xref: /freebsd/sys/netinet/tcp_input.c (revision 16e02ae401ebd9aa7d47f46dc4905f4f8add70a8)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
5  *	The Regents of the University of California.  All rights reserved.
6  * Copyright (c) 2007-2008,2010
7  *	Swinburne University of Technology, Melbourne, Australia.
8  * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
9  * Copyright (c) 2010 The FreeBSD Foundation
10  * Copyright (c) 2010-2011 Juniper Networks, Inc.
11  * All rights reserved.
12  *
13  * Portions of this software were developed at the Centre for Advanced Internet
14  * Architectures, Swinburne University of Technology, by Lawrence Stewart,
15  * James Healy and David Hayes, made possible in part by a grant from the Cisco
16  * University Research Program Fund at Community Foundation Silicon Valley.
17  *
18  * Portions of this software were developed at the Centre for Advanced
19  * Internet Architectures, Swinburne University of Technology, Melbourne,
20  * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
21  *
22  * Portions of this software were developed by Robert N. M. Watson under
23  * contract to Juniper Networks, Inc.
24  *
25  * Redistribution and use in source and binary forms, with or without
26  * modification, are permitted provided that the following conditions
27  * are met:
28  * 1. Redistributions of source code must retain the above copyright
29  *    notice, this list of conditions and the following disclaimer.
30  * 2. Redistributions in binary form must reproduce the above copyright
31  *    notice, this list of conditions and the following disclaimer in the
32  *    documentation and/or other materials provided with the distribution.
33  * 3. Neither the name of the University nor the names of its contributors
34  *    may be used to endorse or promote products derived from this software
35  *    without specific prior written permission.
36  *
37  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
38  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
39  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
40  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
41  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
42  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
43  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
44  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
45  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
46  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
47  * SUCH DAMAGE.
48  *
49  *	@(#)tcp_input.c	8.12 (Berkeley) 5/24/95
50  */
51 
52 #include <sys/cdefs.h>
53 __FBSDID("$FreeBSD$");
54 
55 #include "opt_inet.h"
56 #include "opt_inet6.h"
57 #include "opt_ipsec.h"
58 #include "opt_tcpdebug.h"
59 
60 #include <sys/param.h>
61 #include <sys/arb.h>
62 #include <sys/kernel.h>
63 #ifdef TCP_HHOOK
64 #include <sys/hhook.h>
65 #endif
66 #include <sys/malloc.h>
67 #include <sys/mbuf.h>
68 #include <sys/proc.h>		/* for proc0 declaration */
69 #include <sys/protosw.h>
70 #include <sys/qmath.h>
71 #include <sys/sdt.h>
72 #include <sys/signalvar.h>
73 #include <sys/socket.h>
74 #include <sys/socketvar.h>
75 #include <sys/sysctl.h>
76 #include <sys/syslog.h>
77 #include <sys/systm.h>
78 #include <sys/stats.h>
79 
80 #include <machine/cpu.h>	/* before tcp_seq.h, for tcp_random18() */
81 
82 #include <vm/uma.h>
83 
84 #include <net/if.h>
85 #include <net/if_var.h>
86 #include <net/route.h>
87 #include <net/vnet.h>
88 
89 #define TCPSTATES		/* for logging */
90 
91 #include <netinet/in.h>
92 #include <netinet/in_kdtrace.h>
93 #include <netinet/in_pcb.h>
94 #include <netinet/in_systm.h>
95 #include <netinet/ip.h>
96 #include <netinet/ip_icmp.h>	/* required for icmp_var.h */
97 #include <netinet/icmp_var.h>	/* for ICMP_BANDLIM */
98 #include <netinet/ip_var.h>
99 #include <netinet/ip_options.h>
100 #include <netinet/ip6.h>
101 #include <netinet/icmp6.h>
102 #include <netinet6/in6_pcb.h>
103 #include <netinet6/in6_var.h>
104 #include <netinet6/ip6_var.h>
105 #include <netinet6/nd6.h>
106 #include <netinet/tcp.h>
107 #include <netinet/tcp_fsm.h>
108 #include <netinet/tcp_log_buf.h>
109 #include <netinet/tcp_seq.h>
110 #include <netinet/tcp_timer.h>
111 #include <netinet/tcp_var.h>
112 #include <netinet6/tcp6_var.h>
113 #include <netinet/tcpip.h>
114 #include <netinet/cc/cc.h>
115 #include <netinet/tcp_fastopen.h>
116 #ifdef TCPPCAP
117 #include <netinet/tcp_pcap.h>
118 #endif
119 #include <netinet/tcp_syncache.h>
120 #ifdef TCPDEBUG
121 #include <netinet/tcp_debug.h>
122 #endif /* TCPDEBUG */
123 #ifdef TCP_OFFLOAD
124 #include <netinet/tcp_offload.h>
125 #endif
126 #include <netinet/tcp_ecn.h>
127 #include <netinet/udp.h>
128 
129 #include <netipsec/ipsec_support.h>
130 
131 #include <machine/in_cksum.h>
132 
133 #include <security/mac/mac_framework.h>
134 
135 const int tcprexmtthresh = 3;
136 
137 VNET_DEFINE(int, tcp_log_in_vain) = 0;
138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_VNET | CTLFLAG_RW,
139     &VNET_NAME(tcp_log_in_vain), 0,
140     "Log all incoming TCP segments to closed ports");
141 
142 VNET_DEFINE(int, blackhole) = 0;
143 #define	V_blackhole		VNET(blackhole)
144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
145     &VNET_NAME(blackhole), 0,
146     "Do not send RST on segments to closed ports");
147 
148 VNET_DEFINE(bool, blackhole_local) = false;
149 #define	V_blackhole_local	VNET(blackhole_local)
150 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, blackhole_local, CTLFLAG_VNET |
151     CTLFLAG_RW, &VNET_NAME(blackhole_local), false,
152     "Enforce net.inet.tcp.blackhole for locally originated packets");
153 
154 VNET_DEFINE(int, tcp_delack_enabled) = 1;
155 SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
156     &VNET_NAME(tcp_delack_enabled), 0,
157     "Delay ACK to try and piggyback it onto a data packet");
158 
159 VNET_DEFINE(int, drop_synfin) = 0;
160 SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
161     &VNET_NAME(drop_synfin), 0,
162     "Drop TCP packets with SYN+FIN set");
163 
164 VNET_DEFINE(int, tcp_do_prr_conservative) = 0;
165 SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr_conservative, CTLFLAG_VNET | CTLFLAG_RW,
166     &VNET_NAME(tcp_do_prr_conservative), 0,
167     "Do conservative Proportional Rate Reduction");
168 
169 VNET_DEFINE(int, tcp_do_prr) = 1;
170 SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr, CTLFLAG_VNET | CTLFLAG_RW,
171     &VNET_NAME(tcp_do_prr), 1,
172     "Enable Proportional Rate Reduction per RFC 6937");
173 
174 VNET_DEFINE(int, tcp_do_lrd) = 0;
175 SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_lrd, CTLFLAG_VNET | CTLFLAG_RW,
176     &VNET_NAME(tcp_do_lrd), 1,
177     "Perform Lost Retransmission Detection");
178 
179 VNET_DEFINE(int, tcp_do_newcwv) = 0;
180 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newcwv, CTLFLAG_VNET | CTLFLAG_RW,
181     &VNET_NAME(tcp_do_newcwv), 0,
182     "Enable New Congestion Window Validation per RFC7661");
183 
184 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
185 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
186     &VNET_NAME(tcp_do_rfc3042), 0,
187     "Enable RFC 3042 (Limited Transmit)");
188 
189 VNET_DEFINE(int, tcp_do_rfc3390) = 1;
190 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
191     &VNET_NAME(tcp_do_rfc3390), 0,
192     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
193 
194 VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
195 SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
196     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
197     "Slow-start flight size (initial congestion window) in number of segments");
198 
199 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
200 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
201     &VNET_NAME(tcp_do_rfc3465), 0,
202     "Enable RFC 3465 (Appropriate Byte Counting)");
203 
204 VNET_DEFINE(int, tcp_abc_l_var) = 2;
205 SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
206     &VNET_NAME(tcp_abc_l_var), 2,
207     "Cap the max cwnd increment during slow-start to this number of segments");
208 
209 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
210     CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
211     "TCP ECN");
212 
213 VNET_DEFINE(int, tcp_do_ecn) = 2;
214 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
215     &VNET_NAME(tcp_do_ecn), 0,
216     "TCP ECN support");
217 
218 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
219 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
220     &VNET_NAME(tcp_ecn_maxretries), 0,
221     "Max retries before giving up on ECN");
222 
223 VNET_DEFINE(int, tcp_insecure_syn) = 0;
224 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
225     &VNET_NAME(tcp_insecure_syn), 0,
226     "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
227 
228 VNET_DEFINE(int, tcp_insecure_rst) = 0;
229 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
230     &VNET_NAME(tcp_insecure_rst), 0,
231     "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
232 
233 VNET_DEFINE(int, tcp_recvspace) = 1024*64;
234 #define	V_tcp_recvspace	VNET(tcp_recvspace)
235 SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
236     &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
237 
238 VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
239 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
240     &VNET_NAME(tcp_do_autorcvbuf), 0,
241     "Enable automatic receive buffer sizing");
242 
243 VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
244 SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
245     &VNET_NAME(tcp_autorcvbuf_max), 0,
246     "Max size of automatic receive buffer");
247 
248 VNET_DEFINE(struct inpcbinfo, tcbinfo);
249 
250 /*
251  * TCP statistics are stored in an array of counter(9)s, which size matches
252  * size of struct tcpstat.  TCP running connection count is a regular array.
253  */
254 VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
255 SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
256     tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
257 VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
258 SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
259     CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
260     "TCP connection counts by TCP state");
261 
262 /*
263  * Kernel module interface for updating tcpstat.  The first argument is an index
264  * into tcpstat treated as an array.
265  */
266 void
267 kmod_tcpstat_add(int statnum, int val)
268 {
269 
270 	counter_u64_add(VNET(tcpstat)[statnum], val);
271 }
272 
273 #ifdef TCP_HHOOK
274 /*
275  * Wrapper for the TCP established input helper hook.
276  */
277 void
278 hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
279 {
280 	struct tcp_hhook_data hhook_data;
281 
282 	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
283 		hhook_data.tp = tp;
284 		hhook_data.th = th;
285 		hhook_data.to = to;
286 
287 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
288 		    tp->osd);
289 	}
290 }
291 #endif
292 
293 /*
294  * CC wrapper hook functions
295  */
296 void
297 cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
298     uint16_t type)
299 {
300 #ifdef STATS
301 	int32_t gput;
302 #endif
303 
304 	INP_WLOCK_ASSERT(tp->t_inpcb);
305 
306 	tp->ccv->nsegs = nsegs;
307 	tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
308 	if ((!V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd)) ||
309 	    (V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd) &&
310 	     (tp->snd_cwnd < (tcp_compute_pipe(tp) * 2))))
311 		tp->ccv->flags |= CCF_CWND_LIMITED;
312 	else
313 		tp->ccv->flags &= ~CCF_CWND_LIMITED;
314 
315 	if (type == CC_ACK) {
316 #ifdef STATS
317 		stats_voi_update_abs_s32(tp->t_stats, VOI_TCP_CALCFRWINDIFF,
318 		    ((int32_t)tp->snd_cwnd) - tp->snd_wnd);
319 		if (!IN_RECOVERY(tp->t_flags))
320 			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_ACKLEN,
321 			   tp->ccv->bytes_this_ack / (tcp_maxseg(tp) * nsegs));
322 		if ((tp->t_flags & TF_GPUTINPROG) &&
323 		    SEQ_GEQ(th->th_ack, tp->gput_ack)) {
324 			/*
325 			 * Compute goodput in bits per millisecond.
326 			 */
327 			gput = (((int64_t)(th->th_ack - tp->gput_seq)) << 3) /
328 			    max(1, tcp_ts_getticks() - tp->gput_ts);
329 			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_GPUT,
330 			    gput);
331 			/*
332 			 * XXXLAS: This is a temporary hack, and should be
333 			 * chained off VOI_TCP_GPUT when stats(9) grows an API
334 			 * to deal with chained VOIs.
335 			 */
336 			if (tp->t_stats_gput_prev > 0)
337 				stats_voi_update_abs_s32(tp->t_stats,
338 				    VOI_TCP_GPUT_ND,
339 				    ((gput - tp->t_stats_gput_prev) * 100) /
340 				    tp->t_stats_gput_prev);
341 			tp->t_flags &= ~TF_GPUTINPROG;
342 			tp->t_stats_gput_prev = gput;
343 		}
344 #endif /* STATS */
345 		if (tp->snd_cwnd > tp->snd_ssthresh) {
346 			tp->t_bytes_acked += tp->ccv->bytes_this_ack;
347 			if (tp->t_bytes_acked >= tp->snd_cwnd) {
348 				tp->t_bytes_acked -= tp->snd_cwnd;
349 				tp->ccv->flags |= CCF_ABC_SENTAWND;
350 			}
351 		} else {
352 				tp->ccv->flags &= ~CCF_ABC_SENTAWND;
353 				tp->t_bytes_acked = 0;
354 		}
355 	}
356 
357 	if (CC_ALGO(tp)->ack_received != NULL) {
358 		/* XXXLAS: Find a way to live without this */
359 		tp->ccv->curack = th->th_ack;
360 		CC_ALGO(tp)->ack_received(tp->ccv, type);
361 	}
362 #ifdef STATS
363 	stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_LCWIN, tp->snd_cwnd);
364 #endif
365 }
366 
367 void
368 cc_conn_init(struct tcpcb *tp)
369 {
370 	struct hc_metrics_lite metrics;
371 	struct inpcb *inp = tp->t_inpcb;
372 	u_int maxseg;
373 	int rtt;
374 
375 	INP_WLOCK_ASSERT(tp->t_inpcb);
376 
377 	tcp_hc_get(&inp->inp_inc, &metrics);
378 	maxseg = tcp_maxseg(tp);
379 
380 	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
381 		tp->t_srtt = rtt;
382 		tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
383 		TCPSTAT_INC(tcps_usedrtt);
384 		if (metrics.rmx_rttvar) {
385 			tp->t_rttvar = metrics.rmx_rttvar;
386 			TCPSTAT_INC(tcps_usedrttvar);
387 		} else {
388 			/* default variation is +- 1 rtt */
389 			tp->t_rttvar =
390 			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
391 		}
392 		TCPT_RANGESET(tp->t_rxtcur,
393 		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
394 		    tp->t_rttmin, TCPTV_REXMTMAX);
395 	}
396 	if (metrics.rmx_ssthresh) {
397 		/*
398 		 * There's some sort of gateway or interface
399 		 * buffer limit on the path.  Use this to set
400 		 * the slow start threshold, but set the
401 		 * threshold to no less than 2*mss.
402 		 */
403 		tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
404 		TCPSTAT_INC(tcps_usedssthresh);
405 	}
406 
407 	/*
408 	 * Set the initial slow-start flight size.
409 	 *
410 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
411 	 * reduce the initial CWND to one segment as congestion is likely
412 	 * requiring us to be cautious.
413 	 */
414 	if (tp->snd_cwnd == 1)
415 		tp->snd_cwnd = maxseg;		/* SYN(-ACK) lost */
416 	else
417 		tp->snd_cwnd = tcp_compute_initwnd(maxseg);
418 
419 	if (CC_ALGO(tp)->conn_init != NULL)
420 		CC_ALGO(tp)->conn_init(tp->ccv);
421 }
422 
423 void inline
424 cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
425 {
426 	INP_WLOCK_ASSERT(tp->t_inpcb);
427 
428 #ifdef STATS
429 	stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_CSIG, type);
430 #endif
431 
432 	switch(type) {
433 	case CC_NDUPACK:
434 		if (!IN_FASTRECOVERY(tp->t_flags)) {
435 			tp->snd_recover = tp->snd_max;
436 			if (tp->t_flags2 & TF2_ECN_PERMIT)
437 				tp->t_flags2 |= TF2_ECN_SND_CWR;
438 		}
439 		break;
440 	case CC_ECN:
441 		if (!IN_CONGRECOVERY(tp->t_flags) ||
442 		    /*
443 		     * Allow ECN reaction on ACK to CWR, if
444 		     * that data segment was also CE marked.
445 		     */
446 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
447 			EXIT_CONGRECOVERY(tp->t_flags);
448 			TCPSTAT_INC(tcps_ecn_rcwnd);
449 			tp->snd_recover = tp->snd_max + 1;
450 			if (tp->t_flags2 & TF2_ECN_PERMIT)
451 				tp->t_flags2 |= TF2_ECN_SND_CWR;
452 		}
453 		break;
454 	case CC_RTO:
455 		tp->t_dupacks = 0;
456 		tp->t_bytes_acked = 0;
457 		EXIT_RECOVERY(tp->t_flags);
458 		if (tp->t_flags2 & TF2_ECN_PERMIT)
459 			tp->t_flags2 |= TF2_ECN_SND_CWR;
460 		break;
461 	case CC_RTO_ERR:
462 		TCPSTAT_INC(tcps_sndrexmitbad);
463 		/* RTO was unnecessary, so reset everything. */
464 		tp->snd_cwnd = tp->snd_cwnd_prev;
465 		tp->snd_ssthresh = tp->snd_ssthresh_prev;
466 		tp->snd_recover = tp->snd_recover_prev;
467 		if (tp->t_flags & TF_WASFRECOVERY)
468 			ENTER_FASTRECOVERY(tp->t_flags);
469 		if (tp->t_flags & TF_WASCRECOVERY)
470 			ENTER_CONGRECOVERY(tp->t_flags);
471 		tp->snd_nxt = tp->snd_max;
472 		tp->t_flags &= ~TF_PREVVALID;
473 		tp->t_badrxtwin = 0;
474 		break;
475 	}
476 
477 	if (CC_ALGO(tp)->cong_signal != NULL) {
478 		if (th != NULL)
479 			tp->ccv->curack = th->th_ack;
480 		CC_ALGO(tp)->cong_signal(tp->ccv, type);
481 	}
482 }
483 
484 void inline
485 cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
486 {
487 	INP_WLOCK_ASSERT(tp->t_inpcb);
488 
489 	/* XXXLAS: KASSERT that we're in recovery? */
490 
491 	if (CC_ALGO(tp)->post_recovery != NULL) {
492 		tp->ccv->curack = th->th_ack;
493 		CC_ALGO(tp)->post_recovery(tp->ccv);
494 	}
495 	/* XXXLAS: EXIT_RECOVERY ? */
496 	tp->t_bytes_acked = 0;
497 	tp->sackhint.delivered_data = 0;
498 	tp->sackhint.prr_out = 0;
499 }
500 
501 /*
502  * Indicate whether this ack should be delayed.  We can delay the ack if
503  * following conditions are met:
504  *	- There is no delayed ack timer in progress.
505  *	- Our last ack wasn't a 0-sized window. We never want to delay
506  *	  the ack that opens up a 0-sized window.
507  *	- LRO wasn't used for this segment. We make sure by checking that the
508  *	  segment size is not larger than the MSS.
