xref: /freebsd/sys/netinet/tcp_input.c (revision 2a3e3873a1e4cd958f2b0f85d3b10cfa40575d30)
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 #ifdef TCP_OFFLOAD
109 #include <netinet/tcp_offload.h>
110 #endif
111 
112 #ifdef IPSEC
113 #include <netipsec/ipsec.h>
114 #include <netipsec/ipsec6.h>
115 #endif /*IPSEC*/
116 
117 #include <machine/in_cksum.h>
118 
119 #include <security/mac/mac_framework.h>
120 
121 const int tcprexmtthresh = 3;
122 
123 int tcp_log_in_vain = 0;
124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
125     &tcp_log_in_vain, 0,
126     "Log all incoming TCP segments to closed ports");
127 
128 VNET_DEFINE(int, blackhole) = 0;
129 #define	V_blackhole		VNET(blackhole)
130 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
131     &VNET_NAME(blackhole), 0,
132     "Do not send RST on segments to closed ports");
133 
134 VNET_DEFINE(int, tcp_delack_enabled) = 1;
135 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
136     &VNET_NAME(tcp_delack_enabled), 0,
137     "Delay ACK to try and piggyback it onto a data packet");
138 
139 VNET_DEFINE(int, drop_synfin) = 0;
140 #define	V_drop_synfin		VNET(drop_synfin)
141 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
142     &VNET_NAME(drop_synfin), 0,
143     "Drop TCP packets with SYN+FIN set");
144 
145 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
146 #define	V_tcp_do_rfc3042	VNET(tcp_do_rfc3042)
147 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
148     &VNET_NAME(tcp_do_rfc3042), 0,
149     "Enable RFC 3042 (Limited Transmit)");
150 
151 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
152 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
153     &VNET_NAME(tcp_do_rfc3390), 0,
154     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
155 
156 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
157     "Experimental TCP extensions");
158 
159 VNET_DEFINE(int, tcp_do_initcwnd10) = 1;
160 SYSCTL_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_RW,
161     &VNET_NAME(tcp_do_initcwnd10), 0,
162     "Enable draft-ietf-tcpm-initcwnd-05 (Increasing initial CWND to 10)");
163 
164 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
165 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
166     &VNET_NAME(tcp_do_rfc3465), 0,
167     "Enable RFC 3465 (Appropriate Byte Counting)");
168 
169 VNET_DEFINE(int, tcp_abc_l_var) = 2;
170 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
171     &VNET_NAME(tcp_abc_l_var), 2,
172     "Cap the max cwnd increment during slow-start to this number of segments");
173 
174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
175 
176 VNET_DEFINE(int, tcp_do_ecn) = 0;
177 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
178     &VNET_NAME(tcp_do_ecn), 0,
179     "TCP ECN support");
180 
181 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
182 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
183     &VNET_NAME(tcp_ecn_maxretries), 0,
184     "Max retries before giving up on ECN");
185 
186 VNET_DEFINE(int, tcp_insecure_rst) = 0;
187 #define	V_tcp_insecure_rst	VNET(tcp_insecure_rst)
188 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
189     &VNET_NAME(tcp_insecure_rst), 0,
190     "Follow the old (insecure) criteria for accepting RST packets");
191 
192 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
193 #define	V_tcp_recvspace	VNET(tcp_recvspace)
194 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
195     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
196 
197 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
198 #define	V_tcp_do_autorcvbuf	VNET(tcp_do_autorcvbuf)
199 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
200     &VNET_NAME(tcp_do_autorcvbuf), 0,
201     "Enable automatic receive buffer sizing");
202 
203 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
204 #define	V_tcp_autorcvbuf_inc	VNET(tcp_autorcvbuf_inc)
205 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
206     &VNET_NAME(tcp_autorcvbuf_inc), 0,
207     "Incrementor step size of automatic receive buffer");
208 
209 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
210 #define	V_tcp_autorcvbuf_max	VNET(tcp_autorcvbuf_max)
211 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
212     &VNET_NAME(tcp_autorcvbuf_max), 0,
213     "Max size of automatic receive buffer");
214 
215 VNET_DEFINE(struct inpcbhead, tcb);
216 #define	tcb6	tcb  /* for KAME src sync over BSD*'s */
217 VNET_DEFINE(struct inpcbinfo, tcbinfo);
218 
219 static void	 tcp_dooptions(struct tcpopt *, u_char *, int, int);
220 static void	 tcp_do_segment(struct mbuf *, struct tcphdr *,
221 		     struct socket *, struct tcpcb *, int, int, uint8_t,
222 		     int);
223 static void	 tcp_dropwithreset(struct mbuf *, struct tcphdr *,
224 		     struct tcpcb *, int, int);
225 static void	 tcp_pulloutofband(struct socket *,
226 		     struct tcphdr *, struct mbuf *, int);
227 static void	 tcp_xmit_timer(struct tcpcb *, int);
228 static void	 tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
229 static void inline 	tcp_fields_to_host(struct tcphdr *);
230 #ifdef TCP_SIGNATURE
231 static void inline 	tcp_fields_to_net(struct tcphdr *);
232 static int inline	tcp_signature_verify_input(struct mbuf *, int, int,
233 			    int, struct tcpopt *, struct tcphdr *, u_int);
234 #endif
235 static void inline	cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
236 			    uint16_t type);
237 static void inline	cc_conn_init(struct tcpcb *tp);
238 static void inline	cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
239 static void inline	hhook_run_tcp_est_in(struct tcpcb *tp,
240 			    struct tcphdr *th, struct tcpopt *to);
241 
242 /*
243  * TCP statistics are stored in struct tcpstat_p, which is
244  * an "array" of counter(9)s.  Although it isn't a real
245  * array, we treat it as array to reduce code bloat.
246  */
247 VNET_DEFINE(struct tcpstat_p, tcpstatp);
248 
249 static void
250 vnet_tcpstatp_init(const void *unused)
251 {
252 	counter_u64_t *c;
253 	int i;
254 
255 	for (i = 0, c = (counter_u64_t *)&V_tcpstatp;
256 	    i < sizeof(V_tcpstatp) / sizeof(counter_u64_t);
257 	    i++, c++) {
258 		*c = counter_u64_alloc(M_WAITOK);
259 		counter_u64_zero(*c);
260 	}
261 }
262 VNET_SYSINIT(vnet_tcpstatp_init, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
263 	    vnet_tcpstatp_init, NULL);
264 
265 #ifdef VIMAGE
266 static void
267 vnet_tcpstatp_uninit(const void *unused)
268 {
269 	counter_u64_t *c;
270 	int i;
271 
272 	for (i = 0, c = (counter_u64_t *)&V_tcpstatp;
273 	    i < sizeof(V_tcpstatp) / sizeof(counter_u64_t);
274 	    i++, c++)
275 		counter_u64_free(*c);
276 }
277 VNET_SYSUNINIT(vnet_tcpstatp_uninit, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
278 	    vnet_tcpstatp_uninit, NULL);
279 #endif /* VIMAGE */
280 
281 static int
282 tcpstat_sysctl(SYSCTL_HANDLER_ARGS)
283 {
284 	struct tcpstat tcpstat;
285 	counter_u64_t *c;
286 	uint64_t *v;
287 	int i;
288 
289 	for (i = 0, c = (counter_u64_t *)&V_tcpstatp, v = (uint64_t *)&tcpstat;
290 	    i < sizeof(V_tcpstatp) / sizeof(counter_u64_t);
291 	    i++, c++, v++) {
292 		*v = counter_u64_fetch(*c);
293 		if (req->newptr)
294 			counter_u64_zero(*c);
295 	}
296 
297 	return (SYSCTL_OUT(req, &tcpstat, sizeof(tcpstat)));
298 }
299 
300 SYSCTL_VNET_PROC(_net_inet_tcp, TCPCTL_STATS, stats, CTLTYPE_OPAQUE |
301     CTLFLAG_RW, NULL, 0, tcpstat_sysctl, "I",
302     "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
303 
304 /*
305  * Kernel module interface for updating tcpstat.  The argument is an index
306  * into tcpstat treated as an array.
307  */
308 void
309 kmod_tcpstat_inc(int statnum)
310 {
311 
312 	counter_u64_add((counter_u64_t )&V_tcpstatp + statnum, 1);
313 }
314 
315 /*
316  * Wrapper for the TCP established input helper hook.
317  */
318 static void inline
319 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
320 {
321 	struct tcp_hhook_data hhook_data;
322 
323 	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
324 		hhook_data.tp = tp;
325 		hhook_data.th = th;
326 		hhook_data.to = to;
327 
328 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
329 		    tp->osd);
330 	}
331 }
332 
333 /*
334  * CC wrapper hook functions
335  */
336 static void inline
337 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
338 {
339 	INP_WLOCK_ASSERT(tp->t_inpcb);
340 
341 	tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
342 	if (tp->snd_cwnd <= tp->snd_wnd)
343 		tp->ccv->flags |= CCF_CWND_LIMITED;
344 	else
345 		tp->ccv->flags &= ~CCF_CWND_LIMITED;
346 
347 	if (type == CC_ACK) {
348 		if (tp->snd_cwnd > tp->snd_ssthresh) {
349 			tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
350 			     V_tcp_abc_l_var * tp->t_maxseg);
351 			if (tp->t_bytes_acked >= tp->snd_cwnd) {
352 				tp->t_bytes_acked -= tp->snd_cwnd;
353 				tp->ccv->flags |= CCF_ABC_SENTAWND;
354 			}
355 		} else {
356 				tp->ccv->flags &= ~CCF_ABC_SENTAWND;
357 				tp->t_bytes_acked = 0;
358 		}
359 	}
360 
361 	if (CC_ALGO(tp)->ack_received != NULL) {
362 		/* XXXLAS: Find a way to live without this */
363 		tp->ccv->curack = th->th_ack;
364 		CC_ALGO(tp)->ack_received(tp->ccv, type);
365 	}
366 }
367 
368 static void inline
369 cc_conn_init(struct tcpcb *tp)
370 {
371 	struct hc_metrics_lite metrics;
372 	struct inpcb *inp = tp->t_inpcb;
373 	int rtt;
374 
375 	INP_WLOCK_ASSERT(tp->t_inpcb);
376 
377 	tcp_hc_get(&inp->inp_inc, &metrics);
378 
379 	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
380 		tp->t_srtt = rtt;
381 		tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
382 		TCPSTAT_INC(tcps_usedrtt);
383 		if (metrics.rmx_rttvar) {
384 			tp->t_rttvar = metrics.rmx_rttvar;
385 			TCPSTAT_INC(tcps_usedrttvar);
386 		} else {
387 			/* default variation is +- 1 rtt */
388 			tp->t_rttvar =
389 			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
390 		}
391 		TCPT_RANGESET(tp->t_rxtcur,
392 		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
393 		    tp->t_rttmin, TCPTV_REXMTMAX);
394 	}
395 	if (metrics.rmx_ssthresh) {
396 		/*
397 		 * There's some sort of gateway or interface
398 		 * buffer limit on the path.  Use this to set
399 		 * the slow start threshhold, but set the
400 		 * threshold to no less than 2*mss.
401 		 */
402 		tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
403 		TCPSTAT_INC(tcps_usedssthresh);
404 	}
405 
406 	/*
407 	 * Set the initial slow-start flight size.
408 	 *
409 	 * RFC5681 Section 3.1 specifies the default conservative values.
410 	 * RFC3390 specifies slightly more aggressive values.
411 	 * Draft-ietf-tcpm-initcwnd-05 increases it to ten segments.
412 	 *
413 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
414 	 * reduce the initial CWND to one segment as congestion is likely
415 	 * requiring us to be cautious.
416 	 */
417 	if (tp->snd_cwnd == 1)
418 		tp->snd_cwnd = tp->t_maxseg;		/* SYN(-ACK) lost */
419 	else if (V_tcp_do_initcwnd10)
420 		tp->snd_cwnd = min(10 * tp->t_maxseg,
421 		    max(2 * tp->t_maxseg, 14600));
422 	else if (V_tcp_do_rfc3390)
423 		tp->snd_cwnd = min(4 * tp->t_maxseg,
424 		    max(2 * tp->t_maxseg, 4380));
425 	else {
426 		/* Per RFC5681 Section 3.1 */
427 		if (tp->t_maxseg > 2190)
428 			tp->snd_cwnd = 2 * tp->t_maxseg;
429 		else if (tp->t_maxseg > 1095)
430 			tp->snd_cwnd = 3 * tp->t_maxseg;
431 		else
432 			tp->snd_cwnd = 4 * tp->t_maxseg;
433 	}
434 
435 	if (CC_ALGO(tp)->conn_init != NULL)
436 		CC_ALGO(tp)->conn_init(tp->ccv);
437 }
438 
439 void inline
440 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
441 {
442 	INP_WLOCK_ASSERT(tp->t_inpcb);
443 
444 	switch(type) {
445 	case CC_NDUPACK:
446 		if (!IN_FASTRECOVERY(tp->t_flags)) {
447 			tp->snd_recover = tp->snd_max;
448 			if (tp->t_flags & TF_ECN_PERMIT)
449 				tp->t_flags |= TF_ECN_SND_CWR;
450 		}
451 		break;
452 	case CC_ECN:
453 		if (!IN_CONGRECOVERY(tp->t_flags)) {
454 			TCPSTAT_INC(tcps_ecn_rcwnd);
455 			tp->snd_recover = tp->snd_max;
456 			if (tp->t_flags & TF_ECN_PERMIT)
457 				tp->t_flags |= TF_ECN_SND_CWR;
458 		}
459 		break;
460 	case CC_RTO:
461 		tp->t_dupacks = 0;
462 		tp->t_bytes_acked = 0;
463 		EXIT_RECOVERY(tp->t_flags);
464 		tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
465 		    tp->t_maxseg) * tp->t_maxseg;
466 		tp->snd_cwnd = tp->t_maxseg;
467 		break;
468 	case CC_RTO_ERR:
469 		TCPSTAT_INC(tcps_sndrexmitbad);
470 		/* RTO was unnecessary, so reset everything. */
471 		tp->snd_cwnd = tp->snd_cwnd_prev;
472 		tp->snd_ssthresh = tp->snd_ssthresh_prev;
473 		tp->snd_recover = tp->snd_recover_prev;
474 		if (tp->t_flags & TF_WASFRECOVERY)
475 			ENTER_FASTRECOVERY(tp->t_flags);
476 		if (tp->t_flags & TF_WASCRECOVERY)
477 			ENTER_CONGRECOVERY(tp->t_flags);
478 		tp->snd_nxt = tp->snd_max;
479 		tp->t_flags &= ~TF_PREVVALID;
480 		tp->t_badrxtwin = 0;
481 		break;
482 	}
483 
484 	if (CC_ALGO(tp)->cong_signal != NULL) {
485 		if (th != NULL)
486 			tp->ccv->curack = th->th_ack;
487 		CC_ALGO(tp)->cong_signal(tp->ccv, type);
488 	}
489 }
490 
491 static void inline
492 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
493 {
494 	INP_WLOCK_ASSERT(tp->t_inpcb);
495 
496 	/* XXXLAS: KASSERT that we're in recovery? */
497 
498 	if (CC_ALGO(tp)->post_recovery != NULL) {
499 		tp->ccv->curack = th->th_ack;
500 		CC_ALGO(tp)->post_recovery(tp->ccv);
501 	}
502 	/* XXXLAS: EXIT_RECOVERY ? */
503 	tp->t_bytes_acked = 0;
504 }
505 
506 static inline void
507 tcp_fields_to_host(struct tcphdr *th)
508 {
509 
510 	th->th_seq = ntohl(th->th_seq);
511 	th->th_ack = ntohl(th->th_ack);
512 	th->th_win = ntohs(th->th_win);
513 	th->th_urp = ntohs(th->th_urp);
514 }
515 
516 #ifdef TCP_SIGNATURE
517 static inline void
518 tcp_fields_to_net(struct tcphdr *th)
519 {
520 
521 	th->th_seq = htonl(th->th_seq);
522 	th->th_ack = htonl(th->th_ack);
523 	th->th_win = htons(th->th_win);
524 	th->th_urp = htons(th->th_urp);
525 }
526 
527 static inline int
528 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
529     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
530 {
531 	int ret;
532 
533 	tcp_fields_to_net(th);
534 	ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
535 	tcp_fields_to_host(th);
536 	return (ret);
537 }
538 #endif
539 
540 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
541 #ifdef INET6
542 #define ND6_HINT(tp) \
543 do { \
544 	if ((tp) && (tp)->t_inpcb && \
545 	    ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
546 		nd6_nud_hint(NULL, NULL, 0); \
547 } while (0)
548 #else
549 #define ND6_HINT(tp)
550 #endif
551 
552 /*
553  * Indicate whether this ack should be delayed.  We can delay the ack if
554  *	- there is no delayed ack timer in progress and
555  *	- our last ack wasn't a 0-sized window.  We never want to delay
556  *	  the ack that opens up a 0-sized window and
557  *		- delayed acks are enabled or
558  *		- this is a half-synchronized T/TCP connection.
