2 * Copyright (c) 2002, 2003, 2004 Jeffrey M. Hsu. All rights reserved.
3 * Copyright (c) 2002, 2003, 2004 The DragonFly Project. All rights reserved.
5 * This code is derived from software contributed to The DragonFly Project
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
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15 * documentation and/or other materials provided with the distribution.
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17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
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63 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
66 * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
67 * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.38 2003/05/21 04:46:41 cjc Exp $
68 * $DragonFly: src/sys/netinet/tcp_input.c,v 1.68 2008/08/22 09:14:17 sephe Exp $
71 #include "opt_ipfw.h" /* for ipfw_fwd */
72 #include "opt_inet6.h"
73 #include "opt_ipsec.h"
74 #include "opt_tcpdebug.h"
75 #include "opt_tcp_input.h"
77 #include <sys/param.h>
78 #include <sys/systm.h>
79 #include <sys/kernel.h>
80 #include <sys/sysctl.h>
81 #include <sys/malloc.h>
83 #include <sys/proc.h> /* for proc0 declaration */
84 #include <sys/protosw.h>
85 #include <sys/socket.h>
86 #include <sys/socketvar.h>
87 #include <sys/syslog.h>
88 #include <sys/in_cksum.h>
90 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
91 #include <machine/stdarg.h>
94 #include <net/route.h>
96 #include <netinet/in.h>
97 #include <netinet/in_systm.h>
98 #include <netinet/ip.h>
99 #include <netinet/ip_icmp.h> /* for ICMP_BANDLIM */
100 #include <netinet/in_var.h>
101 #include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
102 #include <netinet/in_pcb.h>
103 #include <netinet/ip_var.h>
104 #include <netinet/ip6.h>
105 #include <netinet/icmp6.h>
106 #include <netinet6/nd6.h>
107 #include <netinet6/ip6_var.h>
108 #include <netinet6/in6_pcb.h>
109 #include <netinet/tcp.h>
110 #include <netinet/tcp_fsm.h>
111 #include <netinet/tcp_seq.h>
112 #include <netinet/tcp_timer.h>
113 #include <netinet/tcp_timer2.h>
114 #include <netinet/tcp_var.h>
115 #include <netinet6/tcp6_var.h>
116 #include <netinet/tcpip.h>
119 #include <netinet/tcp_debug.h>
121 u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
122 struct tcphdr tcp_savetcp;
126 #include <netproto/ipsec/ipsec.h>
127 #include <netproto/ipsec/ipsec6.h>
131 #include <netinet6/ipsec.h>
132 #include <netinet6/ipsec6.h>
133 #include <netproto/key/key.h>
136 MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
138 static int log_in_vain = 0;
139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
140 &log_in_vain, 0, "Log all incoming TCP connections");
142 static int blackhole = 0;
143 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
144 &blackhole, 0, "Do not send RST when dropping refused connections");
146 int tcp_delack_enabled = 1;
147 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
148 &tcp_delack_enabled, 0,
149 "Delay ACK to try and piggyback it onto a data packet");
151 #ifdef TCP_DROP_SYNFIN
152 static int drop_synfin = 0;
153 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
154 &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
157 static int tcp_do_limitedtransmit = 1;
158 SYSCTL_INT(_net_inet_tcp, OID_AUTO, limitedtransmit, CTLFLAG_RW,
159 &tcp_do_limitedtransmit, 0, "Enable RFC 3042 (Limited Transmit)");
161 static int tcp_do_early_retransmit = 1;
162 SYSCTL_INT(_net_inet_tcp, OID_AUTO, earlyretransmit, CTLFLAG_RW,
163 &tcp_do_early_retransmit, 0, "Early retransmit");
165 int tcp_aggregate_acks = 1;
166 SYSCTL_INT(_net_inet_tcp, OID_AUTO, aggregate_acks, CTLFLAG_RW,
167 &tcp_aggregate_acks, 0, "Aggregate built-up acks into one ack");
169 int tcp_do_rfc3390 = 1;
170 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
172 "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
174 static int tcp_do_eifel_detect = 1;
175 SYSCTL_INT(_net_inet_tcp, OID_AUTO, eifel, CTLFLAG_RW,
176 &tcp_do_eifel_detect, 0, "Eifel detection algorithm (RFC 3522)");
178 static int tcp_do_abc = 1;
179 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc, CTLFLAG_RW,
181 "TCP Appropriate Byte Counting (RFC 3465)");
184 * Define as tunable for easy testing with SACK on and off.
185 * Warning: do not change setting in the middle of an existing active TCP flow,
186 * else strange things might happen to that flow.
189 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW,
190 &tcp_do_sack, 0, "Enable SACK Algorithms");
192 int tcp_do_smartsack = 1;
193 SYSCTL_INT(_net_inet_tcp, OID_AUTO, smartsack, CTLFLAG_RW,
194 &tcp_do_smartsack, 0, "Enable Smart SACK Algorithms");
196 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
197 "TCP Segment Reassembly Queue");
199 int tcp_reass_maxseg = 0;
200 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RD,
201 &tcp_reass_maxseg, 0,
202 "Global maximum number of TCP Segments in Reassembly Queue");
204 int tcp_reass_qsize = 0;
205 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
207 "Global number of TCP Segments currently in Reassembly Queue");
209 static int tcp_reass_overflows = 0;
210 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
211 &tcp_reass_overflows, 0,
212 "Global number of TCP Segment Reassembly Queue Overflows");
214 int tcp_do_autorcvbuf = 1;
215 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
216 &tcp_do_autorcvbuf, 0, "Enable automatic receive buffer sizing");
218 int tcp_autorcvbuf_inc = 16*1024;
219 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
220 &tcp_autorcvbuf_inc, 0,
221 "Incrementor step size of automatic receive buffer");
223 int tcp_autorcvbuf_max = 2*1024*1024;
224 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
225 &tcp_autorcvbuf_max, 0, "Max size of automatic receive buffer");
228 static void tcp_dooptions(struct tcpopt *, u_char *, int, boolean_t);
229 static void tcp_pulloutofband(struct socket *,
230 struct tcphdr *, struct mbuf *, int);
231 static int tcp_reass(struct tcpcb *, struct tcphdr *, int *,
233 static void tcp_xmit_timer(struct tcpcb *, int);
234 static void tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *, int);
235 static void tcp_sack_rexmt(struct tcpcb *, struct tcphdr *);
237 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
239 #define ND6_HINT(tp) \
241 if ((tp) && (tp)->t_inpcb && \
242 ((tp)->t_inpcb->inp_vflag & INP_IPV6) && \
243 (tp)->t_inpcb->in6p_route.ro_rt) \
244 nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
251 * Indicate whether this ack should be delayed. We can delay the ack if
252 * - delayed acks are enabled and
253 * - there is no delayed ack timer in progress and
254 * - our last ack wasn't a 0-sized window. We never want to delay
255 * the ack that opens up a 0-sized window.
257 #define DELAY_ACK(tp) \
258 (tcp_delack_enabled && !tcp_callout_pending(tp, tp->tt_delack) && \
259 !(tp->t_flags & TF_RXWIN0SENT))
261 #define acceptable_window_update(tp, th, tiwin) \
262 (SEQ_LT(tp->snd_wl1, th->th_seq) || \
263 (tp->snd_wl1 == th->th_seq && \
264 (SEQ_LT(tp->snd_wl2, th->th_ack) || \
265 (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))
268 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
271 struct tseg_qent *p = NULL;
272 struct tseg_qent *te;
273 struct socket *so = tp->t_inpcb->inp_socket;
277 * Call with th == NULL after become established to
278 * force pre-ESTABLISHED data up to user socket.
284 * Limit the number of segments in the reassembly queue to prevent
285 * holding on to too many segments (and thus running out of mbufs).
286 * Make sure to let the missing segment through which caused this
287 * queue. Always keep one global queue entry spare to be able to
288 * process the missing segment.
290 if (th->th_seq != tp->rcv_nxt &&
291 tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
292 tcp_reass_overflows++;
293 tcpstat.tcps_rcvmemdrop++;
295 /* no SACK block to report */
296 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
300 /* Allocate a new queue entry. */
301 MALLOC(te, struct tseg_qent *, sizeof(struct tseg_qent), M_TSEGQ,
302 M_INTWAIT | M_NULLOK);
304 tcpstat.tcps_rcvmemdrop++;
306 /* no SACK block to report */
307 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
313 * Find a segment which begins after this one does.
315 LIST_FOREACH(q, &tp->t_segq, tqe_q) {
316 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
322 * If there is a preceding segment, it may provide some of
323 * our data already. If so, drop the data from the incoming
324 * segment. If it provides all of our data, drop us.
329 /* conversion to int (in i) handles seq wraparound */
330 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
331 if (i > 0) { /* overlaps preceding segment */
332 tp->t_flags |= (TF_DUPSEG | TF_ENCLOSESEG);
333 /* enclosing block starts w/ preceding segment */
334 tp->encloseblk.rblk_start = p->tqe_th->th_seq;
336 /* preceding encloses incoming segment */
337 tp->encloseblk.rblk_end = p->tqe_th->th_seq +
339 tcpstat.tcps_rcvduppack++;
340 tcpstat.tcps_rcvdupbyte += *tlenp;
345 * Try to present any queued data
346 * at the left window edge to the user.
347 * This is needed after the 3-WHS
350 goto present; /* ??? */
355 /* incoming segment end is enclosing block end */
356 tp->encloseblk.rblk_end = th->th_seq + *tlenp +
357 ((th->th_flags & TH_FIN) != 0);
358 /* trim end of reported D-SACK block */
359 tp->reportblk.rblk_end = th->th_seq;
362 tcpstat.tcps_rcvoopack++;
363 tcpstat.tcps_rcvoobyte += *tlenp;
366 * While we overlap succeeding segments trim them or,
367 * if they are completely covered, dequeue them.
370 tcp_seq_diff_t i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
371 tcp_seq qend = q->tqe_th->th_seq + q->tqe_len;
372 struct tseg_qent *nq;
376 if (!(tp->t_flags & TF_DUPSEG)) { /* first time through */
377 tp->t_flags |= (TF_DUPSEG | TF_ENCLOSESEG);
378 tp->encloseblk = tp->reportblk;
379 /* report trailing duplicate D-SACK segment */
380 tp->reportblk.rblk_start = q->tqe_th->th_seq;
382 if ((tp->t_flags & TF_ENCLOSESEG) &&
383 SEQ_GT(qend, tp->encloseblk.rblk_end)) {
384 /* extend enclosing block if one exists */
385 tp->encloseblk.rblk_end = qend;
387 if (i < q->tqe_len) {
388 q->tqe_th->th_seq += i;
394 nq = LIST_NEXT(q, tqe_q);
395 LIST_REMOVE(q, tqe_q);
402 /* Insert the new segment queue entry into place. */
405 te->tqe_len = *tlenp;
407 /* check if can coalesce with following segment */
408 if (q != NULL && (th->th_seq + *tlenp == q->tqe_th->th_seq)) {
409 tcp_seq tend = te->tqe_th->th_seq + te->tqe_len;
411 te->tqe_len += q->tqe_len;
412 if (q->tqe_th->th_flags & TH_FIN)
413 te->tqe_th->th_flags |= TH_FIN;
414 m_cat(te->tqe_m, q->tqe_m);
415 tp->encloseblk.rblk_end = tend;
417 * When not reporting a duplicate segment, use
418 * the larger enclosing block as the SACK block.
420 if (!(tp->t_flags & TF_DUPSEG))
421 tp->reportblk.rblk_end = tend;
422 LIST_REMOVE(q, tqe_q);
428 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
430 /* check if can coalesce with preceding segment */
431 if (p->tqe_th->th_seq + p->tqe_len == th->th_seq) {
432 p->tqe_len += te->tqe_len;
433 m_cat(p->tqe_m, te->tqe_m);
434 tp->encloseblk.rblk_start = p->tqe_th->th_seq;
436 * When not reporting a duplicate segment, use
437 * the larger enclosing block as the SACK block.
