xref: /freebsd/sys/netinet/tcp_input.c (revision d01498defbe804f66435b44f22da9278acddf082)
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_inet.h"
54 #include "opt_inet6.h"
55 #include "opt_ipsec.h"
56 #include "opt_tcpdebug.h"
57 
58 #include <sys/param.h>
59 #include <sys/kernel.h>
60 #ifdef TCP_HHOOK
61 #include <sys/hhook.h>
62 #endif
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/in.h>
87 #include <netinet/in_kdtrace.h>
88 #include <netinet/in_pcb.h>
89 #include <netinet/in_systm.h>
90 #include <netinet/ip.h>
91 #include <netinet/ip_icmp.h>	/* required for icmp_var.h */
92 #include <netinet/icmp_var.h>	/* for ICMP_BANDLIM */
93 #include <netinet/ip_var.h>
94 #include <netinet/ip_options.h>
95 #include <netinet/ip6.h>
96 #include <netinet/icmp6.h>
97 #include <netinet6/in6_pcb.h>
98 #include <netinet6/in6_var.h>
99 #include <netinet6/ip6_var.h>
100 #include <netinet6/nd6.h>
101 #ifdef TCP_RFC7413
102 #include <netinet/tcp_fastopen.h>
103 #endif
104 #include <netinet/tcp.h>
105 #include <netinet/tcp_fsm.h>
106 #include <netinet/tcp_seq.h>
107 #include <netinet/tcp_timer.h>
108 #include <netinet/tcp_var.h>
109 #include <netinet6/tcp6_var.h>
110 #include <netinet/tcpip.h>
111 #include <netinet/cc/cc.h>
112 #ifdef TCPPCAP
113 #include <netinet/tcp_pcap.h>
114 #endif
115 #include <netinet/tcp_syncache.h>
116 #ifdef TCPDEBUG
117 #include <netinet/tcp_debug.h>
118 #endif /* TCPDEBUG */
119 #ifdef TCP_OFFLOAD
120 #include <netinet/tcp_offload.h>
121 #endif
122 
123 #ifdef IPSEC
124 #include <netipsec/ipsec.h>
125 #include <netipsec/ipsec6.h>
126 #endif /*IPSEC*/
127 
128 #include <machine/in_cksum.h>
129 
130 #include <security/mac/mac_framework.h>
131 
132 const int tcprexmtthresh = 3;
133 
134 int tcp_log_in_vain = 0;
135 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
136     &tcp_log_in_vain, 0,
137     "Log all incoming TCP segments to closed ports");
138 
139 VNET_DEFINE(int, blackhole) = 0;
140 #define	V_blackhole		VNET(blackhole)
141 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
142     &VNET_NAME(blackhole), 0,
143     "Do not send RST on segments to closed ports");
144 
145 VNET_DEFINE(int, tcp_delack_enabled) = 1;
146 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
147     &VNET_NAME(tcp_delack_enabled), 0,
148     "Delay ACK to try and piggyback it onto a data packet");
149 
150 VNET_DEFINE(int, drop_synfin) = 0;
151 #define	V_drop_synfin		VNET(drop_synfin)
152 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
153     &VNET_NAME(drop_synfin), 0,
154     "Drop TCP packets with SYN+FIN set");
155 
156 VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
157 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675_pipe, CTLFLAG_VNET | CTLFLAG_RW,
158     &VNET_NAME(tcp_do_rfc6675_pipe), 0,
159     "Use calculated pipe/in-flight bytes per RFC 6675");
160 
161 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
162 #define	V_tcp_do_rfc3042	VNET(tcp_do_rfc3042)
163 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
164     &VNET_NAME(tcp_do_rfc3042), 0,
165     "Enable RFC 3042 (Limited Transmit)");
166 
167 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
168 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
169     &VNET_NAME(tcp_do_rfc3390), 0,
170     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
171 
172 VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
173 SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
174     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
175     "Slow-start flight size (initial congestion window) in number of segments");
176 
177 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
178 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
179     &VNET_NAME(tcp_do_rfc3465), 0,
180     "Enable RFC 3465 (Appropriate Byte Counting)");
181 
182 VNET_DEFINE(int, tcp_abc_l_var) = 2;
183 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
184     &VNET_NAME(tcp_abc_l_var), 2,
185     "Cap the max cwnd increment during slow-start to this number of segments");
186 
187 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn, CTLFLAG_RW, 0, "TCP ECN");
188 
189 VNET_DEFINE(int, tcp_do_ecn) = 2;
190 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
191     &VNET_NAME(tcp_do_ecn), 0,
192     "TCP ECN support");
193 
194 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
195 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
196     &VNET_NAME(tcp_ecn_maxretries), 0,
197     "Max retries before giving up on ECN");
198 
199 VNET_DEFINE(int, tcp_insecure_syn) = 0;
200 #define	V_tcp_insecure_syn	VNET(tcp_insecure_syn)
201 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
202     &VNET_NAME(tcp_insecure_syn), 0,
203     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
204 
205 VNET_DEFINE(int, tcp_insecure_rst) = 0;
206 #define	V_tcp_insecure_rst	VNET(tcp_insecure_rst)
207 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
208     &VNET_NAME(tcp_insecure_rst), 0,
209     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
210 
211 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
212 #define	V_tcp_recvspace	VNET(tcp_recvspace)
213 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
214     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
215 
216 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
217 #define	V_tcp_do_autorcvbuf	VNET(tcp_do_autorcvbuf)
218 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
219     &VNET_NAME(tcp_do_autorcvbuf), 0,
220     "Enable automatic receive buffer sizing");
221 
222 VNET_DEFINE(int, tcp_autorcvbuf_inc) = 16*1024;
223 #define	V_tcp_autorcvbuf_inc	VNET(tcp_autorcvbuf_inc)
224 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
225     &VNET_NAME(tcp_autorcvbuf_inc), 0,
226     "Incrementor step size of automatic receive buffer");
227 
228 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
229 #define	V_tcp_autorcvbuf_max	VNET(tcp_autorcvbuf_max)
230 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
231     &VNET_NAME(tcp_autorcvbuf_max), 0,
232     "Max size of automatic receive buffer");
233 
234 VNET_DEFINE(struct inpcbhead, tcb);
235 #define	tcb6	tcb  /* for KAME src sync over BSD*'s */
236 VNET_DEFINE(struct inpcbinfo, tcbinfo);
237 
238 /*
239  * TCP statistics are stored in an array of counter(9)s, which size matches
240  * size of struct tcpstat.  TCP running connection count is a regular array.
241  */
242 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
243 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
244     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
245 VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
246 SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
247     CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
248     "TCP connection counts by TCP state");
249 
250 static void
251 tcp_vnet_init(const void *unused)
252 {
253 
254 	COUNTER_ARRAY_ALLOC(V_tcps_states, TCP_NSTATES, M_WAITOK);
255 	VNET_PCPUSTAT_ALLOC(tcpstat, M_WAITOK);
256 }
257 VNET_SYSINIT(tcp_vnet_init, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
258     tcp_vnet_init, NULL);
259 
260 #ifdef VIMAGE
261 static void
262 tcp_vnet_uninit(const void *unused)
263 {
264 
265 	COUNTER_ARRAY_FREE(V_tcps_states, TCP_NSTATES);
266 	VNET_PCPUSTAT_FREE(tcpstat);
267 }
268 VNET_SYSUNINIT(tcp_vnet_uninit, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
269     tcp_vnet_uninit, NULL);
270 #endif /* VIMAGE */
271 
272 /*
273  * Kernel module interface for updating tcpstat.  The argument is an index
274  * into tcpstat treated as an array.
275  */
276 void
277 kmod_tcpstat_inc(int statnum)
278 {
279 
280 	counter_u64_add(VNET(tcpstat)[statnum], 1);
281 }
282 
283 #ifdef TCP_HHOOK
284 /*
285  * Wrapper for the TCP established input helper hook.
286  */
287 void
288 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
289 {
290 	struct tcp_hhook_data hhook_data;
291 
292 	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
293 		hhook_data.tp = tp;
294 		hhook_data.th = th;
295 		hhook_data.to = to;
296 
297 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
298 		    tp->osd);
299 	}
300 }
301 #endif
302 
303 /*
304  * CC wrapper hook functions
305  */
306 void
307 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
308     uint16_t type)
309 {
310 	INP_WLOCK_ASSERT(tp->t_inpcb);
311 
312 	tp->ccv->nsegs = nsegs;
313 	tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
314 	if (tp->snd_cwnd <= tp->snd_wnd)
315 		tp->ccv->flags |= CCF_CWND_LIMITED;
316 	else
317 		tp->ccv->flags &= ~CCF_CWND_LIMITED;
318 
319 	if (type == CC_ACK) {
320 		if (tp->snd_cwnd > tp->snd_ssthresh) {
321 			tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
322 			     nsegs * V_tcp_abc_l_var * tcp_maxseg(tp));
323 			if (tp->t_bytes_acked >= tp->snd_cwnd) {
324 				tp->t_bytes_acked -= tp->snd_cwnd;
325 				tp->ccv->flags |= CCF_ABC_SENTAWND;
326 			}
327 		} else {
328 				tp->ccv->flags &= ~CCF_ABC_SENTAWND;
329 				tp->t_bytes_acked = 0;
330 		}
331 	}
332 
333 	if (CC_ALGO(tp)->ack_received != NULL) {
334 		/* XXXLAS: Find a way to live without this */
335 		tp->ccv->curack = th->th_ack;
336 		CC_ALGO(tp)->ack_received(tp->ccv, type);
337 	}
338 }
339 
340 void
341 cc_conn_init(struct tcpcb *tp)
342 {
343 	struct hc_metrics_lite metrics;
344 	struct inpcb *inp = tp->t_inpcb;
345 	u_int maxseg;
346 	int rtt;
347 
348 	INP_WLOCK_ASSERT(tp->t_inpcb);
349 
350 	tcp_hc_get(&inp->inp_inc, &metrics);
351 	maxseg = tcp_maxseg(tp);
352 
353 	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
354 		tp->t_srtt = rtt;
355 		tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
356 		TCPSTAT_INC(tcps_usedrtt);
357 		if (metrics.rmx_rttvar) {
358 			tp->t_rttvar = metrics.rmx_rttvar;
359 			TCPSTAT_INC(tcps_usedrttvar);
360 		} else {
361 			/* default variation is +- 1 rtt */
362 			tp->t_rttvar =
363 			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
364 		}
365 		TCPT_RANGESET(tp->t_rxtcur,
366 		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
367 		    tp->t_rttmin, TCPTV_REXMTMAX);
368 	}
369 	if (metrics.rmx_ssthresh) {
370 		/*
371 		 * There's some sort of gateway or interface
372 		 * buffer limit on the path.  Use this to set
373 		 * the slow start threshold, but set the
374 		 * threshold to no less than 2*mss.
375 		 */
376 		tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
377 		TCPSTAT_INC(tcps_usedssthresh);
378 	}
379 
380 	/*
381 	 * Set the initial slow-start flight size.
382 	 *
383 	 * RFC5681 Section 3.1 specifies the default conservative values.
384 	 * RFC3390 specifies slightly more aggressive values.
385 	 * RFC6928 increases it to ten segments.
386 	 * Support for user specified value for initial flight size.
387 	 *
388 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
389 	 * reduce the initial CWND to one segment as congestion is likely
390 	 * requiring us to be cautious.
391 	 */
392 	if (tp->snd_cwnd == 1)
393 		tp->snd_cwnd = maxseg;		/* SYN(-ACK) lost */
394 	else if (V_tcp_initcwnd_segments)
395 		tp->snd_cwnd = min(V_tcp_initcwnd_segments * maxseg,
396 		    max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
397 	else if (V_tcp_do_rfc3390)
398 		tp->snd_cwnd = min(4 * maxseg, max(2 * maxseg, 4380));
399 	else {
400 		/* Per RFC5681 Section 3.1 */
401 		if (maxseg > 2190)
402 			tp->snd_cwnd = 2 * maxseg;
403 		else if (maxseg > 1095)
404 			tp->snd_cwnd = 3 * maxseg;
405 		else
406 			tp->snd_cwnd = 4 * maxseg;
407 	}
408 
409 	if (CC_ALGO(tp)->conn_init != NULL)
410 		CC_ALGO(tp)->conn_init(tp->ccv);
411 }
412 
413 void inline
414 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
415 {
416 	u_int maxseg;
417 
418 	INP_WLOCK_ASSERT(tp->t_inpcb);
419 
420 	switch(type) {
421 	case CC_NDUPACK:
422 		if (!IN_FASTRECOVERY(tp->t_flags)) {
423 			tp->snd_recover = tp->snd_max;
424 			if (tp->t_flags & TF_ECN_PERMIT)
425 				tp->t_flags |= TF_ECN_SND_CWR;
426 		}
427 		break;
428 	case CC_ECN:
429 		if (!IN_CONGRECOVERY(tp->t_flags)) {
430 			TCPSTAT_INC(tcps_ecn_rcwnd);
431 			tp->snd_recover = tp->snd_max;
432 			if (tp->t_flags & TF_ECN_PERMIT)
433 				tp->t_flags |= TF_ECN_SND_CWR;
434 		}
435 		break;
436 	case CC_RTO:
437 		maxseg = tcp_maxseg(tp);
438 		tp->t_dupacks = 0;
439 		tp->t_bytes_acked = 0;
440 		EXIT_RECOVERY(tp->t_flags);
441 		tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
442 		    maxseg) * maxseg;
443 		tp->snd_cwnd = maxseg;
444 		break;
445 	case CC_RTO_ERR:
446 		TCPSTAT_INC(tcps_sndrexmitbad);
447 		/* RTO was unnecessary, so reset everything. */
448 		tp->snd_cwnd = tp->snd_cwnd_prev;
449 		tp->snd_ssthresh = tp->snd_ssthresh_prev;
450 		tp->snd_recover = tp->snd_recover_prev;
451 		if (tp->t_flags & TF_WASFRECOVERY)
452 			ENTER_FASTRECOVERY(tp->t_flags);
453 		if (tp->t_flags & TF_WASCRECOVERY)
454 			ENTER_CONGRECOVERY(tp->t_flags);
455 		tp->snd_nxt = tp->snd_max;
456 		tp->t_flags &= ~TF_PREVVALID;
457 		tp->t_badrxtwin = 0;
458 		break;
459 	}
460 
461 	if (CC_ALGO(tp)->cong_signal != NULL) {
462 		if (th != NULL)
463 			tp->ccv->curack = th->th_ack;
464 		CC_ALGO(tp)->cong_signal(tp->ccv, type);
465 	}
466 }
467 
468 void inline
469 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
470 {
471 	INP_WLOCK_ASSERT(tp->t_inpcb);
472 
473 	/* XXXLAS: KASSERT that we're in recovery? */
474 
475 	if (CC_ALGO(tp)->post_recovery != NULL) {
476 		tp->ccv->curack = th->th_ack;
477 		CC_ALGO(tp)->post_recovery(tp->ccv);
478 	}
479 	/* XXXLAS: EXIT_RECOVERY ? */
480 	tp->t_bytes_acked = 0;
481 }
482 
483 #ifdef TCP_SIGNATURE
484 static inline int
485 tcp_signature_verify_input(struct mbuf *m, int off0, int tlen, int optlen,
486     struct tcpopt *to, struct tcphdr *th, u_int tcpbflag)
487 {
488 	int ret;
489 
490 	tcp_fields_to_net(th);
491 	ret = tcp_signature_verify(m, off0, tlen, optlen, to, th, tcpbflag);
492 	tcp_fields_to_host(th);
493 	return (ret);
494 }
495 #endif
496 
497 /*
498  * Indicate whether this ack should be delayed.  We can delay the ack if
499  * following conditions are met:
500  *	- There is no delayed ack timer in progress.
501  *	- Our last ack wasn't a 0-sized window. We never want to delay
502  *	  the ack that opens up a 0-sized window.
503  *	- LRO wasn't used for this segment. We make sure by checking that the
504  *	  segment size is not larger than the MSS.
505  */
506 #define DELAY_ACK(tp, tlen)						\
507 	((!tcp_timer_active(tp, TT_DELACK) &&				\
508 	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
509 	    (tlen <= tp->t_maxseg) &&					\
510 	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
511 
512 static void inline
513 cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
514 {
515 	INP_WLOCK_ASSERT(tp->t_inpcb);
516 
517 	if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
518 		switch (iptos & IPTOS_ECN_MASK) {
519 		case IPTOS_ECN_CE:
520 		    tp->ccv->flags |= CCF_IPHDR_CE;
521 		    break;
522 		case IPTOS_ECN_ECT0:
523 		    tp->ccv->flags &= ~CCF_IPHDR_CE;
524 		    break;
525 		case IPTOS_ECN_ECT1:
526 		    tp->ccv->flags &= ~CCF_IPHDR_CE;
527 		    break;
528 		}
529 
530 		if (th->th_flags & TH_CWR)
531 			tp->ccv->flags |= CCF_TCPHDR_CWR;
532 		else
533 			tp->ccv->flags &= ~CCF_TCPHDR_CWR;
534 
535 		if (tp->t_flags & TF_DELACK)
536 			tp->ccv->flags |= CCF_DELACK;
537 		else
538 			tp->ccv->flags &= ~CCF_DELACK;
539 
540 		CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
541 
542 		if (tp->ccv->flags & CCF_ACKNOW)
543 			tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
544 	}
545 }
546 
547 /*
548  * TCP input handling is split into multiple parts:
549  *   tcp6_input is a thin wrapper around tcp_input for the extended
550  *	ip6_protox[] call format in ip6_input
551  *   tcp_input handles primary segment validation, inpcb lookup and
552  *	SYN processing on listen sockets
553  *   tcp_do_segment processes the ACK and text of the segment for
554  *	establishing, established and closing connections
555  */
556 #ifdef INET6
557 int
558 tcp6_input(struct mbuf **mp, int *offp, int proto)
559 {
560 	struct mbuf *m = *mp;
561 	struct in6_ifaddr *ia6;
562 	struct ip6_hdr *ip6;
563 
564 	IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
565 
566 	/*
567 	 * draft-itojun-ipv6-tcp-to-anycast
568 	 * better place to put this in?
