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freebsd/sys/netinet/tcp_syncache.c
Jeffrey Hsu a12569ec4f Drop Giant around syncache timer processing.
2003-07-17 11:19:25 +00:00

1402 lines
37 KiB
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/*-
* Copyright (c) 2001 Networks Associates Technology, Inc.
* All rights reserved.
*
* This software was developed for the FreeBSD Project by Jonathan Lemon
* and NAI Labs, the Security Research Division of Network Associates, Inc.
* under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
* DARPA CHATS research program.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_mac.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mac.h>
#include <sys/mbuf.h>
#include <sys/md5.h>
#include <sys/proc.h> /* for proc0 declaration */
#include <sys/random.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <net/if.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_var.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#ifdef INET6
#include <netinet6/tcp6_var.h>
#endif
#ifdef IPSEC
#include <netinet6/ipsec.h>
#ifdef INET6
#include <netinet6/ipsec6.h>
#endif
#endif /*IPSEC*/
#ifdef FAST_IPSEC
#include <netipsec/ipsec.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#include <netipsec/key.h>
#define IPSEC
#endif /*FAST_IPSEC*/
#include <machine/in_cksum.h>
#include <vm/uma.h>
static int tcp_syncookies = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
&tcp_syncookies, 0,
"Use TCP SYN cookies if the syncache overflows");
static void syncache_drop(struct syncache *, struct syncache_head *);
static void syncache_free(struct syncache *);
static void syncache_insert(struct syncache *, struct syncache_head *);
struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
static int syncache_respond(struct syncache *, struct mbuf *);
static struct socket *syncache_socket(struct syncache *, struct socket *,
struct mbuf *m);
static void syncache_timer(void *);
static u_int32_t syncookie_generate(struct syncache *);
static struct syncache *syncookie_lookup(struct in_conninfo *,
struct tcphdr *, struct socket *);
/*
* Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
* 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
* the odds are that the user has given up attempting to connect by then.
*/
#define SYNCACHE_MAXREXMTS 3
/* Arbitrary values */
#define TCP_SYNCACHE_HASHSIZE 512
#define TCP_SYNCACHE_BUCKETLIMIT 30
struct tcp_syncache {
struct syncache_head *hashbase;
uma_zone_t zone;
u_int hashsize;
u_int hashmask;
u_int bucket_limit;
u_int cache_count;
u_int cache_limit;
u_int rexmt_limit;
u_int hash_secret;
u_int next_reseed;
TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1];
struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1];
};
static struct tcp_syncache tcp_syncache;
SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD,
&tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD,
&tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
&tcp_syncache.cache_count, 0, "Current number of entries in syncache");
SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD,
&tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
&tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
#define SYNCACHE_HASH(inc, mask) \
((tcp_syncache.hash_secret ^ \
(inc)->inc_faddr.s_addr ^ \
((inc)->inc_faddr.s_addr >> 16) ^ \
(inc)->inc_fport ^ (inc)->inc_lport) & mask)
#define SYNCACHE_HASH6(inc, mask) \
((tcp_syncache.hash_secret ^ \
(inc)->inc6_faddr.s6_addr32[0] ^ \
(inc)->inc6_faddr.s6_addr32[3] ^ \
(inc)->inc_fport ^ (inc)->inc_lport) & mask)
#define ENDPTS_EQ(a, b) ( \
(a)->ie_fport == (b)->ie_fport && \
(a)->ie_lport == (b)->ie_lport && \
(a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
(a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
)
#define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
#define SYNCACHE_TIMEOUT(sc, slot) do { \
sc->sc_rxtslot = (slot); \
sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[(slot)]; \
TAILQ_INSERT_TAIL(&tcp_syncache.timerq[(slot)], sc, sc_timerq); \
if (!callout_active(&tcp_syncache.tt_timerq[(slot)])) \
callout_reset(&tcp_syncache.tt_timerq[(slot)], \
TCPTV_RTOBASE * tcp_backoff[(slot)], \
syncache_timer, (void *)((intptr_t)(slot))); \
} while (0)
static void
syncache_free(struct syncache *sc)
{
struct rtentry *rt;
if (sc->sc_ipopts)
(void) m_free(sc->sc_ipopts);
#ifdef INET6
if (sc->sc_inc.inc_isipv6)
rt = sc->sc_route6.ro_rt;
else
#endif
rt = sc->sc_route.ro_rt;
if (rt != NULL) {
/*
* If this is the only reference to a protocol cloned
* route, remove it immediately.
