_sock_fail ?
628 "sending RST" : "try again"));
629 if (tcp_sc_rst_sock_fail) {
630 rstreason = BANDLIM_UNLIMITED;
636 * Socket is created in state SYN_RECEIVED.
637 * Unlock the listen socket, lock the newly
638 * created socket and update the tp variable.
640 INP_UNLOCK(inp); /* listen socket */
642 INP_LOCK(inp); /* new connection */
644 KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
647 * Process the segment and the data it
648 * contains. tcp_do_segment() consumes
649 * the mbuf chain and unlocks the inpcb.
651 tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen);
652 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
656 * Segment flag validation for new connection attempts:
658 * Our (SYN|ACK) response was rejected.
659 * Check with syncache and remove entry to prevent
662 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
663 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
664 log(LOG_DEBUG, "%s; %s: Listen socket: "
665 "Our SYN|ACK was rejected, connection "
666 "attempt aborted by remote endpoint\n",
668 syncache_chkrst(&inc, th);
672 * Spurious RST. Ignore.
674 if (thflags & TH_RST) {
675 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
676 log(LOG_DEBUG, "%s; %s: Listen socket: "
677 "Spurious RST, segment rejected\n",
682 * We can't do anything without SYN.
684 if ((thflags & TH_SYN) == 0) {
685 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
686 log(LOG_DEBUG, "%s; %s: Listen socket: "
687 "SYN is missing, segment rejected\n",
689 tcpstat.tcps_badsyn++;
693 * (SYN|ACK) is bogus on a listen socket.
695 if (thflags & TH_ACK) {
696 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
697 log(LOG_DEBUG, "%s; %s: Listen socket: "
698 "SYN|ACK invalid, segment rejected\n",
700 syncache_badack(&inc); /* XXX: Not needed! */
701 tcpstat.tcps_badsyn++;
702 rstreason = BANDLIM_RST_OPENPORT;
706 * If the drop_synfin option is enabled, drop all
707 * segments with both the SYN and FIN bits set.
708 * This prevents e.g. nmap from identifying the
710 * XXX: Poor reasoning. nmap has other methods
711 * and is constantly refining its stack detection
713 * XXX: This is a violation of the TCP specification
714 * and was used by RFC1644.
716 if ((thflags & TH_FIN) && drop_synfin) {
717 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
718 log(LOG_DEBUG, "%s; %s: Listen socket: "
719 "SYN|FIN segment rejected (based on "
720 "sysctl setting)\n", s, __func__);
721 tcpstat.tcps_badsyn++;
725 * Segment's flags are (SYN) or (SYN|FIN).
727 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
728 * as they do not affect the state of the TCP FSM.
729 * The data pointed to by TH_URG and th_urp is ignored.
731 KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
732 ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
733 KASSERT(thflags & (TH_SYN),
734 ("%s: Listen socket: TH_SYN not set", __func__));
737 * If deprecated address is forbidden,
738 * we do not accept SYN to deprecated interface
739 * address to prevent any new inbound connection from
740 * getting established.
741 * When we do not accept SYN, we send a TCP RST,
742 * with deprecated source address (instead of dropping
743 * it). We compromise it as it is much better for peer
744 * to send a RST, and RST will be the final packet
747 * If we do not forbid deprecated addresses, we accept
748 * the SYN packet. RFC2462 does not suggest dropping
750 * If we decipher RFC2462 5.5.4, it says like this:
751 * 1. use of deprecated addr with existing
752 * communication is okay - "SHOULD continue to be
754 * 2. use of it with new communication:
755 * (2a) "SHOULD NOT be used if alternate address
756 * with sufficient scope is available"
757 * (2b) nothing mentioned otherwise.
758 * Here we fall into (2b) case as we have no choice in
759 * our source address selection - we must obey the peer.
761 * The wording in RFC2462 is confusing, and there are
762 * multiple description text for deprecated address
763 * handling - worse, they are not exactly the same.
764 * I believe 5.5.4 is the best one, so we follow 5.5.4.
766 if (isipv6 && !ip6_use_deprecated) {
767 struct in6_ifaddr *ia6;
769 if ((ia6 = ip6_getdstifaddr(m)) &&
770 (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
771 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
772 log(LOG_DEBUG, "%s; %s: Listen socket: "
773 "Connection attempt to deprecated "
774 "IPv6 address rejected\n",
776 rstreason = BANDLIM_RST_OPENPORT;
782 * Basic sanity checks on incoming SYN requests:
783 * Don't respond if the destination is a link layer
784 * broadcast according to RFC1122 4.2.3.10, p. 104.
785 * If it is from this socket it must be forged.
786 * Don't respond if the source or destination is a
787 * global or subnet broad- or multicast address.
788 * Note that it is quite possible to receive unicast
789 * link-layer packets with a broadcast IP address. Use
790 * in_broadcast() to find them.
792 if (m->m_flags & (M_BCAST|M_MCAST)) {
793 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
794 log(LOG_DEBUG, "%s; %s: Listen socket: "
795 "Connection attempt from broad- or multicast "
796 "link layer address rejected\n", s, __func__);
801 if (th->th_dport == th->th_sport &&
802 IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
803 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
804 log(LOG_DEBUG, "%s; %s: Listen socket: "
805 "Connection attempt to/from self "
806 "rejected\n", s, __func__);
809 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
810 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
811 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
812 log(LOG_DEBUG, "%s; %s: Listen socket: "
813 "Connection attempt from/to multicast "
814 "address rejected\n", s, __func__);
819 if (th->th_dport == th->th_sport &&
820 ip->ip_dst.s_addr == ip->ip_src.s_addr) {
821 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
822 log(LOG_DEBUG, "%s; %s: Listen socket: "
823 "Connection attempt from/to self "
824 "rejected\n", s, __func__);
827 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
828 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
829 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
830 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
831 if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
832 log(LOG_DEBUG, "%s; %s: Listen socket: "
833 "Connection attempt from/to broad- "
834 "or multicast address rejected\n",
840 * SYN appears to be valid. Create compressed TCP state
844 if (so->so_options & SO_DEBUG)
845 tcp_trace(TA_INPUT, ostate, tp,
846 (void *)tcp_saveipgen, &tcp_savetcp, 0);
848 tcp_dooptions(&to, optp, optlen, TO_SYN);
849 syncache_add(&inc, &to, th, inp, &so, m);
851 * Entry added to syncache and mbuf consumed.
852 * Everything already unlocked by syncache_add().
854 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
859 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
860 * state. tcp_do_segment() always consumes the mbuf chain, unlocks
861 * the inpcb, and unlocks pcbinfo.
863 tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen);
864 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
868 INP_INFO_WLOCK_ASSERT(&tcbinfo);
869 tcp_dropwithreset(m, th, tp, tlen, rstreason);
870 m = NULL; /* mbuf chain got consumed. */
872 INP_INFO_WLOCK_ASSERT(&tcbinfo);
875 INP_INFO_WUNLOCK(&tcbinfo);
877 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
886 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
887 struct tcpcb *tp, int drop_hdrlen, int tlen)
889 int thflags, acked, ourfinisacked, needoutput = 0;
891 int rstreason, todrop, win;
897 * The size of tcp_saveipgen must be the size of the max ip header,
900 u_char tcp_saveipgen[IP6_HDR_LEN];
901 struct tcphdr tcp_savetcp;
904 thflags = th->th_flags;
906 INP_INFO_WLOCK_ASSERT(&tcbinfo);
907 INP_LOCK_ASSERT(tp->t_inpcb);
908 KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
910 KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
914 * Segment received on connection.
915 * Reset idle time and keep-alive timer.
917 tp->t_rcvtime = ticks;
918 if (TCPS_HAVEESTABLISHED(tp->t_state))
919 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
922 * Unscale the window into a 32-bit value.
923 * This value is bogus for the TCPS_SYN_SENT state
924 * and is overwritten later.
926 tiwin = th->th_win << tp->snd_scale;
929 * Parse options on any incoming segment.
931 tcp_dooptions(&to, (u_char *)(th + 1),
932 (th->th_off << 2) - sizeof(struct tcphdr),
933 (thflags & TH_SYN) ? TO_SYN : 0);
936 * If echoed timestamp is later than the current time,
937 * fall back to non RFC1323 RTT calculation. Normalize
938 * timestamp if syncookies were used when this connection
941 if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
942 to.to_tsecr -= tp->ts_offset;
943 if (TSTMP_GT(to.to_tsecr, ticks))
948 * Process options only when we get SYN/ACK back. The SYN case
949 * for incoming connections is handled in tcp_syncache.
950 * XXX this is traditional behavior, may need to be cleaned up.
