2 * SPDX-License-Identifier: BSD-3-Clause
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25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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31 * @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
38 #include "opt_inet6.h"
39 #include "opt_tcpdebug.h"
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>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
53 #include <sys/syslog.h>
55 #include <sys/protosw.h>
56 #include <sys/random.h>
60 #include <net/route.h>
62 #include <net/if_var.h>
65 #include <netinet/in.h>
66 #include <netinet/in_kdtrace.h>
67 #include <netinet/in_pcb.h>
68 #include <netinet/in_systm.h>
69 #include <netinet/in_var.h>
70 #include <netinet/ip.h>
71 #include <netinet/ip_icmp.h>
72 #include <netinet/ip_var.h>
74 #include <netinet/ip6.h>
75 #include <netinet6/in6_pcb.h>
76 #include <netinet6/ip6_var.h>
77 #include <netinet6/scope6_var.h>
78 #include <netinet6/nd6.h>
80 #include <netinet/tcp.h>
81 #include <netinet/tcp_fsm.h>
82 #include <netinet/tcp_seq.h>
83 #include <netinet/tcp_timer.h>
84 #include <netinet/tcp_var.h>
86 #include <netinet6/tcp6_var.h>
88 #include <netinet/tcpip.h>
90 #include <netinet/tcp_debug.h>
93 #include <netinet6/ip6protosw.h>
96 #include <machine/in_cksum.h>
98 #include <security/mac/mac_framework.h>
100 VNET_DEFINE_STATIC(uma_zone_t, tcptw_zone);
101 #define V_tcptw_zone VNET(tcptw_zone)
105 * The timed wait queue contains references to each of the TCP sessions
106 * currently in the TIME_WAIT state. The queue pointers, including the
107 * queue pointers in each tcptw structure, are protected using the global
108 * timewait lock, which must be held over queue iteration and modification.
110 * Rules on tcptw usage:
111 * - a inpcb is always freed _after_ its tcptw
112 * - a tcptw relies on its inpcb reference counting for memory stability
113 * - a tcptw is dereferenceable only while its inpcb is locked
115 VNET_DEFINE_STATIC(TAILQ_HEAD(, tcptw), twq_2msl);
116 #define V_twq_2msl VNET(twq_2msl)
118 /* Global timewait lock */
119 VNET_DEFINE_STATIC(struct rwlock, tw_lock);
120 #define V_tw_lock VNET(tw_lock)
122 #define TW_LOCK_INIT(tw, d) rw_init_flags(&(tw), (d), 0)
123 #define TW_LOCK_DESTROY(tw) rw_destroy(&(tw))
124 #define TW_RLOCK(tw) rw_rlock(&(tw))
125 #define TW_WLOCK(tw) rw_wlock(&(tw))
126 #define TW_RUNLOCK(tw) rw_runlock(&(tw))
127 #define TW_WUNLOCK(tw) rw_wunlock(&(tw))
128 #define TW_LOCK_ASSERT(tw) rw_assert(&(tw), RA_LOCKED)
129 #define TW_RLOCK_ASSERT(tw) rw_assert(&(tw), RA_RLOCKED)
130 #define TW_WLOCK_ASSERT(tw) rw_assert(&(tw), RA_WLOCKED)
131 #define TW_UNLOCK_ASSERT(tw) rw_assert(&(tw), RA_UNLOCKED)
133 static void tcp_tw_2msl_reset(struct tcptw *, int);
134 static void tcp_tw_2msl_stop(struct tcptw *, int);
135 static int tcp_twrespond(struct tcptw *, int);
138 tcptw_auto_size(void)
143 * Max out at half the ephemeral port range so that TIME_WAIT
144 * sockets don't tie up too many ephemeral ports.
