xref: /freebsd/sys/netinet/tcp_timewait.c (revision f1951fd745b894fe6586c298874af98544a5e272)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  *
31  *	@(#)tcp_subr.c	8.2 (Berkeley) 5/24/95
32  */
33 
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36 
37 #include "opt_inet.h"
38 #include "opt_inet6.h"
39 #include "opt_tcpdebug.h"
40 
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/callout.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/malloc.h>
47 #include <sys/mbuf.h>
48 #include <sys/priv.h>
49 #include <sys/proc.h>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
52 #ifndef INVARIANTS
53 #include <sys/syslog.h>
54 #endif
55 #include <sys/protosw.h>
56 #include <sys/random.h>
57 
58 #include <vm/uma.h>
59 
60 #include <net/route.h>
61 #include <net/if.h>
62 #include <net/if_var.h>
63 #include <net/vnet.h>
64 
65 #include <netinet/in.h>
66 #include <netinet/in_pcb.h>
67 #include <netinet/in_systm.h>
68 #include <netinet/in_var.h>
69 #include <netinet/ip.h>
70 #include <netinet/ip_icmp.h>
71 #include <netinet/ip_var.h>
72 #ifdef INET6
73 #include <netinet/ip6.h>
74 #include <netinet6/in6_pcb.h>
75 #include <netinet6/ip6_var.h>
76 #include <netinet6/scope6_var.h>
77 #include <netinet6/nd6.h>
78 #endif
79 #include <netinet/tcp.h>
80 #include <netinet/tcp_fsm.h>
81 #include <netinet/tcp_seq.h>
82 #include <netinet/tcp_timer.h>
83 #include <netinet/tcp_var.h>
84 #ifdef INET6
85 #include <netinet6/tcp6_var.h>
86 #endif
87 #include <netinet/tcpip.h>
88 #ifdef TCPDEBUG
89 #include <netinet/tcp_debug.h>
90 #endif
91 #ifdef INET6
92 #include <netinet6/ip6protosw.h>
93 #endif
94 
95 #include <machine/in_cksum.h>
96 
97 #include <security/mac/mac_framework.h>
98 
99 VNET_DEFINE_STATIC(uma_zone_t, tcptw_zone);
100 #define	V_tcptw_zone		VNET(tcptw_zone)
101 static int	maxtcptw;
102 
103 /*
104  * The timed wait queue contains references to each of the TCP sessions
105  * currently in the TIME_WAIT state.  The queue pointers, including the
106  * queue pointers in each tcptw structure, are protected using the global
107  * timewait lock, which must be held over queue iteration and modification.
108  *
109  * Rules on tcptw usage:
110  *  - a inpcb is always freed _after_ its tcptw
111  *  - a tcptw relies on its inpcb reference counting for memory stability
112  *  - a tcptw is dereferenceable only while its inpcb is locked
113  */
114 VNET_DEFINE_STATIC(TAILQ_HEAD(, tcptw), twq_2msl);
115 #define	V_twq_2msl		VNET(twq_2msl)
116 
117 /* Global timewait lock */
118 VNET_DEFINE_STATIC(struct rwlock, tw_lock);
119 #define	V_tw_lock		VNET(tw_lock)
120 
121 #define	TW_LOCK_INIT(tw, d)	rw_init_flags(&(tw), (d), 0)
122 #define	TW_LOCK_DESTROY(tw)	rw_destroy(&(tw))
123 #define	TW_RLOCK(tw)		rw_rlock(&(tw))
124 #define	TW_WLOCK(tw)		rw_wlock(&(tw))
125 #define	TW_RUNLOCK(tw)		rw_runlock(&(tw))
126 #define	TW_WUNLOCK(tw)		rw_wunlock(&(tw))
127 #define	TW_LOCK_ASSERT(tw)	rw_assert(&(tw), RA_LOCKED)
128 #define	TW_RLOCK_ASSERT(tw)	rw_assert(&(tw), RA_RLOCKED)
129 #define	TW_WLOCK_ASSERT(tw)	rw_assert(&(tw), RA_WLOCKED)
130 #define	TW_UNLOCK_ASSERT(tw)	rw_assert(&(tw), RA_UNLOCKED)
131 
132 static void	tcp_tw_2msl_reset(struct tcptw *, int);
133 static void	tcp_tw_2msl_stop(struct tcptw *, int);
134 static int	tcp_twrespond(struct tcptw *, int);
135 
136 static int
137 tcptw_auto_size(void)
138 {
139 	int halfrange;
140 
141 	/*
142 	 * Max out at half the ephemeral port range so that TIME_WAIT
143 	 * sockets don't tie up too many ephemeral ports.