952 if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
953 if ((to.to_flags & TOF_SCALE) &&
954 (tp->t_flags & TF_REQ_SCALE)) {
955 tp->t_flags |= TF_RCVD_SCALE;
956 tp->snd_scale = to.to_wscale;
957 tp->snd_wnd = th->th_win << tp->snd_scale;
960 if (to.to_flags & TOF_TS) {
961 tp->t_flags |= TF_RCVD_TSTMP;
962 tp->ts_recent = to.to_tsval;
963 tp->ts_recent_age = ticks;
965 /* Initial send window, already scaled. */
966 tp->snd_wnd = th->th_win;
967 if (to.to_flags & TOF_MSS)
968 tcp_mss(tp, to.to_mss);
969 if ((tp->t_flags & TF_SACK_PERMIT) &&
970 (to.to_flags & TOF_SACKPERM) == 0)
971 tp->t_flags &= ~TF_SACK_PERMIT;
975 * Header prediction: check for the two common cases
976 * of a uni-directional data xfer. If the packet has
977 * no control flags, is in-sequence, the window didn't
978 * change and we're not retransmitting, it's a
979 * candidate. If the length is zero and the ack moved
980 * forward, we're the sender side of the xfer. Just
981 * free the data acked & wake any higher level process
982 * that was blocked waiting for space. If the length
983 * is non-zero and the ack didn't move, we're the
984 * receiver side. If we're getting packets in-order
985 * (the reassembly queue is empty), add the data to
986 * the socket buffer and note that we need a delayed ack.
987 * Make sure that the hidden state-flags are also off.
988 * Since we check for TCPS_ESTABLISHED first, it can only
991 if (tp->t_state == TCPS_ESTABLISHED &&
992 th->th_seq == tp->rcv_nxt &&
993 (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
994 tp->snd_nxt == tp->snd_max &&
995 tiwin && tiwin == tp->snd_wnd &&
996 ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
997 LIST_EMPTY(&tp->t_segq) &&
998 ((to.to_flags & TOF_TS) == 0 ||
999 TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1002 * If last ACK falls within this segment's sequence numbers,
1003 * record the timestamp.
1004 * NOTE that the test is modified according to the latest
1005 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1007 if ((to.to_flags & TOF_TS) != 0 &&
1008 SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1009 tp->ts_recent_age = ticks;
1010 tp->ts_recent = to.to_tsval;
1014 if (SEQ_GT(th->th_ack, tp->snd_una) &&
1015 SEQ_LEQ(th->th_ack, tp->snd_max) &&
1016 tp->snd_cwnd >= tp->snd_wnd &&
1017 ((!tcp_do_newreno &&
1018 !(tp->t_flags & TF_SACK_PERMIT) &&
1019 tp->t_dupacks < tcprexmtthresh) ||
1021 (tp->t_flags & TF_SACK_PERMIT)) &&
1022 !IN_FASTRECOVERY(tp) &&
1023 (to.to_flags & TOF_SACK) == 0 &&
1024 TAILQ_EMPTY(&tp->snd_holes)))) {
1026 ("%s: headlocked", __func__));
1027 INP_INFO_WUNLOCK(&tcbinfo);
1030 * this is a pure ack for outstanding data.
1032 ++tcpstat.tcps_predack;
1034 * "bad retransmit" recovery
1036 if (tp->t_rxtshift == 1 &&
1037 ticks < tp->t_badrxtwin) {
1038 ++tcpstat.tcps_sndrexmitbad;
1039 tp->snd_cwnd = tp->snd_cwnd_prev;
1041 tp->snd_ssthresh_prev;
1042 tp->snd_recover = tp->snd_recover_prev;
1043 if (tp->t_flags & TF_WASFRECOVERY)
1044 ENTER_FASTRECOVERY(tp);
1045 tp->snd_nxt = tp->snd_max;
1046 tp->t_badrxtwin = 0;
1050 * Recalculate the transmit timer / rtt.
1052 * Some boxes send broken timestamp replies
1053 * during the SYN+ACK phase, ignore
1054 * timestamps of 0 or we could calculate a
1055 * huge RTT and blow up the retransmit timer.
1057 if ((to.to_flags & TOF_TS) != 0 &&
1059 if (!tp->t_rttlow ||
1060 tp->t_rttlow > ticks - to.to_tsecr)
1061 tp->t_rttlow = ticks - to.to_tsecr;
1063 ticks - to.to_tsecr + 1);
1064 } else if (tp->t_rtttime &&
1065 SEQ_GT(th->th_ack, tp->t_rtseq)) {
1066 if (!tp->t_rttlow ||
1067 tp->t_rttlow > ticks - tp->t_rtttime)
1068 tp->t_rttlow = ticks - tp->t_rtttime;
1070 ticks - tp->t_rtttime);
1072 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1073 acked = th->th_ack - tp->snd_una;
1074 tcpstat.tcps_rcvackpack++;
1075 tcpstat.tcps_rcvackbyte += acked;
1076 sbdrop(&so->so_snd, acked);
1077 if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1078 SEQ_LEQ(th->th_ack, tp->snd_recover))
1079 tp->snd_recover = th->th_ack - 1;
1080 tp->snd_una = th->th_ack;
1082 * pull snd_wl2 up to prevent seq wrap relative
1085 tp->snd_wl2 = th->th_ack;
1088 ND6_HINT(tp); /* some progress has been done */
1091 * If all outstanding data are acked, stop
1092 * retransmit timer, otherwise restart timer
1093 * using current (possibly backed-off) value.
1094 * If process is waiting for space,
1095 * wakeup/selwakeup/signal. If data
1096 * are ready to send, let tcp_output
1097 * decide between more output or persist.
1100 if (so->so_options & SO_DEBUG)
1101 tcp_trace(TA_INPUT, ostate, tp,
1102 (void *)tcp_saveipgen,
1106 if (tp->snd_una == tp->snd_max)
1107 tcp_timer_activate(tp, TT_REXMT, 0);
1108 else if (!tcp_timer_active(tp, TT_PERSIST))
1109 tcp_timer_activate(tp, TT_REXMT,
1113 if (so->so_snd.sb_cc)
1114 (void) tcp_output(tp);
1117 } else if (th->th_ack == tp->snd_una &&
1118 tlen <= sbspace(&so->so_rcv)) {
1119 int newsize = 0; /* automatic sockbuf scaling */
1121 KASSERT(headlocked, ("%s: headlocked", __func__));
1122 INP_INFO_WUNLOCK(&tcbinfo);
1125 * this is a pure, in-sequence data packet
1126 * with nothing on the reassembly queue and
1127 * we have enough buffer space to take it.
1129 /* Clean receiver SACK report if present */
1130 if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1131 tcp_clean_sackreport(tp);
1132 ++tcpstat.tcps_preddat;
1133 tp->rcv_nxt += tlen;
1135 * Pull snd_wl1 up to prevent seq wrap relative to
1138 tp->snd_wl1 = th->th_seq;
1140 * Pull rcv_up up to prevent seq wrap relative to
1143 tp->rcv_up = tp->rcv_nxt;
1144 tcpstat.tcps_rcvpack++;
1145 tcpstat.tcps_rcvbyte += tlen;
1146 ND6_HINT(tp); /* some progress has been done */
1148 if (so->so_options & SO_DEBUG)
1149 tcp_trace(TA_INPUT, ostate, tp,
1150 (void *)tcp_saveipgen, &tcp_savetcp, 0);
1153 * Automatic sizing of receive socket buffer. Often the send
1154 * buffer size is not optimally adjusted to the actual network
1155 * conditions at hand (delay bandwidth product). Setting the
1156 * buffer size too small limits throughput on links with high
1157 * bandwidth and high delay (eg. trans-continental/oceanic links).
1159 * On the receive side the socket buffer memory is only rarely
1160 * used to any significant extent. This allows us to be much
1161 * more aggressive in scaling the receive socket buffer. For
1162 * the case that the buffer space is actually used to a large
1163 * extent and we run out of kernel memory we can simply drop
1164 * the new segments; TCP on the sender will just retransmit it
1165 * later. Setting the buffer size too big may only consume too
1166 * much kernel memory if the application doesn't read() from
1167 * the socket or packet loss or reordering makes use of the
1170 * The criteria to step up the receive buffer one notch are:
1171 * 1. the number of bytes received during the time it takes
1172 * one timestamp to be reflected back to us (the RTT);
1173 * 2. received bytes per RTT is within seven eighth of the
1174 * current socket buffer size;
1175 * 3. receive buffer size has not hit maximal automatic size;
1177 * This algorithm does one step per RTT at most and only if
1178 * we receive a bulk stream w/o packet losses or reorderings.
1179 * Shrinking the buffer during idle times is not necessary as
1180 * it doesn't consume any memory when idle.
1182 * TODO: Only step up if the application is actually serving
1183 * the buffer to better manage the socket buffer resources.