*/
if (rt->rt_flags & RTF_WASCLONED &&
(sc->sc_flags & SCF_KEEPROUTE) == 0 &&
rt->rt_refcnt == 1)
rtrequest(RTM_DELETE, rt_key(rt),
rt->rt_gateway, rt_mask(rt),
rt->rt_flags, NULL);
RTFREE(rt);
}
uma_zfree(tcp_syncache.zone, sc);
}
void
syncache_init(void)
{
int i;
tcp_syncache.cache_count = 0;
tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
tcp_syncache.cache_limit =
tcp_syncache.hashsize * tcp_syncache.bucket_limit;
tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
tcp_syncache.next_reseed = 0;
tcp_syncache.hash_secret = arc4random();
TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
&tcp_syncache.hashsize);
TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
&tcp_syncache.cache_limit);
TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
&tcp_syncache.bucket_limit);
if (!powerof2(tcp_syncache.hashsize)) {
printf("WARNING: syncache hash size is not a power of 2.\n");
tcp_syncache.hashsize = 512; /* safe default */
}
tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
/* Allocate the hash table. */
MALLOC(tcp_syncache.hashbase, struct syncache_head *,
tcp_syncache.hashsize * sizeof(struct syncache_head),
M_SYNCACHE, M_WAITOK);
/* Initialize the hash buckets. */
for (i = 0; i < tcp_syncache.hashsize; i++) {
TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
tcp_syncache.hashbase[i].sch_length = 0;
}
/* Initialize the timer queues. */
for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
TAILQ_INIT(&tcp_syncache.timerq[i]);
callout_init(&tcp_syncache.tt_timerq[i], 1);
}
/*
* Allocate the syncache entries. Allow the zone to allocate one
* more entry than cache limit, so a new entry can bump out an
* older one.
*/
tcp_syncache.cache_limit -= 1;
tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
}
static void
syncache_insert(sc, sch)
struct syncache *sc;
struct syncache_head *sch;
{
struct syncache *sc2;
int s, i;
/*
* Make sure that we don't overflow the per-bucket
* limit or the total cache size limit.
*/
s = splnet();
if (sch->sch_length >= tcp_syncache.bucket_limit) {
/*
* The bucket is full, toss the oldest element.
*/
sc2 = TAILQ_FIRST(&sch->sch_bucket);
sc2->sc_tp->ts_recent = ticks;
syncache_drop(sc2, sch);
tcpstat.tcps_sc_bucketoverflow++;
} else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) {
/*
* The cache is full. Toss the oldest entry in the
* entire cache. This is the front entry in the
* first non-empty timer queue with the largest
* timeout value.
*/
for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]);
if (sc2 != NULL)
break;
}
sc2->sc_tp->ts_recent = ticks;
syncache_drop(sc2, NULL);
tcpstat.tcps_sc_cacheoverflow++;
}
/* Initialize the entry's timer. */
SYNCACHE_TIMEOUT(sc, 0);
/* Put it into the bucket. */
TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
sch->sch_length++;
tcp_syncache.cache_count++;
tcpstat.tcps_sc_added++;
splx(s);
}
static void
syncache_drop(sc, sch)
struct syncache *sc;
struct syncache_head *sch;
{
int s;
if (sch == NULL) {
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
sch = &tcp_syncache.hashbase[
SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
} else
#endif
{
sch = &tcp_syncache.hashbase[
SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
}
}
s = splnet();
TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
sch->sch_length--;
tcp_syncache.cache_count--;
TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq);
if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot]))
callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]);
splx(s);
syncache_free(sc);
}
/*
* Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
* If we have retransmitted an entry the maximum number of times, expire it.
*/
static void
syncache_timer(xslot)
void *xslot;
{
intptr_t slot = (intptr_t)xslot;
struct syncache *sc, *nsc;
struct inpcb *inp;
int s;
s = splnet();
INP_INFO_WLOCK(&tcbinfo);
if (callout_pending(&tcp_syncache.tt_timerq[slot]) ||
!callout_active(&tcp_syncache.tt_timerq[slot])) {
INP_INFO_WUNLOCK(&tcbinfo);
splx(s);
return;
}
callout_deactivate(&tcp_syncache.tt_timerq[slot]);
nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]);
while (nsc != NULL) {
if (ticks < nsc->sc_rxttime)
break;
sc = nsc;
inp = sc->sc_tp->t_inpcb;
if (slot == SYNCACHE_MAXREXMTS ||
slot >= tcp_syncache.rexmt_limit ||
inp == NULL || inp->inp_gencnt != sc->sc_inp_gencnt) {
nsc = TAILQ_NEXT(sc, sc_timerq);
syncache_drop(sc, NULL);
tcpstat.tcps_sc_stale++;
continue;
}
/*
* syncache_respond() may call back into the syncache to
* to modify another entry, so do not obtain the next
* entry on the timer chain until it has completed.
*/
(void) syncache_respond(sc, NULL);
nsc = TAILQ_NEXT(sc, sc_timerq);
tcpstat.tcps_sc_retransmitted++;
TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq);
SYNCACHE_TIMEOUT(sc, slot + 1);
}
if (nsc != NULL)
callout_reset(&tcp_syncache.tt_timerq[slot],
nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot));
INP_INFO_WUNLOCK(&tcbinfo);
splx(s);
}
/*
* Find an entry in the syncache.