439 if (!(tp->t_flags & TF_DUPSEG))
440 tp->reportblk.rblk_start = p->tqe_th->th_seq;
444 LIST_INSERT_AFTER(p, te, tqe_q);
449 * Present data to user, advancing rcv_nxt through
450 * completed sequence space.
452 if (!TCPS_HAVEESTABLISHED(tp->t_state))
454 q = LIST_FIRST(&tp->t_segq);
455 if (q == NULL || q->tqe_th->th_seq != tp->rcv_nxt)
457 tp->rcv_nxt += q->tqe_len;
458 if (!(tp->t_flags & TF_DUPSEG)) {
459 /* no SACK block to report since ACK advanced */
460 tp->reportblk.rblk_start = tp->reportblk.rblk_end;
462 /* no enclosing block to report since ACK advanced */
463 tp->t_flags &= ~TF_ENCLOSESEG;
464 flags = q->tqe_th->th_flags & TH_FIN;
465 LIST_REMOVE(q, tqe_q);
466 KASSERT(LIST_EMPTY(&tp->t_segq) ||
467 LIST_FIRST(&tp->t_segq)->tqe_th->th_seq != tp->rcv_nxt,
468 ("segment not coalesced"));
469 if (so->so_state & SS_CANTRCVMORE)
472 ssb_appendstream(&so->so_rcv, q->tqe_m);
481 * TCP input routine, follows pages 65-76 of the
482 * protocol specification dated September, 1981 very closely.
486 tcp6_input(struct mbuf **mp, int *offp, int proto)
488 struct mbuf *m = *mp;
489 struct in6_ifaddr *ia6;
491 IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
494 * draft-itojun-ipv6-tcp-to-anycast
495 * better place to put this in?
497 ia6 = ip6_getdstifaddr(m);
498 if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
501 ip6 = mtod(m, struct ip6_hdr *);
502 icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
503 offsetof(struct ip6_hdr, ip6_dst));
504 return (IPPROTO_DONE);
507 tcp_input(m, *offp, proto);
508 return (IPPROTO_DONE);
513 tcp_input(struct mbuf *m, ...)
518 struct ip *ip = NULL;
520 struct inpcb *inp = NULL;
525 struct tcpcb *tp = NULL;
527 struct socket *so = 0;
529 boolean_t ourfinisacked, needoutput = FALSE;
532 struct tcpopt to; /* options in this segment */
533 struct sockaddr_in *next_hop = NULL;
534 int rstreason; /* For badport_bandlim accounting purposes */
536 struct ip6_hdr *ip6 = NULL;
540 const boolean_t isipv6 = FALSE;
547 off0 = __va_arg(ap, int);
548 proto = __va_arg(ap, int);
551 tcpstat.tcps_rcvtotal++;
553 if (m->m_pkthdr.fw_flags & IPFORWARD_MBUF_TAGGED) {
556 mtag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
557 KKASSERT(mtag != NULL);
558 next_hop = m_tag_data(mtag);
562 isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? TRUE : FALSE;
566 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
567 ip6 = mtod(m, struct ip6_hdr *);
568 tlen = (sizeof *ip6) + ntohs(ip6->ip6_plen) - off0;
569 if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
570 tcpstat.tcps_rcvbadsum++;
573 th = (struct tcphdr *)((caddr_t)ip6 + off0);
576 * Be proactive about unspecified IPv6 address in source.
577 * As we use all-zero to indicate unbounded/unconnected pcb,
578 * unspecified IPv6 address can be used to confuse us.
580 * Note that packets with unspecified IPv6 destination is
581 * already dropped in ip6_input.
583 if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
589 * Get IP and TCP header together in first mbuf.
590 * Note: IP leaves IP header in first mbuf.
592 if (off0 > sizeof(struct ip)) {
594 off0 = sizeof(struct ip);
596 /* already checked and pulled up in ip_demux() */
597 KASSERT(m->m_len >= sizeof(struct tcpiphdr),
598 ("TCP header not in one mbuf: m->m_len %d", m->m_len));
599 ip = mtod(m, struct ip *);
600 ipov = (struct ipovly *)ip;
601 th = (struct tcphdr *)((caddr_t)ip + off0);
604 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
605 if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
606 th->th_sum = m->m_pkthdr.csum_data;
608 th->th_sum = in_pseudo(ip->ip_src.s_addr,
610 htonl(m->m_pkthdr.csum_data +
613 th->th_sum ^= 0xffff;
616 * Checksum extended TCP header and data.
618 len = sizeof(struct ip) + tlen;
619 bzero(ipov->ih_x1, sizeof ipov->ih_x1);
620 ipov->ih_len = (u_short)tlen;
621 ipov->ih_len = htons(ipov->ih_len);
622 th->th_sum = in_cksum(m, len);
625 tcpstat.tcps_rcvbadsum++;
629 /* Re-initialization for later version check */
630 ip->ip_v = IPVERSION;
635 * Check that TCP offset makes sense,
636 * pull out TCP options and adjust length. XXX
638 off = th->th_off << 2;
639 /* already checked and pulled up in ip_demux() */
640 KASSERT(off >= sizeof(struct tcphdr) && off <= tlen,
641 ("bad TCP data offset %d (tlen %d)", off, tlen));
642 tlen -= off; /* tlen is used instead of ti->ti_len */
643 if (off > sizeof(struct tcphdr)) {
645 IP6_EXTHDR_CHECK(m, off0, off, );
646 ip6 = mtod(m, struct ip6_hdr *);
647 th = (struct tcphdr *)((caddr_t)ip6 + off0);
649 /* already pulled up in ip_demux() */
650 KASSERT(m->m_len >= sizeof(struct ip) + off,
651 ("TCP header and options not in one mbuf: "
652 "m_len %d, off %d", m->m_len, off));
654 optlen = off - sizeof(struct tcphdr);
655 optp = (u_char *)(th + 1);
657 thflags = th->th_flags;
659 #ifdef TCP_DROP_SYNFIN
661 * If the drop_synfin option is enabled, drop all packets with
662 * both the SYN and FIN bits set. This prevents e.g. nmap from
663 * identifying the TCP/IP stack.
665 * This is a violation of the TCP specification.
667 if (drop_synfin && (thflags & (TH_SYN | TH_FIN)) == (TH_SYN | TH_FIN))
672 * Convert TCP protocol specific fields to host format.
674 th->th_seq = ntohl(th->th_seq);
675 th->th_ack = ntohl(th->th_ack);
676 th->th_win = ntohs(th->th_win);
677 th->th_urp = ntohs(th->th_urp);
680 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
681 * until after ip6_savecontrol() is called and before other functions
682 * which don't want those proto headers.
683 * Because ip6_savecontrol() is going to parse the mbuf to
684 * search for data to be passed up to user-land, it wants mbuf
685 * parameters to be unchanged.
686 * XXX: the call of ip6_savecontrol() has been obsoleted based on
687 * latest version of the advanced API (20020110).
689 drop_hdrlen = off0 + off;
692 * Locate pcb for segment.
695 /* IPFIREWALL_FORWARD section */
696 if (next_hop != NULL && !isipv6) { /* IPv6 support is not there yet */
698 * Transparently forwarded. Pretend to be the destination.
699 * already got one like this?
701 cpu = mycpu->gd_cpuid;
702 inp = in_pcblookup_hash(&tcbinfo[cpu],
703 ip->ip_src, th->th_sport,
704 ip->ip_dst, th->th_dport,
705 0, m->m_pkthdr.rcvif);
708 * It's new. Try to find the ambushing socket.
712 * The rest of the ipfw code stores the port in
714 * (The IP address is still in network order.)
716 in_port_t dport = next_hop->sin_port ?
717 htons(next_hop->sin_port) :
720 cpu = tcp_addrcpu(ip->ip_src.s_addr, th->th_sport,
721 next_hop->sin_addr.s_addr, dport);
722 inp = in_pcblookup_hash(&tcbinfo[cpu],
723 ip->ip_src, th->th_sport,
724 next_hop->sin_addr, dport,
725 1, m->m_pkthdr.rcvif);
729 inp = in6_pcblookup_hash(&tcbinfo[0],
730 &ip6->ip6_src, th->th_sport,
731 &ip6->ip6_dst, th->th_dport,
732 1, m->m_pkthdr.rcvif);
734 cpu = mycpu->gd_cpuid;
735 inp = in_pcblookup_hash(&tcbinfo[cpu],
736 ip->ip_src, th->th_sport,
737 ip->ip_dst, th->th_dport,
738 1, m->m_pkthdr.rcvif);
743 * If the state is CLOSED (i.e., TCB does not exist) then
744 * all data in the incoming segment is discarded.
745 * If the TCB exists but is in CLOSED state, it is embryonic,
746 * but should either do a listen or a connect soon.
751 char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2];
753 char dbuf[sizeof "aaa.bbb.ccc.ddd"];
754 char sbuf[sizeof "aaa.bbb.ccc.ddd"];
758 strcat(dbuf, ip6_sprintf(&ip6->ip6_dst));
761 strcat(sbuf, ip6_sprintf(&ip6->ip6_src));
764 strcpy(dbuf, inet_ntoa(ip->ip_dst));
765 strcpy(sbuf, inet_ntoa(ip->ip_src));
767 switch (log_in_vain) {
769 if (!(thflags & TH_SYN))
773 "Connection attempt to TCP %s:%d "
774 "from %s:%d flags:0x%02x\n",
775 dbuf, ntohs(th->th_dport), sbuf,
776 ntohs(th->th_sport), thflags);
785 if (thflags & TH_SYN)
794 rstreason = BANDLIM_RST_CLOSEDPORT;
800 if (ipsec6_in_reject_so(m, inp->inp_socket)) {
801 ipsec6stat.in_polvio++;
805 if (ipsec4_in_reject_so(m, inp->inp_socket)) {
806 ipsecstat.in_polvio++;
813 if (ipsec6_in_reject(m, inp))
816 if (ipsec4_in_reject(m, inp))
820 /* Check the minimum TTL for socket. */
822 if ((isipv6 ? ip6->ip6_hlim : ip->ip_ttl) < inp->inp_ip_minttl)
828 rstreason = BANDLIM_RST_CLOSEDPORT;
831 if (tp->t_state <= TCPS_CLOSED)
834 /* Unscale the window into a 32-bit value. */
835 if (!(thflags & TH_SYN))
836 tiwin = th->th_win << tp->snd_scale;
840 so = inp->inp_socket;
843 if (so->so_options & SO_DEBUG) {
844 ostate = tp->t_state;
846 bcopy(ip6, tcp_saveipgen, sizeof(*ip6));
848 bcopy(ip, tcp_saveipgen, sizeof(*ip));
853 bzero(&to, sizeof to);
855 if (so->so_options & SO_ACCEPTCONN) {
856 struct in_conninfo inc;
859 inc.inc_isipv6 = (isipv6 == TRUE);
862 inc.inc6_faddr = ip6->ip6_src;
863 inc.inc6_laddr = ip6->ip6_dst;
864 inc.inc6_route.ro_rt = NULL; /* XXX */
866 inc.inc_faddr = ip->ip_src;
867 inc.inc_laddr = ip->ip_dst;
868 inc.inc_route.ro_rt = NULL; /* XXX */
870 inc.inc_fport = th->th_sport;
871 inc.inc_lport = th->th_dport;
874 * If the state is LISTEN then ignore segment if it contains
875 * a RST. If the segment contains an ACK then it is bad and
876 * send a RST. If it does not contain a SYN then it is not
877 * interesting; drop it.