509  */
510 #define DELAY_ACK(tp, tlen)						\
511 	((!tcp_timer_active(tp, TT_DELACK) &&				\
512 	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
513 	    (tlen <= tp->t_maxseg) &&					\
514 	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
515 
516 void inline
517 cc_ecnpkt_handler_flags(struct tcpcb *tp, uint16_t flags, uint8_t iptos)
518 {
519 	INP_WLOCK_ASSERT(tp->t_inpcb);
520 
521 	if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
522 		switch (iptos & IPTOS_ECN_MASK) {
523 		case IPTOS_ECN_CE:
524 			tp->ccv->flags |= CCF_IPHDR_CE;
525 			break;
526 		case IPTOS_ECN_ECT0:
527 			/* FALLTHROUGH */
528 		case IPTOS_ECN_ECT1:
529 			/* FALLTHROUGH */
530 		case IPTOS_ECN_NOTECT:
531 			tp->ccv->flags &= ~CCF_IPHDR_CE;
532 			break;
533 		}
534 
535 		if (flags & TH_CWR)
536 			tp->ccv->flags |= CCF_TCPHDR_CWR;
537 		else
538 			tp->ccv->flags &= ~CCF_TCPHDR_CWR;
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 			tp->t_flags |= TF_ACKNOW;
545 		}
546 	}
547 }
548 
549 void inline
550 cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
551 {
552 	cc_ecnpkt_handler_flags(tp, tcp_get_flags(th), iptos);
553 }
554 
555 /*
556  * TCP input handling is split into multiple parts:
557  *   tcp6_input is a thin wrapper around tcp_input for the extended
558  *	ip6_protox[] call format in ip6_input
559  *   tcp_input handles primary segment validation, inpcb lookup and
560  *	SYN processing on listen sockets
561  *   tcp_do_segment processes the ACK and text of the segment for
562  *	establishing, established and closing connections
563  */
564 #ifdef INET6
565 int
566 tcp6_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
567 {
568 	struct mbuf *m;
569 	struct in6_ifaddr *ia6;
570 	struct ip6_hdr *ip6;
571 
572 	m = *mp;
573 	if (m->m_len < *offp + sizeof(struct tcphdr)) {
574 		m = m_pullup(m, *offp + sizeof(struct tcphdr));
575 		if (m == NULL) {
576 			*mp = m;
577 			TCPSTAT_INC(tcps_rcvshort);
578 			return (IPPROTO_DONE);
579 		}
580 	}
581 
582 	/*
583 	 * draft-itojun-ipv6-tcp-to-anycast
584 	 * better place to put this in?
585 	 */
586 	ip6 = mtod(m, struct ip6_hdr *);
587 	ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
588 	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
589 		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
590 			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
591 		*mp = NULL;
592 		return (IPPROTO_DONE);
593 	}
594 
595 	*mp = m;
596 	return (tcp_input_with_port(mp, offp, proto, port));
597 }
598 
599 int
600 tcp6_input(struct mbuf **mp, int *offp, int proto)
601 {
602 
603 	return(tcp6_input_with_port(mp, offp, proto, 0));
604 }
605 #endif /* INET6 */
606 
607 int
608 tcp_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
609 {
610 	struct mbuf *m = *mp;
611 	struct tcphdr *th = NULL;
612 	struct ip *ip = NULL;
613 	struct inpcb *inp = NULL;
614 	struct tcpcb *tp = NULL;
615 	struct socket *so = NULL;
616 	u_char *optp = NULL;
617 	int off0;
618 	int optlen = 0;
619 #ifdef INET
620 	int len;
621 	uint8_t ipttl;
622 #endif
623 	int tlen = 0, off;
624 	int drop_hdrlen;
625 	int thflags;
626 	int rstreason = 0;	/* For badport_bandlim accounting purposes */
627 	int lookupflag;
628 	uint8_t iptos;
629 	struct m_tag *fwd_tag = NULL;
630 #ifdef INET6
631 	struct ip6_hdr *ip6 = NULL;
632 	int isipv6;
633 #else
634 	const void *ip6 = NULL;
635 #endif /* INET6 */
636 	struct tcpopt to;		/* options in this segment */
637 	char *s = NULL;			/* address and port logging */
638 #ifdef TCPDEBUG
639 	/*
640 	 * The size of tcp_saveipgen must be the size of the max ip header,
641 	 * now IPv6.
642 	 */
643 	u_char tcp_saveipgen[IP6_HDR_LEN];
644 	struct tcphdr tcp_savetcp;
645 	short ostate = 0;
646 #endif
647 
648 	NET_EPOCH_ASSERT();
649 
650 #ifdef INET6
651 	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
652 #endif
653 
654 	off0 = *offp;
655 	m = *mp;
656 	*mp = NULL;
657 	to.to_flags = 0;
658 	TCPSTAT_INC(tcps_rcvtotal);
659 
660 #ifdef INET6
661 	if (isipv6) {
662 		ip6 = mtod(m, struct ip6_hdr *);
663 		th = (struct tcphdr *)((caddr_t)ip6 + off0);
664 		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
665 		if (port)
666 			goto skip6_csum;
667 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
668 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
669 				th->th_sum = m->m_pkthdr.csum_data;
670 			else
671 				th->th_sum = in6_cksum_pseudo(ip6, tlen,
672 				    IPPROTO_TCP, m->m_pkthdr.csum_data);
673 			th->th_sum ^= 0xffff;
674 		} else
675 			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
676 		if (th->th_sum) {
677 			TCPSTAT_INC(tcps_rcvbadsum);
678 			goto drop;
679 		}
680 	skip6_csum:
681 		/*
682 		 * Be proactive about unspecified IPv6 address in source.
683 		 * As we use all-zero to indicate unbounded/unconnected pcb,
684 		 * unspecified IPv6 address can be used to confuse us.
685 		 *
686 		 * Note that packets with unspecified IPv6 destination is
687 		 * already dropped in ip6_input.
688 		 */
689 		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
690 			/* XXX stat */
691 			goto drop;
692 		}
693 		iptos = IPV6_TRAFFIC_CLASS(ip6);
694 	}
695 #endif
696 #if defined(INET) && defined(INET6)
697 	else
698 #endif
699 #ifdef INET
700 	{
701 		/*
702 		 * Get IP and TCP header together in first mbuf.
703 		 * Note: IP leaves IP header in first mbuf.
704 		 */
705 		if (off0 > sizeof (struct ip)) {
706 			ip_stripoptions(m);
707 			off0 = sizeof(struct ip);
708 		}
709 		if (m->m_len < sizeof (struct tcpiphdr)) {
710 			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
711 			    == NULL) {
712 				TCPSTAT_INC(tcps_rcvshort);
713 				return (IPPROTO_DONE);
714 			}
715 		}
716 		ip = mtod(m, struct ip *);
717 		th = (struct tcphdr *)((caddr_t)ip + off0);
718 		tlen = ntohs(ip->ip_len) - off0;
719 
720 		iptos = ip->ip_tos;
721 		if (port)
722 			goto skip_csum;
723 		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
724 			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
725 				th->th_sum = m->m_pkthdr.csum_data;
726 			else
727 				th->th_sum = in_pseudo(ip->ip_src.s_addr,
728 				    ip->ip_dst.s_addr,
729 				    htonl(m->m_pkthdr.csum_data + tlen +
730 				    IPPROTO_TCP));
731 			th->th_sum ^= 0xffff;
732 		} else {
733 			struct ipovly *ipov = (struct ipovly *)ip;
734 
735 			/*
736 			 * Checksum extended TCP header and data.
737 			 */
738 			len = off0 + tlen;
739 			ipttl = ip->ip_ttl;
740 			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
741 			ipov->ih_len = htons(tlen);
742 			th->th_sum = in_cksum(m, len);
743 			/* Reset length for SDT probes. */
744 			ip->ip_len = htons(len);
745 			/* Reset TOS bits */
746 			ip->ip_tos = iptos;
747 			/* Re-initialization for later version check */
748 			ip->ip_ttl = ipttl;
749 			ip->ip_v = IPVERSION;
750 			ip->ip_hl = off0 >> 2;
751 		}
752 	skip_csum:
753 		if (th->th_sum && (port == 0)) {
754 			TCPSTAT_INC(tcps_rcvbadsum);
755 			goto drop;
756 		}
757 	}
758 #endif /* INET */
759 
760 	/*
761 	 * Check that TCP offset makes sense,
762 	 * pull out TCP options and adjust length.		XXX
763 	 */
764 	off = th->th_off << 2;
765 	if (off < sizeof (struct tcphdr) || off > tlen) {
766 		TCPSTAT_INC(tcps_rcvbadoff);
767 		goto drop;
768 	}
769 	tlen -= off;	/* tlen is used instead of ti->ti_len */
770 	if (off > sizeof (struct tcphdr)) {
771 #ifdef INET6
772 		if (isipv6) {
773 			if (m->m_len < off0 + off) {
774 				m = m_pullup(m, off0 + off);
775 				if (m == NULL) {
776 					TCPSTAT_INC(tcps_rcvshort);
777 					return (IPPROTO_DONE);
778 				}
779 			}
780 			ip6 = mtod(m, struct ip6_hdr *);
781 			th = (struct tcphdr *)((caddr_t)ip6 + off0);
782 		}
783 #endif
784 #if defined(INET) && defined(INET6)
785 		else
786 #endif
787 #ifdef INET
788 		{
789 			if (m->m_len < sizeof(struct ip) + off) {
790 				if ((m = m_pullup(m, sizeof (struct ip) + off))
791 				    == NULL) {
792 					TCPSTAT_INC(tcps_rcvshort);
793 					return (IPPROTO_DONE);
794 				}
795 				ip = mtod(m, struct ip *);
796 				th = (struct tcphdr *)((caddr_t)ip + off0);
797 			}
798 		}
799 #endif
800 		optlen = off - sizeof (struct tcphdr);
801 		optp = (u_char *)(th + 1);
802 	}
803 	thflags = tcp_get_flags(th);
804 
805 	/*
806 	 * Convert TCP protocol specific fields to host format.
807 	 */
808 	tcp_fields_to_host(th);
809 
810 	/*
811 	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
812 	 */
813 	drop_hdrlen = off0 + off;
814 
815 	/*
816 	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
817 	 */
818         if (
819 #ifdef INET6
820 	    (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
821 #ifdef INET
822 	    || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
823 #endif
824 #endif
825 #if defined(INET) && !defined(INET6)
826 	    (m->m_flags & M_IP_NEXTHOP)
827 #endif
828 	    )
829 		fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
830 
831 	/*
832 	 * For initial SYN packets we don't need write lock on matching
833 	 * PCB, be it a listening one or a synchronized one.  The packet
834 	 * shall not modify its state.
835 	 */
836 	lookupflag = (thflags & (TH_ACK|TH_SYN)) == TH_SYN ?
837 	    INPLOOKUP_RLOCKPCB : INPLOOKUP_WLOCKPCB;
838 findpcb:
839 #ifdef INET6
840 	if (isipv6 && fwd_tag != NULL) {
841 		struct sockaddr_in6 *next_hop6;
842 
843 		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
844 		/*
845 		 * Transparently forwarded. Pretend to be the destination.
846 		 * Already got one like this?
847 		 */
848 		inp = in6_pcblookup_mbuf(&V_tcbinfo,
849 		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
850 		    lookupflag, m->m_pkthdr.rcvif, m);
851 		if (!inp) {
852 			/*
853 			 * It's new.  Try to find the ambushing socket.
854 			 * Because we've rewritten the destination address,
855 			 * any hardware-generated hash is ignored.
856 			 */
857 			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
858 			    th->th_sport, &next_hop6->sin6_addr,
859 			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
860 			    th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
861 			    m->m_pkthdr.rcvif);
862 		}
863 	} else if (isipv6) {
864 		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
865 		    th->th_sport, &ip6->ip6_dst, th->th_dport,
866 		    INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
867 	}
868 #endif /* INET6 */
869 #if defined(INET6) && defined(INET)
870 	else
871 #endif
872 #ifdef INET
873 	if (fwd_tag != NULL) {
874 		struct sockaddr_in *next_hop;
875 
876 		next_hop = (struct sockaddr_in *)(fwd_tag+1);
877 		/*
878 		 * Transparently forwarded. Pretend to be the destination.
879 		 * already got one like this?
880 		 */
881 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
882 		    ip->ip_dst, th->th_dport, lookupflag, m->m_pkthdr.rcvif, m);
883 		if (!inp) {
884 			/*
885 			 * It's new.  Try to find the ambushing socket.
886 			 * Because we've rewritten the destination address,
887 			 * any hardware-generated hash is ignored.
888 			 */
889 			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
890 			    th->th_sport, next_hop->sin_addr,
891 			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
892 			    th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
893 			    m->m_pkthdr.rcvif);
894 		}
895 	} else
896 		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
897 		    th->th_sport, ip->ip_dst, th->th_dport,
898 		    INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
899 #endif /* INET */
900 
901 	/*
902 	 * If the INPCB does not exist then all data in the incoming
903 	 * segment is discarded and an appropriate RST is sent back.
904 	 * XXX MRT Send RST using which routing table?
905 	 */
906 	if (inp == NULL) {
907 		/*
908 		 * Log communication attempts to ports that are not
909 		 * in use.
910 		 */
911 		if ((V_tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
912 		    V_tcp_log_in_vain == 2) {
913 			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
914 				log(LOG_INFO, "%s; %s: Connection attempt "
915 				    "to closed port\n", s, __func__);
916 		}
917 		/*
918 		 * When blackholing do not respond with a RST but
919 		 * completely ignore the segment and drop it.
920 		 */
921 		if (((V_blackhole == 1 && (thflags & TH_SYN)) ||
922 		    V_blackhole == 2) && (V_blackhole_local ||
923 #ifdef INET6
924 		    isipv6 ? !in6_localaddr(&ip6->ip6_src) :
925 #endif
926 #ifdef INET
927 		    !in_localip(ip->ip_src)
928 #else
929 		    true
930 #endif
931 		    ))
932 			goto dropunlock;
933 
934 		rstreason = BANDLIM_RST_CLOSEDPORT;
935 		goto dropwithreset;
936 	}
937 	INP_LOCK_ASSERT(inp);
938 	/*
939 	 * While waiting for inp lock during the lookup, another thread
940 	 * can have dropped the inpcb, in which case we need to loop back
941 	 * and try to find a new inpcb to deliver to.
942 	 */
943 	if (inp->inp_flags & INP_DROPPED) {
944 		INP_UNLOCK(inp);
945 		inp = NULL;
946 		goto findpcb;
947 	}
948 	if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
949 	    (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
950 	    ((inp->inp_socket == NULL) || !SOLISTENING(inp->inp_socket))) {
951 		inp->inp_flowid = m->m_pkthdr.flowid;
952 		inp->inp_flowtype = M_HASHTYPE_GET(m);
953 	}
954 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
955 #ifdef INET6
956 	if (isipv6 && IPSEC_ENABLED(ipv6) &&
957 	    IPSEC_CHECK_POLICY(ipv6, m, inp) != 0) {
958 		goto dropunlock;
959 	}
960 #ifdef INET
961 	else
962 #endif
963 #endif /* INET6 */
964 #ifdef INET
965 	if (IPSEC_ENABLED(ipv4) &&
966 	    IPSEC_CHECK_POLICY(ipv4, m, inp) != 0) {
967 		goto dropunlock;
968 	}
969 #endif /* INET */
970 #endif /* IPSEC */
971 
972 	/*
973 	 * Check the minimum TTL for socket.
974 	 */
975 	if (inp->inp_ip_minttl != 0) {
976 #ifdef INET6
977 		if (isipv6) {
978 			if (inp->inp_ip_minttl > ip6->ip6_hlim)
979 				goto dropunlock;
980 		} else
981 #endif
982 		if (inp->inp_ip_minttl > ip->ip_ttl)
983 			goto dropunlock;
984 	}
985 
986 	/*
987 	 * A previous connection in TIMEWAIT state is supposed to catch stray
988 	 * or duplicate segments arriving late.  If this segment was a
989 	 * legitimate new connection attempt, the old INPCB gets removed and
990 	 * we can try again to find a listening socket.
991 	 */
992 	if (inp->inp_flags & INP_TIMEWAIT) {
993 		tcp_dooptions(&to, optp, optlen,
994 		    (thflags & TH_SYN) ? TO_SYN : 0);
995 		/*
996 		 * NB: tcp_twcheck unlocks the INP and frees the mbuf.
997 		 */
998 		if (tcp_twcheck(inp, &to, th, m, tlen))
999 			goto findpcb;
1000 		return (IPPROTO_DONE);
1001 	}
1002 	/*
1003 	 * The TCPCB may no longer exist if the connection is winding
1004 	 * down or it is in the CLOSED state.  Either way we drop the
1005 	 * segment and send an appropriate response.
1006 	 */
1007 	tp = intotcpcb(inp);
1008 	if (tp == NULL || tp->t_state == TCPS_CLOSED) {
1009 		rstreason = BANDLIM_RST_CLOSEDPORT;
1010 		goto dropwithreset;
1011 	}
1012 
1013 	if ((tp->t_port != port) && (tp->t_state > TCPS_LISTEN)) {
1014 		rstreason = BANDLIM_RST_CLOSEDPORT;
1015 		goto dropwithreset;
1016 	}
1017 
1018 #ifdef TCP_OFFLOAD
1019 	if (tp->t_flags & TF_TOE) {
1020 		tcp_offload_input(tp, m);
1021 		m = NULL;	/* consumed by the TOE driver */
1022 		goto dropunlock;
1023 	}
1024 #endif
1025 
1026 #ifdef MAC
1027 	if (mac_inpcb_check_deliver(inp, m))
1028 		goto dropunlock;
1029 #endif
1030 	so = inp->inp_socket;
1031 	KASSERT(so != NULL, ("%s: so == NULL", __func__));
1032 #ifdef TCPDEBUG
1033 	if (so->so_options & SO_DEBUG) {
1034 		ostate = tp->t_state;
1035 #ifdef INET6
1036 		if (isipv6) {
1037 			bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
1038 		} else
1039 #endif
1040 			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
1041 		tcp_savetcp = *th;
1042 	}
1043 #endif /* TCPDEBUG */
1044 	/*
1045 	 * When the socket is accepting connections (the INPCB is in LISTEN
1046 	 * state) we look into the SYN cache if this is a new connection
1047 	 * attempt or the completion of a previous one.
1048 	 */
1049 	KASSERT(tp->t_state == TCPS_LISTEN || !SOLISTENING(so),
1050 	    ("%s: so accepting but tp %p not listening", __func__, tp));
1051 	if (tp->t_state == TCPS_LISTEN && SOLISTENING(so)) {
1052 		struct in_conninfo inc;
1053 
1054 		bzero(&inc, sizeof(inc));
1055 #ifdef INET6
1056 		if (isipv6) {
1057 			inc.inc_flags |= INC_ISIPV6;
1058 			if (inp->inp_inc.inc_flags & INC_IPV6MINMTU)
1059 				inc.inc_flags |= INC_IPV6MINMTU;
1060 			inc.inc6_faddr = ip6->ip6_src;
1061 			inc.inc6_laddr = ip6->ip6_dst;
1062 		} else
1063 #endif
1064 		{
1065 			inc.inc_faddr = ip->ip_src;
1066 			inc.inc_laddr = ip->ip_dst;
1067 		}
1068 		inc.inc_fport = th->th_sport;
1069 		inc.inc_lport = th->th_dport;
1070 		inc.inc_fibnum = so->so_fibnum;
1071 
1072 		/*
1073 		 * Check for an existing connection attempt in syncache if
1074 		 * the flag is only ACK.  A successful lookup creates a new
1075 		 * socket appended to the listen queue in SYN_RECEIVED state.
