xref: /freebsd/sys/netinet/tcp_input.c (revision 7750ad47a9a7dbc83f87158464170c8640723293)
1 /*-
2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
3  *	The Regents of the University of California.  All rights reserved.
4  * Copyright (c) 2007-2008,2010
5  *	Swinburne University of Technology, Melbourne, Australia.
6  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
7  * Copyright (c) 2010 The FreeBSD Foundation
8  * Copyright (c) 2010-2011 Juniper Networks, Inc.
9  * All rights reserved.
10  *
11  * Portions of this software were developed at the Centre for Advanced Internet
12  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
13  * James Healy and David Hayes, made possible in part by a grant from the Cisco
14  * University Research Program Fund at Community Foundation Silicon Valley.
15  *
16  * Portions of this software were developed at the Centre for Advanced
17  * Internet Architectures, Swinburne University of Technology, Melbourne,
18  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
19  *
20  * Portions of this software were developed by Robert N. M. Watson under
21  * contract to Juniper Networks, Inc.
22  *
23  * Redistribution and use in source and binary forms, with or without
24  * modification, are permitted provided that the following conditions
25  * are met:
26  * 1. Redistributions of source code must retain the above copyright
27  *    notice, this list of conditions and the following disclaimer.
28  * 2. Redistributions in binary form must reproduce the above copyright
29  *    notice, this list of conditions and the following disclaimer in the
30  *    documentation and/or other materials provided with the distribution.
31  * 4. Neither the name of the University nor the names of its contributors
32  *    may be used to endorse or promote products derived from this software
33  *    without specific prior written permission.
34  *
35  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
45  * SUCH DAMAGE.
46  *
47  *	@(#)tcp_input.c	8.12 (Berkeley) 5/24/95
48  */
49 
50 #include <sys/cdefs.h>
51 __FBSDID("$FreeBSD$");
52 
53 #include "opt_ipfw.h"		/* for ipfw_fwd	*/
54 #include "opt_inet.h"
55 #include "opt_inet6.h"
56 #include "opt_ipsec.h"
57 #include "opt_tcpdebug.h"
58 
59 #include <sys/param.h>
60 #include <sys/kernel.h>
61 #include <sys/hhook.h>
62 #include <sys/malloc.h>
63 #include <sys/mbuf.h>
64 #include <sys/proc.h>		/* for proc0 declaration */
65 #include <sys/protosw.h>
66 #include <sys/signalvar.h>
67 #include <sys/socket.h>
68 #include <sys/socketvar.h>
69 #include <sys/sysctl.h>
70 #include <sys/syslog.h>
71 #include <sys/systm.h>
72 
73 #include <machine/cpu.h>	/* before tcp_seq.h, for tcp_random18() */
74 
75 #include <vm/uma.h>
76 
77 #include <net/if.h>
78 #include <net/route.h>
79 #include <net/vnet.h>
80 
81 #define TCPSTATES		/* for logging */
82 
83 #include <netinet/cc.h>
84 #include <netinet/in.h>
85 #include <netinet/in_pcb.h>
86 #include <netinet/in_systm.h>
87 #include <netinet/in_var.h>
88 #include <netinet/ip.h>
89 #include <netinet/ip_icmp.h>	/* required for icmp_var.h */
90 #include <netinet/icmp_var.h>	/* for ICMP_BANDLIM */
91 #include <netinet/ip_var.h>
92 #include <netinet/ip_options.h>
93 #include <netinet/ip6.h>
94 #include <netinet/icmp6.h>
95 #include <netinet6/in6_pcb.h>
96 #include <netinet6/ip6_var.h>
97 #include <netinet6/nd6.h>
98 #include <netinet/tcp_fsm.h>
99 #include <netinet/tcp_seq.h>
100 #include <netinet/tcp_timer.h>
101 #include <netinet/tcp_var.h>
102 #include <netinet6/tcp6_var.h>
103 #include <netinet/tcpip.h>
104 #include <netinet/tcp_syncache.h>
105 #ifdef TCPDEBUG
106 #include <netinet/tcp_debug.h>
107 #endif /* TCPDEBUG */
108 
109 #ifdef IPSEC
110 #include <netipsec/ipsec.h>
111 #include <netipsec/ipsec6.h>
112 #endif /*IPSEC*/
113 
114 #include <machine/in_cksum.h>
115 
116 #include <security/mac/mac_framework.h>
117 
118 const int tcprexmtthresh = 3;
119 
120 VNET_DEFINE(struct tcpstat, tcpstat);
121 SYSCTL_VNET_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW,
122     &VNET_NAME(tcpstat), tcpstat,
123     "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
124 
125 int tcp_log_in_vain = 0;
126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
127     &tcp_log_in_vain, 0,
128     "Log all incoming TCP segments to closed ports");
129 
130 VNET_DEFINE(int, blackhole) = 0;
131 #define	V_blackhole		VNET(blackhole)
132 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
133     &VNET_NAME(blackhole), 0,
134     "Do not send RST on segments to closed ports");
135 
136 VNET_DEFINE(int, tcp_delack_enabled) = 1;
137 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
138     &VNET_NAME(tcp_delack_enabled), 0,
139     "Delay ACK to try and piggyback it onto a data packet");
140 
141 VNET_DEFINE(int, drop_synfin) = 0;
142 #define	V_drop_synfin		VNET(drop_synfin)
143 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
144     &VNET_NAME(drop_synfin), 0,
145     "Drop TCP packets with SYN+FIN set");
146 
147 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
148 #define	V_tcp_do_rfc3042	VNET(tcp_do_rfc3042)
149 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
150     &VNET_NAME(tcp_do_rfc3042), 0,
151     "Enable RFC 3042 (Limited Transmit)");
152 
153 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
154 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
155     &VNET_NAME(tcp_do_rfc3390), 0,
156     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
157 
158 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
159 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
160     &VNET_NAME(tcp_do_rfc3465), 0,
161     "Enable RFC 3465 (Appropriate Byte Counting)");
162 
163 VNET_DEFINE(int, tcp_abc_l_var) = 2;
164 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
165     &VNET_NAME(tcp_abc_l_var), 2,
166     "Cap the max cwnd increment during slow-start to this number of segments");
167 
168 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
169 
170 VNET_DEFINE(int, tcp_do_ecn) = 0;
171 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
172     &VNET_NAME(tcp_do_ecn), 0,
173     "TCP ECN support");
174 
175 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
176 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
177     &VNET_NAME(tcp_ecn_maxretries), 0,
178     "Max retries before giving up on ECN");
179 
180 VNET_DEFINE(int, tcp_insecure_rst) = 0;
181 #define	V_tcp_insecure_rst	VNET(tcp_insecure_rst)
182 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
183     &VNET_NAME(tcp_insecure_rst), 0,
184     "Follow the old (insecure) criteria for accepting RST packets");
185 
186 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
187 #define	V_tcp_recvspace	VNET(tcp_recvspace)
188 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
189     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
190 
191 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
192 #define	V_tcp_do_autorcvbuf	VNET(tcp_do_autorcvbuf)
193 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
194     &VNET_NAME(tcp_do_autorcvbuf), 0,
195     "Enable automatic receive buffer sizing");
196 
197 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
198 #define	V_tcp_autorcvbuf_inc	VNET(tcp_autorcvbuf_inc)
199 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
200     &VNET_NAME(tcp_autorcvbuf_inc), 0,
201     "Incrementor step size of automatic receive buffer");
202 
203 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
204 #define	V_tcp_autorcvbuf_max	VNET(tcp_autorcvbuf_max)
205 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
206     &VNET_NAME(tcp_autorcvbuf_max), 0,
207     "Max size of automatic receive buffer");
208 
209 VNET_DEFINE(struct inpcbhead, tcb);
210 #define	tcb6	tcb  /* for KAME src sync over BSD*'s */
211 VNET_DEFINE(struct inpcbinfo, tcbinfo);
212 
213 static void	 tcp_dooptions(struct tcpopt *, u_char *, int, int);
214 static void	 tcp_do_segment(struct mbuf *, struct tcphdr *,
215 		     struct socket *, struct tcpcb *, int, int, uint8_t,
216 		     int);
217 static void	 tcp_dropwithreset(struct mbuf *, struct tcphdr *,
218 		     struct tcpcb *, int, int);
219 static void	 tcp_pulloutofband(struct socket *,
220 		     struct tcphdr *, struct mbuf *, int);
221 static void	 tcp_xmit_timer(struct tcpcb *, int);
222 static void	 tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
223 static void inline 	tcp_fields_to_host(struct tcphdr *);
224 #ifdef TCP_SIGNATURE
225 static void inline 	tcp_fields_to_net(struct tcphdr *);
226 static int inline	tcp_signature_verify_input(struct mbuf *, int, int,
227 			    int, struct tcpopt *, struct tcphdr *, u_int);
228 #endif
229 static void inline	cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
230 			    uint16_t type);
231 static void inline	cc_conn_init(struct tcpcb *tp);
232 static void inline	cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
233 static void inline	hhook_run_tcp_est_in(struct tcpcb *tp,
234 			    struct tcphdr *th, struct tcpopt *to);
235 
236 /*
237  * Kernel module interface for updating tcpstat.  The argument is an index
238  * into tcpstat treated as an array of u_long.  While this encodes the
239  * general layout of tcpstat into the caller, it doesn't encode its location,
240  * so that future changes to add, for example, per-CPU stats support won't
241  * cause binary compatibility problems for kernel modules.
242  */
243 void
244 kmod_tcpstat_inc(int statnum)
245 {
246 
247 	(*((u_long *)&V_tcpstat + statnum))++;
248 }
249 
250 /*
251  * Wrapper for the TCP established input helper hook.
252  */
253 static void inline
254 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
255 {
256 	struct tcp_hhook_data hhook_data;
257 
258 	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
259 		hhook_data.tp = tp;
260 		hhook_data.th = th;
261 		hhook_data.to = to;
262 
263 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
264 		    tp->osd);
265 	}
266 }
267 
268 /*
269  * CC wrapper hook functions
270  */
271 static void inline
272 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
273 {
274 	INP_WLOCK_ASSERT(tp->t_inpcb);
275 
276 	tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
277 	if (tp->snd_cwnd == min(tp->snd_cwnd, tp->snd_wnd))
278 		tp->ccv->flags |= CCF_CWND_LIMITED;
279 	else
280 		tp->ccv->flags &= ~CCF_CWND_LIMITED;
281 
282 	if (type == CC_ACK) {
283 		if (tp->snd_cwnd > tp->snd_ssthresh) {
284 			tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
285 			     V_tcp_abc_l_var * tp->t_maxseg);
286 			if (tp->t_bytes_acked >= tp->snd_cwnd) {
287 				tp->t_bytes_acked -= tp->snd_cwnd;
288 				tp->ccv->flags |= CCF_ABC_SENTAWND;
289 			}
290 		} else {
291 				tp->ccv->flags &= ~CCF_ABC_SENTAWND;
292 				tp->t_bytes_acked = 0;
293 		}
294 	}
295 
296 	if (CC_ALGO(tp)->ack_received != NULL) {
297 		/* XXXLAS: Find a way to live without this */
298 		tp->ccv->curack = th->th_ack;
299 		CC_ALGO(tp)->ack_received(tp->ccv, type);
300 	}
301 }
302 
303 static void inline
304 cc_conn_init(struct tcpcb *tp)
305 {
306 	struct hc_metrics_lite metrics;
307 	struct inpcb *inp = tp->t_inpcb;
308 	int rtt;
309 
310 	INP_WLOCK_ASSERT(tp->t_inpcb);
311 
312 	tcp_hc_get(&inp->inp_inc, &metrics);
313 
314 	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
315 		tp->t_srtt = rtt;
316 		tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
317 		TCPSTAT_INC(tcps_usedrtt);
318 		if (metrics.rmx_rttvar) {
319 			tp->t_rttvar = metrics.rmx_rttvar;
320 			TCPSTAT_INC(tcps_usedrttvar);
321 		} else {
322 			/* default variation is +- 1 rtt */
323 			tp->t_rttvar =
324 			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
325 		}
326 		TCPT_RANGESET(tp->t_rxtcur,
327 		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
328 		    tp->t_rttmin, TCPTV_REXMTMAX);
329 	}
330 	if (metrics.rmx_ssthresh) {
331 		/*
332 		 * There's some sort of gateway or interface
333 		 * buffer limit on the path.  Use this to set
334 		 * the slow start threshhold, but set the
335 		 * threshold to no less than 2*mss.
336 		 */
337 		tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
338 		TCPSTAT_INC(tcps_usedssthresh);
339 	}
340 
341 	/*
342 	 * Set the initial slow-start flight size.
343 	 *
344 	 * RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
345 	 * XXX: We currently check only in syncache_socket for that.
346 	 */
347 	if (V_tcp_do_rfc3390)
348 		tp->snd_cwnd = min(4 * tp->t_maxseg,
349 		    max(2 * tp->t_maxseg, 4380));
350 	else
351 		tp->snd_cwnd = tp->t_maxseg;
352 
353 	if (CC_ALGO(tp)->conn_init != NULL)
354 		CC_ALGO(tp)->conn_init(tp->ccv);
355 }
356 
357 void inline
358 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
359 {
360 	INP_WLOCK_ASSERT(tp->t_inpcb);
361 
362 	switch(type) {
363 	case CC_NDUPACK:
364 		if (!IN_FASTRECOVERY(tp->t_flags)) {
365 			tp->snd_recover = tp->snd_max;
366 			if (tp->t_flags & TF_ECN_PERMIT)
367 				tp->t_flags |= TF_ECN_SND_CWR;
368 		}
369 		break;
370 	case CC_ECN:
371 		if (!IN_CONGRECOVERY(tp->t_flags)) {
372 			TCPSTAT_INC(tcps_ecn_rcwnd);
373 			tp->snd_recover = tp->snd_max;
374 			if (tp->t_flags & TF_ECN_PERMIT)
375 				tp->t_flags |= TF_ECN_SND_CWR;
376 		}
377 		break;
378 	case CC_RTO:
379 		tp->t_dupacks = 0;
380 		tp->t_bytes_acked = 0;
381 		EXIT_RECOVERY(tp->t_flags);
382 		tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
383 		    tp->t_maxseg) * tp->t_maxseg;
384 		tp->snd_cwnd = tp->t_maxseg;
385 		break;
386 	case CC_RTO_ERR:
387 		TCPSTAT_INC(tcps_sndrexmitbad);
388 		/* RTO was unnecessary, so reset everything. */
389 		tp->snd_cwnd = tp->snd_cwnd_prev;
390 		tp->snd_ssthresh = tp->snd_ssthresh_prev;
391 		tp->snd_recover = tp->snd_recover_prev;
392 		if (tp->t_flags & TF_WASFRECOVERY)
393 			ENTER_FASTRECOVERY(tp->t_flags);
394 		if (tp->t_flags & TF_WASCRECOVERY)
395 			ENTER_CONGRECOVERY(tp->t_flags);
396 		tp->snd_nxt = tp->snd_max;
397 		tp->t_flags &= ~TF_PREVVALID;
398 		tp->t_badrxtwin = 0;
399 		break;
400 	}
401 
402 	if (CC_ALGO(tp)->cong_signal != NULL) {
403 		if (th != NULL)
404 			tp->ccv->curack = th->th_ack;
405 		CC_ALGO(tp)->cong_signal(tp->ccv, type);
406 	}
407 }
408 
409 static void inline
410 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
411 {
412 	INP_WLOCK_ASSERT(tp->t_inpcb);
413 
414 	/* XXXLAS: KASSERT that we're in recovery? */
415 
416 	if (CC_ALGO(tp)->post_recovery != NULL) {
417 		tp->ccv->curack = th->th_ack;
418 		CC_ALGO(tp)->post_recovery(tp->ccv);
419 	}
420 	/* XXXLAS: EXIT_RECOVERY ? */
421 	tp->t_bytes_acked = 0;
422 }
423 
424 static inline void
425 tcp_fields_to_host(struct tcphdr *th)
426 {
427 
428 	th->th_seq = ntohl(th->th_seq);
429 	th->th_ack = ntohl(th->th_ack);
430 	th->th_win = ntohs(th->th_win);
431 	th->th_urp = ntohs(th->th_urp);
432 }
433 
434 #ifdef TCP_SIGNATURE
435 static inline void
436 tcp_fields_to_net(struct tcphdr *th)
437 {
438 
439 	th->th_seq = htonl(th->th_seq);
440 	th->th_ack = htonl(th->th_ack);
441 	th->th_win = htons(th->th_win);
442 	th->th_urp = htons(th->th_urp);
443 }
444 
445 static inline int
446 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
447     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
448 {
449 	int ret;
450 
451 	tcp_fields_to_net(th);
452 	ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
453 	tcp_fields_to_host(th);
454 	return (ret);
455 }
456 #endif
457 
458 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
459 #ifdef INET6
460 #define ND6_HINT(tp) \
461 do { \
462 	if ((tp) && (tp)->t_inpcb && \
463 	    ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
464 		nd6_nud_hint(NULL, NULL, 0); \
465 } while (0)
466 #else
467 #define ND6_HINT(tp)
468 #endif
469 
470 /*
471  * Indicate whether this ack should be delayed.  We can delay the ack if
472  *	- there is no delayed ack timer in progress and
473  *	- our last ack wasn't a 0-sized window.  We never want to delay
474  *	  the ack that opens up a 0-sized window and
475  *		- delayed acks are enabled or
476  *		- this is a half-synchronized T/TCP connection.
