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freebsd-skq/sys/netinet/tcp_input.c
imp 9d11326d86 Mitigate the stream.c attacks 
o Drop all broadcast and multicast source addresses in tcp_input.
o Enable ICMP_BANDLIM in GENERIC.
o Change default to 200/s from 100/s.  This will still stop the attack, but
  is conservative enough to do this close to code freeze.

This is not the optimal patch for the problem, but is likely the least
intrusive patch that can be made for this.

Obtained from: Don Lewis and Matt Dillon.
Reviewed by: freebsd-security
2000-01-28 06:13:09 +00:00

2783 lines
77 KiB
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/*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California. All rights reserved.
*
* 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
*
* @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
* $FreeBSD$
*/
#include "opt_ipfw.h" /* for ipfw_fwd */
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_tcpdebug.h"
#include "opt_tcp_input.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h> /* for proc0 declaration */
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
#include <net/if.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h> /* for ICMP_BANDLIM */
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet/in_var.h>
#include <netinet6/nd6.h>
#include <netinet/icmp6.h>
#endif
#include <netinet/in_pcb.h>
#ifdef INET6
#include <netinet6/in6_pcb.h>
#endif
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet6/ip6_var.h>
#endif
#include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
#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
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
struct tcphdr tcp_savetcp;
#endif /* TCPDEBUG */
#ifdef IPSEC
#include <netinet6/ipsec.h>
#ifdef INET6
#include <netinet6/ipsec6.h>
#endif
#include <netkey/key.h>
#endif /*IPSEC*/
MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
static int tcprexmtthresh = 3;
tcp_seq tcp_iss;
tcp_cc tcp_ccgen;
struct tcpstat tcpstat;
SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RD,
&tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
static int log_in_vain = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW,
&log_in_vain, 0, "Log all incoming TCP connections");
static int blackhole = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
&blackhole, 0, "Do not send RST when dropping refused connections");
int tcp_delack_enabled = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
&tcp_delack_enabled, 0,
"Delay ACK to try and piggyback it onto a data packet");
#ifdef TCP_DROP_SYNFIN
static int drop_synfin = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
&drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
#endif
#ifdef TCP_RESTRICT_RST
static int restrict_rst = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, restrict_rst, CTLFLAG_RW,
&restrict_rst, 0, "Restrict RST emission");
#endif
struct inpcbhead tcb;
#define tcb6 tcb /* for KAME src sync over BSD*'s */
struct inpcbinfo tcbinfo;
static void tcp_dooptions __P((struct tcpcb *,
u_char *, int, struct tcphdr *, struct tcpopt *));
static void tcp_pulloutofband __P((struct socket *,
struct tcphdr *, struct mbuf *, int));
static int tcp_reass __P((struct tcpcb *, struct tcphdr *, int *,
struct mbuf *));
static void tcp_xmit_timer __P((struct tcpcb *, int));
/* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
#ifdef INET6
#define ND6_HINT(tp) \
do { \
if ((tp) && (tp)->t_inpcb && \
((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
(tp)->t_inpcb->in6p_route.ro_rt) \
nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL); \
} while (0)
#else
#define ND6_HINT(tp)
#endif
/*
* Insert segment which inludes th into reassembly queue of tcp with
* control block tp. Return TH_FIN if reassembly now includes
* a segment with FIN. The macro form does the common case inline
* (segment is the next to be received on an established connection,
* and the queue is empty), avoiding linkage into and removal
* from the queue and repetition of various conversions.
* Set DELACK for segments received in order, but ack immediately
* when segments are out of order (so fast retransmit can work).
*/
#define TCP_REASS(tp, th, tlenp, m, so, flags) { \
if ((th)->th_seq == (tp)->rcv_nxt && \
LIST_EMPTY(&(tp)->t_segq) && \
(tp)->t_state == TCPS_ESTABLISHED) { \
if (tcp_delack_enabled) \
callout_reset(tp->tt_delack, tcp_delacktime, \
tcp_timer_delack, tp); \
else \
tp->t_flags |= TF_ACKNOW; \
(tp)->rcv_nxt += *(tlenp); \
flags = (th)->th_flags & TH_FIN; \
tcpstat.tcps_rcvpack++;\
tcpstat.tcps_rcvbyte += *(tlenp);\
ND6_HINT(tp); \
sbappend(&(so)->so_rcv, (m)); \
sorwakeup(so); \
} else { \
(flags) = tcp_reass((tp), (th), (tlenp), (m)); \
tp->t_flags |= TF_ACKNOW; \
} \
}
static int
tcp_reass(tp, th, tlenp, m)
register struct tcpcb *tp;
register struct tcphdr *th;
int *tlenp;
struct mbuf *m;
{
struct tseg_qent *q;
struct tseg_qent *p = NULL;
struct tseg_qent *nq;
struct tseg_qent *te;
struct socket *so = tp->t_inpcb->inp_socket;
int flags;
/*
* Call with th==0 after become established to
* force pre-ESTABLISHED data up to user socket.