559  */
560 #define DELAY_ACK(tp)							\
561 	((!tcp_timer_active(tp, TT_DELACK) &&				\
562 	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
563 	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
564 
565 /*
566  * TCP input handling is split into multiple parts:
567  *   tcp6_input is a thin wrapper around tcp_input for the extended
568  *	ip6_protox[] call format in ip6_input
569  *   tcp_input handles primary segment validation, inpcb lookup and
570  *	SYN processing on listen sockets
571  *   tcp_do_segment processes the ACK and text of the segment for
572  *	establishing, established and closing connections
573  */
574 #ifdef INET6
575 int
576 tcp6_input(struct mbuf **mp, int *offp, int proto)
577 {
578 	struct mbuf *m = *mp;
579 	struct in6_ifaddr *ia6;
580 
581 	IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
582 
583 	/*
584 	 * draft-itojun-ipv6-tcp-to-anycast
585 	 * better place to put this in?
586 	 */
587 	ia6 = ip6_getdstifaddr(m);
588 	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
589 		struct ip6_hdr *ip6;
590 
591 		ifa_free(&ia6->ia_ifa);
592 		ip6 = mtod(m, struct ip6_hdr *);
593 		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
594 			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
595 		return IPPROTO_DONE;
596 	}
597 	if (ia6)
598 		ifa_free(&ia6->ia_ifa);
599 
600 	tcp_input(m, *offp);
601 	return IPPROTO_DONE;
602 }
603 #endif /* INET6 */
604 
605 void
606 tcp_input(struct mbuf *m, int off0)
607 {
608 	struct tcphdr *th = NULL;
609 	struct ip *ip = NULL;
610 	struct inpcb *inp = NULL;
611 	struct tcpcb *tp = NULL;
612 	struct socket *so = NULL;
613 	u_char *optp = NULL;
614 	int optlen = 0;
615 #ifdef INET
616 	int len;
617 #endif
618 	int tlen = 0, off;
619 	int drop_hdrlen;
620 	int thflags;
621 	int rstreason = 0;	/* For badport_bandlim accounting purposes */
622 #ifdef TCP_SIGNATURE
623 	uint8_t sig_checked = 0;
624 #endif
625 	uint8_t iptos = 0;
626 	struct m_tag *fwd_tag = NULL;
627 #ifdef INET6
628 	struct ip6_hdr *ip6 = NULL;
629 	int isipv6;
630 #else
631 	const void *ip6 = NULL;
632 #endif /* INET6 */
633 	struct tcpopt to;		/* options in this segment */
634 	char *s = NULL;			/* address and port logging */
635 	int ti_locked;
636 #define	TI_UNLOCKED	1
637 #define	TI_WLOCKED	2
638 
639 #ifdef TCPDEBUG
640 	/*
641 	 * The size of tcp_saveipgen must be the size of the max ip header,
642 	 * now IPv6.
643 	 */
644 	u_char tcp_saveipgen[IP6_HDR_LEN];
645 	struct tcphdr tcp_savetcp;
646 	short ostate = 0;
647 #endif
648 
649 #ifdef INET6
650 	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
651 #endif
652 
653 	to.to_flags = 0;
654 	TCPSTAT_INC(tcps_rcvtotal);
655 
656 #ifdef INET6
657 	if (isipv6) {
658 		/* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
659 
660 		if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
661 			m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
662 			if (m == NULL) {
663 				TCPSTAT_INC(tcps_rcvshort);
664 				return;
665 			}
666 		}
667 
668 		ip6 = mtod(m, struct ip6_hdr *);
669 		th = (struct tcphdr *)((caddr_t)ip6 + off0);
670 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
671 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
672 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
673 				th->th_sum = m->m_pkthdr.csum_data;
674 			else
675 				th->th_sum = in6_cksum_pseudo(ip6, tlen,
676 				    IPPROTO_TCP, m->m_pkthdr.csum_data);
677 			th->th_sum ^= 0xffff;
678 		} else
679 			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
680 		if (th->th_sum) {
681 			TCPSTAT_INC(tcps_rcvbadsum);
682 			goto drop;
683 		}
684 
685 		/*
686 		 * Be proactive about unspecified IPv6 address in source.
687 		 * As we use all-zero to indicate unbounded/unconnected pcb,
688 		 * unspecified IPv6 address can be used to confuse us.
689 		 *
690 		 * Note that packets with unspecified IPv6 destination is
691 		 * already dropped in ip6_input.
692 		 */
693 		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
694 			/* XXX stat */
695 			goto drop;
696 		}
697 	}
698 #endif
699 #if defined(INET) && defined(INET6)
700 	else
701 #endif
702 #ifdef INET
703 	{
704 		/*
705 		 * Get IP and TCP header together in first mbuf.
706 		 * Note: IP leaves IP header in first mbuf.
707 		 */
708 		if (off0 > sizeof (struct ip)) {
709 			ip_stripoptions(m);
710 			off0 = sizeof(struct ip);
711 		}
712 		if (m->m_len < sizeof (struct tcpiphdr)) {
713 			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
714 			    == NULL) {
715 				TCPSTAT_INC(tcps_rcvshort);
716 				return;
717 			}
718 		}
719 		ip = mtod(m, struct ip *);
720 		th = (struct tcphdr *)((caddr_t)ip + off0);
721 		tlen = ntohs(ip->ip_len) - off0;
722 
723 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
724 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
725 				th->th_sum = m->m_pkthdr.csum_data;
726 			else
727 				th->th_sum = in_pseudo(ip->ip_src.s_addr,
728 				    ip->ip_dst.s_addr,
729 				    htonl(m->m_pkthdr.csum_data + tlen +
730 				    IPPROTO_TCP));
731 			th->th_sum ^= 0xffff;
732 		} else {
733 			struct ipovly *ipov = (struct ipovly *)ip;
734 
735 			/*
736 			 * Checksum extended TCP header and data.
737 			 */
738 			len = off0 + tlen;
739 			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
740 			ipov->ih_len = htons(tlen);
741 			th->th_sum = in_cksum(m, len);
742 		}
743 		if (th->th_sum) {
744 			TCPSTAT_INC(tcps_rcvbadsum);
745 			goto drop;
746 		}
747 		/* Re-initialization for later version check */
748 		ip->ip_v = IPVERSION;
749 	}
750 #endif /* INET */
751 
752 #ifdef INET6
753 	if (isipv6)
754 		iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
755 #endif
756 #if defined(INET) && defined(INET6)
757 	else
758 #endif
759 #ifdef INET
760 		iptos = ip->ip_tos;
761 #endif
762 
763 	/*
764 	 * Check that TCP offset makes sense,
765 	 * pull out TCP options and adjust length.		XXX
766 	 */
767 	off = th->th_off << 2;
768 	if (off < sizeof (struct tcphdr) || off > tlen) {
769 		TCPSTAT_INC(tcps_rcvbadoff);
770 		goto drop;
771 	}
772 	tlen -= off;	/* tlen is used instead of ti->ti_len */
773 	if (off > sizeof (struct tcphdr)) {
774 #ifdef INET6
775 		if (isipv6) {
776 			IP6_EXTHDR_CHECK(m, off0, off, );
777 			ip6 = mtod(m, struct ip6_hdr *);
778 			th = (struct tcphdr *)((caddr_t)ip6 + off0);
779 		}
780 #endif
781 #if defined(INET) && defined(INET6)
782 		else
783 #endif
784 #ifdef INET
785 		{
786 			if (m->m_len < sizeof(struct ip) + off) {
787 				if ((m = m_pullup(m, sizeof (struct ip) + off))
788 				    == NULL) {
789 					TCPSTAT_INC(tcps_rcvshort);
790 					return;
791 				}
792 				ip = mtod(m, struct ip *);
793 				th = (struct tcphdr *)((caddr_t)ip + off0);
794 			}
795 		}
796 #endif
797 		optlen = off - sizeof (struct tcphdr);
798 		optp = (u_char *)(th + 1);
799 	}
800 	thflags = th->th_flags;
801 
802 	/*
803 	 * Convert TCP protocol specific fields to host format.
804 	 */
805 	tcp_fields_to_host(th);
806 
807 	/*
808 	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
809 	 */
810 	drop_hdrlen = off0 + off;
811 
812 	/*
813 	 * Locate pcb for segment; if we're likely to add or remove a
814 	 * connection then first acquire pcbinfo lock.  There are two cases
815 	 * where we might discover later we need a write lock despite the
816 	 * flags: ACKs moving a connection out of the syncache, and ACKs for
817 	 * a connection in TIMEWAIT.
818 	 */
819 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
820 		INP_INFO_WLOCK(&V_tcbinfo);
821 		ti_locked = TI_WLOCKED;
822 	} else
823 		ti_locked = TI_UNLOCKED;
824 
825 	/*
826 	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
827 	 */
828         if (
829 #ifdef INET6
830 	    (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
831 #ifdef INET
832 	    || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
833 #endif
834 #endif
835 #if defined(INET) && !defined(INET6)
836 	    (m->m_flags & M_IP_NEXTHOP)
837 #endif
838 	    )
839 		fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
840 
841 findpcb:
842 #ifdef INVARIANTS
843 	if (ti_locked == TI_WLOCKED) {
844 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
845 	} else {
846 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
847 	}
848 #endif
849 #ifdef INET6
850 	if (isipv6 && fwd_tag != NULL) {
851 		struct sockaddr_in6 *next_hop6;
852 
853 		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
854 		/*
855 		 * Transparently forwarded. Pretend to be the destination.
856 		 * Already got one like this?
857 		 */
858 		inp = in6_pcblookup_mbuf(&V_tcbinfo,
859 		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
860 		    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
861 		if (!inp) {
862 			/*
863 			 * It's new.  Try to find the ambushing socket.
864 			 * Because we've rewritten the destination address,
865 			 * any hardware-generated hash is ignored.
866 			 */
867 			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
868 			    th->th_sport, &next_hop6->sin6_addr,
869 			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
870 			    th->th_dport, INPLOOKUP_WILDCARD |
871 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
872 		}
873 	} else if (isipv6) {
874 		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
875 		    th->th_sport, &ip6->ip6_dst, th->th_dport,
876 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
877 		    m->m_pkthdr.rcvif, m);
878 	}
879 #endif /* INET6 */
880 #if defined(INET6) && defined(INET)
881 	else
882 #endif
883 #ifdef INET
884 	if (fwd_tag != NULL) {
885 		struct sockaddr_in *next_hop;
886 
887 		next_hop = (struct sockaddr_in *)(fwd_tag+1);
888 		/*
889 		 * Transparently forwarded. Pretend to be the destination.
890 		 * already got one like this?
891 		 */
892 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
893 		    ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
894 		    m->m_pkthdr.rcvif, m);
895 		if (!inp) {
896 			/*
897 			 * It's new.  Try to find the ambushing socket.
898 			 * Because we've rewritten the destination address,
899 			 * any hardware-generated hash is ignored.
900 			 */
901 			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
902 			    th->th_sport, next_hop->sin_addr,
903 			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
904 			    th->th_dport, INPLOOKUP_WILDCARD |
905 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
906 		}
907 	} else
908 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
909 		    th->th_sport, ip->ip_dst, th->th_dport,
910 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
911 		    m->m_pkthdr.rcvif, m);
912 #endif /* INET */
913 
914 	/*
915 	 * If the INPCB does not exist then all data in the incoming
916 	 * segment is discarded and an appropriate RST is sent back.
917 	 * XXX MRT Send RST using which routing table?
918 	 */
919 	if (inp == NULL) {
920 		/*
921 		 * Log communication attempts to ports that are not
922 		 * in use.
923 		 */
924 		if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
925 		    tcp_log_in_vain == 2) {
926 			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
927 				log(LOG_INFO, "%s; %s: Connection attempt "
928 				    "to closed port\n", s, __func__);
929 		}
930 		/*
931 		 * When blackholing do not respond with a RST but
932 		 * completely ignore the segment and drop it.
933 		 */
934 		if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
935 		    V_blackhole == 2)
936 			goto dropunlock;
937 
938 		rstreason = BANDLIM_RST_CLOSEDPORT;
939 		goto dropwithreset;
940 	}
941 	INP_WLOCK_ASSERT(inp);
942 	if (!(inp->inp_flags & INP_HW_FLOWID)
943 	    && (m->m_flags & M_FLOWID)
944 	    && ((inp->inp_socket == NULL)
945 		|| !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
946 		inp->inp_flags |= INP_HW_FLOWID;
947 		inp->inp_flags &= ~INP_SW_FLOWID;
948 		inp->inp_flowid = m->m_pkthdr.flowid;
949 	}
950 #ifdef IPSEC
951 #ifdef INET6
952 	if (isipv6 && ipsec6_in_reject(m, inp)) {
953 		V_ipsec6stat.in_polvio++;
954 		goto dropunlock;
955 	} else
956 #endif /* INET6 */
957 	if (ipsec4_in_reject(m, inp) != 0) {
958 		V_ipsec4stat.in_polvio++;
959 		goto dropunlock;
960 	}
961 #endif /* IPSEC */
962 
963 	/*
964 	 * Check the minimum TTL for socket.
965 	 */
966 	if (inp->inp_ip_minttl != 0) {
967 #ifdef INET6
968 		if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
969 			goto dropunlock;
970 		else
971 #endif
972 		if (inp->inp_ip_minttl > ip->ip_ttl)
973 			goto dropunlock;
974 	}
975 
976 	/*
977 	 * A previous connection in TIMEWAIT state is supposed to catch stray
978 	 * or duplicate segments arriving late.  If this segment was a
979 	 * legitimate new connection attempt, the old INPCB gets removed and
980 	 * we can try again to find a listening socket.
981 	 *
982 	 * At this point, due to earlier optimism, we may hold only an inpcb
983 	 * lock, and not the inpcbinfo write lock.  If so, we need to try to
984 	 * acquire it, or if that fails, acquire a reference on the inpcb,
985 	 * drop all locks, acquire a global write lock, and then re-acquire
986 	 * the inpcb lock.  We may at that point discover that another thread
987 	 * has tried to free the inpcb, in which case we need to loop back
988 	 * and try to find a new inpcb to deliver to.
989 	 *
990 	 * XXXRW: It may be time to rethink timewait locking.
991 	 */
992 relocked:
993 	if (inp->inp_flags & INP_TIMEWAIT) {
994 		if (ti_locked == TI_UNLOCKED) {
995 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
996 				in_pcbref(inp);
997 				INP_WUNLOCK(inp);
998 				INP_INFO_WLOCK(&V_tcbinfo);
999 				ti_locked = TI_WLOCKED;
1000 				INP_WLOCK(inp);
1001 				if (in_pcbrele_wlocked(inp)) {
1002 					inp = NULL;
1003 					goto findpcb;
1004 				}
1005 			} else
1006 				ti_locked = TI_WLOCKED;
1007 		}
1008 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1009 
1010 		if (thflags & TH_SYN)
1011 			tcp_dooptions(&to, optp, optlen, TO_SYN);
1012 		/*
1013 		 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
1014 		 */
1015 		if (tcp_twcheck(inp, &to, th, m, tlen))
1016 			goto findpcb;
1017 		INP_INFO_WUNLOCK(&V_tcbinfo);
1018 		return;
1019 	}
1020 	/*
1021 	 * The TCPCB may no longer exist if the connection is winding
1022 	 * down or it is in the CLOSED state.  Either way we drop the
1023 	 * segment and send an appropriate response.
1024 	 */
1025 	tp = intotcpcb(inp);
1026 	if (tp == NULL || tp->t_state == TCPS_CLOSED) {
1027 		rstreason = BANDLIM_RST_CLOSEDPORT;
1028 		goto dropwithreset;
1029 	}
1030 
1031 #ifdef TCP_OFFLOAD
1032 	if (tp->t_flags & TF_TOE) {
1033 		tcp_offload_input(tp, m);
1034 		m = NULL;	/* consumed by the TOE driver */
1035 		goto dropunlock;
1036 	}
1037 #endif
1038 
1039 	/*
1040 	 * We've identified a valid inpcb, but it could be that we need an
1041 	 * inpcbinfo write lock but don't hold it.  In this case, attempt to
1042 	 * acquire using the same strategy as the TIMEWAIT case above.  If we
1043 	 * relock, we have to jump back to 'relocked' as the connection might
1044 	 * now be in TIMEWAIT.
