xref: /freebsd/sys/netinet/tcp_input.c (revision 4c9e27bd0a5f7fda85b0c0bf750575aee300a172)
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_kdtrace.h"
58 #include "opt_tcpdebug.h"
59 
60 #include <sys/param.h>
61 #include <sys/kernel.h>
62 #include <sys/hhook.h>
63 #include <sys/malloc.h>
64 #include <sys/mbuf.h>
65 #include <sys/proc.h>		/* for proc0 declaration */
66 #include <sys/protosw.h>
67 #include <sys/sdt.h>
68 #include <sys/signalvar.h>
69 #include <sys/socket.h>
70 #include <sys/socketvar.h>
71 #include <sys/sysctl.h>
72 #include <sys/syslog.h>
73 #include <sys/systm.h>
74 
75 #include <machine/cpu.h>	/* before tcp_seq.h, for tcp_random18() */
76 
77 #include <vm/uma.h>
78 
79 #include <net/if.h>
80 #include <net/if_var.h>
81 #include <net/route.h>
82 #include <net/vnet.h>
83 
84 #define TCPSTATES		/* for logging */
85 
86 #include <netinet/cc.h>
87 #include <netinet/in.h>
88 #include <netinet/in_kdtrace.h>
89 #include <netinet/in_pcb.h>
90 #include <netinet/in_systm.h>
91 #include <netinet/in_var.h>
92 #include <netinet/ip.h>
93 #include <netinet/ip_icmp.h>	/* required for icmp_var.h */
94 #include <netinet/icmp_var.h>	/* for ICMP_BANDLIM */
95 #include <netinet/ip_var.h>
96 #include <netinet/ip_options.h>
97 #include <netinet/ip6.h>
98 #include <netinet/icmp6.h>
99 #include <netinet6/in6_pcb.h>
100 #include <netinet6/ip6_var.h>
101 #include <netinet6/nd6.h>
102 #include <netinet/tcp_fsm.h>
103 #include <netinet/tcp_seq.h>
104 #include <netinet/tcp_timer.h>
105 #include <netinet/tcp_var.h>
106 #include <netinet6/tcp6_var.h>
107 #include <netinet/tcpip.h>
108 #include <netinet/tcp_syncache.h>
109 #ifdef TCPDEBUG
110 #include <netinet/tcp_debug.h>
111 #endif /* TCPDEBUG */
112 #ifdef TCP_OFFLOAD
113 #include <netinet/tcp_offload.h>
114 #endif
115 
116 #ifdef IPSEC
117 #include <netipsec/ipsec.h>
118 #include <netipsec/ipsec6.h>
119 #endif /*IPSEC*/
120 
121 #include <machine/in_cksum.h>
122 
123 #include <security/mac/mac_framework.h>
124 
125 const int tcprexmtthresh = 3;
126 
127 int tcp_log_in_vain = 0;
128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
129     &tcp_log_in_vain, 0,
130     "Log all incoming TCP segments to closed ports");
131 
132 VNET_DEFINE(int, blackhole) = 0;
133 #define	V_blackhole		VNET(blackhole)
134 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
135     &VNET_NAME(blackhole), 0,
136     "Do not send RST on segments to closed ports");
137 
138 VNET_DEFINE(int, tcp_delack_enabled) = 1;
139 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
140     &VNET_NAME(tcp_delack_enabled), 0,
141     "Delay ACK to try and piggyback it onto a data packet");
142 
143 VNET_DEFINE(int, drop_synfin) = 0;
144 #define	V_drop_synfin		VNET(drop_synfin)
145 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
146     &VNET_NAME(drop_synfin), 0,
147     "Drop TCP packets with SYN+FIN set");
148 
149 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
150 #define	V_tcp_do_rfc3042	VNET(tcp_do_rfc3042)
151 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
152     &VNET_NAME(tcp_do_rfc3042), 0,
153     "Enable RFC 3042 (Limited Transmit)");
154 
155 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
156 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW,
157     &VNET_NAME(tcp_do_rfc3390), 0,
158     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
159 
160 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
161     "Experimental TCP extensions");
162 
163 VNET_DEFINE(int, tcp_do_initcwnd10) = 1;
164 SYSCTL_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_RW,
165     &VNET_NAME(tcp_do_initcwnd10), 0,
166     "Enable draft-ietf-tcpm-initcwnd-05 (Increasing initial CWND to 10)");
167 
168 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
169 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
170     &VNET_NAME(tcp_do_rfc3465), 0,
171     "Enable RFC 3465 (Appropriate Byte Counting)");
172 
173 VNET_DEFINE(int, tcp_abc_l_var) = 2;
174 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
175     &VNET_NAME(tcp_abc_l_var), 2,
176     "Cap the max cwnd increment during slow-start to this number of segments");
177 
178 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
179 
180 VNET_DEFINE(int, tcp_do_ecn) = 0;
181 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_RW,
182     &VNET_NAME(tcp_do_ecn), 0,
183     "TCP ECN support");
184 
185 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
186 SYSCTL_VNET_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_RW,
187     &VNET_NAME(tcp_ecn_maxretries), 0,
188     "Max retries before giving up on ECN");
189 
190 VNET_DEFINE(int, tcp_insecure_rst) = 0;
191 #define	V_tcp_insecure_rst	VNET(tcp_insecure_rst)
192 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_RW,
193     &VNET_NAME(tcp_insecure_rst), 0,
194     "Follow the old (insecure) criteria for accepting RST packets");
195 
196 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
197 #define	V_tcp_recvspace	VNET(tcp_recvspace)
198 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
199     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
200 
201 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
202 #define	V_tcp_do_autorcvbuf	VNET(tcp_do_autorcvbuf)
203 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_RW,
204     &VNET_NAME(tcp_do_autorcvbuf), 0,
205     "Enable automatic receive buffer sizing");
206 
207 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
208 #define	V_tcp_autorcvbuf_inc	VNET(tcp_autorcvbuf_inc)
209 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_RW,
210     &VNET_NAME(tcp_autorcvbuf_inc), 0,
211     "Incrementor step size of automatic receive buffer");
212 
213 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
214 #define	V_tcp_autorcvbuf_max	VNET(tcp_autorcvbuf_max)
215 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_RW,
216     &VNET_NAME(tcp_autorcvbuf_max), 0,
217     "Max size of automatic receive buffer");
218 
219 VNET_DEFINE(struct inpcbhead, tcb);
220 #define	tcb6	tcb  /* for KAME src sync over BSD*'s */
221 VNET_DEFINE(struct inpcbinfo, tcbinfo);
222 
223 static void	 tcp_dooptions(struct tcpopt *, u_char *, int, int);
224 static void	 tcp_do_segment(struct mbuf *, struct tcphdr *,
225 		     struct socket *, struct tcpcb *, int, int, uint8_t,
226 		     int);
227 static void	 tcp_dropwithreset(struct mbuf *, struct tcphdr *,
228 		     struct tcpcb *, int, int);
229 static void	 tcp_pulloutofband(struct socket *,
230 		     struct tcphdr *, struct mbuf *, int);
231 static void	 tcp_xmit_timer(struct tcpcb *, int);
232 static void	 tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
233 static void inline 	tcp_fields_to_host(struct tcphdr *);
234 #ifdef TCP_SIGNATURE
235 static void inline 	tcp_fields_to_net(struct tcphdr *);
236 static int inline	tcp_signature_verify_input(struct mbuf *, int, int,
237 			    int, struct tcpopt *, struct tcphdr *, u_int);
238 #endif
239 static void inline	cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
240 			    uint16_t type);
241 static void inline	cc_conn_init(struct tcpcb *tp);
242 static void inline	cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
243 static void inline	hhook_run_tcp_est_in(struct tcpcb *tp,
244 			    struct tcphdr *th, struct tcpopt *to);
245 
246 /*
247  * TCP statistics are stored in an "array" of counter(9)s.
248  */
249 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
250 VNET_PCPUSTAT_SYSINIT(tcpstat);
251 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
252     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
253 
254 #ifdef VIMAGE
255 VNET_PCPUSTAT_SYSUNINIT(tcpstat);
256 #endif /* VIMAGE */
257 /*
258  * Kernel module interface for updating tcpstat.  The argument is an index
259  * into tcpstat treated as an array.
260  */
261 void
262 kmod_tcpstat_inc(int statnum)
263 {
264 
265 	counter_u64_add(VNET(tcpstat)[statnum], 1);
266 }
267 
268 /*
269  * Wrapper for the TCP established input helper hook.
270  */
271 static void inline
272 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
273 {
274 	struct tcp_hhook_data hhook_data;
275 
276 	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
277 		hhook_data.tp = tp;
278 		hhook_data.th = th;
279 		hhook_data.to = to;
280 
281 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
282 		    tp->osd);
283 	}
284 }
285 
286 /*
287  * CC wrapper hook functions
288  */
289 static void inline
290 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type)
291 {
292 	INP_WLOCK_ASSERT(tp->t_inpcb);
293 
294 	tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
295 	if (tp->snd_cwnd <= tp->snd_wnd)
296 		tp->ccv->flags |= CCF_CWND_LIMITED;
297 	else
298 		tp->ccv->flags &= ~CCF_CWND_LIMITED;
299 
300 	if (type == CC_ACK) {
301 		if (tp->snd_cwnd > tp->snd_ssthresh) {
302 			tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
303 			     V_tcp_abc_l_var * tp->t_maxseg);
304 			if (tp->t_bytes_acked >= tp->snd_cwnd) {
305 				tp->t_bytes_acked -= tp->snd_cwnd;
306 				tp->ccv->flags |= CCF_ABC_SENTAWND;
307 			}
308 		} else {
309 				tp->ccv->flags &= ~CCF_ABC_SENTAWND;
310 				tp->t_bytes_acked = 0;
311 		}
312 	}
313 
314 	if (CC_ALGO(tp)->ack_received != NULL) {
315 		/* XXXLAS: Find a way to live without this */
316 		tp->ccv->curack = th->th_ack;
317 		CC_ALGO(tp)->ack_received(tp->ccv, type);
318 	}
319 }
320 
321 static void inline
322 cc_conn_init(struct tcpcb *tp)
323 {
324 	struct hc_metrics_lite metrics;
325 	struct inpcb *inp = tp->t_inpcb;
326 	int rtt;
327 
328 	INP_WLOCK_ASSERT(tp->t_inpcb);
329 
330 	tcp_hc_get(&inp->inp_inc, &metrics);
331 
332 	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
333 		tp->t_srtt = rtt;
334 		tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
335 		TCPSTAT_INC(tcps_usedrtt);
336 		if (metrics.rmx_rttvar) {
337 			tp->t_rttvar = metrics.rmx_rttvar;
338 			TCPSTAT_INC(tcps_usedrttvar);
339 		} else {
340 			/* default variation is +- 1 rtt */
341 			tp->t_rttvar =
342 			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
343 		}
344 		TCPT_RANGESET(tp->t_rxtcur,
345 		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
346 		    tp->t_rttmin, TCPTV_REXMTMAX);
347 	}
348 	if (metrics.rmx_ssthresh) {
349 		/*
350 		 * There's some sort of gateway or interface
351 		 * buffer limit on the path.  Use this to set
352 		 * the slow start threshhold, but set the
353 		 * threshold to no less than 2*mss.
354 		 */
355 		tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh);
356 		TCPSTAT_INC(tcps_usedssthresh);
357 	}
358 
359 	/*
360 	 * Set the initial slow-start flight size.
361 	 *
362 	 * RFC5681 Section 3.1 specifies the default conservative values.
363 	 * RFC3390 specifies slightly more aggressive values.
364 	 * Draft-ietf-tcpm-initcwnd-05 increases it to ten segments.
365 	 *
366 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
367 	 * reduce the initial CWND to one segment as congestion is likely
368 	 * requiring us to be cautious.
369 	 */
370 	if (tp->snd_cwnd == 1)
371 		tp->snd_cwnd = tp->t_maxseg;		/* SYN(-ACK) lost */
372 	else if (V_tcp_do_initcwnd10)
373 		tp->snd_cwnd = min(10 * tp->t_maxseg,
374 		    max(2 * tp->t_maxseg, 14600));
375 	else if (V_tcp_do_rfc3390)
376 		tp->snd_cwnd = min(4 * tp->t_maxseg,
377 		    max(2 * tp->t_maxseg, 4380));
378 	else {
379 		/* Per RFC5681 Section 3.1 */
380 		if (tp->t_maxseg > 2190)
381 			tp->snd_cwnd = 2 * tp->t_maxseg;
382 		else if (tp->t_maxseg > 1095)
383 			tp->snd_cwnd = 3 * tp->t_maxseg;
384 		else
385 			tp->snd_cwnd = 4 * tp->t_maxseg;
386 	}
387 
388 	if (CC_ALGO(tp)->conn_init != NULL)
389 		CC_ALGO(tp)->conn_init(tp->ccv);
390 }
391 
392 void inline
393 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
394 {
395 	INP_WLOCK_ASSERT(tp->t_inpcb);
396 
397 	switch(type) {
398 	case CC_NDUPACK:
399 		if (!IN_FASTRECOVERY(tp->t_flags)) {
400 			tp->snd_recover = tp->snd_max;
401 			if (tp->t_flags & TF_ECN_PERMIT)
402 				tp->t_flags |= TF_ECN_SND_CWR;
403 		}
404 		break;
405 	case CC_ECN:
406 		if (!IN_CONGRECOVERY(tp->t_flags)) {
407 			TCPSTAT_INC(tcps_ecn_rcwnd);
408 			tp->snd_recover = tp->snd_max;
409 			if (tp->t_flags & TF_ECN_PERMIT)
410 				tp->t_flags |= TF_ECN_SND_CWR;
411 		}
412 		break;
413 	case CC_RTO:
414 		tp->t_dupacks = 0;
415 		tp->t_bytes_acked = 0;
416 		EXIT_RECOVERY(tp->t_flags);
417 		tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
418 		    tp->t_maxseg) * tp->t_maxseg;
419 		tp->snd_cwnd = tp->t_maxseg;
420 		break;
421 	case CC_RTO_ERR:
422 		TCPSTAT_INC(tcps_sndrexmitbad);
423 		/* RTO was unnecessary, so reset everything. */
424 		tp->snd_cwnd = tp->snd_cwnd_prev;
425 		tp->snd_ssthresh = tp->snd_ssthresh_prev;
426 		tp->snd_recover = tp->snd_recover_prev;
427 		if (tp->t_flags & TF_WASFRECOVERY)
428 			ENTER_FASTRECOVERY(tp->t_flags);
429 		if (tp->t_flags & TF_WASCRECOVERY)
430 			ENTER_CONGRECOVERY(tp->t_flags);
431 		tp->snd_nxt = tp->snd_max;
432 		tp->t_flags &= ~TF_PREVVALID;
433 		tp->t_badrxtwin = 0;
434 		break;
435 	}
436 
437 	if (CC_ALGO(tp)->cong_signal != NULL) {
438 		if (th != NULL)
439 			tp->ccv->curack = th->th_ack;
440 		CC_ALGO(tp)->cong_signal(tp->ccv, type);
441 	}
442 }
443 
444 static void inline
445 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
446 {
447 	INP_WLOCK_ASSERT(tp->t_inpcb);
448 
449 	/* XXXLAS: KASSERT that we're in recovery? */
450 
451 	if (CC_ALGO(tp)->post_recovery != NULL) {
452 		tp->ccv->curack = th->th_ack;
453 		CC_ALGO(tp)->post_recovery(tp->ccv);
454 	}
455 	/* XXXLAS: EXIT_RECOVERY ? */
456 	tp->t_bytes_acked = 0;
457 }
458 
459 static inline void
460 tcp_fields_to_host(struct tcphdr *th)
461 {
462 
463 	th->th_seq = ntohl(th->th_seq);
464 	th->th_ack = ntohl(th->th_ack);
465 	th->th_win = ntohs(th->th_win);
466 	th->th_urp = ntohs(th->th_urp);
467 }
468 
469 #ifdef TCP_SIGNATURE
470 static inline void
471 tcp_fields_to_net(struct tcphdr *th)
472 {
473 
474 	th->th_seq = htonl(th->th_seq);
475 	th->th_ack = htonl(th->th_ack);
476 	th->th_win = htons(th->th_win);
477 	th->th_urp = htons(th->th_urp);
478 }
479 
480 static inline int
481 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
482     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
483 {
484 	int ret;
485 
486 	tcp_fields_to_net(th);
487 	ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
488 	tcp_fields_to_host(th);
489 	return (ret);
490 }
491 #endif
492 
493 /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
494 #ifdef INET6
495 #define ND6_HINT(tp) \
496 do { \
497 	if ((tp) && (tp)->t_inpcb && \
498 	    ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \
499 		nd6_nud_hint(NULL, NULL, 0); \
500 } while (0)
501 #else
502 #define ND6_HINT(tp)
503 #endif
504 
505 /*
506  * Indicate whether this ack should be delayed.  We can delay the ack if
507  *	- there is no delayed ack timer in progress and
508  *	- our last ack wasn't a 0-sized window.  We never want to delay
509  *	  the ack that opens up a 0-sized window and
510  *		- delayed acks are enabled or
511  *		- this is a half-synchronized T/TCP connection.