*/
if (th == 0)
goto present;
/* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
MALLOC(te, struct tseg_qent *, sizeof (struct tseg_qent), M_TSEGQ,
M_NOWAIT);
if (te == NULL) {
tcpstat.tcps_rcvmemdrop++;
m_freem(m);
return (0);
}
/*
* Find a segment which begins after this one does.
*/
LIST_FOREACH(q, &tp->t_segq, tqe_q) {
if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
break;
p = q;
}
/*
* If there is a preceding segment, it may provide some of
* our data already. If so, drop the data from the incoming
* segment. If it provides all of our data, drop us.
*/
if (p != NULL) {
register int i;
/* conversion to int (in i) handles seq wraparound */
i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
if (i > 0) {
if (i >= *tlenp) {
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += *tlenp;
m_freem(m);
FREE(te, M_TSEGQ);
/*
* Try to present any queued data
* at the left window edge to the user.
* This is needed after the 3-WHS
* completes.
*/
goto present; /* ??? */
}
m_adj(m, i);
*tlenp -= i;
th->th_seq += i;
}
}
tcpstat.tcps_rcvoopack++;
tcpstat.tcps_rcvoobyte += *tlenp;
/*
* While we overlap succeeding segments trim them or,
* if they are completely covered, dequeue them.
*/
while (q) {
register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
if (i <= 0)
break;
if (i < q->tqe_len) {
q->tqe_th->th_seq += i;
q->tqe_len -= i;
m_adj(q->tqe_m, i);
break;
}
nq = LIST_NEXT(q, tqe_q);
LIST_REMOVE(q, tqe_q);
m_freem(q->tqe_m);
FREE(q, M_TSEGQ);
q = nq;
}
/* Insert the new segment queue entry into place. */
te->tqe_m = m;
te->tqe_th = th;
te->tqe_len = *tlenp;
if (p == NULL) {
LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
} else {
LIST_INSERT_AFTER(p, te, tqe_q);
}
present:
/*
* Present data to user, advancing rcv_nxt through
* completed sequence space.
*/
if (!TCPS_HAVEESTABLISHED(tp->t_state))
return (0);
q = LIST_FIRST(&tp->t_segq);
if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
return (0);
do {
tp->rcv_nxt += q->tqe_len;
flags = q->tqe_th->th_flags & TH_FIN;
nq = LIST_NEXT(q, tqe_q);
LIST_REMOVE(q, tqe_q);
if (so->so_state & SS_CANTRCVMORE)
m_freem(q->tqe_m);
else
sbappend(&so->so_rcv, q->tqe_m);
FREE(q, M_TSEGQ);
q = nq;
} while (q && q->tqe_th->th_seq == tp->rcv_nxt);
ND6_HINT(tp);
sorwakeup(so);
return (flags);
}
/*
* TCP input routine, follows pages 65-76 of the
* protocol specification dated September, 1981 very closely.
*/
#ifdef INET6
int
tcp6_input(mp, offp, proto)
struct mbuf **mp;
int *offp, proto;
{
register struct mbuf *m = *mp;
IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE);
/*
* draft-itojun-ipv6-tcp-to-anycast
* better place to put this in?
*/
if (m->m_flags & M_ANYCAST6) {
struct ip6_hdr *ip6;
ip6 = mtod(m, struct ip6_hdr *);
icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
(caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
return IPPROTO_DONE;
}
tcp_input(m, *offp, proto);
return IPPROTO_DONE;
}
#endif
void
tcp_input(m, off0, proto)
register struct mbuf *m;
int off0, proto;
{
register struct tcphdr *th;
register struct ip *ip = NULL;
register struct ipovly *ipov;
register struct inpcb *inp;
u_char *optp = NULL;
int optlen = 0;
int len, tlen, off;
int drop_hdrlen;
register struct tcpcb *tp = 0;
register int thflags;
struct socket *so = 0;
int todrop, acked, ourfinisacked, needoutput = 0;
struct in_addr laddr;
#ifdef INET6
struct in6_addr laddr6;
#endif
int dropsocket = 0;
int iss = 0;
u_long tiwin;
struct tcpopt to; /* options in this segment */
struct rmxp_tao *taop; /* pointer to our TAO cache entry */
struct rmxp_tao tao_noncached; /* in case there's no cached entry */
#ifdef TCPDEBUG
short ostate = 0;
#endif
#ifdef INET6
struct ip6_hdr *ip6 = NULL;
int isipv6;
#endif /* INET6 */
#ifdef INET6
isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
#endif
bzero((char *)&to, sizeof(to));
tcpstat.tcps_rcvtotal++;
#ifdef INET6
if (isipv6) {
/* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
ip6 = mtod(m, struct ip6_hdr *);
tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
tcpstat.tcps_rcvbadsum++;
goto drop;
}
th = (struct tcphdr *)((caddr_t)ip6 + off0);
} else
#endif /* INET6 */
{
/*
* Get IP and TCP header together in first mbuf.
* Note: IP leaves IP header in first mbuf.