477  */
478 #define DELAY_ACK(tp)							\
479 	((!tcp_timer_active(tp, TT_DELACK) &&				\
480 	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
481 	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
482 
483 /*
484  * TCP input handling is split into multiple parts:
485  *   tcp6_input is a thin wrapper around tcp_input for the extended
486  *	ip6_protox[] call format in ip6_input
487  *   tcp_input handles primary segment validation, inpcb lookup and
488  *	SYN processing on listen sockets
489  *   tcp_do_segment processes the ACK and text of the segment for
490  *	establishing, established and closing connections
491  */
492 #ifdef INET6
493 int
494 tcp6_input(struct mbuf **mp, int *offp, int proto)
495 {
496 	struct mbuf *m = *mp;
497 	struct in6_ifaddr *ia6;
498 
499 	IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
500 
501 	/*
502 	 * draft-itojun-ipv6-tcp-to-anycast
503 	 * better place to put this in?
504 	 */
505 	ia6 = ip6_getdstifaddr(m);
506 	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
507 		struct ip6_hdr *ip6;
508 
509 		ifa_free(&ia6->ia_ifa);
510 		ip6 = mtod(m, struct ip6_hdr *);
511 		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
512 			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
513 		return IPPROTO_DONE;
514 	}
515 
516 	tcp_input(m, *offp);
517 	return IPPROTO_DONE;
518 }
519 #endif /* INET6 */
520 
521 void
522 tcp_input(struct mbuf *m, int off0)
523 {
524 	struct tcphdr *th = NULL;
525 	struct ip *ip = NULL;
526 #ifdef INET
527 	struct ipovly *ipov;
528 #endif
529 	struct inpcb *inp = NULL;
530 	struct tcpcb *tp = NULL;
531 	struct socket *so = NULL;
532 	u_char *optp = NULL;
533 	int optlen = 0;
534 #ifdef INET
535 	int len;
536 #endif
537 	int tlen = 0, off;
538 	int drop_hdrlen;
539 	int thflags;
540 	int rstreason = 0;	/* For badport_bandlim accounting purposes */
541 #ifdef TCP_SIGNATURE
542 	uint8_t sig_checked = 0;
543 #endif
544 	uint8_t iptos = 0;
545 #ifdef IPFIREWALL_FORWARD
546 	struct m_tag *fwd_tag;
547 #endif
548 #ifdef INET6
549 	struct ip6_hdr *ip6 = NULL;
550 	int isipv6;
551 #else
552 	const void *ip6 = NULL;
553 #endif /* INET6 */
554 	struct tcpopt to;		/* options in this segment */
555 	char *s = NULL;			/* address and port logging */
556 	int ti_locked;
557 #define	TI_UNLOCKED	1
558 #define	TI_WLOCKED	2
559 
560 #ifdef TCPDEBUG
561 	/*
562 	 * The size of tcp_saveipgen must be the size of the max ip header,
563 	 * now IPv6.
564 	 */
565 	u_char tcp_saveipgen[IP6_HDR_LEN];
566 	struct tcphdr tcp_savetcp;
567 	short ostate = 0;
568 #endif
569 
570 #ifdef INET6
571 	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
572 #endif
573 
574 	to.to_flags = 0;
575 	TCPSTAT_INC(tcps_rcvtotal);
576 
577 #ifdef INET6
578 	if (isipv6) {
579 		/* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
580 
581 		if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
582 			m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
583 			if (m == NULL) {
584 				TCPSTAT_INC(tcps_rcvshort);
585 				return;
586 			}
587 		}
588 
589 		ip6 = mtod(m, struct ip6_hdr *);
590 		th = (struct tcphdr *)((caddr_t)ip6 + off0);
591 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
592 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
593 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
594 				th->th_sum = m->m_pkthdr.csum_data;
595 			else
596 				th->th_sum = in6_cksum_pseudo(ip6, tlen,
597 				    IPPROTO_TCP, m->m_pkthdr.csum_data);
598 			th->th_sum ^= 0xffff;
599 		} else
600 			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
601 		if (th->th_sum) {
602 			TCPSTAT_INC(tcps_rcvbadsum);
603 			goto drop;
604 		}
605 
606 		/*
607 		 * Be proactive about unspecified IPv6 address in source.
608 		 * As we use all-zero to indicate unbounded/unconnected pcb,
609 		 * unspecified IPv6 address can be used to confuse us.
610 		 *
611 		 * Note that packets with unspecified IPv6 destination is
612 		 * already dropped in ip6_input.
613 		 */
614 		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
615 			/* XXX stat */
616 			goto drop;
617 		}
618 	}
619 #endif
620 #if defined(INET) && defined(INET6)
621 	else
622 #endif
623 #ifdef INET
624 	{
625 		/*
626 		 * Get IP and TCP header together in first mbuf.
627 		 * Note: IP leaves IP header in first mbuf.
628 		 */
629 		if (off0 > sizeof (struct ip)) {
630 			ip_stripoptions(m, (struct mbuf *)0);
631 			off0 = sizeof(struct ip);
632 		}
633 		if (m->m_len < sizeof (struct tcpiphdr)) {
634 			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
635 			    == NULL) {
636 				TCPSTAT_INC(tcps_rcvshort);
637 				return;
638 			}
639 		}
640 		ip = mtod(m, struct ip *);
641 		ipov = (struct ipovly *)ip;
642 		th = (struct tcphdr *)((caddr_t)ip + off0);
643 		tlen = ip->ip_len;
644 
645 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
646 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
647 				th->th_sum = m->m_pkthdr.csum_data;
648 			else
649 				th->th_sum = in_pseudo(ip->ip_src.s_addr,
650 						ip->ip_dst.s_addr,
651 						htonl(m->m_pkthdr.csum_data +
652 							ip->ip_len +
653 							IPPROTO_TCP));
654 			th->th_sum ^= 0xffff;
655 #ifdef TCPDEBUG
656 			ipov->ih_len = (u_short)tlen;
657 			ipov->ih_len = htons(ipov->ih_len);
658 #endif
659 		} else {
660 			/*
661 			 * Checksum extended TCP header and data.
662 			 */
663 			len = sizeof (struct ip) + tlen;
664 			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
665 			ipov->ih_len = (u_short)tlen;
666 			ipov->ih_len = htons(ipov->ih_len);
667 			th->th_sum = in_cksum(m, len);
668 		}
669 		if (th->th_sum) {
670 			TCPSTAT_INC(tcps_rcvbadsum);
671 			goto drop;
672 		}
673 		/* Re-initialization for later version check */
674 		ip->ip_v = IPVERSION;
675 	}
676 #endif /* INET */
677 
678 #ifdef INET6
679 	if (isipv6)
680 		iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
681 #endif
682 #if defined(INET) && defined(INET6)
683 	else
684 #endif
685 #ifdef INET
686 		iptos = ip->ip_tos;
687 #endif
688 
689 	/*
690 	 * Check that TCP offset makes sense,
691 	 * pull out TCP options and adjust length.		XXX
692 	 */
693 	off = th->th_off << 2;
694 	if (off < sizeof (struct tcphdr) || off > tlen) {
695 		TCPSTAT_INC(tcps_rcvbadoff);
696 		goto drop;
697 	}
698 	tlen -= off;	/* tlen is used instead of ti->ti_len */
699 	if (off > sizeof (struct tcphdr)) {
700 #ifdef INET6
701 		if (isipv6) {
702 			IP6_EXTHDR_CHECK(m, off0, off, );
703 			ip6 = mtod(m, struct ip6_hdr *);
704 			th = (struct tcphdr *)((caddr_t)ip6 + off0);
705 		}
706 #endif
707 #if defined(INET) && defined(INET6)
708 		else
709 #endif
710 #ifdef INET
711 		{
712 			if (m->m_len < sizeof(struct ip) + off) {
713 				if ((m = m_pullup(m, sizeof (struct ip) + off))
714 				    == NULL) {
715 					TCPSTAT_INC(tcps_rcvshort);
716 					return;
717 				}
718 				ip = mtod(m, struct ip *);
719 				ipov = (struct ipovly *)ip;
720 				th = (struct tcphdr *)((caddr_t)ip + off0);
721 			}
722 		}
723 #endif
724 		optlen = off - sizeof (struct tcphdr);
725 		optp = (u_char *)(th + 1);
726 	}
727 	thflags = th->th_flags;
728 
729 	/*
730 	 * Convert TCP protocol specific fields to host format.
731 	 */
732 	tcp_fields_to_host(th);
733 
734 	/*
735 	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
736 	 */
737 	drop_hdrlen = off0 + off;
738 
739 	/*
740 	 * Locate pcb for segment; if we're likely to add or remove a
741 	 * connection then first acquire pcbinfo lock.  There are two cases
742 	 * where we might discover later we need a write lock despite the
743 	 * flags: ACKs moving a connection out of the syncache, and ACKs for
744 	 * a connection in TIMEWAIT.
745 	 */
746 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
747 		INP_INFO_WLOCK(&V_tcbinfo);
748 		ti_locked = TI_WLOCKED;
749 	} else
750 		ti_locked = TI_UNLOCKED;
751 
752 findpcb:
753 #ifdef INVARIANTS
754 	if (ti_locked == TI_WLOCKED) {
755 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
756 	} else {
757 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
758 	}
759 #endif
760 
761 #ifdef IPFIREWALL_FORWARD
762 	/*
763 	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
764 	 */
765 	fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
766 #endif /* IPFIREWALL_FORWARD */
767 
768 #ifdef INET6
769 #ifdef IPFIREWALL_FORWARD
770 	if (isipv6 && fwd_tag != NULL) {
771 		struct sockaddr_in6 *next_hop6;
772 
773 		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
774 		/*
775 		 * Transparently forwarded. Pretend to be the destination.
776 		 * Already got one like this?
777 		 */
778 		inp = in6_pcblookup_mbuf(&V_tcbinfo,
779 		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
780 		    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
781 		if (!inp) {
782 			/*
783 			 * It's new.  Try to find the ambushing socket.
784 			 * Because we've rewritten the destination address,
785 			 * any hardware-generated hash is ignored.
786 			 */
787 			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
788 			    th->th_sport, &next_hop6->sin6_addr,
789 			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
790 			    th->th_dport, INPLOOKUP_WILDCARD |
791 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
792 		}
793 		/* Remove the tag from the packet.  We don't need it anymore. */
794 		m_tag_delete(m, fwd_tag);
795 	} else
796 #endif /* IPFIREWALL_FORWARD */
797 	if (isipv6) {
798 		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
799 		    th->th_sport, &ip6->ip6_dst, th->th_dport,
800 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
801 		    m->m_pkthdr.rcvif, m);
802 	}
803 #endif /* INET6 */
804 #if defined(INET6) && defined(INET)
805 	else
806 #endif
807 #ifdef INET
808 #ifdef IPFIREWALL_FORWARD
809 	if (fwd_tag != NULL) {
810 		struct sockaddr_in *next_hop;
811 
812 		next_hop = (struct sockaddr_in *)(fwd_tag+1);
813 		/*
814 		 * Transparently forwarded. Pretend to be the destination.
815 		 * already got one like this?
816 		 */
817 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
818 		    ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
819 		    m->m_pkthdr.rcvif, m);
820 		if (!inp) {
821 			/*
822 			 * It's new.  Try to find the ambushing socket.
823 			 * Because we've rewritten the destination address,
824 			 * any hardware-generated hash is ignored.
825 			 */
826 			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
827 			    th->th_sport, next_hop->sin_addr,
828 			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
829 			    th->th_dport, INPLOOKUP_WILDCARD |
830 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
831 		}
832 		/* Remove the tag from the packet.  We don't need it anymore. */
833 		m_tag_delete(m, fwd_tag);
834 	} else
835 #endif /* IPFIREWALL_FORWARD */
836 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
837 		    th->th_sport, ip->ip_dst, th->th_dport,
838 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
839 		    m->m_pkthdr.rcvif, m);
840 #endif /* INET */
841 
842 	/*
843 	 * If the INPCB does not exist then all data in the incoming
844 	 * segment is discarded and an appropriate RST is sent back.
845 	 * XXX MRT Send RST using which routing table?
846 	 */
847 	if (inp == NULL) {
848 		/*
849 		 * Log communication attempts to ports that are not
850 		 * in use.
851 		 */
852 		if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
853 		    tcp_log_in_vain == 2) {
854 			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
855 				log(LOG_INFO, "%s; %s: Connection attempt "
856 				    "to closed port\n", s, __func__);
857 		}
858 		/*
859 		 * When blackholing do not respond with a RST but
860 		 * completely ignore the segment and drop it.
861 		 */
862 		if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
863 		    V_blackhole == 2)
864 			goto dropunlock;
865 
866 		rstreason = BANDLIM_RST_CLOSEDPORT;
867 		goto dropwithreset;
868 	}
869 	INP_WLOCK_ASSERT(inp);
870 	if (!(inp->inp_flags & INP_HW_FLOWID)
871 	    && (m->m_flags & M_FLOWID)
872 	    && ((inp->inp_socket == NULL)
873 		|| !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
874 		inp->inp_flags |= INP_HW_FLOWID;
875 		inp->inp_flags &= ~INP_SW_FLOWID;
876 		inp->inp_flowid = m->m_pkthdr.flowid;
877 	}
878 #ifdef IPSEC
879 #ifdef INET6
880 	if (isipv6 && ipsec6_in_reject(m, inp)) {
881 		V_ipsec6stat.in_polvio++;
882 		goto dropunlock;
883 	} else
884 #endif /* INET6 */
885 	if (ipsec4_in_reject(m, inp) != 0) {
886 		V_ipsec4stat.in_polvio++;
887 		goto dropunlock;
888 	}
889 #endif /* IPSEC */
890 
891 	/*
892 	 * Check the minimum TTL for socket.
893 	 */
894 	if (inp->inp_ip_minttl != 0) {
895 #ifdef INET6
896 		if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
897 			goto dropunlock;
898 		else
899 #endif
900 		if (inp->inp_ip_minttl > ip->ip_ttl)
901 			goto dropunlock;
902 	}
903 
904 	/*
905 	 * A previous connection in TIMEWAIT state is supposed to catch stray
906 	 * or duplicate segments arriving late.  If this segment was a
907 	 * legitimate new connection attempt the old INPCB gets removed and
908 	 * we can try again to find a listening socket.
909 	 *
910 	 * At this point, due to earlier optimism, we may hold only an inpcb
911 	 * lock, and not the inpcbinfo write lock.  If so, we need to try to
912 	 * acquire it, or if that fails, acquire a reference on the inpcb,
913 	 * drop all locks, acquire a global write lock, and then re-acquire
914 	 * the inpcb lock.  We may at that point discover that another thread
915 	 * has tried to free the inpcb, in which case we need to loop back
916 	 * and try to find a new inpcb to deliver to.
917 	 *
918 	 * XXXRW: It may be time to rethink timewait locking.
919 	 */
920 relocked:
921 	if (inp->inp_flags & INP_TIMEWAIT) {
922 		if (ti_locked == TI_UNLOCKED) {
923 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
924 				in_pcbref(inp);
925 				INP_WUNLOCK(inp);
926 				INP_INFO_WLOCK(&V_tcbinfo);
927 				ti_locked = TI_WLOCKED;
928 				INP_WLOCK(inp);
929 				if (in_pcbrele_wlocked(inp)) {
930 					inp = NULL;
931 					goto findpcb;
932 				}
933 			} else
934 				ti_locked = TI_WLOCKED;
935 		}
936 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
937 
938 		if (thflags & TH_SYN)
939 			tcp_dooptions(&to, optp, optlen, TO_SYN);
940 		/*
941 		 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
942 		 */
943 		if (tcp_twcheck(inp, &to, th, m, tlen))
944 			goto findpcb;
945 		INP_INFO_WUNLOCK(&V_tcbinfo);
946 		return;
947 	}
948 	/*
949 	 * The TCPCB may no longer exist if the connection is winding
950 	 * down or it is in the CLOSED state.  Either way we drop the
951 	 * segment and send an appropriate response.