512  *	- the segment size is not larger than the MSS and LRO wasn't used
513  *	  for this segment.
514  */
515 #define DELAY_ACK(tp, tlen)						\
516 	((!tcp_timer_active(tp, TT_DELACK) &&				\
517 	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
518 	    (tlen <= tp->t_maxopd) &&					\
519 	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
520 
521 /*
522  * TCP input handling is split into multiple parts:
523  *   tcp6_input is a thin wrapper around tcp_input for the extended
524  *	ip6_protox[] call format in ip6_input
525  *   tcp_input handles primary segment validation, inpcb lookup and
526  *	SYN processing on listen sockets
527  *   tcp_do_segment processes the ACK and text of the segment for
528  *	establishing, established and closing connections
529  */
530 #ifdef INET6
531 int
532 tcp6_input(struct mbuf **mp, int *offp, int proto)
533 {
534 	struct mbuf *m = *mp;
535 	struct in6_ifaddr *ia6;
536 
537 	IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
538 
539 	/*
540 	 * draft-itojun-ipv6-tcp-to-anycast
541 	 * better place to put this in?
542 	 */
543 	ia6 = ip6_getdstifaddr(m);
544 	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
545 		struct ip6_hdr *ip6;
546 
547 		ifa_free(&ia6->ia_ifa);
548 		ip6 = mtod(m, struct ip6_hdr *);
549 		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
550 			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
551 		return IPPROTO_DONE;
552 	}
553 	if (ia6)
554 		ifa_free(&ia6->ia_ifa);
555 
556 	tcp_input(m, *offp);
557 	return IPPROTO_DONE;
558 }
559 #endif /* INET6 */
560 
561 void
562 tcp_input(struct mbuf *m, int off0)
563 {
564 	struct tcphdr *th = NULL;
565 	struct ip *ip = NULL;
566 	struct inpcb *inp = NULL;
567 	struct tcpcb *tp = NULL;
568 	struct socket *so = NULL;
569 	u_char *optp = NULL;
570 	int optlen = 0;
571 #ifdef INET
572 	int len;
573 #endif
574 	int tlen = 0, off;
575 	int drop_hdrlen;
576 	int thflags;
577 	int rstreason = 0;	/* For badport_bandlim accounting purposes */
578 #ifdef TCP_SIGNATURE
579 	uint8_t sig_checked = 0;
580 #endif
581 	uint8_t iptos = 0;
582 	struct m_tag *fwd_tag = NULL;
583 #ifdef INET6
584 	struct ip6_hdr *ip6 = NULL;
585 	int isipv6;
586 #else
587 	const void *ip6 = NULL;
588 #endif /* INET6 */
589 	struct tcpopt to;		/* options in this segment */
590 	char *s = NULL;			/* address and port logging */
591 	int ti_locked;
592 #define	TI_UNLOCKED	1
593 #define	TI_WLOCKED	2
594 
595 #ifdef TCPDEBUG
596 	/*
597 	 * The size of tcp_saveipgen must be the size of the max ip header,
598 	 * now IPv6.
599 	 */
600 	u_char tcp_saveipgen[IP6_HDR_LEN];
601 	struct tcphdr tcp_savetcp;
602 	short ostate = 0;
603 #endif
604 
605 #ifdef INET6
606 	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
607 #endif
608 
609 	to.to_flags = 0;
610 	TCPSTAT_INC(tcps_rcvtotal);
611 
612 #ifdef INET6
613 	if (isipv6) {
614 		/* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
615 
616 		if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
617 			m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
618 			if (m == NULL) {
619 				TCPSTAT_INC(tcps_rcvshort);
620 				return;
621 			}
622 		}
623 
624 		ip6 = mtod(m, struct ip6_hdr *);
625 		th = (struct tcphdr *)((caddr_t)ip6 + off0);
626 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
627 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
628 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
629 				th->th_sum = m->m_pkthdr.csum_data;
630 			else
631 				th->th_sum = in6_cksum_pseudo(ip6, tlen,
632 				    IPPROTO_TCP, m->m_pkthdr.csum_data);
633 			th->th_sum ^= 0xffff;
634 		} else
635 			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
636 		if (th->th_sum) {
637 			TCPSTAT_INC(tcps_rcvbadsum);
638 			goto drop;
639 		}
640 
641 		/*
642 		 * Be proactive about unspecified IPv6 address in source.
643 		 * As we use all-zero to indicate unbounded/unconnected pcb,
644 		 * unspecified IPv6 address can be used to confuse us.
645 		 *
646 		 * Note that packets with unspecified IPv6 destination is
647 		 * already dropped in ip6_input.
648 		 */
649 		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
650 			/* XXX stat */
651 			goto drop;
652 		}
653 	}
654 #endif
655 #if defined(INET) && defined(INET6)
656 	else
657 #endif
658 #ifdef INET
659 	{
660 		/*
661 		 * Get IP and TCP header together in first mbuf.
662 		 * Note: IP leaves IP header in first mbuf.
663 		 */
664 		if (off0 > sizeof (struct ip)) {
665 			ip_stripoptions(m);
666 			off0 = sizeof(struct ip);
667 		}
668 		if (m->m_len < sizeof (struct tcpiphdr)) {
669 			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
670 			    == NULL) {
671 				TCPSTAT_INC(tcps_rcvshort);
672 				return;
673 			}
674 		}
675 		ip = mtod(m, struct ip *);
676 		th = (struct tcphdr *)((caddr_t)ip + off0);
677 		tlen = ntohs(ip->ip_len) - off0;
678 
679 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
680 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
681 				th->th_sum = m->m_pkthdr.csum_data;
682 			else
683 				th->th_sum = in_pseudo(ip->ip_src.s_addr,
684 				    ip->ip_dst.s_addr,
685 				    htonl(m->m_pkthdr.csum_data + tlen +
686 				    IPPROTO_TCP));
687 			th->th_sum ^= 0xffff;
688 		} else {
689 			struct ipovly *ipov = (struct ipovly *)ip;
690 
691 			/*
692 			 * Checksum extended TCP header and data.
693 			 */
694 			len = off0 + tlen;
695 			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
696 			ipov->ih_len = htons(tlen);
697 			th->th_sum = in_cksum(m, len);
698 			/* Reset length for SDT probes. */
699 			ip->ip_len = htons(tlen + off0);
700 		}
701 
702 		if (th->th_sum) {
703 			TCPSTAT_INC(tcps_rcvbadsum);
704 			goto drop;
705 		}
706 		/* Re-initialization for later version check */
707 		ip->ip_v = IPVERSION;
708 	}
709 #endif /* INET */
710 
711 #ifdef INET6
712 	if (isipv6)
713 		iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
714 #endif
715 #if defined(INET) && defined(INET6)
716 	else
717 #endif
718 #ifdef INET
719 		iptos = ip->ip_tos;
720 #endif
721 
722 	/*
723 	 * Check that TCP offset makes sense,
724 	 * pull out TCP options and adjust length.		XXX
725 	 */
726 	off = th->th_off << 2;
727 	if (off < sizeof (struct tcphdr) || off > tlen) {
728 		TCPSTAT_INC(tcps_rcvbadoff);
729 		goto drop;
730 	}
731 	tlen -= off;	/* tlen is used instead of ti->ti_len */
732 	if (off > sizeof (struct tcphdr)) {
733 #ifdef INET6
734 		if (isipv6) {
735 			IP6_EXTHDR_CHECK(m, off0, off, );
736 			ip6 = mtod(m, struct ip6_hdr *);
737 			th = (struct tcphdr *)((caddr_t)ip6 + off0);
738 		}
739 #endif
740 #if defined(INET) && defined(INET6)
741 		else
742 #endif
743 #ifdef INET
744 		{
745 			if (m->m_len < sizeof(struct ip) + off) {
746 				if ((m = m_pullup(m, sizeof (struct ip) + off))
747 				    == NULL) {
748 					TCPSTAT_INC(tcps_rcvshort);
749 					return;
750 				}
751 				ip = mtod(m, struct ip *);
752 				th = (struct tcphdr *)((caddr_t)ip + off0);
753 			}
754 		}
755 #endif
756 		optlen = off - sizeof (struct tcphdr);
757 		optp = (u_char *)(th + 1);
758 	}
759 	thflags = th->th_flags;
760 
761 	/*
762 	 * Convert TCP protocol specific fields to host format.
763 	 */
764 	tcp_fields_to_host(th);
765 
766 	/*
767 	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
768 	 */
769 	drop_hdrlen = off0 + off;
770 
771 	/*
772 	 * Locate pcb for segment; if we're likely to add or remove a
773 	 * connection then first acquire pcbinfo lock.  There are two cases
774 	 * where we might discover later we need a write lock despite the
775 	 * flags: ACKs moving a connection out of the syncache, and ACKs for
776 	 * a connection in TIMEWAIT.
777 	 */
778 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0) {
779 		INP_INFO_WLOCK(&V_tcbinfo);
780 		ti_locked = TI_WLOCKED;
781 	} else
782 		ti_locked = TI_UNLOCKED;
783 
784 	/*
785 	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
786 	 */
787         if (
788 #ifdef INET6
789 	    (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
790 #ifdef INET
791 	    || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
792 #endif
793 #endif
794 #if defined(INET) && !defined(INET6)
795 	    (m->m_flags & M_IP_NEXTHOP)
796 #endif
797 	    )
798 		fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
799 
800 findpcb:
801 #ifdef INVARIANTS
802 	if (ti_locked == TI_WLOCKED) {
803 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
804 	} else {
805 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
806 	}
807 #endif
808 #ifdef INET6
809 	if (isipv6 && fwd_tag != NULL) {
810 		struct sockaddr_in6 *next_hop6;
811 
812 		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
813 		/*
814 		 * Transparently forwarded. Pretend to be the destination.
815 		 * Already got one like this?
816 		 */
817 		inp = in6_pcblookup_mbuf(&V_tcbinfo,
818 		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
819 		    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
820 		if (!inp) {
821 			/*
822 			 * It's new.  Try to find the ambushing socket.
823 			 * Because we've rewritten the destination address,
824 			 * any hardware-generated hash is ignored.
825 			 */
826 			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
827 			    th->th_sport, &next_hop6->sin6_addr,
828 			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
829 			    th->th_dport, INPLOOKUP_WILDCARD |
830 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
831 		}
832 	} else if (isipv6) {
833 		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
834 		    th->th_sport, &ip6->ip6_dst, th->th_dport,
835 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
836 		    m->m_pkthdr.rcvif, m);
837 	}
838 #endif /* INET6 */
839 #if defined(INET6) && defined(INET)
840 	else
841 #endif
842 #ifdef INET
843 	if (fwd_tag != NULL) {
844 		struct sockaddr_in *next_hop;
845 
846 		next_hop = (struct sockaddr_in *)(fwd_tag+1);
847 		/*
848 		 * Transparently forwarded. Pretend to be the destination.
849 		 * already got one like this?
850 		 */
851 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
852 		    ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
853 		    m->m_pkthdr.rcvif, m);
854 		if (!inp) {
855 			/*
856 			 * It's new.  Try to find the ambushing socket.
857 			 * Because we've rewritten the destination address,
858 			 * any hardware-generated hash is ignored.
859 			 */
860 			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
861 			    th->th_sport, next_hop->sin_addr,
862 			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
863 			    th->th_dport, INPLOOKUP_WILDCARD |
864 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
865 		}
866 	} else
867 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
868 		    th->th_sport, ip->ip_dst, th->th_dport,
869 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
870 		    m->m_pkthdr.rcvif, m);
871 #endif /* INET */
872 
873 	/*
874 	 * If the INPCB does not exist then all data in the incoming
875 	 * segment is discarded and an appropriate RST is sent back.
876 	 * XXX MRT Send RST using which routing table?
877 	 */
878 	if (inp == NULL) {
879 		/*
880 		 * Log communication attempts to ports that are not
881 		 * in use.
882 		 */
883 		if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
884 		    tcp_log_in_vain == 2) {
885 			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
886 				log(LOG_INFO, "%s; %s: Connection attempt "
887 				    "to closed port\n", s, __func__);
888 		}
889 		/*
890 		 * When blackholing do not respond with a RST but
891 		 * completely ignore the segment and drop it.
892 		 */
893 		if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
894 		    V_blackhole == 2)
895 			goto dropunlock;
896 
897 		rstreason = BANDLIM_RST_CLOSEDPORT;
898 		goto dropwithreset;
899 	}
900 	INP_WLOCK_ASSERT(inp);
901 	if (!(inp->inp_flags & INP_HW_FLOWID)
902 	    && (m->m_flags & M_FLOWID)
903 	    && ((inp->inp_socket == NULL)
904 		|| !(inp->inp_socket->so_options & SO_ACCEPTCONN))) {
905 		inp->inp_flags |= INP_HW_FLOWID;
906 		inp->inp_flags &= ~INP_SW_FLOWID;
907 		inp->inp_flowid = m->m_pkthdr.flowid;
908 	}
909 #ifdef IPSEC
910 #ifdef INET6
911 	if (isipv6 && ipsec6_in_reject(m, inp)) {
912 		IPSEC6STAT_INC(ips_in_polvio);
913 		goto dropunlock;
914 	} else
915 #endif /* INET6 */
916 	if (ipsec4_in_reject(m, inp) != 0) {
917 		IPSECSTAT_INC(ips_in_polvio);
918 		goto dropunlock;
919 	}
920 #endif /* IPSEC */
921 
922 	/*
923 	 * Check the minimum TTL for socket.
924 	 */
925 	if (inp->inp_ip_minttl != 0) {
926 #ifdef INET6
927 		if (isipv6 && inp->inp_ip_minttl > ip6->ip6_hlim)
928 			goto dropunlock;
929 		else
930 #endif
931 		if (inp->inp_ip_minttl > ip->ip_ttl)
932 			goto dropunlock;
933 	}
934 
935 	/*
936 	 * A previous connection in TIMEWAIT state is supposed to catch stray
937 	 * or duplicate segments arriving late.  If this segment was a
938 	 * legitimate new connection attempt, the old INPCB gets removed and
939 	 * we can try again to find a listening socket.
940 	 *
941 	 * At this point, due to earlier optimism, we may hold only an inpcb
942 	 * lock, and not the inpcbinfo write lock.  If so, we need to try to
943 	 * acquire it, or if that fails, acquire a reference on the inpcb,
944 	 * drop all locks, acquire a global write lock, and then re-acquire
945 	 * the inpcb lock.  We may at that point discover that another thread
946 	 * has tried to free the inpcb, in which case we need to loop back
947 	 * and try to find a new inpcb to deliver to.
948 	 *
949 	 * XXXRW: It may be time to rethink timewait locking.
950 	 */
951 relocked:
952 	if (inp->inp_flags & INP_TIMEWAIT) {
953 		if (ti_locked == TI_UNLOCKED) {
954 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
955 				in_pcbref(inp);
956 				INP_WUNLOCK(inp);
957 				INP_INFO_WLOCK(&V_tcbinfo);
958 				ti_locked = TI_WLOCKED;
959 				INP_WLOCK(inp);
960 				if (in_pcbrele_wlocked(inp)) {
961 					inp = NULL;
962 					goto findpcb;
963 				}
964 			} else
965 				ti_locked = TI_WLOCKED;
966 		}
967 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
968 
969 		if (thflags & TH_SYN)
970 			tcp_dooptions(&to, optp, optlen, TO_SYN);
971 		/*
972 		 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
973 		 */
974 		if (tcp_twcheck(inp, &to, th, m, tlen))
975 			goto findpcb;
976 		INP_INFO_WUNLOCK(&V_tcbinfo);
977 		return;
978 	}
979 	/*
980 	 * The TCPCB may no longer exist if the connection is winding
981 	 * down or it is in the CLOSED state.  Either way we drop the
982 	 * segment and send an appropriate response.
983 	 */
984 	tp = intotcpcb(inp);
985 	if (tp == NULL || tp->t_state == TCPS_CLOSED) {
986 		rstreason = BANDLIM_RST_CLOSEDPORT;
987 		goto dropwithreset;
988 	}
989 
990 #ifdef TCP_OFFLOAD
991 	if (tp->t_flags & TF_TOE) {
992 		tcp_offload_input(tp, m);
993 		m = NULL;	/* consumed by the TOE driver */
994 		goto dropunlock;
995 	}
996 #endif
997 
998 	/*
999 	 * We've identified a valid inpcb, but it could be that we need an
1000 	 * inpcbinfo write lock but don't hold it.  In this case, attempt to
1001 	 * acquire using the same strategy as the TIMEWAIT case above.  If we
1002 	 * relock, we have to jump back to 'relocked' as the connection might
1003 	 * now be in TIMEWAIT.