569 	 */
570 	ip6 = mtod(m, struct ip6_hdr *);
571 	ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
572 	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
573 		struct ip6_hdr *ip6;
574 
575 		ifa_free(&ia6->ia_ifa);
576 		ip6 = mtod(m, struct ip6_hdr *);
577 		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
578 			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
579 		return (IPPROTO_DONE);
580 	}
581 	if (ia6)
582 		ifa_free(&ia6->ia_ifa);
583 
584 	return (tcp_input(mp, offp, proto));
585 }
586 #endif /* INET6 */
587 
588 int
589 tcp_input(struct mbuf **mp, int *offp, int proto)
590 {
591 	struct mbuf *m = *mp;
592 	struct tcphdr *th = NULL;
593 	struct ip *ip = NULL;
594 	struct inpcb *inp = NULL;
595 	struct tcpcb *tp = NULL;
596 	struct socket *so = NULL;
597 	u_char *optp = NULL;
598 	int off0;
599 	int optlen = 0;
600 #ifdef INET
601 	int len;
602 #endif
603 	int tlen = 0, off;
604 	int drop_hdrlen;
605 	int thflags;
606 	int rstreason = 0;	/* For badport_bandlim accounting purposes */
607 #ifdef TCP_SIGNATURE
608 	uint8_t sig_checked = 0;
609 #endif
610 	uint8_t iptos;
611 	struct m_tag *fwd_tag = NULL;
612 #ifdef INET6
613 	struct ip6_hdr *ip6 = NULL;
614 	int isipv6;
615 #else
616 	const void *ip6 = NULL;
617 #endif /* INET6 */
618 	struct tcpopt to;		/* options in this segment */
619 	char *s = NULL;			/* address and port logging */
620 	int ti_locked;
621 #ifdef TCPDEBUG
622 	/*
623 	 * The size of tcp_saveipgen must be the size of the max ip header,
624 	 * now IPv6.
625 	 */
626 	u_char tcp_saveipgen[IP6_HDR_LEN];
627 	struct tcphdr tcp_savetcp;
628 	short ostate = 0;
629 #endif
630 
631 #ifdef INET6
632 	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
633 #endif
634 
635 	off0 = *offp;
636 	m = *mp;
637 	*mp = NULL;
638 	to.to_flags = 0;
639 	TCPSTAT_INC(tcps_rcvtotal);
640 
641 #ifdef INET6
642 	if (isipv6) {
643 		/* IP6_EXTHDR_CHECK() is already done at tcp6_input(). */
644 
645 		if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
646 			m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
647 			if (m == NULL) {
648 				TCPSTAT_INC(tcps_rcvshort);
649 				return (IPPROTO_DONE);
650 			}
651 		}
652 
653 		ip6 = mtod(m, struct ip6_hdr *);
654 		th = (struct tcphdr *)((caddr_t)ip6 + off0);
655 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
656 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
657 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
658 				th->th_sum = m->m_pkthdr.csum_data;
659 			else
660 				th->th_sum = in6_cksum_pseudo(ip6, tlen,
661 				    IPPROTO_TCP, m->m_pkthdr.csum_data);
662 			th->th_sum ^= 0xffff;
663 		} else
664 			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
665 		if (th->th_sum) {
666 			TCPSTAT_INC(tcps_rcvbadsum);
667 			goto drop;
668 		}
669 
670 		/*
671 		 * Be proactive about unspecified IPv6 address in source.
672 		 * As we use all-zero to indicate unbounded/unconnected pcb,
673 		 * unspecified IPv6 address can be used to confuse us.
674 		 *
675 		 * Note that packets with unspecified IPv6 destination is
676 		 * already dropped in ip6_input.
677 		 */
678 		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
679 			/* XXX stat */
680 			goto drop;
681 		}
682 		iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
683 	}
684 #endif
685 #if defined(INET) && defined(INET6)
686 	else
687 #endif
688 #ifdef INET
689 	{
690 		/*
691 		 * Get IP and TCP header together in first mbuf.
692 		 * Note: IP leaves IP header in first mbuf.
693 		 */
694 		if (off0 > sizeof (struct ip)) {
695 			ip_stripoptions(m);
696 			off0 = sizeof(struct ip);
697 		}
698 		if (m->m_len < sizeof (struct tcpiphdr)) {
699 			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
700 			    == NULL) {
701 				TCPSTAT_INC(tcps_rcvshort);
702 				return (IPPROTO_DONE);
703 			}
704 		}
705 		ip = mtod(m, struct ip *);
706 		th = (struct tcphdr *)((caddr_t)ip + off0);
707 		tlen = ntohs(ip->ip_len) - off0;
708 
709 		iptos = ip->ip_tos;
710 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
711 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
712 				th->th_sum = m->m_pkthdr.csum_data;
713 			else
714 				th->th_sum = in_pseudo(ip->ip_src.s_addr,
715 				    ip->ip_dst.s_addr,
716 				    htonl(m->m_pkthdr.csum_data + tlen +
717 				    IPPROTO_TCP));
718 			th->th_sum ^= 0xffff;
719 		} else {
720 			struct ipovly *ipov = (struct ipovly *)ip;
721 
722 			/*
723 			 * Checksum extended TCP header and data.
724 			 */
725 			len = off0 + tlen;
726 			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
727 			ipov->ih_len = htons(tlen);
728 			th->th_sum = in_cksum(m, len);
729 			/* Reset length for SDT probes. */
730 			ip->ip_len = htons(len);
731 			/* Reset TOS bits */
732 			ip->ip_tos = iptos;
733 			/* Re-initialization for later version check */
734 			ip->ip_v = IPVERSION;
735 		}
736 
737 		if (th->th_sum) {
738 			TCPSTAT_INC(tcps_rcvbadsum);
739 			goto drop;
740 		}
741 	}
742 #endif /* INET */
743 
744 	/*
745 	 * Check that TCP offset makes sense,
746 	 * pull out TCP options and adjust length.		XXX
747 	 */
748 	off = th->th_off << 2;
749 	if (off < sizeof (struct tcphdr) || off > tlen) {
750 		TCPSTAT_INC(tcps_rcvbadoff);
751 		goto drop;
752 	}
753 	tlen -= off;	/* tlen is used instead of ti->ti_len */
754 	if (off > sizeof (struct tcphdr)) {
755 #ifdef INET6
756 		if (isipv6) {
757 			IP6_EXTHDR_CHECK(m, off0, off, IPPROTO_DONE);
758 			ip6 = mtod(m, struct ip6_hdr *);
759 			th = (struct tcphdr *)((caddr_t)ip6 + off0);
760 		}
761 #endif
762 #if defined(INET) && defined(INET6)
763 		else
764 #endif
765 #ifdef INET
766 		{
767 			if (m->m_len < sizeof(struct ip) + off) {
768 				if ((m = m_pullup(m, sizeof (struct ip) + off))
769 				    == NULL) {
770 					TCPSTAT_INC(tcps_rcvshort);
771 					return (IPPROTO_DONE);
772 				}
773 				ip = mtod(m, struct ip *);
774 				th = (struct tcphdr *)((caddr_t)ip + off0);
775 			}
776 		}
777 #endif
778 		optlen = off - sizeof (struct tcphdr);
779 		optp = (u_char *)(th + 1);
780 	}
781 	thflags = th->th_flags;
782 
783 	/*
784 	 * Convert TCP protocol specific fields to host format.
785 	 */
786 	tcp_fields_to_host(th);
787 
788 	/*
789 	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
790 	 */
791 	drop_hdrlen = off0 + off;
792 
793 	/*
794 	 * Locate pcb for segment; if we're likely to add or remove a
795 	 * connection then first acquire pcbinfo lock.  There are three cases
796 	 * where we might discover later we need a write lock despite the
797 	 * flags: ACKs moving a connection out of the syncache, ACKs for a
798 	 * connection in TIMEWAIT and SYNs not targeting a listening socket.
799 	 */
800 	if ((thflags & (TH_FIN | TH_RST)) != 0) {
801 		INP_INFO_RLOCK(&V_tcbinfo);
802 		ti_locked = TI_RLOCKED;
803 	} else
804 		ti_locked = TI_UNLOCKED;
805 
806 	/*
807 	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
808 	 */
809         if (
810 #ifdef INET6
811 	    (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
812 #ifdef INET
813 	    || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
814 #endif
815 #endif
816 #if defined(INET) && !defined(INET6)
817 	    (m->m_flags & M_IP_NEXTHOP)
818 #endif
819 	    )
820 		fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
821 
822 findpcb:
823 #ifdef INVARIANTS
824 	if (ti_locked == TI_RLOCKED) {
825 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
826 	} else {
827 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
828 	}
829 #endif
830 #ifdef INET6
831 	if (isipv6 && fwd_tag != NULL) {
832 		struct sockaddr_in6 *next_hop6;
833 
834 		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
835 		/*
836 		 * Transparently forwarded. Pretend to be the destination.
837 		 * Already got one like this?
838 		 */
839 		inp = in6_pcblookup_mbuf(&V_tcbinfo,
840 		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
841 		    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif, m);
842 		if (!inp) {
843 			/*
844 			 * It's new.  Try to find the ambushing socket.
845 			 * Because we've rewritten the destination address,
846 			 * any hardware-generated hash is ignored.
847 			 */
848 			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
849 			    th->th_sport, &next_hop6->sin6_addr,
850 			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
851 			    th->th_dport, INPLOOKUP_WILDCARD |
852 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
853 		}
854 	} else if (isipv6) {
855 		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
856 		    th->th_sport, &ip6->ip6_dst, th->th_dport,
857 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
858 		    m->m_pkthdr.rcvif, m);
859 	}
860 #endif /* INET6 */
861 #if defined(INET6) && defined(INET)
862 	else
863 #endif
864 #ifdef INET
865 	if (fwd_tag != NULL) {
866 		struct sockaddr_in *next_hop;
867 
868 		next_hop = (struct sockaddr_in *)(fwd_tag+1);
869 		/*
870 		 * Transparently forwarded. Pretend to be the destination.
871 		 * already got one like this?
872 		 */
873 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
874 		    ip->ip_dst, th->th_dport, INPLOOKUP_WLOCKPCB,
875 		    m->m_pkthdr.rcvif, m);
876 		if (!inp) {
877 			/*
878 			 * It's new.  Try to find the ambushing socket.
879 			 * Because we've rewritten the destination address,
880 			 * any hardware-generated hash is ignored.
881 			 */
882 			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
883 			    th->th_sport, next_hop->sin_addr,
884 			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
885 			    th->th_dport, INPLOOKUP_WILDCARD |
886 			    INPLOOKUP_WLOCKPCB, m->m_pkthdr.rcvif);
887 		}
888 	} else
889 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
890 		    th->th_sport, ip->ip_dst, th->th_dport,
891 		    INPLOOKUP_WILDCARD | INPLOOKUP_WLOCKPCB,
892 		    m->m_pkthdr.rcvif, m);
893 #endif /* INET */
894 
895 	/*
896 	 * If the INPCB does not exist then all data in the incoming
897 	 * segment is discarded and an appropriate RST is sent back.
898 	 * XXX MRT Send RST using which routing table?
899 	 */
900 	if (inp == NULL) {
901 		/*
902 		 * Log communication attempts to ports that are not
903 		 * in use.
904 		 */
905 		if ((tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
906 		    tcp_log_in_vain == 2) {
907 			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
908 				log(LOG_INFO, "%s; %s: Connection attempt "
909 				    "to closed port\n", s, __func__);
910 		}
911 		/*
912 		 * When blackholing do not respond with a RST but
913 		 * completely ignore the segment and drop it.
914 		 */
915 		if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
916 		    V_blackhole == 2)
917 			goto dropunlock;
918 
919 		rstreason = BANDLIM_RST_CLOSEDPORT;
920 		goto dropwithreset;
921 	}
922 	INP_WLOCK_ASSERT(inp);
923 	if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
924 	    (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
925 	    ((inp->inp_socket == NULL) ||
926 	    (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
927 		inp->inp_flowid = m->m_pkthdr.flowid;
928 		inp->inp_flowtype = M_HASHTYPE_GET(m);
929 	}
930 #ifdef IPSEC
931 #ifdef INET6
932 	if (isipv6 && ipsec6_in_reject(m, inp)) {
933 		goto dropunlock;
934 	} else
935 #endif /* INET6 */
936 	if (ipsec4_in_reject(m, inp) != 0) {
937 		goto dropunlock;
938 	}
939 #endif /* IPSEC */
940 
941 	/*
942 	 * Check the minimum TTL for socket.
943 	 */
944 	if (inp->inp_ip_minttl != 0) {
945 #ifdef INET6
946 		if (isipv6) {
947 			if (inp->inp_ip_minttl > ip6->ip6_hlim)
948 				goto dropunlock;
949 		} else
950 #endif
951 		if (inp->inp_ip_minttl > ip->ip_ttl)
952 			goto dropunlock;
953 	}
954 
955 	/*
956 	 * A previous connection in TIMEWAIT state is supposed to catch stray
957 	 * or duplicate segments arriving late.  If this segment was a
958 	 * legitimate new connection attempt, the old INPCB gets removed and
959 	 * we can try again to find a listening socket.
960 	 *
961 	 * At this point, due to earlier optimism, we may hold only an inpcb
962 	 * lock, and not the inpcbinfo write lock.  If so, we need to try to
963 	 * acquire it, or if that fails, acquire a reference on the inpcb,
964 	 * drop all locks, acquire a global write lock, and then re-acquire
965 	 * the inpcb lock.  We may at that point discover that another thread
966 	 * has tried to free the inpcb, in which case we need to loop back
967 	 * and try to find a new inpcb to deliver to.
968 	 *
969 	 * XXXRW: It may be time to rethink timewait locking.
970 	 */
971 relocked:
972 	if (inp->inp_flags & INP_TIMEWAIT) {
973 		if (ti_locked == TI_UNLOCKED) {
974 			if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
975 				in_pcbref(inp);
976 				INP_WUNLOCK(inp);
977 				INP_INFO_RLOCK(&V_tcbinfo);
978 				ti_locked = TI_RLOCKED;
979 				INP_WLOCK(inp);
980 				if (in_pcbrele_wlocked(inp)) {
981 					inp = NULL;
982 					goto findpcb;
983 				}
984 			} else
985 				ti_locked = TI_RLOCKED;
986 		}
987 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
988 
989 		if (thflags & TH_SYN)
990 			tcp_dooptions(&to, optp, optlen, TO_SYN);
991 		/*
992 		 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
993 		 */
994 		if (tcp_twcheck(inp, &to, th, m, tlen))
995 			goto findpcb;
996 		INP_INFO_RUNLOCK(&V_tcbinfo);
997 		return (IPPROTO_DONE);
998 	}
999 	/*
1000 	 * The TCPCB may no longer exist if the connection is winding
1001 	 * down or it is in the CLOSED state.  Either way we drop the
1002 	 * segment and send an appropriate response.
1003 	 */
1004 	tp = intotcpcb(inp);
1005 	if (tp == NULL || tp->t_state == TCPS_CLOSED) {
1006 		rstreason = BANDLIM_RST_CLOSEDPORT;
1007 		goto dropwithreset;
1008 	}
1009 
1010 #ifdef TCP_OFFLOAD
1011 	if (tp->t_flags & TF_TOE) {
1012 		tcp_offload_input(tp, m);
1013 		m = NULL;	/* consumed by the TOE driver */
1014 		goto dropunlock;
1015 	}
1016 #endif
1017 
1018 	/*
1019 	 * We've identified a valid inpcb, but it could be that we need an
1020 	 * inpcbinfo write lock but don't hold it.  In this case, attempt to
1021 	 * acquire using the same strategy as the TIMEWAIT case above.  If we
1022 	 * relock, we have to jump back to 'relocked' as the connection might
1023 	 * now be in TIMEWAIT.
1024 	 */
1025 #ifdef INVARIANTS
1026 	if ((thflags & (TH_FIN | TH_RST)) != 0)
1027 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1028 #endif
1029 	if (!((tp->t_state == TCPS_ESTABLISHED && (thflags & TH_SYN) == 0) ||
1030 	      (tp->t_state == TCPS_LISTEN && (thflags & TH_SYN) &&
1031 	       !IS_FASTOPEN(tp->t_flags)))) {
1032 		if (ti_locked == TI_UNLOCKED) {
1033 			if (INP_INFO_TRY_RLOCK(&V_tcbinfo) == 0) {
1034 				in_pcbref(inp);
1035 				INP_WUNLOCK(inp);
1036 				INP_INFO_RLOCK(&V_tcbinfo);
1037 				ti_locked = TI_RLOCKED;
1038 				INP_WLOCK(inp);
1039 				if (in_pcbrele_wlocked(inp)) {
1040 					inp = NULL;
1041 					goto findpcb;
1042 				}
1043 				goto relocked;
1044 			} else
1045 				ti_locked = TI_RLOCKED;
1046 		}
1047 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1048 	}
1049 
1050 #ifdef MAC
1051 	INP_WLOCK_ASSERT(inp);
1052 	if (mac_inpcb_check_deliver(inp, m))
1053 		goto dropunlock;
1054 #endif
1055 	so = inp->inp_socket;
1056 	KASSERT(so != NULL, ("%s: so == NULL", __func__));
1057 #ifdef TCPDEBUG
1058 	if (so->so_options & SO_DEBUG) {
1059 		ostate = tp->t_state;
1060 #ifdef INET6
1061 		if (isipv6) {
1062 			bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1063 		} else
1064 #endif
1065 			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1066 		tcp_savetcp = *th;
1067 	}
1068 #endif /* TCPDEBUG */
1069 	/*
1070 	 * When the socket is accepting connections (the INPCB is in LISTEN
1071 	 * state) we look into the SYN cache if this is a new connection
1072 	 * attempt or the completion of a previous one.