1076 		 */
1077 		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1078 			/*
1079 			 * Parse the TCP options here because
1080 			 * syncookies need access to the reflected
1081 			 * timestamp.
1082 			 */
1083 			tcp_dooptions(&to, optp, optlen, 0);
1084 			/*
1085 			 * NB: syncache_expand() doesn't unlock
1086 			 * inp and tcpinfo locks.
1087 			 */
1088 			rstreason = syncache_expand(&inc, &to, th, &so, m, port);
1089 			if (rstreason < 0) {
1090 				/*
1091 				 * A failing TCP MD5 signature comparison
1092 				 * must result in the segment being dropped
1093 				 * and must not produce any response back
1094 				 * to the sender.
1095 				 */
1096 				goto dropunlock;
1097 			} else if (rstreason == 0) {
1098 				/*
1099 				 * No syncache entry or ACK was not
1100 				 * for our SYN/ACK.  Send a RST.
1101 				 * NB: syncache did its own logging
1102 				 * of the failure cause.
1103 				 */
1104 				rstreason = BANDLIM_RST_OPENPORT;
1105 				goto dropwithreset;
1106 			}
1107 tfo_socket_result:
1108 			if (so == NULL) {
1109 				/*
1110 				 * We completed the 3-way handshake
1111 				 * but could not allocate a socket
1112 				 * either due to memory shortage,
1113 				 * listen queue length limits or
1114 				 * global socket limits.  Send RST
1115 				 * or wait and have the remote end
1116 				 * retransmit the ACK for another
1117 				 * try.
1118 				 */
1119 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1120 					log(LOG_DEBUG, "%s; %s: Listen socket: "
1121 					    "Socket allocation failed due to "
1122 					    "limits or memory shortage, %s\n",
1123 					    s, __func__,
1124 					    V_tcp_sc_rst_sock_fail ?
1125 					    "sending RST" : "try again");
1126 				if (V_tcp_sc_rst_sock_fail) {
1127 					rstreason = BANDLIM_UNLIMITED;
1128 					goto dropwithreset;
1129 				} else
1130 					goto dropunlock;
1131 			}
1132 			/*
1133 			 * Socket is created in state SYN_RECEIVED.
1134 			 * Unlock the listen socket, lock the newly
1135 			 * created socket and update the tp variable.
1136 			 * If we came here via jump to tfo_socket_result,
1137 			 * then listening socket is read-locked.
1138 			 */
1139 			INP_UNLOCK(inp);	/* listen socket */
1140 			inp = sotoinpcb(so);
1141 			/*
1142 			 * New connection inpcb is already locked by
1143 			 * syncache_expand().
1144 			 */
1145 			INP_WLOCK_ASSERT(inp);
1146 			tp = intotcpcb(inp);
1147 			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1148 			    ("%s: ", __func__));
1149 			/*
1150 			 * Process the segment and the data it
1151 			 * contains.  tcp_do_segment() consumes
1152 			 * the mbuf chain and unlocks the inpcb.
1153 			 */
1154 			TCP_PROBE5(receive, NULL, tp, m, tp, th);
1155 			tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1156 			    iptos);
1157 			return (IPPROTO_DONE);
1158 		}
1159 		/*
1160 		 * Segment flag validation for new connection attempts:
1161 		 *
1162 		 * Our (SYN|ACK) response was rejected.
1163 		 * Check with syncache and remove entry to prevent
1164 		 * retransmits.
1165 		 *
1166 		 * NB: syncache_chkrst does its own logging of failure
1167 		 * causes.
1168 		 */
1169 		if (thflags & TH_RST) {
1170 			syncache_chkrst(&inc, th, m, port);
1171 			goto dropunlock;
1172 		}
1173 		/*
1174 		 * We can't do anything without SYN.
1175 		 */
1176 		if ((thflags & TH_SYN) == 0) {
1177 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1178 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1179 				    "SYN is missing, segment ignored\n",
1180 				    s, __func__);
1181 			TCPSTAT_INC(tcps_badsyn);
1182 			goto dropunlock;
1183 		}
1184 		/*
1185 		 * (SYN|ACK) is bogus on a listen socket.
1186 		 */
1187 		if (thflags & TH_ACK) {
1188 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1189 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1190 				    "SYN|ACK invalid, segment rejected\n",
1191 				    s, __func__);
1192 			syncache_badack(&inc, port);	/* XXX: Not needed! */
1193 			TCPSTAT_INC(tcps_badsyn);
1194 			rstreason = BANDLIM_RST_OPENPORT;
1195 			goto dropwithreset;
1196 		}
1197 		/*
1198 		 * If the drop_synfin option is enabled, drop all
1199 		 * segments with both the SYN and FIN bits set.
1200 		 * This prevents e.g. nmap from identifying the
1201 		 * TCP/IP stack.
1202 		 * XXX: Poor reasoning.  nmap has other methods
1203 		 * and is constantly refining its stack detection
1204 		 * strategies.
1205 		 * XXX: This is a violation of the TCP specification
1206 		 * and was used by RFC1644.
1207 		 */
1208 		if ((thflags & TH_FIN) && V_drop_synfin) {
1209 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1210 				log(LOG_DEBUG, "%s; %s: Listen socket: "
1211 				    "SYN|FIN segment ignored (based on "
1212 				    "sysctl setting)\n", s, __func__);
1213 			TCPSTAT_INC(tcps_badsyn);
1214 			goto dropunlock;
1215 		}
1216 		/*
1217 		 * Segment's flags are (SYN) or (SYN|FIN).
1218 		 *
1219 		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1220 		 * as they do not affect the state of the TCP FSM.
1221 		 * The data pointed to by TH_URG and th_urp is ignored.
1222 		 */
1223 		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1224 		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1225 		KASSERT(thflags & (TH_SYN),
1226 		    ("%s: Listen socket: TH_SYN not set", __func__));
1227 		INP_RLOCK_ASSERT(inp);
1228 #ifdef INET6
1229 		/*
1230 		 * If deprecated address is forbidden,
1231 		 * we do not accept SYN to deprecated interface
1232 		 * address to prevent any new inbound connection from
1233 		 * getting established.
1234 		 * When we do not accept SYN, we send a TCP RST,
1235 		 * with deprecated source address (instead of dropping
1236 		 * it).  We compromise it as it is much better for peer
1237 		 * to send a RST, and RST will be the final packet
1238 		 * for the exchange.
1239 		 *
1240 		 * If we do not forbid deprecated addresses, we accept
1241 		 * the SYN packet.  RFC2462 does not suggest dropping
1242 		 * SYN in this case.
1243 		 * If we decipher RFC2462 5.5.4, it says like this:
1244 		 * 1. use of deprecated addr with existing
1245 		 *    communication is okay - "SHOULD continue to be
1246 		 *    used"
1247 		 * 2. use of it with new communication:
1248 		 *   (2a) "SHOULD NOT be used if alternate address
1249 		 *        with sufficient scope is available"
1250 		 *   (2b) nothing mentioned otherwise.
1251 		 * Here we fall into (2b) case as we have no choice in
1252 		 * our source address selection - we must obey the peer.
1253 		 *
1254 		 * The wording in RFC2462 is confusing, and there are
1255 		 * multiple description text for deprecated address
1256 		 * handling - worse, they are not exactly the same.
1257 		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1258 		 */
1259 		if (isipv6 && !V_ip6_use_deprecated) {
1260 			struct in6_ifaddr *ia6;
1261 
1262 			ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
1263 			if (ia6 != NULL &&
1264 			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1265 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1266 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1267 					"Connection attempt to deprecated "
1268 					"IPv6 address rejected\n",
1269 					s, __func__);
1270 				rstreason = BANDLIM_RST_OPENPORT;
1271 				goto dropwithreset;
1272 			}
1273 		}
1274 #endif /* INET6 */
1275 		/*
1276 		 * Basic sanity checks on incoming SYN requests:
1277 		 *   Don't respond if the destination is a link layer
1278 		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1279 		 *   If it is from this socket it must be forged.
1280 		 *   Don't respond if the source or destination is a
1281 		 *	global or subnet broad- or multicast address.
1282 		 *   Note that it is quite possible to receive unicast
1283 		 *	link-layer packets with a broadcast IP address. Use
1284 		 *	in_broadcast() to find them.
1285 		 */
1286 		if (m->m_flags & (M_BCAST|M_MCAST)) {
1287 			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1288 			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1289 				"Connection attempt from broad- or multicast "
1290 				"link layer address ignored\n", s, __func__);
1291 			goto dropunlock;
1292 		}
1293 #ifdef INET6
1294 		if (isipv6) {
1295 			if (th->th_dport == th->th_sport &&
1296 			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1297 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1298 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1299 					"Connection attempt to/from self "
1300 					"ignored\n", s, __func__);
1301 				goto dropunlock;
1302 			}
1303 			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1304 			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1305 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1306 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1307 					"Connection attempt from/to multicast "
1308 					"address ignored\n", s, __func__);
1309 				goto dropunlock;
1310 			}
1311 		}
1312 #endif
1313 #if defined(INET) && defined(INET6)
1314 		else
1315 #endif
1316 #ifdef INET
1317 		{
1318 			if (th->th_dport == th->th_sport &&
1319 			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1320 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1321 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1322 					"Connection attempt from/to self "
1323 					"ignored\n", s, __func__);
1324 				goto dropunlock;
1325 			}
1326 			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1327 			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1328 			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1329 			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1330 				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1331 				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1332 					"Connection attempt from/to broad- "
1333 					"or multicast address ignored\n",
1334 					s, __func__);
1335 				goto dropunlock;
1336 			}
1337 		}
1338 #endif
1339 		/*
1340 		 * SYN appears to be valid.  Create compressed TCP state
1341 		 * for syncache.
1342 		 */
1343 #ifdef TCPDEBUG
1344 		if (so->so_options & SO_DEBUG)
1345 			tcp_trace(TA_INPUT, ostate, tp,
1346 			    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1347 #endif
1348 		TCP_PROBE3(debug__input, tp, th, m);
1349 		tcp_dooptions(&to, optp, optlen, TO_SYN);
1350 		if ((so = syncache_add(&inc, &to, th, inp, so, m, NULL, NULL,
1351 		    iptos, port)) != NULL)
1352 			goto tfo_socket_result;
1353 
1354 		/*
1355 		 * Entry added to syncache and mbuf consumed.
1356 		 * Only the listen socket is unlocked by syncache_add().
1357 		 */
1358 		return (IPPROTO_DONE);
1359 	} else if (tp->t_state == TCPS_LISTEN) {
1360 		/*
1361 		 * When a listen socket is torn down the SO_ACCEPTCONN
1362 		 * flag is removed first while connections are drained
1363 		 * from the accept queue in a unlock/lock cycle of the
1364 		 * ACCEPT_LOCK, opening a race condition allowing a SYN
1365 		 * attempt go through unhandled.
1366 		 */
1367 		goto dropunlock;
1368 	}
1369 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1370 	if (tp->t_flags & TF_SIGNATURE) {
1371 		tcp_dooptions(&to, optp, optlen, thflags);
1372 		if ((to.to_flags & TOF_SIGNATURE) == 0) {
1373 			TCPSTAT_INC(tcps_sig_err_nosigopt);
1374 			goto dropunlock;
1375 		}
1376 		if (!TCPMD5_ENABLED() ||
1377 		    TCPMD5_INPUT(m, th, to.to_signature) != 0)
1378 			goto dropunlock;
1379 	}
1380 #endif
1381 	TCP_PROBE5(receive, NULL, tp, m, tp, th);
1382 
1383 	/*
1384 	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1385 	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1386 	 * the inpcb, and unlocks pcbinfo.
1387 	 *
1388 	 * XXXGL: in case of a pure SYN arriving on existing connection
1389 	 * TCP stacks won't need to modify the PCB, they would either drop
1390 	 * the segment silently, or send a challenge ACK.  However, we try
1391 	 * to upgrade the lock, because calling convention for stacks is
1392 	 * write-lock on PCB.  If upgrade fails, drop the SYN.
1393 	 */
1394 	if (lookupflag == INPLOOKUP_RLOCKPCB && INP_TRY_UPGRADE(inp) == 0)
1395 		goto dropunlock;
1396 
1397 	tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos);
1398 	return (IPPROTO_DONE);
1399 
1400 dropwithreset:
1401 	TCP_PROBE5(receive, NULL, tp, m, tp, th);
1402 
1403 	if (inp != NULL) {
1404 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1405 		INP_UNLOCK(inp);
1406 	} else
1407 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1408 	m = NULL;	/* mbuf chain got consumed. */
1409 	goto drop;
1410 
1411 dropunlock:
1412 	if (m != NULL)
1413 		TCP_PROBE5(receive, NULL, tp, m, tp, th);
1414 
1415 	if (inp != NULL)
1416 		INP_UNLOCK(inp);
1417 
1418 drop:
1419 	if (s != NULL)
1420 		free(s, M_TCPLOG);
1421 	if (m != NULL)
1422 		m_freem(m);
1423 	return (IPPROTO_DONE);
1424 }
1425 
1426 /*
1427  * Automatic sizing of receive socket buffer.  Often the send
1428  * buffer size is not optimally adjusted to the actual network
1429  * conditions at hand (delay bandwidth product).  Setting the
1430  * buffer size too small limits throughput on links with high
1431  * bandwidth and high delay (eg. trans-continental/oceanic links).
1432  *
1433  * On the receive side the socket buffer memory is only rarely
1434  * used to any significant extent.  This allows us to be much
1435  * more aggressive in scaling the receive socket buffer.  For
1436  * the case that the buffer space is actually used to a large
1437  * extent and we run out of kernel memory we can simply drop
1438  * the new segments; TCP on the sender will just retransmit it
1439  * later.  Setting the buffer size too big may only consume too
1440  * much kernel memory if the application doesn't read() from
1441  * the socket or packet loss or reordering makes use of the
1442  * reassembly queue.
1443  *
1444  * The criteria to step up the receive buffer one notch are:
1445  *  1. Application has not set receive buffer size with
1446  *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
1447  *  2. the number of bytes received during 1/2 of an sRTT
1448  *     is at least 3/8 of the current socket buffer size.
1449  *  3. receive buffer size has not hit maximal automatic size;
1450  *
1451  * If all of the criteria are met we increaset the socket buffer
1452  * by a 1/2 (bounded by the max). This allows us to keep ahead
1453  * of slow-start but also makes it so our peer never gets limited
1454  * by our rwnd which we then open up causing a burst.
1455  *
1456  * This algorithm does two steps per RTT at most and only if
1457  * we receive a bulk stream w/o packet losses or reorderings.
1458  * Shrinking the buffer during idle times is not necessary as
1459  * it doesn't consume any memory when idle.
1460  *
1461  * TODO: Only step up if the application is actually serving
1462  * the buffer to better manage the socket buffer resources.
1463  */
1464 int
1465 tcp_autorcvbuf(struct mbuf *m, struct tcphdr *th, struct socket *so,
1466     struct tcpcb *tp, int tlen)
1467 {
1468 	int newsize = 0;
1469 
1470 	if (V_tcp_do_autorcvbuf && (so->so_rcv.sb_flags & SB_AUTOSIZE) &&
1471 	    tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
1472 	    TCP_TS_TO_TICKS(tcp_ts_getticks() - tp->rfbuf_ts) >
1473 	    ((tp->t_srtt >> TCP_RTT_SHIFT)/2)) {
1474 		if (tp->rfbuf_cnt > ((so->so_rcv.sb_hiwat / 2)/ 4 * 3) &&
1475 		    so->so_rcv.sb_hiwat < V_tcp_autorcvbuf_max) {
1476 			newsize = min((so->so_rcv.sb_hiwat + (so->so_rcv.sb_hiwat/2)), V_tcp_autorcvbuf_max);
1477 		}
1478 		TCP_PROBE6(receive__autoresize, NULL, tp, m, tp, th, newsize);
1479 
1480 		/* Start over with next RTT. */
1481 		tp->rfbuf_ts = 0;
1482 		tp->rfbuf_cnt = 0;
1483 	} else {
1484 		tp->rfbuf_cnt += tlen;	/* add up */
1485 	}
1486 	return (newsize);
1487 }
1488 
1489 int
1490 tcp_input(struct mbuf **mp, int *offp, int proto)
1491 {
1492 	return(tcp_input_with_port(mp, offp, proto, 0));
1493 }
1494 
1495 void
1496 tcp_handle_wakeup(struct tcpcb *tp, struct socket *so)
1497 {
1498 	/*
1499 	 * Since tp might be gone if the session entered
1500 	 * the TIME_WAIT state before coming here, we need
1501 	 * to check if the socket is still connected.
1502 	 */
1503 	if (tp == NULL) {
1504 		return;
1505 	}
1506 	if (so == NULL) {
1507 		return;
1508 	}
1509 	INP_LOCK_ASSERT(tp->t_inpcb);
1510 	if (tp->t_flags & TF_WAKESOR) {
1511 		tp->t_flags &= ~TF_WAKESOR;
1512 		SOCKBUF_LOCK_ASSERT(&so->so_rcv);
1513 		sorwakeup_locked(so);
1514 	}
1515 }
1516 
1517 void
1518 tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1519     struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
1520 {
1521 	uint16_t thflags;
1522 	int acked, ourfinisacked, needoutput = 0, sack_changed;
1523 	int rstreason, todrop, win, incforsyn = 0;
1524 	uint32_t tiwin;
1525 	uint16_t nsegs;
1526 	char *s;
1527 	struct in_conninfo *inc;
1528 	struct mbuf *mfree;
1529 	struct tcpopt to;
1530 	int tfo_syn;
1531 	u_int maxseg;
1532 
1533 #ifdef TCPDEBUG
1534 	/*
1535 	 * The size of tcp_saveipgen must be the size of the max ip header,
1536 	 * now IPv6.
1537 	 */
1538 	u_char tcp_saveipgen[IP6_HDR_LEN];
1539 	struct tcphdr tcp_savetcp;
1540 	short ostate = 0;
1541 #endif
1542 	thflags = tcp_get_flags(th);
1543 	inc = &tp->t_inpcb->inp_inc;
1544 	tp->sackhint.last_sack_ack = 0;
1545 	sack_changed = 0;
1546 	nsegs = max(1, m->m_pkthdr.lro_nsegs);
1547 
1548 	NET_EPOCH_ASSERT();
1549 	INP_WLOCK_ASSERT(tp->t_inpcb);
1550 	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1551 	    __func__));
1552 	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1553 	    __func__));
1554 
1555 #ifdef TCPPCAP
1556 	/* Save segment, if requested. */
1557 	tcp_pcap_add(th, m, &(tp->t_inpkts));
1558 #endif
1559 	TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
1560 	    tlen, NULL, true);
1561 
1562 	if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
1563 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1564 			log(LOG_DEBUG, "%s; %s: "
1565 			    "SYN|FIN segment ignored (based on "
1566 			    "sysctl setting)\n", s, __func__);
1567 			free(s, M_TCPLOG);
1568 		}
1569 		goto drop;
1570 	}
1571 
1572 	/*
1573 	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
1574 	 * check SEQ.ACK first.
1575 	 */
1576 	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
1577 	    (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
1578 		rstreason = BANDLIM_UNLIMITED;
1579 		goto dropwithreset;
1580 	}
1581 
1582 	/*
1583 	 * Segment received on connection.
1584 	 * Reset idle time and keep-alive timer.
1585 	 * XXX: This should be done after segment
1586 	 * validation to ignore broken/spoofed segs.