1004 	 */
1005 #ifdef INVARIANTS
1006 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0)
1007 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1008 #endif
1009 	if (tp->t_state != TCPS_ESTABLISHED) {
1010 		if (ti_locked == TI_UNLOCKED) {
1011 			if (INP_INFO_TRY_WLOCK(&V_tcbinfo) == 0) {
1012 				in_pcbref(inp);
1013 				INP_WUNLOCK(inp);
1014 				INP_INFO_WLOCK(&V_tcbinfo);
1015 				ti_locked = TI_WLOCKED;
1016 				INP_WLOCK(inp);
1017 				if (in_pcbrele_wlocked(inp)) {
1018 					inp = NULL;
1019 					goto findpcb;
1020 				}
1021 				goto relocked;
1022 			} else
1023 				ti_locked = TI_WLOCKED;
1024 		}
1025 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1026 	}
1027 
1028 #ifdef MAC
1029 	INP_WLOCK_ASSERT(inp);
1030 	if (mac_inpcb_check_deliver(inp, m))
1031 		goto dropunlock;
1032 #endif
1033 	so = inp->inp_socket;
1034 	KASSERT(so != NULL, ("%s: so == NULL", __func__));
1035 #ifdef TCPDEBUG
1036 	if (so->so_options & SO_DEBUG) {
1037 		ostate = tp->t_state;
1038 #ifdef INET6
1039 		if (isipv6) {
1040 			bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1041 		} else
1042 #endif
1043 			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1044 		tcp_savetcp = *th;
1045 	}
1046 #endif /* TCPDEBUG */
1047 	/*
1048 	 * When the socket is accepting connections (the INPCB is in LISTEN
1049 	 * state) we look into the SYN cache if this is a new connection
1050 	 * attempt or the completion of a previous one.  Because listen
1051 	 * sockets are never in TCPS_ESTABLISHED, the V_tcbinfo lock will be
1052 	 * held in this case.
1053 	 */
1054 	if (so->so_options & SO_ACCEPTCONN) {
1055 		struct in_conninfo inc;
1056 
1057 		KASSERT(tp->t_state == TCPS_LISTEN, ("%s: so accepting but "
1058 		    "tp not listening", __func__));
1059 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1060 
1061 		bzero(&inc, sizeof(inc));
1062 #ifdef INET6
1063 		if (isipv6) {
1064 			inc.inc_flags |= INC_ISIPV6;
1065 			inc.inc6_faddr = ip6->ip6_src;
1066 			inc.inc6_laddr = ip6->ip6_dst;
1067 		} else
1068 #endif
1069 		{
1070 			inc.inc_faddr = ip->ip_src;
1071 			inc.inc_laddr = ip->ip_dst;
1072 		}
1073 		inc.inc_fport = th->th_sport;
1074 		inc.inc_lport = th->th_dport;
1075 		inc.inc_fibnum = so->so_fibnum;
1076 
1077 		/*
1078 		 * Check for an existing connection attempt in syncache if
1079 		 * the flag is only ACK.  A successful lookup creates a new
1080 		 * socket appended to the listen queue in SYN_RECEIVED state.
1081 		 */
1082 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1083 			/*
1084 			 * Parse the TCP options here because
1085 			 * syncookies need access to the reflected
1086 			 * timestamp.
1087 			 */
1088 			tcp_dooptions(&to, optp, optlen, 0);
1089 			/*
1090 			 * NB: syncache_expand() doesn't unlock
1091 			 * inp and tcpinfo locks.
1092 			 */
1093 			if (!syncache_expand(&inc, &to, th, &so, m)) {
1094 				/*
1095 				 * No syncache entry or ACK was not
1096 				 * for our SYN/ACK.  Send a RST.
1097 				 * NB: syncache did its own logging
1098 				 * of the failure cause.
1099 				 */
1100 				rstreason = BANDLIM_RST_OPENPORT;
1101 				goto dropwithreset;
1102 			}
1103 			if (so == NULL) {
1104 				/*
1105 				 * We completed the 3-way handshake
1106 				 * but could not allocate a socket
1107 				 * either due to memory shortage,
1108 				 * listen queue length limits or
1109 				 * global socket limits.  Send RST
1110 				 * or wait and have the remote end
1111 				 * retransmit the ACK for another
1112 				 * try.
1113 				 */
1114 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1115 					log(LOG_DEBUG, "%s; %s: Listen socket: "
1116 					    "Socket allocation failed due to "
1117 					    "limits or memory shortage, %s\n",
1118 					    s, __func__,
1119 					    V_tcp_sc_rst_sock_fail ?
1120 					    "sending RST" : "try again");
1121 				if (V_tcp_sc_rst_sock_fail) {
1122 					rstreason = BANDLIM_UNLIMITED;
1123 					goto dropwithreset;
1124 				} else
1125 					goto dropunlock;
1126 			}
1127 			/*
1128 			 * Socket is created in state SYN_RECEIVED.
1129 			 * Unlock the listen socket, lock the newly
1130 			 * created socket and update the tp variable.
1131 			 */
1132 			INP_WUNLOCK(inp);	/* listen socket */
1133 			inp = sotoinpcb(so);
1134 			INP_WLOCK(inp);		/* new connection */
1135 			tp = intotcpcb(inp);
1136 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1137 			    ("%s: ", __func__));
1138 #ifdef TCP_SIGNATURE
1139 			if (sig_checked == 0)  {
1140 				tcp_dooptions(&to, optp, optlen,
1141 				    (thflags & TH_SYN) ? TO_SYN : 0);
1142 				if (!tcp_signature_verify_input(m, off0, tlen,
1143 				    optlen, &to, th, tp->t_flags)) {
1144 
1145 					/*
1146 					 * In SYN_SENT state if it receives an
1147 					 * RST, it is allowed for further
1148 					 * processing.
1149 					 */
1150 					if ((thflags & TH_RST) == 0 ||
1151 					    (tp->t_state == TCPS_SYN_SENT) == 0)
1152 						goto dropunlock;
1153 				}
1154 				sig_checked = 1;
1155 			}
1156 #endif
1157 
1158 			/*
1159 			 * Process the segment and the data it
1160 			 * contains.  tcp_do_segment() consumes
1161 			 * the mbuf chain and unlocks the inpcb.
1162 			 */
1163 			tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1164 			    iptos, ti_locked);
1165 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1166 			return;
1167 		}
1168 		/*
1169 		 * Segment flag validation for new connection attempts:
1170 		 *
1171 		 * Our (SYN|ACK) response was rejected.
1172 		 * Check with syncache and remove entry to prevent
1173 		 * retransmits.
1174 		 *
1175 		 * NB: syncache_chkrst does its own logging of failure
1176 		 * causes.
1177 		 */
1178 		if (thflags & TH_RST) {
1179 			syncache_chkrst(&inc, th);
1180 			goto dropunlock;
1181 		}
1182 		/*
1183 		 * We can't do anything without SYN.
1184 		 */
1185 		if ((thflags & TH_SYN) == 0) {
1186 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1187 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1188 				    "SYN is missing, segment ignored\n",
1189 				    s, __func__);
1190 			TCPSTAT_INC(tcps_badsyn);
1191 			goto dropunlock;
1192 		}
1193 		/*
1194 		 * (SYN|ACK) is bogus on a listen socket.
1195 		 */
1196 		if (thflags & TH_ACK) {
1197 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1198 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1199 				    "SYN|ACK invalid, segment rejected\n",
1200 				    s, __func__);
1201 			syncache_badack(&inc);	/* XXX: Not needed! */
1202 			TCPSTAT_INC(tcps_badsyn);
1203 			rstreason = BANDLIM_RST_OPENPORT;
1204 			goto dropwithreset;
1205 		}
1206 		/*
1207 		 * If the drop_synfin option is enabled, drop all
1208 		 * segments with both the SYN and FIN bits set.
1209 		 * This prevents e.g. nmap from identifying the
1210 		 * TCP/IP stack.
1211 		 * XXX: Poor reasoning.  nmap has other methods
1212 		 * and is constantly refining its stack detection
1213 		 * strategies.
1214 		 * XXX: This is a violation of the TCP specification
1215 		 * and was used by RFC1644.
1216 		 */
1217 		if ((thflags & TH_FIN) && V_drop_synfin) {
1218 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1219 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1220 				    "SYN|FIN segment ignored (based on "
1221 				    "sysctl setting)\n", s, __func__);
1222 			TCPSTAT_INC(tcps_badsyn);
1223 			goto dropunlock;
1224 		}
1225 		/*
1226 		 * Segment's flags are (SYN) or (SYN|FIN).
1227 		 *
1228 		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1229 		 * as they do not affect the state of the TCP FSM.
1230 		 * The data pointed to by TH_URG and th_urp is ignored.
1231 		 */
1232 		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1233 		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1234 		KASSERT(thflags & (TH_SYN),
1235 		    ("%s: Listen socket: TH_SYN not set", __func__));
1236 #ifdef INET6
1237 		/*
1238 		 * If deprecated address is forbidden,
1239 		 * we do not accept SYN to deprecated interface
1240 		 * address to prevent any new inbound connection from
1241 		 * getting established.
1242 		 * When we do not accept SYN, we send a TCP RST,
1243 		 * with deprecated source address (instead of dropping
1244 		 * it).  We compromise it as it is much better for peer
1245 		 * to send a RST, and RST will be the final packet
1246 		 * for the exchange.
1247 		 *
1248 		 * If we do not forbid deprecated addresses, we accept
1249 		 * the SYN packet.  RFC2462 does not suggest dropping
1250 		 * SYN in this case.
1251 		 * If we decipher RFC2462 5.5.4, it says like this:
1252 		 * 1. use of deprecated addr with existing
1253 		 *    communication is okay - "SHOULD continue to be
1254 		 *    used"
1255 		 * 2. use of it with new communication:
1256 		 *   (2a) "SHOULD NOT be used if alternate address
1257 		 *        with sufficient scope is available"
1258 		 *   (2b) nothing mentioned otherwise.
1259 		 * Here we fall into (2b) case as we have no choice in
1260 		 * our source address selection - we must obey the peer.
1261 		 *
1262 		 * The wording in RFC2462 is confusing, and there are
1263 		 * multiple description text for deprecated address
1264 		 * handling - worse, they are not exactly the same.
1265 		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1266 		 */
1267 		if (isipv6 && !V_ip6_use_deprecated) {
1268 			struct in6_ifaddr *ia6;
1269 
1270 			ia6 = ip6_getdstifaddr(m);
1271 			if (ia6 != NULL &&
1272 			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1273 				ifa_free(&ia6->ia_ifa);
1274 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1275 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1276 					"Connection attempt to deprecated "
1277 					"IPv6 address rejected\n",
1278 					s, __func__);
1279 				rstreason = BANDLIM_RST_OPENPORT;
1280 				goto dropwithreset;
1281 			}
1282 			if (ia6)
1283 				ifa_free(&ia6->ia_ifa);
1284 		}
1285 #endif /* INET6 */
1286 		/*
1287 		 * Basic sanity checks on incoming SYN requests:
1288 		 *   Don't respond if the destination is a link layer
1289 		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1290 		 *   If it is from this socket it must be forged.
1291 		 *   Don't respond if the source or destination is a
1292 		 *	global or subnet broad- or multicast address.
1293 		 *   Note that it is quite possible to receive unicast
1294 		 *	link-layer packets with a broadcast IP address. Use
1295 		 *	in_broadcast() to find them.
1296 		 */
1297 		if (m->m_flags & (M_BCAST|M_MCAST)) {
1298 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1299 			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1300 				"Connection attempt from broad- or multicast "
1301 				"link layer address ignored\n", s, __func__);
1302 			goto dropunlock;
1303 		}
1304 #ifdef INET6
1305 		if (isipv6) {
1306 			if (th->th_dport == th->th_sport &&
1307 			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1308 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1309 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1310 					"Connection attempt to/from self "
1311 					"ignored\n", s, __func__);
1312 				goto dropunlock;
1313 			}
1314 			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1315 			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1316 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1317 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1318 					"Connection attempt from/to multicast "
1319 					"address ignored\n", s, __func__);
1320 				goto dropunlock;
1321 			}
1322 		}
1323 #endif
1324 #if defined(INET) && defined(INET6)
1325 		else
1326 #endif
1327 #ifdef INET
1328 		{
1329 			if (th->th_dport == th->th_sport &&
1330 			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1331 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1332 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1333 					"Connection attempt from/to self "
1334 					"ignored\n", s, __func__);
1335 				goto dropunlock;
1336 			}
1337 			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1338 			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1339 			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1340 			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1341 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1342 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1343 					"Connection attempt from/to broad- "
1344 					"or multicast address ignored\n",
1345 					s, __func__);
1346 				goto dropunlock;
1347 			}
1348 		}
1349 #endif
1350 		/*
1351 		 * SYN appears to be valid.  Create compressed TCP state
1352 		 * for syncache.
1353 		 */
1354 #ifdef TCPDEBUG
1355 		if (so->so_options & SO_DEBUG)
1356 			tcp_trace(TA_INPUT, ostate, tp,
1357 			    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1358 #endif
1359 		tcp_dooptions(&to, optp, optlen, TO_SYN);
1360 		syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
1361 		/*
1362 		 * Entry added to syncache and mbuf consumed.
1363 		 * Everything already unlocked by syncache_add().
1364 		 */
1365 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1366 		return;
1367 	} else if (tp->t_state == TCPS_LISTEN) {
1368 		/*
1369 		 * When a listen socket is torn down the SO_ACCEPTCONN
1370 		 * flag is removed first while connections are drained
1371 		 * from the accept queue in a unlock/lock cycle of the
1372 		 * ACCEPT_LOCK, opening a race condition allowing a SYN
1373 		 * attempt go through unhandled.
1374 		 */
1375 		goto dropunlock;
1376 	}
1377 
1378 #ifdef TCP_SIGNATURE
1379 	if (sig_checked == 0)  {
1380 		tcp_dooptions(&to, optp, optlen,
1381 		    (thflags & TH_SYN) ? TO_SYN : 0);
1382 		if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
1383 		    th, tp->t_flags)) {
1384 
1385 			/*
1386 			 * In SYN_SENT state if it receives an RST, it is
1387 			 * allowed for further processing.
1388 			 */
1389 			if ((thflags & TH_RST) == 0 ||
1390 			    (tp->t_state == TCPS_SYN_SENT) == 0)
1391 				goto dropunlock;
1392 		}
1393 		sig_checked = 1;
1394 	}
1395 #endif
1396 
1397 	TCP_PROBE5(receive, NULL, tp, m->m_data, tp, th);
1398 
1399 	/*
1400 	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1401 	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1402 	 * the inpcb, and unlocks pcbinfo.
1403 	 */
1404 	tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
1405 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1406 	return;
1407 
1408 dropwithreset:
1409 	TCP_PROBE5(receive, NULL, tp, m->m_data, tp, th);
1410 
1411 	if (ti_locked == TI_WLOCKED) {
1412 		INP_INFO_WUNLOCK(&V_tcbinfo);
1413 		ti_locked = TI_UNLOCKED;
1414 	}
1415 #ifdef INVARIANTS
1416 	else {
1417 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1418 		    "ti_locked: %d", __func__, ti_locked));
1419 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1420 	}
1421 #endif
1422 
1423 	if (inp != NULL) {
1424 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1425 		INP_WUNLOCK(inp);
1426 	} else
1427 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1428 	m = NULL;	/* mbuf chain got consumed. */
1429 	goto drop;
1430 
1431 dropunlock:
1432 	if (m != NULL)
1433 		TCP_PROBE5(receive, NULL, tp, m->m_data, tp, th);
1434 
1435 	if (ti_locked == TI_WLOCKED) {
1436 		INP_INFO_WUNLOCK(&V_tcbinfo);
1437 		ti_locked = TI_UNLOCKED;
1438 	}
1439 #ifdef INVARIANTS
1440 	else {
1441 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1442 		    "ti_locked: %d", __func__, ti_locked));
1443 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1444 	}
1445 #endif
1446 
1447 	if (inp != NULL)
1448 		INP_WUNLOCK(inp);
1449 
1450 drop:
1451 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1452 	if (s != NULL)
1453 		free(s, M_TCPLOG);
1454 	if (m != NULL)
1455 		m_freem(m);
1456 }
1457 
1458 static void
1459 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1460     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
1461     int ti_locked)
1462 {
1463 	int thflags, acked, ourfinisacked, needoutput = 0;
1464 	int rstreason, todrop, win;
1465 	u_long tiwin;
1466 	char *s;
1467 	struct in_conninfo *inc;
1468 	struct mbuf *mfree;
1469 	struct tcpopt to;
1470 
1471 #ifdef TCPDEBUG
1472 	/*
1473 	 * The size of tcp_saveipgen must be the size of the max ip header,
1474 	 * now IPv6.
1475 	 */
1476 	u_char tcp_saveipgen[IP6_HDR_LEN];
1477 	struct tcphdr tcp_savetcp;
1478 	short ostate = 0;
1479 #endif
1480 	thflags = th->th_flags;
1481 	inc = &tp->t_inpcb->inp_inc;
1482 	tp->sackhint.last_sack_ack = 0;
1483 
1484 	/*
1485 	 * If this is either a state-changing packet or current state isn't
1486 	 * established, we require a write lock on tcbinfo.  Otherwise, we
1487 	 * allow the tcbinfo to be in either alocked or unlocked, as the
1488 	 * caller may have unnecessarily acquired a write lock due to a race.