1073 	 */
1074 	KASSERT(tp->t_state == TCPS_LISTEN || !(so->so_options & SO_ACCEPTCONN),
1075 	    ("%s: so accepting but tp %p not listening", __func__, tp));
1076 	if (tp->t_state == TCPS_LISTEN && (so->so_options & SO_ACCEPTCONN)) {
1077 		struct in_conninfo inc;
1078 
1079 		bzero(&inc, sizeof(inc));
1080 #ifdef INET6
1081 		if (isipv6) {
1082 			inc.inc_flags |= INC_ISIPV6;
1083 			inc.inc6_faddr = ip6->ip6_src;
1084 			inc.inc6_laddr = ip6->ip6_dst;
1085 		} else
1086 #endif
1087 		{
1088 			inc.inc_faddr = ip->ip_src;
1089 			inc.inc_laddr = ip->ip_dst;
1090 		}
1091 		inc.inc_fport = th->th_sport;
1092 		inc.inc_lport = th->th_dport;
1093 		inc.inc_fibnum = so->so_fibnum;
1094 
1095 		/*
1096 		 * Check for an existing connection attempt in syncache if
1097 		 * the flag is only ACK.  A successful lookup creates a new
1098 		 * socket appended to the listen queue in SYN_RECEIVED state.
1099 		 */
1100 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1101 
1102 			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1103 			/*
1104 			 * Parse the TCP options here because
1105 			 * syncookies need access to the reflected
1106 			 * timestamp.
1107 			 */
1108 			tcp_dooptions(&to, optp, optlen, 0);
1109 			/*
1110 			 * NB: syncache_expand() doesn't unlock
1111 			 * inp and tcpinfo locks.
1112 			 */
1113 			if (!syncache_expand(&inc, &to, th, &so, m)) {
1114 				/*
1115 				 * No syncache entry or ACK was not
1116 				 * for our SYN/ACK.  Send a RST.
1117 				 * NB: syncache did its own logging
1118 				 * of the failure cause.
1119 				 */
1120 				rstreason = BANDLIM_RST_OPENPORT;
1121 				goto dropwithreset;
1122 			}
1123 #ifdef TCP_RFC7413
1124 new_tfo_socket:
1125 #endif
1126 			if (so == NULL) {
1127 				/*
1128 				 * We completed the 3-way handshake
1129 				 * but could not allocate a socket
1130 				 * either due to memory shortage,
1131 				 * listen queue length limits or
1132 				 * global socket limits.  Send RST
1133 				 * or wait and have the remote end
1134 				 * retransmit the ACK for another
1135 				 * try.
1136 				 */
1137 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1138 					log(LOG_DEBUG, "%s; %s: Listen socket: "
1139 					    "Socket allocation failed due to "
1140 					    "limits or memory shortage, %s\n",
1141 					    s, __func__,
1142 					    V_tcp_sc_rst_sock_fail ?
1143 					    "sending RST" : "try again");
1144 				if (V_tcp_sc_rst_sock_fail) {
1145 					rstreason = BANDLIM_UNLIMITED;
1146 					goto dropwithreset;
1147 				} else
1148 					goto dropunlock;
1149 			}
1150 			/*
1151 			 * Socket is created in state SYN_RECEIVED.
1152 			 * Unlock the listen socket, lock the newly
1153 			 * created socket and update the tp variable.
1154 			 */
1155 			INP_WUNLOCK(inp);	/* listen socket */
1156 			inp = sotoinpcb(so);
1157 			/*
1158 			 * New connection inpcb is already locked by
1159 			 * syncache_expand().
1160 			 */
1161 			INP_WLOCK_ASSERT(inp);
1162 			tp = intotcpcb(inp);
1163 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1164 			    ("%s: ", __func__));
1165 #ifdef TCP_SIGNATURE
1166 			if (sig_checked == 0)  {
1167 				tcp_dooptions(&to, optp, optlen,
1168 				    (thflags & TH_SYN) ? TO_SYN : 0);
1169 				if (!tcp_signature_verify_input(m, off0, tlen,
1170 				    optlen, &to, th, tp->t_flags)) {
1171 
1172 					/*
1173 					 * In SYN_SENT state if it receives an
1174 					 * RST, it is allowed for further
1175 					 * processing.
1176 					 */
1177 					if ((thflags & TH_RST) == 0 ||
1178 					    (tp->t_state == TCPS_SYN_SENT) == 0)
1179 						goto dropunlock;
1180 				}
1181 				sig_checked = 1;
1182 			}
1183 #endif
1184 
1185 			/*
1186 			 * Process the segment and the data it
1187 			 * contains.  tcp_do_segment() consumes
1188 			 * the mbuf chain and unlocks the inpcb.
1189 			 */
1190 			tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1191 			    iptos, ti_locked);
1192 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1193 			return (IPPROTO_DONE);
1194 		}
1195 		/*
1196 		 * Segment flag validation for new connection attempts:
1197 		 *
1198 		 * Our (SYN|ACK) response was rejected.
1199 		 * Check with syncache and remove entry to prevent
1200 		 * retransmits.
1201 		 *
1202 		 * NB: syncache_chkrst does its own logging of failure
1203 		 * causes.
1204 		 */
1205 		if (thflags & TH_RST) {
1206 			syncache_chkrst(&inc, th);
1207 			goto dropunlock;
1208 		}
1209 		/*
1210 		 * We can't do anything without SYN.
1211 		 */
1212 		if ((thflags & TH_SYN) == 0) {
1213 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1214 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1215 				    "SYN is missing, segment ignored\n",
1216 				    s, __func__);
1217 			TCPSTAT_INC(tcps_badsyn);
1218 			goto dropunlock;
1219 		}
1220 		/*
1221 		 * (SYN|ACK) is bogus on a listen socket.
1222 		 */
1223 		if (thflags & TH_ACK) {
1224 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1225 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1226 				    "SYN|ACK invalid, segment rejected\n",
1227 				    s, __func__);
1228 			syncache_badack(&inc);	/* XXX: Not needed! */
1229 			TCPSTAT_INC(tcps_badsyn);
1230 			rstreason = BANDLIM_RST_OPENPORT;
1231 			goto dropwithreset;
1232 		}
1233 		/*
1234 		 * If the drop_synfin option is enabled, drop all
1235 		 * segments with both the SYN and FIN bits set.
1236 		 * This prevents e.g. nmap from identifying the
1237 		 * TCP/IP stack.
1238 		 * XXX: Poor reasoning.  nmap has other methods
1239 		 * and is constantly refining its stack detection
1240 		 * strategies.
1241 		 * XXX: This is a violation of the TCP specification
1242 		 * and was used by RFC1644.
1243 		 */
1244 		if ((thflags & TH_FIN) && V_drop_synfin) {
1245 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1246 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1247 				    "SYN|FIN segment ignored (based on "
1248 				    "sysctl setting)\n", s, __func__);
1249 			TCPSTAT_INC(tcps_badsyn);
1250 			goto dropunlock;
1251 		}
1252 		/*
1253 		 * Segment's flags are (SYN) or (SYN|FIN).
1254 		 *
1255 		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1256 		 * as they do not affect the state of the TCP FSM.
1257 		 * The data pointed to by TH_URG and th_urp is ignored.
1258 		 */
1259 		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1260 		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1261 		KASSERT(thflags & (TH_SYN),
1262 		    ("%s: Listen socket: TH_SYN not set", __func__));
1263 #ifdef INET6
1264 		/*
1265 		 * If deprecated address is forbidden,
1266 		 * we do not accept SYN to deprecated interface
1267 		 * address to prevent any new inbound connection from
1268 		 * getting established.
1269 		 * When we do not accept SYN, we send a TCP RST,
1270 		 * with deprecated source address (instead of dropping
1271 		 * it).  We compromise it as it is much better for peer
1272 		 * to send a RST, and RST will be the final packet
1273 		 * for the exchange.
1274 		 *
1275 		 * If we do not forbid deprecated addresses, we accept
1276 		 * the SYN packet.  RFC2462 does not suggest dropping
1277 		 * SYN in this case.
1278 		 * If we decipher RFC2462 5.5.4, it says like this:
1279 		 * 1. use of deprecated addr with existing
1280 		 *    communication is okay - "SHOULD continue to be
1281 		 *    used"
1282 		 * 2. use of it with new communication:
1283 		 *   (2a) "SHOULD NOT be used if alternate address
1284 		 *        with sufficient scope is available"
1285 		 *   (2b) nothing mentioned otherwise.
1286 		 * Here we fall into (2b) case as we have no choice in
1287 		 * our source address selection - we must obey the peer.
1288 		 *
1289 		 * The wording in RFC2462 is confusing, and there are
1290 		 * multiple description text for deprecated address
1291 		 * handling - worse, they are not exactly the same.
1292 		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1293 		 */
1294 		if (isipv6 && !V_ip6_use_deprecated) {
1295 			struct in6_ifaddr *ia6;
1296 
1297 			ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */);
1298 			if (ia6 != NULL &&
1299 			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1300 				ifa_free(&ia6->ia_ifa);
1301 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1302 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1303 					"Connection attempt to deprecated "
1304 					"IPv6 address rejected\n",
1305 					s, __func__);
1306 				rstreason = BANDLIM_RST_OPENPORT;
1307 				goto dropwithreset;
1308 			}
1309 			if (ia6)
1310 				ifa_free(&ia6->ia_ifa);
1311 		}
1312 #endif /* INET6 */
1313 		/*
1314 		 * Basic sanity checks on incoming SYN requests:
1315 		 *   Don't respond if the destination is a link layer
1316 		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1317 		 *   If it is from this socket it must be forged.
1318 		 *   Don't respond if the source or destination is a
1319 		 *	global or subnet broad- or multicast address.
1320 		 *   Note that it is quite possible to receive unicast
1321 		 *	link-layer packets with a broadcast IP address. Use
1322 		 *	in_broadcast() to find them.
1323 		 */
1324 		if (m->m_flags & (M_BCAST|M_MCAST)) {
1325 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1326 			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1327 				"Connection attempt from broad- or multicast "
1328 				"link layer address ignored\n", s, __func__);
1329 			goto dropunlock;
1330 		}
1331 #ifdef INET6
1332 		if (isipv6) {
1333 			if (th->th_dport == th->th_sport &&
1334 			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1335 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1336 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1337 					"Connection attempt to/from self "
1338 					"ignored\n", s, __func__);
1339 				goto dropunlock;
1340 			}
1341 			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1342 			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1343 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1344 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1345 					"Connection attempt from/to multicast "
1346 					"address ignored\n", s, __func__);
1347 				goto dropunlock;
1348 			}
1349 		}
1350 #endif
1351 #if defined(INET) && defined(INET6)
1352 		else
1353 #endif
1354 #ifdef INET
1355 		{
1356 			if (th->th_dport == th->th_sport &&
1357 			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1358 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1359 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1360 					"Connection attempt from/to self "
1361 					"ignored\n", s, __func__);
1362 				goto dropunlock;
1363 			}
1364 			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1365 			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1366 			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1367 			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1368 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1369 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1370 					"Connection attempt from/to broad- "
1371 					"or multicast address ignored\n",
1372 					s, __func__);
1373 				goto dropunlock;
1374 			}
1375 		}
1376 #endif
1377 		/*
1378 		 * SYN appears to be valid.  Create compressed TCP state
1379 		 * for syncache.
1380 		 */
1381 #ifdef TCPDEBUG
1382 		if (so->so_options & SO_DEBUG)
1383 			tcp_trace(TA_INPUT, ostate, tp,
1384 			    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1385 #endif
1386 		TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
1387 		tcp_dooptions(&to, optp, optlen, TO_SYN);
1388 #ifdef TCP_RFC7413
1389 		if (syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL))
1390 			goto new_tfo_socket;
1391 #else
1392 		syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL);
1393 #endif
1394 		/*
1395 		 * Entry added to syncache and mbuf consumed.
1396 		 * Only the listen socket is unlocked by syncache_add().
1397 		 */
1398 		if (ti_locked == TI_RLOCKED) {
1399 			INP_INFO_RUNLOCK(&V_tcbinfo);
1400 			ti_locked = TI_UNLOCKED;
1401 		}
1402 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1403 		return (IPPROTO_DONE);
1404 	} else if (tp->t_state == TCPS_LISTEN) {
1405 		/*
1406 		 * When a listen socket is torn down the SO_ACCEPTCONN
1407 		 * flag is removed first while connections are drained
1408 		 * from the accept queue in a unlock/lock cycle of the
1409 		 * ACCEPT_LOCK, opening a race condition allowing a SYN
1410 		 * attempt go through unhandled.
1411 		 */
1412 		goto dropunlock;
1413 	}
1414 
1415 #ifdef TCP_SIGNATURE
1416 	if (sig_checked == 0)  {
1417 		tcp_dooptions(&to, optp, optlen,
1418 		    (thflags & TH_SYN) ? TO_SYN : 0);
1419 		if (!tcp_signature_verify_input(m, off0, tlen, optlen, &to,
1420 		    th, tp->t_flags)) {
1421 
1422 			/*
1423 			 * In SYN_SENT state if it receives an RST, it is
1424 			 * allowed for further processing.
1425 			 */
1426 			if ((thflags & TH_RST) == 0 ||
1427 			    (tp->t_state == TCPS_SYN_SENT) == 0)
1428 				goto dropunlock;
1429 		}
1430 		sig_checked = 1;
1431 	}
1432 #endif
1433 
1434 	TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1435 
1436 	/*
1437 	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1438 	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1439 	 * the inpcb, and unlocks pcbinfo.
1440 	 */
1441 	tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos, ti_locked);
1442 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1443 	return (IPPROTO_DONE);
1444 
1445 dropwithreset:
1446 	TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1447 
1448 	if (ti_locked == TI_RLOCKED) {
1449 		INP_INFO_RUNLOCK(&V_tcbinfo);
1450 		ti_locked = TI_UNLOCKED;
1451 	}
1452 #ifdef INVARIANTS
1453 	else {
1454 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropwithreset "
1455 		    "ti_locked: %d", __func__, ti_locked));
1456 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1457 	}
1458 #endif
1459 
1460 	if (inp != NULL) {
1461 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1462 		INP_WUNLOCK(inp);
1463 	} else
1464 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1465 	m = NULL;	/* mbuf chain got consumed. */
1466 	goto drop;
1467 
1468 dropunlock:
1469 	if (m != NULL)
1470 		TCP_PROBE5(receive, NULL, tp, mtod(m, const char *), tp, th);
1471 
1472 	if (ti_locked == TI_RLOCKED) {
1473 		INP_INFO_RUNLOCK(&V_tcbinfo);
1474 		ti_locked = TI_UNLOCKED;
1475 	}
1476 #ifdef INVARIANTS
1477 	else {
1478 		KASSERT(ti_locked == TI_UNLOCKED, ("%s: dropunlock "
1479 		    "ti_locked: %d", __func__, ti_locked));
1480 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1481 	}
1482 #endif
1483 
1484 	if (inp != NULL)
1485 		INP_WUNLOCK(inp);
1486 
1487 drop:
1488 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1489 	if (s != NULL)
1490 		free(s, M_TCPLOG);
1491 	if (m != NULL)
1492 		m_freem(m);
1493 	return (IPPROTO_DONE);
1494 }
1495 
1496 void
1497 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1498     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos,
1499     int ti_locked)
1500 {
1501 	int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
1502 	int rstreason, todrop, win;
1503 	uint32_t tiwin;
1504 	uint16_t nsegs;
1505 	char *s;
1506 	struct in_conninfo *inc;
1507 	struct mbuf *mfree;
1508 	struct tcpopt to;
1509 #ifdef TCP_RFC7413
1510 	int tfo_syn;
1511 #endif
1512 
1513 #ifdef TCPDEBUG
1514 	/*
1515 	 * The size of tcp_saveipgen must be the size of the max ip header,
1516 	 * now IPv6.
1517 	 */
1518 	u_char tcp_saveipgen[IP6_HDR_LEN];
1519 	struct tcphdr tcp_savetcp;
1520 	short ostate = 0;
1521 #endif
1522 	thflags = th->th_flags;
1523 	inc = &tp->t_inpcb->inp_inc;
1524 	tp->sackhint.last_sack_ack = 0;
1525 	sack_changed = 0;
1526 	nsegs = max(1, m->m_pkthdr.lro_nsegs);
1527 
1528 	/*
1529 	 * If this is either a state-changing packet or current state isn't
1530 	 * established, we require a write lock on tcbinfo.  Otherwise, we
1531 	 * allow the tcbinfo to be in either alocked or unlocked, as the
1532 	 * caller may have unnecessarily acquired a write lock due to a race.
1533 	 */
1534 	if ((thflags & (TH_SYN | TH_FIN | TH_RST)) != 0 ||
1535 	    tp->t_state != TCPS_ESTABLISHED) {
1536 		KASSERT(ti_locked == TI_RLOCKED, ("%s ti_locked %d for "
1537 		    "SYN/FIN/RST/!EST", __func__, ti_locked));
1538 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1539 	} else {
1540 #ifdef INVARIANTS
1541 		if (ti_locked == TI_RLOCKED)
1542 			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1543 		else {
1544 			KASSERT(ti_locked == TI_UNLOCKED, ("%s: EST "
1545 			    "ti_locked: %d", __func__, ti_locked));
1546 			INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
1547 		}
1548 #endif
1549 	}
1550 	INP_WLOCK_ASSERT(tp->t_inpcb);
1551 	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1552 	    __func__));
1553 	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1554 	    __func__));
1555 
1556 #ifdef TCPPCAP
1557 	/* Save segment, if requested. */
1558 	tcp_pcap_add(th, m, &(tp->t_inpkts));
1559 #endif
1560 
1561 	/*
1562 	 * Segment received on connection.