952 	 */
953 	tp = intotcpcb(inp);
954 	if (tp == NULL || tp->t_state == TCPS_CLOSED) {
955 		rstreason = BANDLIM_RST_CLOSEDPORT;
956 		goto dropwithreset;
957 	}
958 
959 	/*
960 	 * We've identified a valid inpcb, but it could be that we need an
961 	 * inpcbinfo write lock but don't hold it.  In this case, attempt to
962 	 * acquire using the same strategy as the TIMEWAIT case above.  If we
963 	 * relock, we have to jump back to 'relocked' as the connection might
964 	 * now be in TIMEWAIT.
965 	 */
966 #ifdef INVARIANTS
967 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
968 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
969 #endif
970 	if (tp->t_state != TCPS_ESTABLISHED) {
971 		if (ti_locked == TI_UNLOCKED) {
972 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
973 				in_pcbref(inp);
974 				INP_WUNLOCK(inp);
975 				INP_INFO_WLOCK(&V_tcbinfo);
976 				ti_locked = TI_WLOCKED;
977 				INP_WLOCK(inp);
978 				if (in_pcbrele_wlocked(inp)) {
979 					inp = NULL;
980 					goto findpcb;
981 				}
982 				goto relocked;
983 			} else
984 				ti_locked = TI_WLOCKED;
985 		}
986 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
987 	}
988 
989 #ifdef MAC
990 	INP_WLOCK_ASSERT(inp);
991 	if (mac_inpcb_check_deliver(inp, m))
992 		goto dropunlock;
993 #endif
994 	so = inp->inp_socket;
995 	KASSERT(so != NULL, ("%s: so == NULL", __func__));
996 #ifdef TCPDEBUG
997 	if (so->so_options & SO_DEBUG) {
998 		ostate = tp->t_state;
999 #ifdef INET6
1000 		if (isipv6) {
1001 			bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1002 		} else
1003 #endif
1004 			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1005 		tcp_savetcp = *th;
1006 	}
1007 #endif /* TCPDEBUG */
1008 	/*
1009 	 * When the socket is accepting connections (the INPCB is in LISTEN
1010 	 * state) we look into the SYN cache if this is a new connection
1011 	 * attempt or the completion of a previous one.  Because listen
1012 	 * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
1013 	 * held in this case.
1014 	 */
1015 	if (so->so_options & SO_ACCEPTCONN) {
1016 		struct in_conninfo inc;
1017 
1018 		KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
1019 		    "tp not listening", __func__));
1020 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1021 
1022 		bzero(&inc, sizeof(inc));
1023 #ifdef INET6
1024 		if (isipv6) {
1025 			inc.inc_flags |= INC_ISIPV6;
1026 			inc.inc6_faddr = ip6->ip6_src;
1027 			inc.inc6_laddr = ip6->ip6_dst;
1028 		} else
1029 #endif
1030 		{
1031 			inc.inc_faddr = ip->ip_src;
1032 			inc.inc_laddr = ip->ip_dst;
1033 		}
1034 		inc.inc_fport = th->th_sport;
1035 		inc.inc_lport = th->th_dport;
1036 		inc.inc_fibnum = so->so_fibnum;
1037 
1038 		/*
1039 		 * Check for an existing connection attempt in syncache if
1040 		 * the flag is only ACK.  A successful lookup creates a new
1041 		 * socket appended to the listen queue in SYN_RECEIVED state.
1042 		 */
1043 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1044 			/*
1045 			 * Parse the TCP options here because
1046 			 * syncookies need access to the reflected
1047 			 * timestamp.
1048 			 */
1049 			tcp_dooptions(&to, optp, optlen, 0);
1050 			/*
1051 			 * NB: syncache_expand() doesn't unlock
1052 			 * inp and tcpinfo locks.
1053 			 */
1054 			if (!syncache_expand(&inc, &to, th, &so, m)) {
1055 				/*
1056 				 * No syncache entry or ACK was not
1057 				 * for our SYN/ACK.  Send a RST.
1058 				 * NB: syncache did its own logging
1059 				 * of the failure cause.
1060 				 */
1061 				rstreason = BANDLIM_RST_OPENPORT;
1062 				goto dropwithreset;
1063 			}
1064 			if (so == NULL) {
1065 				/*
1066 				 * We completed the 3-way handshake
1067 				 * but could not allocate a socket
1068 				 * either due to memory shortage,
1069 				 * listen queue length limits or
1070 				 * global socket limits.  Send RST
1071 				 * or wait and have the remote end
1072 				 * retransmit the ACK for another
1073 				 * try.
1074 				 */
1075 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1076 					log(LOG_DEBUG, "%s; %s: Listen socket: "
1077 					    "Socket allocation failed due to "
1078 					    "limits or memory shortage, %s\n",
1079 					    s, __func__,
1080 					    V_tcp_sc_rst_sock_fail ?
1081 					    "sending RST" : "try again");
1082 				if (V_tcp_sc_rst_sock_fail) {
1083 					rstreason = BANDLIM_UNLIMITED;
1084 					goto dropwithreset;
1085 				} else
1086 					goto dropunlock;
1087 			}
1088 			/*
1089 			 * Socket is created in state SYN_RECEIVED.
1090 			 * Unlock the listen socket, lock the newly
1091 			 * created socket and update the tp variable.
1092 			 */
1093 			INP_WUNLOCK(inp);	/* listen socket */
1094 			inp = sotoinpcb(so);
1095 			INP_WLOCK(inp);		/* new connection */
1096 			tp = intotcpcb(inp);
1097 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1098 			    ("%s: ", __func__));
1099 #ifdef TCP_SIGNATURE
1100 			if (sig_checked == 0)  {
1101 				tcp_dooptions(&to, optp, optlen,
1102 				    (thflags & TH_SYN) ? TO_SYN : 0);
1103 				if (!tcp_signature_verify_input(m, off0, tlen,
1104 				    optlen, &to, th, tp->t_flags)) {
1105 
1106 					/*
1107 					 * In SYN_SENT state if it receives an
1108 					 * RST, it is allowed for further
1109 					 * processing.
1110 					 */
1111 					if ((thflags & TH_RST) == 0 ||
1112 					    (tp->t_state == TCPS_SYN_SENT) == 0)
1113 						goto dropunlock;
1114 				}
1115 				sig_checked = 1;
1116 			}
1117 #endif
1118 
1119 			/*
1120 			 * Process the segment and the data it
1121 			 * contains.  tcp_do_segment() consumes
1122 			 * the mbuf chain and unlocks the inpcb.
1123 			 */
1124 			tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1125 			    iptos, ti_locked);
1126 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1127 			return;
1128 		}
1129 		/*
1130 		 * Segment flag validation for new connection attempts:
1131 		 *
1132 		 * Our (SYN|ACK) response was rejected.
1133 		 * Check with syncache and remove entry to prevent
1134 		 * retransmits.
1135 		 *
1136 		 * NB: syncache_chkrst does its own logging of failure
1137 		 * causes.
1138 		 */
1139 		if (thflags & TH_RST) {
1140 			syncache_chkrst(&inc, th);
1141 			goto dropunlock;
1142 		}
1143 		/*
1144 		 * We can't do anything without SYN.
1145 		 */
1146 		if ((thflags & TH_SYN) == 0) {
1147 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1148 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1149 				    "SYN is missing, segment ignored\n",
1150 				    s, __func__);
1151 			TCPSTAT_INC(tcps_badsyn);
1152 			goto dropunlock;
1153 		}
1154 		/*
1155 		 * (SYN|ACK) is bogus on a listen socket.
1156 		 */
1157 		if (thflags & TH_ACK) {
1158 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1159 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1160 				    "SYN|ACK invalid, segment rejected\n",
1161 				    s, __func__);
1162 			syncache_badack(&inc);	/* XXX: Not needed! */
1163 			TCPSTAT_INC(tcps_badsyn);
1164 			rstreason = BANDLIM_RST_OPENPORT;
1165 			goto dropwithreset;
1166 		}
1167 		/*
1168 		 * If the drop_synfin option is enabled, drop all
1169 		 * segments with both the SYN and FIN bits set.
1170 		 * This prevents e.g. nmap from identifying the
1171 		 * TCP/IP stack.
1172 		 * XXX: Poor reasoning.  nmap has other methods
1173 		 * and is constantly refining its stack detection
1174 		 * strategies.
1175 		 * XXX: This is a violation of the TCP specification
1176 		 * and was used by RFC1644.
1177 		 */
1178 		if ((thflags & TH_FIN) && V_drop_synfin) {
1179 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1180 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1181 				    "SYN|FIN segment ignored (based on "
1182 				    "sysctl setting)\n", s, __func__);
1183 			TCPSTAT_INC(tcps_badsyn);
1184 			goto dropunlock;
1185 		}
1186 		/*
1187 		 * Segment's flags are (SYN) or (SYN|FIN).
1188 		 *
1189 		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1190 		 * as they do not affect the state of the TCP FSM.
1191 		 * The data pointed to by TH_URG and th_urp is ignored.
1192 		 */
1193 		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1194 		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1195 		KASSERT(thflags & (TH_SYN),
1196 		    ("%s: Listen socket: TH_SYN not set", __func__));
1197 #ifdef INET6
1198 		/*
1199 		 * If deprecated address is forbidden,
1200 		 * we do not accept SYN to deprecated interface
1201 		 * address to prevent any new inbound connection from
1202 		 * getting established.
1203 		 * When we do not accept SYN, we send a TCP RST,
1204 		 * with deprecated source address (instead of dropping
1205 		 * it).  We compromise it as it is much better for peer
1206 		 * to send a RST, and RST will be the final packet
1207 		 * for the exchange.
1208 		 *
1209 		 * If we do not forbid deprecated addresses, we accept
1210 		 * the SYN packet.  RFC2462 does not suggest dropping
1211 		 * SYN in this case.
1212 		 * If we decipher RFC2462 5.5.4, it says like this:
1213 		 * 1. use of deprecated addr with existing
1214 		 *    communication is okay - "SHOULD continue to be
1215 		 *    used"
1216 		 * 2. use of it with new communication:
1217 		 *   (2a) "SHOULD NOT be used if alternate address
1218 		 *        with sufficient scope is available"
1219 		 *   (2b) nothing mentioned otherwise.
1220 		 * Here we fall into (2b) case as we have no choice in
1221 		 * our source address selection - we must obey the peer.
1222 		 *
1223 		 * The wording in RFC2462 is confusing, and there are
1224 		 * multiple description text for deprecated address
1225 		 * handling - worse, they are not exactly the same.
1226 		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1227 		 */
1228 		if (isipv6 && !V_ip6_use_deprecated) {
1229 			struct in6_ifaddr *ia6;
1230 
1231 			ia6 = ip6_getdstifaddr(m);
1232 			if (ia6 != NULL &&
1233 			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1234 				ifa_free(&ia6->ia_ifa);
1235 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1236 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1237 					"Connection attempt to deprecated "
1238 					"IPv6 address rejected\n",
1239 					s, __func__);
1240 				rstreason = BANDLIM_RST_OPENPORT;
1241 				goto dropwithreset;
1242 			}
1243 			ifa_free(&ia6->ia_ifa);
1244 		}
1245 #endif /* INET6 */
1246 		/*
1247 		 * Basic sanity checks on incoming SYN requests:
1248 		 *   Don't respond if the destination is a link layer
1249 		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1250 		 *   If it is from this socket it must be forged.
1251 		 *   Don't respond if the source or destination is a
1252 		 *	global or subnet broad- or multicast address.
1253 		 *   Note that it is quite possible to receive unicast
1254 		 *	link-layer packets with a broadcast IP address. Use
1255 		 *	in_broadcast() to find them.
1256 		 */
1257 		if (m->m_flags & (M_BCAST|M_MCAST)) {
1258 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1259 			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1260 				"Connection attempt from broad- or multicast "
1261 				"link layer address ignored\n", s, __func__);
1262 			goto dropunlock;
1263 		}
1264 #ifdef INET6
1265 		if (isipv6) {
1266 			if (th->th_dport == th->th_sport &&
1267 			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1268 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1269 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1270 					"Connection attempt to/from self "
1271 					"ignored\n", s, __func__);
1272 				goto dropunlock;
1273 			}
1274 			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1275 			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1276 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1277 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1278 					"Connection attempt from/to multicast "
1279 					"address ignored\n", s, __func__);
1280 				goto dropunlock;
1281 			}
1282 		}
1283 #endif
1284 #if defined(INET) && defined(INET6)
1285 		else
1286 #endif
1287 #ifdef INET
1288 		{
1289 			if (th->th_dport == th->th_sport &&
1290 			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1291 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1292 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1293 					"Connection attempt from/to self "
1294 					"ignored\n", s, __func__);
1295 				goto dropunlock;
1296 			}
1297 			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1298 			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1299 			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1300 			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1301 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1302 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1303 					"Connection attempt from/to broad- "
1304 					"or multicast address ignored\n",
1305 					s, __func__);
1306 				goto dropunlock;
1307 			}
1308 		}
1309 #endif
1310 		/*
1311 		 * SYN appears to be valid.  Create compressed TCP state
1312 		 * for syncache.
1313 		 */
1314 #ifdef TCPDEBUG
1315 		if (so->so_options & SO_DEBUG)
1316 			tcp_trace(TA_INPUT, ostate, tp,
1317 			    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1318 #endif
1319 		tcp_dooptions(&to, optp, optlen, TO_SYN);
1320 		syncache_add(&inc, &to, th, inp, &so, m);
1321 		/*
1322 		 * Entry added to syncache and mbuf consumed.
1323 		 * Everything already unlocked by syncache_add().
1324 		 */
1325 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1326 		return;
1327 	}
1328 
1329 #ifdef TCP_SIGNATURE
1330 	if (sig_checked == 0)  {
1331 		tcp_dooptions(&to, optp, optlen,
1332 		    (thflags & TH_SYN) ? TO_SYN : 0);
1333 		if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
1334 		    th, tp->t_flags)) {
1335 
1336 			/*
1337 			 * In SYN_SENT state if it receives an RST, it is
1338 			 * allowed for further processing.
1339 			 */
1340 			if ((thflags & TH_RST) == 0 ||
1341 			    (tp->t_state == TCPS_SYN_SENT) == 0)
1342 				goto dropunlock;
1343 		}
1344 		sig_checked = 1;
1345 	}
1346 #endif
1347 
1348 	/*
1349 	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1350 	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1351 	 * the inpcb, and unlocks pcbinfo.
1352 	 */
1353 	tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
1354 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1355 	return;
1356 
1357 dropwithreset:
1358 	if (ti_locked == TI_WLOCKED) {
1359 		INP_INFO_WUNLOCK(&V_tcbinfo);
1360 		ti_locked = TI_UNLOCKED;
1361 	}
1362 #ifdef INVARIANTS
1363 	else {
1364 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1365 		    "ti_locked: %d", __func__, ti_locked));
1366 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1367 	}
1368 #endif
1369 
1370 	if (inp != NULL) {
1371 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1372 		INP_WUNLOCK(inp);
1373 	} else
1374 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1375 	m = NULL;	/* mbuf chain got consumed. */
1376 	goto drop;
1377 
1378 dropunlock:
1379 	if (ti_locked == TI_WLOCKED) {
1380 		INP_INFO_WUNLOCK(&V_tcbinfo);
1381 		ti_locked = TI_UNLOCKED;
1382 	}
1383 #ifdef INVARIANTS
1384 	else {
1385 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1386 		    "ti_locked: %d", __func__, ti_locked));
1387 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1388 	}
1389 #endif
1390 
1391 	if (inp != NULL)
1392 		INP_WUNLOCK(inp);
1393 
1394 drop:
1395 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1396 	if (s != NULL)
1397 		free(s, M_TCPLOG);
1398 	if (m != NULL)
1399 		m_freem(m);
1400 }
1401 
1402 static void
1403 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1404     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
1405     int ti_locked)
1406 {
1407 	int thflags, acked, ourfinisacked, needoutput = 0;
1408 	int rstreason, todrop, win;
1409 	u_long tiwin;
1410 	struct tcpopt to;
1411 
1412 #ifdef TCPDEBUG
1413 	/*
1414 	 * The size of tcp_saveipgen must be the size of the max ip header,
1415 	 * now IPv6.
1416 	 */
1417 	u_char tcp_saveipgen[IP6_HDR_LEN];
1418 	struct tcphdr tcp_savetcp;
1419 	short ostate = 0;
1420 #endif
1421 	thflags = th->th_flags;
1422 	tp->sackhint.last_sack_ack = 0;
1423 
1424 	/*
1425 	 * If this is either a state-changing packet or current state isn't
1426 	 * established, we require a write lock on tcbinfo.  Otherwise, we
1427 	 * allow either a read lock or a write lock, as we may have acquired
1428 	 * a write lock due to a race.