146 if (V_ipport_lastauto > V_ipport_firstauto)
147 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
149 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
150 /* Protect against goofy port ranges smaller than 32. */
151 return (imin(imax(halfrange, 32), maxsockets / 5));
155 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
160 new = tcptw_auto_size();
163 error = sysctl_handle_int(oidp, &new, 0, req);
164 if (error == 0 && req->newptr)
167 uma_zone_set_max(V_tcptw_zone, maxtcptw);
172 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
173 &maxtcptw, 0, sysctl_maxtcptw, "IU",
174 "Maximum number of compressed TCP TIME_WAIT entries");
176 VNET_DEFINE_STATIC(int, nolocaltimewait) = 0;
177 #define V_nolocaltimewait VNET(nolocaltimewait)
178 SYSCTL_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_VNET | CTLFLAG_RW,
179 &VNET_NAME(nolocaltimewait), 0,
180 "Do not create compressed TCP TIME_WAIT entries for local connections");
183 tcp_tw_zone_change(void)
187 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
194 V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
195 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
196 TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
198 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
200 uma_zone_set_max(V_tcptw_zone, maxtcptw);
201 TAILQ_INIT(&V_twq_2msl);
202 TW_LOCK_INIT(V_tw_lock, "tcptw");
210 struct epoch_tracker et;
213 while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
217 TW_LOCK_DESTROY(V_tw_lock);
218 uma_zdestroy(V_tcptw_zone);
223 * Move a TCP connection into TIME_WAIT state.
225 * inp is locked, and is unlocked before returning.
228 tcp_twstart(struct tcpcb *tp)
230 struct tcptw twlocal, *tw;
231 struct inpcb *inp = tp->t_inpcb;
236 bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
240 INP_WLOCK_ASSERT(inp);
242 /* A dropped inp should never transition to TIME_WAIT state. */
243 KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
244 "(inp->inp_flags & INP_DROPPED) != 0"));
246 if (V_nolocaltimewait) {
249 local = in6_localaddr(&inp->in6p_faddr);
253 local = in_localip(inp->inp_faddr);
261 * For use only by DTrace. We do not reference the state
262 * after this point so modifying it in place is not a problem.
264 tcp_state_change(tp, TCPS_TIME_WAIT);
269 tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
272 * Reached limit on total number of TIMEWAIT connections
273 * allowed. Remove a connection from TIMEWAIT queue in LRU
274 * fashion to make room for this connection.
276 * XXX: Check if it possible to always have enough room
277 * in advance based on guarantees provided by uma_zalloc().
279 tw = tcp_tw_2msl_scan(1);
288 * For !local case the tcptw will hold a reference on its inpcb
289 * until tcp_twclose is called.
294 * Recover last window size sent.
296 so = inp->inp_socket;
297 recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
298 (long)TCP_MAXWIN << tp->rcv_scale);
299 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
300 recwin < tp->t_maxseg)
302 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
303 recwin < (tp->rcv_adv - tp->rcv_nxt))
304 recwin = (tp->rcv_adv - tp->rcv_nxt);
305 tw->last_win = (u_short)(recwin >> tp->rcv_scale);
308 * Set t_recent if timestamps are used on the connection.
310 if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
311 (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
312 tw->t_recent = tp->ts_recent;
313 tw->ts_offset = tp->ts_offset;
319 tw->snd_nxt = tp->snd_nxt;
320 tw->rcv_nxt = tp->rcv_nxt;
323 tw->t_starttime = tp->t_starttime;
328 * be used for fin-wait-2 state also, then we may need
329 * a ts_recent from the last segment.
331 acknow = tp->t_flags & TF_ACKNOW;
334 * First, discard tcpcb state, which includes stopping its timers and
335 * freeing it. tcp_discardcb() used to also release the inpcb, but
336 * that work is now done in the caller.
338 * Note: soisdisconnected() call used to be made in tcp_discardcb(),
339 * and might not be needed here any longer.