1563 	 * Reset idle time and keep-alive timer.
1564 	 * XXX: This should be done after segment
1565 	 * validation to ignore broken/spoofed segs.
1566 	 */
1567 	tp->t_rcvtime = ticks;
1568 	if (TCPS_HAVEESTABLISHED(tp->t_state))
1569 		tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
1570 
1571 	/*
1572 	 * Scale up the window into a 32-bit value.
1573 	 * For the SYN_SENT state the scale is zero.
1574 	 */
1575 	tiwin = th->th_win << tp->snd_scale;
1576 
1577 	/*
1578 	 * TCP ECN processing.
1579 	 */
1580 	if (tp->t_flags & TF_ECN_PERMIT) {
1581 		if (thflags & TH_CWR)
1582 			tp->t_flags &= ~TF_ECN_SND_ECE;
1583 		switch (iptos & IPTOS_ECN_MASK) {
1584 		case IPTOS_ECN_CE:
1585 			tp->t_flags |= TF_ECN_SND_ECE;
1586 			TCPSTAT_INC(tcps_ecn_ce);
1587 			break;
1588 		case IPTOS_ECN_ECT0:
1589 			TCPSTAT_INC(tcps_ecn_ect0);
1590 			break;
1591 		case IPTOS_ECN_ECT1:
1592 			TCPSTAT_INC(tcps_ecn_ect1);
1593 			break;
1594 		}
1595 
1596 		/* Process a packet differently from RFC3168. */
1597 		cc_ecnpkt_handler(tp, th, iptos);
1598 
1599 		/* Congestion experienced. */
1600 		if (thflags & TH_ECE) {
1601 			cc_cong_signal(tp, th, CC_ECN);
1602 		}
1603 	}
1604 
1605 	/*
1606 	 * Parse options on any incoming segment.
1607 	 */
1608 	tcp_dooptions(&to, (u_char *)(th + 1),
1609 	    (th->th_off << 2) - sizeof(struct tcphdr),
1610 	    (thflags & TH_SYN) ? TO_SYN : 0);
1611 
1612 	/*
1613 	 * If echoed timestamp is later than the current time,
1614 	 * fall back to non RFC1323 RTT calculation.  Normalize
1615 	 * timestamp if syncookies were used when this connection
1616 	 * was established.
1617 	 */
1618 	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1619 		to.to_tsecr -= tp->ts_offset;
1620 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1621 			to.to_tsecr = 0;
1622 	}
1623 	/*
1624 	 * If timestamps were negotiated during SYN/ACK they should
1625 	 * appear on every segment during this session and vice versa.
1626 	 */
1627 	if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1628 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1629 			log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1630 			    "no action\n", s, __func__);
1631 			free(s, M_TCPLOG);
1632 		}
1633 	}
1634 	if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1635 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1636 			log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1637 			    "no action\n", s, __func__);
1638 			free(s, M_TCPLOG);
1639 		}
1640 	}
1641 
1642 	/*
1643 	 * Process options only when we get SYN/ACK back. The SYN case
1644 	 * for incoming connections is handled in tcp_syncache.
1645 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1646 	 * or <SYN,ACK>) segment itself is never scaled.
1647 	 * XXX this is traditional behavior, may need to be cleaned up.
1648 	 */
1649 	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1650 		if ((to.to_flags & TOF_SCALE) &&
1651 		    (tp->t_flags & TF_REQ_SCALE)) {
1652 			tp->t_flags |= TF_RCVD_SCALE;
1653 			tp->snd_scale = to.to_wscale;
1654 		}
1655 		/*
1656 		 * Initial send window.  It will be updated with
1657 		 * the next incoming segment to the scaled value.
1658 		 */
1659 		tp->snd_wnd = th->th_win;
1660 		if (to.to_flags & TOF_TS) {
1661 			tp->t_flags |= TF_RCVD_TSTMP;
1662 			tp->ts_recent = to.to_tsval;
1663 			tp->ts_recent_age = tcp_ts_getticks();
1664 		}
1665 		if (to.to_flags & TOF_MSS)
1666 			tcp_mss(tp, to.to_mss);
1667 		if ((tp->t_flags & TF_SACK_PERMIT) &&
1668 		    (to.to_flags & TOF_SACKPERM) == 0)
1669 			tp->t_flags &= ~TF_SACK_PERMIT;
1670 	}
1671 
1672 	/*
1673 	 * Header prediction: check for the two common cases
1674 	 * of a uni-directional data xfer.  If the packet has
1675 	 * no control flags, is in-sequence, the window didn't
1676 	 * change and we're not retransmitting, it's a
1677 	 * candidate.  If the length is zero and the ack moved
1678 	 * forward, we're the sender side of the xfer.  Just
1679 	 * free the data acked & wake any higher level process
1680 	 * that was blocked waiting for space.  If the length
1681 	 * is non-zero and the ack didn't move, we're the
1682 	 * receiver side.  If we're getting packets in-order
1683 	 * (the reassembly queue is empty), add the data to
1684 	 * the socket buffer and note that we need a delayed ack.
1685 	 * Make sure that the hidden state-flags are also off.
1686 	 * Since we check for TCPS_ESTABLISHED first, it can only
1687 	 * be TH_NEEDSYN.
1688 	 */
1689 	if (tp->t_state == TCPS_ESTABLISHED &&
1690 	    th->th_seq == tp->rcv_nxt &&
1691 	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1692 	    tp->snd_nxt == tp->snd_max &&
1693 	    tiwin && tiwin == tp->snd_wnd &&
1694 	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1695 	    LIST_EMPTY(&tp->t_segq) &&
1696 	    ((to.to_flags & TOF_TS) == 0 ||
1697 	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1698 
1699 		/*
1700 		 * If last ACK falls within this segment's sequence numbers,
1701 		 * record the timestamp.
1702 		 * NOTE that the test is modified according to the latest
1703 		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1704 		 */
1705 		if ((to.to_flags & TOF_TS) != 0 &&
1706 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1707 			tp->ts_recent_age = tcp_ts_getticks();
1708 			tp->ts_recent = to.to_tsval;
1709 		}
1710 
1711 		if (tlen == 0) {
1712 			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1713 			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1714 			    !IN_RECOVERY(tp->t_flags) &&
1715 			    (to.to_flags & TOF_SACK) == 0 &&
1716 			    TAILQ_EMPTY(&tp->snd_holes)) {
1717 				/*
1718 				 * This is a pure ack for outstanding data.
1719 				 */
1720 				if (ti_locked == TI_RLOCKED)
1721 					INP_INFO_RUNLOCK(&V_tcbinfo);
1722 				ti_locked = TI_UNLOCKED;
1723 
1724 				TCPSTAT_INC(tcps_predack);
1725 
1726 				/*
1727 				 * "bad retransmit" recovery.
1728 				 */
1729 				if (tp->t_rxtshift == 1 &&
1730 				    tp->t_flags & TF_PREVVALID &&
1731 				    (int)(ticks - tp->t_badrxtwin) < 0) {
1732 					cc_cong_signal(tp, th, CC_RTO_ERR);
1733 				}
1734 
1735 				/*
1736 				 * Recalculate the transmit timer / rtt.
1737 				 *
1738 				 * Some boxes send broken timestamp replies
1739 				 * during the SYN+ACK phase, ignore
1740 				 * timestamps of 0 or we could calculate a
1741 				 * huge RTT and blow up the retransmit timer.
1742 				 */
1743 				if ((to.to_flags & TOF_TS) != 0 &&
1744 				    to.to_tsecr) {
1745 					uint32_t t;
1746 
1747 					t = tcp_ts_getticks() - to.to_tsecr;
1748 					if (!tp->t_rttlow || tp->t_rttlow > t)
1749 						tp->t_rttlow = t;
1750 					tcp_xmit_timer(tp,
1751 					    TCP_TS_TO_TICKS(t) + 1);
1752 				} else if (tp->t_rtttime &&
1753 				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1754 					if (!tp->t_rttlow ||
1755 					    tp->t_rttlow > ticks - tp->t_rtttime)
1756 						tp->t_rttlow = ticks - tp->t_rtttime;
1757 					tcp_xmit_timer(tp,
1758 							ticks - tp->t_rtttime);
1759 				}
1760 				acked = BYTES_THIS_ACK(tp, th);
1761 
1762 #ifdef TCP_HHOOK
1763 				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1764 				hhook_run_tcp_est_in(tp, th, &to);
1765 #endif
1766 
1767 				TCPSTAT_ADD(tcps_rcvackpack, nsegs);
1768 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1769 				sbdrop(&so->so_snd, acked);
1770 				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1771 				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1772 					tp->snd_recover = th->th_ack - 1;
1773 
1774 				/*
1775 				 * Let the congestion control algorithm update
1776 				 * congestion control related information. This
1777 				 * typically means increasing the congestion
1778 				 * window.
1779 				 */
1780 				cc_ack_received(tp, th, nsegs, CC_ACK);
1781 
1782 				tp->snd_una = th->th_ack;
1783 				/*
1784 				 * Pull snd_wl2 up to prevent seq wrap relative
1785 				 * to th_ack.
1786 				 */
1787 				tp->snd_wl2 = th->th_ack;
1788 				tp->t_dupacks = 0;
1789 				m_freem(m);
1790 
1791 				/*
1792 				 * If all outstanding data are acked, stop
1793 				 * retransmit timer, otherwise restart timer
1794 				 * using current (possibly backed-off) value.
1795 				 * If process is waiting for space,
1796 				 * wakeup/selwakeup/signal.  If data
1797 				 * are ready to send, let tcp_output
1798 				 * decide between more output or persist.
1799 				 */
1800 #ifdef TCPDEBUG
1801 				if (so->so_options & SO_DEBUG)
1802 					tcp_trace(TA_INPUT, ostate, tp,
1803 					    (void *)tcp_saveipgen,
1804 					    &tcp_savetcp, 0);
1805 #endif
1806 				TCP_PROBE3(debug__input, tp, th,
1807 					mtod(m, const char *));
1808 				if (tp->snd_una == tp->snd_max)
1809 					tcp_timer_activate(tp, TT_REXMT, 0);
1810 				else if (!tcp_timer_active(tp, TT_PERSIST))
1811 					tcp_timer_activate(tp, TT_REXMT,
1812 						      tp->t_rxtcur);
1813 				sowwakeup(so);
1814 				if (sbavail(&so->so_snd))
1815 					(void) tp->t_fb->tfb_tcp_output(tp);
1816 				goto check_delack;
1817 			}
1818 		} else if (th->th_ack == tp->snd_una &&
1819 		    tlen <= sbspace(&so->so_rcv)) {
1820 			int newsize = 0;	/* automatic sockbuf scaling */
1821 
1822 			/*
1823 			 * This is a pure, in-sequence data packet with
1824 			 * nothing on the reassembly queue and we have enough
1825 			 * buffer space to take it.
1826 			 */
1827 			if (ti_locked == TI_RLOCKED)
1828 				INP_INFO_RUNLOCK(&V_tcbinfo);
1829 			ti_locked = TI_UNLOCKED;
1830 
1831 			/* Clean receiver SACK report if present */
1832 			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1833 				tcp_clean_sackreport(tp);
1834 			TCPSTAT_INC(tcps_preddat);
1835 			tp->rcv_nxt += tlen;
1836 			/*
1837 			 * Pull snd_wl1 up to prevent seq wrap relative to
1838 			 * th_seq.
1839 			 */
1840 			tp->snd_wl1 = th->th_seq;
1841 			/*
1842 			 * Pull rcv_up up to prevent seq wrap relative to
1843 			 * rcv_nxt.
1844 			 */
1845 			tp->rcv_up = tp->rcv_nxt;
1846 			TCPSTAT_ADD(tcps_rcvpack, nsegs);
1847 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1848 #ifdef TCPDEBUG
1849 			if (so->so_options & SO_DEBUG)
1850 				tcp_trace(TA_INPUT, ostate, tp,
1851 				    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1852 #endif
1853 			TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
1854 
1855 		/*
1856 		 * Automatic sizing of receive socket buffer.  Often the send
1857 		 * buffer size is not optimally adjusted to the actual network
1858 		 * conditions at hand (delay bandwidth product).  Setting the
1859 		 * buffer size too small limits throughput on links with high
1860 		 * bandwidth and high delay (eg. trans-continental/oceanic links).
1861 		 *
1862 		 * On the receive side the socket buffer memory is only rarely
1863 		 * used to any significant extent.  This allows us to be much
1864 		 * more aggressive in scaling the receive socket buffer.  For
1865 		 * the case that the buffer space is actually used to a large
1866 		 * extent and we run out of kernel memory we can simply drop
1867 		 * the new segments; TCP on the sender will just retransmit it
1868 		 * later.  Setting the buffer size too big may only consume too
1869 		 * much kernel memory if the application doesn't read() from
1870 		 * the socket or packet loss or reordering makes use of the
1871 		 * reassembly queue.
1872 		 *
1873 		 * The criteria to step up the receive buffer one notch are:
1874 		 *  1. Application has not set receive buffer size with
1875 		 *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
1876 		 *  2. the number of bytes received during the time it takes
1877 		 *     one timestamp to be reflected back to us (the RTT);
1878 		 *  3. received bytes per RTT is within seven eighth of the
1879 		 *     current socket buffer size;
1880 		 *  4. receive buffer size has not hit maximal automatic size;
1881 		 *
1882 		 * This algorithm does one step per RTT at most and only if
1883 		 * we receive a bulk stream w/o packet losses or reorderings.
1884 		 * Shrinking the buffer during idle times is not necessary as
1885 		 * it doesn't consume any memory when idle.
1886 		 *
1887 		 * TODO: Only step up if the application is actually serving
1888 		 * the buffer to better manage the socket buffer resources.
1889 		 */
1890 			if (V_tcp_do_autorcvbuf &&
1891 			    (to.to_flags & TOF_TS) &&
1892 			    to.to_tsecr &&
1893 			    (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
1894 				if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
1895 				    to.to_tsecr - tp->rfbuf_ts < hz) {
1896 					if (tp->rfbuf_cnt >
1897 					    (so->so_rcv.sb_hiwat / 8 * 7) &&
1898 					    so->so_rcv.sb_hiwat <
1899 					    V_tcp_autorcvbuf_max) {
1900 						newsize =
1901 						    min(so->so_rcv.sb_hiwat +
1902 						    V_tcp_autorcvbuf_inc,
1903 						    V_tcp_autorcvbuf_max);
1904 					}
1905 					/* Start over with next RTT. */
1906 					tp->rfbuf_ts = 0;
1907 					tp->rfbuf_cnt = 0;
1908 				} else
1909 					tp->rfbuf_cnt += tlen;	/* add up */
1910 			}
1911 
1912 			/* Add data to socket buffer. */
1913 			SOCKBUF_LOCK(&so->so_rcv);
1914 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1915 				m_freem(m);
1916 			} else {
1917 				/*
1918 				 * Set new socket buffer size.
1919 				 * Give up when limit is reached.
1920 				 */
1921 				if (newsize)
1922 					if (!sbreserve_locked(&so->so_rcv,
1923 					    newsize, so, NULL))
1924 						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1925 				m_adj(m, drop_hdrlen);	/* delayed header drop */
1926 				sbappendstream_locked(&so->so_rcv, m, 0);
1927 			}
1928 			/* NB: sorwakeup_locked() does an implicit unlock. */
1929 			sorwakeup_locked(so);
1930 			if (DELAY_ACK(tp, tlen)) {
1931 				tp->t_flags |= TF_DELACK;
1932 			} else {
1933 				tp->t_flags |= TF_ACKNOW;
1934 				tp->t_fb->tfb_tcp_output(tp);
1935 			}
1936 			goto check_delack;
1937 		}
1938 	}
1939 
1940 	/*
1941 	 * Calculate amount of space in receive window,
1942 	 * and then do TCP input processing.
1943 	 * Receive window is amount of space in rcv queue,
1944 	 * but not less than advertised window.
1945 	 */
1946 	win = sbspace(&so->so_rcv);
1947 	if (win < 0)
1948 		win = 0;
1949 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1950 
1951 	/* Reset receive buffer auto scaling when not in bulk receive mode. */
1952 	tp->rfbuf_ts = 0;
1953 	tp->rfbuf_cnt = 0;
1954 
1955 	switch (tp->t_state) {
1956 
1957 	/*
1958 	 * If the state is SYN_RECEIVED:
1959 	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1960 	 */
1961 	case TCPS_SYN_RECEIVED:
1962 		if ((thflags & TH_ACK) &&
1963 		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1964 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1965 				rstreason = BANDLIM_RST_OPENPORT;
1966 				goto dropwithreset;
1967 		}
1968 #ifdef TCP_RFC7413
1969 		if (IS_FASTOPEN(tp->t_flags)) {
1970 			/*
1971 			 * When a TFO connection is in SYN_RECEIVED, the
1972 			 * only valid packets are the initial SYN, a
1973 			 * retransmit/copy of the initial SYN (possibly with
1974 			 * a subset of the original data), a valid ACK, a
1975 			 * FIN, or a RST.
1976 			 */
1977 			if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
1978 				rstreason = BANDLIM_RST_OPENPORT;
1979 				goto dropwithreset;
1980 			} else if (thflags & TH_SYN) {
1981 				/* non-initial SYN is ignored */
1982 				if ((tcp_timer_active(tp, TT_DELACK) ||
1983 				     tcp_timer_active(tp, TT_REXMT)))
1984 					goto drop;
1985 			} else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
1986 				goto drop;
1987 			}
1988 		}
1989 #endif
1990 		break;
1991 
1992 	/*
1993 	 * If the state is SYN_SENT:
1994 	 *	if seg contains an ACK, but not for our SYN, drop the input.
1995 	 *	if seg contains a RST, then drop the connection.
1996 	 *	if seg does not contain SYN, then drop it.