1587 	 */
1588 	tp->t_rcvtime = ticks;
1589 
1590 	/*
1591 	 * Scale up the window into a 32-bit value.
1592 	 * For the SYN_SENT state the scale is zero.
1593 	 */
1594 	tiwin = th->th_win << tp->snd_scale;
1595 #ifdef STATS
1596 	stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_FRWIN, tiwin);
1597 #endif
1598 
1599 	/*
1600 	 * TCP ECN processing.
1601 	 */
1602 	if (tcp_ecn_input_segment(tp, thflags, iptos))
1603 		cc_cong_signal(tp, th, CC_ECN);
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 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1613 	if ((tp->t_flags & TF_SIGNATURE) != 0 &&
1614 	    (to.to_flags & TOF_SIGNATURE) == 0) {
1615 		TCPSTAT_INC(tcps_sig_err_sigopt);
1616 		/* XXX: should drop? */
1617 	}
1618 #endif
1619 	/*
1620 	 * If echoed timestamp is later than the current time,
1621 	 * fall back to non RFC1323 RTT calculation.  Normalize
1622 	 * timestamp if syncookies were used when this connection
1623 	 * was established.
1624 	 */
1625 	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1626 		to.to_tsecr -= tp->ts_offset;
1627 		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1628 			to.to_tsecr = 0;
1629 		else if (tp->t_rxtshift == 1 &&
1630 			 tp->t_flags & TF_PREVVALID &&
1631 			 tp->t_badrxtwin != 0 &&
1632 			 TSTMP_LT(to.to_tsecr, tp->t_badrxtwin))
1633 			cc_cong_signal(tp, th, CC_RTO_ERR);
1634 	}
1635 	/*
1636 	 * Process options only when we get SYN/ACK back. The SYN case
1637 	 * for incoming connections is handled in tcp_syncache.
1638 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1639 	 * or <SYN,ACK>) segment itself is never scaled.
1640 	 * XXX this is traditional behavior, may need to be cleaned up.
1641 	 */
1642 	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1643 		/* Handle parallel SYN for ECN */
1644 		tcp_ecn_input_parallel_syn(tp, thflags, iptos);
1645 		if ((to.to_flags & TOF_SCALE) &&
1646 		    (tp->t_flags & TF_REQ_SCALE) &&
1647 		    !(tp->t_flags & TF_NOOPT)) {
1648 			tp->t_flags |= TF_RCVD_SCALE;
1649 			tp->snd_scale = to.to_wscale;
1650 		} else
1651 			tp->t_flags &= ~TF_REQ_SCALE;
1652 		/*
1653 		 * Initial send window.  It will be updated with
1654 		 * the next incoming segment to the scaled value.
1655 		 */
1656 		tp->snd_wnd = th->th_win;
1657 		if ((to.to_flags & TOF_TS) &&
1658 		    (tp->t_flags & TF_REQ_TSTMP) &&
1659 		    !(tp->t_flags & TF_NOOPT)) {
1660 			tp->t_flags |= TF_RCVD_TSTMP;
1661 			tp->ts_recent = to.to_tsval;
1662 			tp->ts_recent_age = tcp_ts_getticks();
1663 		} else
1664 			tp->t_flags &= ~TF_REQ_TSTMP;
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) ||
1669 		    (tp->t_flags & TF_NOOPT)))
1670 			tp->t_flags &= ~TF_SACK_PERMIT;
1671 		if (IS_FASTOPEN(tp->t_flags)) {
1672 			if ((to.to_flags & TOF_FASTOPEN) &&
1673 			    !(tp->t_flags & TF_NOOPT)) {
1674 				uint16_t mss;
1675 
1676 				if (to.to_flags & TOF_MSS)
1677 					mss = to.to_mss;
1678 				else
1679 					if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
1680 						mss = TCP6_MSS;
1681 					else
1682 						mss = TCP_MSS;
1683 				tcp_fastopen_update_cache(tp, mss,
1684 				    to.to_tfo_len, to.to_tfo_cookie);
1685 			} else
1686 				tcp_fastopen_disable_path(tp);
1687 		}
1688 	}
1689 
1690 	/*
1691 	 * If timestamps were negotiated during SYN/ACK and a
1692 	 * segment without a timestamp is received, silently drop
1693 	 * the segment, unless it is a RST segment or missing timestamps are
1694 	 * tolerated.
1695 	 * See section 3.2 of RFC 7323.
1696 	 */
1697 	if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1698 		if (((thflags & TH_RST) != 0) || V_tcp_tolerate_missing_ts) {
1699 			if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1700 				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1701 				    "segment processed normally\n",
1702 				    s, __func__);
1703 				free(s, M_TCPLOG);
1704 			}
1705 		} else {
1706 			if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1707 				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1708 				    "segment silently dropped\n", s, __func__);
1709 				free(s, M_TCPLOG);
1710 			}
1711 			goto drop;
1712 		}
1713 	}
1714 	/*
1715 	 * If timestamps were not negotiated during SYN/ACK and a
1716 	 * segment with a timestamp is received, ignore the
1717 	 * timestamp and process the packet normally.
1718 	 * See section 3.2 of RFC 7323.
1719 	 */
1720 	if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1721 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1722 			log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1723 			    "segment processed normally\n", s, __func__);
1724 			free(s, M_TCPLOG);
1725 		}
1726 	}
1727 
1728 	/*
1729 	 * Header prediction: check for the two common cases
1730 	 * of a uni-directional data xfer.  If the packet has
1731 	 * no control flags, is in-sequence, the window didn't
1732 	 * change and we're not retransmitting, it's a
1733 	 * candidate.  If the length is zero and the ack moved
1734 	 * forward, we're the sender side of the xfer.  Just
1735 	 * free the data acked & wake any higher level process
1736 	 * that was blocked waiting for space.  If the length
1737 	 * is non-zero and the ack didn't move, we're the
1738 	 * receiver side.  If we're getting packets in-order
1739 	 * (the reassembly queue is empty), add the data to
1740 	 * the socket buffer and note that we need a delayed ack.
1741 	 * Make sure that the hidden state-flags are also off.
1742 	 * Since we check for TCPS_ESTABLISHED first, it can only
1743 	 * be TH_NEEDSYN.
1744 	 */
1745 	if (tp->t_state == TCPS_ESTABLISHED &&
1746 	    th->th_seq == tp->rcv_nxt &&
1747 	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1748 	    tp->snd_nxt == tp->snd_max &&
1749 	    tiwin && tiwin == tp->snd_wnd &&
1750 	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1751 	    SEGQ_EMPTY(tp) &&
1752 	    ((to.to_flags & TOF_TS) == 0 ||
1753 	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1754 		/*
1755 		 * If last ACK falls within this segment's sequence numbers,
1756 		 * record the timestamp.
1757 		 * NOTE that the test is modified according to the latest
1758 		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1759 		 */
1760 		if ((to.to_flags & TOF_TS) != 0 &&
1761 		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1762 			tp->ts_recent_age = tcp_ts_getticks();
1763 			tp->ts_recent = to.to_tsval;
1764 		}
1765 
1766 		if (tlen == 0) {
1767 			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1768 			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1769 			    !IN_RECOVERY(tp->t_flags) &&
1770 			    (to.to_flags & TOF_SACK) == 0 &&
1771 			    TAILQ_EMPTY(&tp->snd_holes)) {
1772 				/*
1773 				 * This is a pure ack for outstanding data.
1774 				 */
1775 				TCPSTAT_INC(tcps_predack);
1776 
1777 				/*
1778 				 * "bad retransmit" recovery without timestamps.
1779 				 */
1780 				if ((to.to_flags & TOF_TS) == 0 &&
1781 				    tp->t_rxtshift == 1 &&
1782 				    tp->t_flags & TF_PREVVALID &&
1783 				    tp->t_badrxtwin != 0 &&
1784 				    TSTMP_LT(ticks, tp->t_badrxtwin)) {
1785 					cc_cong_signal(tp, th, CC_RTO_ERR);
1786 				}
1787 
1788 				/*
1789 				 * Recalculate the transmit timer / rtt.
1790 				 *
1791 				 * Some boxes send broken timestamp replies
1792 				 * during the SYN+ACK phase, ignore
1793 				 * timestamps of 0 or we could calculate a
1794 				 * huge RTT and blow up the retransmit timer.
1795 				 */
1796 				if ((to.to_flags & TOF_TS) != 0 &&
1797 				    to.to_tsecr) {
1798 					uint32_t t;
1799 
1800 					t = tcp_ts_getticks() - to.to_tsecr;
1801 					if (!tp->t_rttlow || tp->t_rttlow > t)
1802 						tp->t_rttlow = t;
1803 					tcp_xmit_timer(tp,
1804 					    TCP_TS_TO_TICKS(t) + 1);
1805 				} else if (tp->t_rtttime &&
1806 				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1807 					if (!tp->t_rttlow ||
1808 					    tp->t_rttlow > ticks - tp->t_rtttime)
1809 						tp->t_rttlow = ticks - tp->t_rtttime;
1810 					tcp_xmit_timer(tp,
1811 							ticks - tp->t_rtttime);
1812 				}
1813 				acked = BYTES_THIS_ACK(tp, th);
1814 
1815 #ifdef TCP_HHOOK
1816 				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1817 				hhook_run_tcp_est_in(tp, th, &to);
1818 #endif
1819 
1820 				TCPSTAT_ADD(tcps_rcvackpack, nsegs);
1821 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1822 				sbdrop(&so->so_snd, acked);
1823 				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1824 				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1825 					tp->snd_recover = th->th_ack - 1;
1826 
1827 				/*
1828 				 * Let the congestion control algorithm update
1829 				 * congestion control related information. This
1830 				 * typically means increasing the congestion
1831 				 * window.
1832 				 */
1833 				cc_ack_received(tp, th, nsegs, CC_ACK);
1834 
1835 				tp->snd_una = th->th_ack;
1836 				/*
1837 				 * Pull snd_wl2 up to prevent seq wrap relative
1838 				 * to th_ack.
1839 				 */
1840 				tp->snd_wl2 = th->th_ack;
1841 				tp->t_dupacks = 0;
1842 				m_freem(m);
1843 
1844 				/*
1845 				 * If all outstanding data are acked, stop
1846 				 * retransmit timer, otherwise restart timer
1847 				 * using current (possibly backed-off) value.
1848 				 * If process is waiting for space,
1849 				 * wakeup/selwakeup/signal.  If data
1850 				 * are ready to send, let tcp_output
1851 				 * decide between more output or persist.
1852 				 */
1853 #ifdef TCPDEBUG
1854 				if (so->so_options & SO_DEBUG)
1855 					tcp_trace(TA_INPUT, ostate, tp,
1856 					    (void *)tcp_saveipgen,
1857 					    &tcp_savetcp, 0);
1858 #endif
1859 				TCP_PROBE3(debug__input, tp, th, m);
1860 				if (tp->snd_una == tp->snd_max)
1861 					tcp_timer_activate(tp, TT_REXMT, 0);
1862 				else if (!tcp_timer_active(tp, TT_PERSIST))
1863 					tcp_timer_activate(tp, TT_REXMT,
1864 						      tp->t_rxtcur);
1865 				sowwakeup(so);
1866 				if (sbavail(&so->so_snd))
1867 					(void) tcp_output(tp);
1868 				goto check_delack;
1869 			}
1870 		} else if (th->th_ack == tp->snd_una &&
1871 		    tlen <= sbspace(&so->so_rcv)) {
1872 			int newsize = 0;	/* automatic sockbuf scaling */
1873 
1874 			/*
1875 			 * This is a pure, in-sequence data packet with
1876 			 * nothing on the reassembly queue and we have enough
1877 			 * buffer space to take it.
1878 			 */
1879 			/* Clean receiver SACK report if present */
1880 			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1881 				tcp_clean_sackreport(tp);
1882 			TCPSTAT_INC(tcps_preddat);
1883 			tp->rcv_nxt += tlen;
1884 			if (tlen &&
1885 			    ((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
1886 			    (tp->t_fbyte_in == 0)) {
1887 				tp->t_fbyte_in = ticks;
1888 				if (tp->t_fbyte_in == 0)
1889 					tp->t_fbyte_in = 1;
1890 				if (tp->t_fbyte_out && tp->t_fbyte_in)
1891 					tp->t_flags2 |= TF2_FBYTES_COMPLETE;
1892 			}
1893 			/*
1894 			 * Pull snd_wl1 up to prevent seq wrap relative to
1895 			 * th_seq.
1896 			 */
1897 			tp->snd_wl1 = th->th_seq;
1898 			/*
1899 			 * Pull rcv_up up to prevent seq wrap relative to
1900 			 * rcv_nxt.
1901 			 */
1902 			tp->rcv_up = tp->rcv_nxt;
1903 			TCPSTAT_ADD(tcps_rcvpack, nsegs);
1904 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1905 #ifdef TCPDEBUG
1906 			if (so->so_options & SO_DEBUG)
1907 				tcp_trace(TA_INPUT, ostate, tp,
1908 				    (void *)tcp_saveipgen, &tcp_savetcp, 0);
1909 #endif
1910 			TCP_PROBE3(debug__input, tp, th, m);
1911 
1912 			newsize = tcp_autorcvbuf(m, th, so, tp, tlen);
1913 
1914 			/* Add data to socket buffer. */
1915 			SOCKBUF_LOCK(&so->so_rcv);
1916 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1917 				m_freem(m);
1918 			} else {
1919 				/*
1920 				 * Set new socket buffer size.
1921 				 * Give up when limit is reached.
1922 				 */
1923 				if (newsize)
1924 					if (!sbreserve_locked(&so->so_rcv,
1925 					    newsize, so, NULL))
1926 						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1927 				m_adj(m, drop_hdrlen);	/* delayed header drop */
1928 				sbappendstream_locked(&so->so_rcv, m, 0);
1929 			}
1930 			/* NB: sorwakeup_locked() does an implicit unlock. */
1931 			sorwakeup_locked(so);
1932 			if (DELAY_ACK(tp, tlen)) {
1933 				tp->t_flags |= TF_DELACK;
1934 			} else {
1935 				tp->t_flags |= TF_ACKNOW;
1936 				tcp_output(tp);
1937 			}
1938 			goto check_delack;
1939 		}
1940 	}
1941 
1942 	/*
1943 	 * Calculate amount of space in receive window,
1944 	 * and then do TCP input processing.
1945 	 * Receive window is amount of space in rcv queue,
1946 	 * but not less than advertised window.
1947 	 */
1948 	win = sbspace(&so->so_rcv);
1949 	if (win < 0)
1950 		win = 0;
1951 	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1952 
1953 	switch (tp->t_state) {
1954 	/*
1955 	 * If the state is SYN_RECEIVED:
1956 	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1957 	 */
1958 	case TCPS_SYN_RECEIVED:
1959 		if ((thflags & TH_ACK) &&
1960 		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1961 		     SEQ_GT(th->th_ack, tp->snd_max))) {
1962 				rstreason = BANDLIM_RST_OPENPORT;
1963 				goto dropwithreset;
1964 		}
1965 		if (IS_FASTOPEN(tp->t_flags)) {
1966 			/*
1967 			 * When a TFO connection is in SYN_RECEIVED, the
1968 			 * only valid packets are the initial SYN, a
1969 			 * retransmit/copy of the initial SYN (possibly with
1970 			 * a subset of the original data), a valid ACK, a
1971 			 * FIN, or a RST.
1972 			 */
1973 			if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
1974 				rstreason = BANDLIM_RST_OPENPORT;
1975 				goto dropwithreset;
1976 			} else if (thflags & TH_SYN) {
1977 				/* non-initial SYN is ignored */
1978 				if ((tcp_timer_active(tp, TT_DELACK) ||
1979 				     tcp_timer_active(tp, TT_REXMT)))
1980 					goto drop;
1981 			} else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
1982 				goto drop;
1983 			}
1984 		}
1985 		break;
1986 
1987 	/*
1988 	 * If the state is SYN_SENT:
1989 	 *	if seg contains a RST with valid ACK (SEQ.ACK has already
1990 	 *	    been verified), then drop the connection.
1991 	 *	if seg contains a RST without an ACK, drop the seg.
1992 	 *	if seg does not contain SYN, then drop the seg.
1993 	 * Otherwise this is an acceptable SYN segment
1994 	 *	initialize tp->rcv_nxt and tp->irs
1995 	 *	if seg contains ack then advance tp->snd_una
1996 	 *	if seg contains an ECE and ECN support is enabled, the stream
1997 	 *	    is ECN capable.
1998 	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1999 	 *	arrange for segment to be acked (eventually)
2000 	 *	continue processing rest of data/controls, beginning with URG
2001 	 */
2002 	case TCPS_SYN_SENT:
2003 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
2004 			TCP_PROBE5(connect__refused, NULL, tp,
2005 			    m, tp, th);
2006 			tp = tcp_drop(tp, ECONNREFUSED);
2007 		}
2008 		if (thflags & TH_RST)
2009 			goto drop;
2010 		if (!(thflags & TH_SYN))
2011 			goto drop;
2012 
2013 		tp->irs = th->th_seq;
2014 		tcp_rcvseqinit(tp);
2015 		if (thflags & TH_ACK) {
2016 			int tfo_partial_ack = 0;
2017 
2018 			TCPSTAT_INC(tcps_connects);
2019 			soisconnected(so);
2020 #ifdef MAC
2021 			mac_socketpeer_set_from_mbuf(m, so);
2022 #endif
2023 			/* Do window scaling on this connection? */
2024 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2025 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2026 				tp->rcv_scale = tp->request_r_scale;
2027 			}
2028 			tp->rcv_adv += min(tp->rcv_wnd,
2029 			    TCP_MAXWIN << tp->rcv_scale);
2030 			tp->snd_una++;		/* SYN is acked */
2031 			/*
2032 			 * If not all the data that was sent in the TFO SYN
2033 			 * has been acked, resend the remainder right away.
2034 			 */
2035 			if (IS_FASTOPEN(tp->t_flags) &&
2036 			    (tp->snd_una != tp->snd_max)) {
2037 				tp->snd_nxt = th->th_ack;
2038 				tfo_partial_ack = 1;
2039 			}
2040 			/*
2041 			 * If there's data, delay ACK; if there's also a FIN
2042 			 * ACKNOW will be turned on later.
2043 			 */
2044 			if (DELAY_ACK(tp, tlen) && tlen != 0 && !tfo_partial_ack)
2045 				tcp_timer_activate(tp, TT_DELACK,
2046 				    tcp_delacktime);
2047 			else
2048 				tp->t_flags |= TF_ACKNOW;
2049 
2050 			tcp_ecn_input_syn_sent(tp, thflags, iptos);
2051 
2052 			/*
2053 			 * Received <SYN,ACK> in SYN_SENT[*] state.
2054 			 * Transitions:
2055 			 *	SYN_SENT  --> ESTABLISHED
2056 			 *	SYN_SENT* --> FIN_WAIT_1
2057 			 */
2058 			tp->t_starttime = ticks;
2059 			if (tp->t_flags & TF_NEEDFIN) {
2060 				tcp_state_change(tp, TCPS_FIN_WAIT_1);
2061 				tp->t_flags &= ~TF_NEEDFIN;
2062 				thflags &= ~TH_SYN;
2063 			} else {
2064 				tcp_state_change(tp, TCPS_ESTABLISHED);
2065 				TCP_PROBE5(connect__established, NULL, tp,
2066 				    m, tp, th);
2067 				cc_conn_init(tp);
2068 				tcp_timer_activate(tp, TT_KEEP,
2069 				    TP_KEEPIDLE(tp));
2070 			}
2071 		} else {
2072 			/*
2073 			 * Received initial SYN in SYN-SENT[*] state =>
2074 			 * simultaneous open.