1045 	 */
1046 #ifdef INVARIANTS
1047 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
1048 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1049 #endif
1050 	if (tp->t_state != TCPS_ESTABLISHED) {
1051 		if (ti_locked == TI_UNLOCKED) {
1052 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
1053 				in_pcbref(inp);
1054 				INP_WUNLOCK(inp);
1055 				INP_INFO_WLOCK(&V_tcbinfo);
1056 				ti_locked = TI_WLOCKED;
1057 				INP_WLOCK(inp);
1058 				if (in_pcbrele_wlocked(inp)) {
1059 					inp = NULL;
1060 					goto findpcb;
1061 				}
1062 				goto relocked;
1063 			} else
1064 				ti_locked = TI_WLOCKED;
1065 		}
1066 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1067 	}
1068 
1069 #ifdef MAC
1070 	INP_WLOCK_ASSERT(inp);
1071 	if (mac_inpcb_check_deliver(inp, m))
1072 		goto dropunlock;
1073 #endif
1074 	so = inp->inp_socket;
1075 	KASSERT(so != NULL, ("%s: so == NULL", __func__));
1076 #ifdef TCPDEBUG
1077 	if (so->so_options & SO_DEBUG) {
1078 		ostate = tp->t_state;
1079 #ifdef INET6
1080 		if (isipv6) {
1081 			bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1082 		} else
1083 #endif
1084 			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1085 		tcp_savetcp = *th;
1086 	}
1087 #endif /* TCPDEBUG */
1088 	/*
1089 	 * When the socket is accepting connections (the INPCB is in LISTEN
1090 	 * state) we look into the SYN cache if this is a new connection
1091 	 * attempt or the completion of a previous one.  Because listen
1092 	 * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
1093 	 * held in this case.
1094 	 */
1095 	if (so->so_options & SO_ACCEPTCONN) {
1096 		struct in_conninfo inc;
1097 
1098 		KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
1099 		    "tp not listening", __func__));
1100 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1101 
1102 		bzero(&inc, sizeof(inc));
1103 #ifdef INET6
1104 		if (isipv6) {
1105 			inc.inc_flags |= INC_ISIPV6;
1106 			inc.inc6_faddr = ip6->ip6_src;
1107 			inc.inc6_laddr = ip6->ip6_dst;
1108 		} else
1109 #endif
1110 		{
1111 			inc.inc_faddr = ip->ip_src;
1112 			inc.inc_laddr = ip->ip_dst;
1113 		}
1114 		inc.inc_fport = th->th_sport;
1115 		inc.inc_lport = th->th_dport;
1116 		inc.inc_fibnum = so->so_fibnum;
1117 
1118 		/*
1119 		 * Check for an existing connection attempt in syncache if
1120 		 * the flag is only ACK.  A successful lookup creates a new
1121 		 * socket appended to the listen queue in SYN_RECEIVED state.
1122 		 */
1123 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1124 			/*
1125 			 * Parse the TCP options here because
1126 			 * syncookies need access to the reflected
1127 			 * timestamp.
1128 			 */
1129 			tcp_dooptions(&to, optp, optlen, 0);
1130 			/*
1131 			 * NB: syncache_expand() doesn't unlock
1132 			 * inp and tcpinfo locks.
1133 			 */
1134 			if (!syncache_expand(&inc, &to, th, &so, m)) {
1135 				/*
1136 				 * No syncache entry or ACK was not
1137 				 * for our SYN/ACK.  Send a RST.
1138 				 * NB: syncache did its own logging
1139 				 * of the failure cause.
1140 				 */
1141 				rstreason = BANDLIM_RST_OPENPORT;
1142 				goto dropwithreset;
1143 			}
1144 			if (so == NULL) {
1145 				/*
1146 				 * We completed the 3-way handshake
1147 				 * but could not allocate a socket
1148 				 * either due to memory shortage,
1149 				 * listen queue length limits or
1150 				 * global socket limits.  Send RST
1151 				 * or wait and have the remote end
1152 				 * retransmit the ACK for another
1153 				 * try.
1154 				 */
1155 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1156 					log(LOG_DEBUG, "%s; %s: Listen socket: "
1157 					    "Socket allocation failed due to "
1158 					    "limits or memory shortage, %s\n",
1159 					    s, __func__,
1160 					    V_tcp_sc_rst_sock_fail ?
1161 					    "sending RST" : "try again");
1162 				if (V_tcp_sc_rst_sock_fail) {
1163 					rstreason = BANDLIM_UNLIMITED;
1164 					goto dropwithreset;
1165 				} else
1166 					goto dropunlock;
1167 			}
1168 			/*
1169 			 * Socket is created in state SYN_RECEIVED.
1170 			 * Unlock the listen socket, lock the newly
1171 			 * created socket and update the tp variable.
1172 			 */
1173 			INP_WUNLOCK(inp);	/* listen socket */
1174 			inp = sotoinpcb(so);
1175 			INP_WLOCK(inp);		/* new connection */
1176 			tp = intotcpcb(inp);
1177 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1178 			    ("%s: ", __func__));
1179 #ifdef TCP_SIGNATURE
1180 			if (sig_checked == 0)  {
1181 				tcp_dooptions(&to, optp, optlen,
1182 				    (thflags & TH_SYN) ? TO_SYN : 0);
1183 				if (!tcp_signature_verify_input(m, off0, tlen,
1184 				    optlen, &to, th, tp->t_flags)) {
1185 
1186 					/*
1187 					 * In SYN_SENT state if it receives an
1188 					 * RST, it is allowed for further
1189 					 * processing.
1190 					 */
1191 					if ((thflags & TH_RST) == 0 ||
1192 					    (tp->t_state == TCPS_SYN_SENT) == 0)
1193 						goto dropunlock;
1194 				}
1195 				sig_checked = 1;
1196 			}
1197 #endif
1198 
1199 			/*
1200 			 * Process the segment and the data it
1201 			 * contains.  tcp_do_segment() consumes
1202 			 * the mbuf chain and unlocks the inpcb.
1203 			 */
1204 			tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1205 			    iptos, ti_locked);
1206 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1207 			return;
1208 		}
1209 		/*
1210 		 * Segment flag validation for new connection attempts:
1211 		 *
1212 		 * Our (SYN|ACK) response was rejected.
1213 		 * Check with syncache and remove entry to prevent
1214 		 * retransmits.
1215 		 *
1216 		 * NB: syncache_chkrst does its own logging of failure
1217 		 * causes.
1218 		 */
1219 		if (thflags & TH_RST) {
1220 			syncache_chkrst(&inc, th);
1221 			goto dropunlock;
1222 		}
1223 		/*
1224 		 * We can't do anything without SYN.
1225 		 */
1226 		if ((thflags & TH_SYN) == 0) {
1227 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1228 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1229 				    "SYN is missing, segment ignored\n",
1230 				    s, __func__);
1231 			TCPSTAT_INC(tcps_badsyn);
1232 			goto dropunlock;
1233 		}
1234 		/*
1235 		 * (SYN|ACK) is bogus on a listen socket.
1236 		 */
1237 		if (thflags & TH_ACK) {
1238 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1239 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1240 				    "SYN|ACK invalid, segment rejected\n",
1241 				    s, __func__);
1242 			syncache_badack(&inc);	/* XXX: Not needed! */
1243 			TCPSTAT_INC(tcps_badsyn);
1244 			rstreason = BANDLIM_RST_OPENPORT;
1245 			goto dropwithreset;
1246 		}
1247 		/*
1248 		 * If the drop_synfin option is enabled, drop all
1249 		 * segments with both the SYN and FIN bits set.
1250 		 * This prevents e.g. nmap from identifying the
1251 		 * TCP/IP stack.
1252 		 * XXX: Poor reasoning.  nmap has other methods
1253 		 * and is constantly refining its stack detection
1254 		 * strategies.
1255 		 * XXX: This is a violation of the TCP specification
1256 		 * and was used by RFC1644.
1257 		 */
1258 		if ((thflags & TH_FIN) && V_drop_synfin) {
1259 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1260 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1261 				    "SYN|FIN segment ignored (based on "
1262 				    "sysctl setting)\n", s, __func__);
1263 			TCPSTAT_INC(tcps_badsyn);
1264 			goto dropunlock;
1265 		}
1266 		/*
1267 		 * Segment's flags are (SYN) or (SYN|FIN).
1268 		 *
1269 		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1270 		 * as they do not affect the state of the TCP FSM.
1271 		 * The data pointed to by TH_URG and th_urp is ignored.
1272 		 */
1273 		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1274 		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1275 		KASSERT(thflags & (TH_SYN),
1276 		    ("%s: Listen socket: TH_SYN not set", __func__));
1277 #ifdef INET6
1278 		/*
1279 		 * If deprecated address is forbidden,
1280 		 * we do not accept SYN to deprecated interface
1281 		 * address to prevent any new inbound connection from
1282 		 * getting established.
1283 		 * When we do not accept SYN, we send a TCP RST,
1284 		 * with deprecated source address (instead of dropping
1285 		 * it).  We compromise it as it is much better for peer
1286 		 * to send a RST, and RST will be the final packet
1287 		 * for the exchange.
1288 		 *
1289 		 * If we do not forbid deprecated addresses, we accept
1290 		 * the SYN packet.  RFC2462 does not suggest dropping
1291 		 * SYN in this case.
1292 		 * If we decipher RFC2462 5.5.4, it says like this:
1293 		 * 1. use of deprecated addr with existing
1294 		 *    communication is okay - "SHOULD continue to be
1295 		 *    used"
1296 		 * 2. use of it with new communication:
1297 		 *   (2a) "SHOULD NOT be used if alternate address
1298 		 *        with sufficient scope is available"
1299 		 *   (2b) nothing mentioned otherwise.
1300 		 * Here we fall into (2b) case as we have no choice in
1301 		 * our source address selection - we must obey the peer.
1302 		 *
1303 		 * The wording in RFC2462 is confusing, and there are
1304 		 * multiple description text for deprecated address
1305 		 * handling - worse, they are not exactly the same.
1306 		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1307 		 */
1308 		if (isipv6 && !V_ip6_use_deprecated) {
1309 			struct in6_ifaddr *ia6;
1310 
1311 			ia6 = ip6_getdstifaddr(m);
1312 			if (ia6 != NULL &&
1313 			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1314 				ifa_free(&ia6->ia_ifa);
1315 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1316 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1317 					"Connection attempt to deprecated "
1318 					"IPv6 address rejected\n",
1319 					s, __func__);
1320 				rstreason = BANDLIM_RST_OPENPORT;
1321 				goto dropwithreset;
1322 			}
1323 			if (ia6)
1324 				ifa_free(&ia6->ia_ifa);
1325 		}
1326 #endif /* INET6 */
1327 		/*
1328 		 * Basic sanity checks on incoming SYN requests:
1329 		 *   Don't respond if the destination is a link layer
1330 		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1331 		 *   If it is from this socket it must be forged.
1332 		 *   Don't respond if the source or destination is a
1333 		 *	global or subnet broad- or multicast address.
1334 		 *   Note that it is quite possible to receive unicast
1335 		 *	link-layer packets with a broadcast IP address. Use
1336 		 *	in_broadcast() to find them.
1337 		 */
1338 		if (m->m_flags & (M_BCAST|M_MCAST)) {
1339 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1340 			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1341 				"Connection attempt from broad- or multicast "
1342 				"link layer address ignored\n", s, __func__);
1343 			goto dropunlock;
1344 		}
1345 #ifdef INET6
1346 		if (isipv6) {
1347 			if (th->th_dport == th->th_sport &&
1348 			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1349 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1350 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1351 					"Connection attempt to/from self "
1352 					"ignored\n", s, __func__);
1353 				goto dropunlock;
1354 			}
1355 			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1356 			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1357 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1358 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1359 					"Connection attempt from/to multicast "
1360 					"address ignored\n", s, __func__);
1361 				goto dropunlock;
1362 			}
1363 		}
1364 #endif
1365 #if defined(INET) && defined(INET6)
1366 		else
1367 #endif
1368 #ifdef INET
1369 		{
1370 			if (th->th_dport == th->th_sport &&
1371 			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1372 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1373 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1374 					"Connection attempt from/to self "
1375 					"ignored\n", s, __func__);
1376 				goto dropunlock;
1377 			}
1378 			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1379 			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1380 			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1381 			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1382 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1383 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1384 					"Connection attempt from/to broad- "
1385 					"or multicast address ignored\n",
1386 					s, __func__);
1387 				goto dropunlock;
1388 			}
1389 		}
1390 #endif
1391 		/*
1392 		 * SYN appears to be valid.  Create compressed TCP state
1393 		 * for syncache.
1394 		 */
1395 #ifdef TCPDEBUG
1396 		if (so->so_options & SO_DEBUG)
1397 			tcp_trace(TA_INPUT, ostate, tp,
1398 			    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1399 #endif
1400 		tcp_dooptions(&to, optp, optlen, TO_SYN);
1401 		syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
1402 		/*
1403 		 * Entry added to syncache and mbuf consumed.
1404 		 * Everything already unlocked by syncache_add().
1405 		 */
1406 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1407 		return;
1408 	} else if (tp->t_state == TCPS_LISTEN) {
1409 		/*
1410 		 * When a listen socket is torn down the SO_ACCEPTCONN
1411 		 * flag is removed first while connections are drained
1412 		 * from the accept queue in a unlock/lock cycle of the
1413 		 * ACCEPT_LOCK, opening a race condition allowing a SYN
1414 		 * attempt go through unhandled.
1415 		 */
1416 		goto dropunlock;
1417 	}
1418 
1419 #ifdef TCP_SIGNATURE
1420 	if (sig_checked == 0)  {
1421 		tcp_dooptions(&to, optp, optlen,
1422 		    (thflags & TH_SYN) ? TO_SYN : 0);
1423 		if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
1424 		    th, tp->t_flags)) {
1425 
1426 			/*
1427 			 * In SYN_SENT state if it receives an RST, it is
1428 			 * allowed for further processing.
1429 			 */
1430 			if ((thflags & TH_RST) == 0 ||
1431 			    (tp->t_state == TCPS_SYN_SENT) == 0)
1432 				goto dropunlock;
1433 		}
1434 		sig_checked = 1;
1435 	}
1436 #endif
1437 
1438 	/*
1439 	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1440 	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1441 	 * the inpcb, and unlocks pcbinfo.
1442 	 */
1443 	tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
1444 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1445 	return;
1446 
1447 dropwithreset:
1448 	if (ti_locked == TI_WLOCKED) {
1449 		INP_INFO_WUNLOCK(&V_tcbinfo);
1450 		ti_locked = TI_UNLOCKED;
1451 	}
1452 #ifdef INVARIANTS
1453 	else {
1454 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1455 		    "ti_locked: %d", __func__, ti_locked));
1456 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1457 	}
1458 #endif
1459 
1460 	if (inp != NULL) {
1461 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1462 		INP_WUNLOCK(inp);
1463 	} else
1464 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1465 	m = NULL;	/* mbuf chain got consumed. */
1466 	goto drop;
1467 
1468 dropunlock:
1469 	if (ti_locked == TI_WLOCKED) {
1470 		INP_INFO_WUNLOCK(&V_tcbinfo);
1471 		ti_locked = TI_UNLOCKED;
1472 	}
1473 #ifdef INVARIANTS
1474 	else {
1475 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1476 		    "ti_locked: %d", __func__, ti_locked));
1477 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1478 	}
1479 #endif
1480 
1481 	if (inp != NULL)
1482 		INP_WUNLOCK(inp);
1483 
1484 drop:
1485 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1486 	if (s != NULL)
1487 		free(s, M_TCPLOG);
1488 	if (m != NULL)
1489 		m_freem(m);
1490 }
1491 
1492 static void
1493 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1494     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
1495     int ti_locked)
1496 {
1497 	int thflags, acked, ourfinisacked, needoutput = 0;
1498 	int rstreason, todrop, win;
1499 	u_long tiwin;
1500 	struct tcpopt to;
1501 
1502 #ifdef TCPDEBUG
1503 	/*
1504 	 * The size of tcp_saveipgen must be the size of the max ip header,
1505 	 * now IPv6.
1506 	 */
1507 	u_char tcp_saveipgen[IP6_HDR_LEN];
1508 	struct tcphdr tcp_savetcp;
1509 	short ostate = 0;
1510 #endif
1511 	thflags = th->th_flags;
1512 	tp->sackhint.last_sack_ack = 0;
1513 
1514 	/*
1515 	 * If this is either a state-changing packet or current state isn't
1516 	 * established, we require a write lock on tcbinfo.  Otherwise, we
1517 	 * allow the tcbinfo to be in either alocked or unlocked, as the
1518 	 * caller may have unnecessarily acquired a write lock due to a race.
1519 	 */
1520 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1521 	    tp->t_state != TCPS_ESTABLISHED) {
1522 		KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
1523 		    "SYN/FIN/RST/!EST", __func__, ti_locked));
1524 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1525 	} else {
1526 #ifdef INVARIANTS
1527 		if (ti_locked == TI_WLOCKED)
1528 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1529 		else {
1530 			KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
1531 			    "ti_locked: %d", __func__, ti_locked));
1532 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1533 		}
1534 #endif
1535 	}
1536 	INP_WLOCK_ASSERT(tp->t_inpcb);
1537 	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1538 	    __func__));
1539 	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1540 	    __func__));
1541 
1542 	/*
1543 	 * Segment received on connection.