1489 	 */
1490 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1491 	    tp->t_state != TCPS_ESTABLISHED) {
1492 		KASSERT(ti_locked == TI_WLOCKED, ("%s ti_locked %d for "
1493 		    "SYN/FIN/RST/!EST", __func__, ti_locked));
1494 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1495 	} else {
1496 #ifdef INVARIANTS
1497 		if (ti_locked == TI_WLOCKED)
1498 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
1499 		else {
1500 			KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
1501 			    "ti_locked: %d", __func__, ti_locked));
1502 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1503 		}
1504 #endif
1505 	}
1506 	INP_WLOCK_ASSERT(tp->t_inpcb);
1507 	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1508 	    __func__));
1509 	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1510 	    __func__));
1511 
1512 	/*
1513 	 * Segment received on connection.
1514 	 * Reset idle time and keep-alive timer.
1515 	 * XXX: This should be done after segment
1516 	 * validation to ignore broken/spoofed segs.
1517 	 */
1518 	tp->t_rcvtime = ticks;
1519 	if (TCPS_HAVEESTABLISHED(tp->t_state))
1520 		tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
1521 
1522 	/*
1523 	 * Unscale the window into a 32-bit value.
1524 	 * For the SYN_SENT state the scale is zero.
1525 	 */
1526 	tiwin = th->th_win << tp->snd_scale;
1527 
1528 	/*
1529 	 * TCP ECN processing.
1530 	 */
1531 	if (tp->t_flags & TF_ECN_PERMIT) {
1532 		if (thflags & TH_CWR)
1533 			tp->t_flags &= ~TF_ECN_SND_ECE;
1534 		switch (iptos & IPTOS_ECN_MASK) {
1535 		case IPTOS_ECN_CE:
1536 			tp->t_flags |= TF_ECN_SND_ECE;
1537 			TCPSTAT_INC(tcps_ecn_ce);
1538 			break;
1539 		case IPTOS_ECN_ECT0:
1540 			TCPSTAT_INC(tcps_ecn_ect0);
1541 			break;
1542 		case IPTOS_ECN_ECT1:
1543 			TCPSTAT_INC(tcps_ecn_ect1);
1544 			break;
1545 		}
1546 		/* Congestion experienced. */
1547 		if (thflags & TH_ECE) {
1548 			cc_cong_signal(tp, th, CC_ECN);
1549 		}
1550 	}
1551 
1552 	/*
1553 	 * Parse options on any incoming segment.
1554 	 */
1555 	tcp_dooptions(&to, (u_char *)(th + 1),
1556 	    (th->th_off << 2) - sizeof(struct tcphdr),
1557 	    (thflags & TH_SYN) ? TO_SYN : 0);
1558 
1559 	/*
1560 	 * If echoed timestamp is later than the current time,
1561 	 * fall back to non RFC1323 RTT calculation.  Normalize
1562 	 * timestamp if syncookies were used when this connection
1563 	 * was established.
1564 	 */
1565 	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1566 		to.to_tsecr -= tp->ts_offset;
1567 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1568 			to.to_tsecr = 0;
1569 	}
1570 	/*
1571 	 * If timestamps were negotiated during SYN/ACK they should
1572 	 * appear on every segment during this session and vice versa.
1573 	 */
1574 	if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1575 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1576 			log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1577 			    "no action\n", s, __func__);
1578 			free(s, M_TCPLOG);
1579 		}
1580 	}
1581 	if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1582 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1583 			log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1584 			    "no action\n", s, __func__);
1585 			free(s, M_TCPLOG);
1586 		}
1587 	}
1588 
1589 	/*
1590 	 * Process options only when we get SYN/ACK back. The SYN case
1591 	 * for incoming connections is handled in tcp_syncache.
1592 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1593 	 * or <SYN,ACK>) segment itself is never scaled.
1594 	 * XXX this is traditional behavior, may need to be cleaned up.
1595 	 */
1596 	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1597 		if ((to.to_flags & TOF_SCALE) &&
1598 		    (tp->t_flags & TF_REQ_SCALE)) {
1599 			tp->t_flags |= TF_RCVD_SCALE;
1600 			tp->snd_scale = to.to_wscale;
1601 		}
1602 		/*
1603 		 * Initial send window.  It will be updated with
1604 		 * the next incoming segment to the scaled value.
1605 		 */
1606 		tp->snd_wnd = th->th_win;
1607 		if (to.to_flags & TOF_TS) {
1608 			tp->t_flags |= TF_RCVD_TSTMP;
1609 			tp->ts_recent = to.to_tsval;
1610 			tp->ts_recent_age = tcp_ts_getticks();
1611 		}
1612 		if (to.to_flags & TOF_MSS)
1613 			tcp_mss(tp, to.to_mss);
1614 		if ((tp->t_flags & TF_SACK_PERMIT) &&
1615 		    (to.to_flags & TOF_SACKPERM) == 0)
1616 			tp->t_flags &= ~TF_SACK_PERMIT;
1617 	}
1618 
1619 	/*
1620 	 * Header prediction: check for the two common cases
1621 	 * of a uni-directional data xfer.  If the packet has
1622 	 * no control flags, is in-sequence, the window didn't
1623 	 * change and we're not retransmitting, it's a
1624 	 * candidate.  If the length is zero and the ack moved
1625 	 * forward, we're the sender side of the xfer.  Just
1626 	 * free the data acked & wake any higher level process
1627 	 * that was blocked waiting for space.  If the length
1628 	 * is non-zero and the ack didn't move, we're the
1629 	 * receiver side.  If we're getting packets in-order
1630 	 * (the reassembly queue is empty), add the data to
1631 	 * the socket buffer and note that we need a delayed ack.
1632 	 * Make sure that the hidden state-flags are also off.
1633 	 * Since we check for TCPS_ESTABLISHED first, it can only
1634 	 * be TH_NEEDSYN.
1635 	 */
1636 	if (tp->t_state == TCPS_ESTABLISHED &&
1637 	    th->th_seq == tp->rcv_nxt &&
1638 	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1639 	    tp->snd_nxt == tp->snd_max &&
1640 	    tiwin && tiwin == tp->snd_wnd &&
1641 	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1642 	    LIST_EMPTY(&tp->t_segq) &&
1643 	    ((to.to_flags & TOF_TS) == 0 ||
1644 	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1645 
1646 		/*
1647 		 * If last ACK falls within this segment's sequence numbers,
1648 		 * record the timestamp.
1649 		 * NOTE that the test is modified according to the latest
1650 		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1651 		 */
1652 		if ((to.to_flags & TOF_TS) != 0 &&
1653 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1654 			tp->ts_recent_age = tcp_ts_getticks();
1655 			tp->ts_recent = to.to_tsval;
1656 		}
1657 
1658 		if (tlen == 0) {
1659 			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1660 			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1661 			    !IN_RECOVERY(tp->t_flags) &&
1662 			    (to.to_flags & TOF_SACK) == 0 &&
1663 			    TAILQ_EMPTY(&tp->snd_holes)) {
1664 				/*
1665 				 * This is a pure ack for outstanding data.
1666 				 */
1667 				if (ti_locked == TI_WLOCKED)
1668 					INP_INFO_WUNLOCK(&V_tcbinfo);
1669 				ti_locked = TI_UNLOCKED;
1670 
1671 				TCPSTAT_INC(tcps_predack);
1672 
1673 				/*
1674 				 * "bad retransmit" recovery.
1675 				 */
1676 				if (tp->t_rxtshift == 1 &&
1677 				    tp->t_flags & TF_PREVVALID &&
1678 				    (int)(ticks - tp->t_badrxtwin) < 0) {
1679 					cc_cong_signal(tp, th, CC_RTO_ERR);
1680 				}
1681 
1682 				/*
1683 				 * Recalculate the transmit timer / rtt.
1684 				 *
1685 				 * Some boxes send broken timestamp replies
1686 				 * during the SYN+ACK phase, ignore
1687 				 * timestamps of 0 or we could calculate a
1688 				 * huge RTT and blow up the retransmit timer.
1689 				 */
1690 				if ((to.to_flags & TOF_TS) != 0 &&
1691 				    to.to_tsecr) {
1692 					u_int t;
1693 
1694 					t = tcp_ts_getticks() - to.to_tsecr;
1695 					if (!tp->t_rttlow || tp->t_rttlow > t)
1696 						tp->t_rttlow = t;
1697 					tcp_xmit_timer(tp,
1698 					    TCP_TS_TO_TICKS(t) + 1);
1699 				} else if (tp->t_rtttime &&
1700 				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1701 					if (!tp->t_rttlow ||
1702 					    tp->t_rttlow > ticks - tp->t_rtttime)
1703 						tp->t_rttlow = ticks - tp->t_rtttime;
1704 					tcp_xmit_timer(tp,
1705 							ticks - tp->t_rtttime);
1706 				}
1707 				acked = BYTES_THIS_ACK(tp, th);
1708 
1709 				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1710 				hhook_run_tcp_est_in(tp, th, &to);
1711 
1712 				TCPSTAT_INC(tcps_rcvackpack);
1713 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1714 				sbdrop(&so->so_snd, acked);
1715 				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1716 				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1717 					tp->snd_recover = th->th_ack - 1;
1718 
1719 				/*
1720 				 * Let the congestion control algorithm update
1721 				 * congestion control related information. This
1722 				 * typically means increasing the congestion
1723 				 * window.
1724 				 */
1725 				cc_ack_received(tp, th, CC_ACK);
1726 
1727 				tp->snd_una = th->th_ack;
1728 				/*
1729 				 * Pull snd_wl2 up to prevent seq wrap relative
1730 				 * to th_ack.
1731 				 */
1732 				tp->snd_wl2 = th->th_ack;
1733 				tp->t_dupacks = 0;
1734 				m_freem(m);
1735 				ND6_HINT(tp); /* Some progress has been made. */
1736 
1737 				/*
1738 				 * If all outstanding data are acked, stop
1739 				 * retransmit timer, otherwise restart timer
1740 				 * using current (possibly backed-off) value.
1741 				 * If process is waiting for space,
1742 				 * wakeup/selwakeup/signal.  If data
1743 				 * are ready to send, let tcp_output
1744 				 * decide between more output or persist.
1745 				 */
1746 #ifdef TCPDEBUG
1747 				if (so->so_options & SO_DEBUG)
1748 					tcp_trace(TA_INPUT, ostate, tp,
1749 					    (void *)tcp_saveipgen,
1750 					    &tcp_savetcp, 0);
1751 #endif
1752 				if (tp->snd_una == tp->snd_max)
1753 					tcp_timer_activate(tp, TT_REXMT, 0);
1754 				else if (!tcp_timer_active(tp, TT_PERSIST))
1755 					tcp_timer_activate(tp, TT_REXMT,
1756 						      tp->t_rxtcur);
1757 				sowwakeup(so);
1758 				if (so->so_snd.sb_cc)
1759 					(void) tcp_output(tp);
1760 				goto check_delack;
1761 			}
1762 		} else if (th->th_ack == tp->snd_una &&
1763 		    tlen <= sbspace(&so->so_rcv)) {
1764 			int newsize = 0;	/* automatic sockbuf scaling */
1765 
1766 			/*
1767 			 * This is a pure, in-sequence data packet with
1768 			 * nothing on the reassembly queue and we have enough
1769 			 * buffer space to take it.
1770 			 */
1771 			if (ti_locked == TI_WLOCKED)
1772 				INP_INFO_WUNLOCK(&V_tcbinfo);
1773 			ti_locked = TI_UNLOCKED;
1774 
1775 			/* Clean receiver SACK report if present */
1776 			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1777 				tcp_clean_sackreport(tp);
1778 			TCPSTAT_INC(tcps_preddat);
1779 			tp->rcv_nxt += tlen;
1780 			/*
1781 			 * Pull snd_wl1 up to prevent seq wrap relative to
1782 			 * th_seq.
1783 			 */
1784 			tp->snd_wl1 = th->th_seq;
1785 			/*
1786 			 * Pull rcv_up up to prevent seq wrap relative to
1787 			 * rcv_nxt.
1788 			 */
1789 			tp->rcv_up = tp->rcv_nxt;
1790 			TCPSTAT_INC(tcps_rcvpack);
1791 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1792 			ND6_HINT(tp);	/* Some progress has been made */
1793 #ifdef TCPDEBUG
1794 			if (so->so_options & SO_DEBUG)
1795 				tcp_trace(TA_INPUT, ostate, tp,
1796 				    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1797 #endif
1798 		/*
1799 		 * Automatic sizing of receive socket buffer.  Often the send
1800 		 * buffer size is not optimally adjusted to the actual network
1801 		 * conditions at hand (delay bandwidth product).  Setting the
1802 		 * buffer size too small limits throughput on links with high
1803 		 * bandwidth and high delay (eg. trans-continental/oceanic links).
1804 		 *
1805 		 * On the receive side the socket buffer memory is only rarely
1806 		 * used to any significant extent.  This allows us to be much
1807 		 * more aggressive in scaling the receive socket buffer.  For
1808 		 * the case that the buffer space is actually used to a large
1809 		 * extent and we run out of kernel memory we can simply drop
1810 		 * the new segments; TCP on the sender will just retransmit it
1811 		 * later.  Setting the buffer size too big may only consume too
1812 		 * much kernel memory if the application doesn't read() from
1813 		 * the socket or packet loss or reordering makes use of the
1814 		 * reassembly queue.
1815 		 *
1816 		 * The criteria to step up the receive buffer one notch are:
1817 		 *  1. the number of bytes received during the time it takes
1818 		 *     one timestamp to be reflected back to us (the RTT);
1819 		 *  2. received bytes per RTT is within seven eighth of the
1820 		 *     current socket buffer size;
1821 		 *  3. receive buffer size has not hit maximal automatic size;
1822 		 *
1823 		 * This algorithm does one step per RTT at most and only if
1824 		 * we receive a bulk stream w/o packet losses or reorderings.
1825 		 * Shrinking the buffer during idle times is not necessary as
1826 		 * it doesn't consume any memory when idle.
1827 		 *
1828 		 * TODO: Only step up if the application is actually serving
1829 		 * the buffer to better manage the socket buffer resources.
1830 		 */
1831 			if (V_tcp_do_autorcvbuf &&
1832 			    to.to_tsecr &&
1833 			    (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1834 				if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
1835 				    to.to_tsecr - tp->rfbuf_ts < hz) {
1836 					if (tp->rfbuf_cnt >
1837 					    (so->so_rcv.sb_hiwat / 8 * 7) &&
1838 					    so->so_rcv.sb_hiwat <
1839 					    V_tcp_autorcvbuf_max) {
1840 						newsize =
1841 						    min(so->so_rcv.sb_hiwat +
1842 						    V_tcp_autorcvbuf_inc,
1843 						    V_tcp_autorcvbuf_max);
1844 					}
1845 					/* Start over with next RTT. */
1846 					tp->rfbuf_ts = 0;
1847 					tp->rfbuf_cnt = 0;
1848 				} else
1849 					tp->rfbuf_cnt += tlen;	/* add up */
1850 			}
1851 
1852 			/* Add data to socket buffer. */
1853 			SOCKBUF_LOCK(&so->so_rcv);
1854 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1855 				m_freem(m);
1856 			} else {
1857 				/*
1858 				 * Set new socket buffer size.
1859 				 * Give up when limit is reached.
1860 				 */
1861 				if (newsize)
1862 					if (!sbreserve_locked(&so->so_rcv,
1863 					    newsize, so, NULL))
1864 						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1865 				m_adj(m, drop_hdrlen);	/* delayed header drop */
1866 				sbappendstream_locked(&so->so_rcv, m);
1867 			}
1868 			/* NB: sorwakeup_locked() does an implicit unlock. */
1869 			sorwakeup_locked(so);
1870 			if (DELAY_ACK(tp, tlen)) {
1871 				tp->t_flags |= TF_DELACK;
1872 			} else {
1873 				tp->t_flags |= TF_ACKNOW;
1874 				tcp_output(tp);
1875 			}
1876 			goto check_delack;
1877 		}
1878 	}
1879 
1880 	/*
1881 	 * Calculate amount of space in receive window,
1882 	 * and then do TCP input processing.
1883 	 * Receive window is amount of space in rcv queue,
1884 	 * but not less than advertised window.
1885 	 */
1886 	win = sbspace(&so->so_rcv);
1887 	if (win < 0)
1888 		win = 0;
1889 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1890 
1891 	/* Reset receive buffer auto scaling when not in bulk receive mode. */
1892 	tp->rfbuf_ts = 0;
1893 	tp->rfbuf_cnt = 0;
1894 
1895 	switch (tp->t_state) {
1896 
1897 	/*
1898 	 * If the state is SYN_RECEIVED:
1899 	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1900 	 */
1901 	case TCPS_SYN_RECEIVED:
1902 		if ((thflags & TH_ACK) &&
1903 		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1904 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1905 				rstreason = BANDLIM_RST_OPENPORT;
1906 				goto dropwithreset;
1907 		}
1908 		break;
1909 
1910 	/*
1911 	 * If the state is SYN_SENT:
1912 	 *	if seg contains an ACK, but not for our SYN, drop the input.
1913 	 *	if seg contains a RST, then drop the connection.
1914 	 *	if seg does not contain SYN, then drop it.
1915 	 * Otherwise this is an acceptable SYN segment
1916 	 *	initialize tp->rcv_nxt and tp->irs
1917 	 *	if seg contains ack then advance tp->snd_una
1918 	 *	if seg contains an ECE and ECN support is enabled, the stream
1919 	 *	    is ECN capable.