2075 			 * If it succeeds, connection is * half-synchronized.
2076 			 * Otherwise, do 3-way handshake:
2077 			 *        SYN-SENT -> SYN-RECEIVED
2078 			 *        SYN-SENT* -> SYN-RECEIVED*
2079 			 */
2080 			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
2081 			tcp_timer_activate(tp, TT_REXMT, 0);
2082 			tcp_state_change(tp, TCPS_SYN_RECEIVED);
2083 		}
2084 
2085 		INP_WLOCK_ASSERT(tp->t_inpcb);
2086 
2087 		/*
2088 		 * Advance th->th_seq to correspond to first data byte.
2089 		 * If data, trim to stay within window,
2090 		 * dropping FIN if necessary.
2091 		 */
2092 		th->th_seq++;
2093 		if (tlen > tp->rcv_wnd) {
2094 			todrop = tlen - tp->rcv_wnd;
2095 			m_adj(m, -todrop);
2096 			tlen = tp->rcv_wnd;
2097 			thflags &= ~TH_FIN;
2098 			TCPSTAT_INC(tcps_rcvpackafterwin);
2099 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2100 		}
2101 		tp->snd_wl1 = th->th_seq - 1;
2102 		tp->rcv_up = th->th_seq;
2103 		/*
2104 		 * Client side of transaction: already sent SYN and data.
2105 		 * If the remote host used T/TCP to validate the SYN,
2106 		 * our data will be ACK'd; if so, enter normal data segment
2107 		 * processing in the middle of step 5, ack processing.
2108 		 * Otherwise, goto step 6.
2109 		 */
2110 		if (thflags & TH_ACK)
2111 			goto process_ACK;
2112 
2113 		goto step6;
2114 
2115 	/*
2116 	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
2117 	 *      do normal processing.
2118 	 *
2119 	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
2120 	 */
2121 	case TCPS_LAST_ACK:
2122 	case TCPS_CLOSING:
2123 		break;  /* continue normal processing */
2124 	}
2125 
2126 	/*
2127 	 * States other than LISTEN or SYN_SENT.
2128 	 * First check the RST flag and sequence number since reset segments
2129 	 * are exempt from the timestamp and connection count tests.  This
2130 	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2131 	 * below which allowed reset segments in half the sequence space
2132 	 * to fall though and be processed (which gives forged reset
2133 	 * segments with a random sequence number a 50 percent chance of
2134 	 * killing a connection).
2135 	 * Then check timestamp, if present.
2136 	 * Then check the connection count, if present.
2137 	 * Then check that at least some bytes of segment are within
2138 	 * receive window.  If segment begins before rcv_nxt,
2139 	 * drop leading data (and SYN); if nothing left, just ack.
2140 	 */
2141 	if (thflags & TH_RST) {
2142 		/*
2143 		 * RFC5961 Section 3.2
2144 		 *
2145 		 * - RST drops connection only if SEG.SEQ == RCV.NXT.
2146 		 * - If RST is in window, we send challenge ACK.
2147 		 *
2148 		 * Note: to take into account delayed ACKs, we should
2149 		 *   test against last_ack_sent instead of rcv_nxt.
2150 		 * Note 2: we handle special case of closed window, not
2151 		 *   covered by the RFC.
2152 		 */
2153 		if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2154 		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
2155 		    (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
2156 			KASSERT(tp->t_state != TCPS_SYN_SENT,
2157 			    ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
2158 			    __func__, th, tp));
2159 
2160 			if (V_tcp_insecure_rst ||
2161 			    tp->last_ack_sent == th->th_seq) {
2162 				TCPSTAT_INC(tcps_drops);
2163 				/* Drop the connection. */
2164 				switch (tp->t_state) {
2165 				case TCPS_SYN_RECEIVED:
2166 					so->so_error = ECONNREFUSED;
2167 					goto close;
2168 				case TCPS_ESTABLISHED:
2169 				case TCPS_FIN_WAIT_1:
2170 				case TCPS_FIN_WAIT_2:
2171 				case TCPS_CLOSE_WAIT:
2172 				case TCPS_CLOSING:
2173 				case TCPS_LAST_ACK:
2174 					so->so_error = ECONNRESET;
2175 				close:
2176 					/* FALLTHROUGH */
2177 				default:
2178 					tp = tcp_close(tp);
2179 				}
2180 			} else {
2181 				TCPSTAT_INC(tcps_badrst);
2182 				/* Send challenge ACK. */
2183 				tcp_respond(tp, mtod(m, void *), th, m,
2184 				    tp->rcv_nxt, tp->snd_nxt, TH_ACK);
2185 				tp->last_ack_sent = tp->rcv_nxt;
2186 				m = NULL;
2187 			}
2188 		}
2189 		goto drop;
2190 	}
2191 
2192 	/*
2193 	 * RFC5961 Section 4.2
2194 	 * Send challenge ACK for any SYN in synchronized state.
2195 	 */
2196 	if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
2197 	    tp->t_state != TCPS_SYN_RECEIVED) {
2198 		TCPSTAT_INC(tcps_badsyn);
2199 		if (V_tcp_insecure_syn &&
2200 		    SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2201 		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2202 			tp = tcp_drop(tp, ECONNRESET);
2203 			rstreason = BANDLIM_UNLIMITED;
2204 		} else {
2205 			/* Send challenge ACK. */
2206 			tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
2207 			    tp->snd_nxt, TH_ACK);
2208 			tp->last_ack_sent = tp->rcv_nxt;
2209 			m = NULL;
2210 		}
2211 		goto drop;
2212 	}
2213 
2214 	/*
2215 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2216 	 * and it's less than ts_recent, drop it.
2217 	 */
2218 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2219 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2220 		/* Check to see if ts_recent is over 24 days old.  */
2221 		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2222 			/*
2223 			 * Invalidate ts_recent.  If this segment updates
2224 			 * ts_recent, the age will be reset later and ts_recent
2225 			 * will get a valid value.  If it does not, setting
2226 			 * ts_recent to zero will at least satisfy the
2227 			 * requirement that zero be placed in the timestamp
2228 			 * echo reply when ts_recent isn't valid.  The
2229 			 * age isn't reset until we get a valid ts_recent
2230 			 * because we don't want out-of-order segments to be
2231 			 * dropped when ts_recent is old.
2232 			 */
2233 			tp->ts_recent = 0;
2234 		} else {
2235 			TCPSTAT_INC(tcps_rcvduppack);
2236 			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2237 			TCPSTAT_INC(tcps_pawsdrop);
2238 			if (tlen)
2239 				goto dropafterack;
2240 			goto drop;
2241 		}
2242 	}
2243 
2244 	/*
2245 	 * In the SYN-RECEIVED state, validate that the packet belongs to
2246 	 * this connection before trimming the data to fit the receive
2247 	 * window.  Check the sequence number versus IRS since we know
2248 	 * the sequence numbers haven't wrapped.  This is a partial fix
2249 	 * for the "LAND" DoS attack.
2250 	 */
2251 	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2252 		rstreason = BANDLIM_RST_OPENPORT;
2253 		goto dropwithreset;
2254 	}
2255 
2256 	todrop = tp->rcv_nxt - th->th_seq;
2257 	if (todrop > 0) {
2258 		if (thflags & TH_SYN) {
2259 			thflags &= ~TH_SYN;
2260 			th->th_seq++;
2261 			if (th->th_urp > 1)
2262 				th->th_urp--;
2263 			else
2264 				thflags &= ~TH_URG;
2265 			todrop--;
2266 		}
2267 		/*
2268 		 * Following if statement from Stevens, vol. 2, p. 960.
2269 		 */
2270 		if (todrop > tlen
2271 		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2272 			/*
2273 			 * Any valid FIN must be to the left of the window.
2274 			 * At this point the FIN must be a duplicate or out
2275 			 * of sequence; drop it.
2276 			 */
2277 			thflags &= ~TH_FIN;
2278 
2279 			/*
2280 			 * Send an ACK to resynchronize and drop any data.
2281 			 * But keep on processing for RST or ACK.
2282 			 */
2283 			tp->t_flags |= TF_ACKNOW;
2284 			todrop = tlen;
2285 			TCPSTAT_INC(tcps_rcvduppack);
2286 			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2287 		} else {
2288 			TCPSTAT_INC(tcps_rcvpartduppack);
2289 			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2290 		}
2291 		/*
2292 		 * DSACK - add SACK block for dropped range
2293 		 */
2294 		if ((todrop > 0) && (tp->t_flags & TF_SACK_PERMIT)) {
2295 			tcp_update_sack_list(tp, th->th_seq,
2296 			    th->th_seq + todrop);
2297 			/*
2298 			 * ACK now, as the next in-sequence segment
2299 			 * will clear the DSACK block again
2300 			 */
2301 			tp->t_flags |= TF_ACKNOW;
2302 		}
2303 		drop_hdrlen += todrop;	/* drop from the top afterwards */
2304 		th->th_seq += todrop;
2305 		tlen -= todrop;
2306 		if (th->th_urp > todrop)
2307 			th->th_urp -= todrop;
2308 		else {
2309 			thflags &= ~TH_URG;
2310 			th->th_urp = 0;
2311 		}
2312 	}
2313 
2314 	/*
2315 	 * If new data are received on a connection after the
2316 	 * user processes are gone, then RST the other end.
2317 	 */
2318 	if ((so->so_state & SS_NOFDREF) &&
2319 	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
2320 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2321 			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2322 			    "after socket was closed, "
2323 			    "sending RST and removing tcpcb\n",
2324 			    s, __func__, tcpstates[tp->t_state], tlen);
2325 			free(s, M_TCPLOG);
2326 		}
2327 		tp = tcp_close(tp);
2328 		TCPSTAT_INC(tcps_rcvafterclose);
2329 		rstreason = BANDLIM_UNLIMITED;
2330 		goto dropwithreset;
2331 	}
2332 
2333 	/*
2334 	 * If segment ends after window, drop trailing data
2335 	 * (and PUSH and FIN); if nothing left, just ACK.
2336 	 */
2337 	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2338 	if (todrop > 0) {
2339 		TCPSTAT_INC(tcps_rcvpackafterwin);
2340 		if (todrop >= tlen) {
2341 			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2342 			/*
2343 			 * If window is closed can only take segments at
2344 			 * window edge, and have to drop data and PUSH from
2345 			 * incoming segments.  Continue processing, but
2346 			 * remember to ack.  Otherwise, drop segment
2347 			 * and ack.
2348 			 */
2349 			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2350 				tp->t_flags |= TF_ACKNOW;
2351 				TCPSTAT_INC(tcps_rcvwinprobe);
2352 			} else
2353 				goto dropafterack;
2354 		} else
2355 			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2356 		m_adj(m, -todrop);
2357 		tlen -= todrop;
2358 		thflags &= ~(TH_PUSH|TH_FIN);
2359 	}
2360 
2361 	/*
2362 	 * If last ACK falls within this segment's sequence numbers,
2363 	 * record its timestamp.
2364 	 * NOTE:
2365 	 * 1) That the test incorporates suggestions from the latest
2366 	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2367 	 * 2) That updating only on newer timestamps interferes with
2368 	 *    our earlier PAWS tests, so this check should be solely
2369 	 *    predicated on the sequence space of this segment.
2370 	 * 3) That we modify the segment boundary check to be
2371 	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2372 	 *    instead of RFC1323's
2373 	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2374 	 *    This modified check allows us to overcome RFC1323's
2375 	 *    limitations as described in Stevens TCP/IP Illustrated
2376 	 *    Vol. 2 p.869. In such cases, we can still calculate the
2377 	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2378 	 */
2379 	if ((to.to_flags & TOF_TS) != 0 &&
2380 	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2381 	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2382 		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2383 		tp->ts_recent_age = tcp_ts_getticks();
2384 		tp->ts_recent = to.to_tsval;
2385 	}
2386 
2387 	/*
2388 	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2389 	 * flag is on (half-synchronized state), then queue data for
2390 	 * later processing; else drop segment and return.
2391 	 */
2392 	if ((thflags & TH_ACK) == 0) {
2393 		if (tp->t_state == TCPS_SYN_RECEIVED ||
2394 		    (tp->t_flags & TF_NEEDSYN)) {
2395 			if (tp->t_state == TCPS_SYN_RECEIVED &&
2396 			    IS_FASTOPEN(tp->t_flags)) {
2397 				tp->snd_wnd = tiwin;
2398 				cc_conn_init(tp);
2399 			}
2400 			goto step6;
2401 		} else if (tp->t_flags & TF_ACKNOW)
2402 			goto dropafterack;
2403 		else
2404 			goto drop;
2405 	}
2406 
2407 	/*
2408 	 * Ack processing.
2409 	 */
2410 	switch (tp->t_state) {
2411 	/*
2412 	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2413 	 * ESTABLISHED state and continue processing.
2414 	 * The ACK was checked above.
2415 	 */
2416 	case TCPS_SYN_RECEIVED:
2417 
2418 		TCPSTAT_INC(tcps_connects);
2419 		soisconnected(so);
2420 		/* Do window scaling? */
2421 		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2422 			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2423 			tp->rcv_scale = tp->request_r_scale;
2424 		}
2425 		tp->snd_wnd = tiwin;
2426 		/*
2427 		 * Make transitions:
2428 		 *      SYN-RECEIVED  -> ESTABLISHED
2429 		 *      SYN-RECEIVED* -> FIN-WAIT-1
2430 		 */
2431 		tp->t_starttime = ticks;
2432 		if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
2433 			tcp_fastopen_decrement_counter(tp->t_tfo_pending);
2434 			tp->t_tfo_pending = NULL;
2435 		}
2436 		if (tp->t_flags & TF_NEEDFIN) {
2437 			tcp_state_change(tp, TCPS_FIN_WAIT_1);
2438 			tp->t_flags &= ~TF_NEEDFIN;
2439 		} else {
2440 			tcp_state_change(tp, TCPS_ESTABLISHED);
2441 			TCP_PROBE5(accept__established, NULL, tp,
2442 			    m, tp, th);
2443 			/*
2444 			 * TFO connections call cc_conn_init() during SYN
2445 			 * processing.  Calling it again here for such
2446 			 * connections is not harmless as it would undo the
2447 			 * snd_cwnd reduction that occurs when a TFO SYN|ACK
2448 			 * is retransmitted.
2449 			 */
2450 			if (!IS_FASTOPEN(tp->t_flags))
2451 				cc_conn_init(tp);
2452 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2453 		}
2454 		/*
2455 		 * Account for the ACK of our SYN prior to
2456 		 * regular ACK processing below, except for
2457 		 * simultaneous SYN, which is handled later.
2458 		 */
2459 		if (SEQ_GT(th->th_ack, tp->snd_una) && !(tp->t_flags & TF_NEEDSYN))
2460 			incforsyn = 1;
2461 		/*
2462 		 * If segment contains data or ACK, will call tcp_reass()
2463 		 * later; if not, do so now to pass queued data to user.
2464 		 */
2465 		if (tlen == 0 && (thflags & TH_FIN) == 0) {
2466 			(void) tcp_reass(tp, (struct tcphdr *)0, NULL, 0,
2467 			    (struct mbuf *)0);
2468 			tcp_handle_wakeup(tp, so);
2469 		}
2470 		tp->snd_wl1 = th->th_seq - 1;
2471 		/* FALLTHROUGH */
2472 
2473 	/*
2474 	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2475 	 * ACKs.  If the ack is in the range
2476 	 *	tp->snd_una < th->th_ack <= tp->snd_max
2477 	 * then advance tp->snd_una to th->th_ack and drop
2478 	 * data from the retransmission queue.  If this ACK reflects
2479 	 * more up to date window information we update our window information.
2480 	 */
2481 	case TCPS_ESTABLISHED:
2482 	case TCPS_FIN_WAIT_1:
2483 	case TCPS_FIN_WAIT_2:
2484 	case TCPS_CLOSE_WAIT:
2485 	case TCPS_CLOSING:
2486 	case TCPS_LAST_ACK:
2487 		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2488 			TCPSTAT_INC(tcps_rcvacktoomuch);
2489 			goto dropafterack;
2490 		}
2491 		if ((tp->t_flags & TF_SACK_PERMIT) &&
2492 		    ((to.to_flags & TOF_SACK) ||
2493 		     !TAILQ_EMPTY(&tp->snd_holes))) {
2494 			if (((sack_changed = tcp_sack_doack(tp, &to, th->th_ack)) != 0) &&
2495 			    (tp->t_flags & TF_LRD)) {
2496 				tcp_sack_lost_retransmission(tp, th);
2497 			}
2498 		} else
2499 			/*
2500 			 * Reset the value so that previous (valid) value
2501 			 * from the last ack with SACK doesn't get used.
2502 			 */
2503 			tp->sackhint.sacked_bytes = 0;
2504 
2505 #ifdef TCP_HHOOK
2506 		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2507 		hhook_run_tcp_est_in(tp, th, &to);
2508 #endif
2509 
2510 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2511 			maxseg = tcp_maxseg(tp);
2512 			if (tlen == 0 &&
2513 			    (tiwin == tp->snd_wnd ||
2514 			    (tp->t_flags & TF_SACK_PERMIT))) {
2515 				/*
2516 				 * If this is the first time we've seen a
2517 				 * FIN from the remote, this is not a
2518 				 * duplicate and it needs to be processed
2519 				 * normally.  This happens during a
2520 				 * simultaneous close.
2521 				 */
2522 				if ((thflags & TH_FIN) &&
2523 				    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2524 					tp->t_dupacks = 0;
2525 					break;
2526 				}
2527 				TCPSTAT_INC(tcps_rcvdupack);
2528 				/*
2529 				 * If we have outstanding data (other than
2530 				 * a window probe), this is a completely
2531 				 * duplicate ack (ie, window info didn't
2532 				 * change and FIN isn't set),
2533 				 * the ack is the biggest we've
2534 				 * seen and we've seen exactly our rexmt
2535 				 * threshold of them, assume a packet
2536 				 * has been dropped and retransmit it.
2537 				 * Kludge snd_nxt & the congestion
2538 				 * window so we send only this one
2539 				 * packet.
2540 				 *
2541 				 * We know we're losing at the current
2542 				 * window size so do congestion avoidance
2543 				 * (set ssthresh to half the current window
2544 				 * and pull our congestion window back to
2545 				 * the new ssthresh).
2546 				 *
2547 				 * Dup acks mean that packets have left the
2548 				 * network (they're now cached at the receiver)
2549 				 * so bump cwnd by the amount in the receiver
2550 				 * to keep a constant cwnd packets in the
2551 				 * network.
2552 				 *
2553 				 * When using TCP ECN, notify the peer that
2554 				 * we reduced the cwnd.
2555 				 */
2556 				/*
2557 				 * Following 2 kinds of acks should not affect
2558 				 * dupack counting:
2559 				 * 1) Old acks
2560 				 * 2) Acks with SACK but without any new SACK
2561 				 * information in them. These could result from
2562 				 * any anomaly in the network like a switch
2563 				 * duplicating packets or a possible DoS attack.