*/
if (off0 > sizeof (struct ip)) {
ip_stripoptions(m, (struct mbuf *)0);
off0 = sizeof(struct ip);
}
if (m->m_len < sizeof (struct tcpiphdr)) {
if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
tcpstat.tcps_rcvshort++;
return;
}
}
ip = mtod(m, struct ip *);
ipov = (struct ipovly *)ip;
/*
* Checksum extended TCP header and data.
*/
tlen = ip->ip_len;
len = sizeof (struct ip) + tlen;
bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
ipov->ih_len = (u_short)tlen;
HTONS(ipov->ih_len);
th = (struct tcphdr *)((caddr_t)ip + off0);
th->th_sum = in_cksum(m, len);
if (th->th_sum) {
tcpstat.tcps_rcvbadsum++;
goto drop;
}
#ifdef INET6
/* Re-initialization for later version check */
ip->ip_v = IPVERSION;
#endif
}
/*
* Check that TCP offset makes sense,
* pull out TCP options and adjust length. XXX
*/
off = th->th_off << 2;
if (off < sizeof (struct tcphdr) || off > tlen) {
tcpstat.tcps_rcvbadoff++;
goto drop;
}
tlen -= off; /* tlen is used instead of ti->ti_len */
if (off > sizeof (struct tcphdr)) {
#ifdef INET6
if (isipv6) {
IP6_EXTHDR_CHECK(m, off0, off, );
ip6 = mtod(m, struct ip6_hdr *);
th = (struct tcphdr *)((caddr_t)ip6 + off0);
} else
#endif /* INET6 */
{
if (m->m_len < sizeof(struct ip) + off) {
if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
tcpstat.tcps_rcvshort++;
return;
}
ip = mtod(m, struct ip *);
ipov = (struct ipovly *)ip;
th = (struct tcphdr *)((caddr_t)ip + off0);
}
}
optlen = off - sizeof (struct tcphdr);
optp = (u_char *)(th + 1);
}
thflags = th->th_flags;
#ifdef TCP_DROP_SYNFIN
/*
* If the drop_synfin option is enabled, drop all packets with
* both the SYN and FIN bits set. This prevents e.g. nmap from
* identifying the TCP/IP stack.
*
* This is incompatible with RFC1644 extensions (T/TCP).
*/
if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
goto drop;
#endif
/*
* Convert TCP protocol specific fields to host format.
*/
NTOHL(th->th_seq);
NTOHL(th->th_ack);
NTOHS(th->th_win);
NTOHS(th->th_urp);
/*
* Delay droping TCP, IP headers, IPv6 ext headers, and TCP options,
* until after ip6_savecontrol() is called and before other functions
* which don't want those proto headers.
* Because ip6_savecontrol() is going to parse the mbuf to
* search for data to be passed up to user-land, it wants mbuf
* parameters to be unchanged.
*/
drop_hdrlen = off0 + off;
/*
* Locate pcb for segment.
*/
findpcb:
#ifdef IPFIREWALL_FORWARD
if (ip_fw_fwd_addr != NULL
#ifdef INET6
&& isipv6 == NULL /* IPv6 support is not yet */
#endif /* INET6 */
) {
/*
* Diverted. Pretend to be the destination.
* already got one like this?
*/
inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
ip->ip_dst, th->th_dport, 0, m->m_pkthdr.rcvif);
if (!inp) {
/*
* No, then it's new. Try find the ambushing socket
*/
if (!ip_fw_fwd_addr->sin_port) {
inp = in_pcblookup_hash(&tcbinfo, ip->ip_src,
th->th_sport, ip_fw_fwd_addr->sin_addr,
th->th_dport, 1, m->m_pkthdr.rcvif);
} else {
inp = in_pcblookup_hash(&tcbinfo,
ip->ip_src, th->th_sport,
ip_fw_fwd_addr->sin_addr,
ntohs(ip_fw_fwd_addr->sin_port), 1,
m->m_pkthdr.rcvif);
}
}
ip_fw_fwd_addr = NULL;
} else
#endif /* IPFIREWALL_FORWARD */
{
#ifdef INET6
if (isipv6)
inp = in6_pcblookup_hash(&tcbinfo, &ip6->ip6_src, th->th_sport,
&ip6->ip6_dst, th->th_dport, 1,
m->m_pkthdr.rcvif);
else
#endif /* INET6 */
inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
ip->ip_dst, th->th_dport, 1, m->m_pkthdr.rcvif);
}
#ifdef IPSEC
#ifdef INET6
if (isipv6) {
if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
ipsec6stat.in_polvio++;
goto drop;
}
} else
#endif /* INET6 */
if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
ipsecstat.in_polvio++;
goto drop;
}
#endif /*IPSEC*/
/*
* If the state is CLOSED (i.e., TCB does not exist) then
* all data in the incoming segment is discarded.
* If the TCB exists but is in CLOSED state, it is embryonic,
* but should either do a listen or a connect soon.