879 * If the state is SYN_RECEIVED (syncache) and seg contains
880 * an ACK, but not for our SYN/ACK, send a RST. If the seg
881 * contains a RST, check the sequence number to see if it
882 * is a valid reset segment.
884 if ((thflags & (TH_RST | TH_ACK | TH_SYN)) != TH_SYN) {
885 if ((thflags & (TH_RST | TH_ACK | TH_SYN)) == TH_ACK) {
886 if (!syncache_expand(&inc, th, &so, m)) {
888 * No syncache entry, or ACK was not
889 * for our SYN/ACK. Send a RST.
891 tcpstat.tcps_badsyn++;
892 rstreason = BANDLIM_RST_OPENPORT;
897 * Could not complete 3-way handshake,
898 * connection is being closed down, and
899 * syncache will free mbuf.
903 * Socket is created in state SYN_RECEIVED.
904 * Continue processing segment.
909 * This is what would have happened in
910 * tcp_output() when the SYN,ACK was sent.
912 tp->snd_up = tp->snd_una;
913 tp->snd_max = tp->snd_nxt = tp->iss + 1;
914 tp->last_ack_sent = tp->rcv_nxt;
916 * XXX possible bug - it doesn't appear that tp->snd_wnd is unscaled
917 * until the _second_ ACK is received:
918 * rcv SYN (set wscale opts) --> send SYN/ACK, set snd_wnd = window.
919 * rcv ACK, calculate tiwin --> process SYN_RECEIVED, determine wscale,
920 * move to ESTAB, set snd_wnd to tiwin.
922 tp->snd_wnd = tiwin; /* unscaled */
925 if (thflags & TH_RST) {
926 syncache_chkrst(&inc, th);
929 if (thflags & TH_ACK) {
930 syncache_badack(&inc);
931 tcpstat.tcps_badsyn++;
932 rstreason = BANDLIM_RST_OPENPORT;
939 * Segment's flags are (SYN) or (SYN | FIN).
943 * If deprecated address is forbidden,
944 * we do not accept SYN to deprecated interface
945 * address to prevent any new inbound connection from
946 * getting established.
947 * When we do not accept SYN, we send a TCP RST,
948 * with deprecated source address (instead of dropping
949 * it). We compromise it as it is much better for peer
950 * to send a RST, and RST will be the final packet
953 * If we do not forbid deprecated addresses, we accept
954 * the SYN packet. RFC2462 does not suggest dropping
956 * If we decipher RFC2462 5.5.4, it says like this:
957 * 1. use of deprecated addr with existing
958 * communication is okay - "SHOULD continue to be
960 * 2. use of it with new communication:
961 * (2a) "SHOULD NOT be used if alternate address
962 * with sufficient scope is available"
963 * (2b) nothing mentioned otherwise.
964 * Here we fall into (2b) case as we have no choice in
965 * our source address selection - we must obey the peer.
967 * The wording in RFC2462 is confusing, and there are
968 * multiple description text for deprecated address
969 * handling - worse, they are not exactly the same.
970 * I believe 5.5.4 is the best one, so we follow 5.5.4.
972 if (isipv6 && !ip6_use_deprecated) {
973 struct in6_ifaddr *ia6;
975 if ((ia6 = ip6_getdstifaddr(m)) &&
976 (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
978 rstreason = BANDLIM_RST_OPENPORT;
984 * If it is from this socket, drop it, it must be forged.
985 * Don't bother responding if the destination was a broadcast.
987 if (th->th_dport == th->th_sport) {
989 if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
993 if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
998 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
1000 * Note that it is quite possible to receive unicast
1001 * link-layer packets with a broadcast IP address. Use
1002 * in_broadcast() to find them.
1004 if (m->m_flags & (M_BCAST | M_MCAST))
1007 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1008 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
1011 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1012 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1013 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1014 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
1018 * SYN appears to be valid; create compressed TCP state
1019 * for syncache, or perform t/tcp connection.
1021 if (so->so_qlen <= so->so_qlimit) {
1022 tcp_dooptions(&to, optp, optlen, TRUE);
1023 if (!syncache_add(&inc, &to, th, &so, m))
1027 * Entry added to syncache, mbuf used to
1028 * send SYN,ACK packet.
1032 tp = intotcpcb(inp);
1033 tp->snd_wnd = tiwin;
1034 tp->t_starttime = ticks;
1035 tp->t_state = TCPS_ESTABLISHED;
1038 * If there is a FIN, or if there is data and the
1039 * connection is local, then delay SYN,ACK(SYN) in
1040 * the hope of piggy-backing it on a response
1041 * segment. Otherwise must send ACK now in case
1042 * the other side is slow starting.
1044 if (DELAY_ACK(tp) &&
1045 ((thflags & TH_FIN) ||
1047 ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
1048 (!isipv6 && in_localaddr(inp->inp_faddr)))))) {
1049 tcp_callout_reset(tp, tp->tt_delack,
1050 tcp_delacktime, tcp_timer_delack);
1051 tp->t_flags |= TF_NEEDSYN;
1053 tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1056 tcpstat.tcps_connects++;
1064 /* should not happen - syncache should pick up these connections */
1065 KASSERT(tp->t_state != TCPS_LISTEN, ("tcp_input: TCPS_LISTEN state"));
1068 * This is the second part of the MSS DoS prevention code (after
1069 * minmss on the sending side) and it deals with too many too small
1070 * tcp packets in a too short timeframe (1 second).
1072 * XXX Removed. This code was crap. It does not scale to network
1073 * speed, and default values break NFS. Gone.
1078 * Segment received on connection.
1080 * Reset idle time and keep-alive timer. Don't waste time if less
1081 * then a second has elapsed. Only update t_rcvtime for non-SYN
1084 * Handle the case where one side thinks the connection is established
1085 * but the other side has, say, rebooted without cleaning out the
1086 * connection. The SYNs could be construed as an attack and wind
1087 * up ignored, but in case it isn't an attack we can validate the
1088 * connection by forcing a keepalive.
1090 if (TCPS_HAVEESTABLISHED(tp->t_state) && (ticks - tp->t_rcvtime) > hz) {
1091 if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN) {
1092 tp->t_flags |= TF_KEEPALIVE;
1093 tcp_callout_reset(tp, tp->tt_keep, hz / 2,
1096 tp->t_rcvtime = ticks;
1097 tp->t_flags &= ~TF_KEEPALIVE;
1098 tcp_callout_reset(tp, tp->tt_keep, tcp_keepidle,
1105 * XXX this is tradtitional behavior, may need to be cleaned up.
1107 tcp_dooptions(&to, optp, optlen, (thflags & TH_SYN) != 0);
1108 if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1109 if (to.to_flags & TOF_SCALE) {
1110 tp->t_flags |= TF_RCVD_SCALE;
1111 tp->requested_s_scale = to.to_requested_s_scale;
1113 if (to.to_flags & TOF_TS) {
1114 tp->t_flags |= TF_RCVD_TSTMP;
1115 tp->ts_recent = to.to_tsval;
1116 tp->ts_recent_age = ticks;
1118 if (to.to_flags & TOF_MSS)
1119 tcp_mss(tp, to.to_mss);
1121 * Only set the TF_SACK_PERMITTED per-connection flag
1122 * if we got a SACK_PERMITTED option from the other side
1123 * and the global tcp_do_sack variable is true.
1125 if (tcp_do_sack && (to.to_flags & TOF_SACK_PERMITTED))
1126 tp->t_flags |= TF_SACK_PERMITTED;
1130 * Header prediction: check for the two common cases
1131 * of a uni-directional data xfer. If the packet has
1132 * no control flags, is in-sequence, the window didn't
1133 * change and we're not retransmitting, it's a
1134 * candidate. If the length is zero and the ack moved
1135 * forward, we're the sender side of the xfer. Just
1136 * free the data acked & wake any higher level process
1137 * that was blocked waiting for space. If the length
1138 * is non-zero and the ack didn't move, we're the
1139 * receiver side. If we're getting packets in-order
1140 * (the reassembly queue is empty), add the data to
1141 * the socket buffer and note that we need a delayed ack.
1142 * Make sure that the hidden state-flags are also off.
1143 * Since we check for TCPS_ESTABLISHED above, it can only
1146 if (tp->t_state == TCPS_ESTABLISHED &&
1147 (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1148 !(tp->t_flags & (TF_NEEDSYN | TF_NEEDFIN)) &&
1149 (!(to.to_flags & TOF_TS) ||
1150 TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
1151 th->th_seq == tp->rcv_nxt &&
1152 tp->snd_nxt == tp->snd_max) {
1155 * If last ACK falls within this segment's sequence numbers,
1156 * record the timestamp.
1157 * NOTE that the test is modified according to the latest
1158 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1160 if ((to.to_flags & TOF_TS) &&
1161 SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1162 tp->ts_recent_age = ticks;
1163 tp->ts_recent = to.to_tsval;
1167 if (SEQ_GT(th->th_ack, tp->snd_una) &&
1168 SEQ_LEQ(th->th_ack, tp->snd_max) &&
1169 tp->snd_cwnd >= tp->snd_wnd &&
1170 !IN_FASTRECOVERY(tp)) {
1172 * This is a pure ack for outstanding data.
1174 ++tcpstat.tcps_predack;
1176 * "bad retransmit" recovery
1178 * If Eifel detection applies, then
1179 * it is deterministic, so use it
1180 * unconditionally over the old heuristic.
1181 * Otherwise, fall back to the old heuristic.
1183 if (tcp_do_eifel_detect &&
1184 (to.to_flags & TOF_TS) && to.to_tsecr &&
1185 (tp->t_flags & TF_FIRSTACCACK)) {
1186 /* Eifel detection applicable. */
1187 if (to.to_tsecr < tp->t_rexmtTS) {
1188 tcp_revert_congestion_state(tp);
1189 ++tcpstat.tcps_eifeldetected;
1191 } else if (tp->t_rxtshift == 1 &&
1192 ticks < tp->t_badrxtwin) {
1193 tcp_revert_congestion_state(tp);
1194 ++tcpstat.tcps_rttdetected;
1196 tp->t_flags &= ~(TF_FIRSTACCACK |
1197 TF_FASTREXMT | TF_EARLYREXMT);
1199 * Recalculate the retransmit timer / rtt.
1201 * Some machines (certain windows boxes)
1202 * send broken timestamp replies during the
1203 * SYN+ACK phase, ignore timestamps of 0.
1205 if ((to.to_flags & TOF_TS) && to.to_tsecr) {
1207 ticks - to.to_tsecr + 1);
1208 } else if (tp->t_rtttime &&
1209 SEQ_GT(th->th_ack, tp->t_rtseq)) {
1211 ticks - tp->t_rtttime);
1213 tcp_xmit_bandwidth_limit(tp, th->th_ack);
1214 acked = th->th_ack - tp->snd_una;
1215 tcpstat.tcps_rcvackpack++;
1216 tcpstat.tcps_rcvackbyte += acked;
1217 sbdrop(&so->so_snd.sb, acked);
1218 tp->snd_recover = th->th_ack - 1;
1219 tp->snd_una = th->th_ack;
1222 * Update window information.
1224 if (tiwin != tp->snd_wnd &&
1225 acceptable_window_update(tp, th, tiwin)) {
1226 /* keep track of pure window updates */
1227 if (tp->snd_wl2 == th->th_ack &&
1228 tiwin > tp->snd_wnd)
1229 tcpstat.tcps_rcvwinupd++;
1230 tp->snd_wnd = tiwin;
1231 tp->snd_wl1 = th->th_seq;
1232 tp->snd_wl2 = th->th_ack;
1233 if (tp->snd_wnd > tp->max_sndwnd)
1234 tp->max_sndwnd = tp->snd_wnd;
1237 ND6_HINT(tp); /* some progress has been done */
1239 * If all outstanding data are acked, stop
1240 * retransmit timer, otherwise restart timer
1241 * using current (possibly backed-off) value.