1544 	 * Reset idle time and keep-alive timer.
1545 	 * XXX: This should be done after segment
1546 	 * validation to ignore broken/spoofed segs.
1547 	 */
1548 	tp->t_rcvtime = ticks;
1549 	if (TCPS_HAVEESTABLISHED(tp->t_state))
1550 		tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
1551 
1552 	/*
1553 	 * Unscale the window into a 32-bit value.
1554 	 * For the SYN_SENT state the scale is zero.
1555 	 */
1556 	tiwin = th->th_win << tp->snd_scale;
1557 
1558 	/*
1559 	 * TCP ECN processing.
1560 	 */
1561 	if (tp->t_flags & TF_ECN_PERMIT) {
1562 		if (thflags & TH_CWR)
1563 			tp->t_flags &= ~TF_ECN_SND_ECE;
1564 		switch (iptos & IPTOS_ECN_MASK) {
1565 		case IPTOS_ECN_CE:
1566 			tp->t_flags |= TF_ECN_SND_ECE;
1567 			TCPSTAT_INC(tcps_ecn_ce);
1568 			break;
1569 		case IPTOS_ECN_ECT0:
1570 			TCPSTAT_INC(tcps_ecn_ect0);
1571 			break;
1572 		case IPTOS_ECN_ECT1:
1573 			TCPSTAT_INC(tcps_ecn_ect1);
1574 			break;
1575 		}
1576 		/* Congestion experienced. */
1577 		if (thflags & TH_ECE) {
1578 			cc_cong_signal(tp, th, CC_ECN);
1579 		}
1580 	}
1581 
1582 	/*
1583 	 * Parse options on any incoming segment.
1584 	 */
1585 	tcp_dooptions(&to, (u_char *)(th + 1),
1586 	    (th->th_off << 2) - sizeof(struct tcphdr),
1587 	    (thflags & TH_SYN) ? TO_SYN : 0);
1588 
1589 	/*
1590 	 * If echoed timestamp is later than the current time,
1591 	 * fall back to non RFC1323 RTT calculation.  Normalize
1592 	 * timestamp if syncookies were used when this connection
1593 	 * was established.
1594 	 */
1595 	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1596 		to.to_tsecr -= tp->ts_offset;
1597 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1598 			to.to_tsecr = 0;
1599 	}
1600 
1601 	/*
1602 	 * Process options only when we get SYN/ACK back. The SYN case
1603 	 * for incoming connections is handled in tcp_syncache.
1604 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1605 	 * or <SYN,ACK>) segment itself is never scaled.
1606 	 * XXX this is traditional behavior, may need to be cleaned up.
1607 	 */
1608 	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1609 		if ((to.to_flags & TOF_SCALE) &&
1610 		    (tp->t_flags & TF_REQ_SCALE)) {
1611 			tp->t_flags |= TF_RCVD_SCALE;
1612 			tp->snd_scale = to.to_wscale;
1613 		}
1614 		/*
1615 		 * Initial send window.  It will be updated with
1616 		 * the next incoming segment to the scaled value.
1617 		 */
1618 		tp->snd_wnd = th->th_win;
1619 		if (to.to_flags & TOF_TS) {
1620 			tp->t_flags |= TF_RCVD_TSTMP;
1621 			tp->ts_recent = to.to_tsval;
1622 			tp->ts_recent_age = tcp_ts_getticks();
1623 		}
1624 		if (to.to_flags & TOF_MSS)
1625 			tcp_mss(tp, to.to_mss);
1626 		if ((tp->t_flags & TF_SACK_PERMIT) &&
1627 		    (to.to_flags & TOF_SACKPERM) == 0)
1628 			tp->t_flags &= ~TF_SACK_PERMIT;
1629 	}
1630 
1631 	/*
1632 	 * Header prediction: check for the two common cases
1633 	 * of a uni-directional data xfer.  If the packet has
1634 	 * no control flags, is in-sequence, the window didn't
1635 	 * change and we're not retransmitting, it's a
1636 	 * candidate.  If the length is zero and the ack moved
1637 	 * forward, we're the sender side of the xfer.  Just
1638 	 * free the data acked & wake any higher level process
1639 	 * that was blocked waiting for space.  If the length
1640 	 * is non-zero and the ack didn't move, we're the
1641 	 * receiver side.  If we're getting packets in-order
1642 	 * (the reassembly queue is empty), add the data to
1643 	 * the socket buffer and note that we need a delayed ack.
1644 	 * Make sure that the hidden state-flags are also off.
1645 	 * Since we check for TCPS_ESTABLISHED first, it can only
1646 	 * be TH_NEEDSYN.
1647 	 */
1648 	if (tp->t_state == TCPS_ESTABLISHED &&
1649 	    th->th_seq == tp->rcv_nxt &&
1650 	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1651 	    tp->snd_nxt == tp->snd_max &&
1652 	    tiwin && tiwin == tp->snd_wnd &&
1653 	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1654 	    LIST_EMPTY(&tp->t_segq) &&
1655 	    ((to.to_flags & TOF_TS) == 0 ||
1656 	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1657 
1658 		/*
1659 		 * If last ACK falls within this segment's sequence numbers,
1660 		 * record the timestamp.
1661 		 * NOTE that the test is modified according to the latest
1662 		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1663 		 */
1664 		if ((to.to_flags & TOF_TS) != 0 &&
1665 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1666 			tp->ts_recent_age = tcp_ts_getticks();
1667 			tp->ts_recent = to.to_tsval;
1668 		}
1669 
1670 		if (tlen == 0) {
1671 			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1672 			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1673 			    !IN_RECOVERY(tp->t_flags) &&
1674 			    (to.to_flags & TOF_SACK) == 0 &&
1675 			    TAILQ_EMPTY(&tp->snd_holes)) {
1676 				/*
1677 				 * This is a pure ack for outstanding data.
1678 				 */
1679 				if (ti_locked == TI_WLOCKED)
1680 					INP_INFO_WUNLOCK(&V_tcbinfo);
1681 				ti_locked = TI_UNLOCKED;
1682 
1683 				TCPSTAT_INC(tcps_predack);
1684 
1685 				/*
1686 				 * "bad retransmit" recovery.
1687 				 */
1688 				if (tp->t_rxtshift == 1 &&
1689 				    tp->t_flags & TF_PREVVALID &&
1690 				    (int)(ticks - tp->t_badrxtwin) < 0) {
1691 					cc_cong_signal(tp, th, CC_RTO_ERR);
1692 				}
1693 
1694 				/*
1695 				 * Recalculate the transmit timer / rtt.
1696 				 *
1697 				 * Some boxes send broken timestamp replies
1698 				 * during the SYN+ACK phase, ignore
1699 				 * timestamps of 0 or we could calculate a
1700 				 * huge RTT and blow up the retransmit timer.
1701 				 */
1702 				if ((to.to_flags & TOF_TS) != 0 &&
1703 				    to.to_tsecr) {
1704 					u_int t;
1705 
1706 					t = tcp_ts_getticks() - to.to_tsecr;
1707 					if (!tp->t_rttlow || tp->t_rttlow > t)
1708 						tp->t_rttlow = t;
1709 					tcp_xmit_timer(tp,
1710 					    TCP_TS_TO_TICKS(t) + 1);
1711 				} else if (tp->t_rtttime &&
1712 				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1713 					if (!tp->t_rttlow ||
1714 					    tp->t_rttlow > ticks - tp->t_rtttime)
1715 						tp->t_rttlow = ticks - tp->t_rtttime;
1716 					tcp_xmit_timer(tp,
1717 							ticks - tp->t_rtttime);
1718 				}
1719 				acked = BYTES_THIS_ACK(tp, th);
1720 
1721 				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1722 				hhook_run_tcp_est_in(tp, th, &to);
1723 
1724 				TCPSTAT_INC(tcps_rcvackpack);
1725 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1726 				sbdrop(&so->so_snd, acked);
1727 				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1728 				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1729 					tp->snd_recover = th->th_ack - 1;
1730 
1731 				/*
1732 				 * Let the congestion control algorithm update
1733 				 * congestion control related information. This
1734 				 * typically means increasing the congestion
1735 				 * window.
1736 				 */
1737 				cc_ack_received(tp, th, CC_ACK);
1738 
1739 				tp->snd_una = th->th_ack;
1740 				/*
1741 				 * Pull snd_wl2 up to prevent seq wrap relative
1742 				 * to th_ack.
1743 				 */
1744 				tp->snd_wl2 = th->th_ack;
1745 				tp->t_dupacks = 0;
1746 				m_freem(m);
1747 				ND6_HINT(tp); /* Some progress has been made. */
1748 
1749 				/*
1750 				 * If all outstanding data are acked, stop
1751 				 * retransmit timer, otherwise restart timer
1752 				 * using current (possibly backed-off) value.
1753 				 * If process is waiting for space,
1754 				 * wakeup/selwakeup/signal.  If data
1755 				 * are ready to send, let tcp_output
1756 				 * decide between more output or persist.
1757 				 */
1758 #ifdef TCPDEBUG
1759 				if (so->so_options & SO_DEBUG)
1760 					tcp_trace(TA_INPUT, ostate, tp,
1761 					    (void *)tcp_saveipgen,
1762 					    &tcp_savetcp, 0);
1763 #endif
1764 				if (tp->snd_una == tp->snd_max)
1765 					tcp_timer_activate(tp, TT_REXMT, 0);
1766 				else if (!tcp_timer_active(tp, TT_PERSIST))
1767 					tcp_timer_activate(tp, TT_REXMT,
1768 						      tp->t_rxtcur);
1769 				sowwakeup(so);
1770 				if (so->so_snd.sb_cc)
1771 					(void) tcp_output(tp);
1772 				goto check_delack;
1773 			}
1774 		} else if (th->th_ack == tp->snd_una &&
1775 		    tlen <= sbspace(&so->so_rcv)) {
1776 			int newsize = 0;	/* automatic sockbuf scaling */
1777 
1778 			/*
1779 			 * This is a pure, in-sequence data packet with
1780 			 * nothing on the reassembly queue and we have enough
1781 			 * buffer space to take it.
1782 			 */
1783 			if (ti_locked == TI_WLOCKED)
1784 				INP_INFO_WUNLOCK(&V_tcbinfo);
1785 			ti_locked = TI_UNLOCKED;
1786 
1787 			/* Clean receiver SACK report if present */
1788 			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1789 				tcp_clean_sackreport(tp);
1790 			TCPSTAT_INC(tcps_preddat);
1791 			tp->rcv_nxt += tlen;
1792 			/*
1793 			 * Pull snd_wl1 up to prevent seq wrap relative to
1794 			 * th_seq.
1795 			 */
1796 			tp->snd_wl1 = th->th_seq;
1797 			/*
1798 			 * Pull rcv_up up to prevent seq wrap relative to
1799 			 * rcv_nxt.
1800 			 */
1801 			tp->rcv_up = tp->rcv_nxt;
1802 			TCPSTAT_INC(tcps_rcvpack);
1803 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1804 			ND6_HINT(tp);	/* Some progress has been made */
1805 #ifdef TCPDEBUG
1806 			if (so->so_options & SO_DEBUG)
1807 				tcp_trace(TA_INPUT, ostate, tp,
1808 				    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1809 #endif
1810 		/*
1811 		 * Automatic sizing of receive socket buffer.  Often the send
1812 		 * buffer size is not optimally adjusted to the actual network
1813 		 * conditions at hand (delay bandwidth product).  Setting the
1814 		 * buffer size too small limits throughput on links with high
1815 		 * bandwidth and high delay (eg. trans-continental/oceanic links).
1816 		 *
1817 		 * On the receive side the socket buffer memory is only rarely
1818 		 * used to any significant extent.  This allows us to be much
1819 		 * more aggressive in scaling the receive socket buffer.  For
1820 		 * the case that the buffer space is actually used to a large
1821 		 * extent and we run out of kernel memory we can simply drop
1822 		 * the new segments; TCP on the sender will just retransmit it
1823 		 * later.  Setting the buffer size too big may only consume too
1824 		 * much kernel memory if the application doesn't read() from
1825 		 * the socket or packet loss or reordering makes use of the
1826 		 * reassembly queue.
1827 		 *
1828 		 * The criteria to step up the receive buffer one notch are:
1829 		 *  1. the number of bytes received during the time it takes
1830 		 *     one timestamp to be reflected back to us (the RTT);
1831 		 *  2. received bytes per RTT is within seven eighth of the
1832 		 *     current socket buffer size;
1833 		 *  3. receive buffer size has not hit maximal automatic size;
1834 		 *
1835 		 * This algorithm does one step per RTT at most and only if
1836 		 * we receive a bulk stream w/o packet losses or reorderings.
1837 		 * Shrinking the buffer during idle times is not necessary as
1838 		 * it doesn't consume any memory when idle.
1839 		 *
1840 		 * TODO: Only step up if the application is actually serving
1841 		 * the buffer to better manage the socket buffer resources.
1842 		 */
1843 			if (V_tcp_do_autorcvbuf &&
1844 			    to.to_tsecr &&
1845 			    (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1846 				if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
1847 				    to.to_tsecr - tp->rfbuf_ts < hz) {
1848 					if (tp->rfbuf_cnt >
1849 					    (so->so_rcv.sb_hiwat / 8 * 7) &&
1850 					    so->so_rcv.sb_hiwat <
1851 					    V_tcp_autorcvbuf_max) {
1852 						newsize =
1853 						    min(so->so_rcv.sb_hiwat +
1854 						    V_tcp_autorcvbuf_inc,
1855 						    V_tcp_autorcvbuf_max);
1856 					}
1857 					/* Start over with next RTT. */
1858 					tp->rfbuf_ts = 0;
1859 					tp->rfbuf_cnt = 0;
1860 				} else
1861 					tp->rfbuf_cnt += tlen;	/* add up */
1862 			}
1863 
1864 			/* Add data to socket buffer. */
1865 			SOCKBUF_LOCK(&so->so_rcv);
1866 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1867 				m_freem(m);
1868 			} else {
1869 				/*
1870 				 * Set new socket buffer size.
1871 				 * Give up when limit is reached.
1872 				 */
1873 				if (newsize)
1874 					if (!sbreserve_locked(&so->so_rcv,
1875 					    newsize, so, NULL))
1876 						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1877 				m_adj(m, drop_hdrlen);	/* delayed header drop */
1878 				sbappendstream_locked(&so->so_rcv, m);
1879 			}
1880 			/* NB: sorwakeup_locked() does an implicit unlock. */
1881 			sorwakeup_locked(so);
1882 			if (DELAY_ACK(tp)) {
1883 				tp->t_flags |= TF_DELACK;
1884 			} else {
1885 				tp->t_flags |= TF_ACKNOW;
1886 				tcp_output(tp);
1887 			}
1888 			goto check_delack;
1889 		}
1890 	}
1891 
1892 	/*
1893 	 * Calculate amount of space in receive window,
1894 	 * and then do TCP input processing.
1895 	 * Receive window is amount of space in rcv queue,
1896 	 * but not less than advertised window.
1897 	 */
1898 	win = sbspace(&so->so_rcv);
1899 	if (win < 0)
1900 		win = 0;
1901 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1902 
1903 	/* Reset receive buffer auto scaling when not in bulk receive mode. */
1904 	tp->rfbuf_ts = 0;
1905 	tp->rfbuf_cnt = 0;
1906 
1907 	switch (tp->t_state) {
1908 
1909 	/*
1910 	 * If the state is SYN_RECEIVED:
1911 	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1912 	 */
1913 	case TCPS_SYN_RECEIVED:
1914 		if ((thflags & TH_ACK) &&
1915 		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1916 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1917 				rstreason = BANDLIM_RST_OPENPORT;
1918 				goto dropwithreset;
1919 		}
1920 		break;
1921 
1922 	/*
1923 	 * If the state is SYN_SENT:
1924 	 *	if seg contains an ACK, but not for our SYN, drop the input.
1925 	 *	if seg contains a RST, then drop the connection.
1926 	 *	if seg does not contain SYN, then drop it.
1927 	 * Otherwise this is an acceptable SYN segment
1928 	 *	initialize tp->rcv_nxt and tp->irs
1929 	 *	if seg contains ack then advance tp->snd_una
1930 	 *	if seg contains an ECE and ECN support is enabled, the stream
1931 	 *	    is ECN capable.