*/
struct syncache *
syncache_lookup(inc, schp)
struct in_conninfo *inc;
struct syncache_head **schp;
{
struct syncache *sc;
struct syncache_head *sch;
int s;
#ifdef INET6
if (inc->inc_isipv6) {
sch = &tcp_syncache.hashbase[
SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
*schp = sch;
s = splnet();
TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
splx(s);
return (sc);
}
}
splx(s);
} else
#endif
{
sch = &tcp_syncache.hashbase[
SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
*schp = sch;
s = splnet();
TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
#ifdef INET6
if (sc->sc_inc.inc_isipv6)
continue;
#endif
if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
splx(s);
return (sc);
}
}
splx(s);
}
return (NULL);
}
/*
* This function is called when we get a RST for a
* non-existent connection, so that we can see if the
* connection is in the syn cache. If it is, zap it.
*/
void
syncache_chkrst(inc, th)
struct in_conninfo *inc;
struct tcphdr *th;
{
struct syncache *sc;
struct syncache_head *sch;
sc = syncache_lookup(inc, &sch);
if (sc == NULL)
return;
/*
* If the RST bit is set, check the sequence number to see
* if this is a valid reset segment.
* RFC 793 page 37:
* In all states except SYN-SENT, all reset (RST) segments
* are validated by checking their SEQ-fields. A reset is
* valid if its sequence number is in the window.
*
* The sequence number in the reset segment is normally an
* echo of our outgoing acknowlegement numbers, but some hosts
* send a reset with the sequence number at the rightmost edge
* of our receive window, and we have to handle this case.
*/
if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
syncache_drop(sc, sch);
tcpstat.tcps_sc_reset++;
}
}
void
syncache_badack(inc)
struct in_conninfo *inc;
{
struct syncache *sc;
struct syncache_head *sch;
sc = syncache_lookup(inc, &sch);
if (sc != NULL) {
syncache_drop(sc, sch);
tcpstat.tcps_sc_badack++;
}
}
void
syncache_unreach(inc, th)
struct in_conninfo *inc;
struct tcphdr *th;
{
struct syncache *sc;
struct syncache_head *sch;
/* we are called at splnet() here */
sc = syncache_lookup(inc, &sch);
if (sc == NULL)
return;
/* If the sequence number != sc_iss, then it's a bogus ICMP msg */
if (ntohl(th->th_seq) != sc->sc_iss)
return;
/*
* If we've rertransmitted 3 times and this is our second error,
* we remove the entry. Otherwise, we allow it to continue on.
* This prevents us from incorrectly nuking an entry during a
* spurious network outage.
*
* See tcp_notify().
*/
if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
sc->sc_flags |= SCF_UNREACH;
return;
}
syncache_drop(sc, sch);
tcpstat.tcps_sc_unreach++;
}
/*
* Build a new TCP socket structure from a syncache entry.
*/
static struct socket *
syncache_socket(sc, lso, m)
struct syncache *sc;
struct socket *lso;
struct mbuf *m;
{
struct inpcb *inp = NULL;
struct socket *so;
struct tcpcb *tp;
/*
* Ok, create the full blown connection, and set things up
* as they would have been set up if we had created the
* connection when the SYN arrived. If we can't create
* the connection, abort it.
*/
so = sonewconn(lso, SS_ISCONNECTED);
if (so == NULL) {
/*
* Drop the connection; we will send a RST if the peer
* retransmits the ACK,
*/
tcpstat.tcps_listendrop++;
goto abort;
}
#ifdef MAC
mac_set_socket_peer_from_mbuf(m, so);
#endif
inp = sotoinpcb(so);
/*
* Insert new socket into hash list.
*/
inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
inp->in6p_laddr = sc->sc_inc.inc6_laddr;
} else {
inp->inp_vflag &= ~INP_IPV6;
inp->inp_vflag |= INP_IPV4;
#endif
inp->inp_laddr = sc->sc_inc.inc_laddr;
#ifdef INET6
}
#endif
inp->inp_lport = sc->sc_inc.inc_lport;
if (in_pcbinshash(inp) != 0) {
/*
* Undo the assignments above if we failed to
* put the PCB on the hash lists.
*/
#ifdef INET6
if (sc->sc_inc.inc_isipv6)
inp->in6p_laddr = in6addr_any;
else
#endif
inp->inp_laddr.s_addr = INADDR_ANY;
inp->inp_lport = 0;
goto abort;
}
#ifdef IPSEC
/* copy old policy into new socket's */
if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
printf("syncache_expand: could not copy policy\n");
#endif
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
struct inpcb *oinp = sotoinpcb(lso);
struct in6_addr laddr6;
struct sockaddr_in6 *sin6;
/*
* Inherit socket options from the listening socket.