1242 * If process is waiting for space,
1243 * wakeup/selwakeup/signal. If data
1244 * are ready to send, let tcp_output
1245 * decide between more output or persist.
1247 if (tp->snd_una == tp->snd_max) {
1248 tcp_callout_stop(tp, tp->tt_rexmt);
1249 } else if (!tcp_callout_active(tp,
1251 tcp_callout_reset(tp, tp->tt_rexmt,
1252 tp->t_rxtcur, tcp_timer_rexmt);
1255 if (so->so_snd.ssb_cc > 0)
1259 } else if (tiwin == tp->snd_wnd &&
1260 th->th_ack == tp->snd_una &&
1261 LIST_EMPTY(&tp->t_segq) &&
1262 tlen <= ssb_space(&so->so_rcv)) {
1263 u_long newsize = 0; /* automatic sockbuf scaling */
1265 * This is a pure, in-sequence data packet
1266 * with nothing on the reassembly queue and
1267 * we have enough buffer space to take it.
1269 ++tcpstat.tcps_preddat;
1270 tp->rcv_nxt += tlen;
1271 tcpstat.tcps_rcvpack++;
1272 tcpstat.tcps_rcvbyte += tlen;
1273 ND6_HINT(tp); /* some progress has been done */
1275 * Automatic sizing of receive socket buffer. Often the send
1276 * buffer size is not optimally adjusted to the actual network
1277 * conditions at hand (delay bandwidth product). Setting the
1278 * buffer size too small limits throughput on links with high
1279 * bandwidth and high delay (eg. trans-continental/oceanic links).
1281 * On the receive side the socket buffer memory is only rarely
1282 * used to any significant extent. This allows us to be much
1283 * more aggressive in scaling the receive socket buffer. For
1284 * the case that the buffer space is actually used to a large
1285 * extent and we run out of kernel memory we can simply drop
1286 * the new segments; TCP on the sender will just retransmit it
1287 * later. Setting the buffer size too big may only consume too
1288 * much kernel memory if the application doesn't read() from
1289 * the socket or packet loss or reordering makes use of the
1292 * The criteria to step up the receive buffer one notch are:
1293 * 1. the number of bytes received during the time it takes
1294 * one timestamp to be reflected back to us (the RTT);
1295 * 2. received bytes per RTT is within seven eighth of the
1296 * current socket buffer size;
1297 * 3. receive buffer size has not hit maximal automatic size;
1299 * This algorithm does one step per RTT at most and only if
1300 * we receive a bulk stream w/o packet losses or reorderings.
1301 * Shrinking the buffer during idle times is not necessary as
1302 * it doesn't consume any memory when idle.
1304 * TODO: Only step up if the application is actually serving
1305 * the buffer to better manage the socket buffer resources.
1307 if (tcp_do_autorcvbuf &&
1309 (so->so_rcv.ssb_flags & SSB_AUTOSIZE)) {
1310 if (to.to_tsecr > tp->rfbuf_ts &&
1311 to.to_tsecr - tp->rfbuf_ts < hz) {
1313 (so->so_rcv.ssb_hiwat / 8 * 7) &&
1314 so->so_rcv.ssb_hiwat <
1315 tcp_autorcvbuf_max) {
1317 ulmin(so->so_rcv.ssb_hiwat +
1319 tcp_autorcvbuf_max);
1321 /* Start over with next RTT. */
1325 tp->rfbuf_cnt += tlen; /* add up */
1328 * Add data to socket buffer.
1330 if (so->so_state & SS_CANTRCVMORE) {
1334 * Set new socket buffer size, give up when
1337 * Adjusting the size can mess up ACK
1338 * sequencing when pure window updates are
1339 * being avoided (which is the default),
1343 tp->t_flags |= TF_RXRESIZED;
1344 if (!ssb_reserve(&so->so_rcv, newsize,
1346 so->so_rcv.ssb_flags &= ~SSB_AUTOSIZE;
1349 (TCP_MAXWIN << tp->rcv_scale)) {
1350 so->so_rcv.ssb_flags &= ~SSB_AUTOSIZE;
1353 m_adj(m, drop_hdrlen); /* delayed header drop */
1354 ssb_appendstream(&so->so_rcv, m);
1358 * This code is responsible for most of the ACKs
1359 * the TCP stack sends back after receiving a data
1360 * packet. Note that the DELAY_ACK check fails if
1361 * the delack timer is already running, which results
1362 * in an ack being sent every other packet (which is
1365 * We then further aggregate acks by not actually
1366 * sending one until the protocol thread has completed
1367 * processing the current backlog of packets. This
1368 * does not delay the ack any further, but allows us
1369 * to take advantage of the packet aggregation that
1370 * high speed NICs do (usually blocks of 8-10 packets)
1371 * to send a single ack rather then four or five acks,
1372 * greatly reducing the ack rate, the return channel
1373 * bandwidth, and the protocol overhead on both ends.
1375 * Since this also has the effect of slowing down
1376 * the exponential slow-start ramp-up, systems with
1377 * very large bandwidth-delay products might want
1378 * to turn the feature off.
1380 if (DELAY_ACK(tp)) {
1381 tcp_callout_reset(tp, tp->tt_delack,
1382 tcp_delacktime, tcp_timer_delack);
1383 } else if (tcp_aggregate_acks) {
1384 tp->t_flags |= TF_ACKNOW;
1385 if (!(tp->t_flags & TF_ONOUTPUTQ)) {
1386 tp->t_flags |= TF_ONOUTPUTQ;
1387 tp->tt_cpu = mycpu->gd_cpuid;
1389 &tcpcbackq[tp->tt_cpu],
1393 tp->t_flags |= TF_ACKNOW;
1401 * Calculate amount of space in receive window,
1402 * and then do TCP input processing.
1403 * Receive window is amount of space in rcv queue,
1404 * but not less than advertised window.
1406 recvwin = ssb_space(&so->so_rcv);
1409 tp->rcv_wnd = imax(recvwin, (int)(tp->rcv_adv - tp->rcv_nxt));
1411 /* Reset receive buffer auto scaling when not in bulk receive mode. */
1415 switch (tp->t_state) {
1417 * If the state is SYN_RECEIVED:
1418 * if seg contains an ACK, but not for our SYN/ACK, send a RST.
1420 case TCPS_SYN_RECEIVED:
1421 if ((thflags & TH_ACK) &&
1422 (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1423 SEQ_GT(th->th_ack, tp->snd_max))) {
1424 rstreason = BANDLIM_RST_OPENPORT;
1430 * If the state is SYN_SENT:
1431 * if seg contains an ACK, but not for our SYN, drop the input.
1432 * if seg contains a RST, then drop the connection.
1433 * if seg does not contain SYN, then drop it.
1434 * Otherwise this is an acceptable SYN segment
1435 * initialize tp->rcv_nxt and tp->irs
1436 * if seg contains ack then advance tp->snd_una
1437 * if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1438 * arrange for segment to be acked (eventually)
1439 * continue processing rest of data/controls, beginning with URG
1442 if ((thflags & TH_ACK) &&
1443 (SEQ_LEQ(th->th_ack, tp->iss) ||
1444 SEQ_GT(th->th_ack, tp->snd_max))) {
1445 rstreason = BANDLIM_UNLIMITED;
1448 if (thflags & TH_RST) {
1449 if (thflags & TH_ACK)
1450 tp = tcp_drop(tp, ECONNREFUSED);
1453 if (!(thflags & TH_SYN))
1455 tp->snd_wnd = th->th_win; /* initial send window */
1457 tp->irs = th->th_seq;
1459 if (thflags & TH_ACK) {
1460 /* Our SYN was acked. */
1461 tcpstat.tcps_connects++;
1463 /* Do window scaling on this connection? */
1464 if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
1465 (TF_RCVD_SCALE | TF_REQ_SCALE)) {
1466 tp->snd_scale = tp->requested_s_scale;
1467 tp->rcv_scale = tp->request_r_scale;
1469 tp->rcv_adv += tp->rcv_wnd;
1470 tp->snd_una++; /* SYN is acked */
1471 tcp_callout_stop(tp, tp->tt_rexmt);
1473 * If there's data, delay ACK; if there's also a FIN
1474 * ACKNOW will be turned on later.
1476 if (DELAY_ACK(tp) && tlen != 0) {
1477 tcp_callout_reset(tp, tp->tt_delack,
1478 tcp_delacktime, tcp_timer_delack);
1480 tp->t_flags |= TF_ACKNOW;
1483 * Received <SYN,ACK> in SYN_SENT[*] state.
1485 * SYN_SENT --> ESTABLISHED
1486 * SYN_SENT* --> FIN_WAIT_1
1488 tp->t_starttime = ticks;
1489 if (tp->t_flags & TF_NEEDFIN) {
1490 tp->t_state = TCPS_FIN_WAIT_1;
1491 tp->t_flags &= ~TF_NEEDFIN;
1494 tp->t_state = TCPS_ESTABLISHED;
1495 tcp_callout_reset(tp, tp->tt_keep, tcp_keepidle,
1500 * Received initial SYN in SYN-SENT[*] state =>
1501 * simultaneous open.
1502 * Do 3-way handshake:
1503 * SYN-SENT -> SYN-RECEIVED
1504 * SYN-SENT* -> SYN-RECEIVED*
1506 tp->t_flags |= TF_ACKNOW;
1507 tcp_callout_stop(tp, tp->tt_rexmt);
1508 tp->t_state = TCPS_SYN_RECEIVED;
1513 * Advance th->th_seq to correspond to first data byte.
1514 * If data, trim to stay within window,
1515 * dropping FIN if necessary.
1518 if (tlen > tp->rcv_wnd) {
1519 todrop = tlen - tp->rcv_wnd;
1523 tcpstat.tcps_rcvpackafterwin++;
1524 tcpstat.tcps_rcvbyteafterwin += todrop;
1526 tp->snd_wl1 = th->th_seq - 1;
1527 tp->rcv_up = th->th_seq;
1529 * Client side of transaction: already sent SYN and data.
1530 * If the remote host used T/TCP to validate the SYN,
1531 * our data will be ACK'd; if so, enter normal data segment
1532 * processing in the middle of step 5, ack processing.
1533 * Otherwise, goto step 6.
1535 if (thflags & TH_ACK)
1541 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1542 * do normal processing (we no longer bother with T/TCP).
1546 case TCPS_TIME_WAIT:
1547 break; /* continue normal processing */
1551 * States other than LISTEN or SYN_SENT.
1552 * First check the RST flag and sequence number since reset segments
1553 * are exempt from the timestamp and connection count tests. This
1554 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1555 * below which allowed reset segments in half the sequence space
1556 * to fall though and be processed (which gives forged reset
1557 * segments with a random sequence number a 50 percent chance of
1558 * killing a connection).
1559 * Then check timestamp, if present.
1560 * Then check the connection count, if present.
1561 * Then check that at least some bytes of segment are within
1562 * receive window. If segment begins before rcv_nxt,
1563 * drop leading data (and SYN); if nothing left, just ack.
1566 * If the RST bit is set, check the sequence number to see
1567 * if this is a valid reset segment.
1569 * In all states except SYN-SENT, all reset (RST) segments
1570 * are validated by checking their SEQ-fields. A reset is
1571 * valid if its sequence number is in the window.
1572 * Note: this does not take into account delayed ACKs, so
1573 * we should test against last_ack_sent instead of rcv_nxt.
1574 * The sequence number in the reset segment is normally an
1575 * echo of our outgoing acknowledgement numbers, but some hosts
1576 * send a reset with the sequence number at the rightmost edge
1577 * of our receive window, and we have to handle this case.
1578 * If we have multiple segments in flight, the intial reset
1579 * segment sequence numbers will be to the left of last_ack_sent,
1580 * but they will eventually catch up.