1185 if (tcp_do_autorcvbuf &&
1187 (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1188 if (to.to_tsecr > tp->rfbuf_ts &&
1189 to.to_tsecr - tp->rfbuf_ts < hz) {
1191 (so->so_rcv.sb_hiwat / 8 * 7) &&
1192 so->so_rcv.sb_hiwat <
1193 tcp_autorcvbuf_max) {
1195 min(so->so_rcv.sb_hiwat +
1197 tcp_autorcvbuf_max);
1199 /* Start over with next RTT. */
1203 tp->rfbuf_cnt += tlen; /* add up */
1206 /* Add data to socket buffer. */
1207 SOCKBUF_LOCK(&so->so_rcv);
1208 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1212 * Set new socket buffer size.
1213 * Give up when limit is reached.
1216 if (!sbreserve_locked(&so->so_rcv,
1217 newsize, so, curthread))
1218 so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1219 m_adj(m, drop_hdrlen); /* delayed header drop */
1220 sbappendstream_locked(&so->so_rcv, m);
1222 sorwakeup_locked(so);
1223 if (DELAY_ACK(tp)) {
1224 tp->t_flags |= TF_DELACK;
1226 tp->t_flags |= TF_ACKNOW;
1234 * Calculate amount of space in receive window,
1235 * and then do TCP input processing.
1236 * Receive window is amount of space in rcv queue,
1237 * but not less than advertised window.
1239 win = sbspace(&so->so_rcv);
1242 tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1244 /* Reset receive buffer auto scaling when not in bulk receive mode. */
1248 switch (tp->t_state) {
1251 * If the state is SYN_RECEIVED:
1252 * if seg contains an ACK, but not for our SYN/ACK, send a RST.
1254 case TCPS_SYN_RECEIVED:
1255 if ((thflags & TH_ACK) &&
1256 (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1257 SEQ_GT(th->th_ack, tp->snd_max))) {
1258 rstreason = BANDLIM_RST_OPENPORT;
1264 * If the state is SYN_SENT:
1265 * if seg contains an ACK, but not for our SYN, drop the input.
1266 * if seg contains a RST, then drop the connection.
1267 * if seg does not contain SYN, then drop it.
1268 * Otherwise this is an acceptable SYN segment
1269 * initialize tp->rcv_nxt and tp->irs
1270 * if seg contains ack then advance tp->snd_una
1271 * if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1272 * arrange for segment to be acked (eventually)
1273 * continue processing rest of data/controls, beginning with URG
1276 if ((thflags & TH_ACK) &&
1277 (SEQ_LEQ(th->th_ack, tp->iss) ||
1278 SEQ_GT(th->th_ack, tp->snd_max))) {
1279 rstreason = BANDLIM_UNLIMITED;
1282 if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST))
1283 tp = tcp_drop(tp, ECONNREFUSED);
1284 if (thflags & TH_RST)
1286 if (!(thflags & TH_SYN))
1289 tp->irs = th->th_seq;
1291 if (thflags & TH_ACK) {
1292 tcpstat.tcps_connects++;
1296 mac_set_socket_peer_from_mbuf(m, so);
1299 /* Do window scaling on this connection? */
1300 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1301 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1302 tp->rcv_scale = tp->request_r_scale;
1304 tp->rcv_adv += tp->rcv_wnd;
1305 tp->snd_una++; /* SYN is acked */
1307 * If there's data, delay ACK; if there's also a FIN
1308 * ACKNOW will be turned on later.
1310 if (DELAY_ACK(tp) && tlen != 0)
1311 tcp_timer_activate(tp, TT_DELACK,
1314 tp->t_flags |= TF_ACKNOW;
1316 * Received <SYN,ACK> in SYN_SENT[*] state.
1318 * SYN_SENT --> ESTABLISHED
1319 * SYN_SENT* --> FIN_WAIT_1
1321 tp->t_starttime = ticks;
1322 if (tp->t_flags & TF_NEEDFIN) {
1323 tp->t_state = TCPS_FIN_WAIT_1;
1324 tp->t_flags &= ~TF_NEEDFIN;
1327 tp->t_state = TCPS_ESTABLISHED;
1328 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1332 * Received initial SYN in SYN-SENT[*] state =>
1333 * simultaneous open. If segment contains CC option
1334 * and there is a cached CC, apply TAO test.
1335 * If it succeeds, connection is * half-synchronized.
1336 * Otherwise, do 3-way handshake:
1337 * SYN-SENT -> SYN-RECEIVED
1338 * SYN-SENT* -> SYN-RECEIVED*
1339 * If there was no CC option, clear cached CC value.
1341 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1342 tcp_timer_activate(tp, TT_REXMT, 0);
1343 tp->t_state = TCPS_SYN_RECEIVED;
1346 KASSERT(headlocked, ("%s: trimthenstep6: head not locked",
1348 INP_LOCK_ASSERT(tp->t_inpcb);
1351 * Advance th->th_seq to correspond to first data byte.
1352 * If data, trim to stay within window,
1353 * dropping FIN if necessary.
1356 if (tlen > tp->rcv_wnd) {
1357 todrop = tlen - tp->rcv_wnd;
1361 tcpstat.tcps_rcvpackafterwin++;
1362 tcpstat.tcps_rcvbyteafterwin += todrop;
1364 tp->snd_wl1 = th->th_seq - 1;
1365 tp->rcv_up = th->th_seq;
1367 * Client side of transaction: already sent SYN and data.
1368 * If the remote host used T/TCP to validate the SYN,
1369 * our data will be ACK'd; if so, enter normal data segment
1370 * processing in the middle of step 5, ack processing.
1371 * Otherwise, goto step 6.
1373 if (thflags & TH_ACK)
1379 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1380 * do normal processing.
1382 * NB: Leftover from RFC1644 T/TCP. Cases to be reused later.
1386 break; /* continue normal processing */
1390 * States other than LISTEN or SYN_SENT.
1391 * First check the RST flag and sequence number since reset segments
1392 * are exempt from the timestamp and connection count tests. This
1393 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1394 * below which allowed reset segments in half the sequence space
1395 * to fall though and be processed (which gives forged reset
1396 * segments with a random sequence number a 50 percent chance of
1397 * killing a connection).
1398 * Then check timestamp, if present.
1399 * Then check the connection count, if present.
1400 * Then check that at least some bytes of segment are within
1401 * receive window. If segment begins before rcv_nxt,
1402 * drop leading data (and SYN); if nothing left, just ack.
1405 * If the RST bit is set, check the sequence number to see
1406 * if this is a valid reset segment.
1408 * In all states except SYN-SENT, all reset (RST) segments
1409 * are validated by checking their SEQ-fields. A reset is
1410 * valid if its sequence number is in the window.
1411 * Note: this does not take into account delayed ACKs, so
1412 * we should test against last_ack_sent instead of rcv_nxt.
1413 * The sequence number in the reset segment is normally an
1414 * echo of our outgoing acknowlegement numbers, but some hosts
1415 * send a reset with the sequence number at the rightmost edge
1416 * of our receive window, and we have to handle this case.
1417 * Note 2: Paul Watson's paper "Slipping in the Window" has shown
1418 * that brute force RST attacks are possible. To combat this,
1419 * we use a much stricter check while in the ESTABLISHED state,
1420 * only accepting RSTs where the sequence number is equal to
1421 * last_ack_sent. In all other states (the states in which a
1422 * RST is more likely), the more permissive check is used.
1423 * If we have multiple segments in flight, the intial reset
1424 * segment sequence numbers will be to the left of last_ack_sent,
1425 * but they will eventually catch up.
1426 * In any case, it never made sense to trim reset segments to
1427 * fit the receive window since RFC 1122 says:
1428 * 4.2.2.12 RST Segment: RFC-793 Section 3.4
1430 * A TCP SHOULD allow a received RST segment to include data.
1433 * It has been suggested that a RST segment could contain
1434 * ASCII text that encoded and explained the cause of the
1435 * RST. No standard has yet been established for such
1438 * If the reset segment passes the sequence number test examine
1440 * SYN_RECEIVED STATE:
1441 * If passive open, return to LISTEN state.
1442 * If active open, inform user that connection was refused.
1443 * ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1444 * Inform user that connection was reset, and close tcb.
1445 * CLOSING, LAST_ACK STATES:
1448 * Drop the segment - see Stevens, vol. 2, p. 964 and
1451 if (thflags & TH_RST) {
1452 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1453 SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1454 switch (tp->t_state) {
1456 case TCPS_SYN_RECEIVED:
1457 so->so_error = ECONNREFUSED;
1460 case TCPS_ESTABLISHED:
1461 if (tcp_insecure_rst == 0 &&
1462 !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
1463 SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
1464 !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
1465 SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
1466 tcpstat.tcps_badrst++;
1469 case TCPS_FIN_WAIT_1:
1470 case TCPS_FIN_WAIT_2:
1471 case TCPS_CLOSE_WAIT:
1472 so->so_error = ECONNRESET;
1474 tp->t_state = TCPS_CLOSED;
1475 tcpstat.tcps_drops++;
1476 KASSERT(headlocked, ("%s: trimthenstep6: "
1477 "tcp_close: head not locked", __func__));
1483 KASSERT(headlocked, ("%s: trimthenstep6: "
1484 "tcp_close.2: head not locked", __func__));
1493 * RFC 1323 PAWS: If we have a timestamp reply on this segment
1494 * and it's less than ts_recent, drop it.