* Note that in6p_inputopts are not (and should not be)
* copied, since it stores previously received options and is
* used to detect if each new option is different than the
* previous one and hence should be passed to a user.
* If we copied in6p_inputopts, a user would not be able to
* receive options just after calling the accept system call.
*/
inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
if (oinp->in6p_outputopts)
inp->in6p_outputopts =
ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
inp->in6p_route = sc->sc_route6;
sc->sc_route6.ro_rt = NULL;
MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
M_SONAME, M_NOWAIT | M_ZERO);
if (sin6 == NULL)
goto abort;
sin6->sin6_family = AF_INET6;
sin6->sin6_len = sizeof(*sin6);
sin6->sin6_addr = sc->sc_inc.inc6_faddr;
sin6->sin6_port = sc->sc_inc.inc_fport;
laddr6 = inp->in6p_laddr;
if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
inp->in6p_laddr = sc->sc_inc.inc6_laddr;
if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) {
inp->in6p_laddr = laddr6;
FREE(sin6, M_SONAME);
goto abort;
}
FREE(sin6, M_SONAME);
} else
#endif
{
struct in_addr laddr;
struct sockaddr_in *sin;
inp->inp_options = ip_srcroute();
if (inp->inp_options == NULL) {
inp->inp_options = sc->sc_ipopts;
sc->sc_ipopts = NULL;
}
inp->inp_route = sc->sc_route;
sc->sc_route.ro_rt = NULL;
MALLOC(sin, struct sockaddr_in *, sizeof *sin,
M_SONAME, M_NOWAIT | M_ZERO);
if (sin == NULL)
goto abort;
sin->sin_family = AF_INET;
sin->sin_len = sizeof(*sin);
sin->sin_addr = sc->sc_inc.inc_faddr;
sin->sin_port = sc->sc_inc.inc_fport;
bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
laddr = inp->inp_laddr;
if (inp->inp_laddr.s_addr == INADDR_ANY)
inp->inp_laddr = sc->sc_inc.inc_laddr;
if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) {
inp->inp_laddr = laddr;
FREE(sin, M_SONAME);
goto abort;
}
FREE(sin, M_SONAME);
}
tp = intotcpcb(inp);
tp->t_state = TCPS_SYN_RECEIVED;
tp->iss = sc->sc_iss;
tp->irs = sc->sc_irs;
tcp_rcvseqinit(tp);
tcp_sendseqinit(tp);
tp->snd_wl1 = sc->sc_irs;
tp->rcv_up = sc->sc_irs + 1;
tp->rcv_wnd = sc->sc_wnd;
tp->rcv_adv += tp->rcv_wnd;
tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
if (sc->sc_flags & SCF_NOOPT)
tp->t_flags |= TF_NOOPT;
if (sc->sc_flags & SCF_WINSCALE) {
tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
tp->requested_s_scale = sc->sc_requested_s_scale;
tp->request_r_scale = sc->sc_request_r_scale;
}
if (sc->sc_flags & SCF_TIMESTAMP) {
tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
tp->ts_recent = sc->sc_tsrecent;
tp->ts_recent_age = ticks;
}
if (sc->sc_flags & SCF_CC) {
/*
* Initialization of the tcpcb for transaction;
* set SND.WND = SEG.WND,
* initialize CCsend and CCrecv.
*/
tp->t_flags |= TF_REQ_CC|TF_RCVD_CC;
tp->cc_send = sc->sc_cc_send;
tp->cc_recv = sc->sc_cc_recv;
}
tcp_mss(tp, sc->sc_peer_mss);
/*
* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
*/
if (sc->sc_rxtslot != 0)
tp->snd_cwnd = tp->t_maxseg;
callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
tcpstat.tcps_accepts++;
return (so);
abort:
if (so != NULL)
(void) soabort(so);
return (NULL);
}
/*
* This function gets called when we receive an ACK for a
* socket in the LISTEN state. We look up the connection
* in the syncache, and if its there, we pull it out of
* the cache and turn it into a full-blown connection in
* the SYN-RECEIVED state.
*/
int
syncache_expand(inc, th, sop, m)
struct in_conninfo *inc;
struct tcphdr *th;
struct socket **sop;
struct mbuf *m;
{
struct syncache *sc;
struct syncache_head *sch;
struct socket *so;
sc = syncache_lookup(inc, &sch);
if (sc == NULL) {
/*
* There is no syncache entry, so see if this ACK is
* a returning syncookie. To do this, first:
* A. See if this socket has had a syncache entry dropped in
* the past. We don't want to accept a bogus syncookie
* if we've never received a SYN.
* B. check that the syncookie is valid. If it is, then
* cobble up a fake syncache entry, and return.