2564 				 */
2565 				if (th->th_ack != tp->snd_una ||
2566 				    ((tp->t_flags & TF_SACK_PERMIT) &&
2567 				    (to.to_flags & TOF_SACK) &&
2568 				    !sack_changed))
2569 					break;
2570 				else if (!tcp_timer_active(tp, TT_REXMT))
2571 					tp->t_dupacks = 0;
2572 				else if (++tp->t_dupacks > tcprexmtthresh ||
2573 				     IN_FASTRECOVERY(tp->t_flags)) {
2574 					cc_ack_received(tp, th, nsegs,
2575 					    CC_DUPACK);
2576 					if (V_tcp_do_prr &&
2577 					    IN_FASTRECOVERY(tp->t_flags)) {
2578 						tcp_do_prr_ack(tp, th, &to);
2579 					} else if ((tp->t_flags & TF_SACK_PERMIT) &&
2580 					    (to.to_flags & TOF_SACK) &&
2581 					    IN_FASTRECOVERY(tp->t_flags)) {
2582 						int awnd;
2583 
2584 						/*
2585 						 * Compute the amount of data in flight first.
2586 						 * We can inject new data into the pipe iff
2587 						 * we have less than 1/2 the original window's
2588 						 * worth of data in flight.
2589 						 */
2590 						if (V_tcp_do_newsack)
2591 							awnd = tcp_compute_pipe(tp);
2592 						else
2593 							awnd = (tp->snd_nxt - tp->snd_fack) +
2594 								tp->sackhint.sack_bytes_rexmit;
2595 
2596 						if (awnd < tp->snd_ssthresh) {
2597 							tp->snd_cwnd += maxseg;
2598 							if (tp->snd_cwnd > tp->snd_ssthresh)
2599 								tp->snd_cwnd = tp->snd_ssthresh;
2600 						}
2601 					} else
2602 						tp->snd_cwnd += maxseg;
2603 					(void) tcp_output(tp);
2604 					goto drop;
2605 				} else if (tp->t_dupacks == tcprexmtthresh ||
2606 					    (tp->t_flags & TF_SACK_PERMIT &&
2607 					     V_tcp_do_newsack &&
2608 					     tp->sackhint.sacked_bytes >
2609 					     (tcprexmtthresh - 1) * maxseg)) {
2610 enter_recovery:
2611 					/*
2612 					 * Above is the RFC6675 trigger condition of
2613 					 * more than (dupthresh-1)*maxseg sacked data.
2614 					 * If the count of holes in the
2615 					 * scoreboard is >= dupthresh, we could
2616 					 * also enter loss recovery, but don't
2617 					 * have that value readily available.
2618 					 */
2619 					tp->t_dupacks = tcprexmtthresh;
2620 					tcp_seq onxt = tp->snd_nxt;
2621 
2622 					/*
2623 					 * If we're doing sack, or prr, check
2624 					 * to see if we're already in sack
2625 					 * recovery. If we're not doing sack,
2626 					 * check to see if we're in newreno
2627 					 * recovery.
2628 					 */
2629 					if (V_tcp_do_prr ||
2630 					    (tp->t_flags & TF_SACK_PERMIT)) {
2631 						if (IN_FASTRECOVERY(tp->t_flags)) {
2632 							tp->t_dupacks = 0;
2633 							break;
2634 						}
2635 					} else {
2636 						if (SEQ_LEQ(th->th_ack,
2637 						    tp->snd_recover)) {
2638 							tp->t_dupacks = 0;
2639 							break;
2640 						}
2641 					}
2642 					/* Congestion signal before ack. */
2643 					cc_cong_signal(tp, th, CC_NDUPACK);
2644 					cc_ack_received(tp, th, nsegs,
2645 					    CC_DUPACK);
2646 					tcp_timer_activate(tp, TT_REXMT, 0);
2647 					tp->t_rtttime = 0;
2648 					if (V_tcp_do_prr) {
2649 						/*
2650 						 * snd_ssthresh is already updated by
2651 						 * cc_cong_signal.
2652 						 */
2653 						if ((tp->t_flags & TF_SACK_PERMIT) &&
2654 						    (to.to_flags & TOF_SACK)) {
2655 							tp->sackhint.prr_delivered =
2656 							    tp->sackhint.sacked_bytes;
2657 						} else {
2658 							tp->sackhint.prr_delivered =
2659 							    imin(tp->snd_max - tp->snd_una,
2660 							    imin(INT_MAX / 65536,
2661 								tp->t_dupacks) * maxseg);
2662 						}
2663 						tp->sackhint.recover_fs = max(1,
2664 						    tp->snd_nxt - tp->snd_una);
2665 					}
2666 					if ((tp->t_flags & TF_SACK_PERMIT) &&
2667 					    (to.to_flags & TOF_SACK)) {
2668 						TCPSTAT_INC(
2669 						    tcps_sack_recovery_episode);
2670 						tp->snd_recover = tp->snd_nxt;
2671 						tp->snd_cwnd = maxseg;
2672 						(void) tcp_output(tp);
2673 						if (SEQ_GT(th->th_ack, tp->snd_una))
2674 							goto resume_partialack;
2675 						goto drop;
2676 					}
2677 					tp->snd_nxt = th->th_ack;
2678 					tp->snd_cwnd = maxseg;
2679 					(void) tcp_output(tp);
2680 					KASSERT(tp->snd_limited <= 2,
2681 					    ("%s: tp->snd_limited too big",
2682 					    __func__));
2683 					tp->snd_cwnd = tp->snd_ssthresh +
2684 					     maxseg *
2685 					     (tp->t_dupacks - tp->snd_limited);
2686 					if (SEQ_GT(onxt, tp->snd_nxt))
2687 						tp->snd_nxt = onxt;
2688 					goto drop;
2689 				} else if (V_tcp_do_rfc3042) {
2690 					/*
2691 					 * Process first and second duplicate
2692 					 * ACKs. Each indicates a segment
2693 					 * leaving the network, creating room
2694 					 * for more. Make sure we can send a
2695 					 * packet on reception of each duplicate
2696 					 * ACK by increasing snd_cwnd by one
2697 					 * segment. Restore the original
2698 					 * snd_cwnd after packet transmission.
2699 					 */
2700 					cc_ack_received(tp, th, nsegs,
2701 					    CC_DUPACK);
2702 					uint32_t oldcwnd = tp->snd_cwnd;
2703 					tcp_seq oldsndmax = tp->snd_max;
2704 					u_int sent;
2705 					int avail;
2706 
2707 					KASSERT(tp->t_dupacks == 1 ||
2708 					    tp->t_dupacks == 2,
2709 					    ("%s: dupacks not 1 or 2",
2710 					    __func__));
2711 					if (tp->t_dupacks == 1)
2712 						tp->snd_limited = 0;
2713 					tp->snd_cwnd =
2714 					    (tp->snd_nxt - tp->snd_una) +
2715 					    (tp->t_dupacks - tp->snd_limited) *
2716 					    maxseg;
2717 					/*
2718 					 * Only call tcp_output when there
2719 					 * is new data available to be sent.
2720 					 * Otherwise we would send pure ACKs.
2721 					 */
2722 					SOCKBUF_LOCK(&so->so_snd);
2723 					avail = sbavail(&so->so_snd) -
2724 					    (tp->snd_nxt - tp->snd_una);
2725 					SOCKBUF_UNLOCK(&so->so_snd);
2726 					if (avail > 0)
2727 						(void) tcp_output(tp);
2728 					sent = tp->snd_max - oldsndmax;
2729 					if (sent > maxseg) {
2730 						KASSERT((tp->t_dupacks == 2 &&
2731 						    tp->snd_limited == 0) ||
2732 						   (sent == maxseg + 1 &&
2733 						    tp->t_flags & TF_SENTFIN),
2734 						    ("%s: sent too much",
2735 						    __func__));
2736 						tp->snd_limited = 2;
2737 					} else if (sent > 0)
2738 						++tp->snd_limited;
2739 					tp->snd_cwnd = oldcwnd;
2740 					goto drop;
2741 				}
2742 			}
2743 			break;
2744 		} else {
2745 			/*
2746 			 * This ack is advancing the left edge, reset the
2747 			 * counter.
2748 			 */
2749 			tp->t_dupacks = 0;
2750 			/*
2751 			 * If this ack also has new SACK info, increment the
2752 			 * counter as per rfc6675. The variable
2753 			 * sack_changed tracks all changes to the SACK
2754 			 * scoreboard, including when partial ACKs without
2755 			 * SACK options are received, and clear the scoreboard
2756 			 * from the left side. Such partial ACKs should not be
2757 			 * counted as dupacks here.
2758 			 */
2759 			if ((tp->t_flags & TF_SACK_PERMIT) &&
2760 			    (to.to_flags & TOF_SACK) &&
2761 			    sack_changed) {
2762 				tp->t_dupacks++;
2763 				/* limit overhead by setting maxseg last */
2764 				if (!IN_FASTRECOVERY(tp->t_flags) &&
2765 				    (tp->sackhint.sacked_bytes >
2766 				    ((tcprexmtthresh - 1) *
2767 				    (maxseg = tcp_maxseg(tp))))) {
2768 					goto enter_recovery;
2769 				}
2770 			}
2771 		}
2772 
2773 resume_partialack:
2774 		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2775 		    ("%s: th_ack <= snd_una", __func__));
2776 
2777 		/*
2778 		 * If the congestion window was inflated to account
2779 		 * for the other side's cached packets, retract it.
2780 		 */
2781 		if (IN_FASTRECOVERY(tp->t_flags)) {
2782 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2783 				if (tp->t_flags & TF_SACK_PERMIT)
2784 					if (V_tcp_do_prr && to.to_flags & TOF_SACK) {
2785 						tcp_timer_activate(tp, TT_REXMT, 0);
2786 						tp->t_rtttime = 0;
2787 						tcp_do_prr_ack(tp, th, &to);
2788 						tp->t_flags |= TF_ACKNOW;
2789 						(void) tcp_output(tp);
2790 					} else
2791 						tcp_sack_partialack(tp, th);
2792 				else
2793 					tcp_newreno_partial_ack(tp, th);
2794 			} else
2795 				cc_post_recovery(tp, th);
2796 		} else if (IN_CONGRECOVERY(tp->t_flags)) {
2797 			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2798 				if (V_tcp_do_prr) {
2799 					tp->sackhint.delivered_data = BYTES_THIS_ACK(tp, th);
2800 					tp->snd_fack = th->th_ack;
2801 					tcp_do_prr_ack(tp, th, &to);
2802 					(void) tcp_output(tp);
2803 				}
2804 			} else
2805 				cc_post_recovery(tp, th);
2806 		}
2807 		/*
2808 		 * If we reach this point, ACK is not a duplicate,
2809 		 *     i.e., it ACKs something we sent.
2810 		 */
2811 		if (tp->t_flags & TF_NEEDSYN) {
2812 			/*
2813 			 * T/TCP: Connection was half-synchronized, and our
2814 			 * SYN has been ACK'd (so connection is now fully
2815 			 * synchronized).  Go to non-starred state,
2816 			 * increment snd_una for ACK of SYN, and check if
2817 			 * we can do window scaling.
2818 			 */
2819 			tp->t_flags &= ~TF_NEEDSYN;
2820 			tp->snd_una++;
2821 			/* Do window scaling? */
2822 			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2823 				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2824 				tp->rcv_scale = tp->request_r_scale;
2825 				/* Send window already scaled. */
2826 			}
2827 		}
2828 
2829 process_ACK:
2830 		INP_WLOCK_ASSERT(tp->t_inpcb);
2831 
2832 		/*
2833 		 * Adjust for the SYN bit in sequence space,
2834 		 * but don't account for it in cwnd calculations.
2835 		 * This is for the SYN_RECEIVED, non-simultaneous
2836 		 * SYN case. SYN_SENT and simultaneous SYN are
2837 		 * treated elsewhere.
2838 		 */
2839 		if (incforsyn)
2840 			tp->snd_una++;
2841 		acked = BYTES_THIS_ACK(tp, th);
2842 		KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
2843 		    "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
2844 		    tp->snd_una, th->th_ack, tp, m));
2845 		TCPSTAT_ADD(tcps_rcvackpack, nsegs);
2846 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2847 
2848 		/*
2849 		 * If we just performed our first retransmit, and the ACK
2850 		 * arrives within our recovery window, then it was a mistake
2851 		 * to do the retransmit in the first place.  Recover our
2852 		 * original cwnd and ssthresh, and proceed to transmit where
2853 		 * we left off.
2854 		 */
2855 		if (tp->t_rxtshift == 1 &&
2856 		    tp->t_flags & TF_PREVVALID &&
2857 		    tp->t_badrxtwin != 0 &&
2858 		    to.to_flags & TOF_TS &&
2859 		    to.to_tsecr != 0 &&
2860 		    TSTMP_LT(to.to_tsecr, tp->t_badrxtwin))
2861 			cc_cong_signal(tp, th, CC_RTO_ERR);
2862 
2863 		/*
2864 		 * If we have a timestamp reply, update smoothed
2865 		 * round trip time.  If no timestamp is present but
2866 		 * transmit timer is running and timed sequence
2867 		 * number was acked, update smoothed round trip time.
2868 		 * Since we now have an rtt measurement, cancel the
2869 		 * timer backoff (cf., Phil Karn's retransmit alg.).
2870 		 * Recompute the initial retransmit timer.
2871 		 *
2872 		 * Some boxes send broken timestamp replies
2873 		 * during the SYN+ACK phase, ignore
2874 		 * timestamps of 0 or we could calculate a
2875 		 * huge RTT and blow up the retransmit timer.
2876 		 */
2877 		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2878 			uint32_t t;
2879 
2880 			t = tcp_ts_getticks() - to.to_tsecr;
2881 			if (!tp->t_rttlow || tp->t_rttlow > t)
2882 				tp->t_rttlow = t;
2883 			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2884 		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2885 			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2886 				tp->t_rttlow = ticks - tp->t_rtttime;
2887 			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2888 		}
2889 
2890 		/*
2891 		 * If all outstanding data is acked, stop retransmit
2892 		 * timer and remember to restart (more output or persist).
2893 		 * If there is more data to be acked, restart retransmit
2894 		 * timer, using current (possibly backed-off) value.
2895 		 */
2896 		if (th->th_ack == tp->snd_max) {
2897 			tcp_timer_activate(tp, TT_REXMT, 0);
2898 			needoutput = 1;
2899 		} else if (!tcp_timer_active(tp, TT_PERSIST))
2900 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
2901 
2902 		/*
2903 		 * If no data (only SYN) was ACK'd,
2904 		 *    skip rest of ACK processing.
2905 		 */
2906 		if (acked == 0)
2907 			goto step6;
2908 
2909 		/*
2910 		 * Let the congestion control algorithm update congestion
2911 		 * control related information. This typically means increasing
2912 		 * the congestion window.
2913 		 */
2914 		cc_ack_received(tp, th, nsegs, CC_ACK);
2915 
2916 		SOCKBUF_LOCK(&so->so_snd);
2917 		if (acked > sbavail(&so->so_snd)) {
2918 			if (tp->snd_wnd >= sbavail(&so->so_snd))
2919 				tp->snd_wnd -= sbavail(&so->so_snd);
2920 			else
2921 				tp->snd_wnd = 0;
2922 			mfree = sbcut_locked(&so->so_snd,
2923 			    (int)sbavail(&so->so_snd));
2924 			ourfinisacked = 1;
2925 		} else {
2926 			mfree = sbcut_locked(&so->so_snd, acked);
2927 			if (tp->snd_wnd >= (uint32_t) acked)
2928 				tp->snd_wnd -= acked;
2929 			else
2930 				tp->snd_wnd = 0;
2931 			ourfinisacked = 0;
2932 		}
2933 		/* NB: sowwakeup_locked() does an implicit unlock. */
2934 		sowwakeup_locked(so);
2935 		m_freem(mfree);
2936 		/* Detect una wraparound. */
2937 		if (!IN_RECOVERY(tp->t_flags) &&
2938 		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2939 		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2940 			tp->snd_recover = th->th_ack - 1;
2941 		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2942 		if (IN_RECOVERY(tp->t_flags) &&
2943 		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2944 			EXIT_RECOVERY(tp->t_flags);
2945 		}
2946 		tp->snd_una = th->th_ack;
2947 		if (tp->t_flags & TF_SACK_PERMIT) {
2948 			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2949 				tp->snd_recover = tp->snd_una;
2950 		}
2951 		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2952 			tp->snd_nxt = tp->snd_una;
2953 
2954 		switch (tp->t_state) {
2955 		/*
2956 		 * In FIN_WAIT_1 STATE in addition to the processing
2957 		 * for the ESTABLISHED state if our FIN is now acknowledged
2958 		 * then enter FIN_WAIT_2.
2959 		 */
2960 		case TCPS_FIN_WAIT_1:
2961 			if (ourfinisacked) {
2962 				/*
2963 				 * If we can't receive any more
2964 				 * data, then closing user can proceed.
2965 				 * Starting the timer is contrary to the
2966 				 * specification, but if we don't get a FIN
2967 				 * we'll hang forever.
2968 				 *
2969 				 * XXXjl:
2970 				 * we should release the tp also, and use a
2971 				 * compressed state.
2972 				 */
2973 				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2974 					soisdisconnected(so);
2975 					tcp_timer_activate(tp, TT_2MSL,
2976 					    (tcp_fast_finwait2_recycle ?
2977 					    tcp_finwait2_timeout :
2978 					    TP_MAXIDLE(tp)));
2979 				}
2980 				tcp_state_change(tp, TCPS_FIN_WAIT_2);
2981 			}
2982 			break;
2983 
2984 		/*
2985 		 * In CLOSING STATE in addition to the processing for
2986 		 * the ESTABLISHED state if the ACK acknowledges our FIN
2987 		 * then enter the TIME-WAIT state, otherwise ignore
2988 		 * the segment.
2989 		 */
2990 		case TCPS_CLOSING:
2991 			if (ourfinisacked) {
2992 				tcp_twstart(tp);
2993 				m_freem(m);
2994 				return;
2995 			}
2996 			break;
2997 
2998 		/*
2999 		 * In LAST_ACK, we may still be waiting for data to drain
3000 		 * and/or to be acked, as well as for the ack of our FIN.
3001 		 * If our FIN is now acknowledged, delete the TCB,
3002 		 * enter the closed state and return.
3003 		 */
3004 		case TCPS_LAST_ACK:
3005 			if (ourfinisacked) {
3006 				tp = tcp_close(tp);
3007 				goto drop;
3008 			}
3009 			break;
3010 		}
3011 	}
3012 
3013 step6:
3014 	INP_WLOCK_ASSERT(tp->t_inpcb);
3015 
3016 	/*
3017 	 * Update window information.
3018 	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
3019 	 */
3020 	if ((thflags & TH_ACK) &&
3021 	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
3022 	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
3023 	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
3024 		/* keep track of pure window updates */
3025 		if (tlen == 0 &&
3026 		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
3027 			TCPSTAT_INC(tcps_rcvwinupd);
3028 		tp->snd_wnd = tiwin;
3029 		tp->snd_wl1 = th->th_seq;
3030 		tp->snd_wl2 = th->th_ack;
3031 		if (tp->snd_wnd > tp->max_sndwnd)
3032 			tp->max_sndwnd = tp->snd_wnd;
3033 		needoutput = 1;
3034 	}
3035 
3036 	/*
3037 	 * Process segments with URG.
3038 	 */
3039 	if ((thflags & TH_URG) && th->th_urp &&
3040 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3041 		/*
3042 		 * This is a kludge, but if we receive and accept
3043 		 * random urgent pointers, we'll crash in
3044 		 * soreceive.  It's hard to imagine someone
3045 		 * actually wanting to send this much urgent data.