*/
if (inp == NULL) {
if (log_in_vain) {
#ifdef INET6
char dbuf[INET6_ADDRSTRLEN], sbuf[INET6_ADDRSTRLEN];
#else /* INET6 */
char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"];
#endif /* INET6 */
#ifdef INET6
if (isipv6) {
strcpy(dbuf, ip6_sprintf(&ip6->ip6_dst));
strcpy(sbuf, ip6_sprintf(&ip6->ip6_src));
} else
#endif
{
strcpy(dbuf, inet_ntoa(ip->ip_dst));
strcpy(sbuf, inet_ntoa(ip->ip_src));
}
switch (log_in_vain) {
case 1:
if(thflags & TH_SYN)
log(LOG_INFO,
"Connection attempt to TCP %s:%d from %s:%d\n",
dbuf, ntohs(th->th_dport),
sbuf,
ntohs(th->th_sport));
break;
case 2:
log(LOG_INFO,
"Connection attempt to TCP %s:%d from %s:%d flags:0x%x\n",
dbuf, ntohs(th->th_dport), sbuf,
ntohs(th->th_sport), thflags);
break;
default:
break;
}
}
if (blackhole) {
switch (blackhole) {
case 1:
if (thflags & TH_SYN)
goto drop;
break;
case 2:
goto drop;
default:
goto drop;
}
}
goto maybedropwithreset;
}
tp = intotcpcb(inp);
if (tp == 0)
goto maybedropwithreset;
if (tp->t_state == TCPS_CLOSED)
goto drop;
/* Unscale the window into a 32-bit value. */
if ((thflags & TH_SYN) == 0)
tiwin = th->th_win << tp->snd_scale;
else
tiwin = th->th_win;
#ifdef INET6
/* save packet options if user wanted */
if (inp->in6p_flags & INP_CONTROLOPTS) {
if (inp->in6p_options) {
m_freem(inp->in6p_options);
inp->in6p_options = 0;
}
ip6_savecontrol(inp, &inp->in6p_options, ip6, m);
}
/* else, should also do ip_srcroute() here? */
#endif /* INET6 */
so = inp->inp_socket;
if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG) {
ostate = tp->t_state;
#ifdef INET6
if (isipv6)
bcopy((char *)ip6, (char *)tcp_saveipgen,
sizeof(*ip6));
else
#endif /* INET6 */
bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
tcp_savetcp = *th;
}
#endif
if (so->so_options & SO_ACCEPTCONN) {
register struct tcpcb *tp0 = tp;
struct socket *so2;
#ifdef IPSEC
struct socket *oso;
#endif
#ifdef INET6
struct inpcb *oinp = sotoinpcb(so);
#endif /* INET6 */
#ifndef IPSEC
/*
* Current IPsec implementation makes incorrect IPsec
* cache if this check is done here.
* So delay this until duplicated socket is created.
*/
if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
/*
* Note: dropwithreset makes sure we don't
* send a RST in response to a RST.
*/
if (thflags & TH_ACK) {
tcpstat.tcps_badsyn++;
goto maybedropwithreset;
}
goto drop;
}
#endif
so2 = sonewconn(so, 0);
if (so2 == 0) {
tcpstat.tcps_listendrop++;
so2 = sodropablereq(so);
if (so2) {
tcp_drop(sototcpcb(so2), ETIMEDOUT);
so2 = sonewconn(so, 0);
}
if (!so2)
goto drop;
}
#ifdef IPSEC
oso = so;
#endif
so = so2;
/*
* This is ugly, but ....
*
* Mark socket as temporary until we're
* committed to keeping it. The code at
* ``drop'' and ``dropwithreset'' check the
* flag dropsocket to see if the temporary
* socket created here should be discarded.
* We mark the socket as discardable until
* we're committed to it below in TCPS_LISTEN.
*/
dropsocket++;
inp = (struct inpcb *)so->so_pcb;
#ifdef INET6
if (isipv6)
inp->in6p_laddr = ip6->ip6_dst;
else {
if (ip6_mapped_addr_on) {
inp->inp_vflag &= ~INP_IPV6;
inp->inp_vflag |= INP_IPV4;
}
#endif /* INET6 */
inp->inp_laddr = ip->ip_dst;
#ifdef INET6
}
#endif /* INET6 */
inp->inp_lport = th->th_dport;
if (in_pcbinshash(inp) != 0) {
/*
* Undo the assignments above if we failed to
* put the PCB on the hash lists.
*/
#ifdef INET6
if (isipv6)
inp->in6p_laddr = in6addr_any;
else
#endif /* INET6 */
inp->inp_laddr.s_addr = INADDR_ANY;
inp->inp_lport = 0;
goto drop;
}
#ifdef IPSEC
/*
* To avoid creating incorrectly cached IPsec
* association, this is need to be done here.
*
* Subject: (KAME-snap 748)
* From: Wayne Knowles <w.knowles@niwa.cri.nz>
* ftp://ftp.kame.net/pub/mail-list/snap-users/748
*/
if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
/*
* Note: dropwithreset makes sure we don't
* send a RST in response to a RST.
*/
if (thflags & TH_ACK) {
tcpstat.tcps_badsyn++;
goto maybedropwithreset;
}
goto drop;
}
#endif
#ifdef INET6
if (isipv6) {
/*
* inherit socket options from the listening
* socket.