144 	 */
145 	if (V_ipport_lastauto > V_ipport_firstauto)
146 		halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
147 	else
148 		halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
149 	/* Protect against goofy port ranges smaller than 32. */
150 	return (imin(imax(halfrange, 32), maxsockets / 5));
151 }
152 
153 static int
154 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
155 {
156 	int error, new;
157 
158 	if (maxtcptw == 0)
159 		new = tcptw_auto_size();
160 	else
161 		new = maxtcptw;
162 	error = sysctl_handle_int(oidp, &new, 0, req);
163 	if (error == 0 && req->newptr)
164 		if (new >= 32) {
165 			maxtcptw = new;
166 			uma_zone_set_max(V_tcptw_zone, maxtcptw);
167 		}
168 	return (error);
169 }
170 
171 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
172     &maxtcptw, 0, sysctl_maxtcptw, "IU",
173     "Maximum number of compressed TCP TIME_WAIT entries");
174 
175 VNET_DEFINE_STATIC(int, nolocaltimewait) = 0;
176 #define	V_nolocaltimewait	VNET(nolocaltimewait)
177 SYSCTL_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_VNET | CTLFLAG_RW,
178     &VNET_NAME(nolocaltimewait), 0,
179     "Do not create compressed TCP TIME_WAIT entries for local connections");
180 
181 void
182 tcp_tw_zone_change(void)
183 {
184 
185 	if (maxtcptw == 0)
186 		uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
187 }
188 
189 void
190 tcp_tw_init(void)
191 {
192 
193 	V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
194 	    NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
195 	TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
196 	if (maxtcptw == 0)
197 		uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
198 	else
199 		uma_zone_set_max(V_tcptw_zone, maxtcptw);
200 	TAILQ_INIT(&V_twq_2msl);
201 	TW_LOCK_INIT(V_tw_lock, "tcptw");
202 }
203 
204 #ifdef VIMAGE
205 void
206 tcp_tw_destroy(void)
207 {
208 	struct tcptw *tw;
209 	struct epoch_tracker et;
210 
211 	INP_INFO_RLOCK_ET(&V_tcbinfo, et);
212 	while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
213 		tcp_twclose(tw, 0);
214 	INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
215 
216 	TW_LOCK_DESTROY(V_tw_lock);
217 	uma_zdestroy(V_tcptw_zone);
218 }
219 #endif
220 
221 /*
222  * Move a TCP connection into TIME_WAIT state.
223  *    tcbinfo is locked.
224  *    inp is locked, and is unlocked before returning.
225  */
226 void
227 tcp_twstart(struct tcpcb *tp)
228 {
229 	struct tcptw twlocal, *tw;
230 	struct inpcb *inp = tp->t_inpcb;
231 	struct socket *so;
232 	bool acknow, local;
233 #ifdef INET6
234 	bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
235 #endif
236 
237 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
238 	INP_WLOCK_ASSERT(inp);
239 
240 	/* A dropped inp should never transition to TIME_WAIT state. */
241 	KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
242 	    "(inp->inp_flags & INP_DROPPED) != 0"));
243 
244 	if (V_nolocaltimewait) {
245 #ifdef INET6
246 		if (isipv6)
247 			local = in6_localaddr(&inp->in6p_faddr);
248 		else
249 #endif
250 #ifdef INET
251 			local = in_localip(inp->inp_faddr);
252 #else
253 			local = false;
254 #endif
255 	} else
256 		local = false;
257 
258 	/*
259 	 * For use only by DTrace.  We do not reference the state
260 	 * after this point so modifying it in place is not a problem.