3046 		 */
3047 		SOCKBUF_LOCK(&so->so_rcv);
3048 		if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
3049 			th->th_urp = 0;			/* XXX */
3050 			thflags &= ~TH_URG;		/* XXX */
3051 			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
3052 			goto dodata;			/* XXX */
3053 		}
3054 		/*
3055 		 * If this segment advances the known urgent pointer,
3056 		 * then mark the data stream.  This should not happen
3057 		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
3058 		 * a FIN has been received from the remote side.
3059 		 * In these states we ignore the URG.
3060 		 *
3061 		 * According to RFC961 (Assigned Protocols),
3062 		 * the urgent pointer points to the last octet
3063 		 * of urgent data.  We continue, however,
3064 		 * to consider it to indicate the first octet
3065 		 * of data past the urgent section as the original
3066 		 * spec states (in one of two places).
3067 		 */
3068 		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
3069 			tp->rcv_up = th->th_seq + th->th_urp;
3070 			so->so_oobmark = sbavail(&so->so_rcv) +
3071 			    (tp->rcv_up - tp->rcv_nxt) - 1;
3072 			if (so->so_oobmark == 0)
3073 				so->so_rcv.sb_state |= SBS_RCVATMARK;
3074 			sohasoutofband(so);
3075 			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
3076 		}
3077 		SOCKBUF_UNLOCK(&so->so_rcv);
3078 		/*
3079 		 * Remove out of band data so doesn't get presented to user.
3080 		 * This can happen independent of advancing the URG pointer,
3081 		 * but if two URG's are pending at once, some out-of-band
3082 		 * data may creep in... ick.
3083 		 */
3084 		if (th->th_urp <= (uint32_t)tlen &&
3085 		    !(so->so_options & SO_OOBINLINE)) {
3086 			/* hdr drop is delayed */
3087 			tcp_pulloutofband(so, th, m, drop_hdrlen);
3088 		}
3089 	} else {
3090 		/*
3091 		 * If no out of band data is expected,
3092 		 * pull receive urgent pointer along
3093 		 * with the receive window.
3094 		 */
3095 		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
3096 			tp->rcv_up = tp->rcv_nxt;
3097 	}
3098 dodata:							/* XXX */
3099 	INP_WLOCK_ASSERT(tp->t_inpcb);
3100 
3101 	/*
3102 	 * Process the segment text, merging it into the TCP sequencing queue,
3103 	 * and arranging for acknowledgment of receipt if necessary.
3104 	 * This process logically involves adjusting tp->rcv_wnd as data
3105 	 * is presented to the user (this happens in tcp_usrreq.c,
3106 	 * case PRU_RCVD).  If a FIN has already been received on this
3107 	 * connection then we just ignore the text.
3108 	 */
3109 	tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
3110 		   IS_FASTOPEN(tp->t_flags));
3111 	if ((tlen || (thflags & TH_FIN) || (tfo_syn && tlen > 0)) &&
3112 	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3113 		tcp_seq save_start = th->th_seq;
3114 		tcp_seq save_rnxt  = tp->rcv_nxt;
3115 		int     save_tlen  = tlen;
3116 		m_adj(m, drop_hdrlen);	/* delayed header drop */
3117 		/*
3118 		 * Insert segment which includes th into TCP reassembly queue
3119 		 * with control block tp.  Set thflags to whether reassembly now
3120 		 * includes a segment with FIN.  This handles the common case
3121 		 * inline (segment is the next to be received on an established
3122 		 * connection, and the queue is empty), avoiding linkage into
3123 		 * and removal from the queue and repetition of various
3124 		 * conversions.
3125 		 * Set DELACK for segments received in order, but ack
3126 		 * immediately when segments are out of order (so
3127 		 * fast retransmit can work).
3128 		 */
3129 		if (th->th_seq == tp->rcv_nxt &&
3130 		    SEGQ_EMPTY(tp) &&
3131 		    (TCPS_HAVEESTABLISHED(tp->t_state) ||
3132 		     tfo_syn)) {
3133 			if (DELAY_ACK(tp, tlen) || tfo_syn)
3134 				tp->t_flags |= TF_DELACK;
3135 			else
3136 				tp->t_flags |= TF_ACKNOW;
3137 			tp->rcv_nxt += tlen;
3138 			if (tlen &&
3139 			    ((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
3140 			    (tp->t_fbyte_in == 0)) {
3141 				tp->t_fbyte_in = ticks;
3142 				if (tp->t_fbyte_in == 0)
3143 					tp->t_fbyte_in = 1;
3144 				if (tp->t_fbyte_out && tp->t_fbyte_in)
3145 					tp->t_flags2 |= TF2_FBYTES_COMPLETE;
3146 			}
3147 			thflags = tcp_get_flags(th) & TH_FIN;
3148 			TCPSTAT_INC(tcps_rcvpack);
3149 			TCPSTAT_ADD(tcps_rcvbyte, tlen);
3150 			SOCKBUF_LOCK(&so->so_rcv);
3151 			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
3152 				m_freem(m);
3153 			else
3154 				sbappendstream_locked(&so->so_rcv, m, 0);
3155 			tp->t_flags |= TF_WAKESOR;
3156 		} else {
3157 			/*
3158 			 * XXX: Due to the header drop above "th" is
3159 			 * theoretically invalid by now.  Fortunately
3160 			 * m_adj() doesn't actually frees any mbufs
3161 			 * when trimming from the head.
3162 			 */
3163 			tcp_seq temp = save_start;
3164 
3165 			thflags = tcp_reass(tp, th, &temp, &tlen, m);
3166 			tp->t_flags |= TF_ACKNOW;
3167 		}
3168 		if ((tp->t_flags & TF_SACK_PERMIT) &&
3169 		    (save_tlen > 0) &&
3170 		    TCPS_HAVEESTABLISHED(tp->t_state)) {
3171 			if ((tlen == 0) && (SEQ_LT(save_start, save_rnxt))) {
3172 				/*
3173 				 * DSACK actually handled in the fastpath
3174 				 * above.
3175 				 */
3176 				tcp_update_sack_list(tp, save_start,
3177 				    save_start + save_tlen);
3178 			} else if ((tlen > 0) && SEQ_GT(tp->rcv_nxt, save_rnxt)) {
3179 				if ((tp->rcv_numsacks >= 1) &&
3180 				    (tp->sackblks[0].end == save_start)) {
3181 					/*
3182 					 * Partial overlap, recorded at todrop
3183 					 * above.
3184 					 */
3185 					tcp_update_sack_list(tp,
3186 					    tp->sackblks[0].start,
3187 					    tp->sackblks[0].end);
3188 				} else {
3189 					tcp_update_dsack_list(tp, save_start,
3190 					    save_start + save_tlen);
3191 				}
3192 			} else if (tlen >= save_tlen) {
3193 				/* Update of sackblks. */
3194 				tcp_update_dsack_list(tp, save_start,
3195 				    save_start + save_tlen);
3196 			} else if (tlen > 0) {
3197 				tcp_update_dsack_list(tp, save_start,
3198 				    save_start + tlen);
3199 			}
3200 		}
3201 		tcp_handle_wakeup(tp, so);
3202 #if 0
3203 		/*
3204 		 * Note the amount of data that peer has sent into
3205 		 * our window, in order to estimate the sender's
3206 		 * buffer size.
3207 		 * XXX: Unused.
3208 		 */
3209 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
3210 			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
3211 		else
3212 			len = so->so_rcv.sb_hiwat;
3213 #endif
3214 	} else {
3215 		m_freem(m);
3216 		thflags &= ~TH_FIN;
3217 	}
3218 
3219 	/*
3220 	 * If FIN is received ACK the FIN and let the user know
3221 	 * that the connection is closing.
3222 	 */
3223 	if (thflags & TH_FIN) {
3224 		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3225 			/* The socket upcall is handled by socantrcvmore. */
3226 			socantrcvmore(so);
3227 			/*
3228 			 * If connection is half-synchronized
3229 			 * (ie NEEDSYN flag on) then delay ACK,
3230 			 * so it may be piggybacked when SYN is sent.
3231 			 * Otherwise, since we received a FIN then no
3232 			 * more input can be expected, send ACK now.
3233 			 */
3234 			if (tp->t_flags & TF_NEEDSYN)
3235 				tp->t_flags |= TF_DELACK;
3236 			else
3237 				tp->t_flags |= TF_ACKNOW;
3238 			tp->rcv_nxt++;
3239 		}
3240 		switch (tp->t_state) {
3241 		/*
3242 		 * In SYN_RECEIVED and ESTABLISHED STATES
3243 		 * enter the CLOSE_WAIT state.
3244 		 */
3245 		case TCPS_SYN_RECEIVED:
3246 			tp->t_starttime = ticks;
3247 			/* FALLTHROUGH */
3248 		case TCPS_ESTABLISHED:
3249 			tcp_state_change(tp, TCPS_CLOSE_WAIT);
3250 			break;
3251 
3252 		/*
3253 		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
3254 		 * enter the CLOSING state.
3255 		 */
3256 		case TCPS_FIN_WAIT_1:
3257 			tcp_state_change(tp, TCPS_CLOSING);
3258 			break;
3259 
3260 		/*
3261 		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
3262 		 * starting the time-wait timer, turning off the other
3263 		 * standard timers.
3264 		 */
3265 		case TCPS_FIN_WAIT_2:
3266 			tcp_twstart(tp);
3267 			return;
3268 		}
3269 	}
3270 #ifdef TCPDEBUG
3271 	if (so->so_options & SO_DEBUG)
3272 		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
3273 			  &tcp_savetcp, 0);
3274 #endif
3275 	TCP_PROBE3(debug__input, tp, th, m);
3276 
3277 	/*
3278 	 * Return any desired output.
3279 	 */
3280 	if (needoutput || (tp->t_flags & TF_ACKNOW))
3281 		(void) tcp_output(tp);
3282 
3283 check_delack:
3284 	INP_WLOCK_ASSERT(tp->t_inpcb);
3285 
3286 	if (tp->t_flags & TF_DELACK) {
3287 		tp->t_flags &= ~TF_DELACK;
3288 		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3289 	}
3290 	INP_WUNLOCK(tp->t_inpcb);
3291 	return;
3292 
3293 dropafterack:
3294 	/*
3295 	 * Generate an ACK dropping incoming segment if it occupies
3296 	 * sequence space, where the ACK reflects our state.
3297 	 *
3298 	 * We can now skip the test for the RST flag since all
3299 	 * paths to this code happen after packets containing
3300 	 * RST have been dropped.
3301 	 *
3302 	 * In the SYN-RECEIVED state, don't send an ACK unless the
3303 	 * segment we received passes the SYN-RECEIVED ACK test.
3304 	 * If it fails send a RST.  This breaks the loop in the
3305 	 * "LAND" DoS attack, and also prevents an ACK storm
3306 	 * between two listening ports that have been sent forged
3307 	 * SYN segments, each with the source address of the other.
3308 	 */
3309 	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3310 	    (SEQ_GT(tp->snd_una, th->th_ack) ||
3311 	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
3312 		rstreason = BANDLIM_RST_OPENPORT;
3313 		goto dropwithreset;
3314 	}
3315 #ifdef TCPDEBUG
3316 	if (so->so_options & SO_DEBUG)
3317 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3318 			  &tcp_savetcp, 0);
3319 #endif
3320 	TCP_PROBE3(debug__input, tp, th, m);
3321 	tp->t_flags |= TF_ACKNOW;
3322 	(void) tcp_output(tp);
3323 	INP_WUNLOCK(tp->t_inpcb);
3324 	m_freem(m);
3325 	return;
3326 
3327 dropwithreset:
3328 	if (tp != NULL) {
3329 		tcp_dropwithreset(m, th, tp, tlen, rstreason);
3330 		INP_WUNLOCK(tp->t_inpcb);
3331 	} else
3332 		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3333 	return;
3334 
3335 drop:
3336 	/*
3337 	 * Drop space held by incoming segment and return.
3338 	 */
3339 #ifdef TCPDEBUG
3340 	if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
3341 		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
3342 			  &tcp_savetcp, 0);
3343 #endif
3344 	TCP_PROBE3(debug__input, tp, th, m);
3345 	if (tp != NULL) {
3346 		INP_WUNLOCK(tp->t_inpcb);
3347 	}
3348 	m_freem(m);
3349 }
3350 
3351 /*
3352  * Issue RST and make ACK acceptable to originator of segment.
3353  * The mbuf must still include the original packet header.
3354  * tp may be NULL.
3355  */
3356 void
3357 tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3358     int tlen, int rstreason)
3359 {
3360 #ifdef INET
3361 	struct ip *ip;
3362 #endif
3363 #ifdef INET6
3364 	struct ip6_hdr *ip6;
3365 #endif
3366 
3367 	if (tp != NULL) {
3368 		INP_LOCK_ASSERT(tp->t_inpcb);
3369 	}
3370 
3371 	/* Don't bother if destination was broadcast/multicast. */
3372 	if ((tcp_get_flags(th) & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3373 		goto drop;
3374 #ifdef INET6
3375 	if (mtod(m, struct ip *)->ip_v == 6) {
3376 		ip6 = mtod(m, struct ip6_hdr *);
3377 		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3378 		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3379 			goto drop;
3380 		/* IPv6 anycast check is done at tcp6_input() */
3381 	}
3382 #endif
3383 #if defined(INET) && defined(INET6)
3384 	else
3385 #endif
3386 #ifdef INET
3387 	{
3388 		ip = mtod(m, struct ip *);
3389 		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3390 		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3391 		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3392 		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3393 			goto drop;
3394 	}
3395 #endif
3396 
3397 	/* Perform bandwidth limiting. */
3398 	if (badport_bandlim(rstreason) < 0)
3399 		goto drop;
3400 
3401 	/* tcp_respond consumes the mbuf chain. */
3402 	if (tcp_get_flags(th) & TH_ACK) {
3403 		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3404 		    th->th_ack, TH_RST);
3405 	} else {
3406 		if (tcp_get_flags(th) & TH_SYN)
3407 			tlen++;
3408 		if (tcp_get_flags(th) & TH_FIN)
3409 			tlen++;
3410 		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3411 		    (tcp_seq)0, TH_RST|TH_ACK);
3412 	}
3413 	return;
3414 drop:
3415 	m_freem(m);
3416 }
3417 
3418 /*
3419  * Parse TCP options and place in tcpopt.
3420  */
3421 void
3422 tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3423 {
3424 	int opt, optlen;
3425 
3426 	to->to_flags = 0;
3427 	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3428 		opt = cp[0];
3429 		if (opt == TCPOPT_EOL)
3430 			break;
3431 		if (opt == TCPOPT_NOP)
3432 			optlen = 1;
3433 		else {
3434 			if (cnt < 2)
3435 				break;
3436 			optlen = cp[1];
3437 			if (optlen < 2 || optlen > cnt)
3438 				break;
3439 		}
3440 		switch (opt) {
3441 		case TCPOPT_MAXSEG:
3442 			if (optlen != TCPOLEN_MAXSEG)
3443 				continue;
3444 			if (!(flags & TO_SYN))
3445 				continue;
3446 			to->to_flags |= TOF_MSS;
3447 			bcopy((char *)cp + 2,
3448 			    (char *)&to->to_mss, sizeof(to->to_mss));
3449 			to->to_mss = ntohs(to->to_mss);
3450 			break;
3451 		case TCPOPT_WINDOW:
3452 			if (optlen != TCPOLEN_WINDOW)
3453 				continue;
3454 			if (!(flags & TO_SYN))
3455 				continue;
3456 			to->to_flags |= TOF_SCALE;
3457 			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3458 			break;
3459 		case TCPOPT_TIMESTAMP:
3460 			if (optlen != TCPOLEN_TIMESTAMP)
3461 				continue;
3462 			to->to_flags |= TOF_TS;
3463 			bcopy((char *)cp + 2,
3464 			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3465 			to->to_tsval = ntohl(to->to_tsval);
3466 			bcopy((char *)cp + 6,
3467 			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3468 			to->to_tsecr = ntohl(to->to_tsecr);
3469 			break;
3470 		case TCPOPT_SIGNATURE:
3471 			/*
3472 			 * In order to reply to a host which has set the
3473 			 * TCP_SIGNATURE option in its initial SYN, we have
3474 			 * to record the fact that the option was observed
3475 			 * here for the syncache code to perform the correct
3476 			 * response.
3477 			 */
3478 			if (optlen != TCPOLEN_SIGNATURE)
3479 				continue;
3480 			to->to_flags |= TOF_SIGNATURE;
3481 			to->to_signature = cp + 2;
3482 			break;
3483 		case TCPOPT_SACK_PERMITTED:
3484 			if (optlen != TCPOLEN_SACK_PERMITTED)
3485 				continue;
3486 			if (!(flags & TO_SYN))
3487 				continue;
3488 			if (!V_tcp_do_sack)
3489 				continue;
3490 			to->to_flags |= TOF_SACKPERM;
3491 			break;
3492 		case TCPOPT_SACK:
3493 			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3494 				continue;
3495 			if (flags & TO_SYN)
3496 				continue;
3497 			to->to_flags |= TOF_SACK;
3498 			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3499 			to->to_sacks = cp + 2;
3500 			TCPSTAT_INC(tcps_sack_rcv_blocks);
3501 			break;
3502 		case TCPOPT_FAST_OPEN:
3503 			/*
3504 			 * Cookie length validation is performed by the
3505 			 * server side cookie checking code or the client
3506 			 * side cookie cache update code.
3507 			 */
3508 			if (!(flags & TO_SYN))
3509 				continue;
3510 			if (!V_tcp_fastopen_client_enable &&
3511 			    !V_tcp_fastopen_server_enable)
3512 				continue;
3513 			to->to_flags |= TOF_FASTOPEN;
3514 			to->to_tfo_len = optlen - 2;
3515 			to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
3516 			break;
3517 		default:
3518 			continue;
3519 		}
3520 	}
3521 }
3522 
3523 /*
3524  * Pull out of band byte out of a segment so
3525  * it doesn't appear in the user's data queue.
3526  * It is still reflected in the segment length for
3527  * sequencing purposes.
3528  */
3529 void
3530 tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3531     int off)
3532 {
3533 	int cnt = off + th->th_urp - 1;
3534 
3535 	while (cnt >= 0) {
3536 		if (m->m_len > cnt) {
3537 			char *cp = mtod(m, caddr_t) + cnt;
3538 			struct tcpcb *tp = sototcpcb(so);
3539 
3540 			INP_WLOCK_ASSERT(tp->t_inpcb);
3541 
3542 			tp->t_iobc = *cp;
3543 			tp->t_oobflags |= TCPOOB_HAVEDATA;
3544 			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3545 			m->m_len--;
3546 			if (m->m_flags & M_PKTHDR)
3547 				m->m_pkthdr.len--;
3548 			return;
3549 		}
3550 		cnt -= m->m_len;
3551 		m = m->m_next;
3552 		if (m == NULL)
3553 			break;
3554 	}
3555 	panic("tcp_pulloutofband");
3556 }
3557 
3558 /*
3559  * Collect new round-trip time estimate
3560  * and update averages and current timeout.