*/
if (!tcp_syncookies)
return (0);
sc = syncookie_lookup(inc, th, *sop);
if (sc == NULL)
return (0);
sch = NULL;
tcpstat.tcps_sc_recvcookie++;
}
/*
* If seg contains an ACK, but not for our SYN/ACK, send a RST.
*/
if (th->th_ack != sc->sc_iss + 1)
return (0);
so = syncache_socket(sc, *sop, m);
if (so == NULL) {
#if 0
resetandabort:
/* XXXjlemon check this - is this correct? */
(void) tcp_respond(NULL, m, m, th,
th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
#endif
m_freem(m); /* XXX only needed for above */
tcpstat.tcps_sc_aborted++;
} else {
sc->sc_flags |= SCF_KEEPROUTE;
tcpstat.tcps_sc_completed++;
}
if (sch == NULL)
syncache_free(sc);
else
syncache_drop(sc, sch);
*sop = so;
return (1);
}
/*
* Given a LISTEN socket and an inbound SYN request, add
* this to the syn cache, and send back a segment:
* <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
* to the source.
*
* IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
* Doing so would require that we hold onto the data and deliver it
* to the application. However, if we are the target of a SYN-flood
* DoS attack, an attacker could send data which would eventually
* consume all available buffer space if it were ACKed. By not ACKing
* the data, we avoid this DoS scenario.
*/
int
syncache_add(inc, to, th, sop, m)
struct in_conninfo *inc;
struct tcpopt *to;
struct tcphdr *th;
struct socket **sop;
struct mbuf *m;
{
struct tcpcb *tp;
struct socket *so;
struct syncache *sc = NULL;
struct syncache_head *sch;
struct mbuf *ipopts = NULL;
struct rmxp_tao *taop;
int i, s, win;
so = *sop;
tp = sototcpcb(so);
/*
* Remember the IP options, if any.
*/
#ifdef INET6
if (!inc->inc_isipv6)
#endif
ipopts = ip_srcroute();
/*
* See if we already have an entry for this connection.
* If we do, resend the SYN,ACK, and reset the retransmit timer.
*
* XXX
* should the syncache be re-initialized with the contents
* of the new SYN here (which may have different options?)
*/
sc = syncache_lookup(inc, &sch);
if (sc != NULL) {
tcpstat.tcps_sc_dupsyn++;
if (ipopts) {
/*
* If we were remembering a previous source route,
* forget it and use the new one we've been given.
*/
if (sc->sc_ipopts)
(void) m_free(sc->sc_ipopts);
sc->sc_ipopts = ipopts;
}
/*
* Update timestamp if present.
*/
if (sc->sc_flags & SCF_TIMESTAMP)
sc->sc_tsrecent = to->to_tsval;
/*
* PCB may have changed, pick up new values.
*/
sc->sc_tp = tp;
sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
if (syncache_respond(sc, m) == 0) {
s = splnet();
TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot],
sc, sc_timerq);
SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot);
splx(s);
tcpstat.tcps_sndacks++;
tcpstat.tcps_sndtotal++;
}
*sop = NULL;
return (1);
}
sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
if (sc == NULL) {
/*
* The zone allocator couldn't provide more entries.
* Treat this as if the cache was full; drop the oldest
* entry and insert the new one.
*/
s = splnet();
for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
sc = TAILQ_FIRST(&tcp_syncache.timerq[i]);
if (sc != NULL)
break;
}
sc->sc_tp->ts_recent = ticks;
syncache_drop(sc, NULL);
splx(s);
tcpstat.tcps_sc_zonefail++;
sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
if (sc == NULL) {
if (ipopts)
(void) m_free(ipopts);
return (0);
}
}
/*
* Fill in the syncache values.
*/
bzero(sc, sizeof(*sc));
sc->sc_tp = tp;
sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
sc->sc_ipopts = ipopts;
sc->sc_inc.inc_fport = inc->inc_fport;
sc->sc_inc.inc_lport = inc->inc_lport;
#ifdef INET6
sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
if (inc->inc_isipv6) {
sc->sc_inc.inc6_faddr = inc->inc6_faddr;
sc->sc_inc.inc6_laddr = inc->inc6_laddr;
sc->sc_route6.ro_rt = NULL;
} else
#endif
{
sc->sc_inc.inc_faddr = inc->inc_faddr;
sc->sc_inc.inc_laddr = inc->inc_laddr;
sc->sc_route.ro_rt = NULL;
}
sc->sc_irs = th->th_seq;
sc->sc_flags = 0;
sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
if (tcp_syncookies)
sc->sc_iss = syncookie_generate(sc);
else
sc->sc_iss = arc4random();
/* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */
win = sbspace(&so->so_rcv);
win = imax(win, 0);
win = imin(win, TCP_MAXWIN);
sc->sc_wnd = win;
if (tcp_do_rfc1323) {
/*
* A timestamp received in a SYN makes
* it ok to send timestamp requests and replies.