1920 	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1921 	 *	arrange for segment to be acked (eventually)
1922 	 *	continue processing rest of data/controls, beginning with URG
1923 	 */
1924 	case TCPS_SYN_SENT:
1925 		if ((thflags & TH_ACK) &&
1926 		    (SEQ_LEQ(th->th_ack, tp->iss) ||
1927 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1928 			rstreason = BANDLIM_UNLIMITED;
1929 			goto dropwithreset;
1930 		}
1931 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
1932 			TCP_PROBE5(connect_refused, NULL, tp, m->m_data, tp,
1933 			    th);
1934 			tp = tcp_drop(tp, ECONNREFUSED);
1935 		}
1936 		if (thflags & TH_RST)
1937 			goto drop;
1938 		if (!(thflags & TH_SYN))
1939 			goto drop;
1940 
1941 		tp->irs = th->th_seq;
1942 		tcp_rcvseqinit(tp);
1943 		if (thflags & TH_ACK) {
1944 			TCPSTAT_INC(tcps_connects);
1945 			soisconnected(so);
1946 #ifdef MAC
1947 			mac_socketpeer_set_from_mbuf(m, so);
1948 #endif
1949 			/* Do window scaling on this connection? */
1950 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
1951 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
1952 				tp->rcv_scale = tp->request_r_scale;
1953 			}
1954 			tp->rcv_adv += imin(tp->rcv_wnd,
1955 			    TCP_MAXWIN << tp->rcv_scale);
1956 			tp->snd_una++;		/* SYN is acked */
1957 			/*
1958 			 * If there's data, delay ACK; if there's also a FIN
1959 			 * ACKNOW will be turned on later.
1960 			 */
1961 			if (DELAY_ACK(tp, tlen) && tlen != 0)
1962 				tcp_timer_activate(tp, TT_DELACK,
1963 				    tcp_delacktime);
1964 			else
1965 				tp->t_flags |= TF_ACKNOW;
1966 
1967 			if ((thflags & TH_ECE) && V_tcp_do_ecn) {
1968 				tp->t_flags |= TF_ECN_PERMIT;
1969 				TCPSTAT_INC(tcps_ecn_shs);
1970 			}
1971 
1972 			/*
1973 			 * Received <SYN,ACK> in SYN_SENT[*] state.
1974 			 * Transitions:
1975 			 *	SYN_SENT  --> ESTABLISHED
1976 			 *	SYN_SENT* --> FIN_WAIT_1
1977 			 */
1978 			tp->t_starttime = ticks;
1979 			if (tp->t_flags & TF_NEEDFIN) {
1980 				tcp_state_change(tp, TCPS_FIN_WAIT_1);
1981 				tp->t_flags &= ~TF_NEEDFIN;
1982 				thflags &= ~TH_SYN;
1983 			} else {
1984 				tcp_state_change(tp, TCPS_ESTABLISHED);
1985 				TCP_PROBE5(connect_established, NULL, tp,
1986 				    m->m_data, tp, th);
1987 				cc_conn_init(tp);
1988 				tcp_timer_activate(tp, TT_KEEP,
1989 				    TP_KEEPIDLE(tp));
1990 			}
1991 		} else {
1992 			/*
1993 			 * Received initial SYN in SYN-SENT[*] state =>
1994 			 * simultaneous open.  If segment contains CC option
1995 			 * and there is a cached CC, apply TAO test.
1996 			 * If it succeeds, connection is * half-synchronized.
1997 			 * Otherwise, do 3-way handshake:
1998 			 *        SYN-SENT -> SYN-RECEIVED
1999 			 *        SYN-SENT* -> SYN-RECEIVED*
2000 			 * If there was no CC option, clear cached CC value.
2001 			 */
2002 			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2003 			tcp_timer_activate(tp, TT_REXMT, 0);
2004 			tcp_state_change(tp, TCPS_SYN_RECEIVED);
2005 		}
2006 
2007 		KASSERT(ti_locked == TI_WLOCKED, ("%s: trimthenstep6: "
2008 		    "ti_locked %d", __func__, ti_locked));
2009 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2010 		INP_WLOCK_ASSERT(tp->t_inpcb);
2011 
2012 		/*
2013 		 * Advance th->th_seq to correspond to first data byte.
2014 		 * If data, trim to stay within window,
2015 		 * dropping FIN if necessary.
2016 		 */
2017 		th->th_seq++;
2018 		if (tlen > tp->rcv_wnd) {
2019 			todrop = tlen - tp->rcv_wnd;
2020 			m_adj(m, -todrop);
2021 			tlen = tp->rcv_wnd;
2022 			thflags &= ~TH_FIN;
2023 			TCPSTAT_INC(tcps_rcvpackafterwin);
2024 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2025 		}
2026 		tp->snd_wl1 = th->th_seq - 1;
2027 		tp->rcv_up = th->th_seq;
2028 		/*
2029 		 * Client side of transaction: already sent SYN and data.
2030 		 * If the remote host used T/TCP to validate the SYN,
2031 		 * our data will be ACK'd; if so, enter normal data segment
2032 		 * processing in the middle of step 5, ack processing.
2033 		 * Otherwise, goto step 6.
2034 		 */
2035 		if (thflags & TH_ACK)
2036 			goto process_ACK;
2037 
2038 		goto step6;
2039 
2040 	/*
2041 	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2042 	 *      do normal processing.
2043 	 *
2044 	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2045 	 */
2046 	case TCPS_LAST_ACK:
2047 	case TCPS_CLOSING:
2048 		break;  /* continue normal processing */
2049 	}
2050 
2051 	/*
2052 	 * States other than LISTEN or SYN_SENT.
2053 	 * First check the RST flag and sequence number since reset segments
2054 	 * are exempt from the timestamp and connection count tests.  This
2055 	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2056 	 * below which allowed reset segments in half the sequence space
2057 	 * to fall though and be processed (which gives forged reset
2058 	 * segments with a random sequence number a 50 percent chance of
2059 	 * killing a connection).
2060 	 * Then check timestamp, if present.
2061 	 * Then check the connection count, if present.
2062 	 * Then check that at least some bytes of segment are within
2063 	 * receive window.  If segment begins before rcv_nxt,
2064 	 * drop leading data (and SYN); if nothing left, just ack.
2065 	 *
2066 	 *
2067 	 * If the RST bit is set, check the sequence number to see
2068 	 * if this is a valid reset segment.
2069 	 * RFC 793 page 37:
2070 	 *   In all states except SYN-SENT, all reset (RST) segments
2071 	 *   are validated by checking their SEQ-fields.  A reset is
2072 	 *   valid if its sequence number is in the window.
2073 	 * Note: this does not take into account delayed ACKs, so
2074 	 *   we should test against last_ack_sent instead of rcv_nxt.
2075 	 *   The sequence number in the reset segment is normally an
2076 	 *   echo of our outgoing acknowlegement numbers, but some hosts
2077 	 *   send a reset with the sequence number at the rightmost edge
2078 	 *   of our receive window, and we have to handle this case.
2079 	 * Note 2: Paul Watson's paper "Slipping in the Window" has shown
2080 	 *   that brute force RST attacks are possible.  To combat this,
2081 	 *   we use a much stricter check while in the ESTABLISHED state,
2082 	 *   only accepting RSTs where the sequence number is equal to
2083 	 *   last_ack_sent.  In all other states (the states in which a
2084 	 *   RST is more likely), the more permissive check is used.
2085 	 * If we have multiple segments in flight, the initial reset
2086 	 * segment sequence numbers will be to the left of last_ack_sent,
2087 	 * but they will eventually catch up.
2088 	 * In any case, it never made sense to trim reset segments to
2089 	 * fit the receive window since RFC 1122 says:
2090 	 *   4.2.2.12  RST Segment: RFC-793 Section 3.4
2091 	 *
2092 	 *    A TCP SHOULD allow a received RST segment to include data.
2093 	 *
2094 	 *    DISCUSSION
2095 	 *         It has been suggested that a RST segment could contain
2096 	 *         ASCII text that encoded and explained the cause of the
2097 	 *         RST.  No standard has yet been established for such
2098 	 *         data.
2099 	 *
2100 	 * If the reset segment passes the sequence number test examine
2101 	 * the state:
2102 	 *    SYN_RECEIVED STATE:
2103 	 *	If passive open, return to LISTEN state.
2104 	 *	If active open, inform user that connection was refused.
2105 	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
2106 	 *	Inform user that connection was reset, and close tcb.
2107 	 *    CLOSING, LAST_ACK STATES:
2108 	 *	Close the tcb.
2109 	 *    TIME_WAIT STATE:
2110 	 *	Drop the segment - see Stevens, vol. 2, p. 964 and
2111 	 *      RFC 1337.
2112 	 */
2113 	if (thflags & TH_RST) {
2114 		if (SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2115 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2116 			switch (tp->t_state) {
2117 
2118 			case TCPS_SYN_RECEIVED:
2119 				so->so_error = ECONNREFUSED;
2120 				goto close;
2121 
2122 			case TCPS_ESTABLISHED:
2123 				if (V_tcp_insecure_rst == 0 &&
2124 				    !(SEQ_GEQ(th->th_seq, tp->rcv_nxt - 1) &&
2125 				    SEQ_LEQ(th->th_seq, tp->rcv_nxt + 1)) &&
2126 				    !(SEQ_GEQ(th->th_seq, tp->last_ack_sent - 1) &&
2127 				    SEQ_LEQ(th->th_seq, tp->last_ack_sent + 1))) {
2128 					TCPSTAT_INC(tcps_badrst);
2129 					goto drop;
2130 				}
2131 				/* FALLTHROUGH */
2132 			case TCPS_FIN_WAIT_1:
2133 			case TCPS_FIN_WAIT_2:
2134 			case TCPS_CLOSE_WAIT:
2135 				so->so_error = ECONNRESET;
2136 			close:
2137 				KASSERT(ti_locked == TI_WLOCKED,
2138 				    ("tcp_do_segment: TH_RST 1 ti_locked %d",
2139 				    ti_locked));
2140 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2141 
2142 				tcp_state_change(tp, TCPS_CLOSED);
2143 				TCPSTAT_INC(tcps_drops);
2144 				tp = tcp_close(tp);
2145 				break;
2146 
2147 			case TCPS_CLOSING:
2148 			case TCPS_LAST_ACK:
2149 				KASSERT(ti_locked == TI_WLOCKED,
2150 				    ("tcp_do_segment: TH_RST 2 ti_locked %d",
2151 				    ti_locked));
2152 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2153 
2154 				tp = tcp_close(tp);
2155 				break;
2156 			}
2157 		}
2158 		goto drop;
2159 	}
2160 
2161 	/*
2162 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2163 	 * and it's less than ts_recent, drop it.
2164 	 */
2165 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2166 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2167 
2168 		/* Check to see if ts_recent is over 24 days old.  */
2169 		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2170 			/*
2171 			 * Invalidate ts_recent.  If this segment updates
2172 			 * ts_recent, the age will be reset later and ts_recent
2173 			 * will get a valid value.  If it does not, setting
2174 			 * ts_recent to zero will at least satisfy the
2175 			 * requirement that zero be placed in the timestamp
2176 			 * echo reply when ts_recent isn't valid.  The
2177 			 * age isn't reset until we get a valid ts_recent
2178 			 * because we don't want out-of-order segments to be
2179 			 * dropped when ts_recent is old.
2180 			 */
2181 			tp->ts_recent = 0;
2182 		} else {
2183 			TCPSTAT_INC(tcps_rcvduppack);
2184 			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2185 			TCPSTAT_INC(tcps_pawsdrop);
2186 			if (tlen)
2187 				goto dropafterack;
2188 			goto drop;
2189 		}
2190 	}
2191 
2192 	/*
2193 	 * In the SYN-RECEIVED state, validate that the packet belongs to
2194 	 * this connection before trimming the data to fit the receive
2195 	 * window.  Check the sequence number versus IRS since we know
2196 	 * the sequence numbers haven't wrapped.  This is a partial fix
2197 	 * for the "LAND" DoS attack.
2198 	 */
2199 	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2200 		rstreason = BANDLIM_RST_OPENPORT;
2201 		goto dropwithreset;
2202 	}
2203 
2204 	todrop = tp->rcv_nxt - th->th_seq;
2205 	if (todrop > 0) {
2206 		/*
2207 		 * If this is a duplicate SYN for our current connection,
2208 		 * advance over it and pretend and it's not a SYN.
2209 		 */
2210 		if (thflags & TH_SYN && th->th_seq == tp->irs) {
2211 			thflags &= ~TH_SYN;
2212 			th->th_seq++;
2213 			if (th->th_urp > 1)
2214 				th->th_urp--;
2215 			else
2216 				thflags &= ~TH_URG;
2217 			todrop--;
2218 		}
2219 		/*
2220 		 * Following if statement from Stevens, vol. 2, p. 960.
2221 		 */
2222 		if (todrop > tlen
2223 		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2224 			/*
2225 			 * Any valid FIN must be to the left of the window.
2226 			 * At this point the FIN must be a duplicate or out
2227 			 * of sequence; drop it.
2228 			 */
2229 			thflags &= ~TH_FIN;
2230 
2231 			/*
2232 			 * Send an ACK to resynchronize and drop any data.
2233 			 * But keep on processing for RST or ACK.
2234 			 */
2235 			tp->t_flags |= TF_ACKNOW;
2236 			todrop = tlen;
2237 			TCPSTAT_INC(tcps_rcvduppack);
2238 			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2239 		} else {
2240 			TCPSTAT_INC(tcps_rcvpartduppack);
2241 			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2242 		}
2243 		drop_hdrlen += todrop;	/* drop from the top afterwards */
2244 		th->th_seq += todrop;
2245 		tlen -= todrop;
2246 		if (th->th_urp > todrop)
2247 			th->th_urp -= todrop;
2248 		else {
2249 			thflags &= ~TH_URG;
2250 			th->th_urp = 0;
2251 		}
2252 	}
2253 
2254 	/*
2255 	 * If new data are received on a connection after the
2256 	 * user processes are gone, then RST the other end.
2257 	 */
2258 	if ((so->so_state & SS_NOFDREF) &&
2259 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2260 		KASSERT(ti_locked == TI_WLOCKED, ("%s: SS_NOFDEREF && "
2261 		    "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
2262 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2263 
2264 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2265 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2266 			    "after socket was closed, "
2267 			    "sending RST and removing tcpcb\n",
2268 			    s, __func__, tcpstates[tp->t_state], tlen);
2269 			free(s, M_TCPLOG);
2270 		}
2271 		tp = tcp_close(tp);
2272 		TCPSTAT_INC(tcps_rcvafterclose);
2273 		rstreason = BANDLIM_UNLIMITED;
2274 		goto dropwithreset;
2275 	}
2276 
2277 	/*
2278 	 * If segment ends after window, drop trailing data
2279 	 * (and PUSH and FIN); if nothing left, just ACK.
2280 	 */
2281 	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2282 	if (todrop > 0) {
2283 		TCPSTAT_INC(tcps_rcvpackafterwin);
2284 		if (todrop >= tlen) {
2285 			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2286 			/*
2287 			 * If window is closed can only take segments at
2288 			 * window edge, and have to drop data and PUSH from
2289 			 * incoming segments.  Continue processing, but
2290 			 * remember to ack.  Otherwise, drop segment
2291 			 * and ack.
2292 			 */
2293 			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2294 				tp->t_flags |= TF_ACKNOW;
2295 				TCPSTAT_INC(tcps_rcvwinprobe);
2296 			} else
2297 				goto dropafterack;
2298 		} else
2299 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2300 		m_adj(m, -todrop);
2301 		tlen -= todrop;
2302 		thflags &= ~(TH_PUSH|TH_FIN);
2303 	}
2304 
2305 	/*
2306 	 * If last ACK falls within this segment's sequence numbers,
2307 	 * record its timestamp.
2308 	 * NOTE:
2309 	 * 1) That the test incorporates suggestions from the latest
2310 	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2311 	 * 2) That updating only on newer timestamps interferes with
2312 	 *    our earlier PAWS tests, so this check should be solely
2313 	 *    predicated on the sequence space of this segment.
2314 	 * 3) That we modify the segment boundary check to be
2315 	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2316 	 *    instead of RFC1323's
2317 	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2318 	 *    This modified check allows us to overcome RFC1323's
2319 	 *    limitations as described in Stevens TCP/IP Illustrated
2320 	 *    Vol. 2 p.869. In such cases, we can still calculate the
2321 	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2322 	 */
2323 	if ((to.to_flags & TOF_TS) != 0 &&
2324 	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2325 	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2326 		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2327 		tp->ts_recent_age = tcp_ts_getticks();
2328 		tp->ts_recent = to.to_tsval;
2329 	}
2330 
2331 	/*
2332 	 * If a SYN is in the window, then this is an
2333 	 * error and we send an RST and drop the connection.
2334 	 */
2335 	if (thflags & TH_SYN) {
2336 		KASSERT(ti_locked == TI_WLOCKED,
2337 		    ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
2338 		INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2339 
2340 		tp = tcp_drop(tp, ECONNRESET);
2341 		rstreason = BANDLIM_UNLIMITED;
2342 		goto drop;
2343 	}
2344 
2345 	/*
2346 	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2347 	 * flag is on (half-synchronized state), then queue data for
2348 	 * later processing; else drop segment and return.