1581 * In any case, it never made sense to trim reset segments to
1582 * fit the receive window since RFC 1122 says:
1583 * 4.2.2.12 RST Segment: RFC-793 Section 3.4
1585 * A TCP SHOULD allow a received RST segment to include data.
1588 * It has been suggested that a RST segment could contain
1589 * ASCII text that encoded and explained the cause of the
1590 * RST. No standard has yet been established for such
1593 * If the reset segment passes the sequence number test examine
1595 * SYN_RECEIVED STATE:
1596 * If passive open, return to LISTEN state.
1597 * If active open, inform user that connection was refused.
1598 * ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
1599 * Inform user that connection was reset, and close tcb.
1600 * CLOSING, LAST_ACK STATES:
1603 * Drop the segment - see Stevens, vol. 2, p. 964 and
1606 if (thflags & TH_RST) {
1607 if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
1608 SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
1609 switch (tp->t_state) {
1611 case TCPS_SYN_RECEIVED:
1612 so->so_error = ECONNREFUSED;
1615 case TCPS_ESTABLISHED:
1616 case TCPS_FIN_WAIT_1:
1617 case TCPS_FIN_WAIT_2:
1618 case TCPS_CLOSE_WAIT:
1619 so->so_error = ECONNRESET;
1621 tp->t_state = TCPS_CLOSED;
1622 tcpstat.tcps_drops++;
1631 case TCPS_TIME_WAIT:
1639 * RFC 1323 PAWS: If we have a timestamp reply on this segment
1640 * and it's less than ts_recent, drop it.
1642 if ((to.to_flags & TOF_TS) && tp->ts_recent != 0 &&
1643 TSTMP_LT(to.to_tsval, tp->ts_recent)) {
1645 /* Check to see if ts_recent is over 24 days old. */
1646 if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
1648 * Invalidate ts_recent. If this segment updates
1649 * ts_recent, the age will be reset later and ts_recent
1650 * will get a valid value. If it does not, setting
1651 * ts_recent to zero will at least satisfy the
1652 * requirement that zero be placed in the timestamp
1653 * echo reply when ts_recent isn't valid. The
1654 * age isn't reset until we get a valid ts_recent
1655 * because we don't want out-of-order segments to be
1656 * dropped when ts_recent is old.
1660 tcpstat.tcps_rcvduppack++;
1661 tcpstat.tcps_rcvdupbyte += tlen;
1662 tcpstat.tcps_pawsdrop++;
1670 * In the SYN-RECEIVED state, validate that the packet belongs to
1671 * this connection before trimming the data to fit the receive
1672 * window. Check the sequence number versus IRS since we know
1673 * the sequence numbers haven't wrapped. This is a partial fix
1674 * for the "LAND" DoS attack.
1676 if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
1677 rstreason = BANDLIM_RST_OPENPORT;
1681 todrop = tp->rcv_nxt - th->th_seq;
1683 if (TCP_DO_SACK(tp)) {
1684 /* Report duplicate segment at head of packet. */
1685 tp->reportblk.rblk_start = th->th_seq;
1686 tp->reportblk.rblk_end = th->th_seq + tlen;
1687 if (thflags & TH_FIN)
1688 ++tp->reportblk.rblk_end;
1689 if (SEQ_GT(tp->reportblk.rblk_end, tp->rcv_nxt))
1690 tp->reportblk.rblk_end = tp->rcv_nxt;
1691 tp->t_flags |= (TF_DUPSEG | TF_SACKLEFT | TF_ACKNOW);
1693 if (thflags & TH_SYN) {
1703 * Following if statement from Stevens, vol. 2, p. 960.
1705 if (todrop > tlen ||
1706 (todrop == tlen && !(thflags & TH_FIN))) {
1708 * Any valid FIN must be to the left of the window.
1709 * At this point the FIN must be a duplicate or out
1710 * of sequence; drop it.
1715 * Send an ACK to resynchronize and drop any data.
1716 * But keep on processing for RST or ACK.
1718 tp->t_flags |= TF_ACKNOW;
1720 tcpstat.tcps_rcvduppack++;
1721 tcpstat.tcps_rcvdupbyte += todrop;
1723 tcpstat.tcps_rcvpartduppack++;
1724 tcpstat.tcps_rcvpartdupbyte += todrop;
1726 drop_hdrlen += todrop; /* drop from the top afterwards */
1727 th->th_seq += todrop;
1729 if (th->th_urp > todrop)
1730 th->th_urp -= todrop;
1738 * If new data are received on a connection after the
1739 * user processes are gone, then RST the other end.
1741 if ((so->so_state & SS_NOFDREF) &&
1742 tp->t_state > TCPS_CLOSE_WAIT && tlen) {
1744 tcpstat.tcps_rcvafterclose++;
1745 rstreason = BANDLIM_UNLIMITED;
1750 * If segment ends after window, drop trailing data
1751 * (and PUSH and FIN); if nothing left, just ACK.
1753 todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
1755 tcpstat.tcps_rcvpackafterwin++;
1756 if (todrop >= tlen) {
1757 tcpstat.tcps_rcvbyteafterwin += tlen;
1759 * If a new connection request is received
1760 * while in TIME_WAIT, drop the old connection
1761 * and start over if the sequence numbers
1762 * are above the previous ones.
1764 if (thflags & TH_SYN &&
1765 tp->t_state == TCPS_TIME_WAIT &&
1766 SEQ_GT(th->th_seq, tp->rcv_nxt)) {
1771 * If window is closed can only take segments at
1772 * window edge, and have to drop data and PUSH from
1773 * incoming segments. Continue processing, but
1774 * remember to ack. Otherwise, drop segment
1777 if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
1778 tp->t_flags |= TF_ACKNOW;
1779 tcpstat.tcps_rcvwinprobe++;
1783 tcpstat.tcps_rcvbyteafterwin += todrop;
1786 thflags &= ~(TH_PUSH | TH_FIN);
1790 * If last ACK falls within this segment's sequence numbers,
1791 * record its timestamp.
1793 * 1) That the test incorporates suggestions from the latest
1794 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1795 * 2) That updating only on newer timestamps interferes with
1796 * our earlier PAWS tests, so this check should be solely
1797 * predicated on the sequence space of this segment.
1798 * 3) That we modify the segment boundary check to be
1799 * Last.ACK.Sent <= SEG.SEQ + SEG.LEN
1800 * instead of RFC1323's
1801 * Last.ACK.Sent < SEG.SEQ + SEG.LEN,
1802 * This modified check allows us to overcome RFC1323's
1803 * limitations as described in Stevens TCP/IP Illustrated
1804 * Vol. 2 p.869. In such cases, we can still calculate the
1805 * RTT correctly when RCV.NXT == Last.ACK.Sent.
1807 if ((to.to_flags & TOF_TS) && SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
1808 SEQ_LEQ(tp->last_ack_sent, (th->th_seq + tlen
1809 + ((thflags & TH_SYN) != 0)
1810 + ((thflags & TH_FIN) != 0)))) {
1811 tp->ts_recent_age = ticks;
1812 tp->ts_recent = to.to_tsval;
1816 * If a SYN is in the window, then this is an
1817 * error and we send an RST and drop the connection.
1819 if (thflags & TH_SYN) {
1820 tp = tcp_drop(tp, ECONNRESET);
1821 rstreason = BANDLIM_UNLIMITED;
1826 * If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
1827 * flag is on (half-synchronized state), then queue data for
1828 * later processing; else drop segment and return.
1830 if (!(thflags & TH_ACK)) {
1831 if (tp->t_state == TCPS_SYN_RECEIVED ||
1832 (tp->t_flags & TF_NEEDSYN))
1841 switch (tp->t_state) {
1843 * In SYN_RECEIVED state, the ACK acknowledges our SYN, so enter
1844 * ESTABLISHED state and continue processing.
1845 * The ACK was checked above.
1847 case TCPS_SYN_RECEIVED:
1849 tcpstat.tcps_connects++;
1851 /* Do window scaling? */
1852 if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
1853 (TF_RCVD_SCALE | TF_REQ_SCALE)) {
1854 tp->snd_scale = tp->requested_s_scale;
1855 tp->rcv_scale = tp->request_r_scale;
1859 * SYN-RECEIVED -> ESTABLISHED
1860 * SYN-RECEIVED* -> FIN-WAIT-1
1862 tp->t_starttime = ticks;
1863 if (tp->t_flags & TF_NEEDFIN) {
1864 tp->t_state = TCPS_FIN_WAIT_1;
1865 tp->t_flags &= ~TF_NEEDFIN;
1867 tp->t_state = TCPS_ESTABLISHED;
1868 tcp_callout_reset(tp, tp->tt_keep, tcp_keepidle,
1872 * If segment contains data or ACK, will call tcp_reass()
1873 * later; if not, do so now to pass queued data to user.
1875 if (tlen == 0 && !(thflags & TH_FIN))
1876 tcp_reass(tp, NULL, NULL, NULL);
1880 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1881 * ACKs. If the ack is in the range
1882 * tp->snd_una < th->th_ack <= tp->snd_max
1883 * then advance tp->snd_una to th->th_ack and drop
1884 * data from the retransmission queue. If this ACK reflects
1885 * more up to date window information we update our window information.
1887 case TCPS_ESTABLISHED:
1888 case TCPS_FIN_WAIT_1:
1889 case TCPS_FIN_WAIT_2:
1890 case TCPS_CLOSE_WAIT:
1893 case TCPS_TIME_WAIT:
1895 if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
1896 if (TCP_DO_SACK(tp))
1897 tcp_sack_update_scoreboard(tp, &to);
1898 if (tlen != 0 || tiwin != tp->snd_wnd) {
1902 tcpstat.tcps_rcvdupack++;
1903 if (!tcp_callout_active(tp, tp->tt_rexmt) ||
1904 th->th_ack != tp->snd_una) {
1909 * We have outstanding data (other than
1910 * a window probe), this is a completely
1911 * duplicate ack (ie, window info didn't
1912 * change), the ack is the biggest we've
1913 * seen and we've seen exactly our rexmt
1914 * threshhold of them, so assume a packet
1915 * has been dropped and retransmit it.
1916 * Kludge snd_nxt & the congestion
1917 * window so we send only this one
1920 if (IN_FASTRECOVERY(tp)) {
1921 if (TCP_DO_SACK(tp)) {
1922 /* No artifical cwnd inflation. */
1923 tcp_sack_rexmt(tp, th);
1926 * Dup acks mean that packets
1927 * have left the network
1928 * (they're now cached at the
1929 * receiver) so bump cwnd by
1930 * the amount in the receiver
1931 * to keep a constant cwnd
1932 * packets in the network.