1997 	 * Otherwise this is an acceptable SYN segment
1998 	 *	initialize tp->rcv_nxt and tp->irs
1999 	 *	if seg contains ack then advance tp->snd_una
2000 	 *	if seg contains an ECE and ECN support is enabled, the stream
2001 	 *	    is ECN capable.
2002 	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
2003 	 *	arrange for segment to be acked (eventually)
2004 	 *	continue processing rest of data/controls, beginning with URG
2005 	 */
2006 	case TCPS_SYN_SENT:
2007 		if ((thflags & TH_ACK) &&
2008 		    (SEQ_LEQ(th->th_ack, tp->iss) ||
2009 		     SEQ_GT(th->th_ack, tp->snd_max))) {
2010 			rstreason = BANDLIM_UNLIMITED;
2011 			goto dropwithreset;
2012 		}
2013 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
2014 			TCP_PROBE5(connect__refused, NULL, tp,
2015 			    mtod(m, const char *), tp, th);
2016 			tp = tcp_drop(tp, ECONNREFUSED);
2017 		}
2018 		if (thflags & TH_RST)
2019 			goto drop;
2020 		if (!(thflags & TH_SYN))
2021 			goto drop;
2022 
2023 		tp->irs = th->th_seq;
2024 		tcp_rcvseqinit(tp);
2025 		if (thflags & TH_ACK) {
2026 			TCPSTAT_INC(tcps_connects);
2027 			soisconnected(so);
2028 #ifdef MAC
2029 			mac_socketpeer_set_from_mbuf(m, so);
2030 #endif
2031 			/* Do window scaling on this connection? */
2032 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2033 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2034 				tp->rcv_scale = tp->request_r_scale;
2035 			}
2036 			tp->rcv_adv += min(tp->rcv_wnd,
2037 			    TCP_MAXWIN << tp->rcv_scale);
2038 			tp->snd_una++;		/* SYN is acked */
2039 			/*
2040 			 * If there's data, delay ACK; if there's also a FIN
2041 			 * ACKNOW will be turned on later.
2042 			 */
2043 			if (DELAY_ACK(tp, tlen) && tlen != 0)
2044 				tcp_timer_activate(tp, TT_DELACK,
2045 				    tcp_delacktime);
2046 			else
2047 				tp->t_flags |= TF_ACKNOW;
2048 
2049 			if ((thflags & TH_ECE) && V_tcp_do_ecn) {
2050 				tp->t_flags |= TF_ECN_PERMIT;
2051 				TCPSTAT_INC(tcps_ecn_shs);
2052 			}
2053 
2054 			/*
2055 			 * Received <SYN,ACK> in SYN_SENT[*] state.
2056 			 * Transitions:
2057 			 *	SYN_SENT  --> ESTABLISHED
2058 			 *	SYN_SENT* --> FIN_WAIT_1
2059 			 */
2060 			tp->t_starttime = ticks;
2061 			if (tp->t_flags & TF_NEEDFIN) {
2062 				tcp_state_change(tp, TCPS_FIN_WAIT_1);
2063 				tp->t_flags &= ~TF_NEEDFIN;
2064 				thflags &= ~TH_SYN;
2065 			} else {
2066 				tcp_state_change(tp, TCPS_ESTABLISHED);
2067 				TCP_PROBE5(connect__established, NULL, tp,
2068 				    mtod(m, const char *), tp, th);
2069 				cc_conn_init(tp);
2070 				tcp_timer_activate(tp, TT_KEEP,
2071 				    TP_KEEPIDLE(tp));
2072 			}
2073 		} else {
2074 			/*
2075 			 * Received initial SYN in SYN-SENT[*] state =>
2076 			 * simultaneous open.
2077 			 * If it succeeds, connection is * half-synchronized.
2078 			 * Otherwise, do 3-way handshake:
2079 			 *        SYN-SENT -> SYN-RECEIVED
2080 			 *        SYN-SENT* -> SYN-RECEIVED*
2081 			 */
2082 			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2083 			tcp_timer_activate(tp, TT_REXMT, 0);
2084 			tcp_state_change(tp, TCPS_SYN_RECEIVED);
2085 		}
2086 
2087 		KASSERT(ti_locked == TI_RLOCKED, ("%s: trimthenstep6: "
2088 		    "ti_locked %d", __func__, ti_locked));
2089 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2090 		INP_WLOCK_ASSERT(tp->t_inpcb);
2091 
2092 		/*
2093 		 * Advance th->th_seq to correspond to first data byte.
2094 		 * If data, trim to stay within window,
2095 		 * dropping FIN if necessary.
2096 		 */
2097 		th->th_seq++;
2098 		if (tlen > tp->rcv_wnd) {
2099 			todrop = tlen - tp->rcv_wnd;
2100 			m_adj(m, -todrop);
2101 			tlen = tp->rcv_wnd;
2102 			thflags &= ~TH_FIN;
2103 			TCPSTAT_INC(tcps_rcvpackafterwin);
2104 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2105 		}
2106 		tp->snd_wl1 = th->th_seq - 1;
2107 		tp->rcv_up = th->th_seq;
2108 		/*
2109 		 * Client side of transaction: already sent SYN and data.
2110 		 * If the remote host used T/TCP to validate the SYN,
2111 		 * our data will be ACK'd; if so, enter normal data segment
2112 		 * processing in the middle of step 5, ack processing.
2113 		 * Otherwise, goto step 6.
2114 		 */
2115 		if (thflags & TH_ACK)
2116 			goto process_ACK;
2117 
2118 		goto step6;
2119 
2120 	/*
2121 	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2122 	 *      do normal processing.
2123 	 *
2124 	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2125 	 */
2126 	case TCPS_LAST_ACK:
2127 	case TCPS_CLOSING:
2128 		break;  /* continue normal processing */
2129 	}
2130 
2131 	/*
2132 	 * States other than LISTEN or SYN_SENT.
2133 	 * First check the RST flag and sequence number since reset segments
2134 	 * are exempt from the timestamp and connection count tests.  This
2135 	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2136 	 * below which allowed reset segments in half the sequence space
2137 	 * to fall though and be processed (which gives forged reset
2138 	 * segments with a random sequence number a 50 percent chance of
2139 	 * killing a connection).
2140 	 * Then check timestamp, if present.
2141 	 * Then check the connection count, if present.
2142 	 * Then check that at least some bytes of segment are within
2143 	 * receive window.  If segment begins before rcv_nxt,
2144 	 * drop leading data (and SYN); if nothing left, just ack.
2145 	 */
2146 	if (thflags & TH_RST) {
2147 		/*
2148 		 * RFC5961 Section 3.2
2149 		 *
2150 		 * - RST drops connection only if SEG.SEQ == RCV.NXT.
2151 		 * - If RST is in window, we send challenge ACK.
2152 		 *
2153 		 * Note: to take into account delayed ACKs, we should
2154 		 *   test against last_ack_sent instead of rcv_nxt.
2155 		 * Note 2: we handle special case of closed window, not
2156 		 *   covered by the RFC.
2157 		 */
2158 		if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2159 		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
2160 		    (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
2161 
2162 			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2163 			KASSERT(ti_locked == TI_RLOCKED,
2164 			    ("%s: TH_RST ti_locked %d, th %p tp %p",
2165 			    __func__, ti_locked, th, tp));
2166 			KASSERT(tp->t_state != TCPS_SYN_SENT,
2167 			    ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
2168 			    __func__, th, tp));
2169 
2170 			if (V_tcp_insecure_rst ||
2171 			    tp->last_ack_sent == th->th_seq) {
2172 				TCPSTAT_INC(tcps_drops);
2173 				/* Drop the connection. */
2174 				switch (tp->t_state) {
2175 				case TCPS_SYN_RECEIVED:
2176 					so->so_error = ECONNREFUSED;
2177 					goto close;
2178 				case TCPS_ESTABLISHED:
2179 				case TCPS_FIN_WAIT_1:
2180 				case TCPS_FIN_WAIT_2:
2181 				case TCPS_CLOSE_WAIT:
2182 					so->so_error = ECONNRESET;
2183 				close:
2184 					tcp_state_change(tp, TCPS_CLOSED);
2185 					/* FALLTHROUGH */
2186 				default:
2187 					tp = tcp_close(tp);
2188 				}
2189 			} else {
2190 				TCPSTAT_INC(tcps_badrst);
2191 				/* Send challenge ACK. */
2192 				tcp_respond(tp, mtod(m, void *), th, m,
2193 				    tp->rcv_nxt, tp->snd_nxt, TH_ACK);
2194 				tp->last_ack_sent = tp->rcv_nxt;
2195 				m = NULL;
2196 			}
2197 		}
2198 		goto drop;
2199 	}
2200 
2201 	/*
2202 	 * RFC5961 Section 4.2
2203 	 * Send challenge ACK for any SYN in synchronized state.
2204 	 */
2205 	if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
2206 	    tp->t_state != TCPS_SYN_RECEIVED) {
2207 		KASSERT(ti_locked == TI_RLOCKED,
2208 		    ("tcp_do_segment: TH_SYN ti_locked %d", ti_locked));
2209 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2210 
2211 		TCPSTAT_INC(tcps_badsyn);
2212 		if (V_tcp_insecure_syn &&
2213 		    SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2214 		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2215 			tp = tcp_drop(tp, ECONNRESET);
2216 			rstreason = BANDLIM_UNLIMITED;
2217 		} else {
2218 			/* Send challenge ACK. */
2219 			tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
2220 			    tp->snd_nxt, TH_ACK);
2221 			tp->last_ack_sent = tp->rcv_nxt;
2222 			m = NULL;
2223 		}
2224 		goto drop;
2225 	}
2226 
2227 	/*
2228 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2229 	 * and it's less than ts_recent, drop it.
2230 	 */
2231 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2232 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2233 
2234 		/* Check to see if ts_recent is over 24 days old.  */
2235 		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2236 			/*
2237 			 * Invalidate ts_recent.  If this segment updates
2238 			 * ts_recent, the age will be reset later and ts_recent
2239 			 * will get a valid value.  If it does not, setting
2240 			 * ts_recent to zero will at least satisfy the
2241 			 * requirement that zero be placed in the timestamp
2242 			 * echo reply when ts_recent isn't valid.  The
2243 			 * age isn't reset until we get a valid ts_recent
2244 			 * because we don't want out-of-order segments to be
2245 			 * dropped when ts_recent is old.
2246 			 */
2247 			tp->ts_recent = 0;
2248 		} else {
2249 			TCPSTAT_INC(tcps_rcvduppack);
2250 			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2251 			TCPSTAT_INC(tcps_pawsdrop);
2252 			if (tlen)
2253 				goto dropafterack;
2254 			goto drop;
2255 		}
2256 	}
2257 
2258 	/*
2259 	 * In the SYN-RECEIVED state, validate that the packet belongs to
2260 	 * this connection before trimming the data to fit the receive
2261 	 * window.  Check the sequence number versus IRS since we know
2262 	 * the sequence numbers haven't wrapped.  This is a partial fix
2263 	 * for the "LAND" DoS attack.
2264 	 */
2265 	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2266 		rstreason = BANDLIM_RST_OPENPORT;
2267 		goto dropwithreset;
2268 	}
2269 
2270 	todrop = tp->rcv_nxt - th->th_seq;
2271 	if (todrop > 0) {
2272 		if (thflags & TH_SYN) {
2273 			thflags &= ~TH_SYN;
2274 			th->th_seq++;
2275 			if (th->th_urp > 1)
2276 				th->th_urp--;
2277 			else
2278 				thflags &= ~TH_URG;
2279 			todrop--;
2280 		}
2281 		/*
2282 		 * Following if statement from Stevens, vol. 2, p. 960.
2283 		 */
2284 		if (todrop > tlen
2285 		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2286 			/*
2287 			 * Any valid FIN must be to the left of the window.
2288 			 * At this point the FIN must be a duplicate or out
2289 			 * of sequence; drop it.
2290 			 */
2291 			thflags &= ~TH_FIN;
2292 
2293 			/*
2294 			 * Send an ACK to resynchronize and drop any data.
2295 			 * But keep on processing for RST or ACK.
2296 			 */
2297 			tp->t_flags |= TF_ACKNOW;
2298 			todrop = tlen;
2299 			TCPSTAT_INC(tcps_rcvduppack);
2300 			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2301 		} else {
2302 			TCPSTAT_INC(tcps_rcvpartduppack);
2303 			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2304 		}
2305 		drop_hdrlen += todrop;	/* drop from the top afterwards */
2306 		th->th_seq += todrop;
2307 		tlen -= todrop;
2308 		if (th->th_urp > todrop)
2309 			th->th_urp -= todrop;
2310 		else {
2311 			thflags &= ~TH_URG;
2312 			th->th_urp = 0;
2313 		}
2314 	}
2315 
2316 	/*
2317 	 * If new data are received on a connection after the
2318 	 * user processes are gone, then RST the other end.
2319 	 */
2320 	if ((so->so_state & SS_NOFDREF) &&
2321 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2322 		KASSERT(ti_locked == TI_RLOCKED, ("%s: SS_NOFDEREF && "
2323 		    "CLOSE_WAIT && tlen ti_locked %d", __func__, ti_locked));
2324 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2325 
2326 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2327 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2328 			    "after socket was closed, "
2329 			    "sending RST and removing tcpcb\n",
2330 			    s, __func__, tcpstates[tp->t_state], tlen);
2331 			free(s, M_TCPLOG);
2332 		}
2333 		tp = tcp_close(tp);
2334 		TCPSTAT_INC(tcps_rcvafterclose);
2335 		rstreason = BANDLIM_UNLIMITED;
2336 		goto dropwithreset;
2337 	}
2338 
2339 	/*
2340 	 * If segment ends after window, drop trailing data
2341 	 * (and PUSH and FIN); if nothing left, just ACK.
2342 	 */
2343 	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2344 	if (todrop > 0) {
2345 		TCPSTAT_INC(tcps_rcvpackafterwin);
2346 		if (todrop >= tlen) {
2347 			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2348 			/*
2349 			 * If window is closed can only take segments at
2350 			 * window edge, and have to drop data and PUSH from
2351 			 * incoming segments.  Continue processing, but
2352 			 * remember to ack.  Otherwise, drop segment
2353 			 * and ack.
2354 			 */
2355 			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2356 				tp->t_flags |= TF_ACKNOW;
2357 				TCPSTAT_INC(tcps_rcvwinprobe);
2358 			} else
2359 				goto dropafterack;
2360 		} else
2361 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2362 		m_adj(m, -todrop);
2363 		tlen -= todrop;
2364 		thflags &= ~(TH_PUSH|TH_FIN);
2365 	}
2366 
2367 	/*
2368 	 * If last ACK falls within this segment's sequence numbers,
2369 	 * record its timestamp.
2370 	 * NOTE:
2371 	 * 1) That the test incorporates suggestions from the latest
2372 	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2373 	 * 2) That updating only on newer timestamps interferes with
2374 	 *    our earlier PAWS tests, so this check should be solely
2375 	 *    predicated on the sequence space of this segment.
2376 	 * 3) That we modify the segment boundary check to be
2377 	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2378 	 *    instead of RFC1323's
2379 	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2380 	 *    This modified check allows us to overcome RFC1323's
2381 	 *    limitations as described in Stevens TCP/IP Illustrated
2382 	 *    Vol. 2 p.869. In such cases, we can still calculate the
2383 	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2384 	 */
2385 	if ((to.to_flags & TOF_TS) != 0 &&
2386 	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2387 	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2388 		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2389 		tp->ts_recent_age = tcp_ts_getticks();
2390 		tp->ts_recent = to.to_tsval;
2391 	}
2392 
2393 	/*
2394 	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2395 	 * flag is on (half-synchronized state), then queue data for
2396 	 * later processing; else drop segment and return.
2397 	 */
2398 	if ((thflags & TH_ACK) == 0) {
2399 		if (tp->t_state == TCPS_SYN_RECEIVED ||
2400 		    (tp->t_flags & TF_NEEDSYN)) {
2401 #ifdef TCP_RFC7413
2402 			if (tp->t_state == TCPS_SYN_RECEIVED &&
2403 			    IS_FASTOPEN(tp->t_flags)) {
2404 				tp->snd_wnd = tiwin;
2405 				cc_conn_init(tp);
2406 			}
2407 #endif
2408 			goto step6;
2409 		} else if (tp->t_flags & TF_ACKNOW)
2410 			goto dropafterack;
2411 		else
2412 			goto drop;
2413 	}
2414 
2415 	/*
2416 	 * Ack processing.
2417 	 */
2418 	switch (tp->t_state) {
2419 
2420 	/*
2421 	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2422 	 * ESTABLISHED state and continue processing.
2423 	 * The ACK was checked above.
2424 	 */
2425 	case TCPS_SYN_RECEIVED:
2426 
2427 		TCPSTAT_INC(tcps_connects);
2428 		soisconnected(so);
2429 		/* Do window scaling? */
2430 		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2431 			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2432 			tp->rcv_scale = tp->request_r_scale;
2433 			tp->snd_wnd = tiwin;
2434 		}
2435 		/*
2436 		 * Make transitions:
2437 		 *      SYN-RECEIVED  -> ESTABLISHED
2438 		 *      SYN-RECEIVED* -> FIN-WAIT-1
2439 		 */
2440 		tp->t_starttime = ticks;
2441 		if (tp->t_flags & TF_NEEDFIN) {
2442 			tcp_state_change(tp, TCPS_FIN_WAIT_1);
2443 			tp->t_flags &= ~TF_NEEDFIN;
2444 		} else {
2445 			tcp_state_change(tp, TCPS_ESTABLISHED);
2446 			TCP_PROBE5(accept__established, NULL, tp,
2447 			    mtod(m, const char *), tp, th);
2448 #ifdef TCP_RFC7413
2449 			if (tp->t_tfo_pending) {
2450 				tcp_fastopen_decrement_counter(tp->t_tfo_pending);
2451 				tp->t_tfo_pending = NULL;
2452 
2453 				/*
2454 				 * Account for the ACK of our SYN prior to
2455 				 * regular ACK processing below.