1429 	 *
1430 	 * Require a global write lock for SYN/FIN/RST segments or
1431 	 * non-established connections; otherwise accept either a read or
1432 	 * write lock, as we may have conservatively acquired a write lock in
1433 	 * certain cases in tcp_input() (is this still true?).  Currently we
1434 	 * will never enter with no lock, so we try to drop it quickly in the
1435 	 * common pure ack/pure data cases.
1436 	 */
1437 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1438 	    tp->t_state != TCPS_ESTABLISHED) {
1439 		KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
1440 		    "SYN/FIN/RST/!EST", __func__, ti_locked));
1441 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1442 	} else {
1443 #ifdef INVARIANTS
1444 		if (ti_locked == TI_WLOCKED)
1445 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1446 		else {
1447 			KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
1448 			    "ti_locked: %d", __func__, ti_locked));
1449 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1450 		}
1451 #endif
1452 	}
1453 	INP_WLOCK_ASSERT(tp->t_inpcb);
1454 	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1455 	    __func__));
1456 	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1457 	    __func__));
1458 
1459 	/*
1460 	 * Segment received on connection.
1461 	 * Reset idle time and keep-alive timer.
1462 	 * XXX: This should be done after segment
1463 	 * validation to ignore broken/spoofed segs.
1464 	 */
1465 	tp->t_rcvtime = ticks;
1466 	if (TCPS_HAVEESTABLISHED(tp->t_state))
1467 		tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
1468 
1469 	/*
1470 	 * Unscale the window into a 32-bit value.
1471 	 * For the SYN_SENT state the scale is zero.
1472 	 */
1473 	tiwin = th->th_win << tp->snd_scale;
1474 
1475 	/*
1476 	 * TCP ECN processing.
1477 	 */
1478 	if (tp->t_flags & TF_ECN_PERMIT) {
1479 		if (thflags & TH_CWR)
1480 			tp->t_flags &= ~TF_ECN_SND_ECE;
1481 		switch (iptos & IPTOS_ECN_MASK) {
1482 		case IPTOS_ECN_CE:
1483 			tp->t_flags |= TF_ECN_SND_ECE;
1484 			TCPSTAT_INC(tcps_ecn_ce);
1485 			break;
1486 		case IPTOS_ECN_ECT0:
1487 			TCPSTAT_INC(tcps_ecn_ect0);
1488 			break;
1489 		case IPTOS_ECN_ECT1:
1490 			TCPSTAT_INC(tcps_ecn_ect1);
1491 			break;
1492 		}
1493 		/* Congestion experienced. */
1494 		if (thflags & TH_ECE) {
1495 			cc_cong_signal(tp, th, CC_ECN);
1496 		}
1497 	}
1498 
1499 	/*
1500 	 * Parse options on any incoming segment.
1501 	 */
1502 	tcp_dooptions(&to, (u_char *)(th + 1),
1503 	    (th->th_off << 2) - sizeof(struct tcphdr),
1504 	    (thflags & TH_SYN) ? TO_SYN : 0);
1505 
1506 	/*
1507 	 * If echoed timestamp is later than the current time,
1508 	 * fall back to non RFC1323 RTT calculation.  Normalize
1509 	 * timestamp if syncookies were used when this connection
1510 	 * was established.
1511 	 */
1512 	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1513 		to.to_tsecr -= tp->ts_offset;
1514 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1515 			to.to_tsecr = 0;
1516 	}
1517 
1518 	/*
1519 	 * Process options only when we get SYN/ACK back. The SYN case
1520 	 * for incoming connections is handled in tcp_syncache.
1521 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1522 	 * or <SYN,ACK>) segment itself is never scaled.
1523 	 * XXX this is traditional behavior, may need to be cleaned up.
1524 	 */
1525 	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1526 		if ((to.to_flags & TOF_SCALE) &&
1527 		    (tp->t_flags & TF_REQ_SCALE)) {
1528 			tp->t_flags |= TF_RCVD_SCALE;
1529 			tp->snd_scale = to.to_wscale;
1530 		}
1531 		/*
1532 		 * Initial send window.  It will be updated with
1533 		 * the next incoming segment to the scaled value.
1534 		 */
1535 		tp->snd_wnd = th->th_win;
1536 		if (to.to_flags & TOF_TS) {
1537 			tp->t_flags |= TF_RCVD_TSTMP;
1538 			tp->ts_recent = to.to_tsval;
1539 			tp->ts_recent_age = tcp_ts_getticks();
1540 		}
1541 		if (to.to_flags & TOF_MSS)
1542 			tcp_mss(tp, to.to_mss);
1543 		if ((tp->t_flags & TF_SACK_PERMIT) &&
1544 		    (to.to_flags & TOF_SACKPERM) == 0)
1545 			tp->t_flags &= ~TF_SACK_PERMIT;
1546 	}
1547 
1548 	/*
1549 	 * Header prediction: check for the two common cases
1550 	 * of a uni-directional data xfer.  If the packet has
1551 	 * no control flags, is in-sequence, the window didn't
1552 	 * change and we're not retransmitting, it's a
1553 	 * candidate.  If the length is zero and the ack moved
1554 	 * forward, we're the sender side of the xfer.  Just
1555 	 * free the data acked & wake any higher level process
1556 	 * that was blocked waiting for space.  If the length
1557 	 * is non-zero and the ack didn't move, we're the
1558 	 * receiver side.  If we're getting packets in-order
1559 	 * (the reassembly queue is empty), add the data to
1560 	 * the socket buffer and note that we need a delayed ack.
1561 	 * Make sure that the hidden state-flags are also off.
1562 	 * Since we check for TCPS_ESTABLISHED first, it can only
1563 	 * be TH_NEEDSYN.
1564 	 */
1565 	if (tp->t_state == TCPS_ESTABLISHED &&
1566 	    th->th_seq == tp->rcv_nxt &&
1567 	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1568 	    tp->snd_nxt == tp->snd_max &&
1569 	    tiwin && tiwin == tp->snd_wnd &&
1570 	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1571 	    LIST_EMPTY(&tp->t_segq) &&
1572 	    ((to.to_flags & TOF_TS) == 0 ||
1573 	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1574 
1575 		/*
1576 		 * If last ACK falls within this segment's sequence numbers,
1577 		 * record the timestamp.
1578 		 * NOTE that the test is modified according to the latest
1579 		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1580 		 */
1581 		if ((to.to_flags & TOF_TS) != 0 &&
1582 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1583 			tp->ts_recent_age = tcp_ts_getticks();
1584 			tp->ts_recent = to.to_tsval;
1585 		}
1586 
1587 		if (tlen == 0) {
1588 			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1589 			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1590 			    !IN_RECOVERY(tp->t_flags) &&
1591 			    (to.to_flags & TOF_SACK) == 0 &&
1592 			    TAILQ_EMPTY(&tp->snd_holes)) {
1593 				/*
1594 				 * This is a pure ack for outstanding data.
1595 				 */
1596 				if (ti_locked == TI_WLOCKED)
1597 					INP_INFO_WUNLOCK(&V_tcbinfo);
1598 				ti_locked = TI_UNLOCKED;
1599 
1600 				TCPSTAT_INC(tcps_predack);
1601 
1602 				/*
1603 				 * "bad retransmit" recovery.
1604 				 */
1605 				if (tp->t_rxtshift == 1 &&
1606 				    tp->t_flags & TF_PREVVALID &&
1607 				    (int)(ticks - tp->t_badrxtwin) < 0) {
1608 					cc_cong_signal(tp, th, CC_RTO_ERR);
1609 				}
1610 
1611 				/*
1612 				 * Recalculate the transmit timer / rtt.
1613 				 *
1614 				 * Some boxes send broken timestamp replies
1615 				 * during the SYN+ACK phase, ignore
1616 				 * timestamps of 0 or we could calculate a
1617 				 * huge RTT and blow up the retransmit timer.
1618 				 */
1619 				if ((to.to_flags & TOF_TS) != 0 &&
1620 				    to.to_tsecr) {
1621 					u_int t;
1622 
1623 					t = tcp_ts_getticks() - to.to_tsecr;
1624 					if (!tp->t_rttlow || tp->t_rttlow > t)
1625 						tp->t_rttlow = t;
1626 					tcp_xmit_timer(tp,
1627 					    TCP_TS_TO_TICKS(t) + 1);
1628 				} else if (tp->t_rtttime &&
1629 				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1630 					if (!tp->t_rttlow ||
1631 					    tp->t_rttlow > ticks - tp->t_rtttime)
1632 						tp->t_rttlow = ticks - tp->t_rtttime;
1633 					tcp_xmit_timer(tp,
1634 							ticks - tp->t_rtttime);
1635 				}
1636 				acked = BYTES_THIS_ACK(tp, th);
1637 
1638 				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1639 				hhook_run_tcp_est_in(tp, th, &to);
1640 
1641 				TCPSTAT_INC(tcps_rcvackpack);
1642 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1643 				sbdrop(&so->so_snd, acked);
1644 				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1645 				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1646 					tp->snd_recover = th->th_ack - 1;
1647 
1648 				/*
1649 				 * Let the congestion control algorithm update
1650 				 * congestion control related information. This
1651 				 * typically means increasing the congestion
1652 				 * window.
1653 				 */
1654 				cc_ack_received(tp, th, CC_ACK);
1655 
1656 				tp->snd_una = th->th_ack;
1657 				/*
1658 				 * Pull snd_wl2 up to prevent seq wrap relative
1659 				 * to th_ack.
1660 				 */
1661 				tp->snd_wl2 = th->th_ack;
1662 				tp->t_dupacks = 0;
1663 				m_freem(m);
1664 				ND6_HINT(tp); /* Some progress has been made. */
1665 
1666 				/*
1667 				 * If all outstanding data are acked, stop
1668 				 * retransmit timer, otherwise restart timer
1669 				 * using current (possibly backed-off) value.
1670 				 * If process is waiting for space,
1671 				 * wakeup/selwakeup/signal.  If data
1672 				 * are ready to send, let tcp_output
1673 				 * decide between more output or persist.
1674 				 */
1675 #ifdef TCPDEBUG
1676 				if (so->so_options & SO_DEBUG)
1677 					tcp_trace(TA_INPUT, ostate, tp,
1678 					    (void *)tcp_saveipgen,
1679 					    &tcp_savetcp, 0);
1680 #endif
1681 				if (tp->snd_una == tp->snd_max)
1682 					tcp_timer_activate(tp, TT_REXMT, 0);
1683 				else if (!tcp_timer_active(tp, TT_PERSIST))
1684 					tcp_timer_activate(tp, TT_REXMT,
1685 						      tp->t_rxtcur);
1686 				sowwakeup(so);
1687 				if (so->so_snd.sb_cc)
1688 					(void) tcp_output(tp);
1689 				goto check_delack;
1690 			}
1691 		} else if (th->th_ack == tp->snd_una &&
1692 		    tlen <= sbspace(&so->so_rcv)) {
1693 			int newsize = 0;	/* automatic sockbuf scaling */
1694 
1695 			/*
1696 			 * This is a pure, in-sequence data packet with
1697 			 * nothing on the reassembly queue and we have enough
1698 			 * buffer space to take it.
1699 			 */
1700 			if (ti_locked == TI_WLOCKED)
1701 				INP_INFO_WUNLOCK(&V_tcbinfo);
1702 			ti_locked = TI_UNLOCKED;
1703 
1704 			/* Clean receiver SACK report if present */
1705 			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1706 				tcp_clean_sackreport(tp);
1707 			TCPSTAT_INC(tcps_preddat);
1708 			tp->rcv_nxt += tlen;
1709 			/*
1710 			 * Pull snd_wl1 up to prevent seq wrap relative to
1711 			 * th_seq.
1712 			 */
1713 			tp->snd_wl1 = th->th_seq;
1714 			/*
1715 			 * Pull rcv_up up to prevent seq wrap relative to
1716 			 * rcv_nxt.
1717 			 */
1718 			tp->rcv_up = tp->rcv_nxt;
1719 			TCPSTAT_INC(tcps_rcvpack);
1720 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1721 			ND6_HINT(tp);	/* Some progress has been made */
1722 #ifdef TCPDEBUG
1723 			if (so->so_options & SO_DEBUG)
1724 				tcp_trace(TA_INPUT, ostate, tp,
1725 				    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1726 #endif
1727 		/*
1728 		 * Automatic sizing of receive socket buffer.  Often the send
1729 		 * buffer size is not optimally adjusted to the actual network
1730 		 * conditions at hand (delay bandwidth product).  Setting the
1731 		 * buffer size too small limits throughput on links with high
1732 		 * bandwidth and high delay (eg. trans-continental/oceanic links).
1733 		 *
1734 		 * On the receive side the socket buffer memory is only rarely
1735 		 * used to any significant extent.  This allows us to be much
1736 		 * more aggressive in scaling the receive socket buffer.  For
1737 		 * the case that the buffer space is actually used to a large
1738 		 * extent and we run out of kernel memory we can simply drop
1739 		 * the new segments; TCP on the sender will just retransmit it
1740 		 * later.  Setting the buffer size too big may only consume too
1741 		 * much kernel memory if the application doesn't read() from
1742 		 * the socket or packet loss or reordering makes use of the
1743 		 * reassembly queue.
1744 		 *
1745 		 * The criteria to step up the receive buffer one notch are:
1746 		 *  1. the number of bytes received during the time it takes
1747 		 *     one timestamp to be reflected back to us (the RTT);
1748 		 *  2. received bytes per RTT is within seven eighth of the
1749 		 *     current socket buffer size;
1750 		 *  3. receive buffer size has not hit maximal automatic size;
1751 		 *
1752 		 * This algorithm does one step per RTT at most and only if
1753 		 * we receive a bulk stream w/o packet losses or reorderings.
1754 		 * Shrinking the buffer during idle times is not necessary as
1755 		 * it doesn't consume any memory when idle.
1756 		 *
1757 		 * TODO: Only step up if the application is actually serving
1758 		 * the buffer to better manage the socket buffer resources.
1759 		 */
1760 			if (V_tcp_do_autorcvbuf &&
1761 			    to.to_tsecr &&
1762 			    (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1763 				if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
1764 				    to.to_tsecr - tp->rfbuf_ts < hz) {
1765 					if (tp->rfbuf_cnt >
1766 					    (so->so_rcv.sb_hiwat / 8 * 7) &&
1767 					    so->so_rcv.sb_hiwat <
1768 					    V_tcp_autorcvbuf_max) {
1769 						newsize =
1770 						    min(so->so_rcv.sb_hiwat +
1771 						    V_tcp_autorcvbuf_inc,
1772 						    V_tcp_autorcvbuf_max);
1773 					}
1774 					/* Start over with next RTT. */
1775 					tp->rfbuf_ts = 0;
1776 					tp->rfbuf_cnt = 0;
1777 				} else
1778 					tp->rfbuf_cnt += tlen;	/* add up */
1779 			}
1780 
1781 			/* Add data to socket buffer. */
1782 			SOCKBUF_LOCK(&so->so_rcv);
1783 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1784 				m_freem(m);
1785 			} else {
1786 				/*
1787 				 * Set new socket buffer size.
1788 				 * Give up when limit is reached.
1789 				 */
1790 				if (newsize)
1791 					if (!sbreserve_locked(&so->so_rcv,
1792 					    newsize, so, NULL))
1793 						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1794 				m_adj(m, drop_hdrlen);	/* delayed header drop */
1795 				sbappendstream_locked(&so->so_rcv, m);
1796 			}
1797 			/* NB: sorwakeup_locked() does an implicit unlock. */
1798 			sorwakeup_locked(so);
1799 			if (DELAY_ACK(tp)) {
1800 				tp->t_flags |= TF_DELACK;
1801 			} else {
1802 				tp->t_flags |= TF_ACKNOW;
1803 				tcp_output(tp);
1804 			}
1805 			goto check_delack;
1806 		}
1807 	}
1808 
1809 	/*
1810 	 * Calculate amount of space in receive window,
1811 	 * and then do TCP input processing.
1812 	 * Receive window is amount of space in rcv queue,
1813 	 * but not less than advertised window.
1814 	 */
1815 	win = sbspace(&so->so_rcv);
1816 	if (win < 0)
1817 		win = 0;
1818 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1819 
1820 	/* Reset receive buffer auto scaling when not in bulk receive mode. */
1821 	tp->rfbuf_ts = 0;
1822 	tp->rfbuf_cnt = 0;
1823 
1824 	switch (tp->t_state) {
1825 
1826 	/*
1827 	 * If the state is SYN_RECEIVED:
1828 	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1829 	 */
1830 	case TCPS_SYN_RECEIVED:
1831 		if ((thflags & TH_ACK) &&
1832 		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1833 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1834 				rstreason = BANDLIM_RST_OPENPORT;
1835 				goto dropwithreset;
1836 		}
1837 		break;
1838 
1839 	/*
1840 	 * If the state is SYN_SENT:
1841 	 *	if seg contains an ACK, but not for our SYN, drop the input.