1934 tp->snd_cwnd += tp->t_maxseg;
1937 } else if (SEQ_LT(th->th_ack, tp->snd_recover)) {
1940 } else if (++tp->t_dupacks == tcprexmtthresh) {
1941 tcp_seq old_snd_nxt;
1945 if (tcp_do_eifel_detect &&
1946 (tp->t_flags & TF_RCVD_TSTMP)) {
1947 tcp_save_congestion_state(tp);
1948 tp->t_flags |= TF_FASTREXMT;
1951 * We know we're losing at the current
1952 * window size, so do congestion avoidance:
1953 * set ssthresh to half the current window
1954 * and pull our congestion window back to the
1957 win = min(tp->snd_wnd, tp->snd_cwnd) / 2 /
1961 tp->snd_ssthresh = win * tp->t_maxseg;
1962 ENTER_FASTRECOVERY(tp);
1963 tp->snd_recover = tp->snd_max;
1964 tcp_callout_stop(tp, tp->tt_rexmt);
1966 old_snd_nxt = tp->snd_nxt;
1967 tp->snd_nxt = th->th_ack;
1968 tp->snd_cwnd = tp->t_maxseg;
1970 ++tcpstat.tcps_sndfastrexmit;
1971 tp->snd_cwnd = tp->snd_ssthresh;
1972 tp->rexmt_high = tp->snd_nxt;
1973 if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
1974 tp->snd_nxt = old_snd_nxt;
1975 KASSERT(tp->snd_limited <= 2,
1976 ("tp->snd_limited too big"));
1977 if (TCP_DO_SACK(tp))
1978 tcp_sack_rexmt(tp, th);
1980 tp->snd_cwnd += tp->t_maxseg *
1981 (tp->t_dupacks - tp->snd_limited);
1982 } else if (tcp_do_limitedtransmit) {
1983 u_long oldcwnd = tp->snd_cwnd;
1984 tcp_seq oldsndmax = tp->snd_max;
1985 tcp_seq oldsndnxt = tp->snd_nxt;
1986 /* outstanding data */
1987 uint32_t ownd = tp->snd_max - tp->snd_una;
1990 #define iceildiv(n, d) (((n)+(d)-1) / (d))
1992 KASSERT(tp->t_dupacks == 1 ||
1994 ("dupacks not 1 or 2"));
1995 if (tp->t_dupacks == 1)
1996 tp->snd_limited = 0;
1997 tp->snd_nxt = tp->snd_max;
1998 tp->snd_cwnd = ownd +
1999 (tp->t_dupacks - tp->snd_limited) *
2004 * Other acks may have been processed,
2005 * snd_nxt cannot be reset to a value less
2008 if (SEQ_LT(oldsndnxt, oldsndmax)) {
2009 if (SEQ_GT(oldsndnxt, tp->snd_una))
2010 tp->snd_nxt = oldsndnxt;
2012 tp->snd_nxt = tp->snd_una;
2014 tp->snd_cwnd = oldcwnd;
2015 sent = tp->snd_max - oldsndmax;
2016 if (sent > tp->t_maxseg) {
2017 KASSERT((tp->t_dupacks == 2 &&
2018 tp->snd_limited == 0) ||
2019 (sent == tp->t_maxseg + 1 &&
2020 tp->t_flags & TF_SENTFIN),
2022 KASSERT(sent <= tp->t_maxseg * 2,
2023 ("sent too many segments"));
2024 tp->snd_limited = 2;
2025 tcpstat.tcps_sndlimited += 2;
2026 } else if (sent > 0) {
2028 ++tcpstat.tcps_sndlimited;
2029 } else if (tcp_do_early_retransmit &&
2030 (tcp_do_eifel_detect &&
2031 (tp->t_flags & TF_RCVD_TSTMP)) &&
2032 ownd < 4 * tp->t_maxseg &&
2033 tp->t_dupacks + 1 >=
2034 iceildiv(ownd, tp->t_maxseg) &&
2035 (!TCP_DO_SACK(tp) ||
2036 ownd <= tp->t_maxseg ||
2037 tcp_sack_has_sacked(&tp->scb,
2038 ownd - tp->t_maxseg))) {
2039 ++tcpstat.tcps_sndearlyrexmit;
2040 tp->t_flags |= TF_EARLYREXMT;
2041 goto fastretransmit;
2047 KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una"));
2049 if (SEQ_GT(th->th_ack, tp->snd_max)) {
2051 * Detected optimistic ACK attack.
2052 * Force slow-start to de-synchronize attack.
2054 tp->snd_cwnd = tp->t_maxseg;
2057 tcpstat.tcps_rcvacktoomuch++;
2061 * If we reach this point, ACK is not a duplicate,
2062 * i.e., it ACKs something we sent.
2064 if (tp->t_flags & TF_NEEDSYN) {
2066 * T/TCP: Connection was half-synchronized, and our
2067 * SYN has been ACK'd (so connection is now fully
2068 * synchronized). Go to non-starred state,
2069 * increment snd_una for ACK of SYN, and check if
2070 * we can do window scaling.
2072 tp->t_flags &= ~TF_NEEDSYN;
2074 /* Do window scaling? */
2075 if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
2076 (TF_RCVD_SCALE | TF_REQ_SCALE)) {
2077 tp->snd_scale = tp->requested_s_scale;
2078 tp->rcv_scale = tp->request_r_scale;
2083 acked = th->th_ack - tp->snd_una;
2084 tcpstat.tcps_rcvackpack++;
2085 tcpstat.tcps_rcvackbyte += acked;
2087 if (tcp_do_eifel_detect && acked > 0 &&
2088 (to.to_flags & TOF_TS) && (to.to_tsecr != 0) &&
2089 (tp->t_flags & TF_FIRSTACCACK)) {
2090 /* Eifel detection applicable. */
2091 if (to.to_tsecr < tp->t_rexmtTS) {
2092 ++tcpstat.tcps_eifeldetected;
2093 tcp_revert_congestion_state(tp);
2094 if (tp->t_rxtshift == 1 &&
2095 ticks >= tp->t_badrxtwin)
2096 ++tcpstat.tcps_rttcantdetect;
2098 } else if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
2100 * If we just performed our first retransmit,
2101 * and the ACK arrives within our recovery window,
2102 * then it was a mistake to do the retransmit
2103 * in the first place. Recover our original cwnd
2104 * and ssthresh, and proceed to transmit where we
2107 tcp_revert_congestion_state(tp);
2108 ++tcpstat.tcps_rttdetected;
2112 * If we have a timestamp reply, update smoothed
2113 * round trip time. If no timestamp is present but
2114 * transmit timer is running and timed sequence
2115 * number was acked, update smoothed round trip time.
2116 * Since we now have an rtt measurement, cancel the
2117 * timer backoff (cf., Phil Karn's retransmit alg.).
2118 * Recompute the initial retransmit timer.
2120 * Some machines (certain windows boxes) send broken
2121 * timestamp replies during the SYN+ACK phase, ignore
2124 if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0))
2125 tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
2126 else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
2127 tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2128 tcp_xmit_bandwidth_limit(tp, th->th_ack);
2131 * If no data (only SYN) was ACK'd,
2132 * skip rest of ACK processing.
2137 /* Stop looking for an acceptable ACK since one was received. */
2138 tp->t_flags &= ~(TF_FIRSTACCACK | TF_FASTREXMT | TF_EARLYREXMT);
2140 if (acked > so->so_snd.ssb_cc) {
2141 tp->snd_wnd -= so->so_snd.ssb_cc;
2142 sbdrop(&so->so_snd.sb, (int)so->so_snd.ssb_cc);
2143 ourfinisacked = TRUE;
2145 sbdrop(&so->so_snd.sb, acked);
2146 tp->snd_wnd -= acked;
2147 ourfinisacked = FALSE;
2152 * Update window information.
2153 * Don't look at window if no ACK:
2154 * TAC's send garbage on first SYN.
2156 if (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2157 (tp->snd_wl1 == th->th_seq &&
2158 (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2159 (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)))) {
2160 /* keep track of pure window updates */
2161 if (tlen == 0 && tp->snd_wl2 == th->th_ack &&
2162 tiwin > tp->snd_wnd)
2163 tcpstat.tcps_rcvwinupd++;
2164 tp->snd_wnd = tiwin;
2165 tp->snd_wl1 = th->th_seq;
2166 tp->snd_wl2 = th->th_ack;
2167 if (tp->snd_wnd > tp->max_sndwnd)
2168 tp->max_sndwnd = tp->snd_wnd;
2172 tp->snd_una = th->th_ack;
2173 if (TCP_DO_SACK(tp))
2174 tcp_sack_update_scoreboard(tp, &to);
2175 if (IN_FASTRECOVERY(tp)) {
2176 if (SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2177 EXIT_FASTRECOVERY(tp);
2180 * If the congestion window was inflated
2181 * to account for the other side's
2182 * cached packets, retract it.
2184 if (!TCP_DO_SACK(tp))
2185 tp->snd_cwnd = tp->snd_ssthresh;
2188 * Window inflation should have left us
2189 * with approximately snd_ssthresh outstanding
2190 * data. But, in case we would be inclined
2191 * to send a burst, better do it using
2194 if (SEQ_GT(th->th_ack + tp->snd_cwnd,
2195 tp->snd_max + 2 * tp->t_maxseg))
2197 (tp->snd_max - tp->snd_una) +
2202 if (TCP_DO_SACK(tp)) {
2203 tp->snd_max_rexmt = tp->snd_max;
2204 tcp_sack_rexmt(tp, th);
2206 tcp_newreno_partial_ack(tp, th, acked);
2212 * Open the congestion window. When in slow-start,
2213 * open exponentially: maxseg per packet. Otherwise,
2214 * open linearly: maxseg per window.
2216 if (tp->snd_cwnd <= tp->snd_ssthresh) {
2218 (SEQ_LT(tp->snd_nxt, tp->snd_max) ?
2219 tp->t_maxseg : 2 * tp->t_maxseg);
2222 tp->snd_cwnd += tcp_do_abc ?
2223 min(acked, abc_sslimit) : tp->t_maxseg;
2225 /* linear increase */
2226 tp->snd_wacked += tcp_do_abc ? acked :
2228 if (tp->snd_wacked >= tp->snd_cwnd) {
2229 tp->snd_wacked -= tp->snd_cwnd;
2230 tp->snd_cwnd += tp->t_maxseg;
2233 tp->snd_cwnd = min(tp->snd_cwnd,
2234 TCP_MAXWIN << tp->snd_scale);
2235 tp->snd_recover = th->th_ack - 1;
2237 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2238 tp->snd_nxt = tp->snd_una;
2241 * If all outstanding data is acked, stop retransmit
2242 * timer and remember to restart (more output or persist).
2243 * If there is more data to be acked, restart retransmit
2244 * timer, using current (possibly backed-off) value.
2246 if (th->th_ack == tp->snd_max) {
2247 tcp_callout_stop(tp, tp->tt_rexmt);
2249 } else if (!tcp_callout_active(tp, tp->tt_persist)) {
2250 tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
2254 switch (tp->t_state) {
2256 * In FIN_WAIT_1 STATE in addition to the processing
2257 * for the ESTABLISHED state if our FIN is now acknowledged
2258 * then enter FIN_WAIT_2.
2260 case TCPS_FIN_WAIT_1:
2261 if (ourfinisacked) {
2263 * If we can't receive any more
2264 * data, then closing user can proceed.
2265 * Starting the timer is contrary to the
2266 * specification, but if we don't get a FIN
2267 * we'll hang forever.
2269 if (so->so_state & SS_CANTRCVMORE) {
2270 soisdisconnected(so);
2271 tcp_callout_reset(tp, tp->tt_2msl,
2272 tcp_maxidle, tcp_timer_2msl);
2274 tp->t_state = TCPS_FIN_WAIT_2;
2279 * In CLOSING STATE in addition to the processing for
2280 * the ESTABLISHED state if the ACK acknowledges our FIN
2281 * then enter the TIME-WAIT state, otherwise ignore
2285 if (ourfinisacked) {
2286 tp->t_state = TCPS_TIME_WAIT;
2287 tcp_canceltimers(tp);
2288 tcp_callout_reset(tp, tp->tt_2msl,
2289 2 * tcp_msl, tcp_timer_2msl);
2290 soisdisconnected(so);
2295 * In LAST_ACK, we may still be waiting for data to drain
2296 * and/or to be acked, as well as for the ack of our FIN.
2297 * If our FIN is now acknowledged, delete the TCB,
2298 * enter the closed state and return.
2301 if (ourfinisacked) {
2308 * In TIME_WAIT state the only thing that should arrive
2309 * is a retransmission of the remote FIN. Acknowledge
2310 * it and restart the finack timer.
2312 case TCPS_TIME_WAIT:
2313 tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_msl,
2321 * Update window information.