2456 				 */
2457 				tp->snd_una++;
2458 			}
2459 			/*
2460 			 * TFO connections call cc_conn_init() during SYN
2461 			 * processing.  Calling it again here for such
2462 			 * connections is not harmless as it would undo the
2463 			 * snd_cwnd reduction that occurs when a TFO SYN|ACK
2464 			 * is retransmitted.
2465 			 */
2466 			if (!IS_FASTOPEN(tp->t_flags))
2467 #endif
2468 				cc_conn_init(tp);
2469 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2470 		}
2471 		/*
2472 		 * If segment contains data or ACK, will call tcp_reass()
2473 		 * later; if not, do so now to pass queued data to user.
2474 		 */
2475 		if (tlen == 0 && (thflags & TH_FIN) == 0)
2476 			(void) tcp_reass(tp, (struct tcphdr *)0, 0,
2477 			    (struct mbuf *)0);
2478 		tp->snd_wl1 = th->th_seq - 1;
2479 		/* FALLTHROUGH */
2480 
2481 	/*
2482 	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2483 	 * ACKs.  If the ack is in the range
2484 	 *	tp->snd_una < th->th_ack <= tp->snd_max
2485 	 * then advance tp->snd_una to th->th_ack and drop
2486 	 * data from the retransmission queue.  If this ACK reflects
2487 	 * more up to date window information we update our window information.
2488 	 */
2489 	case TCPS_ESTABLISHED:
2490 	case TCPS_FIN_WAIT_1:
2491 	case TCPS_FIN_WAIT_2:
2492 	case TCPS_CLOSE_WAIT:
2493 	case TCPS_CLOSING:
2494 	case TCPS_LAST_ACK:
2495 		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2496 			TCPSTAT_INC(tcps_rcvacktoomuch);
2497 			goto dropafterack;
2498 		}
2499 		if ((tp->t_flags & TF_SACK_PERMIT) &&
2500 		    ((to.to_flags & TOF_SACK) ||
2501 		     !TAILQ_EMPTY(&tp->snd_holes)))
2502 			sack_changed = tcp_sack_doack(tp, &to, th->th_ack);
2503 		else
2504 			/*
2505 			 * Reset the value so that previous (valid) value
2506 			 * from the last ack with SACK doesn't get used.
2507 			 */
2508 			tp->sackhint.sacked_bytes = 0;
2509 
2510 #ifdef TCP_HHOOK
2511 		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2512 		hhook_run_tcp_est_in(tp, th, &to);
2513 #endif
2514 
2515 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2516 			u_int maxseg;
2517 
2518 			maxseg = tcp_maxseg(tp);
2519 			if (tlen == 0 &&
2520 			    (tiwin == tp->snd_wnd ||
2521 			    (tp->t_flags & TF_SACK_PERMIT))) {
2522 				/*
2523 				 * If this is the first time we've seen a
2524 				 * FIN from the remote, this is not a
2525 				 * duplicate and it needs to be processed
2526 				 * normally.  This happens during a
2527 				 * simultaneous close.
2528 				 */
2529 				if ((thflags & TH_FIN) &&
2530 				    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2531 					tp->t_dupacks = 0;
2532 					break;
2533 				}
2534 				TCPSTAT_INC(tcps_rcvdupack);
2535 				/*
2536 				 * If we have outstanding data (other than
2537 				 * a window probe), this is a completely
2538 				 * duplicate ack (ie, window info didn't
2539 				 * change and FIN isn't set),
2540 				 * the ack is the biggest we've
2541 				 * seen and we've seen exactly our rexmt
2542 				 * threshold of them, assume a packet
2543 				 * has been dropped and retransmit it.
2544 				 * Kludge snd_nxt & the congestion
2545 				 * window so we send only this one
2546 				 * packet.
2547 				 *
2548 				 * We know we're losing at the current
2549 				 * window size so do congestion avoidance
2550 				 * (set ssthresh to half the current window
2551 				 * and pull our congestion window back to
2552 				 * the new ssthresh).
2553 				 *
2554 				 * Dup acks mean that packets have left the
2555 				 * network (they're now cached at the receiver)
2556 				 * so bump cwnd by the amount in the receiver
2557 				 * to keep a constant cwnd packets in the
2558 				 * network.
2559 				 *
2560 				 * When using TCP ECN, notify the peer that
2561 				 * we reduced the cwnd.
2562 				 */
2563 				/*
2564 				 * Following 2 kinds of acks should not affect
2565 				 * dupack counting:
2566 				 * 1) Old acks
2567 				 * 2) Acks with SACK but without any new SACK
2568 				 * information in them. These could result from
2569 				 * any anomaly in the network like a switch
2570 				 * duplicating packets or a possible DoS attack.
2571 				 */
2572 				if (th->th_ack != tp->snd_una ||
2573 				    ((tp->t_flags & TF_SACK_PERMIT) &&
2574 				    !sack_changed))
2575 					break;
2576 				else if (!tcp_timer_active(tp, TT_REXMT))
2577 					tp->t_dupacks = 0;
2578 				else if (++tp->t_dupacks > tcprexmtthresh ||
2579 				     IN_FASTRECOVERY(tp->t_flags)) {
2580 					cc_ack_received(tp, th, nsegs,
2581 					    CC_DUPACK);
2582 					if ((tp->t_flags & TF_SACK_PERMIT) &&
2583 					    IN_FASTRECOVERY(tp->t_flags)) {
2584 						int awnd;
2585 
2586 						/*
2587 						 * Compute the amount of data in flight first.
2588 						 * We can inject new data into the pipe iff
2589 						 * we have less than 1/2 the original window's
2590 						 * worth of data in flight.
2591 						 */
2592 						if (V_tcp_do_rfc6675_pipe)
2593 							awnd = tcp_compute_pipe(tp);
2594 						else
2595 							awnd = (tp->snd_nxt - tp->snd_fack) +
2596 								tp->sackhint.sack_bytes_rexmit;
2597 
2598 						if (awnd < tp->snd_ssthresh) {
2599 							tp->snd_cwnd += maxseg;
2600 							if (tp->snd_cwnd > tp->snd_ssthresh)
2601 								tp->snd_cwnd = tp->snd_ssthresh;
2602 						}
2603 					} else
2604 						tp->snd_cwnd += maxseg;
2605 					(void) tp->t_fb->tfb_tcp_output(tp);
2606 					goto drop;
2607 				} else if (tp->t_dupacks == tcprexmtthresh) {
2608 					tcp_seq onxt = tp->snd_nxt;
2609 
2610 					/*
2611 					 * If we're doing sack, check to
2612 					 * see if we're already in sack
2613 					 * recovery. If we're not doing sack,
2614 					 * check to see if we're in newreno
2615 					 * recovery.
2616 					 */
2617 					if (tp->t_flags & TF_SACK_PERMIT) {
2618 						if (IN_FASTRECOVERY(tp->t_flags)) {
2619 							tp->t_dupacks = 0;
2620 							break;
2621 						}
2622 					} else {
2623 						if (SEQ_LEQ(th->th_ack,
2624 						    tp->snd_recover)) {
2625 							tp->t_dupacks = 0;
2626 							break;
2627 						}
2628 					}
2629 					/* Congestion signal before ack. */
2630 					cc_cong_signal(tp, th, CC_NDUPACK);
2631 					cc_ack_received(tp, th, nsegs,
2632 					    CC_DUPACK);
2633 					tcp_timer_activate(tp, TT_REXMT, 0);
2634 					tp->t_rtttime = 0;
2635 					if (tp->t_flags & TF_SACK_PERMIT) {
2636 						TCPSTAT_INC(
2637 						    tcps_sack_recovery_episode);
2638 						tp->sack_newdata = tp->snd_nxt;
2639 						tp->snd_cwnd = maxseg;
2640 						(void) tp->t_fb->tfb_tcp_output(tp);
2641 						goto drop;
2642 					}
2643 					tp->snd_nxt = th->th_ack;
2644 					tp->snd_cwnd = maxseg;
2645 					(void) tp->t_fb->tfb_tcp_output(tp);
2646 					KASSERT(tp->snd_limited <= 2,
2647 					    ("%s: tp->snd_limited too big",
2648 					    __func__));
2649 					tp->snd_cwnd = tp->snd_ssthresh +
2650 					     maxseg *
2651 					     (tp->t_dupacks - tp->snd_limited);
2652 					if (SEQ_GT(onxt, tp->snd_nxt))
2653 						tp->snd_nxt = onxt;
2654 					goto drop;
2655 				} else if (V_tcp_do_rfc3042) {
2656 					/*
2657 					 * Process first and second duplicate
2658 					 * ACKs. Each indicates a segment
2659 					 * leaving the network, creating room
2660 					 * for more. Make sure we can send a
2661 					 * packet on reception of each duplicate
2662 					 * ACK by increasing snd_cwnd by one
2663 					 * segment. Restore the original
2664 					 * snd_cwnd after packet transmission.
2665 					 */
2666 					cc_ack_received(tp, th, nsegs,
2667 					    CC_DUPACK);
2668 					uint32_t oldcwnd = tp->snd_cwnd;
2669 					tcp_seq oldsndmax = tp->snd_max;
2670 					u_int sent;
2671 					int avail;
2672 
2673 					KASSERT(tp->t_dupacks == 1 ||
2674 					    tp->t_dupacks == 2,
2675 					    ("%s: dupacks not 1 or 2",
2676 					    __func__));
2677 					if (tp->t_dupacks == 1)
2678 						tp->snd_limited = 0;
2679 					tp->snd_cwnd =
2680 					    (tp->snd_nxt - tp->snd_una) +
2681 					    (tp->t_dupacks - tp->snd_limited) *
2682 					    maxseg;
2683 					/*
2684 					 * Only call tcp_output when there
2685 					 * is new data available to be sent.
2686 					 * Otherwise we would send pure ACKs.
2687 					 */
2688 					SOCKBUF_LOCK(&so->so_snd);
2689 					avail = sbavail(&so->so_snd) -
2690 					    (tp->snd_nxt - tp->snd_una);
2691 					SOCKBUF_UNLOCK(&so->so_snd);
2692 					if (avail > 0)
2693 						(void) tp->t_fb->tfb_tcp_output(tp);
2694 					sent = tp->snd_max - oldsndmax;
2695 					if (sent > maxseg) {
2696 						KASSERT((tp->t_dupacks == 2 &&
2697 						    tp->snd_limited == 0) ||
2698 						   (sent == maxseg + 1 &&
2699 						    tp->t_flags & TF_SENTFIN),
2700 						    ("%s: sent too much",
2701 						    __func__));
2702 						tp->snd_limited = 2;
2703 					} else if (sent > 0)
2704 						++tp->snd_limited;
2705 					tp->snd_cwnd = oldcwnd;
2706 					goto drop;
2707 				}
2708 			}
2709 			break;
2710 		} else {
2711 			/*
2712 			 * This ack is advancing the left edge, reset the
2713 			 * counter.
2714 			 */
2715 			tp->t_dupacks = 0;
2716 			/*
2717 			 * If this ack also has new SACK info, increment the
2718 			 * counter as per rfc6675.
2719 			 */
2720 			if ((tp->t_flags & TF_SACK_PERMIT) && sack_changed)
2721 				tp->t_dupacks++;
2722 		}
2723 
2724 		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2725 		    ("%s: th_ack <= snd_una", __func__));
2726 
2727 		/*
2728 		 * If the congestion window was inflated to account
2729 		 * for the other side's cached packets, retract it.
2730 		 */
2731 		if (IN_FASTRECOVERY(tp->t_flags)) {
2732 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2733 				if (tp->t_flags & TF_SACK_PERMIT)
2734 					tcp_sack_partialack(tp, th);
2735 				else
2736 					tcp_newreno_partial_ack(tp, th);
2737 			} else
2738 				cc_post_recovery(tp, th);
2739 		}
2740 		/*
2741 		 * If we reach this point, ACK is not a duplicate,
2742 		 *     i.e., it ACKs something we sent.
2743 		 */
2744 		if (tp->t_flags & TF_NEEDSYN) {
2745 			/*
2746 			 * T/TCP: Connection was half-synchronized, and our
2747 			 * SYN has been ACK'd (so connection is now fully
2748 			 * synchronized).  Go to non-starred state,
2749 			 * increment snd_una for ACK of SYN, and check if
2750 			 * we can do window scaling.
2751 			 */
2752 			tp->t_flags &= ~TF_NEEDSYN;
2753 			tp->snd_una++;
2754 			/* Do window scaling? */
2755 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2756 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2757 				tp->rcv_scale = tp->request_r_scale;
2758 				/* Send window already scaled. */
2759 			}
2760 		}
2761 
2762 process_ACK:
2763 		INP_WLOCK_ASSERT(tp->t_inpcb);
2764 
2765 		acked = BYTES_THIS_ACK(tp, th);
2766 		KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
2767 		    "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
2768 		    tp->snd_una, th->th_ack, tp, m));
2769 		TCPSTAT_ADD(tcps_rcvackpack, nsegs);
2770 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2771 
2772 		/*
2773 		 * If we just performed our first retransmit, and the ACK
2774 		 * arrives within our recovery window, then it was a mistake
2775 		 * to do the retransmit in the first place.  Recover our
2776 		 * original cwnd and ssthresh, and proceed to transmit where
2777 		 * we left off.
2778 		 */
2779 		if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID &&
2780 		    (int)(ticks - tp->t_badrxtwin) < 0)
2781 			cc_cong_signal(tp, th, CC_RTO_ERR);
2782 
2783 		/*
2784 		 * If we have a timestamp reply, update smoothed
2785 		 * round trip time.  If no timestamp is present but
2786 		 * transmit timer is running and timed sequence
2787 		 * number was acked, update smoothed round trip time.
2788 		 * Since we now have an rtt measurement, cancel the
2789 		 * timer backoff (cf., Phil Karn's retransmit alg.).
2790 		 * Recompute the initial retransmit timer.
2791 		 *
2792 		 * Some boxes send broken timestamp replies
2793 		 * during the SYN+ACK phase, ignore
2794 		 * timestamps of 0 or we could calculate a
2795 		 * huge RTT and blow up the retransmit timer.
2796 		 */
2797 		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2798 			uint32_t t;
2799 
2800 			t = tcp_ts_getticks() - to.to_tsecr;
2801 			if (!tp->t_rttlow || tp->t_rttlow > t)
2802 				tp->t_rttlow = t;
2803 			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2804 		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2805 			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2806 				tp->t_rttlow = ticks - tp->t_rtttime;
2807 			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2808 		}
2809 
2810 		/*
2811 		 * If all outstanding data is acked, stop retransmit
2812 		 * timer and remember to restart (more output or persist).
2813 		 * If there is more data to be acked, restart retransmit
2814 		 * timer, using current (possibly backed-off) value.
2815 		 */
2816 		if (th->th_ack == tp->snd_max) {
2817 			tcp_timer_activate(tp, TT_REXMT, 0);
2818 			needoutput = 1;
2819 		} else if (!tcp_timer_active(tp, TT_PERSIST))
2820 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2821 
2822 		/*
2823 		 * If no data (only SYN) was ACK'd,
2824 		 *    skip rest of ACK processing.
2825 		 */
2826 		if (acked == 0)
2827 			goto step6;
2828 
2829 		/*
2830 		 * Let the congestion control algorithm update congestion
2831 		 * control related information. This typically means increasing
2832 		 * the congestion window.
2833 		 */
2834 		cc_ack_received(tp, th, nsegs, CC_ACK);
2835 
2836 		SOCKBUF_LOCK(&so->so_snd);
2837 		if (acked > sbavail(&so->so_snd)) {
2838 			if (tp->snd_wnd >= sbavail(&so->so_snd))
2839 				tp->snd_wnd -= sbavail(&so->so_snd);
2840 			else
2841 				tp->snd_wnd = 0;
2842 			mfree = sbcut_locked(&so->so_snd,
2843 			    (int)sbavail(&so->so_snd));
2844 			ourfinisacked = 1;
2845 		} else {
2846 			mfree = sbcut_locked(&so->so_snd, acked);
2847 			if (tp->snd_wnd >= (uint32_t) acked)
2848 				tp->snd_wnd -= acked;
2849 			else
2850 				tp->snd_wnd = 0;
2851 			ourfinisacked = 0;
2852 		}
2853 		/* NB: sowwakeup_locked() does an implicit unlock. */
2854 		sowwakeup_locked(so);
2855 		m_freem(mfree);
2856 		/* Detect una wraparound. */
2857 		if (!IN_RECOVERY(tp->t_flags) &&
2858 		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2859 		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2860 			tp->snd_recover = th->th_ack - 1;
2861 		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2862 		if (IN_RECOVERY(tp->t_flags) &&
2863 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2864 			EXIT_RECOVERY(tp->t_flags);
2865 		}
2866 		tp->snd_una = th->th_ack;
2867 		if (tp->t_flags & TF_SACK_PERMIT) {
2868 			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2869 				tp->snd_recover = tp->snd_una;
2870 		}
2871 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2872 			tp->snd_nxt = tp->snd_una;
2873 
2874 		switch (tp->t_state) {
2875 
2876 		/*
2877 		 * In FIN_WAIT_1 STATE in addition to the processing
2878 		 * for the ESTABLISHED state if our FIN is now acknowledged
2879 		 * then enter FIN_WAIT_2.
2880 		 */
2881 		case TCPS_FIN_WAIT_1:
2882 			if (ourfinisacked) {
2883 				/*
2884 				 * If we can't receive any more
2885 				 * data, then closing user can proceed.
2886 				 * Starting the timer is contrary to the
2887 				 * specification, but if we don't get a FIN
2888 				 * we'll hang forever.