342 soisdisconnected(so);
343 tw->tw_so_options = so->so_options;
344 inp->inp_flags |= INP_TIMEWAIT;
346 tcp_twrespond(tw, TH_ACK);
350 in_pcbref(inp); /* Reference from tw */
351 tw->tw_cred = crhold(so->so_cred);
353 TCPSTATES_INC(TCPS_TIME_WAIT);
354 tcp_tw_2msl_reset(tw, 0);
358 * If the inpcb owns the sole reference to the socket, then we can
359 * detach and free the socket as it is not needed in time wait.
361 if (inp->inp_flags & INP_SOCKREF) {
362 KASSERT(so->so_state & SS_PROTOREF,
363 ("tcp_twstart: !SS_PROTOREF"));
364 inp->inp_flags &= ~INP_SOCKREF;
367 so->so_state &= ~SS_PROTOREF;
374 * Returns 1 if the TIME_WAIT state was killed and we should start over,
375 * looking for a pcb in the listen state. Returns 0 otherwise.
378 tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
379 struct mbuf *m, int tlen)
386 INP_WLOCK_ASSERT(inp);
389 * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
390 * still present. This is undesirable, but temporarily necessary
391 * until we work out how to handle inpcb's who's timewait state has
398 thflags = th->th_flags;
401 * NOTE: for FIN_WAIT_2 (to be added later),
402 * must validate sequence number before accepting RST
406 * If the segment contains RST:
407 * Drop the segment - see Stevens, vol. 2, p. 964 and
410 if (thflags & TH_RST)
414 /* PAWS not needed at the moment */
416 * RFC 1323 PAWS: If we have a timestamp reply on this segment
417 * and it's less than ts_recent, drop it.
419 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
420 TSTMP_LT(to.to_tsval, tp->ts_recent)) {
421 if ((thflags & TH_ACK) == 0)
426 * ts_recent is never updated because we never accept new segments.
431 * If a new connection request is received
432 * while in TIME_WAIT, drop the old connection
433 * and start over if the sequence numbers
434 * are above the previous ones.
436 if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
442 * Drop the segment if it does not contain an ACK.
444 if ((thflags & TH_ACK) == 0)
448 * Reset the 2MSL timer if this is a duplicate FIN.
450 if (thflags & TH_FIN) {
451 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
452 if (seq + 1 == tw->rcv_nxt)
453 tcp_tw_2msl_reset(tw, 1);
457 * Acknowledge the segment if it has data or is not a duplicate ACK.
459 if (thflags != TH_ACK || tlen != 0 ||
460 th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) {
461 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
462 tcp_twrespond(tw, TH_ACK);
466 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
474 tcp_twclose(struct tcptw *tw, int reuse)
480 * At this point, we are in one of two situations:
482 * (1) We have no socket, just an inpcb<->twtcp pair. We can free
485 * (2) We have a socket -- if we own a reference, release it and
486 * notify the socket layer.
489 KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
490 KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
492 INP_WLOCK_ASSERT(inp);
494 tcp_tw_2msl_stop(tw, reuse);
495 inp->inp_ppcb = NULL;
498 so = inp->inp_socket;
501 * If there's a socket, handle two cases: first, we own a
502 * strong reference, which we will now release, or we don't
503 * in which case another reference exists (XXXRW: think
504 * about this more), and we don't need to take action.
506 if (inp->inp_flags & INP_SOCKREF) {
507 inp->inp_flags &= ~INP_SOCKREF;
510 KASSERT(so->so_state & SS_PROTOREF,
511 ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
512 so->so_state &= ~SS_PROTOREF;
516 * If we don't own the only reference, the socket and
517 * inpcb need to be left around to be handled by
518 * tcp_usr_detach() later.