2349 	 */
2350 	if ((thflags & TH_ACK) == 0) {
2351 		if (tp->t_state == TCPS_SYN_RECEIVED ||
2352 		    (tp->t_flags & TF_NEEDSYN))
2353 			goto step6;
2354 		else if (tp->t_flags & TF_ACKNOW)
2355 			goto dropafterack;
2356 		else
2357 			goto drop;
2358 	}
2359 
2360 	/*
2361 	 * Ack processing.
2362 	 */
2363 	switch (tp->t_state) {
2364 
2365 	/*
2366 	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2367 	 * ESTABLISHED state and continue processing.
2368 	 * The ACK was checked above.
2369 	 */
2370 	case TCPS_SYN_RECEIVED:
2371 
2372 		TCPSTAT_INC(tcps_connects);
2373 		soisconnected(so);
2374 		/* Do window scaling? */
2375 		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2376 			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2377 			tp->rcv_scale = tp->request_r_scale;
2378 			tp->snd_wnd = tiwin;
2379 		}
2380 		/*
2381 		 * Make transitions:
2382 		 *      SYN-RECEIVED  -> ESTABLISHED
2383 		 *      SYN-RECEIVED* -> FIN-WAIT-1
2384 		 */
2385 		tp->t_starttime = ticks;
2386 		if (tp->t_flags & TF_NEEDFIN) {
2387 			tcp_state_change(tp, TCPS_FIN_WAIT_1);
2388 			tp->t_flags &= ~TF_NEEDFIN;
2389 		} else {
2390 			tcp_state_change(tp, TCPS_ESTABLISHED);
2391 			TCP_PROBE5(accept_established, NULL, tp, m->m_data, tp,
2392 			    th);
2393 			cc_conn_init(tp);
2394 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2395 		}
2396 		/*
2397 		 * If segment contains data or ACK, will call tcp_reass()
2398 		 * later; if not, do so now to pass queued data to user.
2399 		 */
2400 		if (tlen == 0 && (thflags & TH_FIN) == 0)
2401 			(void) tcp_reass(tp, (struct tcphdr *)0, 0,
2402 			    (struct mbuf *)0);
2403 		tp->snd_wl1 = th->th_seq - 1;
2404 		/* FALLTHROUGH */
2405 
2406 	/*
2407 	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2408 	 * ACKs.  If the ack is in the range
2409 	 *	tp->snd_una < th->th_ack <= tp->snd_max
2410 	 * then advance tp->snd_una to th->th_ack and drop
2411 	 * data from the retransmission queue.  If this ACK reflects
2412 	 * more up to date window information we update our window information.
2413 	 */
2414 	case TCPS_ESTABLISHED:
2415 	case TCPS_FIN_WAIT_1:
2416 	case TCPS_FIN_WAIT_2:
2417 	case TCPS_CLOSE_WAIT:
2418 	case TCPS_CLOSING:
2419 	case TCPS_LAST_ACK:
2420 		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2421 			TCPSTAT_INC(tcps_rcvacktoomuch);
2422 			goto dropafterack;
2423 		}
2424 		if ((tp->t_flags & TF_SACK_PERMIT) &&
2425 		    ((to.to_flags & TOF_SACK) ||
2426 		     !TAILQ_EMPTY(&tp->snd_holes)))
2427 			tcp_sack_doack(tp, &to, th->th_ack);
2428 
2429 		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2430 		hhook_run_tcp_est_in(tp, th, &to);
2431 
2432 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2433 			if (tlen == 0 && tiwin == tp->snd_wnd) {
2434 				TCPSTAT_INC(tcps_rcvdupack);
2435 				/*
2436 				 * If we have outstanding data (other than
2437 				 * a window probe), this is a completely
2438 				 * duplicate ack (ie, window info didn't
2439 				 * change), the ack is the biggest we've
2440 				 * seen and we've seen exactly our rexmt
2441 				 * threshhold of them, assume a packet
2442 				 * has been dropped and retransmit it.
2443 				 * Kludge snd_nxt & the congestion
2444 				 * window so we send only this one
2445 				 * packet.
2446 				 *
2447 				 * We know we're losing at the current
2448 				 * window size so do congestion avoidance
2449 				 * (set ssthresh to half the current window
2450 				 * and pull our congestion window back to
2451 				 * the new ssthresh).
2452 				 *
2453 				 * Dup acks mean that packets have left the
2454 				 * network (they're now cached at the receiver)
2455 				 * so bump cwnd by the amount in the receiver
2456 				 * to keep a constant cwnd packets in the
2457 				 * network.
2458 				 *
2459 				 * When using TCP ECN, notify the peer that
2460 				 * we reduced the cwnd.
2461 				 */
2462 				if (!tcp_timer_active(tp, TT_REXMT) ||
2463 				    th->th_ack != tp->snd_una)
2464 					tp->t_dupacks = 0;
2465 				else if (++tp->t_dupacks > tcprexmtthresh ||
2466 				     IN_FASTRECOVERY(tp->t_flags)) {
2467 					cc_ack_received(tp, th, CC_DUPACK);
2468 					if ((tp->t_flags & TF_SACK_PERMIT) &&
2469 					    IN_FASTRECOVERY(tp->t_flags)) {
2470 						int awnd;
2471 
2472 						/*
2473 						 * Compute the amount of data in flight first.
2474 						 * We can inject new data into the pipe iff
2475 						 * we have less than 1/2 the original window's
2476 						 * worth of data in flight.
2477 						 */
2478 						awnd = (tp->snd_nxt - tp->snd_fack) +
2479 							tp->sackhint.sack_bytes_rexmit;
2480 						if (awnd < tp->snd_ssthresh) {
2481 							tp->snd_cwnd += tp->t_maxseg;
2482 							if (tp->snd_cwnd > tp->snd_ssthresh)
2483 								tp->snd_cwnd = tp->snd_ssthresh;
2484 						}
2485 					} else
2486 						tp->snd_cwnd += tp->t_maxseg;
2487 					if ((thflags & TH_FIN) &&
2488 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2489 						/*
2490 						 * If its a fin we need to process
2491 						 * it to avoid a race where both
2492 						 * sides enter FIN-WAIT and send FIN|ACK
2493 						 * at the same time.
2494 						 */
2495 						break;
2496 					}
2497 					(void) tcp_output(tp);
2498 					goto drop;
2499 				} else if (tp->t_dupacks == tcprexmtthresh) {
2500 					tcp_seq onxt = tp->snd_nxt;
2501 
2502 					/*
2503 					 * If we're doing sack, check to
2504 					 * see if we're already in sack
2505 					 * recovery. If we're not doing sack,
2506 					 * check to see if we're in newreno
2507 					 * recovery.
2508 					 */
2509 					if (tp->t_flags & TF_SACK_PERMIT) {
2510 						if (IN_FASTRECOVERY(tp->t_flags)) {
2511 							tp->t_dupacks = 0;
2512 							break;
2513 						}
2514 					} else {
2515 						if (SEQ_LEQ(th->th_ack,
2516 						    tp->snd_recover)) {
2517 							tp->t_dupacks = 0;
2518 							break;
2519 						}
2520 					}
2521 					/* Congestion signal before ack. */
2522 					cc_cong_signal(tp, th, CC_NDUPACK);
2523 					cc_ack_received(tp, th, CC_DUPACK);
2524 					tcp_timer_activate(tp, TT_REXMT, 0);
2525 					tp->t_rtttime = 0;
2526 					if (tp->t_flags & TF_SACK_PERMIT) {
2527 						TCPSTAT_INC(
2528 						    tcps_sack_recovery_episode);
2529 						tp->sack_newdata = tp->snd_nxt;
2530 						tp->snd_cwnd = tp->t_maxseg;
2531 						(void) tcp_output(tp);
2532 						goto drop;
2533 					}
2534 					tp->snd_nxt = th->th_ack;
2535 					tp->snd_cwnd = tp->t_maxseg;
2536 					if ((thflags & TH_FIN) &&
2537 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2538 						/*
2539 						 * If its a fin we need to process
2540 						 * it to avoid a race where both
2541 						 * sides enter FIN-WAIT and send FIN|ACK
2542 						 * at the same time.
2543 						 */
2544 						break;
2545 					}
2546 					(void) tcp_output(tp);
2547 					KASSERT(tp->snd_limited <= 2,
2548 					    ("%s: tp->snd_limited too big",
2549 					    __func__));
2550 					tp->snd_cwnd = tp->snd_ssthresh +
2551 					     tp->t_maxseg *
2552 					     (tp->t_dupacks - tp->snd_limited);
2553 					if (SEQ_GT(onxt, tp->snd_nxt))
2554 						tp->snd_nxt = onxt;
2555 					goto drop;
2556 				} else if (V_tcp_do_rfc3042) {
2557 					cc_ack_received(tp, th, CC_DUPACK);
2558 					u_long oldcwnd = tp->snd_cwnd;
2559 					tcp_seq oldsndmax = tp->snd_max;
2560 					u_int sent;
2561 					int avail;
2562 
2563 					KASSERT(tp->t_dupacks == 1 ||
2564 					    tp->t_dupacks == 2,
2565 					    ("%s: dupacks not 1 or 2",
2566 					    __func__));
2567 					if (tp->t_dupacks == 1)
2568 						tp->snd_limited = 0;
2569 					tp->snd_cwnd =
2570 					    (tp->snd_nxt - tp->snd_una) +
2571 					    (tp->t_dupacks - tp->snd_limited) *
2572 					    tp->t_maxseg;
2573 					if ((thflags & TH_FIN) &&
2574 					    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2575 						/*
2576 						 * If its a fin we need to process
2577 						 * it to avoid a race where both
2578 						 * sides enter FIN-WAIT and send FIN|ACK
2579 						 * at the same time.
2580 						 */
2581 						break;
2582 					}
2583 					/*
2584 					 * Only call tcp_output when there
2585 					 * is new data available to be sent.
2586 					 * Otherwise we would send pure ACKs.
2587 					 */
2588 					SOCKBUF_LOCK(&so->so_snd);
2589 					avail = so->so_snd.sb_cc -
2590 					    (tp->snd_nxt - tp->snd_una);
2591 					SOCKBUF_UNLOCK(&so->so_snd);
2592 					if (avail > 0)
2593 						(void) tcp_output(tp);
2594 					sent = tp->snd_max - oldsndmax;
2595 					if (sent > tp->t_maxseg) {
2596 						KASSERT((tp->t_dupacks == 2 &&
2597 						    tp->snd_limited == 0) ||
2598 						   (sent == tp->t_maxseg + 1 &&
2599 						    tp->t_flags & TF_SENTFIN),
2600 						    ("%s: sent too much",
2601 						    __func__));
2602 						tp->snd_limited = 2;
2603 					} else if (sent > 0)
2604 						++tp->snd_limited;
2605 					tp->snd_cwnd = oldcwnd;
2606 					goto drop;
2607 				}
2608 			} else
2609 				tp->t_dupacks = 0;
2610 			break;
2611 		}
2612 
2613 		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2614 		    ("%s: th_ack <= snd_una", __func__));
2615 
2616 		/*
2617 		 * If the congestion window was inflated to account
2618 		 * for the other side's cached packets, retract it.
2619 		 */
2620 		if (IN_FASTRECOVERY(tp->t_flags)) {
2621 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2622 				if (tp->t_flags & TF_SACK_PERMIT)
2623 					tcp_sack_partialack(tp, th);
2624 				else
2625 					tcp_newreno_partial_ack(tp, th);
2626 			} else
2627 				cc_post_recovery(tp, th);
2628 		}
2629 		tp->t_dupacks = 0;
2630 		/*
2631 		 * If we reach this point, ACK is not a duplicate,
2632 		 *     i.e., it ACKs something we sent.
2633 		 */
2634 		if (tp->t_flags & TF_NEEDSYN) {
2635 			/*
2636 			 * T/TCP: Connection was half-synchronized, and our
2637 			 * SYN has been ACK'd (so connection is now fully
2638 			 * synchronized).  Go to non-starred state,
2639 			 * increment snd_una for ACK of SYN, and check if
2640 			 * we can do window scaling.
2641 			 */
2642 			tp->t_flags &= ~TF_NEEDSYN;
2643 			tp->snd_una++;
2644 			/* Do window scaling? */
2645 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2646 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2647 				tp->rcv_scale = tp->request_r_scale;
2648 				/* Send window already scaled. */
2649 			}
2650 		}
2651 
2652 process_ACK:
2653 		INP_WLOCK_ASSERT(tp->t_inpcb);
2654 
2655 		acked = BYTES_THIS_ACK(tp, th);
2656 		TCPSTAT_INC(tcps_rcvackpack);
2657 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2658 
2659 		/*
2660 		 * If we just performed our first retransmit, and the ACK
2661 		 * arrives within our recovery window, then it was a mistake
2662 		 * to do the retransmit in the first place.  Recover our
2663 		 * original cwnd and ssthresh, and proceed to transmit where
2664 		 * we left off.
2665 		 */
2666 		if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
2667 		    (int)(ticks - tp->t_badrxtwin) < 0)
2668 			cc_cong_signal(tp, th, CC_RTO_ERR);
2669 
2670 		/*
2671 		 * If we have a timestamp reply, update smoothed
2672 		 * round trip time.  If no timestamp is present but
2673 		 * transmit timer is running and timed sequence
2674 		 * number was acked, update smoothed round trip time.
2675 		 * Since we now have an rtt measurement, cancel the
2676 		 * timer backoff (cf., Phil Karn's retransmit alg.).
2677 		 * Recompute the initial retransmit timer.
2678 		 *
2679 		 * Some boxes send broken timestamp replies
2680 		 * during the SYN+ACK phase, ignore
2681 		 * timestamps of 0 or we could calculate a
2682 		 * huge RTT and blow up the retransmit timer.
2683 		 */
2684 		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2685 			u_int t;
2686 
2687 			t = tcp_ts_getticks() - to.to_tsecr;
2688 			if (!tp->t_rttlow || tp->t_rttlow > t)
2689 				tp->t_rttlow = t;
2690 			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2691 		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2692 			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2693 				tp->t_rttlow = ticks - tp->t_rtttime;
2694 			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2695 		}
2696 
2697 		/*
2698 		 * If all outstanding data is acked, stop retransmit
2699 		 * timer and remember to restart (more output or persist).
2700 		 * If there is more data to be acked, restart retransmit
2701 		 * timer, using current (possibly backed-off) value.
2702 		 */
2703 		if (th->th_ack == tp->snd_max) {
2704 			tcp_timer_activate(tp, TT_REXMT, 0);
2705 			needoutput = 1;
2706 		} else if (!tcp_timer_active(tp, TT_PERSIST))
2707 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2708 
2709 		/*
2710 		 * If no data (only SYN) was ACK'd,
2711 		 *    skip rest of ACK processing.
2712 		 */
2713 		if (acked == 0)
2714 			goto step6;
2715 
2716 		/*
2717 		 * Let the congestion control algorithm update congestion
2718 		 * control related information. This typically means increasing
2719 		 * the congestion window.
2720 		 */
2721 		cc_ack_received(tp, th, CC_ACK);
2722 
2723 		SOCKBUF_LOCK(&so->so_snd);
2724 		if (acked > so->so_snd.sb_cc) {
2725 			tp->snd_wnd -= so->so_snd.sb_cc;
2726 			mfree = sbcut_locked(&so->so_snd,
2727 			    (int)so->so_snd.sb_cc);
2728 			ourfinisacked = 1;
2729 		} else {
2730 			mfree = sbcut_locked(&so->so_snd, acked);
2731 			tp->snd_wnd -= acked;
2732 			ourfinisacked = 0;
2733 		}
2734 		/* NB: sowwakeup_locked() does an implicit unlock. */
2735 		sowwakeup_locked(so);
2736 		m_freem(mfree);
2737 		/* Detect una wraparound. */
2738 		if (!IN_RECOVERY(tp->t_flags) &&
2739 		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2740 		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2741 			tp->snd_recover = th->th_ack - 1;
2742 		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2743 		if (IN_RECOVERY(tp->t_flags) &&
2744 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2745 			EXIT_RECOVERY(tp->t_flags);
2746 		}
2747 		tp->snd_una = th->th_ack;
2748 		if (tp->t_flags & TF_SACK_PERMIT) {
2749 			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2750 				tp->snd_recover = tp->snd_una;
2751 		}
2752 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2753 			tp->snd_nxt = tp->snd_una;
2754 
2755 		switch (tp->t_state) {
2756 
2757 		/*
2758 		 * In FIN_WAIT_1 STATE in addition to the processing
2759 		 * for the ESTABLISHED state if our FIN is now acknowledged
2760 		 * then enter FIN_WAIT_2.
2761 		 */
2762 		case TCPS_FIN_WAIT_1:
2763 			if (ourfinisacked) {
2764 				/*
2765 				 * If we can't receive any more
2766 				 * data, then closing user can proceed.
2767 				 * Starting the timer is contrary to the
2768 				 * specification, but if we don't get a FIN
2769 				 * we'll hang forever.