*/
inp->inp_flags |=
oinp->inp_flags & INP_CONTROLOPTS;
if (inp->inp_flags & INP_CONTROLOPTS) {
if (inp->in6p_options) {
m_freem(inp->in6p_options);
inp->in6p_options = 0;
}
ip6_savecontrol(inp,
&inp->in6p_options,
ip6, m);
}
} else
#endif /* INET6 */
inp->inp_options = ip_srcroute();
#ifdef IPSEC
/* copy old policy into new socket's */
if (ipsec_copy_policy(sotoinpcb(oso)->inp_sp,
inp->inp_sp))
printf("tcp_input: could not copy policy\n");
#endif
tp = intotcpcb(inp);
tp->t_state = TCPS_LISTEN;
tp->t_flags |= tp0->t_flags & (TF_NOPUSH|TF_NOOPT);
/* Compute proper scaling value from buffer space */
while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
TCP_MAXWIN << tp->request_r_scale <
so->so_rcv.sb_hiwat)
tp->request_r_scale++;
}
}
/*
* Segment received on connection.
* Reset idle time and keep-alive timer.
*/
tp->t_rcvtime = ticks;
if (TCPS_HAVEESTABLISHED(tp->t_state))
callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
/*
* Process options if not in LISTEN state,
* else do it below (after getting remote address).
*/
if (tp->t_state != TCPS_LISTEN)
tcp_dooptions(tp, optp, optlen, th, &to);
/*
* Header prediction: check for the two common cases
* of a uni-directional data xfer. If the packet has
* no control flags, is in-sequence, the window didn't
* change and we're not retransmitting, it's a
* candidate. If the length is zero and the ack moved
* forward, we're the sender side of the xfer. Just
* free the data acked & wake any higher level process
* that was blocked waiting for space. If the length
* is non-zero and the ack didn't move, we're the
* receiver side. If we're getting packets in-order
* (the reassembly queue is empty), add the data to
* the socket buffer and note that we need a delayed ack.
* Make sure that the hidden state-flags are also off.
* Since we check for TCPS_ESTABLISHED above, it can only
* be TH_NEEDSYN.
*/
if (tp->t_state == TCPS_ESTABLISHED &&
(thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
((to.to_flag & TOF_TS) == 0 ||
TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
/*
* Using the CC option is compulsory if once started:
* the segment is OK if no T/TCP was negotiated or
* if the segment has a CC option equal to CCrecv
*/
((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
((to.to_flag & TOF_CC) != 0 && to.to_cc == tp->cc_recv)) &&
th->th_seq == tp->rcv_nxt &&
tiwin && tiwin == tp->snd_wnd &&
tp->snd_nxt == tp->snd_max) {
/*
* If last ACK falls within this segment's sequence numbers,
* record the timestamp.
* NOTE that the test is modified according to the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
*/
if ((to.to_flag & TOF_TS) != 0 &&
SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
tp->ts_recent_age = ticks;
tp->ts_recent = to.to_tsval;
}
if (tlen == 0) {
if (SEQ_GT(th->th_ack, tp->snd_una) &&
SEQ_LEQ(th->th_ack, tp->snd_max) &&
tp->snd_cwnd >= tp->snd_wnd &&
tp->t_dupacks < tcprexmtthresh) {
/*
* this is a pure ack for outstanding data.
*/
++tcpstat.tcps_predack;
/*
* "bad retransmit" recovery
*/
if (tp->t_rxtshift == 1 &&
ticks < tp->t_badrxtwin) {
tp->snd_cwnd = tp->snd_cwnd_prev;
tp->snd_ssthresh =
tp->snd_ssthresh_prev;
tp->snd_nxt = tp->snd_max;
tp->t_badrxtwin = 0;
}
if ((to.to_flag & TOF_TS) != 0)
tcp_xmit_timer(tp,
ticks - to.to_tsecr + 1);
else if (tp->t_rtttime &&
SEQ_GT(th->th_ack, tp->t_rtseq))
tcp_xmit_timer(tp, ticks - tp->t_rtttime);
acked = th->th_ack - tp->snd_una;
tcpstat.tcps_rcvackpack++;
tcpstat.tcps_rcvackbyte += acked;
sbdrop(&so->so_snd, acked);
tp->snd_una = th->th_ack;
m_freem(m);
ND6_HINT(tp); /* some progress has been done */
/*
* If all outstanding data are acked, stop
* retransmit timer, otherwise restart timer
* using current (possibly backed-off) value.
* If process is waiting for space,
* wakeup/selwakeup/signal. If data
* are ready to send, let tcp_output
* decide between more output or persist.
*/
if (tp->snd_una == tp->snd_max)
callout_stop(tp->tt_rexmt);
else if (!callout_active(tp->tt_persist))
callout_reset(tp->tt_rexmt,
tp->t_rxtcur,
tcp_timer_rexmt, tp);
sowwakeup(so);
if (so->so_snd.sb_cc)
(void) tcp_output(tp);
return;
}
} else if (th->th_ack == tp->snd_una &&
LIST_EMPTY(&tp->t_segq) &&
tlen <= sbspace(&so->so_rcv)) {
/*
* this is a pure, in-sequence data packet
* with nothing on the reassembly queue and
* we have enough buffer space to take it.