2322 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2324 if ((thflags & TH_ACK) &&
2325 acceptable_window_update(tp, th, tiwin)) {
2326 /* keep track of pure window updates */
2327 if (tlen == 0 && tp->snd_wl2 == th->th_ack &&
2328 tiwin > tp->snd_wnd)
2329 tcpstat.tcps_rcvwinupd++;
2330 tp->snd_wnd = tiwin;
2331 tp->snd_wl1 = th->th_seq;
2332 tp->snd_wl2 = th->th_ack;
2333 if (tp->snd_wnd > tp->max_sndwnd)
2334 tp->max_sndwnd = tp->snd_wnd;
2339 * Process segments with URG.
2341 if ((thflags & TH_URG) && th->th_urp &&
2342 !TCPS_HAVERCVDFIN(tp->t_state)) {
2344 * This is a kludge, but if we receive and accept
2345 * random urgent pointers, we'll crash in
2346 * soreceive. It's hard to imagine someone
2347 * actually wanting to send this much urgent data.
2349 if (th->th_urp + so->so_rcv.ssb_cc > sb_max) {
2350 th->th_urp = 0; /* XXX */
2351 thflags &= ~TH_URG; /* XXX */
2352 goto dodata; /* XXX */
2355 * If this segment advances the known urgent pointer,
2356 * then mark the data stream. This should not happen
2357 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2358 * a FIN has been received from the remote side.
2359 * In these states we ignore the URG.
2361 * According to RFC961 (Assigned Protocols),
2362 * the urgent pointer points to the last octet
2363 * of urgent data. We continue, however,
2364 * to consider it to indicate the first octet
2365 * of data past the urgent section as the original
2366 * spec states (in one of two places).
2368 if (SEQ_GT(th->th_seq + th->th_urp, tp->rcv_up)) {
2369 tp->rcv_up = th->th_seq + th->th_urp;
2370 so->so_oobmark = so->so_rcv.ssb_cc +
2371 (tp->rcv_up - tp->rcv_nxt) - 1;
2372 if (so->so_oobmark == 0)
2373 so->so_state |= SS_RCVATMARK;
2375 tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2378 * Remove out of band data so doesn't get presented to user.
2379 * This can happen independent of advancing the URG pointer,
2380 * but if two URG's are pending at once, some out-of-band
2381 * data may creep in... ick.
2383 if (th->th_urp <= (u_long)tlen &&
2384 !(so->so_options & SO_OOBINLINE)) {
2385 /* hdr drop is delayed */
2386 tcp_pulloutofband(so, th, m, drop_hdrlen);
2390 * If no out of band data is expected,
2391 * pull receive urgent pointer along
2392 * with the receive window.
2394 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2395 tp->rcv_up = tp->rcv_nxt;
2400 * Process the segment text, merging it into the TCP sequencing queue,
2401 * and arranging for acknowledgment of receipt if necessary.
2402 * This process logically involves adjusting tp->rcv_wnd as data
2403 * is presented to the user (this happens in tcp_usrreq.c,
2404 * case PRU_RCVD). If a FIN has already been received on this
2405 * connection then we just ignore the text.
2407 if ((tlen || (thflags & TH_FIN)) && !TCPS_HAVERCVDFIN(tp->t_state)) {
2408 m_adj(m, drop_hdrlen); /* delayed header drop */
2410 * Insert segment which includes th into TCP reassembly queue
2411 * with control block tp. Set thflags to whether reassembly now
2412 * includes a segment with FIN. This handles the common case
2413 * inline (segment is the next to be received on an established
2414 * connection, and the queue is empty), avoiding linkage into
2415 * and removal from the queue and repetition of various
2417 * Set DELACK for segments received in order, but ack
2418 * immediately when segments are out of order (so
2419 * fast retransmit can work).
2421 if (th->th_seq == tp->rcv_nxt &&
2422 LIST_EMPTY(&tp->t_segq) &&
2423 TCPS_HAVEESTABLISHED(tp->t_state)) {
2424 if (DELAY_ACK(tp)) {
2425 tcp_callout_reset(tp, tp->tt_delack,
2426 tcp_delacktime, tcp_timer_delack);
2428 tp->t_flags |= TF_ACKNOW;
2430 tp->rcv_nxt += tlen;
2431 thflags = th->th_flags & TH_FIN;
2432 tcpstat.tcps_rcvpack++;
2433 tcpstat.tcps_rcvbyte += tlen;
2435 if (so->so_state & SS_CANTRCVMORE)
2438 ssb_appendstream(&so->so_rcv, m);
2441 if (!(tp->t_flags & TF_DUPSEG)) {
2442 /* Initialize SACK report block. */
2443 tp->reportblk.rblk_start = th->th_seq;
2444 tp->reportblk.rblk_end = th->th_seq + tlen +
2445 ((thflags & TH_FIN) != 0);
2447 thflags = tcp_reass(tp, th, &tlen, m);
2448 tp->t_flags |= TF_ACKNOW;
2452 * Note the amount of data that peer has sent into
2453 * our window, in order to estimate the sender's
2456 len = so->so_rcv.ssb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2463 * If FIN is received ACK the FIN and let the user know
2464 * that the connection is closing.
2466 if (thflags & TH_FIN) {
2467 if (!TCPS_HAVERCVDFIN(tp->t_state)) {
2470 * If connection is half-synchronized
2471 * (ie NEEDSYN flag on) then delay ACK,
2472 * so it may be piggybacked when SYN is sent.
2473 * Otherwise, since we received a FIN then no
2474 * more input can be expected, send ACK now.
2476 if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN)) {
2477 tcp_callout_reset(tp, tp->tt_delack,
2478 tcp_delacktime, tcp_timer_delack);
2480 tp->t_flags |= TF_ACKNOW;
2485 switch (tp->t_state) {
2487 * In SYN_RECEIVED and ESTABLISHED STATES
2488 * enter the CLOSE_WAIT state.
2490 case TCPS_SYN_RECEIVED:
2491 tp->t_starttime = ticks;
2493 case TCPS_ESTABLISHED:
2494 tp->t_state = TCPS_CLOSE_WAIT;
2498 * If still in FIN_WAIT_1 STATE FIN has not been acked so
2499 * enter the CLOSING state.
2501 case TCPS_FIN_WAIT_1:
2502 tp->t_state = TCPS_CLOSING;
2506 * In FIN_WAIT_2 state enter the TIME_WAIT state,
2507 * starting the time-wait timer, turning off the other
2510 case TCPS_FIN_WAIT_2:
2511 tp->t_state = TCPS_TIME_WAIT;
2512 tcp_canceltimers(tp);
2513 tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_msl,
2515 soisdisconnected(so);
2519 * In TIME_WAIT state restart the 2 MSL time_wait timer.
2521 case TCPS_TIME_WAIT:
2522 tcp_callout_reset(tp, tp->tt_2msl, 2 * tcp_msl,
2529 if (so->so_options & SO_DEBUG)
2530 tcp_trace(TA_INPUT, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2534 * Return any desired output.
2536 if (needoutput || (tp->t_flags & TF_ACKNOW))
2542 * Generate an ACK dropping incoming segment if it occupies
2543 * sequence space, where the ACK reflects our state.
2545 * We can now skip the test for the RST flag since all
2546 * paths to this code happen after packets containing
2547 * RST have been dropped.
2549 * In the SYN-RECEIVED state, don't send an ACK unless the
2550 * segment we received passes the SYN-RECEIVED ACK test.
2551 * If it fails send a RST. This breaks the loop in the
2552 * "LAND" DoS attack, and also prevents an ACK storm
2553 * between two listening ports that have been sent forged
2554 * SYN segments, each with the source address of the other.
2556 if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2557 (SEQ_GT(tp->snd_una, th->th_ack) ||
2558 SEQ_GT(th->th_ack, tp->snd_max)) ) {
2559 rstreason = BANDLIM_RST_OPENPORT;
2563 if (so->so_options & SO_DEBUG)
2564 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2567 tp->t_flags |= TF_ACKNOW;
2573 * Generate a RST, dropping incoming segment.
2574 * Make ACK acceptable to originator of segment.
2575 * Don't bother to respond if destination was broadcast/multicast.
2577 if ((thflags & TH_RST) || m->m_flags & (M_BCAST | M_MCAST))
2580 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
2581 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
2584 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
2585 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
2586 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
2587 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
2590 /* IPv6 anycast check is done at tcp6_input() */
2593 * Perform bandwidth limiting.
2596 if (badport_bandlim(rstreason) < 0)
2601 if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2602 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2604 if (thflags & TH_ACK)
2605 /* mtod() below is safe as long as hdr dropping is delayed */
2606 tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
2609 if (thflags & TH_SYN)
2611 /* mtod() below is safe as long as hdr dropping is delayed */
2612 tcp_respond(tp, mtod(m, void *), th, m, th->th_seq + tlen,
2613 (tcp_seq)0, TH_RST | TH_ACK);
2619 * Drop space held by incoming segment and return.
2622 if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
2623 tcp_trace(TA_DROP, ostate, tp, tcp_saveipgen, &tcp_savetcp, 0);
2630 * Parse TCP options and place in tcpopt.
2633 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, boolean_t is_syn)
2638 for (; cnt > 0; cnt -= optlen, cp += optlen) {
2640 if (opt == TCPOPT_EOL)
2642 if (opt == TCPOPT_NOP)
2648 if (optlen < 2 || optlen > cnt)
2653 if (optlen != TCPOLEN_MAXSEG)
2657 to->to_flags |= TOF_MSS;
2658 bcopy(cp + 2, &to->to_mss, sizeof to->to_mss);
2659 to->to_mss = ntohs(to->to_mss);
2662 if (optlen != TCPOLEN_WINDOW)
2666 to->to_flags |= TOF_SCALE;
2667 to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
2669 case TCPOPT_TIMESTAMP:
2670 if (optlen != TCPOLEN_TIMESTAMP)
2672 to->to_flags |= TOF_TS;
2673 bcopy(cp + 2, &to->to_tsval, sizeof to->to_tsval);
2674 to->to_tsval = ntohl(to->to_tsval);
2675 bcopy(cp + 6, &to->to_tsecr, sizeof to->to_tsecr);
2676 to->to_tsecr = ntohl(to->to_tsecr);
2678 * If echoed timestamp is later than the current time,
2679 * fall back to non RFC1323 RTT calculation.
2681 if (to->to_tsecr != 0 && TSTMP_GT(to->to_tsecr, ticks))
2684 case TCPOPT_SACK_PERMITTED:
2685 if (optlen != TCPOLEN_SACK_PERMITTED)
2689 to->to_flags |= TOF_SACK_PERMITTED;
2692 if ((optlen - 2) & 0x07) /* not multiple of 8 */
2694 to->to_nsackblocks = (optlen - 2) / 8;
2695 to->to_sackblocks = (struct raw_sackblock *) (cp + 2);
2696 to->to_flags |= TOF_SACK;
2697 for (i = 0; i < to->to_nsackblocks; i++) {
2698 struct raw_sackblock *r = &to->to_sackblocks[i];
2700 r->rblk_start = ntohl(r->rblk_start);
2701 r->rblk_end = ntohl(r->rblk_end);
2711 * Pull out of band byte out of a segment so
2712 * it doesn't appear in the user's data queue.
2713 * It is still reflected in the segment length for
2714 * sequencing purposes.
2715 * "off" is the delayed to be dropped hdrlen.
2718 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m, int off)
2720 int cnt = off + th->th_urp - 1;
2723 if (m->m_len > cnt) {
2724 char *cp = mtod(m, caddr_t) + cnt;
2725 struct tcpcb *tp = sototcpcb(so);
2728 tp->t_oobflags |= TCPOOB_HAVEDATA;
2729 bcopy(cp + 1, cp, m->m_len - cnt - 1);
2731 if (m->m_flags & M_PKTHDR)
2740 panic("tcp_pulloutofband");
2744 * Collect new round-trip time estimate
2745 * and update averages and current timeout.