261 	 */
262 	tcp_state_change(tp, TCPS_TIME_WAIT);
263 
264 	if (local)
265 		tw = &twlocal;
266 	else
267 		tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
268 	if (tw == NULL) {
269 		/*
270 		 * Reached limit on total number of TIMEWAIT connections
271 		 * allowed. Remove a connection from TIMEWAIT queue in LRU
272 		 * fashion to make room for this connection.
273 		 *
274 		 * XXX:  Check if it possible to always have enough room
275 		 * in advance based on guarantees provided by uma_zalloc().
276 		 */
277 		tw = tcp_tw_2msl_scan(1);
278 		if (tw == NULL) {
279 			tp = tcp_close(tp);
280 			if (tp != NULL)
281 				INP_WUNLOCK(inp);
282 			return;
283 		}
284 	}
285 	/*
286 	 * For !local case the tcptw will hold a reference on its inpcb
287 	 * until tcp_twclose is called.
288 	 */
289 	tw->tw_inpcb = inp;
290 
291 	/*
292 	 * Recover last window size sent.
293 	 */
294 	if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
295 		tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
296 	else
297 		tw->last_win = 0;
298 
299 	/*
300 	 * Set t_recent if timestamps are used on the connection.
301 	 */
302 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
303 	    (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
304 		tw->t_recent = tp->ts_recent;
305 		tw->ts_offset = tp->ts_offset;
306 	} else {
307 		tw->t_recent = 0;
308 		tw->ts_offset = 0;
309 	}
310 
311 	tw->snd_nxt = tp->snd_nxt;
312 	tw->rcv_nxt = tp->rcv_nxt;
313 	tw->iss     = tp->iss;
314 	tw->irs     = tp->irs;
315 	tw->t_starttime = tp->t_starttime;
316 	tw->tw_time = 0;
317 
318 /* XXX
319  * If this code will
320  * be used for fin-wait-2 state also, then we may need
321  * a ts_recent from the last segment.
322  */
323 	acknow = tp->t_flags & TF_ACKNOW;
324 
325 	/*
326 	 * First, discard tcpcb state, which includes stopping its timers and
327 	 * freeing it.  tcp_discardcb() used to also release the inpcb, but
328 	 * that work is now done in the caller.
329 	 *
330 	 * Note: soisdisconnected() call used to be made in tcp_discardcb(),
331 	 * and might not be needed here any longer.
332 	 */
333 	tcp_discardcb(tp);
334 	so = inp->inp_socket;
335 	soisdisconnected(so);
336 	tw->tw_so_options = so->so_options;
337 	inp->inp_flags |= INP_TIMEWAIT;
338 	if (acknow)
339 		tcp_twrespond(tw, TH_ACK);
340 	if (local)
341 		in_pcbdrop(inp);
342 	else {
343 		in_pcbref(inp);	/* Reference from tw */
344 		tw->tw_cred = crhold(so->so_cred);
345 		inp->inp_ppcb = tw;
346 		TCPSTATES_INC(TCPS_TIME_WAIT);
347 		tcp_tw_2msl_reset(tw, 0);
348 	}
349 
350 	/*
351 	 * If the inpcb owns the sole reference to the socket, then we can
352 	 * detach and free the socket as it is not needed in time wait.
353 	 */
354 	if (inp->inp_flags & INP_SOCKREF) {
355 		KASSERT(so->so_state & SS_PROTOREF,
356 		    ("tcp_twstart: !SS_PROTOREF"));
357 		inp->inp_flags &= ~INP_SOCKREF;
358 		INP_WUNLOCK(inp);
359 		SOCK_LOCK(so);
360 		so->so_state &= ~SS_PROTOREF;
361 		sofree(so);
362 	} else
363 		INP_WUNLOCK(inp);
364 }
365 
366 /*
367  * Returns 1 if the TIME_WAIT state was killed and we should start over,
368  * looking for a pcb in the listen state.  Returns 0 otherwise.