*/
++tcpstat.tcps_preddat;
tp->rcv_nxt += tlen;
tcpstat.tcps_rcvpack++;
tcpstat.tcps_rcvbyte += tlen;
ND6_HINT(tp); /* some progress has been done */
/*
* Add data to socket buffer.
*/
m_adj(m, drop_hdrlen); /* delayed header drop */
sbappend(&so->so_rcv, m);
sorwakeup(so);
if (tcp_delack_enabled) {
callout_reset(tp->tt_delack, tcp_delacktime,
tcp_timer_delack, tp);
} else {
tp->t_flags |= TF_ACKNOW;
tcp_output(tp);
}
return;
}
}
/*
* Calculate amount of space in receive window,
* and then do TCP input processing.
* Receive window is amount of space in rcv queue,
* but not less than advertised window.
*/
{ int win;
win = sbspace(&so->so_rcv);
if (win < 0)
win = 0;
tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
}
switch (tp->t_state) {
/*
* If the state is LISTEN then ignore segment if it contains an RST.
* If the segment contains an ACK then it is bad and send a RST.
* If it does not contain a SYN then it is not interesting; drop it.
* If it is from this socket, drop it, it must be forged.
* Don't bother responding if the destination was a broadcast.
* Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
* tp->iss, and send a segment:
* <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
* Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
* Fill in remote peer address fields if not previously specified.
* Enter SYN_RECEIVED state, and process any other fields of this
* segment in this state.
*/
case TCPS_LISTEN: {
register struct sockaddr_in *sin;
#ifdef INET6
register struct sockaddr_in6 *sin6;
#endif
if (thflags & TH_RST)
goto drop;
if (thflags & TH_ACK)
goto maybedropwithreset;
if ((thflags & TH_SYN) == 0)
goto drop;
if (th->th_dport == th->th_sport) {
#ifdef INET6
if (isipv6) {
if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
&ip6->ip6_src))
goto drop;
} else
#endif /* INET6 */
if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
goto drop;
}
/*
* RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
* in_broadcast() should never return true on a received
* packet with M_BCAST not set.
*
* Packets with a multicast source address should also
* be discarded.
*/
if (m->m_flags & (M_BCAST|M_MCAST))
goto drop;
#ifdef INET6
if (isipv6) {
if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
goto drop;
} else
#endif
if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
ip->ip_src.s_addr == htonl(INADDR_BROADCAST))
goto drop;
#ifdef INET6
if (isipv6) {
MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
M_SONAME, M_NOWAIT);
if (sin6 == NULL)
goto drop;
bzero(sin6, sizeof(*sin6));
sin6->sin6_family = AF_INET6;
sin6->sin6_len = sizeof(*sin6);
sin6->sin6_addr = ip6->ip6_src;
sin6->sin6_port = th->th_sport;
laddr6 = inp->in6p_laddr;
if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
inp->in6p_laddr = ip6->ip6_dst;
if (in6_pcbconnect(inp, (struct sockaddr *)sin6,
&proc0)) {
inp->in6p_laddr = laddr6;
FREE(sin6, M_SONAME);
goto drop;
}
FREE(sin6, M_SONAME);
} else
#endif
{
MALLOC(sin, struct sockaddr_in *, sizeof *sin, M_SONAME,
M_NOWAIT);
if (sin == NULL)
goto drop;
sin->sin_family = AF_INET;
sin->sin_len = sizeof(*sin);
sin->sin_addr = ip->ip_src;
sin->sin_port = th->th_sport;
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 = ip->ip_dst;
if (in_pcbconnect(inp, (struct sockaddr *)sin, &proc0)) {
inp->inp_laddr = laddr;
FREE(sin, M_SONAME);
goto drop;
}
FREE(sin, M_SONAME);
}
tp->t_template = tcp_template(tp);
if (tp->t_template == 0) {
tp = tcp_drop(tp, ENOBUFS);
dropsocket = 0; /* socket is already gone */
goto drop;
}
if ((taop = tcp_gettaocache(inp)) == NULL) {
taop = &tao_noncached;
bzero(taop, sizeof(*taop));
}
tcp_dooptions(tp, optp, optlen, th, &to);
if (iss)
tp->iss = iss;
else
tp->iss = tcp_iss;
tcp_iss += TCP_ISSINCR/4;
tp->irs = th->th_seq;
tcp_sendseqinit(tp);
tcp_rcvseqinit(tp);
/*
* Initialization of the tcpcb for transaction;
* set SND.WND = SEG.WND,
* initialize CCsend and CCrecv.
*/
tp->snd_wnd = tiwin; /* initial send-window */
tp->cc_send = CC_INC(tcp_ccgen);
tp->cc_recv = to.to_cc;
/*
* 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.