1932 	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1933 	 *	arrange for segment to be acked (eventually)
1934 	 *	continue processing rest of data/controls, beginning with URG
1935 	 */
1936 	case TCPS_SYN_SENT:
1937 		if ((thflags & TH_ACK) &&
1938 		    (SEQ_LEQ(th->th_ack, tp->iss) ||
1939 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1940 			rstreason = BANDLIM_UNLIMITED;
1941 			goto dropwithreset;
1942 		}
1943 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST))
1944 			tp = tcp_drop(tp, ECONNREFUSED);
1945 		if (thflags & TH_RST)
1946 			goto drop;
1947 		if (!(thflags & TH_SYN))
1948 			goto drop;
1949 
1950 		tp->irs = th->th_seq;
1951 		tcp_rcvseqinit(tp);
1952 		if (thflags & TH_ACK) {
1953 			TCPSTAT_INC(tcps_connects);
1954 			soisconnected(so);
1955 #ifdef MAC
1956 			mac_socketpeer_set_from_mbuf(m, so);
1957 #endif
1958 			/* Do window scaling on this connection? */
1959 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1960 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
1961 				tp->rcv_scale = tp->request_r_scale;
1962 			}
1963 			tp->rcv_adv += imin(tp->rcv_wnd,
1964 			    TCP_MAXWIN << tp->rcv_scale);
1965 			tp->snd_una++;		/* SYN is acked */
1966 			/*
1967 			 * If there's data, delay ACK; if there's also a FIN
1968 			 * ACKNOW will be turned on later.
1969 			 */
1970 			if (DELAY_ACK(tp) && tlen != 0)
1971 				tcp_timer_activate(tp, TT_DELACK,
1972 				    tcp_delacktime);
1973 			else
1974 				tp->t_flags |= TF_ACKNOW;
1975 
1976 			if ((thflags & TH_ECE) && V_tcp_do_ecn) {
1977 				tp->t_flags |= TF_ECN_PERMIT;
1978 				TCPSTAT_INC(tcps_ecn_shs);
1979 			}
1980 
1981 			/*
1982 			 * Received <SYN,ACK> in SYN_SENT[*] state.
1983 			 * Transitions:
1984 			 *	SYN_SENT  --> ESTABLISHED
1985 			 *	SYN_SENT* --> FIN_WAIT_1
1986 			 */
1987 			tp->t_starttime = ticks;
1988 			if (tp->t_flags & TF_NEEDFIN) {
1989 				tp->t_state = TCPS_FIN_WAIT_1;
1990 				tp->t_flags &= ~TF_NEEDFIN;
1991 				thflags &= ~TH_SYN;
1992 			} else {
1993 				tp->t_state = TCPS_ESTABLISHED;
1994 				cc_conn_init(tp);
1995 				tcp_timer_activate(tp, TT_KEEP,
1996 				    TP_KEEPIDLE(tp));
1997 			}
1998 		} else {
1999 			/*
2000 			 * Received initial SYN in SYN-SENT[*] state =>
2001 			 * simultaneous open.  If segment contains CC option
2002 			 * and there is a cached CC, apply TAO test.
2003 			 * If it succeeds, connection is * half-synchronized.
2004 			 * Otherwise, do 3-way handshake:
2005 			 *        SYN-SENT -> SYN-RECEIVED
2006 			 *        SYN-SENT* -> SYN-RECEIVED*
2007 			 * If there was no CC option, clear cached CC value.
2008 			 */
2009 			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2010 			tcp_timer_activate(tp, TT_REXMT, 0);
2011 			tp->t_state = TCPS_SYN_RECEIVED;
2012 		}
2013 
2014 		KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
2015 		    "ti_locked %d", __func__, ti_locked));
2016 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2017 		INP_WLOCK_ASSERT(tp->t_inpcb);
2018 
2019 		/*
2020 		 * Advance th->th_seq to correspond to first data byte.
2021 		 * If data, trim to stay within window,
2022 		 * dropping FIN if necessary.
2023 		 */
2024 		th->th_seq++;
2025 		if (tlen > tp->rcv_wnd) {
2026 			todrop = tlen - tp->rcv_wnd;
2027 			m_adj(m, -todrop);
2028 			tlen = tp->rcv_wnd;
2029 			thflags &= ~TH_FIN;
2030 			TCPSTAT_INC(tcps_rcvpackafterwin);
2031 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2032 		}
2033 		tp->snd_wl1 = th->th_seq - 1;
2034 		tp->rcv_up = th->th_seq;
2035 		/*
2036 		 * Client side of transaction: already sent SYN and data.
2037 		 * If the remote host used T/TCP to validate the SYN,
2038 		 * our data will be ACK'd; if so, enter normal data segment
2039 		 * processing in the middle of step 5, ack processing.
2040 		 * Otherwise, goto step 6.
2041 		 */
2042 		if (thflags & TH_ACK)
2043 			goto process_ACK;
2044 
2045 		goto step6;
2046 
2047 	/*
2048 	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2049 	 *      do normal processing.
2050 	 *
2051 	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2052 	 */
2053 	case TCPS_LAST_ACK:
2054 	case TCPS_CLOSING:
2055 		break;  /* continue normal processing */
2056 	}
2057 
2058 	/*
2059 	 * States other than LISTEN or SYN_SENT.
2060 	 * First check the RST flag and sequence number since reset segments
2061 	 * are exempt from the timestamp and connection count tests.  This
2062 	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2063 	 * below which allowed reset segments in half the sequence space
2064 	 * to fall though and be processed (which gives forged reset
2065 	 * segments with a random sequence number a 50 percent chance of
2066 	 * killing a connection).
2067 	 * Then check timestamp, if present.
2068 	 * Then check the connection count, if present.
2069 	 * Then check that at least some bytes of segment are within
2070 	 * receive window.  If segment begins before rcv_nxt,
2071 	 * drop leading data (and SYN); if nothing left, just ack.
2072 	 *
2073 	 *
2074 	 * If the RST bit is set, check the sequence number to see
2075 	 * if this is a valid reset segment.
2076 	 * RFC 793 page 37:
2077 	 *   In all states except SYN-SENT, all reset (RST) segments
2078 	 *   are validated by checking their SEQ-fields.  A reset is
2079 	 *   valid if its sequence number is in the window.
2080 	 * Note: this does not take into account delayed ACKs, so
2081 	 *   we should test against last_ack_sent instead of rcv_nxt.
2082 	 *   The sequence number in the reset segment is normally an
2083 	 *   echo of our outgoing acknowlegement numbers, but some hosts
2084 	 *   send a reset with the sequence number at the rightmost edge
2085 	 *   of our receive window, and we have to handle this case.
2086 	 * Note 2: Paul Watson's paper "Slipping in the Window" has shown
2087 	 *   that brute force RST attacks are possible.  To combat this,
2088 	 *   we use a much stricter check while in the ESTABLISHED state,
2089 	 *   only accepting RSTs where the sequence number is equal to
2090 	 *   last_ack_sent.  In all other states (the states in which a
2091 	 *   RST is more likely), the more permissive check is used.
2092 	 * If we have multiple segments in flight, the initial reset
2093 	 * segment sequence numbers will be to the left of last_ack_sent,
2094 	 * but they will eventually catch up.
2095 	 * In any case, it never made sense to trim reset segments to
2096 	 * fit the receive window since RFC 1122 says:
2097 	 *   4.2.2.12  RST Segment: RFC-793 Section 3.4
2098 	 *
2099 	 *    A TCP SHOULD allow a received RST segment to include data.
2100 	 *
2101 	 *    DISCUSSION
2102 	 *         It has been suggested that a RST segment could contain
2103 	 *         ASCII text that encoded and explained the cause of the
2104 	 *         RST.  No standard has yet been established for such
2105 	 *         data.
2106 	 *
2107 	 * If the reset segment passes the sequence number test examine
2108 	 * the state:
2109 	 *    SYN_RECEIVED STATE:
2110 	 *	If passive open, return to LISTEN state.
2111 	 *	If active open, inform user that connection was refused.
2112 	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
2113 	 *	Inform user that connection was reset, and close tcb.
2114 	 *    CLOSING, LAST_ACK STATES:
2115 	 *	Close the tcb.
2116 	 *    TIME_WAIT STATE:
2117 	 *	Drop the segment - see Stevens, vol. 2, p. 964 and
2118 	 *      RFC 1337.
2119 	 */
2120 	if (thflags & TH_RST) {
2121 		if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2122 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2123 			switch (tp->t_state) {
2124 
2125 			case TCPS_SYN_RECEIVED:
2126 				so->so_error = ECONNREFUSED;
2127 				goto close;
2128 
2129 			case TCPS_ESTABLISHED:
2130 				if (V_tcp_insecure_rst == 0 &&
2131 				    !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
2132 				    SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
2133 				    !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2134 				    SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
2135 					TCPSTAT_INC(tcps_badrst);
2136 					goto drop;
2137 				}
2138 				/* FALLTHROUGH */
2139 			case TCPS_FIN_WAIT_1:
2140 			case TCPS_FIN_WAIT_2:
2141 			case TCPS_CLOSE_WAIT:
2142 				so->so_error = ECONNRESET;
2143 			close:
2144 				KASSERT(ti_locked == TI_WLOCKED,
2145 				    ("tcp_do_segment: TH_RST 1 ti_locked %d",
2146 				    ti_locked));
2147 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2148 
2149 				tp->t_state = TCPS_CLOSED;
2150 				TCPSTAT_INC(tcps_drops);
2151 				tp = tcp_close(tp);
2152 				break;
2153 
2154 			case TCPS_CLOSING:
2155 			case TCPS_LAST_ACK:
2156 				KASSERT(ti_locked == TI_WLOCKED,
2157 				    ("tcp_do_segment: TH_RST 2 ti_locked %d",
2158 				    ti_locked));
2159 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2160 
2161 				tp = tcp_close(tp);
2162 				break;
2163 			}
2164 		}
2165 		goto drop;
2166 	}
2167 
2168 	/*
2169 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2170 	 * and it's less than ts_recent, drop it.
2171 	 */
2172 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2173 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2174 
2175 		/* Check to see if ts_recent is over 24 days old.  */
2176 		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2177 			/*
2178 			 * Invalidate ts_recent.  If this segment updates
2179 			 * ts_recent, the age will be reset later and ts_recent
2180 			 * will get a valid value.  If it does not, setting
2181 			 * ts_recent to zero will at least satisfy the
2182 			 * requirement that zero be placed in the timestamp
2183 			 * echo reply when ts_recent isn't valid.  The
2184 			 * age isn't reset until we get a valid ts_recent
2185 			 * because we don't want out-of-order segments to be
2186 			 * dropped when ts_recent is old.
2187 			 */
2188 			tp->ts_recent = 0;
2189 		} else {
2190 			TCPSTAT_INC(tcps_rcvduppack);
2191 			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2192 			TCPSTAT_INC(tcps_pawsdrop);
2193 			if (tlen)
2194 				goto dropafterack;
2195 			goto drop;
2196 		}
2197 	}
2198 
2199 	/*
2200 	 * In the SYN-RECEIVED state, validate that the packet belongs to
2201 	 * this connection before trimming the data to fit the receive
2202 	 * window.  Check the sequence number versus IRS since we know
2203 	 * the sequence numbers haven't wrapped.  This is a partial fix
2204 	 * for the "LAND" DoS attack.
2205 	 */
2206 	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2207 		rstreason = BANDLIM_RST_OPENPORT;
2208 		goto dropwithreset;
2209 	}
2210 
2211 	todrop = tp->rcv_nxt - th->th_seq;
2212 	if (todrop > 0) {
2213 		/*
2214 		 * If this is a duplicate SYN for our current connection,
2215 		 * advance over it and pretend and it's not a SYN.
2216 		 */
2217 		if (thflags & TH_SYN && th->th_seq == tp->irs) {
2218 			thflags &= ~TH_SYN;
2219 			th->th_seq++;
2220 			if (th->th_urp > 1)
2221 				th->th_urp--;
2222 			else
2223 				thflags &= ~TH_URG;
2224 			todrop--;
2225 		}
2226 		/*
2227 		 * Following if statement from Stevens, vol. 2, p. 960.
2228 		 */
2229 		if (todrop > tlen
2230 		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2231 			/*
2232 			 * Any valid FIN must be to the left of the window.
2233 			 * At this point the FIN must be a duplicate or out
2234 			 * of sequence; drop it.
2235 			 */
2236 			thflags &= ~TH_FIN;
2237 
2238 			/*
2239 			 * Send an ACK to resynchronize and drop any data.
2240 			 * But keep on processing for RST or ACK.
2241 			 */
2242 			tp->t_flags |= TF_ACKNOW;
2243 			todrop = tlen;
2244 			TCPSTAT_INC(tcps_rcvduppack);
2245 			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2246 		} else {
2247 			TCPSTAT_INC(tcps_rcvpartduppack);
2248 			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2249 		}
2250 		drop_hdrlen += todrop;	/* drop from the top afterwards */
2251 		th->th_seq += todrop;
2252 		tlen -= todrop;
2253 		if (th->th_urp > todrop)
2254 			th->th_urp -= todrop;
2255 		else {
2256 			thflags &= ~TH_URG;
2257 			th->th_urp = 0;
2258 		}
2259 	}
2260 
2261 	/*
2262 	 * If new data are received on a connection after the
2263 	 * user processes are gone, then RST the other end.
2264 	 */
2265 	if ((so->so_state & SS_NOFDREF) &&
2266 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2267 		char *s;
2268 
2269 		KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
2270 		    "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
2271 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2272 
2273 		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
2274 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data after socket "
2275 			    "was closed, sending RST and removing tcpcb\n",
2276 			    s, __func__, tcpstates[tp->t_state], tlen);
2277 			free(s, M_TCPLOG);
2278 		}
2279 		tp = tcp_close(tp);
2280 		TCPSTAT_INC(tcps_rcvafterclose);
2281 		rstreason = BANDLIM_UNLIMITED;
2282 		goto dropwithreset;
2283 	}
2284 
2285 	/*
2286 	 * If segment ends after window, drop trailing data
2287 	 * (and PUSH and FIN); if nothing left, just ACK.
2288 	 */
2289 	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2290 	if (todrop > 0) {
2291 		TCPSTAT_INC(tcps_rcvpackafterwin);
2292 		if (todrop >= tlen) {
2293 			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2294 			/*
2295 			 * If window is closed can only take segments at
2296 			 * window edge, and have to drop data and PUSH from
2297 			 * incoming segments.  Continue processing, but
2298 			 * remember to ack.  Otherwise, drop segment
2299 			 * and ack.
2300 			 */
2301 			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2302 				tp->t_flags |= TF_ACKNOW;
2303 				TCPSTAT_INC(tcps_rcvwinprobe);
2304 			} else
2305 				goto dropafterack;
2306 		} else
2307 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2308 		m_adj(m, -todrop);
2309 		tlen -= todrop;
2310 		thflags &= ~(TH_PUSH|TH_FIN);
2311 	}
2312 
2313 	/*
2314 	 * If last ACK falls within this segment's sequence numbers,
2315 	 * record its timestamp.
2316 	 * NOTE:
2317 	 * 1) That the test incorporates suggestions from the latest
2318 	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2319 	 * 2) That updating only on newer timestamps interferes with
2320 	 *    our earlier PAWS tests, so this check should be solely
2321 	 *    predicated on the sequence space of this segment.
2322 	 * 3) That we modify the segment boundary check to be
2323 	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2324 	 *    instead of RFC1323's
2325 	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2326 	 *    This modified check allows us to overcome RFC1323's
2327 	 *    limitations as described in Stevens TCP/IP Illustrated
2328 	 *    Vol. 2 p.869. In such cases, we can still calculate the
2329 	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2330 	 */
2331 	if ((to.to_flags & TOF_TS) != 0 &&
2332 	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2333 	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2334 		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2335 		tp->ts_recent_age = tcp_ts_getticks();
2336 		tp->ts_recent = to.to_tsval;
2337 	}
2338 
2339 	/*
2340 	 * If a SYN is in the window, then this is an
2341 	 * error and we send an RST and drop the connection.
2342 	 */
2343 	if (thflags & TH_SYN) {
2344 		KASSERT(ti_locked == TI_WLOCKED,
2345 		    ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
2346 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2347 
2348 		tp = tcp_drop(tp, ECONNRESET);
2349 		rstreason = BANDLIM_UNLIMITED;
2350 		goto drop;
2351 	}
2352 
2353 	/*
2354 	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2355 	 * flag is on (half-synchronized state), then queue data for
2356 	 * later processing; else drop segment and return.
2357 	 */
2358 	if ((thflags & TH_ACK) == 0) {
2359 		if (tp->t_state == TCPS_SYN_RECEIVED ||
2360 		    (tp->t_flags & TF_NEEDSYN))
2361 			goto step6;
2362 		else if (tp->t_flags & TF_ACKNOW)
2363 			goto dropafterack;
2364 		else
2365 			goto drop;
2366 	}
2367 
2368 	/*
2369 	 * Ack processing.