524 * The socket has been already cleaned-up for us, only free the
529 TCPSTAT_INC(tcps_closed);
533 tcp_twrespond(struct tcptw *tw, int flags)
535 struct inpcb *inp = tw->tw_inpcb;
536 #if defined(INET6) || defined(INET)
537 struct tcphdr *th = NULL;
541 struct ip *ip = NULL;
543 u_int hdrlen, optlen;
544 int error = 0; /* Keep compiler happy */
547 struct ip6_hdr *ip6 = NULL;
548 int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
550 hdrlen = 0; /* Keep compiler happy */
552 INP_WLOCK_ASSERT(inp);
554 m = m_gethdr(M_NOWAIT, MT_DATA);
557 m->m_data += max_linkhdr;
560 mac_inpcb_create_mbuf(inp, m);
565 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
566 ip6 = mtod(m, struct ip6_hdr *);
567 th = (struct tcphdr *)(ip6 + 1);
568 tcpip_fillheaders(inp, ip6, th);
571 #if defined(INET6) && defined(INET)
576 hdrlen = sizeof(struct tcpiphdr);
577 ip = mtod(m, struct ip *);
578 th = (struct tcphdr *)(ip + 1);
579 tcpip_fillheaders(inp, ip, th);
585 * Send a timestamp and echo-reply if both our side and our peer
586 * have sent timestamps in our SYN's and this is not a RST.
588 if (tw->t_recent && flags == TH_ACK) {
589 to.to_flags |= TOF_TS;
590 to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
591 to.to_tsecr = tw->t_recent;
593 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
595 m->m_len = hdrlen + optlen;
596 m->m_pkthdr.len = m->m_len;
598 KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
600 th->th_seq = htonl(tw->snd_nxt);
601 th->th_ack = htonl(tw->rcv_nxt);
602 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
603 th->th_flags = flags;
604 th->th_win = htons(tw->last_win);
606 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
609 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
610 th->th_sum = in6_cksum_pseudo(ip6,
611 sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
612 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
613 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th);
614 error = ip6_output(m, inp->in6p_outputopts, NULL,
615 (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
618 #if defined(INET6) && defined(INET)
623 m->m_pkthdr.csum_flags = CSUM_TCP;
624 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
625 htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
626 ip->ip_len = htons(m->m_pkthdr.len);
627 if (V_path_mtu_discovery)
628 ip->ip_off |= htons(IP_DF);
629 TCP_PROBE5(send, NULL, NULL, ip, NULL, th);
630 error = ip_output(m, inp->inp_options, NULL,
631 ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
636 TCPSTAT_INC(tcps_sndacks);
638 TCPSTAT_INC(tcps_sndctrl);
639 TCPSTAT_INC(tcps_sndtotal);
644 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
648 INP_WLOCK_ASSERT(tw->tw_inpcb);
652 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
653 tw->tw_time = ticks + 2 * tcp_msl;
654 TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
655 TW_WUNLOCK(V_tw_lock);
659 tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
663 int released __unused;
671 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
674 TW_WUNLOCK(V_tw_lock);
679 released = in_pcbrele_wlocked(inp);
680 KASSERT(!released, ("%s: inp should not be released here", __func__));
683 uma_zfree(V_tcptw_zone, tw);
684 TCPSTATES_DEC(TCPS_TIME_WAIT);
688 tcp_tw_2msl_scan(int reuse)
697 tw = TAILQ_FIRST(&V_twq_2msl);
698 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) {
699 TW_RUNLOCK(V_tw_lock);
702 KASSERT(tw->tw_inpcb != NULL, ("%s: tw->tw_inpcb == NULL",
707 TW_RUNLOCK(V_tw_lock);
711 if (in_pcbrele_wlocked(inp)) {
712 if (__predict_true(tw == NULL)) {
715 /* This should not happen as in TIMEWAIT
716 * state the inp should not be destroyed
717 * before its tcptw. If INVARIANTS is
721 panic("%s: Panic before an infinite "
722 "loop: INP_TIMEWAIT && (INP_FREED "
723 "|| inp last reference) && tw != "
726 log(LOG_ERR, "%s: Avoid an infinite "
727 "loop: INP_TIMEWAIT && (INP_FREED "
728 "|| inp last reference) && tw != "
736 /* tcp_twclose() has already been called */
741 tcp_twclose(tw, reuse);