2770 				 *
2771 				 * XXXjl:
2772 				 * we should release the tp also, and use a
2773 				 * compressed state.
2774 				 */
2775 				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2776 					soisdisconnected(so);
2777 					tcp_timer_activate(tp, TT_2MSL,
2778 					    (tcp_fast_finwait2_recycle ?
2779 					    tcp_finwait2_timeout :
2780 					    TP_MAXIDLE(tp)));
2781 				}
2782 				tcp_state_change(tp, TCPS_FIN_WAIT_2);
2783 			}
2784 			break;
2785 
2786 		/*
2787 		 * In CLOSING STATE in addition to the processing for
2788 		 * the ESTABLISHED state if the ACK acknowledges our FIN
2789 		 * then enter the TIME-WAIT state, otherwise ignore
2790 		 * the segment.
2791 		 */
2792 		case TCPS_CLOSING:
2793 			if (ourfinisacked) {
2794 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2795 				tcp_twstart(tp);
2796 				INP_INFO_WUNLOCK(&V_tcbinfo);
2797 				m_freem(m);
2798 				return;
2799 			}
2800 			break;
2801 
2802 		/*
2803 		 * In LAST_ACK, we may still be waiting for data to drain
2804 		 * and/or to be acked, as well as for the ack of our FIN.
2805 		 * If our FIN is now acknowledged, delete the TCB,
2806 		 * enter the closed state and return.
2807 		 */
2808 		case TCPS_LAST_ACK:
2809 			if (ourfinisacked) {
2810 				INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
2811 				tp = tcp_close(tp);
2812 				goto drop;
2813 			}
2814 			break;
2815 		}
2816 	}
2817 
2818 step6:
2819 	INP_WLOCK_ASSERT(tp->t_inpcb);
2820 
2821 	/*
2822 	 * Update window information.
2823 	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2824 	 */
2825 	if ((thflags & TH_ACK) &&
2826 	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2827 	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2828 	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2829 		/* keep track of pure window updates */
2830 		if (tlen == 0 &&
2831 		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2832 			TCPSTAT_INC(tcps_rcvwinupd);
2833 		tp->snd_wnd = tiwin;
2834 		tp->snd_wl1 = th->th_seq;
2835 		tp->snd_wl2 = th->th_ack;
2836 		if (tp->snd_wnd > tp->max_sndwnd)
2837 			tp->max_sndwnd = tp->snd_wnd;
2838 		needoutput = 1;
2839 	}
2840 
2841 	/*
2842 	 * Process segments with URG.
2843 	 */
2844 	if ((thflags & TH_URG) && th->th_urp &&
2845 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2846 		/*
2847 		 * This is a kludge, but if we receive and accept
2848 		 * random urgent pointers, we'll crash in
2849 		 * soreceive.  It's hard to imagine someone
2850 		 * actually wanting to send this much urgent data.
2851 		 */
2852 		SOCKBUF_LOCK(&so->so_rcv);
2853 		if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
2854 			th->th_urp = 0;			/* XXX */
2855 			thflags &= ~TH_URG;		/* XXX */
2856 			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
2857 			goto dodata;			/* XXX */
2858 		}
2859 		/*
2860 		 * If this segment advances the known urgent pointer,
2861 		 * then mark the data stream.  This should not happen
2862 		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2863 		 * a FIN has been received from the remote side.
2864 		 * In these states we ignore the URG.
2865 		 *
2866 		 * According to RFC961 (Assigned Protocols),
2867 		 * the urgent pointer points to the last octet
2868 		 * of urgent data.  We continue, however,
2869 		 * to consider it to indicate the first octet
2870 		 * of data past the urgent section as the original
2871 		 * spec states (in one of two places).
2872 		 */
2873 		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2874 			tp->rcv_up = th->th_seq + th->th_urp;
2875 			so->so_oobmark = so->so_rcv.sb_cc +
2876 			    (tp->rcv_up - tp->rcv_nxt) - 1;
2877 			if (so->so_oobmark == 0)
2878 				so->so_rcv.sb_state |= SBS_RCVATMARK;
2879 			sohasoutofband(so);
2880 			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
2881 		}
2882 		SOCKBUF_UNLOCK(&so->so_rcv);
2883 		/*
2884 		 * Remove out of band data so doesn't get presented to user.
2885 		 * This can happen independent of advancing the URG pointer,
2886 		 * but if two URG's are pending at once, some out-of-band
2887 		 * data may creep in... ick.
2888 		 */
2889 		if (th->th_urp <= (u_long)tlen &&
2890 		    !(so->so_options & SO_OOBINLINE)) {
2891 			/* hdr drop is delayed */
2892 			tcp_pulloutofband(so, th, m, drop_hdrlen);
2893 		}
2894 	} else {
2895 		/*
2896 		 * If no out of band data is expected,
2897 		 * pull receive urgent pointer along
2898 		 * with the receive window.
2899 		 */
2900 		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
2901 			tp->rcv_up = tp->rcv_nxt;
2902 	}
2903 dodata:							/* XXX */
2904 	INP_WLOCK_ASSERT(tp->t_inpcb);
2905 
2906 	/*
2907 	 * Process the segment text, merging it into the TCP sequencing queue,
2908 	 * and arranging for acknowledgment of receipt if necessary.
2909 	 * This process logically involves adjusting tp->rcv_wnd as data
2910 	 * is presented to the user (this happens in tcp_usrreq.c,
2911 	 * case PRU_RCVD).  If a FIN has already been received on this
2912 	 * connection then we just ignore the text.
2913 	 */
2914 	if ((tlen || (thflags & TH_FIN)) &&
2915 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2916 		tcp_seq save_start = th->th_seq;
2917 		m_adj(m, drop_hdrlen);	/* delayed header drop */
2918 		/*
2919 		 * Insert segment which includes th into TCP reassembly queue
2920 		 * with control block tp.  Set thflags to whether reassembly now
2921 		 * includes a segment with FIN.  This handles the common case
2922 		 * inline (segment is the next to be received on an established
2923 		 * connection, and the queue is empty), avoiding linkage into
2924 		 * and removal from the queue and repetition of various
2925 		 * conversions.
2926 		 * Set DELACK for segments received in order, but ack
2927 		 * immediately when segments are out of order (so
2928 		 * fast retransmit can work).
2929 		 */
2930 		if (th->th_seq == tp->rcv_nxt &&
2931 		    LIST_EMPTY(&tp->t_segq) &&
2932 		    TCPS_HAVEESTABLISHED(tp->t_state)) {
2933 			if (DELAY_ACK(tp, tlen))
2934 				tp->t_flags |= TF_DELACK;
2935 			else
2936 				tp->t_flags |= TF_ACKNOW;
2937 			tp->rcv_nxt += tlen;
2938 			thflags = th->th_flags & TH_FIN;
2939 			TCPSTAT_INC(tcps_rcvpack);
2940 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
2941 			ND6_HINT(tp);
2942 			SOCKBUF_LOCK(&so->so_rcv);
2943 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
2944 				m_freem(m);
2945 			else
2946 				sbappendstream_locked(&so->so_rcv, m);
2947 			/* NB: sorwakeup_locked() does an implicit unlock. */
2948 			sorwakeup_locked(so);
2949 		} else {
2950 			/*
2951 			 * XXX: Due to the header drop above "th" is
2952 			 * theoretically invalid by now.  Fortunately
2953 			 * m_adj() doesn't actually frees any mbufs
2954 			 * when trimming from the head.
2955 			 */
2956 			thflags = tcp_reass(tp, th, &tlen, m);
2957 			tp->t_flags |= TF_ACKNOW;
2958 		}
2959 		if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
2960 			tcp_update_sack_list(tp, save_start, save_start + tlen);
2961 #if 0
2962 		/*
2963 		 * Note the amount of data that peer has sent into
2964 		 * our window, in order to estimate the sender's
2965 		 * buffer size.
2966 		 * XXX: Unused.
2967 		 */
2968 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
2969 			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
2970 		else
2971 			len = so->so_rcv.sb_hiwat;
2972 #endif
2973 	} else {
2974 		m_freem(m);
2975 		thflags &= ~TH_FIN;
2976 	}
2977 
2978 	/*
2979 	 * If FIN is received ACK the FIN and let the user know
2980 	 * that the connection is closing.
2981 	 */
2982 	if (thflags & TH_FIN) {
2983 		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2984 			socantrcvmore(so);
2985 			/*
2986 			 * If connection is half-synchronized
2987 			 * (ie NEEDSYN flag on) then delay ACK,
2988 			 * so it may be piggybacked when SYN is sent.
2989 			 * Otherwise, since we received a FIN then no
2990 			 * more input can be expected, send ACK now.
2991 			 */
2992 			if (tp->t_flags & TF_NEEDSYN)
2993 				tp->t_flags |= TF_DELACK;
2994 			else
2995 				tp->t_flags |= TF_ACKNOW;
2996 			tp->rcv_nxt++;
2997 		}
2998 		switch (tp->t_state) {
2999 
3000 		/*
3001 		 * In SYN_RECEIVED and ESTABLISHED STATES
3002 		 * enter the CLOSE_WAIT state.
3003 		 */
3004 		case TCPS_SYN_RECEIVED:
3005 			tp->t_starttime = ticks;
3006 			/* FALLTHROUGH */
3007 		case TCPS_ESTABLISHED:
3008 			tcp_state_change(tp, TCPS_CLOSE_WAIT);
3009 			break;
3010 
3011 		/*
3012 		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
3013 		 * enter the CLOSING state.
3014 		 */
3015 		case TCPS_FIN_WAIT_1:
3016 			tcp_state_change(tp, TCPS_CLOSING);
3017 			break;
3018 
3019 		/*
3020 		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
3021 		 * starting the time-wait timer, turning off the other
3022 		 * standard timers.
3023 		 */
3024 		case TCPS_FIN_WAIT_2:
3025 			INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
3026 			KASSERT(ti_locked == TI_WLOCKED, ("%s: dodata "
3027 			    "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
3028 			    ti_locked));
3029 
3030 			tcp_twstart(tp);
3031 			INP_INFO_WUNLOCK(&V_tcbinfo);
3032 			return;
3033 		}
3034 	}
3035 	if (ti_locked == TI_WLOCKED)
3036 		INP_INFO_WUNLOCK(&V_tcbinfo);
3037 	ti_locked = TI_UNLOCKED;
3038 
3039 #ifdef TCPDEBUG
3040 	if (so->so_options & SO_DEBUG)
3041 		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3042 			  &tcp_savetcp, 0);
3043 #endif
3044 
3045 	/*
3046 	 * Return any desired output.
3047 	 */
3048 	if (needoutput || (tp->t_flags & TF_ACKNOW))
3049 		(void) tcp_output(tp);
3050 
3051 check_delack:
3052 	KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
3053 	    __func__, ti_locked));
3054 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3055 	INP_WLOCK_ASSERT(tp->t_inpcb);
3056 
3057 	if (tp->t_flags & TF_DELACK) {
3058 		tp->t_flags &= ~TF_DELACK;
3059 		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3060 	}
3061 	INP_WUNLOCK(tp->t_inpcb);
3062 	return;
3063 
3064 dropafterack:
3065 	/*
3066 	 * Generate an ACK dropping incoming segment if it occupies
3067 	 * sequence space, where the ACK reflects our state.
3068 	 *
3069 	 * We can now skip the test for the RST flag since all
3070 	 * paths to this code happen after packets containing
3071 	 * RST have been dropped.
3072 	 *
3073 	 * In the SYN-RECEIVED state, don't send an ACK unless the
3074 	 * segment we received passes the SYN-RECEIVED ACK test.
3075 	 * If it fails send a RST.  This breaks the loop in the
3076 	 * "LAND" DoS attack, and also prevents an ACK storm
3077 	 * between two listening ports that have been sent forged
3078 	 * SYN segments, each with the source address of the other.
3079 	 */
3080 	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3081 	    (SEQ_GT(tp->snd_una, th->th_ack) ||
3082 	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
3083 		rstreason = BANDLIM_RST_OPENPORT;
3084 		goto dropwithreset;
3085 	}
3086 #ifdef TCPDEBUG
3087 	if (so->so_options & SO_DEBUG)
3088 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3089 			  &tcp_savetcp, 0);
3090 #endif
3091 	if (ti_locked == TI_WLOCKED)
3092 		INP_INFO_WUNLOCK(&V_tcbinfo);
3093 	ti_locked = TI_UNLOCKED;
3094 
3095 	tp->t_flags |= TF_ACKNOW;
3096 	(void) tcp_output(tp);
3097 	INP_WUNLOCK(tp->t_inpcb);
3098 	m_freem(m);
3099 	return;
3100 
3101 dropwithreset:
3102 	if (ti_locked == TI_WLOCKED)
3103 		INP_INFO_WUNLOCK(&V_tcbinfo);
3104 	ti_locked = TI_UNLOCKED;
3105 
3106 	if (tp != NULL) {
3107 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
3108 		INP_WUNLOCK(tp->t_inpcb);
3109 	} else
3110 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3111 	return;
3112 
3113 drop:
3114 	if (ti_locked == TI_WLOCKED) {
3115 		INP_INFO_WUNLOCK(&V_tcbinfo);
3116 		ti_locked = TI_UNLOCKED;
3117 	}
3118 #ifdef INVARIANTS
3119 	else
3120 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3121 #endif
3122 
3123 	/*
3124 	 * Drop space held by incoming segment and return.
3125 	 */
3126 #ifdef TCPDEBUG
3127 	if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3128 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3129 			  &tcp_savetcp, 0);
3130 #endif
3131 	if (tp != NULL)
3132 		INP_WUNLOCK(tp->t_inpcb);
3133 	m_freem(m);
3134 }
3135 
3136 /*
3137  * Issue RST and make ACK acceptable to originator of segment.
3138  * The mbuf must still include the original packet header.
3139  * tp may be NULL.
3140  */
3141 static void
3142 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3143     int tlen, int rstreason)
3144 {
3145 #ifdef INET
3146 	struct ip *ip;
3147 #endif
3148 #ifdef INET6
3149 	struct ip6_hdr *ip6;
3150 #endif
3151 
3152 	if (tp != NULL) {
3153 		INP_WLOCK_ASSERT(tp->t_inpcb);
3154 	}
3155 
3156 	/* Don't bother if destination was broadcast/multicast. */
3157 	if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3158 		goto drop;
3159 #ifdef INET6
3160 	if (mtod(m, struct ip *)->ip_v == 6) {
3161 		ip6 = mtod(m, struct ip6_hdr *);
3162 		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3163 		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3164 			goto drop;
3165 		/* IPv6 anycast check is done at tcp6_input() */
3166 	}
3167 #endif
3168 #if defined(INET) && defined(INET6)
3169 	else
3170 #endif
3171 #ifdef INET
3172 	{
3173 		ip = mtod(m, struct ip *);
3174 		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3175 		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3176 		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3177 		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3178 			goto drop;
3179 	}
3180 #endif
3181 
3182 	/* Perform bandwidth limiting. */
3183 	if (badport_bandlim(rstreason) < 0)
3184 		goto drop;
3185 
3186 	/* tcp_respond consumes the mbuf chain. */
3187 	if (th->th_flags & TH_ACK) {
3188 		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3189 		    th->th_ack, TH_RST);
3190 	} else {
3191 		if (th->th_flags & TH_SYN)
3192 			tlen++;
3193 		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3194 		    (tcp_seq)0, TH_RST|TH_ACK);
3195 	}
3196 	return;
3197 drop:
3198 	m_freem(m);
3199 }
3200 
3201 /*
3202  * Parse TCP options and place in tcpopt.
3203  */
3204 static void
3205 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3206 {
3207 	int opt, optlen;
3208 
3209 	to->to_flags = 0;
3210 	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3211 		opt = cp[0];
3212 		if (opt == TCPOPT_EOL)
3213 			break;
3214 		if (opt == TCPOPT_NOP)
3215 			optlen = 1;
3216 		else {
3217 			if (cnt < 2)
3218 				break;
3219 			optlen = cp[1];
3220 			if (optlen < 2 || optlen > cnt)
3221 				break;
3222 		}
3223 		switch (opt) {
3224 		case TCPOPT_MAXSEG:
3225 			if (optlen != TCPOLEN_MAXSEG)
3226 				continue;
3227 			if (!(flags & TO_SYN))
3228 				continue;
3229 			to->to_flags |= TOF_MSS;
3230 			bcopy((char *)cp + 2,
3231 			    (char *)&to->to_mss, sizeof(to->to_mss));
3232 			to->to_mss = ntohs(to->to_mss);
3233 			break;
3234 		case TCPOPT_WINDOW:
3235 			if (optlen != TCPOLEN_WINDOW)
3236 				continue;
3237 			if (!(flags & TO_SYN))
3238 				continue;
3239 			to->to_flags |= TOF_SCALE;
3240 			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3241 			break;
3242 		case TCPOPT_TIMESTAMP:
3243 			if (optlen != TCPOLEN_TIMESTAMP)
3244 				continue;
3245 			to->to_flags |= TOF_TS;
3246 			bcopy((char *)cp + 2,
3247 			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3248 			to->to_tsval = ntohl(to->to_tsval);
3249 			bcopy((char *)cp + 6,
3250 			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3251 			to->to_tsecr = ntohl(to->to_tsecr);
3252 			break;
3253 #ifdef TCP_SIGNATURE
3254 		/*
3255 		 * XXX In order to reply to a host which has set the
3256 		 * TCP_SIGNATURE option in its initial SYN, we have to
3257 		 * record the fact that the option was observed here
3258 		 * for the syncache code to perform the correct response.