3561  */
3562 void
3563 tcp_xmit_timer(struct tcpcb *tp, int rtt)
3564 {
3565 	int delta;
3566 
3567 	INP_WLOCK_ASSERT(tp->t_inpcb);
3568 
3569 	TCPSTAT_INC(tcps_rttupdated);
3570 	tp->t_rttupdated++;
3571 #ifdef STATS
3572 	stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT,
3573 	    imax(0, rtt * 1000 / hz));
3574 #endif
3575 	if ((tp->t_srtt != 0) && (tp->t_rxtshift <= TCP_RTT_INVALIDATE)) {
3576 		/*
3577 		 * srtt is stored as fixed point with 5 bits after the
3578 		 * binary point (i.e., scaled by 8).  The following magic
3579 		 * is equivalent to the smoothing algorithm in rfc793 with
3580 		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3581 		 * point).  Adjust rtt to origin 0.
3582 		 */
3583 		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3584 			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3585 
3586 		if ((tp->t_srtt += delta) <= 0)
3587 			tp->t_srtt = 1;
3588 
3589 		/*
3590 		 * We accumulate a smoothed rtt variance (actually, a
3591 		 * smoothed mean difference), then set the retransmit
3592 		 * timer to smoothed rtt + 4 times the smoothed variance.
3593 		 * rttvar is stored as fixed point with 4 bits after the
3594 		 * binary point (scaled by 16).  The following is
3595 		 * equivalent to rfc793 smoothing with an alpha of .75
3596 		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3597 		 * rfc793's wired-in beta.
3598 		 */
3599 		if (delta < 0)
3600 			delta = -delta;
3601 		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3602 		if ((tp->t_rttvar += delta) <= 0)
3603 			tp->t_rttvar = 1;
3604 		if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
3605 		    tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3606 	} else {
3607 		/*
3608 		 * No rtt measurement yet - use the unsmoothed rtt.
3609 		 * Set the variance to half the rtt (so our first
3610 		 * retransmit happens at 3*rtt).
3611 		 */
3612 		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3613 		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3614 		tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
3615 	}
3616 	tp->t_rtttime = 0;
3617 	tp->t_rxtshift = 0;
3618 
3619 	/*
3620 	 * the retransmit should happen at rtt + 4 * rttvar.
3621 	 * Because of the way we do the smoothing, srtt and rttvar
3622 	 * will each average +1/2 tick of bias.  When we compute
3623 	 * the retransmit timer, we want 1/2 tick of rounding and
3624 	 * 1 extra tick because of +-1/2 tick uncertainty in the
3625 	 * firing of the timer.  The bias will give us exactly the
3626 	 * 1.5 tick we need.  But, because the bias is
3627 	 * statistical, we have to test that we don't drop below
3628 	 * the minimum feasible timer (which is 2 ticks).
3629 	 */
3630 	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3631 		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3632 
3633 	/*
3634 	 * We received an ack for a packet that wasn't retransmitted;
3635 	 * it is probably safe to discard any error indications we've
3636 	 * received recently.  This isn't quite right, but close enough
3637 	 * for now (a route might have failed after we sent a segment,
3638 	 * and the return path might not be symmetrical).
3639 	 */
3640 	tp->t_softerror = 0;
3641 }
3642 
3643 /*
3644  * Determine a reasonable value for maxseg size.
3645  * If the route is known, check route for mtu.
3646  * If none, use an mss that can be handled on the outgoing interface
3647  * without forcing IP to fragment.  If no route is found, route has no mtu,
3648  * or the destination isn't local, use a default, hopefully conservative
3649  * size (usually 512 or the default IP max size, but no more than the mtu
3650  * of the interface), as we can't discover anything about intervening
3651  * gateways or networks.  We also initialize the congestion/slow start
3652  * window to be a single segment if the destination isn't local.
3653  * While looking at the routing entry, we also initialize other path-dependent
3654  * parameters from pre-set or cached values in the routing entry.
3655  *
3656  * NOTE that resulting t_maxseg doesn't include space for TCP options or
3657  * IP options, e.g. IPSEC data, since length of this data may vary, and
3658  * thus it is calculated for every segment separately in tcp_output().
3659  *
3660  * NOTE that this routine is only called when we process an incoming
3661  * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3662  * settings are handled in tcp_mssopt().
3663  */
3664 void
3665 tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3666     struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3667 {
3668 	int mss = 0;
3669 	uint32_t maxmtu = 0;
3670 	struct inpcb *inp = tp->t_inpcb;
3671 	struct hc_metrics_lite metrics;
3672 #ifdef INET6
3673 	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3674 	size_t min_protoh = isipv6 ?
3675 			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3676 			    sizeof (struct tcpiphdr);
3677 #else
3678 	 size_t min_protoh = sizeof(struct tcpiphdr);
3679 #endif
3680 
3681 	INP_WLOCK_ASSERT(tp->t_inpcb);
3682 
3683 	if (tp->t_port)
3684 		min_protoh += V_tcp_udp_tunneling_overhead;
3685 	if (mtuoffer != -1) {
3686 		KASSERT(offer == -1, ("%s: conflict", __func__));
3687 		offer = mtuoffer - min_protoh;
3688 	}
3689 
3690 	/* Initialize. */
3691 #ifdef INET6
3692 	if (isipv6) {
3693 		maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3694 		tp->t_maxseg = V_tcp_v6mssdflt;
3695 	}
3696 #endif
3697 #if defined(INET) && defined(INET6)
3698 	else
3699 #endif
3700 #ifdef INET
3701 	{
3702 		maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3703 		tp->t_maxseg = V_tcp_mssdflt;
3704 	}
3705 #endif
3706 
3707 	/*
3708 	 * No route to sender, stay with default mss and return.
3709 	 */
3710 	if (maxmtu == 0) {
3711 		/*
3712 		 * In case we return early we need to initialize metrics
3713 		 * to a defined state as tcp_hc_get() would do for us
3714 		 * if there was no cache hit.
3715 		 */
3716 		if (metricptr != NULL)
3717 			bzero(metricptr, sizeof(struct hc_metrics_lite));
3718 		return;
3719 	}
3720 
3721 	/* What have we got? */
3722 	switch (offer) {
3723 		case 0:
3724 			/*
3725 			 * Offer == 0 means that there was no MSS on the SYN
3726 			 * segment, in this case we use tcp_mssdflt as
3727 			 * already assigned to t_maxseg above.
3728 			 */
3729 			offer = tp->t_maxseg;
3730 			break;
3731 
3732 		case -1:
3733 			/*
3734 			 * Offer == -1 means that we didn't receive SYN yet.
3735 			 */
3736 			/* FALLTHROUGH */
3737 
3738 		default:
3739 			/*
3740 			 * Prevent DoS attack with too small MSS. Round up
3741 			 * to at least minmss.
3742 			 */
3743 			offer = max(offer, V_tcp_minmss);
3744 	}
3745 
3746 	/*
3747 	 * rmx information is now retrieved from tcp_hostcache.
3748 	 */
3749 	tcp_hc_get(&inp->inp_inc, &metrics);
3750 	if (metricptr != NULL)
3751 		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3752 
3753 	/*
3754 	 * If there's a discovered mtu in tcp hostcache, use it.
3755 	 * Else, use the link mtu.
3756 	 */
3757 	if (metrics.rmx_mtu)
3758 		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3759 	else {
3760 #ifdef INET6
3761 		if (isipv6) {
3762 			mss = maxmtu - min_protoh;
3763 			if (!V_path_mtu_discovery &&
3764 			    !in6_localaddr(&inp->in6p_faddr))
3765 				mss = min(mss, V_tcp_v6mssdflt);
3766 		}
3767 #endif
3768 #if defined(INET) && defined(INET6)
3769 		else
3770 #endif
3771 #ifdef INET
3772 		{
3773 			mss = maxmtu - min_protoh;
3774 			if (!V_path_mtu_discovery &&
3775 			    !in_localaddr(inp->inp_faddr))
3776 				mss = min(mss, V_tcp_mssdflt);
3777 		}
3778 #endif
3779 		/*
3780 		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3781 		 * probably violates the TCP spec.
3782 		 * The problem is that, since we don't know the
3783 		 * other end's MSS, we are supposed to use a conservative
3784 		 * default.  But, if we do that, then MTU discovery will
3785 		 * never actually take place, because the conservative
3786 		 * default is much less than the MTUs typically seen
3787 		 * on the Internet today.  For the moment, we'll sweep
3788 		 * this under the carpet.
3789 		 *
3790 		 * The conservative default might not actually be a problem
3791 		 * if the only case this occurs is when sending an initial
3792 		 * SYN with options and data to a host we've never talked
3793 		 * to before.  Then, they will reply with an MSS value which
3794 		 * will get recorded and the new parameters should get
3795 		 * recomputed.  For Further Study.
3796 		 */
3797 	}
3798 	mss = min(mss, offer);
3799 
3800 	/*
3801 	 * Sanity check: make sure that maxseg will be large
3802 	 * enough to allow some data on segments even if the
3803 	 * all the option space is used (40bytes).  Otherwise
3804 	 * funny things may happen in tcp_output.
3805 	 *
3806 	 * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3807 	 */
3808 	mss = max(mss, 64);
3809 
3810 	tp->t_maxseg = mss;
3811 }
3812 
3813 void
3814 tcp_mss(struct tcpcb *tp, int offer)
3815 {
3816 	int mss;
3817 	uint32_t bufsize;
3818 	struct inpcb *inp;
3819 	struct socket *so;
3820 	struct hc_metrics_lite metrics;
3821 	struct tcp_ifcap cap;
3822 
3823 	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3824 
3825 	bzero(&cap, sizeof(cap));
3826 	tcp_mss_update(tp, offer, -1, &metrics, &cap);
3827 
3828 	mss = tp->t_maxseg;
3829 	inp = tp->t_inpcb;
3830 
3831 	/*
3832 	 * If there's a pipesize, change the socket buffer to that size,
3833 	 * don't change if sb_hiwat is different than default (then it
3834 	 * has been changed on purpose with setsockopt).
3835 	 * Make the socket buffers an integral number of mss units;
3836 	 * if the mss is larger than the socket buffer, decrease the mss.
3837 	 */
3838 	so = inp->inp_socket;
3839 	SOCKBUF_LOCK(&so->so_snd);
3840 	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3841 		bufsize = metrics.rmx_sendpipe;
3842 	else
3843 		bufsize = so->so_snd.sb_hiwat;
3844 	if (bufsize < mss)
3845 		mss = bufsize;
3846 	else {
3847 		bufsize = roundup(bufsize, mss);
3848 		if (bufsize > sb_max)
3849 			bufsize = sb_max;
3850 		if (bufsize > so->so_snd.sb_hiwat)
3851 			(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
3852 	}
3853 	SOCKBUF_UNLOCK(&so->so_snd);
3854 	/*
3855 	 * Sanity check: make sure that maxseg will be large
3856 	 * enough to allow some data on segments even if the
3857 	 * all the option space is used (40bytes).  Otherwise
3858 	 * funny things may happen in tcp_output.
3859 	 *
3860 	 * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3861 	 */
3862 	tp->t_maxseg = max(mss, 64);
3863 
3864 	SOCKBUF_LOCK(&so->so_rcv);
3865 	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3866 		bufsize = metrics.rmx_recvpipe;
3867 	else
3868 		bufsize = so->so_rcv.sb_hiwat;
3869 	if (bufsize > mss) {
3870 		bufsize = roundup(bufsize, mss);
3871 		if (bufsize > sb_max)
3872 			bufsize = sb_max;
3873 		if (bufsize > so->so_rcv.sb_hiwat)
3874 			(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
3875 	}
3876 	SOCKBUF_UNLOCK(&so->so_rcv);
3877 
3878 	/* Check the interface for TSO capabilities. */
3879 	if (cap.ifcap & CSUM_TSO) {
3880 		tp->t_flags |= TF_TSO;
3881 		tp->t_tsomax = cap.tsomax;
3882 		tp->t_tsomaxsegcount = cap.tsomaxsegcount;
3883 		tp->t_tsomaxsegsize = cap.tsomaxsegsize;
3884 	}
3885 }
3886 
3887 /*
3888  * Determine the MSS option to send on an outgoing SYN.
3889  */
3890 int
3891 tcp_mssopt(struct in_conninfo *inc)
3892 {
3893 	int mss = 0;
3894 	uint32_t thcmtu = 0;
3895 	uint32_t maxmtu = 0;
3896 	size_t min_protoh;
3897 
3898 	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3899 
3900 #ifdef INET6
3901 	if (inc->inc_flags & INC_ISIPV6) {
3902 		mss = V_tcp_v6mssdflt;
3903 		maxmtu = tcp_maxmtu6(inc, NULL);
3904 		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3905 	}
3906 #endif
3907 #if defined(INET) && defined(INET6)
3908 	else
3909 #endif
3910 #ifdef INET
3911 	{
3912 		mss = V_tcp_mssdflt;
3913 		maxmtu = tcp_maxmtu(inc, NULL);
3914 		min_protoh = sizeof(struct tcpiphdr);
3915 	}
3916 #endif
3917 #if defined(INET6) || defined(INET)
3918 	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3919 #endif
3920 
3921 	if (maxmtu && thcmtu)
3922 		mss = min(maxmtu, thcmtu) - min_protoh;
3923 	else if (maxmtu || thcmtu)
3924 		mss = max(maxmtu, thcmtu) - min_protoh;
3925 
3926 	return (mss);
3927 }
3928 
3929 void
3930 tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
3931 {
3932 	int snd_cnt = 0, limit = 0, del_data = 0, pipe = 0;
3933 	int maxseg = tcp_maxseg(tp);
3934 
3935 	INP_WLOCK_ASSERT(tp->t_inpcb);
3936 
3937 	/*
3938 	 * Compute the amount of data that this ACK is indicating
3939 	 * (del_data) and an estimate of how many bytes are in the
3940 	 * network.
3941 	 */
3942 	if (((tp->t_flags & TF_SACK_PERMIT) &&
3943 	    (to->to_flags & TOF_SACK)) ||
3944 	    (IN_CONGRECOVERY(tp->t_flags) &&
3945 	     !IN_FASTRECOVERY(tp->t_flags))) {
3946 		del_data = tp->sackhint.delivered_data;
3947 		if (V_tcp_do_newsack)
3948 			pipe = tcp_compute_pipe(tp);
3949 		else
3950 			pipe = (tp->snd_nxt - tp->snd_fack) +
3951 				tp->sackhint.sack_bytes_rexmit;
3952 	} else {
3953 		if (tp->sackhint.prr_delivered < (tcprexmtthresh * maxseg +
3954 					     tp->snd_recover - tp->snd_una))
3955 			del_data = maxseg;
3956 		pipe = imax(0, tp->snd_max - tp->snd_una -
3957 			    imin(INT_MAX / 65536, tp->t_dupacks) * maxseg);
3958 	}
3959 	tp->sackhint.prr_delivered += del_data;
3960 	/*
3961 	 * Proportional Rate Reduction
3962 	 */
3963 	if (pipe >= tp->snd_ssthresh) {
3964 		if (tp->sackhint.recover_fs == 0)
3965 			tp->sackhint.recover_fs =
3966 			    imax(1, tp->snd_nxt - tp->snd_una);
3967 		snd_cnt = howmany((long)tp->sackhint.prr_delivered *
3968 			    tp->snd_ssthresh, tp->sackhint.recover_fs) -
3969 			    tp->sackhint.prr_out;
3970 	} else {
3971 		if (V_tcp_do_prr_conservative || (del_data == 0))
3972 			limit = tp->sackhint.prr_delivered -
3973 				tp->sackhint.prr_out;
3974 		else
3975 			limit = imax(tp->sackhint.prr_delivered -
3976 				    tp->sackhint.prr_out, del_data) +
3977 				    maxseg;
3978 		snd_cnt = imin((tp->snd_ssthresh - pipe), limit);
3979 	}
3980 	snd_cnt = imax(snd_cnt, 0) / maxseg;
3981 	/*
3982 	 * Send snd_cnt new data into the network in response to this ack.
3983 	 * If there is going to be a SACK retransmission, adjust snd_cwnd
3984 	 * accordingly.
3985 	 */
3986 	if (IN_FASTRECOVERY(tp->t_flags)) {
3987 		if ((tp->t_flags & TF_SACK_PERMIT) &&
3988 		    (to->to_flags & TOF_SACK)) {
3989 			tp->snd_cwnd = tp->snd_nxt - tp->snd_recover +
3990 					    tp->sackhint.sack_bytes_rexmit +
3991 					    (snd_cnt * maxseg);
3992 		} else {
3993 			tp->snd_cwnd = (tp->snd_max - tp->snd_una) +
3994 					    (snd_cnt * maxseg);
3995 		}
3996 	} else if (IN_CONGRECOVERY(tp->t_flags))
3997 		tp->snd_cwnd = pipe - del_data + (snd_cnt * maxseg);
3998 	tp->snd_cwnd = imax(maxseg, tp->snd_cwnd);
3999 }
4000 
4001 /*
4002  * On a partial ack arrives, force the retransmission of the
4003  * next unacknowledged segment.  Do not clear tp->t_dupacks.
4004  * By setting snd_nxt to ti_ack, this forces retransmission timer to
4005  * be started again.
4006  */
4007 void
4008 tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
4009 {
4010 	tcp_seq onxt = tp->snd_nxt;
4011 	uint32_t ocwnd = tp->snd_cwnd;
4012 	u_int maxseg = tcp_maxseg(tp);
4013 
4014 	INP_WLOCK_ASSERT(tp->t_inpcb);
4015 
4016 	tcp_timer_activate(tp, TT_REXMT, 0);
4017 	tp->t_rtttime = 0;
4018 	tp->snd_nxt = th->th_ack;
4019 	/*
4020 	 * Set snd_cwnd to one segment beyond acknowledged offset.
4021 	 * (tp->snd_una has not yet been updated when this function is called.)
4022 	 */
4023 	tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
4024 	tp->t_flags |= TF_ACKNOW;
4025 	(void) tcp_output(tp);
4026 	tp->snd_cwnd = ocwnd;
4027 	if (SEQ_GT(onxt, tp->snd_nxt))
4028 		tp->snd_nxt = onxt;
4029 	/*
4030 	 * Partial window deflation.  Relies on fact that tp->snd_una
4031 	 * not updated yet.
4032 	 */
4033 	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
4034 		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
4035 	else
4036 		tp->snd_cwnd = 0;
4037 	tp->snd_cwnd += maxseg;
4038 }
4039 
4040 int
4041 tcp_compute_pipe(struct tcpcb *tp)
4042 {
4043 	return (tp->snd_max - tp->snd_una +
4044 		tp->sackhint.sack_bytes_rexmit -
4045 		tp->sackhint.sacked_bytes);
4046 }
4047 
4048 uint32_t
4049 tcp_compute_initwnd(uint32_t maxseg)
4050 {
4051 	/*
4052 	 * Calculate the Initial Window, also used as Restart Window
4053 	 *
4054 	 * RFC5681 Section 3.1 specifies the default conservative values.
4055 	 * RFC3390 specifies slightly more aggressive values.
4056 	 * RFC6928 increases it to ten segments.
4057 	 * Support for user specified value for initial flight size.
4058 	 */
4059 	if (V_tcp_initcwnd_segments)
4060 		return min(V_tcp_initcwnd_segments * maxseg,
4061 		    max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
4062 	else if (V_tcp_do_rfc3390)
4063 		return min(4 * maxseg, max(2 * maxseg, 4380));
4064 	else {
4065 		/* Per RFC5681 Section 3.1 */
4066 		if (maxseg > 2190)
4067 			return (2 * maxseg);
4068 		else if (maxseg > 1095)
4069 			return (3 * maxseg);
4070 		else
4071 			return (4 * maxseg);
4072 	}
4073 }
4074