2748 tcp_xmit_timer(struct tcpcb *tp, int rtt)
2752 tcpstat.tcps_rttupdated++;
2754 if (tp->t_srtt != 0) {
2756 * srtt is stored as fixed point with 5 bits after the
2757 * binary point (i.e., scaled by 8). The following magic
2758 * is equivalent to the smoothing algorithm in rfc793 with
2759 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
2760 * point). Adjust rtt to origin 0.
2762 delta = ((rtt - 1) << TCP_DELTA_SHIFT)
2763 - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
2765 if ((tp->t_srtt += delta) <= 0)
2769 * We accumulate a smoothed rtt variance (actually, a
2770 * smoothed mean difference), then set the retransmit
2771 * timer to smoothed rtt + 4 times the smoothed variance.
2772 * rttvar is stored as fixed point with 4 bits after the
2773 * binary point (scaled by 16). The following is
2774 * equivalent to rfc793 smoothing with an alpha of .75
2775 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces
2776 * rfc793's wired-in beta.
2780 delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
2781 if ((tp->t_rttvar += delta) <= 0)
2783 if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
2784 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2787 * No rtt measurement yet - use the unsmoothed rtt.
2788 * Set the variance to half the rtt (so our first
2789 * retransmit happens at 3*rtt).
2791 tp->t_srtt = rtt << TCP_RTT_SHIFT;
2792 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
2793 tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
2799 * the retransmit should happen at rtt + 4 * rttvar.
2800 * Because of the way we do the smoothing, srtt and rttvar
2801 * will each average +1/2 tick of bias. When we compute
2802 * the retransmit timer, we want 1/2 tick of rounding and
2803 * 1 extra tick because of +-1/2 tick uncertainty in the
2804 * firing of the timer. The bias will give us exactly the
2805 * 1.5 tick we need. But, because the bias is
2806 * statistical, we have to test that we don't drop below
2807 * the minimum feasible timer (which is 2 ticks).
2809 TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
2810 max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
2813 * We received an ack for a packet that wasn't retransmitted;
2814 * it is probably safe to discard any error indications we've
2815 * received recently. This isn't quite right, but close enough
2816 * for now (a route might have failed after we sent a segment,
2817 * and the return path might not be symmetrical).
2819 tp->t_softerror = 0;
2823 * Determine a reasonable value for maxseg size.
2824 * If the route is known, check route for mtu.
2825 * If none, use an mss that can be handled on the outgoing
2826 * interface without forcing IP to fragment; if bigger than
2827 * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
2828 * to utilize large mbufs. If no route is found, route has no mtu,
2829 * or the destination isn't local, use a default, hopefully conservative
2830 * size (usually 512 or the default IP max size, but no more than the mtu
2831 * of the interface), as we can't discover anything about intervening
2832 * gateways or networks. We also initialize the congestion/slow start
2833 * window to be a single segment if the destination isn't local.
2834 * While looking at the routing entry, we also initialize other path-dependent
2835 * parameters from pre-set or cached values in the routing entry.
2837 * Also take into account the space needed for options that we
2838 * send regularly. Make maxseg shorter by that amount to assure
2839 * that we can send maxseg amount of data even when the options
2840 * are present. Store the upper limit of the length of options plus
2843 * NOTE that this routine is only called when we process an incoming
2844 * segment, for outgoing segments only tcp_mssopt is called.
2847 tcp_mss(struct tcpcb *tp, int offer)
2853 struct inpcb *inp = tp->t_inpcb;
2856 boolean_t isipv6 = ((inp->inp_vflag & INP_IPV6) ? TRUE : FALSE);
2857 size_t min_protoh = isipv6 ?
2858 sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
2859 sizeof(struct tcpiphdr);
2861 const boolean_t isipv6 = FALSE;
2862 const size_t min_protoh = sizeof(struct tcpiphdr);
2866 rt = tcp_rtlookup6(&inp->inp_inc);
2868 rt = tcp_rtlookup(&inp->inp_inc);
2870 tp->t_maxopd = tp->t_maxseg =
2871 (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
2875 so = inp->inp_socket;
2878 * Offer == 0 means that there was no MSS on the SYN segment,
2879 * in this case we use either the interface mtu or tcp_mssdflt.
2881 * An offer which is too large will be cut down later.
2885 if (in6_localaddr(&inp->in6p_faddr)) {
2886 offer = ND_IFINFO(rt->rt_ifp)->linkmtu -
2889 offer = tcp_v6mssdflt;
2892 if (in_localaddr(inp->inp_faddr))
2893 offer = ifp->if_mtu - min_protoh;
2895 offer = tcp_mssdflt;
2900 * Prevent DoS attack with too small MSS. Round up
2901 * to at least minmss.
2903 * Sanity check: make sure that maxopd will be large
2904 * enough to allow some data on segments even is the
2905 * all the option space is used (40bytes). Otherwise
2906 * funny things may happen in tcp_output.
2908 offer = max(offer, tcp_minmss);
2909 offer = max(offer, 64);
2911 rt->rt_rmx.rmx_mssopt = offer;
2914 * While we're here, check if there's an initial rtt
2915 * or rttvar. Convert from the route-table units
2916 * to scaled multiples of the slow timeout timer.
2918 if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
2920 * XXX the lock bit for RTT indicates that the value
2921 * is also a minimum value; this is subject to time.
2923 if (rt->rt_rmx.rmx_locks & RTV_RTT)
2924 tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
2925 tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
2926 tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
2927 tcpstat.tcps_usedrtt++;
2928 if (rt->rt_rmx.rmx_rttvar) {
2929 tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
2930 (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
2931 tcpstat.tcps_usedrttvar++;
2933 /* default variation is +- 1 rtt */
2935 tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
2937 TCPT_RANGESET(tp->t_rxtcur,
2938 ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
2939 tp->t_rttmin, TCPTV_REXMTMAX);
2943 * if there's an mtu associated with the route, use it
2944 * else, use the link mtu. Take the smaller of mss or offer
2947 if (rt->rt_rmx.rmx_mtu) {
2948 mss = rt->rt_rmx.rmx_mtu - min_protoh;
2951 mss = ND_IFINFO(rt->rt_ifp)->linkmtu - min_protoh;
2953 mss = ifp->if_mtu - min_protoh;
2955 mss = min(mss, offer);
2958 * maxopd stores the maximum length of data AND options
2959 * in a segment; maxseg is the amount of data in a normal
2960 * segment. We need to store this value (maxopd) apart
2961 * from maxseg, because now every segment carries options
2962 * and thus we normally have somewhat less data in segments.
2966 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
2967 ((tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
2968 mss -= TCPOLEN_TSTAMP_APPA;
2970 #if (MCLBYTES & (MCLBYTES - 1)) == 0
2972 mss &= ~(MCLBYTES-1);
2975 mss = mss / MCLBYTES * MCLBYTES;
2978 * If there's a pipesize, change the socket buffer
2979 * to that size. Make the socket buffers an integral
2980 * number of mss units; if the mss is larger than
2981 * the socket buffer, decrease the mss.
2984 if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
2986 bufsize = so->so_snd.ssb_hiwat;
2990 bufsize = roundup(bufsize, mss);
2991 if (bufsize > sb_max)
2993 if (bufsize > so->so_snd.ssb_hiwat)
2994 ssb_reserve(&so->so_snd, bufsize, so, NULL);
2999 if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
3001 bufsize = so->so_rcv.ssb_hiwat;
3002 if (bufsize > mss) {
3003 bufsize = roundup(bufsize, mss);
3004 if (bufsize > sb_max)
3006 if (bufsize > so->so_rcv.ssb_hiwat)
3007 ssb_reserve(&so->so_rcv, bufsize, so, NULL);
3011 * Set the slow-start flight size depending on whether this
3012 * is a local network or not.
3015 tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380));
3019 if (rt->rt_rmx.rmx_ssthresh) {
3021 * There's some sort of gateway or interface
3022 * buffer limit on the path. Use this to set
3023 * the slow start threshhold, but set the
3024 * threshold to no less than 2*mss.
3026 tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
3027 tcpstat.tcps_usedssthresh++;
3032 * Determine the MSS option to send on an outgoing SYN.
3035 tcp_mssopt(struct tcpcb *tp)
3040 ((tp->t_inpcb->inp_vflag & INP_IPV6) ? TRUE : FALSE);
3041 int min_protoh = isipv6 ?
3042 sizeof(struct ip6_hdr) + sizeof(struct tcphdr) :
3043 sizeof(struct tcpiphdr);
3045 const boolean_t isipv6 = FALSE;
3046 const size_t min_protoh = sizeof(struct tcpiphdr);
3050 rt = tcp_rtlookup6(&tp->t_inpcb->inp_inc);
3052 rt = tcp_rtlookup(&tp->t_inpcb->inp_inc);
3054 return (isipv6 ? tcp_v6mssdflt : tcp_mssdflt);
3056 return (rt->rt_ifp->if_mtu - min_protoh);
3060 * When a partial ack arrives, force the retransmission of the
3061 * next unacknowledged segment. Do not exit Fast Recovery.
3063 * Implement the Slow-but-Steady variant of NewReno by restarting the
3064 * the retransmission timer. Turn it off here so it can be restarted
3065 * later in tcp_output().
3068 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th, int acked)
3070 tcp_seq old_snd_nxt = tp->snd_nxt;
3071 u_long ocwnd = tp->snd_cwnd;
3073 tcp_callout_stop(tp, tp->tt_rexmt);
3075 tp->snd_nxt = th->th_ack;
3076 /* Set snd_cwnd to one segment beyond acknowledged offset. */
3077 tp->snd_cwnd = tp->t_maxseg;
3078 tp->t_flags |= TF_ACKNOW;
3080 if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
3081 tp->snd_nxt = old_snd_nxt;
3082 /* partial window deflation */
3084 tp->snd_cwnd = ocwnd - acked + tp->t_maxseg;
3086 tp->snd_cwnd = tp->t_maxseg;
3090 * In contrast to the Slow-but-Steady NewReno variant,
3091 * we do not reset the retransmission timer for SACK retransmissions,
3092 * except when retransmitting snd_una.
3095 tcp_sack_rexmt(struct tcpcb *tp, struct tcphdr *th)
3097 uint32_t pipe, seglen;
3100 tcp_seq old_snd_nxt = tp->snd_nxt;
3101 u_long ocwnd = tp->snd_cwnd;
3102 int nseg = 0; /* consecutive new segments */
3103 #define MAXBURST 4 /* limit burst of new packets on partial ack */
3106 pipe = tcp_sack_compute_pipe(tp);
3107 while ((tcp_seq_diff_t)(ocwnd - pipe) >= (tcp_seq_diff_t)tp->t_maxseg &&
3108 (!tcp_do_smartsack || nseg < MAXBURST) &&
3109 tcp_sack_nextseg(tp, &nextrexmt, &seglen, &lostdup)) {
3111 tcp_seq old_snd_max;
3114 if (nextrexmt == tp->snd_max)
3116 tp->snd_nxt = nextrexmt;
3117 tp->snd_cwnd = nextrexmt - tp->snd_una + seglen;
3118 old_snd_max = tp->snd_max;
3119 if (nextrexmt == tp->snd_una)
3120 tcp_callout_stop(tp, tp->tt_rexmt);
3121 error = tcp_output(tp);
3124 sent = tp->snd_nxt - nextrexmt;
3129 tcpstat.tcps_sndsackpack++;
3130 tcpstat.tcps_sndsackbyte += sent;
3131 if (SEQ_LT(nextrexmt, old_snd_max) &&
3132 SEQ_LT(tp->rexmt_high, tp->snd_nxt))
3133 tp->rexmt_high = seq_min(tp->snd_nxt, old_snd_max);
3135 if (SEQ_GT(old_snd_nxt, tp->snd_nxt))
3136 tp->snd_nxt = old_snd_nxt;
3137 tp->snd_cwnd = ocwnd;
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