1496 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
1497 TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1499 /* Check to see if ts_recent is over 24 days old. */
1500 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1502 * Invalidate ts_recent. If this segment updates
1503 * ts_recent, the age will be reset later and ts_recent
1504 * will get a valid value. If it does not, setting
1505 * ts_recent to zero will at least satisfy the
1506 * requirement that zero be placed in the timestamp
1507 * echo reply when ts_recent isn't valid. The
1508 * age isn't reset until we get a valid ts_recent
1509 * because we don't want out-of-order segments to be
1510 * dropped when ts_recent is old.
1514 tcpstat.tcps_rcvduppack++;
1515 tcpstat.tcps_rcvdupbyte += tlen;
1516 tcpstat.tcps_pawsdrop++;
1524 * In the SYN-RECEIVED state, validate that the packet belongs to
1525 * this connection before trimming the data to fit the receive
1526 * window. Check the sequence number versus IRS since we know
1527 * the sequence numbers haven't wrapped. This is a partial fix
1528 * for the "LAND" DoS attack.
1530 if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1531 rstreason = BANDLIM_RST_OPENPORT;
1535 todrop = tp->rcv_nxt - th->th_seq;
1537 if (thflags & TH_SYN) {
1547 * Following if statement from Stevens, vol. 2, p. 960.
1550 || (todrop == tlen && (thflags & TH_FIN) == 0)) {
1552 * Any valid FIN must be to the left of the window.
1553 * At this point the FIN must be a duplicate or out
1554 * of sequence; drop it.
1559 * Send an ACK to resynchronize and drop any data.
1560 * But keep on processing for RST or ACK.
1562 tp->t_flags |= TF_ACKNOW;
1564 tcpstat.tcps_rcvduppack++;
1565 tcpstat.tcps_rcvdupbyte += todrop;
1567 tcpstat.tcps_rcvpartduppack++;
1568 tcpstat.tcps_rcvpartdupbyte += todrop;
1570 drop_hdrlen += todrop; /* drop from the top afterwards */
1571 th->th_seq += todrop;
1573 if (th->th_urp > todrop)
1574 th->th_urp -= todrop;
1582 * If new data are received on a connection after the
1583 * user processes are gone, then RST the other end.
1585 if ((so->so_state & SS_NOFDREF) &&
1586 tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1587 KASSERT(headlocked, ("%s: trimthenstep6: tcp_close.3: head "
1588 "not locked", __func__));
1590 tcpstat.tcps_rcvafterclose++;
1591 rstreason = BANDLIM_UNLIMITED;
1596 * If segment ends after window, drop trailing data
1597 * (and PUSH and FIN); if nothing left, just ACK.
1599 todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
1601 tcpstat.tcps_rcvpackafterwin++;
1602 if (todrop >= tlen) {
1603 tcpstat.tcps_rcvbyteafterwin += tlen;
1605 * If window is closed can only take segments at
1606 * window edge, and have to drop data and PUSH from
1607 * incoming segments. Continue processing, but
1608 * remember to ack. Otherwise, drop segment
1611 if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1612 tp->t_flags |= TF_ACKNOW;
1613 tcpstat.tcps_rcvwinprobe++;
1617 tcpstat.tcps_rcvbyteafterwin += todrop;
1620 thflags &= ~(TH_PUSH|TH_FIN);
1624 * If last ACK falls within this segment's sequence numbers,
1625 * record its timestamp.
1627 * 1) That the test incorporates suggestions from the latest
1628 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1629 * 2) That updating only on newer timestamps interferes with
1630 * our earlier PAWS tests, so this check should be solely
1631 * predicated on the sequence space of this segment.
1632 * 3) That we modify the segment boundary check to be
1633 * Last.ACK.Sent <= SEG.SEQ + SEG.Len
1634 * instead of RFC1323's
1635 * Last.ACK.Sent < SEG.SEQ + SEG.Len,
1636 * This modified check allows us to overcome RFC1323's
1637 * limitations as described in Stevens TCP/IP Illustrated
1638 * Vol. 2 p.869. In such cases, we can still calculate the
1639 * RTT correctly when RCV.NXT == Last.ACK.Sent.
1641 if ((to.to_flags & TOF_TS) != 0 &&
1642 SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1643 SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
1644 ((thflags & (TH_SYN|TH_FIN)) != 0))) {
1645 tp->ts_recent_age = ticks;
1646 tp->ts_recent = to.to_tsval;
1650 * If a SYN is in the window, then this is an
1651 * error and we send an RST and drop the connection.
1653 if (thflags & TH_SYN) {
1654 KASSERT(headlocked, ("%s: tcp_drop: trimthenstep6: "
1655 "head not locked", __func__));
1656 tp = tcp_drop(tp, ECONNRESET);
1657 rstreason = BANDLIM_UNLIMITED;
1662 * If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
1663 * flag is on (half-synchronized state), then queue data for
1664 * later processing; else drop segment and return.
1666 if ((thflags & TH_ACK) == 0) {
1667 if (tp->t_state == TCPS_SYN_RECEIVED ||
1668 (tp->t_flags & TF_NEEDSYN))
1670 else if (tp->t_flags & TF_ACKNOW)
1679 switch (tp->t_state) {
1682 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
1683 * ESTABLISHED state and continue processing.
1684 * The ACK was checked above.
1686 case TCPS_SYN_RECEIVED:
1688 tcpstat.tcps_connects++;
1690 /* Do window scaling? */
1691 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1692 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1693 tp->rcv_scale = tp->request_r_scale;
1694 tp->snd_wnd = tiwin;
1698 * SYN-RECEIVED -> ESTABLISHED
1699 * SYN-RECEIVED* -> FIN-WAIT-1
1701 tp->t_starttime = ticks;
1702 if (tp->t_flags & TF_NEEDFIN) {
1703 tp->t_state = TCPS_FIN_WAIT_1;
1704 tp->t_flags &= ~TF_NEEDFIN;
1706 tp->t_state = TCPS_ESTABLISHED;
1707 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
1710 * If segment contains data or ACK, will call tcp_reass()
1711 * later; if not, do so now to pass queued data to user.
1713 if (tlen == 0 && (thflags & TH_FIN) == 0)
1714 (void) tcp_reass(tp, (struct tcphdr *)0, 0,
1716 tp->snd_wl1 = th->th_seq - 1;
1720 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1721 * ACKs. If the ack is in the range
1722 * tp->snd_una < th->th_ack <= tp->snd_max
1723 * then advance tp->snd_una to th->th_ack and drop
1724 * data from the retransmission queue. If this ACK reflects
1725 * more up to date window information we update our window information.
1727 case TCPS_ESTABLISHED:
1728 case TCPS_FIN_WAIT_1:
1729 case TCPS_FIN_WAIT_2:
1730 case TCPS_CLOSE_WAIT:
1733 if (SEQ_GT(th->th_ack, tp->snd_max)) {
1734 tcpstat.tcps_rcvacktoomuch++;
1737 if ((tp->t_flags & TF_SACK_PERMIT) &&
1738 ((to.to_flags & TOF_SACK) ||
1739 !TAILQ_EMPTY(&tp->snd_holes)))
1740 tcp_sack_doack(tp, &to, th->th_ack);
1741 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1742 if (tlen == 0 && tiwin == tp->snd_wnd) {
1743 tcpstat.tcps_rcvdupack++;
1745 * If we have outstanding data (other than
1746 * a window probe), this is a completely
1747 * duplicate ack (ie, window info didn't
1748 * change), the ack is the biggest we've
1749 * seen and we've seen exactly our rexmt
1750 * threshhold of them, assume a packet
1751 * has been dropped and retransmit it.
1752 * Kludge snd_nxt & the congestion
1753 * window so we send only this one
1756 * We know we're losing at the current
1757 * window size so do congestion avoidance
1758 * (set ssthresh to half the current window
1759 * and pull our congestion window back to
1760 * the new ssthresh).
1762 * Dup acks mean that packets have left the
1763 * network (they're now cached at the receiver)
1764 * so bump cwnd by the amount in the receiver
1765 * to keep a constant cwnd packets in the
1768 if (!tcp_timer_active(tp, TT_REXMT) ||
1769 th->th_ack != tp->snd_una)
1771 else if (++tp->t_dupacks > tcprexmtthresh ||
1773 (tp->t_flags & TF_SACK_PERMIT)) &&
1774 IN_FASTRECOVERY(tp))) {
1775 if ((tp->t_flags & TF_SACK_PERMIT) &&
1776 IN_FASTRECOVERY(tp)) {
1780 * Compute the amount of data in flight first.