369  */
370 int
371 tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
372     struct mbuf *m, int tlen)
373 {
374 	struct tcptw *tw;
375 	int thflags;
376 	tcp_seq seq;
377 
378 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
379 	INP_WLOCK_ASSERT(inp);
380 
381 	/*
382 	 * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
383 	 * still present.  This is undesirable, but temporarily necessary
384 	 * until we work out how to handle inpcb's who's timewait state has
385 	 * been removed.
386 	 */
387 	tw = intotw(inp);
388 	if (tw == NULL)
389 		goto drop;
390 
391 	thflags = th->th_flags;
392 
393 	/*
394 	 * NOTE: for FIN_WAIT_2 (to be added later),
395 	 * must validate sequence number before accepting RST
396 	 */
397 
398 	/*
399 	 * If the segment contains RST:
400 	 *	Drop the segment - see Stevens, vol. 2, p. 964 and
401 	 *      RFC 1337.
402 	 */
403 	if (thflags & TH_RST)
404 		goto drop;
405 
406 #if 0
407 /* PAWS not needed at the moment */
408 	/*
409 	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
410 	 * and it's less than ts_recent, drop it.
411 	 */
412 	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
413 	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
414 		if ((thflags & TH_ACK) == 0)
415 			goto drop;
416 		goto ack;
417 	}
418 	/*
419 	 * ts_recent is never updated because we never accept new segments.
420 	 */
421 #endif
422 
423 	/*
424 	 * If a new connection request is received
425 	 * while in TIME_WAIT, drop the old connection
426 	 * and start over if the sequence numbers
427 	 * are above the previous ones.
428 	 */
429 	if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
430 		tcp_twclose(tw, 0);
431 		return (1);
432 	}
433 
434 	/*
435 	 * Drop the segment if it does not contain an ACK.
436 	 */
437 	if ((thflags & TH_ACK) == 0)
438 		goto drop;
439 
440 	/*
441 	 * Reset the 2MSL timer if this is a duplicate FIN.
442 	 */
443 	if (thflags & TH_FIN) {
444 		seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
445 		if (seq + 1 == tw->rcv_nxt)
446 			tcp_tw_2msl_reset(tw, 1);
447 	}
448 
449 	/*
450 	 * Acknowledge the segment if it has data or is not a duplicate ACK.
451 	 */
452 	if (thflags != TH_ACK || tlen != 0 ||
453 	    th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
454 		tcp_twrespond(tw, TH_ACK);
455 drop:
456 	INP_WUNLOCK(inp);
457 	m_freem(m);
458 	return (0);
459 }
460 
461 void
462 tcp_twclose(struct tcptw *tw, int reuse)
463 {
464 	struct socket *so;
465 	struct inpcb *inp;
466 
467 	/*
468 	 * At this point, we are in one of two situations:
469 	 *
470 	 * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
471 	 *     all state.
472 	 *
473 	 * (2) We have a socket -- if we own a reference, release it and
474 	 *     notify the socket layer.
475 	 */
476 	inp = tw->tw_inpcb;
477 	KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
478 	KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
479 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);	/* in_pcbfree() */
480 	INP_WLOCK_ASSERT(inp);
481 
482 	tcp_tw_2msl_stop(tw, reuse);
483 	inp->inp_ppcb = NULL;
484 	in_pcbdrop(inp);
485 
486 	so = inp->inp_socket;
487 	if (so != NULL) {
488 		/*
489 		 * If there's a socket, handle two cases: first, we own a
490 		 * strong reference, which we will now release, or we don't
491 		 * in which case another reference exists (XXXRW: think
492 		 * about this more), and we don't need to take action.
493 		 */
494 		if (inp->inp_flags & INP_SOCKREF) {
495 			inp->inp_flags &= ~INP_SOCKREF;
496 			INP_WUNLOCK(inp);
497 			SOCK_LOCK(so);
498 			KASSERT(so->so_state & SS_PROTOREF,
499 			    ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
500 			so->so_state &= ~SS_PROTOREF;
501 			sofree(so);
502 		} else {
503 			/*
504 			 * If we don't own the only reference, the socket and
505 			 * inpcb need to be left around to be handled by
506 			 * tcp_usr_detach() later.