2889 				 *
2890 				 * XXXjl:
2891 				 * we should release the tp also, and use a
2892 				 * compressed state.
2893 				 */
2894 				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2895 					soisdisconnected(so);
2896 					tcp_timer_activate(tp, TT_2MSL,
2897 					    (tcp_fast_finwait2_recycle ?
2898 					    tcp_finwait2_timeout :
2899 					    TP_MAXIDLE(tp)));
2900 				}
2901 				tcp_state_change(tp, TCPS_FIN_WAIT_2);
2902 			}
2903 			break;
2904 
2905 		/*
2906 		 * In CLOSING STATE in addition to the processing for
2907 		 * the ESTABLISHED state if the ACK acknowledges our FIN
2908 		 * then enter the TIME-WAIT state, otherwise ignore
2909 		 * the segment.
2910 		 */
2911 		case TCPS_CLOSING:
2912 			if (ourfinisacked) {
2913 				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2914 				tcp_twstart(tp);
2915 				INP_INFO_RUNLOCK(&V_tcbinfo);
2916 				m_freem(m);
2917 				return;
2918 			}
2919 			break;
2920 
2921 		/*
2922 		 * In LAST_ACK, we may still be waiting for data to drain
2923 		 * and/or to be acked, as well as for the ack of our FIN.
2924 		 * If our FIN is now acknowledged, delete the TCB,
2925 		 * enter the closed state and return.
2926 		 */
2927 		case TCPS_LAST_ACK:
2928 			if (ourfinisacked) {
2929 				INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
2930 				tp = tcp_close(tp);
2931 				goto drop;
2932 			}
2933 			break;
2934 		}
2935 	}
2936 
2937 step6:
2938 	INP_WLOCK_ASSERT(tp->t_inpcb);
2939 
2940 	/*
2941 	 * Update window information.
2942 	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
2943 	 */
2944 	if ((thflags & TH_ACK) &&
2945 	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
2946 	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
2947 	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
2948 		/* keep track of pure window updates */
2949 		if (tlen == 0 &&
2950 		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
2951 			TCPSTAT_INC(tcps_rcvwinupd);
2952 		tp->snd_wnd = tiwin;
2953 		tp->snd_wl1 = th->th_seq;
2954 		tp->snd_wl2 = th->th_ack;
2955 		if (tp->snd_wnd > tp->max_sndwnd)
2956 			tp->max_sndwnd = tp->snd_wnd;
2957 		needoutput = 1;
2958 	}
2959 
2960 	/*
2961 	 * Process segments with URG.
2962 	 */
2963 	if ((thflags & TH_URG) && th->th_urp &&
2964 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
2965 		/*
2966 		 * This is a kludge, but if we receive and accept
2967 		 * random urgent pointers, we'll crash in
2968 		 * soreceive.  It's hard to imagine someone
2969 		 * actually wanting to send this much urgent data.
2970 		 */
2971 		SOCKBUF_LOCK(&so->so_rcv);
2972 		if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
2973 			th->th_urp = 0;			/* XXX */
2974 			thflags &= ~TH_URG;		/* XXX */
2975 			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
2976 			goto dodata;			/* XXX */
2977 		}
2978 		/*
2979 		 * If this segment advances the known urgent pointer,
2980 		 * then mark the data stream.  This should not happen
2981 		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
2982 		 * a FIN has been received from the remote side.
2983 		 * In these states we ignore the URG.
2984 		 *
2985 		 * According to RFC961 (Assigned Protocols),
2986 		 * the urgent pointer points to the last octet
2987 		 * of urgent data.  We continue, however,
2988 		 * to consider it to indicate the first octet
2989 		 * of data past the urgent section as the original
2990 		 * spec states (in one of two places).
2991 		 */
2992 		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
2993 			tp->rcv_up = th->th_seq + th->th_urp;
2994 			so->so_oobmark = sbavail(&so->so_rcv) +
2995 			    (tp->rcv_up - tp->rcv_nxt) - 1;
2996 			if (so->so_oobmark == 0)
2997 				so->so_rcv.sb_state |= SBS_RCVATMARK;
2998 			sohasoutofband(so);
2999 			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
3000 		}
3001 		SOCKBUF_UNLOCK(&so->so_rcv);
3002 		/*
3003 		 * Remove out of band data so doesn't get presented to user.
3004 		 * This can happen independent of advancing the URG pointer,
3005 		 * but if two URG's are pending at once, some out-of-band
3006 		 * data may creep in... ick.
3007 		 */
3008 		if (th->th_urp <= (uint32_t)tlen &&
3009 		    !(so->so_options & SO_OOBINLINE)) {
3010 			/* hdr drop is delayed */
3011 			tcp_pulloutofband(so, th, m, drop_hdrlen);
3012 		}
3013 	} else {
3014 		/*
3015 		 * If no out of band data is expected,
3016 		 * pull receive urgent pointer along
3017 		 * with the receive window.
3018 		 */
3019 		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
3020 			tp->rcv_up = tp->rcv_nxt;
3021 	}
3022 dodata:							/* XXX */
3023 	INP_WLOCK_ASSERT(tp->t_inpcb);
3024 
3025 	/*
3026 	 * Process the segment text, merging it into the TCP sequencing queue,
3027 	 * and arranging for acknowledgment of receipt if necessary.
3028 	 * This process logically involves adjusting tp->rcv_wnd as data
3029 	 * is presented to the user (this happens in tcp_usrreq.c,
3030 	 * case PRU_RCVD).  If a FIN has already been received on this
3031 	 * connection then we just ignore the text.
3032 	 */
3033 #ifdef TCP_RFC7413
3034 	tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
3035 		   IS_FASTOPEN(tp->t_flags));
3036 #else
3037 #define	tfo_syn	(false)
3038 #endif
3039 	if ((tlen || (thflags & TH_FIN) || tfo_syn) &&
3040 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3041 		tcp_seq save_start = th->th_seq;
3042 		m_adj(m, drop_hdrlen);	/* delayed header drop */
3043 		/*
3044 		 * Insert segment which includes th into TCP reassembly queue
3045 		 * with control block tp.  Set thflags to whether reassembly now
3046 		 * includes a segment with FIN.  This handles the common case
3047 		 * inline (segment is the next to be received on an established
3048 		 * connection, and the queue is empty), avoiding linkage into
3049 		 * and removal from the queue and repetition of various
3050 		 * conversions.
3051 		 * Set DELACK for segments received in order, but ack
3052 		 * immediately when segments are out of order (so
3053 		 * fast retransmit can work).
3054 		 */
3055 		if (th->th_seq == tp->rcv_nxt &&
3056 		    LIST_EMPTY(&tp->t_segq) &&
3057 		    (TCPS_HAVEESTABLISHED(tp->t_state) ||
3058 		     tfo_syn)) {
3059 			if (DELAY_ACK(tp, tlen) || tfo_syn)
3060 				tp->t_flags |= TF_DELACK;
3061 			else
3062 				tp->t_flags |= TF_ACKNOW;
3063 			tp->rcv_nxt += tlen;
3064 			thflags = th->th_flags & TH_FIN;
3065 			TCPSTAT_INC(tcps_rcvpack);
3066 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
3067 			SOCKBUF_LOCK(&so->so_rcv);
3068 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
3069 				m_freem(m);
3070 			else
3071 				sbappendstream_locked(&so->so_rcv, m, 0);
3072 			/* NB: sorwakeup_locked() does an implicit unlock. */
3073 			sorwakeup_locked(so);
3074 		} else {
3075 			/*
3076 			 * XXX: Due to the header drop above "th" is
3077 			 * theoretically invalid by now.  Fortunately
3078 			 * m_adj() doesn't actually frees any mbufs
3079 			 * when trimming from the head.
3080 			 */
3081 			thflags = tcp_reass(tp, th, &tlen, m);
3082 			tp->t_flags |= TF_ACKNOW;
3083 		}
3084 		if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT))
3085 			tcp_update_sack_list(tp, save_start, save_start + tlen);
3086 #if 0
3087 		/*
3088 		 * Note the amount of data that peer has sent into
3089 		 * our window, in order to estimate the sender's
3090 		 * buffer size.
3091 		 * XXX: Unused.
3092 		 */
3093 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
3094 			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
3095 		else
3096 			len = so->so_rcv.sb_hiwat;
3097 #endif
3098 	} else {
3099 		m_freem(m);
3100 		thflags &= ~TH_FIN;
3101 	}
3102 
3103 	/*
3104 	 * If FIN is received ACK the FIN and let the user know
3105 	 * that the connection is closing.
3106 	 */
3107 	if (thflags & TH_FIN) {
3108 		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3109 			socantrcvmore(so);
3110 			/*
3111 			 * If connection is half-synchronized
3112 			 * (ie NEEDSYN flag on) then delay ACK,
3113 			 * so it may be piggybacked when SYN is sent.
3114 			 * Otherwise, since we received a FIN then no
3115 			 * more input can be expected, send ACK now.
3116 			 */
3117 			if (tp->t_flags & TF_NEEDSYN)
3118 				tp->t_flags |= TF_DELACK;
3119 			else
3120 				tp->t_flags |= TF_ACKNOW;
3121 			tp->rcv_nxt++;
3122 		}
3123 		switch (tp->t_state) {
3124 
3125 		/*
3126 		 * In SYN_RECEIVED and ESTABLISHED STATES
3127 		 * enter the CLOSE_WAIT state.
3128 		 */
3129 		case TCPS_SYN_RECEIVED:
3130 			tp->t_starttime = ticks;
3131 			/* FALLTHROUGH */
3132 		case TCPS_ESTABLISHED:
3133 			tcp_state_change(tp, TCPS_CLOSE_WAIT);
3134 			break;
3135 
3136 		/*
3137 		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
3138 		 * enter the CLOSING state.
3139 		 */
3140 		case TCPS_FIN_WAIT_1:
3141 			tcp_state_change(tp, TCPS_CLOSING);
3142 			break;
3143 
3144 		/*
3145 		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
3146 		 * starting the time-wait timer, turning off the other
3147 		 * standard timers.
3148 		 */
3149 		case TCPS_FIN_WAIT_2:
3150 			INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
3151 			KASSERT(ti_locked == TI_RLOCKED, ("%s: dodata "
3152 			    "TCP_FIN_WAIT_2 ti_locked: %d", __func__,
3153 			    ti_locked));
3154 
3155 			tcp_twstart(tp);
3156 			INP_INFO_RUNLOCK(&V_tcbinfo);
3157 			return;
3158 		}
3159 	}
3160 	if (ti_locked == TI_RLOCKED)
3161 		INP_INFO_RUNLOCK(&V_tcbinfo);
3162 	ti_locked = TI_UNLOCKED;
3163 
3164 #ifdef TCPDEBUG
3165 	if (so->so_options & SO_DEBUG)
3166 		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3167 			  &tcp_savetcp, 0);
3168 #endif
3169 	TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
3170 
3171 	/*
3172 	 * Return any desired output.
3173 	 */
3174 	if (needoutput || (tp->t_flags & TF_ACKNOW))
3175 		(void) tp->t_fb->tfb_tcp_output(tp);
3176 
3177 check_delack:
3178 	KASSERT(ti_locked == TI_UNLOCKED, ("%s: check_delack ti_locked %d",
3179 	    __func__, ti_locked));
3180 	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3181 	INP_WLOCK_ASSERT(tp->t_inpcb);
3182 
3183 	if (tp->t_flags & TF_DELACK) {
3184 		tp->t_flags &= ~TF_DELACK;
3185 		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3186 	}
3187 	INP_WUNLOCK(tp->t_inpcb);
3188 	return;
3189 
3190 dropafterack:
3191 	/*
3192 	 * Generate an ACK dropping incoming segment if it occupies
3193 	 * sequence space, where the ACK reflects our state.
3194 	 *
3195 	 * We can now skip the test for the RST flag since all
3196 	 * paths to this code happen after packets containing
3197 	 * RST have been dropped.
3198 	 *
3199 	 * In the SYN-RECEIVED state, don't send an ACK unless the
3200 	 * segment we received passes the SYN-RECEIVED ACK test.
3201 	 * If it fails send a RST.  This breaks the loop in the
3202 	 * "LAND" DoS attack, and also prevents an ACK storm
3203 	 * between two listening ports that have been sent forged
3204 	 * SYN segments, each with the source address of the other.
3205 	 */
3206 	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3207 	    (SEQ_GT(tp->snd_una, th->th_ack) ||
3208 	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
3209 		rstreason = BANDLIM_RST_OPENPORT;
3210 		goto dropwithreset;
3211 	}
3212 #ifdef TCPDEBUG
3213 	if (so->so_options & SO_DEBUG)
3214 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3215 			  &tcp_savetcp, 0);
3216 #endif
3217 	TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
3218 	if (ti_locked == TI_RLOCKED)
3219 		INP_INFO_RUNLOCK(&V_tcbinfo);
3220 	ti_locked = TI_UNLOCKED;
3221 
3222 	tp->t_flags |= TF_ACKNOW;
3223 	(void) tp->t_fb->tfb_tcp_output(tp);
3224 	INP_WUNLOCK(tp->t_inpcb);
3225 	m_freem(m);
3226 	return;
3227 
3228 dropwithreset:
3229 	if (ti_locked == TI_RLOCKED)
3230 		INP_INFO_RUNLOCK(&V_tcbinfo);
3231 	ti_locked = TI_UNLOCKED;
3232 
3233 	if (tp != NULL) {
3234 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
3235 		INP_WUNLOCK(tp->t_inpcb);
3236 	} else
3237 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3238 	return;
3239 
3240 drop:
3241 	if (ti_locked == TI_RLOCKED) {
3242 		INP_INFO_RUNLOCK(&V_tcbinfo);
3243 		ti_locked = TI_UNLOCKED;
3244 	}
3245 #ifdef INVARIANTS
3246 	else
3247 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
3248 #endif
3249 
3250 	/*
3251 	 * Drop space held by incoming segment and return.
3252 	 */
3253 #ifdef TCPDEBUG
3254 	if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3255 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3256 			  &tcp_savetcp, 0);
3257 #endif
3258 	TCP_PROBE3(debug__input, tp, th, mtod(m, const char *));
3259 	if (tp != NULL)
3260 		INP_WUNLOCK(tp->t_inpcb);
3261 	m_freem(m);
3262 #ifndef TCP_RFC7413
3263 #undef	tfo_syn
3264 #endif
3265 }
3266 
3267 /*
3268  * Issue RST and make ACK acceptable to originator of segment.
3269  * The mbuf must still include the original packet header.
3270  * tp may be NULL.
3271  */
3272 void
3273 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3274     int tlen, int rstreason)
3275 {
3276 #ifdef INET
3277 	struct ip *ip;
3278 #endif
3279 #ifdef INET6
3280 	struct ip6_hdr *ip6;
3281 #endif
3282 
3283 	if (tp != NULL) {
3284 		INP_WLOCK_ASSERT(tp->t_inpcb);
3285 	}
3286 
3287 	/* Don't bother if destination was broadcast/multicast. */
3288 	if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3289 		goto drop;
3290 #ifdef INET6
3291 	if (mtod(m, struct ip *)->ip_v == 6) {
3292 		ip6 = mtod(m, struct ip6_hdr *);
3293 		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3294 		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3295 			goto drop;
3296 		/* IPv6 anycast check is done at tcp6_input() */
3297 	}
3298 #endif
3299 #if defined(INET) && defined(INET6)
3300 	else
3301 #endif
3302 #ifdef INET
3303 	{
3304 		ip = mtod(m, struct ip *);
3305 		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3306 		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3307 		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3308 		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3309 			goto drop;
3310 	}
3311 #endif
3312 
3313 	/* Perform bandwidth limiting. */
3314 	if (badport_bandlim(rstreason) < 0)
3315 		goto drop;
3316 
3317 	/* tcp_respond consumes the mbuf chain. */
3318 	if (th->th_flags & TH_ACK) {
3319 		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3320 		    th->th_ack, TH_RST);
3321 	} else {
3322 		if (th->th_flags & TH_SYN)
3323 			tlen++;
3324 		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3325 		    (tcp_seq)0, TH_RST|TH_ACK);
3326 	}
3327 	return;
3328 drop:
3329 	m_freem(m);
3330 }
3331 
3332 /*
3333  * Parse TCP options and place in tcpopt.
3334  */
3335 void
3336 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3337 {
3338 	int opt, optlen;
3339 
3340 	to->to_flags = 0;
3341 	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3342 		opt = cp[0];
3343 		if (opt == TCPOPT_EOL)
3344 			break;
3345 		if (opt == TCPOPT_NOP)
3346 			optlen = 1;
3347 		else {
3348 			if (cnt < 2)
3349 				break;
3350 			optlen = cp[1];
3351 			if (optlen < 2 || optlen > cnt)
3352 				break;
3353 		}
3354 		switch (opt) {
3355 		case TCPOPT_MAXSEG:
3356 			if (optlen != TCPOLEN_MAXSEG)
3357 				continue;
3358 			if (!(flags & TO_SYN))
3359 				continue;
3360 			to->to_flags |= TOF_MSS;
3361 			bcopy((char *)cp + 2,
3362 			    (char *)&to->to_mss, sizeof(to->to_mss));
3363 			to->to_mss = ntohs(to->to_mss);
3364 			break;
3365 		case TCPOPT_WINDOW:
3366 			if (optlen != TCPOLEN_WINDOW)
3367 				continue;
3368 			if (!(flags & TO_SYN))
3369 				continue;
3370 			to->to_flags |= TOF_SCALE;
3371 			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3372 			break;
3373 		case TCPOPT_TIMESTAMP:
3374 			if (optlen != TCPOLEN_TIMESTAMP)
3375 				continue;
3376 			to->to_flags |= TOF_TS;
3377 			bcopy((char *)cp + 2,
3378 			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3379 			to->to_tsval = ntohl(to->to_tsval);
3380 			bcopy((char *)cp + 6,
3381 			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3382 			to->to_tsecr = ntohl(to->to_tsecr);
3383 			break;
3384 #ifdef TCP_SIGNATURE
3385 		/*
3386 		 * XXX In order to reply to a host which has set the
3387 		 * TCP_SIGNATURE option in its initial SYN, we have to
3388 		 * record the fact that the option was observed here
3389 		 * for the syncache code to perform the correct response.