1781 * We can inject new data into the pipe iff
1782 * we have less than 1/2 the original window's
1783 * worth of data in flight.
1785 awnd = (tp->snd_nxt - tp->snd_fack) +
1786 tp->sackhint.sack_bytes_rexmit;
1787 if (awnd < tp->snd_ssthresh) {
1788 tp->snd_cwnd += tp->t_maxseg;
1789 if (tp->snd_cwnd > tp->snd_ssthresh)
1790 tp->snd_cwnd = tp->snd_ssthresh;
1793 tp->snd_cwnd += tp->t_maxseg;
1794 (void) tcp_output(tp);
1796 } else if (tp->t_dupacks == tcprexmtthresh) {
1797 tcp_seq onxt = tp->snd_nxt;
1801 * If we're doing sack, check to
1802 * see if we're already in sack
1803 * recovery. If we're not doing sack,
1804 * check to see if we're in newreno
1807 if (tp->t_flags & TF_SACK_PERMIT) {
1808 if (IN_FASTRECOVERY(tp)) {
1812 } else if (tcp_do_newreno) {
1813 if (SEQ_LEQ(th->th_ack,
1819 win = min(tp->snd_wnd, tp->snd_cwnd) /
1823 tp->snd_ssthresh = win * tp->t_maxseg;
1824 ENTER_FASTRECOVERY(tp);
1825 tp->snd_recover = tp->snd_max;
1826 tcp_timer_activate(tp, TT_REXMT, 0);
1828 if (tp->t_flags & TF_SACK_PERMIT) {
1829 tcpstat.tcps_sack_recovery_episode++;
1830 tp->sack_newdata = tp->snd_nxt;
1831 tp->snd_cwnd = tp->t_maxseg;
1832 (void) tcp_output(tp);
1835 tp->snd_nxt = th->th_ack;
1836 tp->snd_cwnd = tp->t_maxseg;
1837 (void) tcp_output(tp);
1838 KASSERT(tp->snd_limited <= 2,
1839 ("%s: tp->snd_limited too big",
1841 tp->snd_cwnd = tp->snd_ssthresh +
1843 (tp->t_dupacks - tp->snd_limited);
1844 if (SEQ_GT(onxt, tp->snd_nxt))
1847 } else if (tcp_do_rfc3042) {
1848 u_long oldcwnd = tp->snd_cwnd;
1849 tcp_seq oldsndmax = tp->snd_max;
1852 KASSERT(tp->t_dupacks == 1 ||
1854 ("%s: dupacks not 1 or 2",
1856 if (tp->t_dupacks == 1)
1857 tp->snd_limited = 0;
1859 (tp->snd_nxt - tp->snd_una) +
1860 (tp->t_dupacks - tp->snd_limited) *
1862 (void) tcp_output(tp);
1863 sent = tp->snd_max - oldsndmax;
1864 if (sent > tp->t_maxseg) {
1865 KASSERT((tp->t_dupacks == 2 &&
1866 tp->snd_limited == 0) ||
1867 (sent == tp->t_maxseg + 1 &&
1868 tp->t_flags & TF_SENTFIN),
1869 ("%s: sent too much",
1871 tp->snd_limited = 2;
1872 } else if (sent > 0)
1874 tp->snd_cwnd = oldcwnd;
1882 KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
1883 ("%s: th_ack <= snd_una", __func__));
1886 * If the congestion window was inflated to account
1887 * for the other side's cached packets, retract it.
1889 if (tcp_do_newreno || (tp->t_flags & TF_SACK_PERMIT)) {
1890 if (IN_FASTRECOVERY(tp)) {
1891 if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1892 if (tp->t_flags & TF_SACK_PERMIT)
1893 tcp_sack_partialack(tp, th);
1895 tcp_newreno_partial_ack(tp, th);
1898 * Out of fast recovery.
1899 * Window inflation should have left us
1900 * with approximately snd_ssthresh
1902 * But in case we would be inclined to
1903 * send a burst, better to do it via
1904 * the slow start mechanism.
1906 if (SEQ_GT(th->th_ack +
1909 tp->snd_cwnd = tp->snd_max -
1913 tp->snd_cwnd = tp->snd_ssthresh;
1917 if (tp->t_dupacks >= tcprexmtthresh &&
1918 tp->snd_cwnd > tp->snd_ssthresh)
1919 tp->snd_cwnd = tp->snd_ssthresh;
1923 * If we reach this point, ACK is not a duplicate,
1924 * i.e., it ACKs something we sent.
1926 if (tp->t_flags & TF_NEEDSYN) {
1928 * T/TCP: Connection was half-synchronized, and our
1929 * SYN has been ACK'd (so connection is now fully
1930 * synchronized). Go to non-starred state,
1931 * increment snd_una for ACK of SYN, and check if
1932 * we can do window scaling.
1934 tp->t_flags &= ~TF_NEEDSYN;
1936 /* Do window scaling? */
1937 if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1938 (TF_RCVD_SCALE|TF_REQ_SCALE)) {
1939 tp->rcv_scale = tp->request_r_scale;
1940 /* Send window already scaled. */
1945 KASSERT(headlocked, ("%s: process_ACK: head not locked",
1947 INP_LOCK_ASSERT(tp->t_inpcb);
1949 acked = th->th_ack - tp->snd_una;
1950 tcpstat.tcps_rcvackpack++;
1951 tcpstat.tcps_rcvackbyte += acked;
1954 * If we just performed our first retransmit, and the ACK
1955 * arrives within our recovery window, then it was a mistake
1956 * to do the retransmit in the first place. Recover our
1957 * original cwnd and ssthresh, and proceed to transmit where
1960 if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
1961 ++tcpstat.tcps_sndrexmitbad;
1962 tp->snd_cwnd = tp->snd_cwnd_prev;
1963 tp->snd_ssthresh = tp->snd_ssthresh_prev;
1964 tp->snd_recover = tp->snd_recover_prev;
1965 if (tp->t_flags & TF_WASFRECOVERY)
1966 ENTER_FASTRECOVERY(tp);
1967 tp->snd_nxt = tp->snd_max;
1968 tp->t_badrxtwin = 0; /* XXX probably not required */
1972 * If we have a timestamp reply, update smoothed
1973 * round trip time. If no timestamp is present but
1974 * transmit timer is running and timed sequence
1975 * number was acked, update smoothed round trip time.
1976 * Since we now have an rtt measurement, cancel the
1977 * timer backoff (cf., Phil Karn's retransmit alg.).
1978 * Recompute the initial retransmit timer.
1980 * Some boxes send broken timestamp replies
1981 * during the SYN+ACK phase, ignore
1982 * timestamps of 0 or we could calculate a
1983 * huge RTT and blow up the retransmit timer.
1985 if ((to.to_flags & TOF_TS) != 0 &&
1987 if (!tp->t_rttlow || tp->t_rttlow > ticks - to.to_tsecr)
1988 tp->t_rttlow = ticks - to.to_tsecr;
1989 tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
1990 } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
1991 if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
1992 tp->t_rttlow = ticks - tp->t_rtttime;
1993 tcp_xmit_timer(tp, ticks - tp->t_rtttime);
1995 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1998 * If all outstanding data is acked, stop retransmit
1999 * timer and remember to restart (more output or persist).
2000 * If there is more data to be acked, restart retransmit
2001 * timer, using current (possibly backed-off) value.
2003 if (th->th_ack == tp->snd_max) {
2004 tcp_timer_activate(tp, TT_REXMT, 0);
2006 } else if (!tcp_timer_active(tp, TT_PERSIST))
2007 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2010 * If no data (only SYN) was ACK'd,
2011 * skip rest of ACK processing.
2017 * When new data is acked, open the congestion window.
2018 * If the window gives us less than ssthresh packets
2019 * in flight, open exponentially (maxseg per packet).
2020 * Otherwise open linearly: maxseg per window
2021 * (maxseg^2 / cwnd per packet).