507 			 */
508 			INP_WUNLOCK(inp);
509 		}
510 	} else {
511 		/*
512 		 * The socket has been already cleaned-up for us, only free the
513 		 * inpcb.
514 		 */
515 		in_pcbfree(inp);
516 	}
517 	TCPSTAT_INC(tcps_closed);
518 }
519 
520 static int
521 tcp_twrespond(struct tcptw *tw, int flags)
522 {
523 	struct inpcb *inp = tw->tw_inpcb;
524 #if defined(INET6) || defined(INET)
525 	struct tcphdr *th = NULL;
526 #endif
527 	struct mbuf *m;
528 #ifdef INET
529 	struct ip *ip = NULL;
530 #endif
531 	u_int hdrlen, optlen;
532 	int error = 0;			/* Keep compiler happy */
533 	struct tcpopt to;
534 #ifdef INET6
535 	struct ip6_hdr *ip6 = NULL;
536 	int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
537 #endif
538 	hdrlen = 0;                     /* Keep compiler happy */
539 
540 	INP_WLOCK_ASSERT(inp);
541 
542 	m = m_gethdr(M_NOWAIT, MT_DATA);
543 	if (m == NULL)
544 		return (ENOBUFS);
545 	m->m_data += max_linkhdr;
546 
547 #ifdef MAC
548 	mac_inpcb_create_mbuf(inp, m);
549 #endif
550 
551 #ifdef INET6
552 	if (isipv6) {
553 		hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
554 		ip6 = mtod(m, struct ip6_hdr *);
555 		th = (struct tcphdr *)(ip6 + 1);
556 		tcpip_fillheaders(inp, ip6, th);
557 	}
558 #endif
559 #if defined(INET6) && defined(INET)
560 	else
561 #endif
562 #ifdef INET
563 	{
564 		hdrlen = sizeof(struct tcpiphdr);
565 		ip = mtod(m, struct ip *);
566 		th = (struct tcphdr *)(ip + 1);
567 		tcpip_fillheaders(inp, ip, th);
568 	}
569 #endif
570 	to.to_flags = 0;
571 
572 	/*
573 	 * Send a timestamp and echo-reply if both our side and our peer
574 	 * have sent timestamps in our SYN's and this is not a RST.
575 	 */
576 	if (tw->t_recent && flags == TH_ACK) {
577 		to.to_flags |= TOF_TS;
578 		to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
579 		to.to_tsecr = tw->t_recent;
580 	}
581 	optlen = tcp_addoptions(&to, (u_char *)(th + 1));
582 
583 	m->m_len = hdrlen + optlen;
584 	m->m_pkthdr.len = m->m_len;
585 
586 	KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
587 
588 	th->th_seq = htonl(tw->snd_nxt);
589 	th->th_ack = htonl(tw->rcv_nxt);
590 	th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
591 	th->th_flags = flags;
592 	th->th_win = htons(tw->last_win);
593 
594 	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
595 #ifdef INET6
596 	if (isipv6) {
597 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
598 		th->th_sum = in6_cksum_pseudo(ip6,
599 		    sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
600 		ip6->ip6_hlim = in6_selecthlim(inp, NULL);
601 		error = ip6_output(m, inp->in6p_outputopts, NULL,
602 		    (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
603 	}
604 #endif
605 #if defined(INET6) && defined(INET)
606 	else
607 #endif
608 #ifdef INET
609 	{
610 		m->m_pkthdr.csum_flags = CSUM_TCP;
611 		th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
612 		    htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
613 		ip->ip_len = htons(m->m_pkthdr.len);
614 		if (V_path_mtu_discovery)
615 			ip->ip_off |= htons(IP_DF);
616 		error = ip_output(m, inp->inp_options, NULL,
617 		    ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
618 		    NULL, inp);
619 	}
620 #endif
621 	if (flags & TH_ACK)
622 		TCPSTAT_INC(tcps_sndacks);
623 	else
624 		TCPSTAT_INC(tcps_sndctrl);
625 	TCPSTAT_INC(tcps_sndtotal);
626 	return (error);
627 }
628 
629 static void
630 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
631 {
632 