*/
if ((to.to_flag & TOF_CC) != 0) {
if (((tp->t_flags & TF_NOPUSH) != 0) &&
taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
taop->tao_cc = to.to_cc;
tp->t_starttime = ticks;
tp->t_state = TCPS_ESTABLISHED;
/*
* If there is a FIN, or if there is data and the
* connection is local, then delay SYN,ACK(SYN) in
* the hope of piggy-backing it on a response
* segment. Otherwise must send ACK now in case
* the other side is slow starting.
*/
if (tcp_delack_enabled && ((thflags & TH_FIN) ||
(tlen != 0 &&
#ifdef INET6
((isipv6 && in6_localaddr(&inp->in6p_faddr))
||
(!isipv6 &&
#endif
in_localaddr(inp->inp_faddr)
#ifdef INET6
))
#endif
))) {
callout_reset(tp->tt_delack, tcp_delacktime,
tcp_timer_delack, tp);
tp->t_flags |= TF_NEEDSYN;
} else
tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
/*
* Limit the `virtual advertised window' to TCP_MAXWIN
* here. Even if we requested window scaling, it will
* become effective only later when our SYN is acked.
*/
tp->rcv_adv += min(tp->rcv_wnd, TCP_MAXWIN);
tcpstat.tcps_connects++;
soisconnected(so);
callout_reset(tp->tt_keep, tcp_keepinit,
tcp_timer_keep, tp);
dropsocket = 0; /* committed to socket */
tcpstat.tcps_accepts++;
goto trimthenstep6;
}
/* else do standard 3-way handshake */
} else {
/*
* No CC option, but maybe CC.NEW:
* invalidate cached value.
*/
taop->tao_cc = 0;
}
/*
* TAO test failed or there was no CC option,
* do a standard 3-way handshake.
*/
tp->t_flags |= TF_ACKNOW;
tp->t_state = TCPS_SYN_RECEIVED;
callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
dropsocket = 0; /* committed to socket */
tcpstat.tcps_accepts++;
ND6_HINT((struct tcpcb *)inp->inp_ppcb);
goto trimthenstep6;
}
/*
* If the state is SYN_RECEIVED:
* if seg contains an ACK, but not for our SYN/ACK, send a RST.
*/
case TCPS_SYN_RECEIVED:
if ((thflags & TH_ACK) &&
(SEQ_LEQ(th->th_ack, tp->snd_una) ||
SEQ_GT(th->th_ack, tp->snd_max)))
goto maybedropwithreset;
break;
/*
* If the state is SYN_SENT:
* if seg contains an ACK, but not for our SYN, drop the input.
* if seg contains a RST, then drop the connection.
* if seg does not contain SYN, then drop it.
* Otherwise this is an acceptable SYN segment
* initialize tp->rcv_nxt and tp->irs
* if seg contains ack then advance tp->snd_una
* if SYN has been acked change to ESTABLISHED else SYN_RCVD state
* arrange for segment to be acked (eventually)
* continue processing rest of data/controls, beginning with URG
*/
case TCPS_SYN_SENT:
if ((taop = tcp_gettaocache(inp)) == NULL) {
taop = &tao_noncached;
bzero(taop, sizeof(*taop));
}
if ((thflags & TH_ACK) &&
(SEQ_LEQ(th->th_ack, tp->iss) ||
SEQ_GT(th->th_ack, tp->snd_max))) {
/*
* If we have a cached CCsent for the remote host,
* hence we haven't just crashed and restarted,
* do not send a RST. This may be a retransmission
* from the other side after our earlier ACK was lost.
* Our new SYN, when it arrives, will serve as the
* needed ACK.
*/
if (taop->tao_ccsent != 0)
goto drop;
else
goto dropwithreset;
}
if (thflags & TH_RST) {
if (thflags & TH_ACK)
tp = tcp_drop(tp, ECONNREFUSED);
goto drop;
}
if ((thflags & TH_SYN) == 0)
goto drop;
tp->snd_wnd = th->th_win; /* initial send window */
tp->cc_recv = to.to_cc; /* foreign CC */
tp->irs = th->th_seq;
tcp_rcvseqinit(tp);
if (thflags & TH_ACK) {
/*
* Our SYN was acked. If segment contains CC.ECHO
* option, check it to make sure this segment really
* matches our SYN. If not, just drop it as old
* duplicate, but send an RST if we're still playing
* by the old rules. If no CC.ECHO option, make sure
* we don't get fooled into using T/TCP.
*/
if (to.to_flag & TOF_CCECHO) {
if (tp->cc_send != to.to_ccecho) {
if (taop->tao_ccsent != 0)
goto drop;
else
goto dropwithreset;
}
} else
tp->t_flags &= ~TF_RCVD_CC;
tcpstat.tcps_connects++;
soisconnected(so);
/* Do window scaling on this connection? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
/* Segment is acceptable, update cache if undefined. */
if (taop->tao_ccsent == 0)
taop->tao_ccsent = to.to_ccecho;
tp->rcv_adv += tp->rcv_wnd;
tp->snd_una++; /* SYN is acked */
/*
* If there's data, delay ACK; if there's also a FIN
* ACKNOW will be turned on later.