2023 if ((!tcp_do_newreno && !(tp->t_flags & TF_SACK_PERMIT)) ||
2024 !IN_FASTRECOVERY(tp)) {
2025 u_int cw = tp->snd_cwnd;
2026 u_int incr = tp->t_maxseg;
2027 if (cw > tp->snd_ssthresh)
2028 incr = incr * incr / cw;
2029 tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
2031 SOCKBUF_LOCK(&so->so_snd);
2032 if (acked > so->so_snd.sb_cc) {
2033 tp->snd_wnd -= so->so_snd.sb_cc;
2034 sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2037 sbdrop_locked(&so->so_snd, acked);
2038 tp->snd_wnd -= acked;
2041 sowwakeup_locked(so);
2042 /* detect una wraparound */
2043 if ((tcp_do_newreno || (tp->t_flags & TF_SACK_PERMIT)) &&
2044 !IN_FASTRECOVERY(tp) &&
2045 SEQ_GT(tp->snd_una, tp->snd_recover) &&
2046 SEQ_LEQ(th->th_ack, tp->snd_recover))
2047 tp->snd_recover = th->th_ack - 1;
2048 if ((tcp_do_newreno || (tp->t_flags & TF_SACK_PERMIT)) &&
2049 IN_FASTRECOVERY(tp) &&
2050 SEQ_GEQ(th->th_ack, tp->snd_recover))
2051 EXIT_FASTRECOVERY(tp);
2052 tp->snd_una = th->th_ack;
2053 if (tp->t_flags & TF_SACK_PERMIT) {
2054 if (SEQ_GT(tp->snd_una, tp->snd_recover))
2055 tp->snd_recover = tp->snd_una;
2057 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2058 tp->snd_nxt = tp->snd_una;
2060 switch (tp->t_state) {
2063 * In FIN_WAIT_1 STATE in addition to the processing
2064 * for the ESTABLISHED state if our FIN is now acknowledged
2065 * then enter FIN_WAIT_2.
2067 case TCPS_FIN_WAIT_1:
2068 if (ourfinisacked) {
2070 * If we can't receive any more
2071 * data, then closing user can proceed.
2072 * Starting the timer is contrary to the
2073 * specification, but if we don't get a FIN
2074 * we'll hang forever.
2077 * we should release the tp also, and use a
2080 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2083 soisdisconnected(so);
2084 timeout = (tcp_fast_finwait2_recycle) ?
2085 tcp_finwait2_timeout : tcp_maxidle;
2086 tcp_timer_activate(tp, TT_2MSL, timeout);
2088 tp->t_state = TCPS_FIN_WAIT_2;
2093 * In CLOSING STATE in addition to the processing for
2094 * the ESTABLISHED state if the ACK acknowledges our FIN
2095 * then enter the TIME-WAIT state, otherwise ignore
2099 if (ourfinisacked) {
2100 KASSERT(headlocked, ("%s: process_ACK: "
2101 "head not locked", __func__));
2103 INP_INFO_WUNLOCK(&tcbinfo);
2111 * In LAST_ACK, we may still be waiting for data to drain
2112 * and/or to be acked, as well as for the ack of our FIN.
2113 * If our FIN is now acknowledged, delete the TCB,
2114 * enter the closed state and return.
2117 if (ourfinisacked) {
2118 KASSERT(headlocked, ("%s: process_ACK: "
2119 "tcp_close: head not locked", __func__));
2128 KASSERT(headlocked, ("%s: step6: head not locked", __func__));
2129 INP_LOCK_ASSERT(tp->t_inpcb);
2132 * Update window information.
2133 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2135 if ((thflags & TH_ACK) &&
2136 (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2137 (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2138 (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2139 /* keep track of pure window updates */
2141 tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2142 tcpstat.tcps_rcvwinupd++;
2143 tp->snd_wnd = tiwin;
2144 tp->snd_wl1 = th->th_seq;
2145 tp->snd_wl2 = th->th_ack;
2146 if (tp->snd_wnd > tp->max_sndwnd)
2147 tp->max_sndwnd = tp->snd_wnd;
2152 * Process segments with URG.
2154 if ((thflags & TH_URG) && th->th_urp &&
2155 TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2157 * This is a kludge, but if we receive and accept
2158 * random urgent pointers, we'll crash in
2159 * soreceive. It's hard to imagine someone
2160 * actually wanting to send this much urgent data.
2162 SOCKBUF_LOCK(&so->so_rcv);
2163 if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2164 th->th_urp = 0; /* XXX */
2165 thflags &= ~TH_URG; /* XXX */
2166 SOCKBUF_UNLOCK(&so->so_rcv); /* XXX */
2167 goto dodata; /* XXX */
2170 * If this segment advances the known urgent pointer,
2171 * then mark the data stream. This should not happen
2172 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2173 * a FIN has been received from the remote side.
2174 * In these states we ignore the URG.
2176 * According to RFC961 (Assigned Protocols),
2177 * the urgent pointer points to the last octet
2178 * of urgent data. We continue, however,
2179 * to consider it to indicate the first octet
2180 * of data past the urgent section as the original
2181 * spec states (in one of two places).
2183 if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2184 tp->rcv_up = th->th_seq + th->th_urp;
2185 so->so_oobmark = so->so_rcv.sb_cc +
2186 (tp->rcv_up - tp->rcv_nxt) - 1;
2187 if (so->so_oobmark == 0)
2188 so->so_rcv.sb_state |= SBS_RCVATMARK;
2190 tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2192 SOCKBUF_UNLOCK(&so->so_rcv);
2194 * Remove out of band data so doesn't get presented to user.
2195 * This can happen independent of advancing the URG pointer,
2196 * but if two URG's are pending at once, some out-of-band
2197 * data may creep in... ick.
2199 if (th->th_urp <= (u_long)tlen &&
2200 !(so->so_options & SO_OOBINLINE)) {
2201 /* hdr drop is delayed */
2202 tcp_pulloutofband(so, th, m, drop_hdrlen);
2206 * If no out of band data is expected,
2207 * pull receive urgent pointer along
2208 * with the receive window.
2210 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2211 tp->rcv_up = tp->rcv_nxt;
2214 KASSERT(headlocked, ("%s: dodata: head not locked", __func__));
2215 INP_LOCK_ASSERT(tp->t_inpcb);
2218 * Process the segment text, merging it into the TCP sequencing queue,
2219 * and arranging for acknowledgment of receipt if necessary.
2220 * This process logically involves adjusting tp->rcv_wnd as data
2221 * is presented to the user (this happens in tcp_usrreq.c,
2222 * case PRU_RCVD). If a FIN has already been received on this
2223 * connection then we just ignore the text.
2225 if ((tlen || (thflags & TH_FIN)) &&
2226 TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2227 tcp_seq save_start = th->th_seq;
2228 tcp_seq save_end = th->th_seq + tlen;
2229 m_adj(m, drop_hdrlen); /* delayed header drop */
2231 * Insert segment which includes th into TCP reassembly queue
2232 * with control block tp. Set thflags to whether reassembly now
2233 * includes a segment with FIN. This handles the common case
2234 * inline (segment is the next to be received on an established
2235 * connection, and the queue is empty), avoiding linkage into
2236 * and removal from the queue and repetition of various
2238 * Set DELACK for segments received in order, but ack
2239 * immediately when segments are out of order (so
2240 * fast retransmit can work).
2242 if (th->th_seq == tp->rcv_nxt &&
2243 LIST_EMPTY(&tp->t_segq) &&
2244 TCPS_HAVEESTABLISHED(tp->t_state)) {
2246 tp->t_flags |= TF_DELACK;
2248 tp->t_flags |= TF_ACKNOW;
2249 tp->rcv_nxt += tlen;
2250 thflags = th->th_flags & TH_FIN;
2251 tcpstat.tcps_rcvpack++;
2252 tcpstat.tcps_rcvbyte += tlen;
2254 SOCKBUF_LOCK(&so->so_rcv);
2255 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2258 sbappendstream_locked(&so->so_rcv, m);
2259 sorwakeup_locked(so);
2261 thflags = tcp_reass(tp, th, &tlen, m);
2262 tp->t_flags |= TF_ACKNOW;
2264 if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
2265 tcp_update_sack_list(tp, save_start, save_end);
2268 * Note the amount of data that peer has sent into
2269 * our window, in order to estimate the sender's
2273 len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2281 * If FIN is received ACK the FIN and let the user know
2282 * that the connection is closing.
2284 if (thflags & TH_FIN) {
2285 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2288 * If connection is half-synchronized
2289 * (ie NEEDSYN flag on) then delay ACK,
2290 * so it may be piggybacked when SYN is sent.
2291 * Otherwise, since we received a FIN then no
2292 * more input can be expected, send ACK now.
2294 if (tp->t_flags & TF_NEEDSYN)
2295 tp->t_flags |= TF_DELACK;
2297 tp->t_flags |= TF_ACKNOW;
2300 switch (tp->t_state) {
2303 * In SYN_RECEIVED and ESTABLISHED STATES
2304 * enter the CLOSE_WAIT state.
2306 case TCPS_SYN_RECEIVED:
2307 tp->t_starttime = ticks;
2309 case TCPS_ESTABLISHED:
2310 tp->t_state = TCPS_CLOSE_WAIT;
2314 * If still in FIN_WAIT_1 STATE FIN has not been acked so
2315 * enter the CLOSING state.
2317 case TCPS_FIN_WAIT_1:
2318 tp->t_state = TCPS_CLOSING;
2322 * In FIN_WAIT_2 state enter the TIME_WAIT state,
2323 * starting the time-wait timer, turning off the other
2326 case TCPS_FIN_WAIT_2:
2327 KASSERT(headlocked == 1, ("%s: dodata: "
2328 "TCP_FIN_WAIT_2: head not locked", __func__));
2330 INP_INFO_WUNLOCK(&tcbinfo);
2334 INP_INFO_WUNLOCK(&tcbinfo);
2337 if (so->so_options & SO_DEBUG)
2338 tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2343 * Return any desired output.