2370 	 */
2371 	switch (tp->t_state) {
2372 
2373 	/*
2374 	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2375 	 * ESTABLISHED state and continue processing.
2376 	 * The ACK was checked above.
2377 	 */
2378 	case TCPS_SYN_RECEIVED:
2379 
2380 		TCPSTAT_INC(tcps_connects);
2381 		soisconnected(so);
2382 		/* Do window scaling? */
2383 		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2384 			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2385 			tp->rcv_scale = tp->request_r_scale;
2386 			tp->snd_wnd = tiwin;
2387 		}
2388 		/*
2389 		 * Make transitions:
2390 		 *      SYN-RECEIVED  -> ESTABLISHED
2391 		 *      SYN-RECEIVED* -> FIN-WAIT-1
2392 		 */
2393 		tp->t_starttime = ticks;
2394 		if (tp->t_flags & TF_NEEDFIN) {
2395 			tp->t_state = TCPS_FIN_WAIT_1;
2396 			tp->t_flags &= ~TF_NEEDFIN;
2397 		} else {
2398 			tp->t_state = TCPS_ESTABLISHED;
2399 			cc_conn_init(tp);
2400 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2401 		}
2402 		/*
2403 		 * If segment contains data or ACK, will call tcp_reass()
2404 		 * later; if not, do so now to pass queued data to user.
2405 		 */
2406 		if (tlen == 0 && (thflags & TH_FIN) == 0)
2407 			(void) tcp_reass(tp, (struct tcphdr *)0, 0,
2408 			    (struct mbuf *)0);
2409 		tp->snd_wl1 = th->th_seq - 1;
2410 		/* FALLTHROUGH */
2411 
2412 	/*
2413 	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2414 	 * ACKs.  If the ack is in the range
2415 	 *	tp->snd_una < th->th_ack <= tp->snd_max
2416 	 * then advance tp->snd_una to th->th_ack and drop
2417 	 * data from the retransmission queue.  If this ACK reflects
2418 	 * more up to date window information we update our window information.
2419 	 */
2420 	case TCPS_ESTABLISHED:
2421 	case TCPS_FIN_WAIT_1:
2422 	case TCPS_FIN_WAIT_2:
2423 	case TCPS_CLOSE_WAIT:
2424 	case TCPS_CLOSING:
2425 	case TCPS_LAST_ACK:
2426 		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2427 			TCPSTAT_INC(tcps_rcvacktoomuch);
2428 			goto dropafterack;
2429 		}
2430 		if ((tp->t_flags & TF_SACK_PERMIT) &&
2431 		    ((to.to_flags & TOF_SACK) ||
2432 		     !TAILQ_EMPTY(&tp->snd_holes)))
2433 			tcp_sack_doack(tp, &to, th->th_ack);
2434 
2435 		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2436 		hhook_run_tcp_est_in(tp, th, &to);
2437 
2438 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2439 			if (tlen == 0 && tiwin == tp->snd_wnd) {
2440 				TCPSTAT_INC(tcps_rcvdupack);
2441 				/*
2442 				 * If we have outstanding data (other than
2443 				 * a window probe), this is a completely
2444 				 * duplicate ack (ie, window info didn't
2445 				 * change), the ack is the biggest we've
2446 				 * seen and we've seen exactly our rexmt
2447 				 * threshhold of them, assume a packet
2448 				 * has been dropped and retransmit it.
2449 				 * Kludge snd_nxt & the congestion
2450 				 * window so we send only this one
2451 				 * packet.
2452 				 *
2453 				 * We know we're losing at the current
2454 				 * window size so do congestion avoidance
2455 				 * (set ssthresh to half the current window
2456 				 * and pull our congestion window back to
2457 				 * the new ssthresh).
2458 				 *
2459 				 * Dup acks mean that packets have left the
2460 				 * network (they're now cached at the receiver)
2461 				 * so bump cwnd by the amount in the receiver
2462 				 * to keep a constant cwnd packets in the
2463 				 * network.
2464 				 *
2465 				 * When using TCP ECN, notify the peer that
2466 				 * we reduced the cwnd.
2467 				 */
2468 				if (!tcp_timer_active(tp, TT_REXMT) ||
2469 				    th->th_ack != tp->snd_una)
2470 					tp->t_dupacks = 0;
2471 				else if (++tp->t_dupacks > tcprexmtthresh ||
2472 				     IN_FASTRECOVERY(tp->t_flags)) {
2473 					cc_ack_received(tp, th, CC_DUPACK);
2474 					if ((tp->t_flags & TF_SACK_PERMIT) &&
2475 					    IN_FASTRECOVERY(tp->t_flags)) {
2476 						int awnd;
2477 
2478 						/*
2479 						 * Compute the amount of data in flight first.
2480 						 * We can inject new data into the pipe iff
2481 						 * we have less than 1/2 the original window's
2482 						 * worth of data in flight.
2483 						 */
2484 						awnd = (tp->snd_nxt - tp->snd_fack) +
2485 							tp->sackhint.sack_bytes_rexmit;
2486 						if (awnd < tp->snd_ssthresh) {
2487 							tp->snd_cwnd += tp->t_maxseg;
2488 							if (tp->snd_cwnd > tp->snd_ssthresh)
2489 								tp->snd_cwnd = tp->snd_ssthresh;
2490 						}
2491 					} else
2492 						tp->snd_cwnd += tp->t_maxseg;
2493 					if ((thflags & TH_FIN) &&
2494 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2495 						/*
2496 						 * If its a fin we need to process
2497 						 * it to avoid a race where both
2498 						 * sides enter FIN-WAIT and send FIN|ACK
2499 						 * at the same time.
2500 						 */
2501 						break;
2502 					}
2503 					(void) tcp_output(tp);
2504 					goto drop;
2505 				} else if (tp->t_dupacks == tcprexmtthresh) {
2506 					tcp_seq onxt = tp->snd_nxt;
2507 
2508 					/*
2509 					 * If we're doing sack, check to
2510 					 * see if we're already in sack
2511 					 * recovery. If we're not doing sack,
2512 					 * check to see if we're in newreno
2513 					 * recovery.
2514 					 */
2515 					if (tp->t_flags & TF_SACK_PERMIT) {
2516 						if (IN_FASTRECOVERY(tp->t_flags)) {
2517 							tp->t_dupacks = 0;
2518 							break;
2519 						}
2520 					} else {
2521 						if (SEQ_LEQ(th->th_ack,
2522 						    tp->snd_recover)) {
2523 							tp->t_dupacks = 0;
2524 							break;
2525 						}
2526 					}
2527 					/* Congestion signal before ack. */
2528 					cc_cong_signal(tp, th, CC_NDUPACK);
2529 					cc_ack_received(tp, th, CC_DUPACK);
2530 					tcp_timer_activate(tp, TT_REXMT, 0);
2531 					tp->t_rtttime = 0;
2532 					if (tp->t_flags & TF_SACK_PERMIT) {
2533 						TCPSTAT_INC(
2534 						    tcps_sack_recovery_episode);
2535 						tp->sack_newdata = tp->snd_nxt;
2536 						tp->snd_cwnd = tp->t_maxseg;
2537 						(void) tcp_output(tp);
2538 						goto drop;
2539 					}
2540 					tp->snd_nxt = th->th_ack;
2541 					tp->snd_cwnd = tp->t_maxseg;
2542 					if ((thflags & TH_FIN) &&
2543 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2544 						/*
2545 						 * If its a fin we need to process
2546 						 * it to avoid a race where both
2547 						 * sides enter FIN-WAIT and send FIN|ACK
2548 						 * at the same time.
2549 						 */
2550 						break;
2551 					}
2552 					(void) tcp_output(tp);
2553 					KASSERT(tp->snd_limited <= 2,
2554 					    ("%s: tp->snd_limited too big",
2555 					    __func__));
2556 					tp->snd_cwnd = tp->snd_ssthresh +
2557 					     tp->t_maxseg *
2558 					     (tp->t_dupacks - tp->snd_limited);
2559 					if (SEQ_GT(onxt, tp->snd_nxt))
2560 						tp->snd_nxt = onxt;
2561 					goto drop;
2562 				} else if (V_tcp_do_rfc3042) {
2563 					cc_ack_received(tp, th, CC_DUPACK);
2564 					u_long oldcwnd = tp->snd_cwnd;
2565 					tcp_seq oldsndmax = tp->snd_max;
2566 					u_int sent;
2567 					int avail;
2568 
2569 					KASSERT(tp->t_dupacks == 1 ||
2570 					    tp->t_dupacks == 2,
2571 					    ("%s: dupacks not 1 or 2",
2572 					    __func__));
2573 					if (tp->t_dupacks == 1)
2574 						tp->snd_limited = 0;
2575 					tp->snd_cwnd =
2576 					    (tp->snd_nxt - tp->snd_una) +
2577 					    (tp->t_dupacks - tp->snd_limited) *
2578 					    tp->t_maxseg;
2579 					if ((thflags & TH_FIN) &&
2580 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2581 						/*
2582 						 * If its a fin we need to process
2583 						 * it to avoid a race where both
2584 						 * sides enter FIN-WAIT and send FIN|ACK
2585 						 * at the same time.
2586 						 */
2587 						break;
2588 					}
2589 					/*
2590 					 * Only call tcp_output when there
2591 					 * is new data available to be sent.
2592 					 * Otherwise we would send pure ACKs.
2593 					 */
2594 					SOCKBUF_LOCK(&so->so_snd);
2595 					avail = so->so_snd.sb_cc -
2596 					    (tp->snd_nxt - tp->snd_una);
2597 					SOCKBUF_UNLOCK(&so->so_snd);
2598 					if (avail > 0)
2599 						(void) tcp_output(tp);
2600 					sent = tp->snd_max - oldsndmax;
2601 					if (sent > tp->t_maxseg) {
2602 						KASSERT((tp->t_dupacks == 2 &&
2603 						    tp->snd_limited == 0) ||
2604 						   (sent == tp->t_maxseg + 1 &&
2605 						    tp->t_flags & TF_SENTFIN),
2606 						    ("%s: sent too much",
2607 						    __func__));
2608 						tp->snd_limited = 2;
2609 					} else if (sent > 0)
2610 						++tp->snd_limited;
2611 					tp->snd_cwnd = oldcwnd;
2612 					goto drop;
2613 				}
2614 			} else
2615 				tp->t_dupacks = 0;
2616 			break;
2617 		}
2618 
2619 		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2620 		    ("%s: th_ack <= snd_una", __func__));
2621 
2622 		/*
2623 		 * If the congestion window was inflated to account
2624 		 * for the other side's cached packets, retract it.
2625 		 */
2626 		if (IN_FASTRECOVERY(tp->t_flags)) {
2627 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2628 				if (tp->t_flags & TF_SACK_PERMIT)
2629 					tcp_sack_partialack(tp, th);
2630 				else
2631 					tcp_newreno_partial_ack(tp, th);
2632 			} else
2633 				cc_post_recovery(tp, th);
2634 		}
2635 		tp->t_dupacks = 0;
2636 		/*
2637 		 * If we reach this point, ACK is not a duplicate,
2638 		 *     i.e., it ACKs something we sent.
2639 		 */
2640 		if (tp->t_flags & TF_NEEDSYN) {
2641 			/*
2642 			 * T/TCP: Connection was half-synchronized, and our
2643 			 * SYN has been ACK'd (so connection is now fully
2644 			 * synchronized).  Go to non-starred state,
2645 			 * increment snd_una for ACK of SYN, and check if
2646 			 * we can do window scaling.
2647 			 */
2648 			tp->t_flags &= ~TF_NEEDSYN;
2649 			tp->snd_una++;
2650 			/* Do window scaling? */
2651 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2652 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2653 				tp->rcv_scale = tp->request_r_scale;
2654 				/* Send window already scaled. */
2655 			}
2656 		}
2657 
2658 process_ACK:
2659 		INP_WLOCK_ASSERT(tp->t_inpcb);
2660 
2661 		acked = BYTES_THIS_ACK(tp, th);
2662 		TCPSTAT_INC(tcps_rcvackpack);
2663 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2664 
2665 		/*
2666 		 * If we just performed our first retransmit, and the ACK
2667 		 * arrives within our recovery window, then it was a mistake
2668 		 * to do the retransmit in the first place.  Recover our
2669 		 * original cwnd and ssthresh, and proceed to transmit where
2670 		 * we left off.
2671 		 */
2672 		if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
2673 		    (int)(ticks - tp->t_badrxtwin) < 0)
2674 			cc_cong_signal(tp, th, CC_RTO_ERR);
2675 
2676 		/*
2677 		 * If we have a timestamp reply, update smoothed
2678 		 * round trip time.  If no timestamp is present but
2679 		 * transmit timer is running and timed sequence
2680 		 * number was acked, update smoothed round trip time.
2681 		 * Since we now have an rtt measurement, cancel the
2682 		 * timer backoff (cf., Phil Karn's retransmit alg.).
2683 		 * Recompute the initial retransmit timer.
2684 		 *
2685 		 * Some boxes send broken timestamp replies
2686 		 * during the SYN+ACK phase, ignore
2687 		 * timestamps of 0 or we could calculate a
2688 		 * huge RTT and blow up the retransmit timer.
2689 		 */
2690 		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2691 			u_int t;
2692 
2693 			t = tcp_ts_getticks() - to.to_tsecr;
2694 			if (!tp->t_rttlow || tp->t_rttlow > t)
2695 				tp->t_rttlow = t;
2696 			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2697 		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2698 			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2699 				tp->t_rttlow = ticks - tp->t_rtttime;
2700 			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2701 		}
2702 
2703 		/*
2704 		 * If all outstanding data is acked, stop retransmit
2705 		 * timer and remember to restart (more output or persist).
2706 		 * If there is more data to be acked, restart retransmit
2707 		 * timer, using current (possibly backed-off) value.
2708 		 */
2709 		if (th->th_ack == tp->snd_max) {
2710 			tcp_timer_activate(tp, TT_REXMT, 0);
2711 			needoutput = 1;
2712 		} else if (!tcp_timer_active(tp, TT_PERSIST))
2713 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2714 
2715 		/*
2716 		 * If no data (only SYN) was ACK'd,
2717 		 *    skip rest of ACK processing.
2718 		 */
2719 		if (acked == 0)
2720 			goto step6;
2721 
2722 		/*
2723 		 * Let the congestion control algorithm update congestion
2724 		 * control related information. This typically means increasing
2725 		 * the congestion window.
2726 		 */
2727 		cc_ack_received(tp, th, CC_ACK);
2728 
2729 		SOCKBUF_LOCK(&so->so_snd);
2730 		if (acked > so->so_snd.sb_cc) {
2731 			tp->snd_wnd -= so->so_snd.sb_cc;
2732 			sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
2733 			ourfinisacked = 1;
2734 		} else {
2735 			sbdrop_locked(&so->so_snd, acked);
2736 			tp->snd_wnd -= acked;
2737 			ourfinisacked = 0;
2738 		}
2739 		/* NB: sowwakeup_locked() does an implicit unlock. */
2740 		sowwakeup_locked(so);
2741 		/* Detect una wraparound. */
2742 		if (!IN_RECOVERY(tp->t_flags) &&
2743 		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2744 		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2745 			tp->snd_recover = th->th_ack - 1;
2746 		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2747 		if (IN_RECOVERY(tp->t_flags) &&
2748 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2749 			EXIT_RECOVERY(tp->t_flags);
2750 		}
2751 		tp->snd_una = th->th_ack;
2752 		if (tp->t_flags & TF_SACK_PERMIT) {
2753 			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2754 				tp->snd_recover = tp->snd_una;
2755 		}
2756 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2757 			tp->snd_nxt = tp->snd_una;
2758 
2759 		switch (tp->t_state) {
2760 
2761 		/*
2762 		 * In FIN_WAIT_1 STATE in addition to the processing
2763 		 * for the ESTABLISHED state if our FIN is now acknowledged
2764 		 * then enter FIN_WAIT_2.
2765 		 */
2766 		case TCPS_FIN_WAIT_1:
2767 			if (ourfinisacked) {
2768 				/*
2769 				 * If we can't receive any more
2770 				 * data, then closing user can proceed.
2771 				 * Starting the timer is contrary to the
2772 				 * specification, but if we don't get a FIN
2773 				 * we'll hang forever.
2774 				 *
2775 				 * XXXjl:
2776 				 * we should release the tp also, and use a
2777 				 * compressed state.
2778 				 */
2779 				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2780 					soisdisconnected(so);
2781 					tcp_timer_activate(tp, TT_2MSL,
2782 					    (tcp_fast_finwait2_recycle ?
2783 					    tcp_finwait2_timeout :
2784 					    TP_MAXIDLE(tp)));
2785 				}
2786 				tp->t_state = TCPS_FIN_WAIT_2;
2787 			}
2788 			break;
2789 
2790 		/*
2791 		 * In CLOSING STATE in addition to the processing for
2792 		 * the ESTABLISHED state if the ACK acknowledges our FIN
2793 		 * then enter the TIME-WAIT state, otherwise ignore
2794 		 * the segment.