1842 	 *	if seg contains a RST, then drop the connection.
1843 	 *	if seg does not contain SYN, then drop it.
1844 	 * Otherwise this is an acceptable SYN segment
1845 	 *	initialize tp->rcv_nxt and tp->irs
1846 	 *	if seg contains ack then advance tp->snd_una
1847 	 *	if seg contains an ECE and ECN support is enabled, the stream
1848 	 *	    is ECN capable.
1849 	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1850 	 *	arrange for segment to be acked (eventually)
1851 	 *	continue processing rest of data/controls, beginning with URG
1852 	 */
1853 	case TCPS_SYN_SENT:
1854 		if ((thflags & TH_ACK) &&
1855 		    (SEQ_LEQ(th->th_ack, tp->iss) ||
1856 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1857 			rstreason = BANDLIM_UNLIMITED;
1858 			goto dropwithreset;
1859 		}
1860 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST))
1861 			tp = tcp_drop(tp, ECONNREFUSED);
1862 		if (thflags & TH_RST)
1863 			goto drop;
1864 		if (!(thflags & TH_SYN))
1865 			goto drop;
1866 
1867 		tp->irs = th->th_seq;
1868 		tcp_rcvseqinit(tp);
1869 		if (thflags & TH_ACK) {
1870 			TCPSTAT_INC(tcps_connects);
1871 			soisconnected(so);
1872 #ifdef MAC
1873 			mac_socketpeer_set_from_mbuf(m, so);
1874 #endif
1875 			/* Do window scaling on this connection? */
1876 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1877 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
1878 				tp->rcv_scale = tp->request_r_scale;
1879 			}
1880 			tp->rcv_adv += imin(tp->rcv_wnd,
1881 			    TCP_MAXWIN << tp->rcv_scale);
1882 			tp->snd_una++;		/* SYN is acked */
1883 			/*
1884 			 * If there's data, delay ACK; if there's also a FIN
1885 			 * ACKNOW will be turned on later.
1886 			 */
1887 			if (DELAY_ACK(tp) && tlen != 0)
1888 				tcp_timer_activate(tp, TT_DELACK,
1889 				    tcp_delacktime);
1890 			else
1891 				tp->t_flags |= TF_ACKNOW;
1892 
1893 			if ((thflags & TH_ECE) && V_tcp_do_ecn) {
1894 				tp->t_flags |= TF_ECN_PERMIT;
1895 				TCPSTAT_INC(tcps_ecn_shs);
1896 			}
1897 
1898 			/*
1899 			 * Received <SYN,ACK> in SYN_SENT[*] state.
1900 			 * Transitions:
1901 			 *	SYN_SENT  --> ESTABLISHED
1902 			 *	SYN_SENT* --> FIN_WAIT_1
1903 			 */
1904 			tp->t_starttime = ticks;
1905 			if (tp->t_flags & TF_NEEDFIN) {
1906 				tp->t_state = TCPS_FIN_WAIT_1;
1907 				tp->t_flags &= ~TF_NEEDFIN;
1908 				thflags &= ~TH_SYN;
1909 			} else {
1910 				tp->t_state = TCPS_ESTABLISHED;
1911 				cc_conn_init(tp);
1912 				tcp_timer_activate(tp, TT_KEEP,
1913 				    TP_KEEPIDLE(tp));
1914 			}
1915 		} else {
1916 			/*
1917 			 * Received initial SYN in SYN-SENT[*] state =>
1918 			 * simultaneous open.  If segment contains CC option
1919 			 * and there is a cached CC, apply TAO test.
1920 			 * If it succeeds, connection is * half-synchronized.
1921 			 * Otherwise, do 3-way handshake:
1922 			 *        SYN-SENT -> SYN-RECEIVED
1923 			 *        SYN-SENT* -> SYN-RECEIVED*
1924 			 * If there was no CC option, clear cached CC value.
1925 			 */
1926 			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
1927 			tcp_timer_activate(tp, TT_REXMT, 0);
1928 			tp->t_state = TCPS_SYN_RECEIVED;
1929 		}
1930 
1931 		KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
1932 		    "ti_locked %d", __func__, ti_locked));
1933 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1934 		INP_WLOCK_ASSERT(tp->t_inpcb);
1935 
1936 		/*
1937 		 * Advance th->th_seq to correspond to first data byte.
1938 		 * If data, trim to stay within window,
1939 		 * dropping FIN if necessary.
1940 		 */
1941 		th->th_seq++;
1942 		if (tlen > tp->rcv_wnd) {
1943 			todrop = tlen - tp->rcv_wnd;
1944 			m_adj(m, -todrop);
1945 			tlen = tp->rcv_wnd;
1946 			thflags &= ~TH_FIN;
1947 			TCPSTAT_INC(tcps_rcvpackafterwin);
1948 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
1949 		}
1950 		tp->snd_wl1 = th->th_seq - 1;
1951 		tp->rcv_up = th->th_seq;
1952 		/*
1953 		 * Client side of transaction: already sent SYN and data.
1954 		 * If the remote host used T/TCP to validate the SYN,
1955 		 * our data will be ACK'd; if so, enter normal data segment
1956 		 * processing in the middle of step 5, ack processing.
1957 		 * Otherwise, goto step 6.
1958 		 */
1959 		if (thflags & TH_ACK)
1960 			goto process_ACK;
1961 
1962 		goto step6;
1963 
1964 	/*
1965 	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
1966 	 *      do normal processing.
1967 	 *
1968 	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
1969 	 */
1970 	case TCPS_LAST_ACK:
1971 	case TCPS_CLOSING:
1972 		break;  /* continue normal processing */
1973 	}
1974 
1975 	/*
1976 	 * States other than LISTEN or SYN_SENT.
1977 	 * First check the RST flag and sequence number since reset segments
1978 	 * are exempt from the timestamp and connection count tests.  This
1979 	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
1980 	 * below which allowed reset segments in half the sequence space
1981 	 * to fall though and be processed (which gives forged reset
1982 	 * segments with a random sequence number a 50 percent chance of
1983 	 * killing a connection).
1984 	 * Then check timestamp, if present.
1985 	 * Then check the connection count, if present.
1986 	 * Then check that at least some bytes of segment are within
1987 	 * receive window.  If segment begins before rcv_nxt,
1988 	 * drop leading data (and SYN); if nothing left, just ack.
1989 	 *
1990 	 *
1991 	 * If the RST bit is set, check the sequence number to see
1992 	 * if this is a valid reset segment.
1993 	 * RFC 793 page 37:
1994 	 *   In all states except SYN-SENT, all reset (RST) segments
1995 	 *   are validated by checking their SEQ-fields.  A reset is
1996 	 *   valid if its sequence number is in the window.
1997 	 * Note: this does not take into account delayed ACKs, so
1998 	 *   we should test against last_ack_sent instead of rcv_nxt.
1999 	 *   The sequence number in the reset segment is normally an
2000 	 *   echo of our outgoing acknowlegement numbers, but some hosts
2001 	 *   send a reset with the sequence number at the rightmost edge
2002 	 *   of our receive window, and we have to handle this case.
2003 	 * Note 2: Paul Watson's paper "Slipping in the Window" has shown
2004 	 *   that brute force RST attacks are possible.  To combat this,
2005 	 *   we use a much stricter check while in the ESTABLISHED state,
2006 	 *   only accepting RSTs where the sequence number is equal to
2007 	 *   last_ack_sent.  In all other states (the states in which a
2008 	 *   RST is more likely), the more permissive check is used.
2009 	 * If we have multiple segments in flight, the initial reset
2010 	 * segment sequence numbers will be to the left of last_ack_sent,
2011 	 * but they will eventually catch up.
2012 	 * In any case, it never made sense to trim reset segments to
2013 	 * fit the receive window since RFC 1122 says:
2014 	 *   4.2.2.12  RST Segment: RFC-793 Section 3.4
2015 	 *
2016 	 *    A TCP SHOULD allow a received RST segment to include data.
2017 	 *
2018 	 *    DISCUSSION
2019 	 *         It has been suggested that a RST segment could contain
2020 	 *         ASCII text that encoded and explained the cause of the
2021 	 *         RST.  No standard has yet been established for such
2022 	 *         data.
2023 	 *
2024 	 * If the reset segment passes the sequence number test examine
2025 	 * the state:
2026 	 *    SYN_RECEIVED STATE:
2027 	 *	If passive open, return to LISTEN state.
2028 	 *	If active open, inform user that connection was refused.
2029 	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
2030 	 *	Inform user that connection was reset, and close tcb.
2031 	 *    CLOSING, LAST_ACK STATES:
2032 	 *	Close the tcb.
2033 	 *    TIME_WAIT STATE:
2034 	 *	Drop the segment - see Stevens, vol. 2, p. 964 and
2035 	 *      RFC 1337.
2036 	 */
2037 	if (thflags & TH_RST) {
2038 		if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2039 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2040 			switch (tp->t_state) {
2041 
2042 			case TCPS_SYN_RECEIVED:
2043 				so->so_error = ECONNREFUSED;
2044 				goto close;
2045 
2046 			case TCPS_ESTABLISHED:
2047 				if (V_tcp_insecure_rst == 0 &&
2048 				    !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
2049 				    SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
2050 				    !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2051 				    SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
2052 					TCPSTAT_INC(tcps_badrst);
2053 					goto drop;
2054 				}
2055 				/* FALLTHROUGH */
2056 			case TCPS_FIN_WAIT_1:
2057 			case TCPS_FIN_WAIT_2:
2058 			case TCPS_CLOSE_WAIT:
2059 				so->so_error = ECONNRESET;
2060 			close:
2061 				KASSERT(ti_locked == TI_WLOCKED,
2062 				    ("tcp_do_segment: TH_RST 1 ti_locked %d",
2063 				    ti_locked));
2064 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2065 
2066 				tp->t_state = TCPS_CLOSED;
2067 				TCPSTAT_INC(tcps_drops);
2068 				tp = tcp_close(tp);
2069 				break;
2070 
2071 			case TCPS_CLOSING:
2072 			case TCPS_LAST_ACK:
2073 				KASSERT(ti_locked == TI_WLOCKED,
2074 				    ("tcp_do_segment: TH_RST 2 ti_locked %d",
2075 				    ti_locked));
2076 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2077 
2078 				tp = tcp_close(tp);
2079 				break;
2080 			}
2081 		}
2082 		goto drop;
2083 	}
2084 
2085 	/*
2086 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2087 	 * and it's less than ts_recent, drop it.
2088 	 */
2089 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2090 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2091 
2092 		/* Check to see if ts_recent is over 24 days old.  */
2093 		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2094 			/*
2095 			 * Invalidate ts_recent.  If this segment updates
2096 			 * ts_recent, the age will be reset later and ts_recent
2097 			 * will get a valid value.  If it does not, setting
2098 			 * ts_recent to zero will at least satisfy the
2099 			 * requirement that zero be placed in the timestamp
2100 			 * echo reply when ts_recent isn't valid.  The
2101 			 * age isn't reset until we get a valid ts_recent
2102 			 * because we don't want out-of-order segments to be
2103 			 * dropped when ts_recent is old.
2104 			 */
2105 			tp->ts_recent = 0;
2106 		} else {
2107 			TCPSTAT_INC(tcps_rcvduppack);
2108 			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2109 			TCPSTAT_INC(tcps_pawsdrop);
2110 			if (tlen)
2111 				goto dropafterack;
2112 			goto drop;
2113 		}
2114 	}
2115 
2116 	/*
2117 	 * In the SYN-RECEIVED state, validate that the packet belongs to
2118 	 * this connection before trimming the data to fit the receive
2119 	 * window.  Check the sequence number versus IRS since we know
2120 	 * the sequence numbers haven't wrapped.  This is a partial fix
2121 	 * for the "LAND" DoS attack.
2122 	 */
2123 	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2124 		rstreason = BANDLIM_RST_OPENPORT;
2125 		goto dropwithreset;
2126 	}
2127 
2128 	todrop = tp->rcv_nxt - th->th_seq;
2129 	if (todrop > 0) {
2130 		/*
2131 		 * If this is a duplicate SYN for our current connection,
2132 		 * advance over it and pretend and it's not a SYN.
2133 		 */
2134 		if (thflags & TH_SYN && th->th_seq == tp->irs) {
2135 			thflags &= ~TH_SYN;
2136 			th->th_seq++;
2137 			if (th->th_urp > 1)
2138 				th->th_urp--;
2139 			else
2140 				thflags &= ~TH_URG;
2141 			todrop--;
2142 		}
2143 		/*
2144 		 * Following if statement from Stevens, vol. 2, p. 960.
2145 		 */
2146 		if (todrop > tlen
2147 		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2148 			/*
2149 			 * Any valid FIN must be to the left of the window.
2150 			 * At this point the FIN must be a duplicate or out
2151 			 * of sequence; drop it.
2152 			 */
2153 			thflags &= ~TH_FIN;
2154 
2155 			/*
2156 			 * Send an ACK to resynchronize and drop any data.
2157 			 * But keep on processing for RST or ACK.
2158 			 */
2159 			tp->t_flags |= TF_ACKNOW;
2160 			todrop = tlen;
2161 			TCPSTAT_INC(tcps_rcvduppack);
2162 			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2163 		} else {
2164 			TCPSTAT_INC(tcps_rcvpartduppack);
2165 			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2166 		}
2167 		drop_hdrlen += todrop;	/* drop from the top afterwards */
2168 		th->th_seq += todrop;
2169 		tlen -= todrop;
2170 		if (th->th_urp > todrop)
2171 			th->th_urp -= todrop;
2172 		else {
2173 			thflags &= ~TH_URG;
2174 			th->th_urp = 0;
2175 		}
2176 	}
2177 
2178 	/*
2179 	 * If new data are received on a connection after the
2180 	 * user processes are gone, then RST the other end.
2181 	 */
2182 	if ((so->so_state & SS_NOFDREF) &&
2183 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2184 		char *s;
2185 
2186 		KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
2187 		    "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
2188 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2189 
2190 		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
2191 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data after socket "
2192 			    "was closed, sending RST and removing tcpcb\n",
2193 			    s, __func__, tcpstates[tp->t_state], tlen);
2194 			free(s, M_TCPLOG);
2195 		}
2196 		tp = tcp_close(tp);
2197 		TCPSTAT_INC(tcps_rcvafterclose);
2198 		rstreason = BANDLIM_UNLIMITED;
2199 		goto dropwithreset;
2200 	}
2201 
2202 	/*
2203 	 * If segment ends after window, drop trailing data
2204 	 * (and PUSH and FIN); if nothing left, just ACK.
2205 	 */
2206 	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2207 	if (todrop > 0) {
2208 		TCPSTAT_INC(tcps_rcvpackafterwin);
2209 		if (todrop >= tlen) {
2210 			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2211 			/*
2212 			 * If window is closed can only take segments at
2213 			 * window edge, and have to drop data and PUSH from
2214 			 * incoming segments.  Continue processing, but
2215 			 * remember to ack.  Otherwise, drop segment
2216 			 * and ack.
2217 			 */
2218 			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2219 				tp->t_flags |= TF_ACKNOW;
2220 				TCPSTAT_INC(tcps_rcvwinprobe);
2221 			} else
2222 				goto dropafterack;
2223 		} else
2224 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2225 		m_adj(m, -todrop);
2226 		tlen -= todrop;
2227 		thflags &= ~(TH_PUSH|TH_FIN);
2228 	}
2229 
2230 	/*
2231 	 * If last ACK falls within this segment's sequence numbers,
2232 	 * record its timestamp.
2233 	 * NOTE:
2234 	 * 1) That the test incorporates suggestions from the latest
2235 	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2236 	 * 2) That updating only on newer timestamps interferes with
2237 	 *    our earlier PAWS tests, so this check should be solely
2238 	 *    predicated on the sequence space of this segment.
2239 	 * 3) That we modify the segment boundary check to be
2240 	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2241 	 *    instead of RFC1323's
2242 	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2243 	 *    This modified check allows us to overcome RFC1323's
2244 	 *    limitations as described in Stevens TCP/IP Illustrated
2245 	 *    Vol. 2 p.869. In such cases, we can still calculate the
2246 	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2247 	 */
2248 	if ((to.to_flags & TOF_TS) != 0 &&
2249 	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2250 	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2251 		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2252 		tp->ts_recent_age = tcp_ts_getticks();
2253 		tp->ts_recent = to.to_tsval;
2254 	}
2255 
2256 	/*
2257 	 * If a SYN is in the window, then this is an
2258 	 * error and we send an RST and drop the connection.