2345 if (needoutput || (tp->t_flags & TF_ACKNOW))
2346 (void) tcp_output(tp);
2349 KASSERT(headlocked == 0, ("%s: check_delack: head locked",
2351 INP_INFO_UNLOCK_ASSERT(&tcbinfo);
2352 INP_LOCK_ASSERT(tp->t_inpcb);
2353 if (tp->t_flags & TF_DELACK) {
2354 tp->t_flags &= ~TF_DELACK;
2355 tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
2357 INP_UNLOCK(tp->t_inpcb);
2361 KASSERT(headlocked, ("%s: dropafterack: head not locked", __func__));
2363 * Generate an ACK dropping incoming segment if it occupies
2364 * sequence space, where the ACK reflects our state.
2366 * We can now skip the test for the RST flag since all
2367 * paths to this code happen after packets containing
2368 * RST have been dropped.
2370 * In the SYN-RECEIVED state, don't send an ACK unless the
2371 * segment we received passes the SYN-RECEIVED ACK test.
2372 * If it fails send a RST. This breaks the loop in the
2373 * "LAND" DoS attack, and also prevents an ACK storm
2374 * between two listening ports that have been sent forged
2375 * SYN segments, each with the source address of the other.
2377 if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2378 (SEQ_GT(tp->snd_una, th->th_ack) ||
2379 SEQ_GT(th->th_ack, tp->snd_max)) ) {
2380 rstreason = BANDLIM_RST_OPENPORT;
2384 if (so->so_options & SO_DEBUG)
2385 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2388 KASSERT(headlocked, ("%s: headlocked should be 1", __func__));
2389 INP_INFO_WUNLOCK(&tcbinfo);
2390 tp->t_flags |= TF_ACKNOW;
2391 (void) tcp_output(tp);
2392 INP_UNLOCK(tp->t_inpcb);
2397 KASSERT(headlocked, ("%s: dropwithreset: head not locked", __func__));
2399 tcp_dropwithreset(m, th, tp, tlen, rstreason);
2402 INP_UNLOCK(tp->t_inpcb);
2404 INP_INFO_WUNLOCK(&tcbinfo);
2409 * Drop space held by incoming segment and return.
2412 if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2413 tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2417 INP_UNLOCK(tp->t_inpcb);
2419 INP_INFO_WUNLOCK(&tcbinfo);
2425 * Issue RST and make ACK acceptable to originator of segment.
2426 * The mbuf must still include the original packet header.
2430 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
2431 int tlen, int rstreason)
2435 struct ip6_hdr *ip6;
2437 /* Don't bother if destination was broadcast/multicast. */
2438 if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
2441 if (mtod(m, struct ip *)->ip_v == 6) {
2442 ip6 = mtod(m, struct ip6_hdr *);
2443 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2444 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2446 /* IPv6 anycast check is done at tcp6_input() */
2450 ip = mtod(m, struct ip *);
2451 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2452 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2453 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2454 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2458 /* Perform bandwidth limiting. */
2459 if (badport_bandlim(rstreason) < 0)
2462 /* tcp_respond consumes the mbuf chain. */
2463 if (th->th_flags & TH_ACK) {
2464 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
2465 th->th_ack, TH_RST);
2467 if (th->th_flags & TH_SYN)
2469 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
2470 (tcp_seq)0, TH_RST|TH_ACK);
2479 * Parse TCP options and place in tcpopt.
2482 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
2487 for (; cnt > 0; cnt -= optlen, cp += optlen) {
2489 if (opt == TCPOPT_EOL)
2491 if (opt == TCPOPT_NOP)
2497 if (optlen < 2 || optlen > cnt)
2502 if (optlen != TCPOLEN_MAXSEG)
2504 if (!(flags & TO_SYN))
2506 to->to_flags |= TOF_MSS;
2507 bcopy((char *)cp + 2,
2508 (char *)&to->to_mss, sizeof(to->to_mss));
2509 to->to_mss = ntohs(to->to_mss);
2512 if (optlen != TCPOLEN_WINDOW)
2514 if (!(flags & TO_SYN))
2516 to->to_flags |= TOF_SCALE;
2517 to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
2519 case TCPOPT_TIMESTAMP:
2520 if (optlen != TCPOLEN_TIMESTAMP)
2522 to->to_flags |= TOF_TS;
2523 bcopy((char *)cp + 2,
2524 (char *)&to->to_tsval, sizeof(to->to_tsval));
2525 to->to_tsval = ntohl(to->to_tsval);
2526 bcopy((char *)cp + 6,
2527 (char *)&to->to_tsecr, sizeof(to->to_tsecr));
2528 to->to_tsecr = ntohl(to->to_tsecr);
2530 #ifdef TCP_SIGNATURE
2532 * XXX In order to reply to a host which has set the
2533 * TCP_SIGNATURE option in its initial SYN, we have to
2534 * record the fact that the option was observed here
2535 * for the syncache code to perform the correct response.
2537 case TCPOPT_SIGNATURE:
2538 if (optlen != TCPOLEN_SIGNATURE)
2540 to->to_flags |= TOF_SIGNATURE;
2541 to->to_signature = cp + 2;
2544 case TCPOPT_SACK_PERMITTED:
2545 if (optlen != TCPOLEN_SACK_PERMITTED)
2547 if (!(flags & TO_SYN))
2551 to->to_flags |= TOF_SACKPERM;
2554 if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
2558 to->to_flags |= TOF_SACK;
2559 to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
2560 to->to_sacks = cp + 2;
2561 tcpstat.tcps_sack_rcv_blocks++;
2570 * Pull out of band byte out of a segment so
2571 * it doesn't appear in the user's data queue.
2572 * It is still reflected in the segment length for
2573 * sequencing purposes.
2576 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
2579 int cnt = off + th->th_urp - 1;
2582 if (m->m_len > cnt) {
2583 char *cp = mtod(m, caddr_t) + cnt;
2584 struct tcpcb *tp = sototcpcb(so);
2587 tp->t_oobflags |= TCPOOB_HAVEDATA;
2588 bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
2590 if (m->m_flags & M_PKTHDR)
2599 panic("tcp_pulloutofband");
2603 * Collect new round-trip time estimate
2604 * and update averages and current timeout.
2607 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2611 INP_LOCK_ASSERT(tp->t_inpcb);
2613 tcpstat.tcps_rttupdated++;
2615 if (tp->t_srtt != 0) {
2617 * srtt is stored as fixed point with 5 bits after the
2618 * binary point (i.e., scaled by 8). The following magic
2619 * is equivalent to the smoothing algorithm in rfc793 with
2620 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2621 * point). Adjust rtt to origin 0.
2623 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2624 - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2626 if ((tp->t_srtt += delta) <= 0)
2630 * We accumulate a smoothed rtt variance (actually, a
2631 * smoothed mean difference), then set the retransmit
2632 * timer to smoothed rtt + 4 times the smoothed variance.
2633 * rttvar is stored as fixed point with 4 bits after the
2634 * binary point (scaled by 16). The following is
2635 * equivalent to rfc793 smoothing with an alpha of .75
2636 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces
2637 * rfc793's wired-in beta.
2641 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2642 if ((tp->t_rttvar += delta) <= 0)
2644 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2645 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2648 * No rtt measurement yet - use the unsmoothed rtt.
2649 * Set the variance to half the rtt (so our first
2650 * retransmit happens at 3*rtt).
2652 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2653 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2654 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2660 * the retransmit should happen at rtt + 4 * rttvar.
2661 * Because of the way we do the smoothing, srtt and rttvar
2662 * will each average +1/2 tick of bias. When we compute
2663 * the retransmit timer, we want 1/2 tick of rounding and
2664 * 1 extra tick because of +-1/2 tick uncertainty in the
2665 * firing of the timer. The bias will give us exactly the
2666 * 1.5 tick we need. But, because the bias is
2667 * statistical, we have to test that we don't drop below
2668 * the minimum feasible timer (which is 2 ticks).
2670 TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2671 max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2674 * We received an ack for a packet that wasn't retransmitted;
2675 * it is probably safe to discard any error indications we've
2676 * received recently. This isn't quite right, but close enough
2677 * for now (a route might have failed after we sent a segment,
2678 * and the return path might not be symmetrical).
2680 tp->t_softerror = 0;
2684 * Determine a reasonable value for maxseg size.
2685 * If the route is known, check route for mtu.
2686 * If none, use an mss that can be handled on the outgoing
2687 * interface without forcing IP to fragment; if bigger than
2688 * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2689 * to utilize large mbufs. If no route is found, route has no mtu,
2690 * or the destination isn't local, use a default, hopefully conservative
2691 * size (usually 512 or the default IP max size, but no more than the mtu
2692 * of the interface), as we can't discover anything about intervening
2693 * gateways or networks. We also initialize the congestion/slow start
2694 * window to be a single segment if the destination isn't local.