2795 		 */
2796 		case TCPS_CLOSING:
2797 			if (ourfinisacked) {
2798 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2799 				tcp_twstart(tp);
2800 				INP_INFO_WUNLOCK(&V_tcbinfo);
2801 				m_freem(m);
2802 				return;
2803 			}
2804 			break;
2805 
2806 		/*
2807 		 * In LAST_ACK, we may still be waiting for data to drain
2808 		 * and/or to be acked, as well as for the ack of our FIN.
2809 		 * If our FIN is now acknowledged, delete the TCB,
2810 		 * enter the closed state and return.
2811 		 */
2812 		case TCPS_LAST_ACK:
2813 			if (ourfinisacked) {
2814 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2815 				tp = tcp_close(tp);
2816 				goto drop;
2817 			}
2818 			break;
2819 		}
2820 	}
2821 
2822 step6:
2823 	INP_WLOCK_ASSERT(tp->t_inpcb);
2824 
2825 	/*
2826 	 * Update window information.
2827 	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2828 	 */
2829 	if ((thflags & TH_ACK) &&
2830 	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2831 	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2832 	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2833 		/* keep track of pure window updates */
2834 		if (tlen == 0 &&
2835 		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2836 			TCPSTAT_INC(tcps_rcvwinupd);
2837 		tp->snd_wnd = tiwin;
2838 		tp->snd_wl1 = th->th_seq;
2839 		tp->snd_wl2 = th->th_ack;
2840 		if (tp->snd_wnd > tp->max_sndwnd)
2841 			tp->max_sndwnd = tp->snd_wnd;
2842 		needoutput = 1;
2843 	}
2844 
2845 	/*
2846 	 * Process segments with URG.
2847 	 */
2848 	if ((thflags & TH_URG) && th->th_urp &&
2849 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2850 		/*
2851 		 * This is a kludge, but if we receive and accept
2852 		 * random urgent pointers, we'll crash in
2853 		 * soreceive.  It's hard to imagine someone
2854 		 * actually wanting to send this much urgent data.
2855 		 */
2856 		SOCKBUF_LOCK(&so->so_rcv);
2857 		if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2858 			th->th_urp = 0;			/* XXX */
2859 			thflags &= ~TH_URG;		/* XXX */
2860 			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
2861 			goto dodata;			/* XXX */
2862 		}
2863 		/*
2864 		 * If this segment advances the known urgent pointer,
2865 		 * then mark the data stream.  This should not happen
2866 		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2867 		 * a FIN has been received from the remote side.
2868 		 * In these states we ignore the URG.
2869 		 *
2870 		 * According to RFC961 (Assigned Protocols),
2871 		 * the urgent pointer points to the last octet
2872 		 * of urgent data.  We continue, however,
2873 		 * to consider it to indicate the first octet
2874 		 * of data past the urgent section as the original
2875 		 * spec states (in one of two places).
2876 		 */
2877 		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2878 			tp->rcv_up = th->th_seq + th->th_urp;
2879 			so->so_oobmark = so->so_rcv.sb_cc +
2880 			    (tp->rcv_up - tp->rcv_nxt) - 1;
2881 			if (so->so_oobmark == 0)
2882 				so->so_rcv.sb_state |= SBS_RCVATMARK;
2883 			sohasoutofband(so);
2884 			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2885 		}
2886 		SOCKBUF_UNLOCK(&so->so_rcv);
2887 		/*
2888 		 * Remove out of band data so doesn't get presented to user.
2889 		 * This can happen independent of advancing the URG pointer,
2890 		 * but if two URG's are pending at once, some out-of-band
2891 		 * data may creep in... ick.
2892 		 */
2893 		if (th->th_urp <= (u_long)tlen &&
2894 		    !(so->so_options & SO_OOBINLINE)) {
2895 			/* hdr drop is delayed */
2896 			tcp_pulloutofband(so, th, m, drop_hdrlen);
2897 		}
2898 	} else {
2899 		/*
2900 		 * If no out of band data is expected,
2901 		 * pull receive urgent pointer along
2902 		 * with the receive window.
2903 		 */
2904 		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2905 			tp->rcv_up = tp->rcv_nxt;
2906 	}
2907 dodata:							/* XXX */
2908 	INP_WLOCK_ASSERT(tp->t_inpcb);
2909 
2910 	/*
2911 	 * Process the segment text, merging it into the TCP sequencing queue,
2912 	 * and arranging for acknowledgment of receipt if necessary.
2913 	 * This process logically involves adjusting tp->rcv_wnd as data
2914 	 * is presented to the user (this happens in tcp_usrreq.c,
2915 	 * case PRU_RCVD).  If a FIN has already been received on this
2916 	 * connection then we just ignore the text.
2917 	 */
2918 	if ((tlen || (thflags & TH_FIN)) &&
2919 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2920 		tcp_seq save_start = th->th_seq;
2921 		m_adj(m, drop_hdrlen);	/* delayed header drop */
2922 		/*
2923 		 * Insert segment which includes th into TCP reassembly queue
2924 		 * with control block tp.  Set thflags to whether reassembly now
2925 		 * includes a segment with FIN.  This handles the common case
2926 		 * inline (segment is the next to be received on an established
2927 		 * connection, and the queue is empty), avoiding linkage into
2928 		 * and removal from the queue and repetition of various
2929 		 * conversions.
2930 		 * Set DELACK for segments received in order, but ack
2931 		 * immediately when segments are out of order (so
2932 		 * fast retransmit can work).
2933 		 */
2934 		if (th->th_seq == tp->rcv_nxt &&
2935 		    LIST_EMPTY(&tp->t_segq) &&
2936 		    TCPS_HAVEESTABLISHED(tp->t_state)) {
2937 			if (DELAY_ACK(tp))
2938 				tp->t_flags |= TF_DELACK;
2939 			else
2940 				tp->t_flags |= TF_ACKNOW;
2941 			tp->rcv_nxt += tlen;
2942 			thflags = th->th_flags & TH_FIN;
2943 			TCPSTAT_INC(tcps_rcvpack);
2944 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
2945 			ND6_HINT(tp);
2946 			SOCKBUF_LOCK(&so->so_rcv);
2947 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2948 				m_freem(m);
2949 			else
2950 				sbappendstream_locked(&so->so_rcv, m);
2951 			/* NB: sorwakeup_locked() does an implicit unlock. */
2952 			sorwakeup_locked(so);
2953 		} else {
2954 			/*
2955 			 * XXX: Due to the header drop above "th" is
2956 			 * theoretically invalid by now.  Fortunately
2957 			 * m_adj() doesn't actually frees any mbufs
2958 			 * when trimming from the head.
2959 			 */
2960 			thflags = tcp_reass(tp, th, &tlen, m);
2961 			tp->t_flags |= TF_ACKNOW;
2962 		}
2963 		if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
2964 			tcp_update_sack_list(tp, save_start, save_start + tlen);
2965 #if 0
2966 		/*
2967 		 * Note the amount of data that peer has sent into
2968 		 * our window, in order to estimate the sender's
2969 		 * buffer size.
2970 		 * XXX: Unused.
2971 		 */
2972 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
2973 			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2974 		else
2975 			len = so->so_rcv.sb_hiwat;
2976 #endif
2977 	} else {
2978 		m_freem(m);
2979 		thflags &= ~TH_FIN;
2980 	}
2981 
2982 	/*
2983 	 * If FIN is received ACK the FIN and let the user know
2984 	 * that the connection is closing.
2985 	 */
2986 	if (thflags & TH_FIN) {
2987 		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2988 			socantrcvmore(so);
2989 			/*
2990 			 * If connection is half-synchronized
2991 			 * (ie NEEDSYN flag on) then delay ACK,
2992 			 * so it may be piggybacked when SYN is sent.
2993 			 * Otherwise, since we received a FIN then no
2994 			 * more input can be expected, send ACK now.
2995 			 */
2996 			if (tp->t_flags & TF_NEEDSYN)
2997 				tp->t_flags |= TF_DELACK;
2998 			else
2999 				tp->t_flags |= TF_ACKNOW;
3000 			tp->rcv_nxt++;
3001 		}
3002 		switch (tp->t_state) {
3003 
3004 		/*
3005 		 * In SYN_RECEIVED and ESTABLISHED STATES
3006 		 * enter the CLOSE_WAIT state.
3007 		 */
3008 		case TCPS_SYN_RECEIVED:
3009 			tp->t_starttime = ticks;
3010 			/* FALLTHROUGH */
3011 		case TCPS_ESTABLISHED:
3012 			tp->t_state = TCPS_CLOSE_WAIT;
3013 			break;
3014 
3015 		/*
3016 		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
3017 		 * enter the CLOSING state.
3018 		 */
3019 		case TCPS_FIN_WAIT_1:
3020 			tp->t_state = TCPS_CLOSING;
3021 			break;
3022 
3023 		/*
3024 		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
3025 		 * starting the time-wait timer, turning off the other
3026 		 * standard timers.
3027 		 */
3028 		case TCPS_FIN_WAIT_2:
3029 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
3030 			KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
3031 			    "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
3032 			    ti_locked));
3033 
3034 			tcp_twstart(tp);
3035 			INP_INFO_WUNLOCK(&V_tcbinfo);
3036 			return;
3037 		}
3038 	}
3039 	if (ti_locked == TI_WLOCKED)
3040 		INP_INFO_WUNLOCK(&V_tcbinfo);
3041 	ti_locked = TI_UNLOCKED;
3042 
3043 #ifdef TCPDEBUG
3044 	if (so->so_options & SO_DEBUG)
3045 		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3046 			  &tcp_savetcp, 0);
3047 #endif
3048 
3049 	/*
3050 	 * Return any desired output.
3051 	 */
3052 	if (needoutput || (tp->t_flags & TF_ACKNOW))
3053 		(void) tcp_output(tp);
3054 
3055 check_delack:
3056 	KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
3057 	    __func__, ti_locked));
3058 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3059 	INP_WLOCK_ASSERT(tp->t_inpcb);
3060 
3061 	if (tp->t_flags & TF_DELACK) {
3062 		tp->t_flags &= ~TF_DELACK;
3063 		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3064 	}
3065 	INP_WUNLOCK(tp->t_inpcb);
3066 	return;
3067 
3068 dropafterack:
3069 	/*
3070 	 * Generate an ACK dropping incoming segment if it occupies
3071 	 * sequence space, where the ACK reflects our state.
3072 	 *
3073 	 * We can now skip the test for the RST flag since all
3074 	 * paths to this code happen after packets containing
3075 	 * RST have been dropped.
3076 	 *
3077 	 * In the SYN-RECEIVED state, don't send an ACK unless the
3078 	 * segment we received passes the SYN-RECEIVED ACK test.
3079 	 * If it fails send a RST.  This breaks the loop in the
3080 	 * "LAND" DoS attack, and also prevents an ACK storm
3081 	 * between two listening ports that have been sent forged
3082 	 * SYN segments, each with the source address of the other.
3083 	 */
3084 	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3085 	    (SEQ_GT(tp->snd_una, th->th_ack) ||
3086 	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
3087 		rstreason = BANDLIM_RST_OPENPORT;
3088 		goto dropwithreset;
3089 	}
3090 #ifdef TCPDEBUG
3091 	if (so->so_options & SO_DEBUG)
3092 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3093 			  &tcp_savetcp, 0);
3094 #endif
3095 	if (ti_locked == TI_WLOCKED)
3096 		INP_INFO_WUNLOCK(&V_tcbinfo);
3097 	ti_locked = TI_UNLOCKED;
3098 
3099 	tp->t_flags |= TF_ACKNOW;
3100 	(void) tcp_output(tp);
3101 	INP_WUNLOCK(tp->t_inpcb);
3102 	m_freem(m);
3103 	return;
3104 
3105 dropwithreset:
3106 	if (ti_locked == TI_WLOCKED)
3107 		INP_INFO_WUNLOCK(&V_tcbinfo);
3108 	ti_locked = TI_UNLOCKED;
3109 
3110 	if (tp != NULL) {
3111 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
3112 		INP_WUNLOCK(tp->t_inpcb);
3113 	} else
3114 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3115 	return;
3116 
3117 drop:
3118 	if (ti_locked == TI_WLOCKED) {
3119 		INP_INFO_WUNLOCK(&V_tcbinfo);
3120 		ti_locked = TI_UNLOCKED;
3121 	}
3122 #ifdef INVARIANTS
3123 	else
3124 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3125 #endif
3126 
3127 	/*
3128 	 * Drop space held by incoming segment and return.
3129 	 */
3130 #ifdef TCPDEBUG
3131 	if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3132 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3133 			  &tcp_savetcp, 0);
3134 #endif
3135 	if (tp != NULL)
3136 		INP_WUNLOCK(tp->t_inpcb);
3137 	m_freem(m);
3138 }
3139 
3140 /*
3141  * Issue RST and make ACK acceptable to originator of segment.
3142  * The mbuf must still include the original packet header.
3143  * tp may be NULL.
3144  */
3145 static void
3146 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3147     int tlen, int rstreason)
3148 {
3149 #ifdef INET
3150 	struct ip *ip;
3151 #endif
3152 #ifdef INET6
3153 	struct ip6_hdr *ip6;
3154 #endif
3155 
3156 	if (tp != NULL) {
3157 		INP_WLOCK_ASSERT(tp->t_inpcb);
3158 	}
3159 
3160 	/* Don't bother if destination was broadcast/multicast. */
3161 	if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3162 		goto drop;
3163 #ifdef INET6
3164 	if (mtod(m, struct ip *)->ip_v == 6) {
3165 		ip6 = mtod(m, struct ip6_hdr *);
3166 		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3167 		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3168 			goto drop;
3169 		/* IPv6 anycast check is done at tcp6_input() */
3170 	}
3171 #endif
3172 #if defined(INET) && defined(INET6)
3173 	else
3174 #endif
3175 #ifdef INET
3176 	{
3177 		ip = mtod(m, struct ip *);
3178 		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3179 		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3180 		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3181 		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3182 			goto drop;
3183 	}
3184 #endif
3185 
3186 	/* Perform bandwidth limiting. */
3187 	if (badport_bandlim(rstreason) < 0)
3188 		goto drop;
3189 
3190 	/* tcp_respond consumes the mbuf chain. */
3191 	if (th->th_flags & TH_ACK) {
3192 		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3193 		    th->th_ack, TH_RST);
3194 	} else {
3195 		if (th->th_flags & TH_SYN)
3196 			tlen++;
3197 		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3198 		    (tcp_seq)0, TH_RST|TH_ACK);
3199 	}
3200 	return;
3201 drop:
3202 	m_freem(m);
3203 }
3204 
3205 /*
3206  * Parse TCP options and place in tcpopt.
3207  */
3208 static void
3209 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3210 {
3211 	int opt, optlen;
3212 
3213 	to->to_flags = 0;
3214 	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3215 		opt = cp[0];
3216 		if (opt == TCPOPT_EOL)
3217 			break;
3218 		if (opt == TCPOPT_NOP)
3219 			optlen = 1;
3220 		else {
3221 			if (cnt < 2)
3222 				break;
3223 			optlen = cp[1];
3224 			if (optlen < 2 || optlen > cnt)
3225 				break;
3226 		}
3227 		switch (opt) {
3228 		case TCPOPT_MAXSEG:
3229 			if (optlen != TCPOLEN_MAXSEG)
3230 				continue;
3231 			if (!(flags & TO_SYN))
3232 				continue;
3233 			to->to_flags |= TOF_MSS;
3234 			bcopy((char *)cp + 2,
3235 			    (char *)&to->to_mss, sizeof(to->to_mss));
3236 			to->to_mss = ntohs(to->to_mss);
3237 			break;
3238 		case TCPOPT_WINDOW:
3239 			if (optlen != TCPOLEN_WINDOW)
3240 				continue;
3241 			if (!(flags & TO_SYN))
3242 				continue;
3243 			to->to_flags |= TOF_SCALE;
3244 			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3245 			break;
3246 		case TCPOPT_TIMESTAMP:
3247 			if (optlen != TCPOLEN_TIMESTAMP)
3248 				continue;
3249 			to->to_flags |= TOF_TS;
3250 			bcopy((char *)cp + 2,
3251 			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3252 			to->to_tsval = ntohl(to->to_tsval);
3253 			bcopy((char *)cp + 6,
3254 			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3255 			to->to_tsecr = ntohl(to->to_tsecr);
3256 			break;
3257 #ifdef TCP_SIGNATURE
3258 		/*
3259 		 * XXX In order to reply to a host which has set the
3260 		 * TCP_SIGNATURE option in its initial SYN, we have to
3261 		 * record the fact that the option was observed here
3262 		 * for the syncache code to perform the correct response.