2259 	 */
2260 	if (thflags & TH_SYN) {
2261 		KASSERT(ti_locked == TI_WLOCKED,
2262 		    ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
2263 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2264 
2265 		tp = tcp_drop(tp, ECONNRESET);
2266 		rstreason = BANDLIM_UNLIMITED;
2267 		goto drop;
2268 	}
2269 
2270 	/*
2271 	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2272 	 * flag is on (half-synchronized state), then queue data for
2273 	 * later processing; else drop segment and return.
2274 	 */
2275 	if ((thflags & TH_ACK) == 0) {
2276 		if (tp->t_state == TCPS_SYN_RECEIVED ||
2277 		    (tp->t_flags & TF_NEEDSYN))
2278 			goto step6;
2279 		else if (tp->t_flags & TF_ACKNOW)
2280 			goto dropafterack;
2281 		else
2282 			goto drop;
2283 	}
2284 
2285 	/*
2286 	 * Ack processing.
2287 	 */
2288 	switch (tp->t_state) {
2289 
2290 	/*
2291 	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2292 	 * ESTABLISHED state and continue processing.
2293 	 * The ACK was checked above.
2294 	 */
2295 	case TCPS_SYN_RECEIVED:
2296 
2297 		TCPSTAT_INC(tcps_connects);
2298 		soisconnected(so);
2299 		/* Do window scaling? */
2300 		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2301 			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2302 			tp->rcv_scale = tp->request_r_scale;
2303 			tp->snd_wnd = tiwin;
2304 		}
2305 		/*
2306 		 * Make transitions:
2307 		 *      SYN-RECEIVED  -> ESTABLISHED
2308 		 *      SYN-RECEIVED* -> FIN-WAIT-1
2309 		 */
2310 		tp->t_starttime = ticks;
2311 		if (tp->t_flags & TF_NEEDFIN) {
2312 			tp->t_state = TCPS_FIN_WAIT_1;
2313 			tp->t_flags &= ~TF_NEEDFIN;
2314 		} else {
2315 			tp->t_state = TCPS_ESTABLISHED;
2316 			cc_conn_init(tp);
2317 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2318 		}
2319 		/*
2320 		 * If segment contains data or ACK, will call tcp_reass()
2321 		 * later; if not, do so now to pass queued data to user.
2322 		 */
2323 		if (tlen == 0 && (thflags & TH_FIN) == 0)
2324 			(void) tcp_reass(tp, (struct tcphdr *)0, 0,
2325 			    (struct mbuf *)0);
2326 		tp->snd_wl1 = th->th_seq - 1;
2327 		/* FALLTHROUGH */
2328 
2329 	/*
2330 	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2331 	 * ACKs.  If the ack is in the range
2332 	 *	tp->snd_una < th->th_ack <= tp->snd_max
2333 	 * then advance tp->snd_una to th->th_ack and drop
2334 	 * data from the retransmission queue.  If this ACK reflects
2335 	 * more up to date window information we update our window information.
2336 	 */
2337 	case TCPS_ESTABLISHED:
2338 	case TCPS_FIN_WAIT_1:
2339 	case TCPS_FIN_WAIT_2:
2340 	case TCPS_CLOSE_WAIT:
2341 	case TCPS_CLOSING:
2342 	case TCPS_LAST_ACK:
2343 		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2344 			TCPSTAT_INC(tcps_rcvacktoomuch);
2345 			goto dropafterack;
2346 		}
2347 		if ((tp->t_flags & TF_SACK_PERMIT) &&
2348 		    ((to.to_flags & TOF_SACK) ||
2349 		     !TAILQ_EMPTY(&tp->snd_holes)))
2350 			tcp_sack_doack(tp, &to, th->th_ack);
2351 
2352 		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2353 		hhook_run_tcp_est_in(tp, th, &to);
2354 
2355 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2356 			if (tlen == 0 && tiwin == tp->snd_wnd) {
2357 				TCPSTAT_INC(tcps_rcvdupack);
2358 				/*
2359 				 * If we have outstanding data (other than
2360 				 * a window probe), this is a completely
2361 				 * duplicate ack (ie, window info didn't
2362 				 * change), the ack is the biggest we've
2363 				 * seen and we've seen exactly our rexmt
2364 				 * threshhold of them, assume a packet
2365 				 * has been dropped and retransmit it.
2366 				 * Kludge snd_nxt & the congestion
2367 				 * window so we send only this one
2368 				 * packet.
2369 				 *
2370 				 * We know we're losing at the current
2371 				 * window size so do congestion avoidance
2372 				 * (set ssthresh to half the current window
2373 				 * and pull our congestion window back to
2374 				 * the new ssthresh).
2375 				 *
2376 				 * Dup acks mean that packets have left the
2377 				 * network (they're now cached at the receiver)
2378 				 * so bump cwnd by the amount in the receiver
2379 				 * to keep a constant cwnd packets in the
2380 				 * network.
2381 				 *
2382 				 * When using TCP ECN, notify the peer that
2383 				 * we reduced the cwnd.
2384 				 */
2385 				if (!tcp_timer_active(tp, TT_REXMT) ||
2386 				    th->th_ack != tp->snd_una)
2387 					tp->t_dupacks = 0;
2388 				else if (++tp->t_dupacks > tcprexmtthresh ||
2389 				     IN_FASTRECOVERY(tp->t_flags)) {
2390 					cc_ack_received(tp, th, CC_DUPACK);
2391 					if ((tp->t_flags & TF_SACK_PERMIT) &&
2392 					    IN_FASTRECOVERY(tp->t_flags)) {
2393 						int awnd;
2394 
2395 						/*
2396 						 * Compute the amount of data in flight first.
2397 						 * We can inject new data into the pipe iff
2398 						 * we have less than 1/2 the original window's
2399 						 * worth of data in flight.
2400 						 */
2401 						awnd = (tp->snd_nxt - tp->snd_fack) +
2402 							tp->sackhint.sack_bytes_rexmit;
2403 						if (awnd < tp->snd_ssthresh) {
2404 							tp->snd_cwnd += tp->t_maxseg;
2405 							if (tp->snd_cwnd > tp->snd_ssthresh)
2406 								tp->snd_cwnd = tp->snd_ssthresh;
2407 						}
2408 					} else
2409 						tp->snd_cwnd += tp->t_maxseg;
2410 					(void) tcp_output(tp);
2411 					goto drop;
2412 				} else if (tp->t_dupacks == tcprexmtthresh) {
2413 					tcp_seq onxt = tp->snd_nxt;
2414 
2415 					/*
2416 					 * If we're doing sack, check to
2417 					 * see if we're already in sack
2418 					 * recovery. If we're not doing sack,
2419 					 * check to see if we're in newreno
2420 					 * recovery.
2421 					 */
2422 					if (tp->t_flags & TF_SACK_PERMIT) {
2423 						if (IN_FASTRECOVERY(tp->t_flags)) {
2424 							tp->t_dupacks = 0;
2425 							break;
2426 						}
2427 					} else {
2428 						if (SEQ_LEQ(th->th_ack,
2429 						    tp->snd_recover)) {
2430 							tp->t_dupacks = 0;
2431 							break;
2432 						}
2433 					}
2434 					/* Congestion signal before ack. */
2435 					cc_cong_signal(tp, th, CC_NDUPACK);
2436 					cc_ack_received(tp, th, CC_DUPACK);
2437 					tcp_timer_activate(tp, TT_REXMT, 0);
2438 					tp->t_rtttime = 0;
2439 					if (tp->t_flags & TF_SACK_PERMIT) {
2440 						TCPSTAT_INC(
2441 						    tcps_sack_recovery_episode);
2442 						tp->sack_newdata = tp->snd_nxt;
2443 						tp->snd_cwnd = tp->t_maxseg;
2444 						(void) tcp_output(tp);
2445 						goto drop;
2446 					}
2447 					tp->snd_nxt = th->th_ack;
2448 					tp->snd_cwnd = tp->t_maxseg;
2449 					(void) tcp_output(tp);
2450 					KASSERT(tp->snd_limited <= 2,
2451 					    ("%s: tp->snd_limited too big",
2452 					    __func__));
2453 					tp->snd_cwnd = tp->snd_ssthresh +
2454 					     tp->t_maxseg *
2455 					     (tp->t_dupacks - tp->snd_limited);
2456 					if (SEQ_GT(onxt, tp->snd_nxt))
2457 						tp->snd_nxt = onxt;
2458 					goto drop;
2459 				} else if (V_tcp_do_rfc3042) {
2460 					cc_ack_received(tp, th, CC_DUPACK);
2461 					u_long oldcwnd = tp->snd_cwnd;
2462 					tcp_seq oldsndmax = tp->snd_max;
2463 					u_int sent;
2464 
2465 					KASSERT(tp->t_dupacks == 1 ||
2466 					    tp->t_dupacks == 2,
2467 					    ("%s: dupacks not 1 or 2",
2468 					    __func__));
2469 					if (tp->t_dupacks == 1)
2470 						tp->snd_limited = 0;
2471 					tp->snd_cwnd =
2472 					    (tp->snd_nxt - tp->snd_una) +
2473 					    (tp->t_dupacks - tp->snd_limited) *
2474 					    tp->t_maxseg;
2475 					(void) tcp_output(tp);
2476 					sent = tp->snd_max - oldsndmax;
2477 					if (sent > tp->t_maxseg) {
2478 						KASSERT((tp->t_dupacks == 2 &&
2479 						    tp->snd_limited == 0) ||
2480 						   (sent == tp->t_maxseg + 1 &&
2481 						    tp->t_flags & TF_SENTFIN),
2482 						    ("%s: sent too much",
2483 						    __func__));
2484 						tp->snd_limited = 2;
2485 					} else if (sent > 0)
2486 						++tp->snd_limited;
2487 					tp->snd_cwnd = oldcwnd;
2488 					goto drop;
2489 				}
2490 			} else
2491 				tp->t_dupacks = 0;
2492 			break;
2493 		}
2494 
2495 		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2496 		    ("%s: th_ack <= snd_una", __func__));
2497 
2498 		/*
2499 		 * If the congestion window was inflated to account
2500 		 * for the other side's cached packets, retract it.
2501 		 */
2502 		if (IN_FASTRECOVERY(tp->t_flags)) {
2503 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2504 				if (tp->t_flags & TF_SACK_PERMIT)
2505 					tcp_sack_partialack(tp, th);
2506 				else
2507 					tcp_newreno_partial_ack(tp, th);
2508 			} else
2509 				cc_post_recovery(tp, th);
2510 		}
2511 		tp->t_dupacks = 0;
2512 		/*
2513 		 * If we reach this point, ACK is not a duplicate,
2514 		 *     i.e., it ACKs something we sent.
2515 		 */
2516 		if (tp->t_flags & TF_NEEDSYN) {
2517 			/*
2518 			 * T/TCP: Connection was half-synchronized, and our
2519 			 * SYN has been ACK'd (so connection is now fully
2520 			 * synchronized).  Go to non-starred state,
2521 			 * increment snd_una for ACK of SYN, and check if
2522 			 * we can do window scaling.
2523 			 */
2524 			tp->t_flags &= ~TF_NEEDSYN;
2525 			tp->snd_una++;
2526 			/* Do window scaling? */
2527 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2528 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2529 				tp->rcv_scale = tp->request_r_scale;
2530 				/* Send window already scaled. */
2531 			}
2532 		}
2533 
2534 process_ACK:
2535 		INP_WLOCK_ASSERT(tp->t_inpcb);
2536 
2537 		acked = BYTES_THIS_ACK(tp, th);
2538 		TCPSTAT_INC(tcps_rcvackpack);
2539 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2540 
2541 		/*
2542 		 * If we just performed our first retransmit, and the ACK
2543 		 * arrives within our recovery window, then it was a mistake
2544 		 * to do the retransmit in the first place.  Recover our
2545 		 * original cwnd and ssthresh, and proceed to transmit where
2546 		 * we left off.
2547 		 */
2548 		if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
2549 		    (int)(ticks - tp->t_badrxtwin) < 0)
2550 			cc_cong_signal(tp, th, CC_RTO_ERR);
2551 
2552 		/*
2553 		 * If we have a timestamp reply, update smoothed
2554 		 * round trip time.  If no timestamp is present but
2555 		 * transmit timer is running and timed sequence
2556 		 * number was acked, update smoothed round trip time.
2557 		 * Since we now have an rtt measurement, cancel the
2558 		 * timer backoff (cf., Phil Karn's retransmit alg.).
2559 		 * Recompute the initial retransmit timer.
2560 		 *
2561 		 * Some boxes send broken timestamp replies
2562 		 * during the SYN+ACK phase, ignore
2563 		 * timestamps of 0 or we could calculate a
2564 		 * huge RTT and blow up the retransmit timer.
2565 		 */
2566 		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2567 			u_int t;
2568 
2569 			t = tcp_ts_getticks() - to.to_tsecr;
2570 			if (!tp->t_rttlow || tp->t_rttlow > t)
2571 				tp->t_rttlow = t;
2572 			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2573 		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2574 			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2575 				tp->t_rttlow = ticks - tp->t_rtttime;
2576 			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2577 		}
2578 
2579 		/*
2580 		 * If all outstanding data is acked, stop retransmit
2581 		 * timer and remember to restart (more output or persist).
2582 		 * If there is more data to be acked, restart retransmit
2583 		 * timer, using current (possibly backed-off) value.
2584 		 */
2585 		if (th->th_ack == tp->snd_max) {
2586 			tcp_timer_activate(tp, TT_REXMT, 0);
2587 			needoutput = 1;
2588 		} else if (!tcp_timer_active(tp, TT_PERSIST))
2589 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2590 
2591 		/*
2592 		 * If no data (only SYN) was ACK'd,
2593 		 *    skip rest of ACK processing.
2594 		 */
2595 		if (acked == 0)
2596 			goto step6;
2597 
2598 		/*
2599 		 * Let the congestion control algorithm update congestion
2600 		 * control related information. This typically means increasing
2601 		 * the congestion window.
2602 		 */
2603 		cc_ack_received(tp, th, CC_ACK);
2604 
2605 		SOCKBUF_LOCK(&so->so_snd);
2606 		if (acked > so->so_snd.sb_cc) {
2607 			tp->snd_wnd -= so->so_snd.sb_cc;
2608 			sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2609 			ourfinisacked = 1;
2610 		} else {
2611 			sbdrop_locked(&so->so_snd, acked);
2612 			tp->snd_wnd -= acked;
2613 			ourfinisacked = 0;
2614 		}
2615 		/* NB: sowwakeup_locked() does an implicit unlock. */
2616 		sowwakeup_locked(so);
2617 		/* Detect una wraparound. */
2618 		if (!IN_RECOVERY(tp->t_flags) &&
2619 		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2620 		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2621 			tp->snd_recover = th->th_ack - 1;
2622 		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2623 		if (IN_RECOVERY(tp->t_flags) &&
2624 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2625 			EXIT_RECOVERY(tp->t_flags);
2626 		}
2627 		tp->snd_una = th->th_ack;
2628 		if (tp->t_flags & TF_SACK_PERMIT) {
2629 			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2630 				tp->snd_recover = tp->snd_una;
2631 		}
2632 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2633 			tp->snd_nxt = tp->snd_una;
2634 
2635 		switch (tp->t_state) {
2636 
2637 		/*
2638 		 * In FIN_WAIT_1 STATE in addition to the processing
2639 		 * for the ESTABLISHED state if our FIN is now acknowledged
2640 		 * then enter FIN_WAIT_2.
2641 		 */
2642 		case TCPS_FIN_WAIT_1:
2643 			if (ourfinisacked) {
2644 				/*
2645 				 * If we can't receive any more
2646 				 * data, then closing user can proceed.
2647 				 * Starting the timer is contrary to the
2648 				 * specification, but if we don't get a FIN
2649 				 * we'll hang forever.
2650 				 *
2651 				 * XXXjl:
2652 				 * we should release the tp also, and use a
2653 				 * compressed state.
2654 				 */
2655 				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2656 					soisdisconnected(so);
2657 					tcp_timer_activate(tp, TT_2MSL,
2658 					    (tcp_fast_finwait2_recycle ?
2659 					    tcp_finwait2_timeout :
2660 					    TP_MAXIDLE(tp)));
2661 				}
2662 				tp->t_state = TCPS_FIN_WAIT_2;
2663 			}
2664 			break;
2665 
2666 		/*
2667 		 * In CLOSING STATE in addition to the processing for
2668 		 * the ESTABLISHED state if the ACK acknowledges our FIN
2669 		 * then enter the TIME-WAIT state, otherwise ignore
2670 		 * the segment.
2671 		 */
2672 		case TCPS_CLOSING:
2673 			if (ourfinisacked) {
2674 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2675 				tcp_twstart(tp);
2676 				INP_INFO_WUNLOCK(&V_tcbinfo);
2677 				m_freem(m);
2678 				return;
2679 			}
2680 			break;
2681 
2682 		/*
2683 		 * In LAST_ACK, we may still be waiting for data to drain
2684 		 * and/or to be acked, as well as for the ack of our FIN.