2695 * While looking at the routing entry, we also initialize other path-dependent
2696 * parameters from pre-set or cached values in the routing entry.
2698 * Also take into account the space needed for options that we
2699 * send regularly. Make maxseg shorter by that amount to assure
2700 * that we can send maxseg amount of data even when the options
2701 * are present. Store the upper limit of the length of options plus
2705 * In case of T/TCP, we call this routine during implicit connection
2706 * setup as well (offer = -1), to initialize maxseg from the cached
2709 * NOTE that this routine is only called when we process an incoming
2710 * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt().
2713 tcp_mss(struct tcpcb *tp, int offer)
2718 struct inpcb *inp = tp->t_inpcb;
2720 struct hc_metrics_lite metrics;
2721 int origoffer = offer;
2724 int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
2725 size_t min_protoh = isipv6 ?
2726 sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
2727 sizeof (struct tcpiphdr);
2729 const size_t min_protoh = sizeof(struct tcpiphdr);
2735 maxmtu = tcp_maxmtu6(&inp->inp_inc, &mtuflags);
2736 tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt;
2740 maxmtu = tcp_maxmtu(&inp->inp_inc, &mtuflags);
2741 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
2743 so = inp->inp_socket;
2746 * no route to sender, stay with default mss and return
2751 /* what have we got? */
2755 * Offer == 0 means that there was no MSS on the SYN
2756 * segment, in this case we use tcp_mssdflt.
2760 isipv6 ? tcp_v6mssdflt :
2767 * Offer == -1 means that we didn't receive SYN yet.
2773 * Prevent DoS attack with too small MSS. Round up
2774 * to at least minmss.
2776 offer = max(offer, tcp_minmss);
2778 * Sanity check: make sure that maxopd will be large
2779 * enough to allow some data on segments even if the
2780 * all the option space is used (40bytes). Otherwise
2781 * funny things may happen in tcp_output.
2783 offer = max(offer, 64);
2787 * rmx information is now retrieved from tcp_hostcache
2789 tcp_hc_get(&inp->inp_inc, &metrics);
2792 * if there's a discovered mtu int tcp hostcache, use it
2793 * else, use the link mtu.
2795 if (metrics.rmx_mtu)
2796 mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
2800 mss = maxmtu - min_protoh;
2801 if (!path_mtu_discovery &&
2802 !in6_localaddr(&inp->in6p_faddr))
2803 mss = min(mss, tcp_v6mssdflt);
2807 mss = maxmtu - min_protoh;
2808 if (!path_mtu_discovery &&
2809 !in_localaddr(inp->inp_faddr))
2810 mss = min(mss, tcp_mssdflt);
2813 mss = min(mss, offer);
2816 * maxopd stores the maximum length of data AND options
2817 * in a segment; maxseg is the amount of data in a normal
2818 * segment. We need to store this value (maxopd) apart
2819 * from maxseg, because now every segment carries options
2820 * and thus we normally have somewhat less data in segments.
2825 * origoffer==-1 indicates, that no segments were received yet.
2826 * In this case we just guess.
2828 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
2830 (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2831 mss -= TCPOLEN_TSTAMP_APPA;
2834 #if (MCLBYTES & (MCLBYTES - 1)) == 0
2836 mss &= ~(MCLBYTES-1);
2839 mss = mss / MCLBYTES * MCLBYTES;
2844 * If there's a pipesize, change the socket buffer to that size,
2845 * don't change if sb_hiwat is different than default (then it
2846 * has been changed on purpose with setsockopt).
2847 * Make the socket buffers an integral number of mss units;
2848 * if the mss is larger than the socket buffer, decrease the mss.
2850 SOCKBUF_LOCK(&so->so_snd);
2851 if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe)
2852 bufsize = metrics.rmx_sendpipe;
2854 bufsize = so->so_snd.sb_hiwat;
2858 bufsize = roundup(bufsize, mss);
2859 if (bufsize > sb_max)
2861 if (bufsize > so->so_snd.sb_hiwat)
2862 (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
2864 SOCKBUF_UNLOCK(&so->so_snd);
2867 SOCKBUF_LOCK(&so->so_rcv);
2868 if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe)
2869 bufsize = metrics.rmx_recvpipe;
2871 bufsize = so->so_rcv.sb_hiwat;
2872 if (bufsize > mss) {
2873 bufsize = roundup(bufsize, mss);
2874 if (bufsize > sb_max)
2876 if (bufsize > so->so_rcv.sb_hiwat)
2877 (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
2879 SOCKBUF_UNLOCK(&so->so_rcv);
2881 * While we're here, check the others too
2883 if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
2885 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2886 tcpstat.tcps_usedrtt++;
2887 if (metrics.rmx_rttvar) {
2888 tp->t_rttvar = metrics.rmx_rttvar;
2889 tcpstat.tcps_usedrttvar++;
2891 /* default variation is +- 1 rtt */
2893 tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2895 TCPT_RANGESET(tp->t_rxtcur,
2896 ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2897 tp->t_rttmin, TCPTV_REXMTMAX);
2899 if (metrics.rmx_ssthresh) {
2901 * There's some sort of gateway or interface
2902 * buffer limit on the path. Use this to set
2903 * the slow start threshhold, but set the
2904 * threshold to no less than 2*mss.
2906 tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh);
2907 tcpstat.tcps_usedssthresh++;
2909 if (metrics.rmx_bandwidth)
2910 tp->snd_bandwidth = metrics.rmx_bandwidth;
2913 * Set the slow-start flight size depending on whether this
2914 * is a local network or not.
2916 * Extend this so we cache the cwnd too and retrieve it here.
2917 * Make cwnd even bigger than RFC3390 suggests but only if we
2918 * have previous experience with the remote host. Be careful
2919 * not make cwnd bigger than remote receive window or our own
2920 * send socket buffer. Maybe put some additional upper bound
2921 * on the retrieved cwnd. Should do incremental updates to
2922 * hostcache when cwnd collapses so next connection doesn't
2923 * overloads the path again.
2925 * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
2926 * We currently check only in syncache_socket for that.
2928 #define TCP_METRICS_CWND
2929 #ifdef TCP_METRICS_CWND
2930 if (metrics.rmx_cwnd)
2931 tp->snd_cwnd = max(mss,
2932 min(metrics.rmx_cwnd / 2,
2933 min(tp->snd_wnd, so->so_snd.sb_hiwat)));
2937 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
2939 else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
2940 (!isipv6 && in_localaddr(inp->inp_faddr)))
2942 else if (in_localaddr(inp->inp_faddr))
2944 tp->snd_cwnd = mss * ss_fltsz_local;
2946 tp->snd_cwnd = mss * ss_fltsz;
2948 /* Check the interface for TSO capabilities. */
2949 if (mtuflags & CSUM_TSO)
2950 tp->t_flags |= TF_TSO;
2954 * Determine the MSS option to send on an outgoing SYN.
2957 tcp_mssopt(struct in_conninfo *inc)
2964 int isipv6 = inc->inc_isipv6 ? 1 : 0;
2967 KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
2971 mss = tcp_v6mssdflt;
2972 maxmtu = tcp_maxmtu6(inc, NULL);
2973 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
2974 min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
2979 maxmtu = tcp_maxmtu(inc, NULL);
2980 thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
2981 min_protoh = sizeof(struct tcpiphdr);
2983 if (maxmtu && thcmtu)
2984 mss = min(maxmtu, thcmtu) - min_protoh;
2985 else if (maxmtu || thcmtu)
2986 mss = max(maxmtu, thcmtu) - min_protoh;
2993 * On a partial ack arrives, force the retransmission of the
2994 * next unacknowledged segment. Do not clear tp->t_dupacks.
2995 * By setting snd_nxt to ti_ack, this forces retransmission timer to
2999 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3001 tcp_seq onxt = tp->snd_nxt;
3002 u_long ocwnd = tp->snd_cwnd;
3004 tcp_timer_activate(tp, TT_REXMT, 0);
3006 tp->snd_nxt = th->th_ack;
3008 * Set snd_cwnd to one segment beyond acknowledged offset.
3009 * (tp->snd_una has not yet been updated when this function is called.)
3011 tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
3012 tp->t_flags |= TF_ACKNOW;
3013 (void) tcp_output(tp);
3014 tp->snd_cwnd = ocwnd;
3015 if (SEQ_GT(onxt, tp->snd_nxt))
3018 * Partial window deflation. Relies on fact that tp->snd_una
3021 if (tp->snd_cwnd > th->th_ack - tp->snd_una)
3022 tp->snd_cwnd -= th->th_ack - tp->snd_una;
3025 tp->snd_cwnd += tp->t_maxseg;
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