*/
if (to->to_flags & TOF_TS) {
sc->sc_tsrecent = to->to_tsval;
sc->sc_flags |= SCF_TIMESTAMP;
}
if (to->to_flags & TOF_SCALE) {
int wscale = 0;
/* Compute proper scaling value from buffer space */
while (wscale < TCP_MAX_WINSHIFT &&
(TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat)
wscale++;
sc->sc_request_r_scale = wscale;
sc->sc_requested_s_scale = to->to_requested_s_scale;
sc->sc_flags |= SCF_WINSCALE;
}
}
if (tcp_do_rfc1644) {
/*
* A CC or CC.new option received in a SYN makes
* it ok to send CC in subsequent segments.
*/
if (to->to_flags & (TOF_CC|TOF_CCNEW)) {
sc->sc_cc_recv = to->to_cc;
sc->sc_cc_send = CC_INC(tcp_ccgen);
sc->sc_flags |= SCF_CC;
}
}
if (tp->t_flags & TF_NOOPT)
sc->sc_flags = SCF_NOOPT;
/*
* XXX
* We have the option here of not doing TAO (even if the segment
* qualifies) and instead fall back to a normal 3WHS via the syncache.
* This allows us to apply synflood protection to TAO-qualifying SYNs
* also. However, there should be a hueristic to determine when to
* do this, and is not present at the moment.
*/
/*
* Perform TAO test on incoming CC (SEG.CC) option, if any.
* - compare SEG.CC against cached CC from the same host, if any.
* - if SEG.CC > chached value, SYN must be new and is accepted
* immediately: save new CC in the cache, mark the socket
* connected, enter ESTABLISHED state, turn on flag to
* send a SYN in the next segment.
* A virtual advertised window is set in rcv_adv to
* initialize SWS prevention. Then enter normal segment
* processing: drop SYN, process data and FIN.
* - otherwise do a normal 3-way handshake.
*/
taop = tcp_gettaocache(&sc->sc_inc);
if ((to->to_flags & TOF_CC) != 0) {
if (((tp->t_flags & TF_NOPUSH) != 0) &&
sc->sc_flags & SCF_CC &&
taop != NULL && taop->tao_cc != 0 &&
CC_GT(to->to_cc, taop->tao_cc)) {
sc->sc_rxtslot = 0;
so = syncache_socket(sc, *sop, m);
if (so != NULL) {
sc->sc_flags |= SCF_KEEPROUTE;
taop->tao_cc = to->to_cc;
*sop = so;
}
syncache_free(sc);
return (so != NULL);
}
} else {
/*
* No CC option, but maybe CC.NEW: invalidate cached value.
*/
if (taop != NULL)
taop->tao_cc = 0;
}
/*
* TAO test failed or there was no CC option,
* do a standard 3-way handshake.
*/
if (syncache_respond(sc, m) == 0) {
syncache_insert(sc, sch);
tcpstat.tcps_sndacks++;
tcpstat.tcps_sndtotal++;
} else {
syncache_free(sc);
tcpstat.tcps_sc_dropped++;
}
*sop = NULL;
return (1);
}
static int
syncache_respond(sc, m)
struct syncache *sc;
struct mbuf *m;
{
u_int8_t *optp;
int optlen, error;
u_int16_t tlen, hlen, mssopt;
struct ip *ip = NULL;
struct rtentry *rt;
struct tcphdr *th;
#ifdef INET6
struct ip6_hdr *ip6 = NULL;
#endif
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
rt = tcp_rtlookup6(&sc->sc_inc);
if (rt != NULL)
mssopt = rt->rt_ifp->if_mtu -
(sizeof(struct ip6_hdr) + sizeof(struct tcphdr));
else
mssopt = tcp_v6mssdflt;
hlen = sizeof(struct ip6_hdr);
} else
#endif
{
rt = tcp_rtlookup(&sc->sc_inc);
if (rt != NULL)
mssopt = rt->rt_ifp->if_mtu -
(sizeof(struct ip) + sizeof(struct tcphdr));
else
mssopt = tcp_mssdflt;
hlen = sizeof(struct ip);
}
/* Compute the size of the TCP options. */
if (sc->sc_flags & SCF_NOOPT) {
optlen = 0;
} else {
optlen = TCPOLEN_MAXSEG +
((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) +
((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0);
}
tlen = hlen + sizeof(struct tcphdr) + optlen;
/*
* XXX
* assume that the entire packet will fit in a header mbuf
*/
KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
/*
* XXX shouldn't this reuse the mbuf if possible ?
* Create the IP+TCP header from scratch.