2685 		 * If our FIN is now acknowledged, delete the TCB,
2686 		 * enter the closed state and return.
2687 		 */
2688 		case TCPS_LAST_ACK:
2689 			if (ourfinisacked) {
2690 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2691 				tp = tcp_close(tp);
2692 				goto drop;
2693 			}
2694 			break;
2695 		}
2696 	}
2697 
2698 step6:
2699 	INP_WLOCK_ASSERT(tp->t_inpcb);
2700 
2701 	/*
2702 	 * Update window information.
2703 	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2704 	 */
2705 	if ((thflags & TH_ACK) &&
2706 	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2707 	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2708 	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2709 		/* keep track of pure window updates */
2710 		if (tlen == 0 &&
2711 		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2712 			TCPSTAT_INC(tcps_rcvwinupd);
2713 		tp->snd_wnd = tiwin;
2714 		tp->snd_wl1 = th->th_seq;
2715 		tp->snd_wl2 = th->th_ack;
2716 		if (tp->snd_wnd > tp->max_sndwnd)
2717 			tp->max_sndwnd = tp->snd_wnd;
2718 		needoutput = 1;
2719 	}
2720 
2721 	/*
2722 	 * Process segments with URG.
2723 	 */
2724 	if ((thflags & TH_URG) && th->th_urp &&
2725 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2726 		/*
2727 		 * This is a kludge, but if we receive and accept
2728 		 * random urgent pointers, we'll crash in
2729 		 * soreceive.  It's hard to imagine someone
2730 		 * actually wanting to send this much urgent data.
2731 		 */
2732 		SOCKBUF_LOCK(&so->so_rcv);
2733 		if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2734 			th->th_urp = 0;			/* XXX */
2735 			thflags &= ~TH_URG;		/* XXX */
2736 			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
2737 			goto dodata;			/* XXX */
2738 		}
2739 		/*
2740 		 * If this segment advances the known urgent pointer,
2741 		 * then mark the data stream.  This should not happen
2742 		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2743 		 * a FIN has been received from the remote side.
2744 		 * In these states we ignore the URG.
2745 		 *
2746 		 * According to RFC961 (Assigned Protocols),
2747 		 * the urgent pointer points to the last octet
2748 		 * of urgent data.  We continue, however,
2749 		 * to consider it to indicate the first octet
2750 		 * of data past the urgent section as the original
2751 		 * spec states (in one of two places).
2752 		 */
2753 		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2754 			tp->rcv_up = th->th_seq + th->th_urp;
2755 			so->so_oobmark = so->so_rcv.sb_cc +
2756 			    (tp->rcv_up - tp->rcv_nxt) - 1;
2757 			if (so->so_oobmark == 0)
2758 				so->so_rcv.sb_state |= SBS_RCVATMARK;
2759 			sohasoutofband(so);
2760 			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2761 		}
2762 		SOCKBUF_UNLOCK(&so->so_rcv);
2763 		/*
2764 		 * Remove out of band data so doesn't get presented to user.
2765 		 * This can happen independent of advancing the URG pointer,
2766 		 * but if two URG's are pending at once, some out-of-band
2767 		 * data may creep in... ick.
2768 		 */
2769 		if (th->th_urp <= (u_long)tlen &&
2770 		    !(so->so_options & SO_OOBINLINE)) {
2771 			/* hdr drop is delayed */
2772 			tcp_pulloutofband(so, th, m, drop_hdrlen);
2773 		}
2774 	} else {
2775 		/*
2776 		 * If no out of band data is expected,
2777 		 * pull receive urgent pointer along
2778 		 * with the receive window.
2779 		 */
2780 		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2781 			tp->rcv_up = tp->rcv_nxt;
2782 	}
2783 dodata:							/* XXX */
2784 	INP_WLOCK_ASSERT(tp->t_inpcb);
2785 
2786 	/*
2787 	 * Process the segment text, merging it into the TCP sequencing queue,
2788 	 * and arranging for acknowledgment of receipt if necessary.
2789 	 * This process logically involves adjusting tp->rcv_wnd as data
2790 	 * is presented to the user (this happens in tcp_usrreq.c,
2791 	 * case PRU_RCVD).  If a FIN has already been received on this
2792 	 * connection then we just ignore the text.
2793 	 */
2794 	if ((tlen || (thflags & TH_FIN)) &&
2795 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2796 		tcp_seq save_start = th->th_seq;
2797 		m_adj(m, drop_hdrlen);	/* delayed header drop */
2798 		/*
2799 		 * Insert segment which includes th into TCP reassembly queue
2800 		 * with control block tp.  Set thflags to whether reassembly now
2801 		 * includes a segment with FIN.  This handles the common case
2802 		 * inline (segment is the next to be received on an established
2803 		 * connection, and the queue is empty), avoiding linkage into
2804 		 * and removal from the queue and repetition of various
2805 		 * conversions.
2806 		 * Set DELACK for segments received in order, but ack
2807 		 * immediately when segments are out of order (so
2808 		 * fast retransmit can work).
2809 		 */
2810 		if (th->th_seq == tp->rcv_nxt &&
2811 		    LIST_EMPTY(&tp->t_segq) &&
2812 		    TCPS_HAVEESTABLISHED(tp->t_state)) {
2813 			if (DELAY_ACK(tp))
2814 				tp->t_flags |= TF_DELACK;
2815 			else
2816 				tp->t_flags |= TF_ACKNOW;
2817 			tp->rcv_nxt += tlen;
2818 			thflags = th->th_flags & TH_FIN;
2819 			TCPSTAT_INC(tcps_rcvpack);
2820 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
2821 			ND6_HINT(tp);
2822 			SOCKBUF_LOCK(&so->so_rcv);
2823 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2824 				m_freem(m);
2825 			else
2826 				sbappendstream_locked(&so->so_rcv, m);
2827 			/* NB: sorwakeup_locked() does an implicit unlock. */
2828 			sorwakeup_locked(so);
2829 		} else {
2830 			/*
2831 			 * XXX: Due to the header drop above "th" is
2832 			 * theoretically invalid by now.  Fortunately
2833 			 * m_adj() doesn't actually frees any mbufs
2834 			 * when trimming from the head.
2835 			 */
2836 			thflags = tcp_reass(tp, th, &tlen, m);
2837 			tp->t_flags |= TF_ACKNOW;
2838 		}
2839 		if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
2840 			tcp_update_sack_list(tp, save_start, save_start + tlen);
2841 #if 0
2842 		/*
2843 		 * Note the amount of data that peer has sent into
2844 		 * our window, in order to estimate the sender's
2845 		 * buffer size.
2846 		 * XXX: Unused.
2847 		 */
2848 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
2849 			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2850 		else
2851 			len = so->so_rcv.sb_hiwat;
2852 #endif
2853 	} else {
2854 		m_freem(m);
2855 		thflags &= ~TH_FIN;
2856 	}
2857 
2858 	/*
2859 	 * If FIN is received ACK the FIN and let the user know
2860 	 * that the connection is closing.
2861 	 */
2862 	if (thflags & TH_FIN) {
2863 		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2864 			socantrcvmore(so);
2865 			/*
2866 			 * If connection is half-synchronized
2867 			 * (ie NEEDSYN flag on) then delay ACK,
2868 			 * so it may be piggybacked when SYN is sent.
2869 			 * Otherwise, since we received a FIN then no
2870 			 * more input can be expected, send ACK now.
2871 			 */
2872 			if (tp->t_flags & TF_NEEDSYN)
2873 				tp->t_flags |= TF_DELACK;
2874 			else
2875 				tp->t_flags |= TF_ACKNOW;
2876 			tp->rcv_nxt++;
2877 		}
2878 		switch (tp->t_state) {
2879 
2880 		/*
2881 		 * In SYN_RECEIVED and ESTABLISHED STATES
2882 		 * enter the CLOSE_WAIT state.
2883 		 */
2884 		case TCPS_SYN_RECEIVED:
2885 			tp->t_starttime = ticks;
2886 			/* FALLTHROUGH */
2887 		case TCPS_ESTABLISHED:
2888 			tp->t_state = TCPS_CLOSE_WAIT;
2889 			break;
2890 
2891 		/*
2892 		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
2893 		 * enter the CLOSING state.
2894 		 */
2895 		case TCPS_FIN_WAIT_1:
2896 			tp->t_state = TCPS_CLOSING;
2897 			break;
2898 
2899 		/*
2900 		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
2901 		 * starting the time-wait timer, turning off the other
2902 		 * standard timers.
2903 		 */
2904 		case TCPS_FIN_WAIT_2:
2905 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2906 			KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
2907 			    "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
2908 			    ti_locked));
2909 
2910 			tcp_twstart(tp);
2911 			INP_INFO_WUNLOCK(&V_tcbinfo);
2912 			return;
2913 		}
2914 	}
2915 	if (ti_locked == TI_WLOCKED)
2916 		INP_INFO_WUNLOCK(&V_tcbinfo);
2917 	ti_locked = TI_UNLOCKED;
2918 
2919 #ifdef TCPDEBUG
2920 	if (so->so_options & SO_DEBUG)
2921 		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
2922 			  &tcp_savetcp, 0);
2923 #endif
2924 
2925 	/*
2926 	 * Return any desired output.
2927 	 */
2928 	if (needoutput || (tp->t_flags & TF_ACKNOW))
2929 		(void) tcp_output(tp);
2930 
2931 check_delack:
2932 	KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
2933 	    __func__, ti_locked));
2934 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
2935 	INP_WLOCK_ASSERT(tp->t_inpcb);
2936 
2937 	if (tp->t_flags & TF_DELACK) {
2938 		tp->t_flags &= ~TF_DELACK;
2939 		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
2940 	}
2941 	INP_WUNLOCK(tp->t_inpcb);
2942 	return;
2943 
2944 dropafterack:
2945 	/*
2946 	 * Generate an ACK dropping incoming segment if it occupies
2947 	 * sequence space, where the ACK reflects our state.
2948 	 *
2949 	 * We can now skip the test for the RST flag since all
2950 	 * paths to this code happen after packets containing
2951 	 * RST have been dropped.
2952 	 *
2953 	 * In the SYN-RECEIVED state, don't send an ACK unless the
2954 	 * segment we received passes the SYN-RECEIVED ACK test.
2955 	 * If it fails send a RST.  This breaks the loop in the
2956 	 * "LAND" DoS attack, and also prevents an ACK storm
2957 	 * between two listening ports that have been sent forged
2958 	 * SYN segments, each with the source address of the other.
2959 	 */
2960 	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
2961 	    (SEQ_GT(tp->snd_una, th->th_ack) ||
2962 	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
2963 		rstreason = BANDLIM_RST_OPENPORT;
2964 		goto dropwithreset;
2965 	}
2966 #ifdef TCPDEBUG
2967 	if (so->so_options & SO_DEBUG)
2968 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
2969 			  &tcp_savetcp, 0);
2970 #endif
2971 	if (ti_locked == TI_WLOCKED)
2972 		INP_INFO_WUNLOCK(&V_tcbinfo);
2973 	ti_locked = TI_UNLOCKED;
2974 
2975 	tp->t_flags |= TF_ACKNOW;
2976 	(void) tcp_output(tp);
2977 	INP_WUNLOCK(tp->t_inpcb);
2978 	m_freem(m);
2979 	return;
2980 
2981 dropwithreset:
2982 	if (ti_locked == TI_WLOCKED)
2983 		INP_INFO_WUNLOCK(&V_tcbinfo);
2984 	ti_locked = TI_UNLOCKED;
2985 
2986 	if (tp != NULL) {
2987 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
2988 		INP_WUNLOCK(tp->t_inpcb);
2989 	} else
2990 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
2991 	return;
2992 
2993 drop:
2994 	if (ti_locked == TI_WLOCKED) {
2995 		INP_INFO_WUNLOCK(&V_tcbinfo);
2996 		ti_locked = TI_UNLOCKED;
2997 	}
2998 #ifdef INVARIANTS
2999 	else
3000 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3001 #endif
3002 
3003 	/*
3004 	 * Drop space held by incoming segment and return.
3005 	 */
3006 #ifdef TCPDEBUG
3007 	if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3008 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3009 			  &tcp_savetcp, 0);
3010 #endif
3011 	if (tp != NULL)
3012 		INP_WUNLOCK(tp->t_inpcb);
3013 	m_freem(m);
3014 }
3015 
3016 /*
3017  * Issue RST and make ACK acceptable to originator of segment.
3018  * The mbuf must still include the original packet header.
3019  * tp may be NULL.
3020  */
3021 static void
3022 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3023     int tlen, int rstreason)
3024 {
3025 #ifdef INET
3026 	struct ip *ip;
3027 #endif
3028 #ifdef INET6
3029 	struct ip6_hdr *ip6;
3030 #endif
3031 
3032 	if (tp != NULL) {
3033 		INP_WLOCK_ASSERT(tp->t_inpcb);
3034 	}
3035 
3036 	/* Don't bother if destination was broadcast/multicast. */
3037 	if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3038 		goto drop;
3039 #ifdef INET6
3040 	if (mtod(m, struct ip *)->ip_v == 6) {
3041 		ip6 = mtod(m, struct ip6_hdr *);
3042 		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3043 		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3044 			goto drop;
3045 		/* IPv6 anycast check is done at tcp6_input() */
3046 	}
3047 #endif
3048 #if defined(INET) && defined(INET6)
3049 	else
3050 #endif
3051 #ifdef INET
3052 	{
3053 		ip = mtod(m, struct ip *);
3054 		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3055 		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3056 		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3057 		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3058 			goto drop;
3059 	}
3060 #endif
3061 
3062 	/* Perform bandwidth limiting. */
3063 	if (badport_bandlim(rstreason) < 0)
3064 		goto drop;
3065 
3066 	/* tcp_respond consumes the mbuf chain. */
3067 	if (th->th_flags & TH_ACK) {
3068 		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3069 		    th->th_ack, TH_RST);
3070 	} else {
3071 		if (th->th_flags & TH_SYN)
3072 			tlen++;
3073 		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3074 		    (tcp_seq)0, TH_RST|TH_ACK);
3075 	}
3076 	return;
3077 drop:
3078 	m_freem(m);
3079 }
3080 
3081 /*
3082  * Parse TCP options and place in tcpopt.
3083  */
3084 static void
3085 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3086 {
3087 	int opt, optlen;
3088 
3089 	to->to_flags = 0;
3090 	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3091 		opt = cp[0];
3092 		if (opt == TCPOPT_EOL)
3093 			break;
3094 		if (opt == TCPOPT_NOP)
3095 			optlen = 1;
3096 		else {
3097 			if (cnt < 2)
3098 				break;
3099 			optlen = cp[1];
3100 			if (optlen < 2 || optlen > cnt)
3101 				break;
3102 		}
3103 		switch (opt) {
3104 		case TCPOPT_MAXSEG:
3105 			if (optlen != TCPOLEN_MAXSEG)
3106 				continue;
3107 			if (!(flags & TO_SYN))
3108 				continue;
3109 			to->to_flags |= TOF_MSS;
3110 			bcopy((char *)cp + 2,
3111 			    (char *)&to->to_mss, sizeof(to->to_mss));
3112 			to->to_mss = ntohs(to->to_mss);
3113 			break;
3114 		case TCPOPT_WINDOW:
3115 			if (optlen != TCPOLEN_WINDOW)
3116 				continue;
3117 			if (!(flags & TO_SYN))
3118 				continue;
3119 			to->to_flags |= TOF_SCALE;
3120 			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3121 			break;
3122 		case TCPOPT_TIMESTAMP:
3123 			if (optlen != TCPOLEN_TIMESTAMP)
3124 				continue;
3125 			to->to_flags |= TOF_TS;
3126 			bcopy((char *)cp + 2,
3127 			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3128 			to->to_tsval = ntohl(to->to_tsval);
3129 			bcopy((char *)cp + 6,
3130 			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3131 			to->to_tsecr = ntohl(to->to_tsecr);
3132 			break;
3133 #ifdef TCP_SIGNATURE
3134 		/*
3135 		 * XXX In order to reply to a host which has set the
3136 		 * TCP_SIGNATURE option in its initial SYN, we have to
3137 		 * record the fact that the option was observed here
3138 		 * for the syncache code to perform the correct response.