3263 		 */
3264 		case TCPOPT_SIGNATURE:
3265 			if (optlen != TCPOLEN_SIGNATURE)
3266 				continue;
3267 			to->to_flags |= TOF_SIGNATURE;
3268 			to->to_signature = cp + 2;
3269 			break;
3270 #endif
3271 		case TCPOPT_SACK_PERMITTED:
3272 			if (optlen != TCPOLEN_SACK_PERMITTED)
3273 				continue;
3274 			if (!(flags & TO_SYN))
3275 				continue;
3276 			if (!V_tcp_do_sack)
3277 				continue;
3278 			to->to_flags |= TOF_SACKPERM;
3279 			break;
3280 		case TCPOPT_SACK:
3281 			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3282 				continue;
3283 			if (flags & TO_SYN)
3284 				continue;
3285 			to->to_flags |= TOF_SACK;
3286 			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3287 			to->to_sacks = cp + 2;
3288 			TCPSTAT_INC(tcps_sack_rcv_blocks);
3289 			break;
3290 		default:
3291 			continue;
3292 		}
3293 	}
3294 }
3295 
3296 /*
3297  * Pull out of band byte out of a segment so
3298  * it doesn't appear in the user's data queue.
3299  * It is still reflected in the segment length for
3300  * sequencing purposes.
3301  */
3302 static void
3303 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3304     int off)
3305 {
3306 	int cnt = off + th->th_urp - 1;
3307 
3308 	while (cnt >= 0) {
3309 		if (m->m_len > cnt) {
3310 			char *cp = mtod(m, caddr_t) + cnt;
3311 			struct tcpcb *tp = sototcpcb(so);
3312 
3313 			INP_WLOCK_ASSERT(tp->t_inpcb);
3314 
3315 			tp->t_iobc = *cp;
3316 			tp->t_oobflags |= TCPOOB_HAVEDATA;
3317 			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3318 			m->m_len--;
3319 			if (m->m_flags & M_PKTHDR)
3320 				m->m_pkthdr.len--;
3321 			return;
3322 		}
3323 		cnt -= m->m_len;
3324 		m = m->m_next;
3325 		if (m == NULL)
3326 			break;
3327 	}
3328 	panic("tcp_pulloutofband");
3329 }
3330 
3331 /*
3332  * Collect new round-trip time estimate
3333  * and update averages and current timeout.
3334  */
3335 static void
3336 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3337 {
3338 	int delta;
3339 
3340 	INP_WLOCK_ASSERT(tp->t_inpcb);
3341 
3342 	TCPSTAT_INC(tcps_rttupdated);
3343 	tp->t_rttupdated++;
3344 	if (tp->t_srtt != 0) {
3345 		/*
3346 		 * srtt is stored as fixed point with 5 bits after the
3347 		 * binary point (i.e., scaled by 8).  The following magic
3348 		 * is equivalent to the smoothing algorithm in rfc793 with
3349 		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3350 		 * point).  Adjust rtt to origin 0.
3351 		 */
3352 		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3353 			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3354 
3355 		if ((tp->t_srtt += delta) <= 0)
3356 			tp->t_srtt = 1;
3357 
3358 		/*
3359 		 * We accumulate a smoothed rtt variance (actually, a
3360 		 * smoothed mean difference), then set the retransmit
3361 		 * timer to smoothed rtt + 4 times the smoothed variance.
3362 		 * rttvar is stored as fixed point with 4 bits after the
3363 		 * binary point (scaled by 16).  The following is
3364 		 * equivalent to rfc793 smoothing with an alpha of .75
3365 		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3366 		 * rfc793's wired-in beta.
3367 		 */
3368 		if (delta < 0)
3369 			delta = -delta;
3370 		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3371 		if ((tp->t_rttvar += delta) <= 0)
3372 			tp->t_rttvar = 1;
3373 		if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3374 		    tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3375 	} else {
3376 		/*
3377 		 * No rtt measurement yet - use the unsmoothed rtt.
3378 		 * Set the variance to half the rtt (so our first
3379 		 * retransmit happens at 3*rtt).
3380 		 */
3381 		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3382 		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3383 		tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3384 	}
3385 	tp->t_rtttime = 0;
3386 	tp->t_rxtshift = 0;
3387 
3388 	/*
3389 	 * the retransmit should happen at rtt + 4 * rttvar.
3390 	 * Because of the way we do the smoothing, srtt and rttvar
3391 	 * will each average +1/2 tick of bias.  When we compute
3392 	 * the retransmit timer, we want 1/2 tick of rounding and
3393 	 * 1 extra tick because of +-1/2 tick uncertainty in the
3394 	 * firing of the timer.  The bias will give us exactly the
3395 	 * 1.5 tick we need.  But, because the bias is
3396 	 * statistical, we have to test that we don't drop below
3397 	 * the minimum feasible timer (which is 2 ticks).
3398 	 */
3399 	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3400 		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3401 
3402 	/*
3403 	 * We received an ack for a packet that wasn't retransmitted;
3404 	 * it is probably safe to discard any error indications we've
3405 	 * received recently.  This isn't quite right, but close enough
3406 	 * for now (a route might have failed after we sent a segment,
3407 	 * and the return path might not be symmetrical).
3408 	 */
3409 	tp->t_softerror = 0;
3410 }
3411 
3412 /*
3413  * Determine a reasonable value for maxseg size.
3414  * If the route is known, check route for mtu.
3415  * If none, use an mss that can be handled on the outgoing interface
3416  * without forcing IP to fragment.  If no route is found, route has no mtu,
3417  * or the destination isn't local, use a default, hopefully conservative
3418  * size (usually 512 or the default IP max size, but no more than the mtu
3419  * of the interface), as we can't discover anything about intervening
3420  * gateways or networks.  We also initialize the congestion/slow start
3421  * window to be a single segment if the destination isn't local.
3422  * While looking at the routing entry, we also initialize other path-dependent
3423  * parameters from pre-set or cached values in the routing entry.
3424  *
3425  * Also take into account the space needed for options that we
3426  * send regularly.  Make maxseg shorter by that amount to assure
3427  * that we can send maxseg amount of data even when the options
3428  * are present.  Store the upper limit of the length of options plus
3429  * data in maxopd.
3430  *
3431  * NOTE that this routine is only called when we process an incoming
3432  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3433  * settings are handled in tcp_mssopt().
3434  */
3435 void
3436 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3437     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3438 {
3439 	int mss = 0;
3440 	u_long maxmtu = 0;
3441 	struct inpcb *inp = tp->t_inpcb;
3442 	struct hc_metrics_lite metrics;
3443 	int origoffer;
3444 #ifdef INET6
3445 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3446 	size_t min_protoh = isipv6 ?
3447 			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3448 			    sizeof (struct tcpiphdr);
3449 #else
3450 	const size_t min_protoh = sizeof(struct tcpiphdr);
3451 #endif
3452 
3453 	INP_WLOCK_ASSERT(tp->t_inpcb);
3454 
3455 	if (mtuoffer != -1) {
3456 		KASSERT(offer == -1, ("%s: conflict", __func__));
3457 		offer = mtuoffer - min_protoh;
3458 	}
3459 	origoffer = offer;
3460 
3461 	/* Initialize. */
3462 #ifdef INET6
3463 	if (isipv6) {
3464 		maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3465 		tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
3466 	}
3467 #endif
3468 #if defined(INET) && defined(INET6)
3469 	else
3470 #endif
3471 #ifdef INET
3472 	{
3473 		maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3474 		tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
3475 	}
3476 #endif
3477 
3478 	/*
3479 	 * No route to sender, stay with default mss and return.
3480 	 */
3481 	if (maxmtu == 0) {
3482 		/*
3483 		 * In case we return early we need to initialize metrics
3484 		 * to a defined state as tcp_hc_get() would do for us
3485 		 * if there was no cache hit.
3486 		 */
3487 		if (metricptr != NULL)
3488 			bzero(metricptr, sizeof(struct hc_metrics_lite));
3489 		return;
3490 	}
3491 
3492 	/* What have we got? */
3493 	switch (offer) {
3494 		case 0:
3495 			/*
3496 			 * Offer == 0 means that there was no MSS on the SYN
3497 			 * segment, in this case we use tcp_mssdflt as
3498 			 * already assigned to t_maxopd above.
3499 			 */
3500 			offer = tp->t_maxopd;
3501 			break;
3502 
3503 		case -1:
3504 			/*
3505 			 * Offer == -1 means that we didn't receive SYN yet.
3506 			 */
3507 			/* FALLTHROUGH */
3508 
3509 		default:
3510 			/*
3511 			 * Prevent DoS attack with too small MSS. Round up
3512 			 * to at least minmss.
3513 			 */
3514 			offer = max(offer, V_tcp_minmss);
3515 	}
3516 
3517 	/*
3518 	 * rmx information is now retrieved from tcp_hostcache.
3519 	 */
3520 	tcp_hc_get(&inp->inp_inc, &metrics);
3521 	if (metricptr != NULL)
3522 		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3523 
3524 	/*
3525 	 * If there's a discovered mtu int tcp hostcache, use it
3526 	 * else, use the link mtu.
3527 	 */
3528 	if (metrics.rmx_mtu)
3529 		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3530 	else {
3531 #ifdef INET6
3532 		if (isipv6) {
3533 			mss = maxmtu - min_protoh;
3534 			if (!V_path_mtu_discovery &&
3535 			    !in6_localaddr(&inp->in6p_faddr))
3536 				mss = min(mss, V_tcp_v6mssdflt);
3537 		}
3538 #endif
3539 #if defined(INET) && defined(INET6)
3540 		else
3541 #endif
3542 #ifdef INET
3543 		{
3544 			mss = maxmtu - min_protoh;
3545 			if (!V_path_mtu_discovery &&
3546 			    !in_localaddr(inp->inp_faddr))
3547 				mss = min(mss, V_tcp_mssdflt);
3548 		}
3549 #endif
3550 		/*
3551 		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3552 		 * probably violates the TCP spec.
3553 		 * The problem is that, since we don't know the
3554 		 * other end's MSS, we are supposed to use a conservative
3555 		 * default.  But, if we do that, then MTU discovery will
3556 		 * never actually take place, because the conservative
3557 		 * default is much less than the MTUs typically seen
3558 		 * on the Internet today.  For the moment, we'll sweep
3559 		 * this under the carpet.
3560 		 *
3561 		 * The conservative default might not actually be a problem
3562 		 * if the only case this occurs is when sending an initial
3563 		 * SYN with options and data to a host we've never talked
3564 		 * to before.  Then, they will reply with an MSS value which
3565 		 * will get recorded and the new parameters should get
3566 		 * recomputed.  For Further Study.
3567 		 */
3568 	}
3569 	mss = min(mss, offer);
3570 
3571 	/*
3572 	 * Sanity check: make sure that maxopd will be large
3573 	 * enough to allow some data on segments even if the
3574 	 * all the option space is used (40bytes).  Otherwise
3575 	 * funny things may happen in tcp_output.
3576 	 */
3577 	mss = max(mss, 64);
3578 
3579 	/*
3580 	 * maxopd stores the maximum length of data AND options
3581 	 * in a segment; maxseg is the amount of data in a normal
3582 	 * segment.  We need to store this value (maxopd) apart
3583 	 * from maxseg, because now every segment carries options
3584 	 * and thus we normally have somewhat less data in segments.
3585 	 */
3586 	tp->t_maxopd = mss;
3587 
3588 	/*
3589 	 * origoffer==-1 indicates that no segments were received yet.
3590 	 * In this case we just guess.
3591 	 */
3592 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3593 	    (origoffer == -1 ||
3594 	     (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3595 		mss -= TCPOLEN_TSTAMP_APPA;
3596 
3597 	tp->t_maxseg = mss;
3598 }
3599 
3600 void
3601 tcp_mss(struct tcpcb *tp, int offer)
3602 {
3603 	int mss;
3604 	u_long bufsize;
3605 	struct inpcb *inp;
3606 	struct socket *so;
3607 	struct hc_metrics_lite metrics;
3608 	struct tcp_ifcap cap;
3609 
3610 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3611 
3612 	bzero(&cap, sizeof(cap));
3613 	tcp_mss_update(tp, offer, -1, &metrics, &cap);
3614 
3615 	mss = tp->t_maxseg;
3616 	inp = tp->t_inpcb;
3617 
3618 	/*
3619 	 * If there's a pipesize, change the socket buffer to that size,
3620 	 * don't change if sb_hiwat is different than default (then it
3621 	 * has been changed on purpose with setsockopt).
3622 	 * Make the socket buffers an integral number of mss units;
3623 	 * if the mss is larger than the socket buffer, decrease the mss.
3624 	 */
3625 	so = inp->inp_socket;
3626 	SOCKBUF_LOCK(&so->so_snd);
3627 	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3628 		bufsize = metrics.rmx_sendpipe;
3629 	else
3630 		bufsize = so->so_snd.sb_hiwat;
3631 	if (bufsize < mss)
3632 		mss = bufsize;
3633 	else {
3634 		bufsize = roundup(bufsize, mss);
3635 		if (bufsize > sb_max)
3636 			bufsize = sb_max;
3637 		if (bufsize > so->so_snd.sb_hiwat)
3638 			(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3639 	}
3640 	SOCKBUF_UNLOCK(&so->so_snd);
3641 	tp->t_maxseg = mss;
3642 
3643 	SOCKBUF_LOCK(&so->so_rcv);
3644 	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3645 		bufsize = metrics.rmx_recvpipe;
3646 	else
3647 		bufsize = so->so_rcv.sb_hiwat;
3648 	if (bufsize > mss) {
3649 		bufsize = roundup(bufsize, mss);
3650 		if (bufsize > sb_max)
3651 			bufsize = sb_max;
3652 		if (bufsize > so->so_rcv.sb_hiwat)
3653 			(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3654 	}
3655 	SOCKBUF_UNLOCK(&so->so_rcv);
3656 
3657 	/* Check the interface for TSO capabilities. */
3658 	if (cap.ifcap & CSUM_TSO) {
3659 		tp->t_flags |= TF_TSO;
3660 		tp->t_tsomax = cap.tsomax;
3661 	}
3662 }
3663 
3664 /*
3665  * Determine the MSS option to send on an outgoing SYN.
3666  */
3667 int
3668 tcp_mssopt(struct in_conninfo *inc)
3669 {
3670 	int mss = 0;
3671 	u_long maxmtu = 0;
3672 	u_long thcmtu = 0;
3673 	size_t min_protoh;
3674 
3675 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3676 
3677 #ifdef INET6
3678 	if (inc->inc_flags & INC_ISIPV6) {
3679 		mss = V_tcp_v6mssdflt;
3680 		maxmtu = tcp_maxmtu6(inc, NULL);
3681 		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3682 	}
3683 #endif
3684 #if defined(INET) && defined(INET6)
3685 	else
3686 #endif
3687 #ifdef INET
3688 	{
3689 		mss = V_tcp_mssdflt;
3690 		maxmtu = tcp_maxmtu(inc, NULL);
3691 		min_protoh = sizeof(struct tcpiphdr);
3692 	}
3693 #endif
3694 #if defined(INET6) || defined(INET)
3695 	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3696 #endif
3697 
3698 	if (maxmtu && thcmtu)
3699 		mss = min(maxmtu, thcmtu) - min_protoh;
3700 	else if (maxmtu || thcmtu)
3701 		mss = max(maxmtu, thcmtu) - min_protoh;
3702 
3703 	return (mss);
3704 }
3705 
3706 
3707 /*
3708  * On a partial ack arrives, force the retransmission of the
3709  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3710  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3711  * be started again.
3712  */
3713 static void
3714 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3715 {
3716 	tcp_seq onxt = tp->snd_nxt;
3717 	u_long  ocwnd = tp->snd_cwnd;
3718 
3719 	INP_WLOCK_ASSERT(tp->t_inpcb);
3720 
3721 	tcp_timer_activate(tp, TT_REXMT, 0);
3722 	tp->t_rtttime = 0;
3723 	tp->snd_nxt = th->th_ack;
3724 	/*
3725 	 * Set snd_cwnd to one segment beyond acknowledged offset.
3726 	 * (tp->snd_una has not yet been updated when this function is called.)
3727 	 */
3728 	tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
3729 	tp->t_flags |= TF_ACKNOW;
3730 	(void) tcp_output(tp);
3731 	tp->snd_cwnd = ocwnd;
3732 	if (SEQ_GT(onxt, tp->snd_nxt))
3733 		tp->snd_nxt = onxt;
3734 	/*
3735 	 * Partial window deflation.  Relies on fact that tp->snd_una
3736 	 * not updated yet.
3737 	 */
3738 	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3739 		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3740 	else
3741 		tp->snd_cwnd = 0;
3742 	tp->snd_cwnd += tp->t_maxseg;
3743 }
3744