633 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
634 	INP_WLOCK_ASSERT(tw->tw_inpcb);
635 
636 	TW_WLOCK(V_tw_lock);
637 	if (rearm)
638 		TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
639 	tw->tw_time = ticks + 2 * tcp_msl;
640 	TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
641 	TW_WUNLOCK(V_tw_lock);
642 }
643 
644 static void
645 tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
646 {
647 	struct ucred *cred;
648 	struct inpcb *inp;
649 	int released __unused;
650 
651 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
652 
653 	TW_WLOCK(V_tw_lock);
654 	inp = tw->tw_inpcb;
655 	tw->tw_inpcb = NULL;
656 
657 	TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
658 	cred = tw->tw_cred;
659 	tw->tw_cred = NULL;
660 	TW_WUNLOCK(V_tw_lock);
661 
662 	if (cred != NULL)
663 		crfree(cred);
664 
665 	released = in_pcbrele_wlocked(inp);
666 	KASSERT(!released, ("%s: inp should not be released here", __func__));
667 
668 	if (!reuse)
669 		uma_zfree(V_tcptw_zone, tw);
670 	TCPSTATES_DEC(TCPS_TIME_WAIT);
671 }
672 
673 struct tcptw *
674 tcp_tw_2msl_scan(int reuse)
675 {
676 	struct tcptw *tw;
677 	struct inpcb *inp;
678 	struct epoch_tracker et;
679 
680 #ifdef INVARIANTS
681 	if (reuse) {
682 		/*
683 		 * Exclusive pcbinfo lock is not required in reuse case even if
684 		 * two inpcb locks can be acquired simultaneously:
685 		 *  - the inpcb transitioning to TIME_WAIT state in
686 		 *    tcp_tw_start(),
687 		 *  - the inpcb closed by tcp_twclose().
688 		 *
689 		 * It is because only inpcbs in FIN_WAIT2 or CLOSING states can
690 		 * transition in TIME_WAIT state.  Then a pcbcb cannot be in
691 		 * TIME_WAIT list and transitioning to TIME_WAIT state at same
692 		 * time.
693 		 */
694 		INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
695 	}
696 #endif
697 
698 	for (;;) {
699 		TW_RLOCK(V_tw_lock);
700 		tw = TAILQ_FIRST(&V_twq_2msl);
701 		if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) {
702 			TW_RUNLOCK(V_tw_lock);
703 			break;
704 		}
705 		KASSERT(tw->tw_inpcb != NULL, ("%s: tw->tw_inpcb == NULL",
706 		    __func__));
707 
708 		inp = tw->tw_inpcb;
709 		in_pcbref(inp);
710 		TW_RUNLOCK(V_tw_lock);
711 
712 		INP_INFO_RLOCK_ET(&V_tcbinfo, et);
713 		INP_WLOCK(inp);
714 		tw = intotw(inp);
715 		if (in_pcbrele_wlocked(inp)) {
716 			if (__predict_true(tw == NULL)) {
717 				INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
718 				continue;
719 			} else {
720 				/* This should not happen as in TIMEWAIT
721 				 * state the inp should not be destroyed
722 				 * before its tcptw. If INVARIANTS is
723 				 * defined panic.
724 				 */
725 #ifdef INVARIANTS
726 				panic("%s: Panic before an infinite "
727 					  "loop: INP_TIMEWAIT && (INP_FREED "
728 					  "|| inp last reference) && tw != "
729 					  "NULL", __func__);
730 #else
731 				log(LOG_ERR, "%s: Avoid an infinite "
732 					"loop: INP_TIMEWAIT && (INP_FREED "
733 					"|| inp last reference) && tw != "
734 					"NULL", __func__);
735 #endif
736 				INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
737 				break;
738 			}
739 		}
740 
741 		if (tw == NULL) {
742 			/* tcp_twclose() has already been called */
743 			INP_WUNLOCK(inp);
744 			INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
745 			continue;
746 		}
747 
748 		tcp_twclose(tw, reuse);
749 		INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
750 		if (reuse)
751 			return tw;
752 	}
753 
754 	return NULL;
755 }
756