3390 		 */
3391 		case TCPOPT_SIGNATURE:
3392 			if (optlen != TCPOLEN_SIGNATURE)
3393 				continue;
3394 			to->to_flags |= TOF_SIGNATURE;
3395 			to->to_signature = cp + 2;
3396 			break;
3397 #endif
3398 		case TCPOPT_SACK_PERMITTED:
3399 			if (optlen != TCPOLEN_SACK_PERMITTED)
3400 				continue;
3401 			if (!(flags & TO_SYN))
3402 				continue;
3403 			if (!V_tcp_do_sack)
3404 				continue;
3405 			to->to_flags |= TOF_SACKPERM;
3406 			break;
3407 		case TCPOPT_SACK:
3408 			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3409 				continue;
3410 			if (flags & TO_SYN)
3411 				continue;
3412 			to->to_flags |= TOF_SACK;
3413 			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3414 			to->to_sacks = cp + 2;
3415 			TCPSTAT_INC(tcps_sack_rcv_blocks);
3416 			break;
3417 #ifdef TCP_RFC7413
3418 		case TCPOPT_FAST_OPEN:
3419 			if ((optlen != TCPOLEN_FAST_OPEN_EMPTY) &&
3420 			    (optlen < TCPOLEN_FAST_OPEN_MIN) &&
3421 			    (optlen > TCPOLEN_FAST_OPEN_MAX))
3422 				continue;
3423 			if (!(flags & TO_SYN))
3424 				continue;
3425 			if (!V_tcp_fastopen_enabled)
3426 				continue;
3427 			to->to_flags |= TOF_FASTOPEN;
3428 			to->to_tfo_len = optlen - 2;
3429 			to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
3430 			break;
3431 #endif
3432 		default:
3433 			continue;
3434 		}
3435 	}
3436 }
3437 
3438 /*
3439  * Pull out of band byte out of a segment so
3440  * it doesn't appear in the user's data queue.
3441  * It is still reflected in the segment length for
3442  * sequencing purposes.
3443  */
3444 void
3445 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3446     int off)
3447 {
3448 	int cnt = off + th->th_urp - 1;
3449 
3450 	while (cnt >= 0) {
3451 		if (m->m_len > cnt) {
3452 			char *cp = mtod(m, caddr_t) + cnt;
3453 			struct tcpcb *tp = sototcpcb(so);
3454 
3455 			INP_WLOCK_ASSERT(tp->t_inpcb);
3456 
3457 			tp->t_iobc = *cp;
3458 			tp->t_oobflags |= TCPOOB_HAVEDATA;
3459 			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3460 			m->m_len--;
3461 			if (m->m_flags & M_PKTHDR)
3462 				m->m_pkthdr.len--;
3463 			return;
3464 		}
3465 		cnt -= m->m_len;
3466 		m = m->m_next;
3467 		if (m == NULL)
3468 			break;
3469 	}
3470 	panic("tcp_pulloutofband");
3471 }
3472 
3473 /*
3474  * Collect new round-trip time estimate
3475  * and update averages and current timeout.
3476  */
3477 void
3478 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3479 {
3480 	int delta;
3481 
3482 	INP_WLOCK_ASSERT(tp->t_inpcb);
3483 
3484 	TCPSTAT_INC(tcps_rttupdated);
3485 	tp->t_rttupdated++;
3486 	if (tp->t_srtt != 0) {
3487 		/*
3488 		 * srtt is stored as fixed point with 5 bits after the
3489 		 * binary point (i.e., scaled by 8).  The following magic
3490 		 * is equivalent to the smoothing algorithm in rfc793 with
3491 		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3492 		 * point).  Adjust rtt to origin 0.
3493 		 */
3494 		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3495 			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3496 
3497 		if ((tp->t_srtt += delta) <= 0)
3498 			tp->t_srtt = 1;
3499 
3500 		/*
3501 		 * We accumulate a smoothed rtt variance (actually, a
3502 		 * smoothed mean difference), then set the retransmit
3503 		 * timer to smoothed rtt + 4 times the smoothed variance.
3504 		 * rttvar is stored as fixed point with 4 bits after the
3505 		 * binary point (scaled by 16).  The following is
3506 		 * equivalent to rfc793 smoothing with an alpha of .75
3507 		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3508 		 * rfc793's wired-in beta.
3509 		 */
3510 		if (delta < 0)
3511 			delta = -delta;
3512 		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3513 		if ((tp->t_rttvar += delta) <= 0)
3514 			tp->t_rttvar = 1;
3515 		if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3516 		    tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3517 	} else {
3518 		/*
3519 		 * No rtt measurement yet - use the unsmoothed rtt.
3520 		 * Set the variance to half the rtt (so our first
3521 		 * retransmit happens at 3*rtt).
3522 		 */
3523 		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3524 		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3525 		tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3526 	}
3527 	tp->t_rtttime = 0;
3528 	tp->t_rxtshift = 0;
3529 
3530 	/*
3531 	 * the retransmit should happen at rtt + 4 * rttvar.
3532 	 * Because of the way we do the smoothing, srtt and rttvar
3533 	 * will each average +1/2 tick of bias.  When we compute
3534 	 * the retransmit timer, we want 1/2 tick of rounding and
3535 	 * 1 extra tick because of +-1/2 tick uncertainty in the
3536 	 * firing of the timer.  The bias will give us exactly the
3537 	 * 1.5 tick we need.  But, because the bias is
3538 	 * statistical, we have to test that we don't drop below
3539 	 * the minimum feasible timer (which is 2 ticks).
3540 	 */
3541 	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3542 		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3543 
3544 	/*
3545 	 * We received an ack for a packet that wasn't retransmitted;
3546 	 * it is probably safe to discard any error indications we've
3547 	 * received recently.  This isn't quite right, but close enough
3548 	 * for now (a route might have failed after we sent a segment,
3549 	 * and the return path might not be symmetrical).
3550 	 */
3551 	tp->t_softerror = 0;
3552 }
3553 
3554 /*
3555  * Determine a reasonable value for maxseg size.
3556  * If the route is known, check route for mtu.
3557  * If none, use an mss that can be handled on the outgoing interface
3558  * without forcing IP to fragment.  If no route is found, route has no mtu,
3559  * or the destination isn't local, use a default, hopefully conservative
3560  * size (usually 512 or the default IP max size, but no more than the mtu
3561  * of the interface), as we can't discover anything about intervening
3562  * gateways or networks.  We also initialize the congestion/slow start
3563  * window to be a single segment if the destination isn't local.
3564  * While looking at the routing entry, we also initialize other path-dependent
3565  * parameters from pre-set or cached values in the routing entry.
3566  *
3567  * NOTE that resulting t_maxseg doesn't include space for TCP options or
3568  * IP options, e.g. IPSEC data, since length of this data may vary, and
3569  * thus it is calculated for every segment separately in tcp_output().
3570  *
3571  * NOTE that this routine is only called when we process an incoming
3572  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3573  * settings are handled in tcp_mssopt().
3574  */
3575 void
3576 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3577     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3578 {
3579 	int mss = 0;
3580 	uint32_t maxmtu = 0;
3581 	struct inpcb *inp = tp->t_inpcb;
3582 	struct hc_metrics_lite metrics;
3583 #ifdef INET6
3584 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3585 	size_t min_protoh = isipv6 ?
3586 			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3587 			    sizeof (struct tcpiphdr);
3588 #else
3589 	const size_t min_protoh = sizeof(struct tcpiphdr);
3590 #endif
3591 
3592 	INP_WLOCK_ASSERT(tp->t_inpcb);
3593 
3594 	if (mtuoffer != -1) {
3595 		KASSERT(offer == -1, ("%s: conflict", __func__));
3596 		offer = mtuoffer - min_protoh;
3597 	}
3598 
3599 	/* Initialize. */
3600 #ifdef INET6
3601 	if (isipv6) {
3602 		maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3603 		tp->t_maxseg = V_tcp_v6mssdflt;
3604 	}
3605 #endif
3606 #if defined(INET) && defined(INET6)
3607 	else
3608 #endif
3609 #ifdef INET
3610 	{
3611 		maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3612 		tp->t_maxseg = V_tcp_mssdflt;
3613 	}
3614 #endif
3615 
3616 	/*
3617 	 * No route to sender, stay with default mss and return.
3618 	 */
3619 	if (maxmtu == 0) {
3620 		/*
3621 		 * In case we return early we need to initialize metrics
3622 		 * to a defined state as tcp_hc_get() would do for us
3623 		 * if there was no cache hit.
3624 		 */
3625 		if (metricptr != NULL)
3626 			bzero(metricptr, sizeof(struct hc_metrics_lite));
3627 		return;
3628 	}
3629 
3630 	/* What have we got? */
3631 	switch (offer) {
3632 		case 0:
3633 			/*
3634 			 * Offer == 0 means that there was no MSS on the SYN
3635 			 * segment, in this case we use tcp_mssdflt as
3636 			 * already assigned to t_maxseg above.
3637 			 */
3638 			offer = tp->t_maxseg;
3639 			break;
3640 
3641 		case -1:
3642 			/*
3643 			 * Offer == -1 means that we didn't receive SYN yet.
3644 			 */
3645 			/* FALLTHROUGH */
3646 
3647 		default:
3648 			/*
3649 			 * Prevent DoS attack with too small MSS. Round up
3650 			 * to at least minmss.
3651 			 */
3652 			offer = max(offer, V_tcp_minmss);
3653 	}
3654 
3655 	/*
3656 	 * rmx information is now retrieved from tcp_hostcache.
3657 	 */
3658 	tcp_hc_get(&inp->inp_inc, &metrics);
3659 	if (metricptr != NULL)
3660 		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3661 
3662 	/*
3663 	 * If there's a discovered mtu in tcp hostcache, use it.
3664 	 * Else, use the link mtu.
3665 	 */
3666 	if (metrics.rmx_mtu)
3667 		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3668 	else {
3669 #ifdef INET6
3670 		if (isipv6) {
3671 			mss = maxmtu - min_protoh;
3672 			if (!V_path_mtu_discovery &&
3673 			    !in6_localaddr(&inp->in6p_faddr))
3674 				mss = min(mss, V_tcp_v6mssdflt);
3675 		}
3676 #endif
3677 #if defined(INET) && defined(INET6)
3678 		else
3679 #endif
3680 #ifdef INET
3681 		{
3682 			mss = maxmtu - min_protoh;
3683 			if (!V_path_mtu_discovery &&
3684 			    !in_localaddr(inp->inp_faddr))
3685 				mss = min(mss, V_tcp_mssdflt);
3686 		}
3687 #endif
3688 		/*
3689 		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3690 		 * probably violates the TCP spec.
3691 		 * The problem is that, since we don't know the
3692 		 * other end's MSS, we are supposed to use a conservative
3693 		 * default.  But, if we do that, then MTU discovery will
3694 		 * never actually take place, because the conservative
3695 		 * default is much less than the MTUs typically seen
3696 		 * on the Internet today.  For the moment, we'll sweep
3697 		 * this under the carpet.
3698 		 *
3699 		 * The conservative default might not actually be a problem
3700 		 * if the only case this occurs is when sending an initial
3701 		 * SYN with options and data to a host we've never talked
3702 		 * to before.  Then, they will reply with an MSS value which
3703 		 * will get recorded and the new parameters should get
3704 		 * recomputed.  For Further Study.
3705 		 */
3706 	}
3707 	mss = min(mss, offer);
3708 
3709 	/*
3710 	 * Sanity check: make sure that maxseg will be large
3711 	 * enough to allow some data on segments even if the
3712 	 * all the option space is used (40bytes).  Otherwise
3713 	 * funny things may happen in tcp_output.
3714 	 *
3715 	 * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3716 	 */
3717 	mss = max(mss, 64);
3718 
3719 	tp->t_maxseg = mss;
3720 }
3721 
3722 void
3723 tcp_mss(struct tcpcb *tp, int offer)
3724 {
3725 	int mss;
3726 	uint32_t bufsize;
3727 	struct inpcb *inp;
3728 	struct socket *so;
3729 	struct hc_metrics_lite metrics;
3730 	struct tcp_ifcap cap;
3731 
3732 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3733 
3734 	bzero(&cap, sizeof(cap));
3735 	tcp_mss_update(tp, offer, -1, &metrics, &cap);
3736 
3737 	mss = tp->t_maxseg;
3738 	inp = tp->t_inpcb;
3739 
3740 	/*
3741 	 * If there's a pipesize, change the socket buffer to that size,
3742 	 * don't change if sb_hiwat is different than default (then it
3743 	 * has been changed on purpose with setsockopt).
3744 	 * Make the socket buffers an integral number of mss units;
3745 	 * if the mss is larger than the socket buffer, decrease the mss.
3746 	 */
3747 	so = inp->inp_socket;
3748 	SOCKBUF_LOCK(&so->so_snd);
3749 	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3750 		bufsize = metrics.rmx_sendpipe;
3751 	else
3752 		bufsize = so->so_snd.sb_hiwat;
3753 	if (bufsize < mss)
3754 		mss = bufsize;
3755 	else {
3756 		bufsize = roundup(bufsize, mss);
3757 		if (bufsize > sb_max)
3758 			bufsize = sb_max;
3759 		if (bufsize > so->so_snd.sb_hiwat)
3760 			(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3761 	}
3762 	SOCKBUF_UNLOCK(&so->so_snd);
3763 	tp->t_maxseg = mss;
3764 
3765 	SOCKBUF_LOCK(&so->so_rcv);
3766 	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3767 		bufsize = metrics.rmx_recvpipe;
3768 	else
3769 		bufsize = so->so_rcv.sb_hiwat;
3770 	if (bufsize > mss) {
3771 		bufsize = roundup(bufsize, mss);
3772 		if (bufsize > sb_max)
3773 			bufsize = sb_max;
3774 		if (bufsize > so->so_rcv.sb_hiwat)
3775 			(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3776 	}
3777 	SOCKBUF_UNLOCK(&so->so_rcv);
3778 
3779 	/* Check the interface for TSO capabilities. */
3780 	if (cap.ifcap & CSUM_TSO) {
3781 		tp->t_flags |= TF_TSO;
3782 		tp->t_tsomax = cap.tsomax;
3783 		tp->t_tsomaxsegcount = cap.tsomaxsegcount;
3784 		tp->t_tsomaxsegsize = cap.tsomaxsegsize;
3785 	}
3786 }
3787 
3788 /*
3789  * Determine the MSS option to send on an outgoing SYN.
3790  */
3791 int
3792 tcp_mssopt(struct in_conninfo *inc)
3793 {
3794 	int mss = 0;
3795 	uint32_t thcmtu = 0;
3796 	uint32_t maxmtu = 0;
3797 	size_t min_protoh;
3798 
3799 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3800 
3801 #ifdef INET6
3802 	if (inc->inc_flags & INC_ISIPV6) {
3803 		mss = V_tcp_v6mssdflt;
3804 		maxmtu = tcp_maxmtu6(inc, NULL);
3805 		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3806 	}
3807 #endif
3808 #if defined(INET) && defined(INET6)
3809 	else
3810 #endif
3811 #ifdef INET
3812 	{
3813 		mss = V_tcp_mssdflt;
3814 		maxmtu = tcp_maxmtu(inc, NULL);
3815 		min_protoh = sizeof(struct tcpiphdr);
3816 	}
3817 #endif
3818 #if defined(INET6) || defined(INET)
3819 	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3820 #endif
3821 
3822 	if (maxmtu && thcmtu)
3823 		mss = min(maxmtu, thcmtu) - min_protoh;
3824 	else if (maxmtu || thcmtu)
3825 		mss = max(maxmtu, thcmtu) - min_protoh;
3826 
3827 	return (mss);
3828 }
3829 
3830 
3831 /*
3832  * On a partial ack arrives, force the retransmission of the
3833  * next unacknowledged segment.  Do not clear tp->t_dupacks.
3834  * By setting snd_nxt to ti_ack, this forces retransmission timer to
3835  * be started again.
3836  */
3837 void
3838 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3839 {
3840 	tcp_seq onxt = tp->snd_nxt;
3841 	uint32_t ocwnd = tp->snd_cwnd;
3842 	u_int maxseg = tcp_maxseg(tp);
3843 
3844 	INP_WLOCK_ASSERT(tp->t_inpcb);
3845 
3846 	tcp_timer_activate(tp, TT_REXMT, 0);
3847 	tp->t_rtttime = 0;
3848 	tp->snd_nxt = th->th_ack;
3849 	/*
3850 	 * Set snd_cwnd to one segment beyond acknowledged offset.
3851 	 * (tp->snd_una has not yet been updated when this function is called.)
3852 	 */
3853 	tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
3854 	tp->t_flags |= TF_ACKNOW;
3855 	(void) tp->t_fb->tfb_tcp_output(tp);
3856 	tp->snd_cwnd = ocwnd;
3857 	if (SEQ_GT(onxt, tp->snd_nxt))
3858 		tp->snd_nxt = onxt;
3859 	/*
3860 	 * Partial window deflation.  Relies on fact that tp->snd_una
3861 	 * not updated yet.
3862 	 */
3863 	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
3864 		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
3865 	else
3866 		tp->snd_cwnd = 0;
3867 	tp->snd_cwnd += maxseg;
3868 }
3869 
3870 int
3871 tcp_compute_pipe(struct tcpcb *tp)
3872 {
3873 	return (tp->snd_max - tp->snd_una +
3874 		tp->sackhint.sack_bytes_rexmit -
3875 		tp->sackhint.sacked_bytes);
3876 }
3877