3139 		 */
3140 		case TCPOPT_SIGNATURE:
3141 			if (optlen != TCPOLEN_SIGNATURE)
3142 				continue;
3143 			to->to_flags |= TOF_SIGNATURE;
3144 			to->to_signature = cp + 2;
3145 			break;
3146 #endif
3147 		case TCPOPT_SACK_PERMITTED:
3148 			if (optlen != TCPOLEN_SACK_PERMITTED)
3149 				continue;
3150 			if (!(flags & TO_SYN))
3151 				continue;
3152 			if (!V_tcp_do_sack)
3153 				continue;
3154 			to->to_flags |= TOF_SACKPERM;
3155 			break;
3156 		case TCPOPT_SACK:
3157 			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3158 				continue;
3159 			if (flags & TO_SYN)
3160 				continue;
3161 			to->to_flags |= TOF_SACK;
3162 			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3163 			to->to_sacks = cp + 2;
3164 			TCPSTAT_INC(tcps_sack_rcv_blocks);
3165 			break;
3166 		default:
3167 			continue;
3168 		}
3169 	}
3170 }
3171 
3172 /*
3173  * Pull out of band byte out of a segment so
3174  * it doesn't appear in the user's data queue.
3175  * It is still reflected in the segment length for
3176  * sequencing purposes.
3177  */
3178 static void
3179 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3180     int off)
3181 {
3182 	int cnt = off + th->th_urp - 1;
3183 
3184 	while (cnt >= 0) {
3185 		if (m->m_len > cnt) {
3186 			char *cp = mtod(m, caddr_t) + cnt;
3187 			struct tcpcb *tp = sototcpcb(so);
3188 
3189 			INP_WLOCK_ASSERT(tp->t_inpcb);
3190 
3191 			tp->t_iobc = *cp;
3192 			tp->t_oobflags |= TCPOOB_HAVEDATA;
3193 			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3194 			m->m_len--;
3195 			if (m->m_flags & M_PKTHDR)
3196 				m->m_pkthdr.len--;
3197 			return;
3198 		}
3199 		cnt -= m->m_len;
3200 		m = m->m_next;
3201 		if (m == NULL)
3202 			break;
3203 	}
3204 	panic("tcp_pulloutofband");
3205 }
3206 
3207 /*
3208  * Collect new round-trip time estimate
3209  * and update averages and current timeout.
3210  */
3211 static void
3212 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3213 {
3214 	int delta;
3215 
3216 	INP_WLOCK_ASSERT(tp->t_inpcb);
3217 
3218 	TCPSTAT_INC(tcps_rttupdated);
3219 	tp->t_rttupdated++;
3220 	if (tp->t_srtt != 0) {
3221 		/*
3222 		 * srtt is stored as fixed point with 5 bits after the
3223 		 * binary point (i.e., scaled by 8).  The following magic
3224 		 * is equivalent to the smoothing algorithm in rfc793 with
3225 		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3226 		 * point).  Adjust rtt to origin 0.
3227 		 */
3228 		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3229 			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3230 
3231 		if ((tp->t_srtt += delta) <= 0)
3232 			tp->t_srtt = 1;
3233 
3234 		/*
3235 		 * We accumulate a smoothed rtt variance (actually, a
3236 		 * smoothed mean difference), then set the retransmit
3237 		 * timer to smoothed rtt + 4 times the smoothed variance.
3238 		 * rttvar is stored as fixed point with 4 bits after the
3239 		 * binary point (scaled by 16).  The following is
3240 		 * equivalent to rfc793 smoothing with an alpha of .75
3241 		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3242 		 * rfc793's wired-in beta.
3243 		 */
3244 		if (delta < 0)
3245 			delta = -delta;
3246 		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3247 		if ((tp->t_rttvar += delta) <= 0)
3248 			tp->t_rttvar = 1;
3249 		if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3250 		    tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3251 	} else {
3252 		/*
3253 		 * No rtt measurement yet - use the unsmoothed rtt.
3254 		 * Set the variance to half the rtt (so our first
3255 		 * retransmit happens at 3*rtt).
3256 		 */
3257 		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3258 		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3259 		tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3260 	}
3261 	tp->t_rtttime = 0;
3262 	tp->t_rxtshift = 0;
3263 
3264 	/*
3265 	 * the retransmit should happen at rtt + 4 * rttvar.
3266 	 * Because of the way we do the smoothing, srtt and rttvar
3267 	 * will each average +1/2 tick of bias.  When we compute
3268 	 * the retransmit timer, we want 1/2 tick of rounding and
3269 	 * 1 extra tick because of +-1/2 tick uncertainty in the
3270 	 * firing of the timer.  The bias will give us exactly the
3271 	 * 1.5 tick we need.  But, because the bias is
3272 	 * statistical, we have to test that we don't drop below
3273 	 * the minimum feasible timer (which is 2 ticks).
3274 	 */
3275 	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3276 		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3277 
3278 	/*
3279 	 * We received an ack for a packet that wasn't retransmitted;
3280 	 * it is probably safe to discard any error indications we've
3281 	 * received recently.  This isn't quite right, but close enough
3282 	 * for now (a route might have failed after we sent a segment,
3283 	 * and the return path might not be symmetrical).
3284 	 */
3285 	tp->t_softerror = 0;
3286 }
3287 
3288 /*
3289  * Determine a reasonable value for maxseg size.
3290  * If the route is known, check route for mtu.
3291  * If none, use an mss that can be handled on the outgoing
3292  * interface without forcing IP to fragment; if bigger than
3293  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
3294  * to utilize large mbufs.  If no route is found, route has no mtu,
3295  * or the destination isn't local, use a default, hopefully conservative
3296  * size (usually 512 or the default IP max size, but no more than the mtu
3297  * of the interface), as we can't discover anything about intervening
3298  * gateways or networks.  We also initialize the congestion/slow start
3299  * window to be a single segment if the destination isn't local.
3300  * While looking at the routing entry, we also initialize other path-dependent
3301  * parameters from pre-set or cached values in the routing entry.
3302  *
3303  * Also take into account the space needed for options that we
3304  * send regularly.  Make maxseg shorter by that amount to assure
3305  * that we can send maxseg amount of data even when the options
3306  * are present.  Store the upper limit of the length of options plus
3307  * data in maxopd.
3308  *
3309  * NOTE that this routine is only called when we process an incoming
3310  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3311  * settings are handled in tcp_mssopt().
3312  */
3313 void
3314 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3315     struct hc_metrics_lite *metricptr, int *mtuflags)
3316 {
3317 	int mss = 0;
3318 	u_long maxmtu = 0;
3319 	struct inpcb *inp = tp->t_inpcb;
3320 	struct hc_metrics_lite metrics;
3321 	int origoffer;
3322 #ifdef INET6
3323 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3324 	size_t min_protoh = isipv6 ?
3325 			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3326 			    sizeof (struct tcpiphdr);
3327 #else
3328 	const size_t min_protoh = sizeof(struct tcpiphdr);
3329 #endif
3330 
3331 	INP_WLOCK_ASSERT(tp->t_inpcb);
3332 
3333 	if (mtuoffer != -1) {
3334 		KASSERT(offer == -1, ("%s: conflict", __func__));
3335 		offer = mtuoffer - min_protoh;
3336 	}
3337 	origoffer = offer;
3338 
3339 	/* Initialize. */
3340 #ifdef INET6
3341 	if (isipv6) {
3342 		maxmtu = tcp_maxmtu6(&inp->inp_inc, mtuflags);
3343 		tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
3344 	}
3345 #endif
3346 #if defined(INET) && defined(INET6)
3347 	else
3348 #endif
3349 #ifdef INET
3350 	{
3351 		maxmtu = tcp_maxmtu(&inp->inp_inc, mtuflags);
3352 		tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
3353 	}
3354 #endif
3355 
3356 	/*
3357 	 * No route to sender, stay with default mss and return.
3358 	 */
3359 	if (maxmtu == 0) {
3360 		/*
3361 		 * In case we return early we need to initialize metrics
3362 		 * to a defined state as tcp_hc_get() would do for us
3363 		 * if there was no cache hit.
3364 		 */
3365 		if (metricptr != NULL)
3366 			bzero(metricptr, sizeof(struct hc_metrics_lite));
3367 		return;
3368 	}
3369 
3370 	/* What have we got? */
3371 	switch (offer) {
3372 		case 0:
3373 			/*
3374 			 * Offer == 0 means that there was no MSS on the SYN
3375 			 * segment, in this case we use tcp_mssdflt as
3376 			 * already assigned to t_maxopd above.
3377 			 */
3378 			offer = tp->t_maxopd;
3379 			break;
3380 
3381 		case -1:
3382 			/*
3383 			 * Offer == -1 means that we didn't receive SYN yet.
3384 			 */
3385 			/* FALLTHROUGH */
3386 
3387 		default:
3388 			/*
3389 			 * Prevent DoS attack with too small MSS. Round up
3390 			 * to at least minmss.
3391 			 */
3392 			offer = max(offer, V_tcp_minmss);
3393 	}
3394 
3395 	/*
3396 	 * rmx information is now retrieved from tcp_hostcache.
3397 	 */
3398 	tcp_hc_get(&inp->inp_inc, &metrics);
3399 	if (metricptr != NULL)
3400 		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3401 
3402 	/*
3403 	 * If there's a discovered mtu int tcp hostcache, use it
3404 	 * else, use the link mtu.
3405 	 */
3406 	if (metrics.rmx_mtu)
3407 		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3408 	else {
3409 #ifdef INET6
3410 		if (isipv6) {
3411 			mss = maxmtu - min_protoh;
3412 			if (!V_path_mtu_discovery &&
3413 			    !in6_localaddr(&inp->in6p_faddr))
3414 				mss = min(mss, V_tcp_v6mssdflt);
3415 		}
3416 #endif
3417 #if defined(INET) && defined(INET6)
3418 		else
3419 #endif
3420 #ifdef INET
3421 		{
3422 			mss = maxmtu - min_protoh;
3423 			if (!V_path_mtu_discovery &&
3424 			    !in_localaddr(inp->inp_faddr))
3425 				mss = min(mss, V_tcp_mssdflt);
3426 		}
3427 #endif
3428 		/*
3429 		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3430 		 * probably violates the TCP spec.
3431 		 * The problem is that, since we don't know the
3432 		 * other end's MSS, we are supposed to use a conservative
3433 		 * default.  But, if we do that, then MTU discovery will
3434 		 * never actually take place, because the conservative
3435 		 * default is much less than the MTUs typically seen
3436 		 * on the Internet today.  For the moment, we'll sweep
3437 		 * this under the carpet.
3438 		 *
3439 		 * The conservative default might not actually be a problem
3440 		 * if the only case this occurs is when sending an initial
3441 		 * SYN with options and data to a host we've never talked
3442 		 * to before.  Then, they will reply with an MSS value which
3443 		 * will get recorded and the new parameters should get
3444 		 * recomputed.  For Further Study.
3445 		 */
3446 	}
3447 	mss = min(mss, offer);
3448 
3449 	/*
3450 	 * Sanity check: make sure that maxopd will be large
3451 	 * enough to allow some data on segments even if the
3452 	 * all the option space is used (40bytes).  Otherwise
3453 	 * funny things may happen in tcp_output.
3454 	 */
3455 	mss = max(mss, 64);
3456 
3457 	/*
3458 	 * maxopd stores the maximum length of data AND options
3459 	 * in a segment; maxseg is the amount of data in a normal
3460 	 * segment.  We need to store this value (maxopd) apart
3461 	 * from maxseg, because now every segment carries options
3462 	 * and thus we normally have somewhat less data in segments.
3463 	 */
3464 	tp->t_maxopd = mss;
3465 
3466 	/*
3467 	 * origoffer==-1 indicates that no segments were received yet.
3468 	 * In this case we just guess.
3469 	 */
3470 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3471 	    (origoffer == -1 ||
3472 	     (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3473 		mss -= TCPOLEN_TSTAMP_APPA;
3474 
3475 #if	(MCLBYTES & (MCLBYTES - 1)) == 0
3476 	if (mss > MCLBYTES)
3477 		mss &= ~(MCLBYTES-1);
3478 #else
3479 	if (mss > MCLBYTES)
3480 		mss = mss / MCLBYTES * MCLBYTES;
3481 #endif
3482 	tp->t_maxseg = mss;
3483 }
3484 
3485 void
3486 tcp_mss(struct tcpcb *tp, int offer)
3487 {
3488 	int mss;
3489 	u_long bufsize;
3490 	struct inpcb *inp;
3491 	struct socket *so;
3492 	struct hc_metrics_lite metrics;
3493 	int mtuflags = 0;
3494 
3495 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3496 
3497 	tcp_mss_update(tp, offer, -1, &metrics, &mtuflags);
3498 
3499 	mss = tp->t_maxseg;
3500 	inp = tp->t_inpcb;
3501 
3502 	/*
3503 	 * If there's a pipesize, change the socket buffer to that size,
3504 	 * don't change if sb_hiwat is different than default (then it
3505 	 * has been changed on purpose with setsockopt).
3506 	 * Make the socket buffers an integral number of mss units;
3507 	 * if the mss is larger than the socket buffer, decrease the mss.
3508 	 */
3509 	so = inp->inp_socket;
3510 	SOCKBUF_LOCK(&so->so_snd);
3511 	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3512 		bufsize = metrics.rmx_sendpipe;
3513 	else
3514 		bufsize = so->so_snd.sb_hiwat;
3515 	if (bufsize < mss)
3516 		mss = bufsize;
3517 	else {
3518 		bufsize = roundup(bufsize, mss);
3519 		if (bufsize > sb_max)
3520 			bufsize = sb_max;
3521 		if (bufsize > so->so_snd.sb_hiwat)
3522 			(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3523 	}
3524 	SOCKBUF_UNLOCK(&so->so_snd);
3525 	tp->t_maxseg = mss;
3526 
3527 	SOCKBUF_LOCK(&so->so_rcv);
3528 	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3529 		bufsize = metrics.rmx_recvpipe;
3530 	else
3531 		bufsize = so->so_rcv.sb_hiwat;
3532 	if (bufsize > mss) {
3533 		bufsize = roundup(bufsize, mss);
3534 		if (bufsize > sb_max)
3535 			bufsize = sb_max;
3536 		if (bufsize > so->so_rcv.sb_hiwat)
3537 			(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3538 	}
3539 	SOCKBUF_UNLOCK(&so->so_rcv);
3540 
3541 	/* Check the interface for TSO capabilities. */
3542 	if (mtuflags & CSUM_TSO)
3543 		tp->t_flags |= TF_TSO;
3544 }
3545 
3546 /*
3547  * Determine the MSS option to send on an outgoing SYN.
3548  */
3549 int
3550 tcp_mssopt(struct in_conninfo *inc)
3551 {
3552 	int mss = 0;
3553 	u_long maxmtu = 0;
3554 	u_long thcmtu = 0;
3555 	size_t min_protoh;
3556 
3557 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3558 
3559 #ifdef INET6
3560 	if (inc->inc_flags & INC_ISIPV6) {
3561 		mss = V_tcp_v6mssdflt;
3562 		maxmtu = tcp_maxmtu6(inc, NULL);
3563 		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3564 	}
3565 #endif
3566 #if defined(INET) && defined(INET6)
3567 	else
3568 #endif
3569 #ifdef INET
3570 	{
3571 		mss = V_tcp_mssdflt;
3572 		maxmtu = tcp_maxmtu(inc, NULL);
3573 		min_protoh = sizeof(struct tcpiphdr);
3574 	}
3575 #endif
3576 #if defined(INET6) || defined(INET)
3577 	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3578 #endif
3579 
3580 	if (maxmtu && thcmtu)
3581 		mss = min(maxmtu, thcmtu) - min_protoh;
3582 	else if (maxmtu || thcmtu)
3583 		mss = max(maxmtu, thcmtu) - min_protoh;
3584 
3585 	return (mss);
3586 }
3587 
3588 
3589 /*
3590  * On a partial ack arrives, force the retransmission of the
3591  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3592  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3593  * be started again.
3594  */
3595 static void
3596 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3597 {
3598 	tcp_seq onxt = tp->snd_nxt;
3599 	u_long  ocwnd = tp->snd_cwnd;
3600 
3601 	INP_WLOCK_ASSERT(tp->t_inpcb);
3602 
3603 	tcp_timer_activate(tp, TT_REXMT, 0);
3604 	tp->t_rtttime = 0;
3605 	tp->snd_nxt = th->th_ack;
3606 	/*
3607 	 * Set snd_cwnd to one segment beyond acknowledged offset.
3608 	 * (tp->snd_una has not yet been updated when this function is called.)
3609 	 */
3610 	tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
3611 	tp->t_flags |= TF_ACKNOW;
3612 	(void) tcp_output(tp);
3613 	tp->snd_cwnd = ocwnd;
3614 	if (SEQ_GT(onxt, tp->snd_nxt))
3615 		tp->snd_nxt = onxt;
3616 	/*
3617 	 * Partial window deflation.  Relies on fact that tp->snd_una
3618 	 * not updated yet.
3619 	 */
3620 	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3621 		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3622 	else
3623 		tp->snd_cwnd = 0;
3624 	tp->snd_cwnd += tp->t_maxseg;
3625 }
3626