3259 		 */
3260 		case TCPOPT_SIGNATURE:
3261 			if (optlen != TCPOLEN_SIGNATURE)
3262 				continue;
3263 			to->to_flags |= TOF_SIGNATURE;
3264 			to->to_signature = cp + 2;
3265 			break;
3266 #endif
3267 		case TCPOPT_SACK_PERMITTED:
3268 			if (optlen != TCPOLEN_SACK_PERMITTED)
3269 				continue;
3270 			if (!(flags & TO_SYN))
3271 				continue;
3272 			if (!V_tcp_do_sack)
3273 				continue;
3274 			to->to_flags |= TOF_SACKPERM;
3275 			break;
3276 		case TCPOPT_SACK:
3277 			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3278 				continue;
3279 			if (flags & TO_SYN)
3280 				continue;
3281 			to->to_flags |= TOF_SACK;
3282 			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3283 			to->to_sacks = cp + 2;
3284 			TCPSTAT_INC(tcps_sack_rcv_blocks);
3285 			break;
3286 		default:
3287 			continue;
3288 		}
3289 	}
3290 }
3291 
3292 /*
3293  * Pull out of band byte out of a segment so
3294  * it doesn't appear in the user's data queue.
3295  * It is still reflected in the segment length for
3296  * sequencing purposes.
3297  */
3298 static void
3299 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3300     int off)
3301 {
3302 	int cnt = off + th->th_urp - 1;
3303 
3304 	while (cnt >= 0) {
3305 		if (m->m_len > cnt) {
3306 			char *cp = mtod(m, caddr_t) + cnt;
3307 			struct tcpcb *tp = sototcpcb(so);
3308 
3309 			INP_WLOCK_ASSERT(tp->t_inpcb);
3310 
3311 			tp->t_iobc = *cp;
3312 			tp->t_oobflags |= TCPOOB_HAVEDATA;
3313 			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3314 			m->m_len--;
3315 			if (m->m_flags & M_PKTHDR)
3316 				m->m_pkthdr.len--;
3317 			return;
3318 		}
3319 		cnt -= m->m_len;
3320 		m = m->m_next;
3321 		if (m == NULL)
3322 			break;
3323 	}
3324 	panic("tcp_pulloutofband");
3325 }
3326 
3327 /*
3328  * Collect new round-trip time estimate
3329  * and update averages and current timeout.
3330  */
3331 static void
3332 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3333 {
3334 	int delta;
3335 
3336 	INP_WLOCK_ASSERT(tp->t_inpcb);
3337 
3338 	TCPSTAT_INC(tcps_rttupdated);
3339 	tp->t_rttupdated++;
3340 	if (tp->t_srtt != 0) {
3341 		/*
3342 		 * srtt is stored as fixed point with 5 bits after the
3343 		 * binary point (i.e., scaled by 8).  The following magic
3344 		 * is equivalent to the smoothing algorithm in rfc793 with
3345 		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3346 		 * point).  Adjust rtt to origin 0.
3347 		 */
3348 		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3349 			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3350 
3351 		if ((tp->t_srtt += delta) <= 0)
3352 			tp->t_srtt = 1;
3353 
3354 		/*
3355 		 * We accumulate a smoothed rtt variance (actually, a
3356 		 * smoothed mean difference), then set the retransmit
3357 		 * timer to smoothed rtt + 4 times the smoothed variance.
3358 		 * rttvar is stored as fixed point with 4 bits after the
3359 		 * binary point (scaled by 16).  The following is
3360 		 * equivalent to rfc793 smoothing with an alpha of .75
3361 		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3362 		 * rfc793's wired-in beta.
3363 		 */
3364 		if (delta < 0)
3365 			delta = -delta;
3366 		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3367 		if ((tp->t_rttvar += delta) <= 0)
3368 			tp->t_rttvar = 1;
3369 		if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3370 		    tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3371 	} else {
3372 		/*
3373 		 * No rtt measurement yet - use the unsmoothed rtt.
3374 		 * Set the variance to half the rtt (so our first
3375 		 * retransmit happens at 3*rtt).
3376 		 */
3377 		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3378 		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3379 		tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3380 	}
3381 	tp->t_rtttime = 0;
3382 	tp->t_rxtshift = 0;
3383 
3384 	/*
3385 	 * the retransmit should happen at rtt + 4 * rttvar.
3386 	 * Because of the way we do the smoothing, srtt and rttvar
3387 	 * will each average +1/2 tick of bias.  When we compute
3388 	 * the retransmit timer, we want 1/2 tick of rounding and
3389 	 * 1 extra tick because of +-1/2 tick uncertainty in the
3390 	 * firing of the timer.  The bias will give us exactly the
3391 	 * 1.5 tick we need.  But, because the bias is
3392 	 * statistical, we have to test that we don't drop below
3393 	 * the minimum feasible timer (which is 2 ticks).
3394 	 */
3395 	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3396 		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3397 
3398 	/*
3399 	 * We received an ack for a packet that wasn't retransmitted;
3400 	 * it is probably safe to discard any error indications we've
3401 	 * received recently.  This isn't quite right, but close enough
3402 	 * for now (a route might have failed after we sent a segment,
3403 	 * and the return path might not be symmetrical).
3404 	 */
3405 	tp->t_softerror = 0;
3406 }
3407 
3408 /*
3409  * Determine a reasonable value for maxseg size.
3410  * If the route is known, check route for mtu.
3411  * If none, use an mss that can be handled on the outgoing interface
3412  * without forcing IP to fragment.  If no route is found, route has no mtu,
3413  * or the destination isn't local, use a default, hopefully conservative
3414  * size (usually 512 or the default IP max size, but no more than the mtu
3415  * of the interface), as we can't discover anything about intervening
3416  * gateways or networks.  We also initialize the congestion/slow start
3417  * window to be a single segment if the destination isn't local.
3418  * While looking at the routing entry, we also initialize other path-dependent
3419  * parameters from pre-set or cached values in the routing entry.
3420  *
3421  * Also take into account the space needed for options that we
3422  * send regularly.  Make maxseg shorter by that amount to assure
3423  * that we can send maxseg amount of data even when the options
3424  * are present.  Store the upper limit of the length of options plus
3425  * data in maxopd.
3426  *
3427  * NOTE that this routine is only called when we process an incoming
3428  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3429  * settings are handled in tcp_mssopt().
3430  */
3431 void
3432 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3433     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3434 {
3435 	int mss = 0;
3436 	u_long maxmtu = 0;
3437 	struct inpcb *inp = tp->t_inpcb;
3438 	struct hc_metrics_lite metrics;
3439 	int origoffer;
3440 #ifdef INET6
3441 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3442 	size_t min_protoh = isipv6 ?
3443 			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3444 			    sizeof (struct tcpiphdr);
3445 #else
3446 	const size_t min_protoh = sizeof(struct tcpiphdr);
3447 #endif
3448 
3449 	INP_WLOCK_ASSERT(tp->t_inpcb);
3450 
3451 	if (mtuoffer != -1) {
3452 		KASSERT(offer == -1, ("%s: conflict", __func__));
3453 		offer = mtuoffer - min_protoh;
3454 	}
3455 	origoffer = offer;
3456 
3457 	/* Initialize. */
3458 #ifdef INET6
3459 	if (isipv6) {
3460 		maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3461 		tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt;
3462 	}
3463 #endif
3464 #if defined(INET) && defined(INET6)
3465 	else
3466 #endif
3467 #ifdef INET
3468 	{
3469 		maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3470 		tp->t_maxopd = tp->t_maxseg = V_tcp_mssdflt;
3471 	}
3472 #endif
3473 
3474 	/*
3475 	 * No route to sender, stay with default mss and return.
3476 	 */
3477 	if (maxmtu == 0) {
3478 		/*
3479 		 * In case we return early we need to initialize metrics
3480 		 * to a defined state as tcp_hc_get() would do for us
3481 		 * if there was no cache hit.
3482 		 */
3483 		if (metricptr != NULL)
3484 			bzero(metricptr, sizeof(struct hc_metrics_lite));
3485 		return;
3486 	}
3487 
3488 	/* What have we got? */
3489 	switch (offer) {
3490 		case 0:
3491 			/*
3492 			 * Offer == 0 means that there was no MSS on the SYN
3493 			 * segment, in this case we use tcp_mssdflt as
3494 			 * already assigned to t_maxopd above.
3495 			 */
3496 			offer = tp->t_maxopd;
3497 			break;
3498 
3499 		case -1:
3500 			/*
3501 			 * Offer == -1 means that we didn't receive SYN yet.
3502 			 */
3503 			/* FALLTHROUGH */
3504 
3505 		default:
3506 			/*
3507 			 * Prevent DoS attack with too small MSS. Round up
3508 			 * to at least minmss.
3509 			 */
3510 			offer = max(offer, V_tcp_minmss);
3511 	}
3512 
3513 	/*
3514 	 * rmx information is now retrieved from tcp_hostcache.
3515 	 */
3516 	tcp_hc_get(&inp->inp_inc, &metrics);
3517 	if (metricptr != NULL)
3518 		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3519 
3520 	/*
3521 	 * If there's a discovered mtu int tcp hostcache, use it
3522 	 * else, use the link mtu.
3523 	 */
3524 	if (metrics.rmx_mtu)
3525 		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3526 	else {
3527 #ifdef INET6
3528 		if (isipv6) {
3529 			mss = maxmtu - min_protoh;
3530 			if (!V_path_mtu_discovery &&
3531 			    !in6_localaddr(&inp->in6p_faddr))
3532 				mss = min(mss, V_tcp_v6mssdflt);
3533 		}
3534 #endif
3535 #if defined(INET) && defined(INET6)
3536 		else
3537 #endif
3538 #ifdef INET
3539 		{
3540 			mss = maxmtu - min_protoh;
3541 			if (!V_path_mtu_discovery &&
3542 			    !in_localaddr(inp->inp_faddr))
3543 				mss = min(mss, V_tcp_mssdflt);
3544 		}
3545 #endif
3546 		/*
3547 		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3548 		 * probably violates the TCP spec.
3549 		 * The problem is that, since we don't know the
3550 		 * other end's MSS, we are supposed to use a conservative
3551 		 * default.  But, if we do that, then MTU discovery will
3552 		 * never actually take place, because the conservative
3553 		 * default is much less than the MTUs typically seen
3554 		 * on the Internet today.  For the moment, we'll sweep
3555 		 * this under the carpet.
3556 		 *
3557 		 * The conservative default might not actually be a problem
3558 		 * if the only case this occurs is when sending an initial
3559 		 * SYN with options and data to a host we've never talked
3560 		 * to before.  Then, they will reply with an MSS value which
3561 		 * will get recorded and the new parameters should get
3562 		 * recomputed.  For Further Study.
3563 		 */
3564 	}
3565 	mss = min(mss, offer);
3566 
3567 	/*
3568 	 * Sanity check: make sure that maxopd will be large
3569 	 * enough to allow some data on segments even if the
3570 	 * all the option space is used (40bytes).  Otherwise
3571 	 * funny things may happen in tcp_output.
3572 	 */
3573 	mss = max(mss, 64);
3574 
3575 	/*
3576 	 * maxopd stores the maximum length of data AND options
3577 	 * in a segment; maxseg is the amount of data in a normal
3578 	 * segment.  We need to store this value (maxopd) apart
3579 	 * from maxseg, because now every segment carries options
3580 	 * and thus we normally have somewhat less data in segments.
3581 	 */
3582 	tp->t_maxopd = mss;
3583 
3584 	/*
3585 	 * origoffer==-1 indicates that no segments were received yet.
3586 	 * In this case we just guess.
3587 	 */
3588 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
3589 	    (origoffer == -1 ||
3590 	     (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
3591 		mss -= TCPOLEN_TSTAMP_APPA;
3592 
3593 	tp->t_maxseg = mss;
3594 }
3595 
3596 void
3597 tcp_mss(struct tcpcb *tp, int offer)
3598 {
3599 	int mss;
3600 	u_long bufsize;
3601 	struct inpcb *inp;
3602 	struct socket *so;
3603 	struct hc_metrics_lite metrics;
3604 	struct tcp_ifcap cap;
3605 
3606 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3607 
3608 	bzero(&cap, sizeof(cap));
3609 	tcp_mss_update(tp, offer, -1, &metrics, &cap);
3610 
3611 	mss = tp->t_maxseg;
3612 	inp = tp->t_inpcb;
3613 
3614 	/*
3615 	 * If there's a pipesize, change the socket buffer to that size,
3616 	 * don't change if sb_hiwat is different than default (then it
3617 	 * has been changed on purpose with setsockopt).
3618 	 * Make the socket buffers an integral number of mss units;
3619 	 * if the mss is larger than the socket buffer, decrease the mss.
3620 	 */
3621 	so = inp->inp_socket;
3622 	SOCKBUF_LOCK(&so->so_snd);
3623 	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3624 		bufsize = metrics.rmx_sendpipe;
3625 	else
3626 		bufsize = so->so_snd.sb_hiwat;
3627 	if (bufsize < mss)
3628 		mss = bufsize;
3629 	else {
3630 		bufsize = roundup(bufsize, mss);
3631 		if (bufsize > sb_max)
3632 			bufsize = sb_max;
3633 		if (bufsize > so->so_snd.sb_hiwat)
3634 			(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3635 	}
3636 	SOCKBUF_UNLOCK(&so->so_snd);
3637 	tp->t_maxseg = mss;
3638 
3639 	SOCKBUF_LOCK(&so->so_rcv);
3640 	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3641 		bufsize = metrics.rmx_recvpipe;
3642 	else
3643 		bufsize = so->so_rcv.sb_hiwat;
3644 	if (bufsize > mss) {
3645 		bufsize = roundup(bufsize, mss);
3646 		if (bufsize > sb_max)
3647 			bufsize = sb_max;
3648 		if (bufsize > so->so_rcv.sb_hiwat)
3649 			(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3650 	}
3651 	SOCKBUF_UNLOCK(&so->so_rcv);
3652 
3653 	/* Check the interface for TSO capabilities. */
3654 	if (cap.ifcap & CSUM_TSO) {
3655 		tp->t_flags |= TF_TSO;
3656 		tp->t_tsomax = cap.tsomax;
3657 	}
3658 }
3659 
3660 /*
3661  * Determine the MSS option to send on an outgoing SYN.
3662  */
3663 int
3664 tcp_mssopt(struct in_conninfo *inc)
3665 {
3666 	int mss = 0;
3667 	u_long maxmtu = 0;
3668 	u_long thcmtu = 0;
3669 	size_t min_protoh;
3670 
3671 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3672 
3673 #ifdef INET6
3674 	if (inc->inc_flags & INC_ISIPV6) {
3675 		mss = V_tcp_v6mssdflt;
3676 		maxmtu = tcp_maxmtu6(inc, NULL);
3677 		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3678 	}
3679 #endif
3680 #if defined(INET) && defined(INET6)
3681 	else
3682 #endif
3683 #ifdef INET
3684 	{
3685 		mss = V_tcp_mssdflt;
3686 		maxmtu = tcp_maxmtu(inc, NULL);
3687 		min_protoh = sizeof(struct tcpiphdr);
3688 	}
3689 #endif
3690 #if defined(INET6) || defined(INET)
3691 	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3692 #endif
3693 
3694 	if (maxmtu && thcmtu)
3695 		mss = min(maxmtu, thcmtu) - min_protoh;
3696 	else if (maxmtu || thcmtu)
3697 		mss = max(maxmtu, thcmtu) - min_protoh;
3698 
3699 	return (mss);
3700 }
3701 
3702 
3703 /*
3704  * On a partial ack arrives, force the retransmission of the
3705  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3706  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3707  * be started again.
3708  */
3709 static void
3710 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3711 {
3712 	tcp_seq onxt = tp->snd_nxt;
3713 	u_long  ocwnd = tp->snd_cwnd;
3714 
3715 	INP_WLOCK_ASSERT(tp->t_inpcb);
3716 
3717 	tcp_timer_activate(tp, TT_REXMT, 0);
3718 	tp->t_rtttime = 0;
3719 	tp->snd_nxt = th->th_ack;
3720 	/*
3721 	 * Set snd_cwnd to one segment beyond acknowledged offset.
3722 	 * (tp->snd_una has not yet been updated when this function is called.)
3723 	 */
3724 	tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th);
3725 	tp->t_flags |= TF_ACKNOW;
3726 	(void) tcp_output(tp);
3727 	tp->snd_cwnd = ocwnd;
3728 	if (SEQ_GT(onxt, tp->snd_nxt))
3729 		tp->snd_nxt = onxt;
3730 	/*
3731 	 * Partial window deflation.  Relies on fact that tp->snd_una
3732 	 * not updated yet.
3733 	 */
3734 	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3735 		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3736 	else
3737 		tp->snd_cwnd = 0;
3738 	tp->snd_cwnd += tp->t_maxseg;
3739 }
3740