*/
if (m)
m_freem(m);
m = m_gethdr(M_DONTWAIT, MT_HEADER);
if (m == NULL)
return (ENOBUFS);
m->m_data += max_linkhdr;
m->m_len = tlen;
m->m_pkthdr.len = tlen;
m->m_pkthdr.rcvif = NULL;
#ifdef MAC
mac_create_mbuf_from_socket(sc->sc_tp->t_inpcb->inp_socket, m);
#endif
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
ip6 = mtod(m, struct ip6_hdr *);
ip6->ip6_vfc = IPV6_VERSION;
ip6->ip6_nxt = IPPROTO_TCP;
ip6->ip6_src = sc->sc_inc.inc6_laddr;
ip6->ip6_dst = sc->sc_inc.inc6_faddr;
ip6->ip6_plen = htons(tlen - hlen);
/* ip6_hlim is set after checksum */
/* ip6_flow = ??? */
th = (struct tcphdr *)(ip6 + 1);
} else
#endif
{
ip = mtod(m, struct ip *);
ip->ip_v = IPVERSION;
ip->ip_hl = sizeof(struct ip) >> 2;
ip->ip_len = tlen;
ip->ip_id = 0;
ip->ip_off = 0;
ip->ip_sum = 0;
ip->ip_p = IPPROTO_TCP;
ip->ip_src = sc->sc_inc.inc_laddr;
ip->ip_dst = sc->sc_inc.inc_faddr;
ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl; /* XXX */
ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos; /* XXX */
/*
* See if we should do MTU discovery. Route lookups are
* expensive, so we will only unset the DF bit if:
*
* 1) path_mtu_discovery is disabled
* 2) the SCF_UNREACH flag has been set
*/
if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
ip->ip_off |= IP_DF;
th = (struct tcphdr *)(ip + 1);
}
th->th_sport = sc->sc_inc.inc_lport;
th->th_dport = sc->sc_inc.inc_fport;
th->th_seq = htonl(sc->sc_iss);
th->th_ack = htonl(sc->sc_irs + 1);
th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
th->th_x2 = 0;
th->th_flags = TH_SYN|TH_ACK;
th->th_win = htons(sc->sc_wnd);
th->th_urp = 0;
/* Tack on the TCP options. */
if (optlen != 0) {
optp = (u_int8_t *)(th + 1);
*optp++ = TCPOPT_MAXSEG;
*optp++ = TCPOLEN_MAXSEG;
*optp++ = (mssopt >> 8) & 0xff;
*optp++ = mssopt & 0xff;
if (sc->sc_flags & SCF_WINSCALE) {
*((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
sc->sc_request_r_scale);
optp += 4;
}
if (sc->sc_flags & SCF_TIMESTAMP) {
u_int32_t *lp = (u_int32_t *)(optp);
/* Form timestamp option per appendix A of RFC 1323. */
*lp++ = htonl(TCPOPT_TSTAMP_HDR);
*lp++ = htonl(ticks);
*lp = htonl(sc->sc_tsrecent);
optp += TCPOLEN_TSTAMP_APPA;
}
/*
* Send CC and CC.echo if we received CC from our peer.
*/
if (sc->sc_flags & SCF_CC) {
u_int32_t *lp = (u_int32_t *)(optp);
*lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC));
*lp++ = htonl(sc->sc_cc_send);
*lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO));
*lp = htonl(sc->sc_cc_recv);
optp += TCPOLEN_CC_APPA * 2;
}
}
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
struct route_in6 *ro6 = &sc->sc_route6;
th->th_sum = 0;
th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
ip6->ip6_hlim = in6_selecthlim(NULL,
ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL);
error = ip6_output(m, NULL, ro6, 0, NULL, NULL,
sc->sc_tp->t_inpcb);
} else
#endif
{
th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
htons(tlen - hlen + IPPROTO_TCP));
m->m_pkthdr.csum_flags = CSUM_TCP;
m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL,
sc->sc_tp->t_inpcb);
}
return (error);
}
/*
* cookie layers:
*
* |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
* | peer iss |
* | MD5(laddr,faddr,secret,lport,fport) |. . . . . . .|
* | 0 |(A)| |
* (A): peer mss index
*/
/*
* The values below are chosen to minimize the size of the tcp_secret
* table, as well as providing roughly a 16 second lifetime for the cookie.
*/
#define SYNCOOKIE_WNDBITS 5 /* exposed bits for window indexing */
#define SYNCOOKIE_TIMESHIFT 1 /* scale ticks to window time units */
#define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1)
#define SYNCOOKIE_NSECRETS (1 << SYNCOOKIE_WNDBITS)
#define SYNCOOKIE_TIMEOUT \
(hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
#define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
static struct {
u_int32_t ts_secbits[4];
u_int ts_expire;
} tcp_secret[SYNCOOKIE_NSECRETS];
static int tcp_msstab[] = { 0, 536, 1460, 8960 };
static MD5_CTX syn_ctx;
#define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
struct md5_add {
u_int32_t laddr, faddr;
u_int32_t secbits[4];
u_int16_t lport, fport;
};
#ifdef CTASSERT
CTASSERT(sizeof(struct md5_add) == 28);
#endif
/*
* Consider the problem of a recreated (and retransmitted) cookie. If the
* original SYN was accepted, the connection is established. The second
* SYN is inflight, and if it arrives with an ISN that falls within the
* receive window, the connection is killed.
*
* However, since cookies have other problems, this may not be worth
* worrying about.
*/
static u_int32_t
syncookie_generate(struct syncache *sc)
{
u_int32_t md5_buffer[4];
u_int32_t data;
int idx, i;
struct md5_add add;
idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
if (tcp_secret[idx].ts_expire < ticks) {
for (i = 0; i < 4; i++)
tcp_secret[idx].ts_secbits[i] = arc4random();
tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
}
for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--)
if (tcp_msstab[data] <= sc->sc_peer_mss)
break;
data = (data << SYNCOOKIE_WNDBITS) | idx;
data ^= sc->sc_irs; /* peer's iss */
MD5Init(&syn_ctx);
#ifdef INET6
if (sc->sc_inc.inc_isipv6) {
MD5Add(sc->sc_inc.inc6_laddr);
MD5Add(sc->sc_inc.inc6_faddr);
add.laddr = 0;
add.faddr = 0;
} else
#endif
{
add.laddr = sc->sc_inc.inc_laddr.s_addr;
add.faddr = sc->sc_inc.inc_faddr.s_addr;
}
add.lport = sc->sc_inc.inc_lport;
add.fport = sc->sc_inc.inc_fport;
add.secbits[0] = tcp_secret[idx].ts_secbits[0];
add.secbits[1] = tcp_secret[idx].ts_secbits[1];
add.secbits[2] = tcp_secret[idx].ts_secbits[2];
add.secbits[3] = tcp_secret[idx].ts_secbits[3];
MD5Add(add);
MD5Final((u_char *)&md5_buffer, &syn_ctx);
data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
return (data);
}
static struct syncache *
syncookie_lookup(inc, th, so)
struct in_conninfo *inc;
struct tcphdr *th;
struct socket *so;
{
u_int32_t md5_buffer[4];
struct syncache *sc;
u_int32_t data;
int wnd, idx;
struct md5_add add;
data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */
idx = data & SYNCOOKIE_WNDMASK;
if (tcp_secret[idx].ts_expire < ticks ||
sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
return (NULL);
MD5Init(&syn_ctx);
#ifdef INET6
if (inc->inc_isipv6) {
MD5Add(inc->inc6_laddr);
MD5Add(inc->inc6_faddr);
add.laddr = 0;
add.faddr = 0;
} else
#endif
{
add.laddr = inc->inc_laddr.s_addr;
add.faddr = inc->inc_faddr.s_addr;
}
add.lport = inc->inc_lport;
add.fport = inc->inc_fport;
add.secbits[0] = tcp_secret[idx].ts_secbits[0];
add.secbits[1] = tcp_secret[idx].ts_secbits[1];
add.secbits[2] = tcp_secret[idx].ts_secbits[2];
add.secbits[3] = tcp_secret[idx].ts_secbits[3];
MD5Add(add);
MD5Final((u_char *)&md5_buffer, &syn_ctx);
data ^= md5_buffer[0];
if ((data & ~SYNCOOKIE_DATAMASK) != 0)
return (NULL);
data = data >> SYNCOOKIE_WNDBITS;
sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
if (sc == NULL)
return (NULL);
/*
* Fill in the syncache values.
* XXX duplicate code from syncache_add
*/
sc->sc_ipopts = NULL;
sc->sc_inc.inc_fport = inc->inc_fport;
sc->sc_inc.inc_lport = inc->inc_lport;
#ifdef INET6
sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
if (inc->inc_isipv6) {
sc->sc_inc.inc6_faddr = inc->inc6_faddr;
sc->sc_inc.inc6_laddr = inc->inc6_laddr;
sc->sc_route6.ro_rt = NULL;
} else
#endif
{
sc->sc_inc.inc_faddr = inc->inc_faddr;
sc->sc_inc.inc_laddr = inc->inc_laddr;
sc->sc_route.ro_rt = NULL;
}
sc->sc_irs = th->th_seq - 1;
sc->sc_iss = th->th_ack - 1;
wnd = sbspace(&so->so_rcv);
wnd = imax(wnd, 0);
wnd = imin(wnd, TCP_MAXWIN);
sc->sc_wnd = wnd;
sc->sc_flags = 0;
sc->sc_rxtslot = 0;
sc->sc_peer_mss = tcp_msstab[data];
return (sc);
}
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