*/
if (tcp_delack_enabled && tlen != 0)
callout_reset(tp->tt_delack, tcp_delacktime,
tcp_timer_delack, tp);
else
tp->t_flags |= TF_ACKNOW;
/*
* Received <SYN,ACK> in SYN_SENT[*] state.
* Transitions:
* SYN_SENT --> ESTABLISHED
* SYN_SENT* --> FIN_WAIT_1
*/
tp->t_starttime = ticks;
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
thflags &= ~TH_SYN;
} else {
tp->t_state = TCPS_ESTABLISHED;
callout_reset(tp->tt_keep, tcp_keepidle,
tcp_timer_keep, tp);
}
} else {
/*
* Received initial SYN in SYN-SENT[*] state => simul-
* taneous open. If segment contains CC option and there is
* a cached CC, apply TAO test; if it succeeds, connection is
* half-synchronized. Otherwise, do 3-way handshake:
* SYN-SENT -> SYN-RECEIVED
* SYN-SENT* -> SYN-RECEIVED*
* If there was no CC option, clear cached CC value.
*/
tp->t_flags |= TF_ACKNOW;
callout_stop(tp->tt_rexmt);
if (to.to_flag & TOF_CC) {
if (taop->tao_cc != 0 &&
CC_GT(to.to_cc, taop->tao_cc)) {
/*
* update cache and make transition:
* SYN-SENT -> ESTABLISHED*
* SYN-SENT* -> FIN-WAIT-1*
*/
taop->tao_cc = to.to_cc;
tp->t_starttime = ticks;
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
} else {
tp->t_state = TCPS_ESTABLISHED;
callout_reset(tp->tt_keep,
tcp_keepidle,
tcp_timer_keep,
tp);
}
tp->t_flags |= TF_NEEDSYN;
} else
tp->t_state = TCPS_SYN_RECEIVED;
} else {
/* CC.NEW or no option => invalidate cache */
taop->tao_cc = 0;
tp->t_state = TCPS_SYN_RECEIVED;
}
}
trimthenstep6:
/*
* Advance th->th_seq to correspond to first data byte.
* If data, trim to stay within window,
* dropping FIN if necessary.
*/
th->th_seq++;
if (tlen > tp->rcv_wnd) {
todrop = tlen - tp->rcv_wnd;
m_adj(m, -todrop);
tlen = tp->rcv_wnd;
thflags &= ~TH_FIN;
tcpstat.tcps_rcvpackafterwin++;
tcpstat.tcps_rcvbyteafterwin += todrop;
}
tp->snd_wl1 = th->th_seq - 1;
tp->rcv_up = th->th_seq;
/*
* Client side of transaction: already sent SYN and data.
* If the remote host used T/TCP to validate the SYN,
* our data will be ACK'd; if so, enter normal data segment
* processing in the middle of step 5, ack processing.
* Otherwise, goto step 6.
*/
if (thflags & TH_ACK)
goto process_ACK;
goto step6;
/*
* If the state is LAST_ACK or CLOSING or TIME_WAIT:
* if segment contains a SYN and CC [not CC.NEW] option:
* if state == TIME_WAIT and connection duration > MSL,
* drop packet and send RST;
*
* if SEG.CC > CCrecv then is new SYN, and can implicitly
* ack the FIN (and data) in retransmission queue.
* Complete close and delete TCPCB. Then reprocess
* segment, hoping to find new TCPCB in LISTEN state;
*
* else must be old SYN; drop it.
* else do normal processing.
*/
case TCPS_LAST_ACK:
case TCPS_CLOSING:
case TCPS_TIME_WAIT:
if ((thflags & TH_SYN) &&
(to.to_flag & TOF_CC) && tp->cc_recv != 0) {
if (tp->t_state == TCPS_TIME_WAIT &&
(ticks - tp->t_starttime) > tcp_msl)
goto dropwithreset;
if (CC_GT(to.to_cc, tp->cc_recv)) {
tp = tcp_close(tp);
goto findpcb;
}
else
goto drop;
}
break; /* continue normal processing */
}
/*
* States other than LISTEN or SYN_SENT.
* First check the RST flag and sequence number since reset segments
* are exempt from the timestamp and connection count tests. This
* fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
* below which allowed reset segments in half the sequence space
* to fall though and be processed (which gives forged reset
* segments with a random sequence number a 50 percent chance of
* killing a connection).
* Then check timestamp, if present.
* Then check the connection count, if present.
* Then check that at least some bytes of segment are within
* receive window. If segment begins before rcv_nxt,
* drop leading data (and SYN); if nothing left, just ack.
*
*
* 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.
* Note: this does not take into account delayed ACKs, so
* we should test against last_ack_sent instead of rcv_nxt.
* 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 we have multiple segments in flight, the intial reset
* segment sequence numbers will be to the left of last_ack_sent,
* but they will eventually catch up.
* In any case, it never made sense to trim reset segments to
* fit the receive window since RFC 1122 says:
* 4.2.2.12 RST Segment: RFC-793 Section 3.4
*
* A TCP SHOULD allow a received RST segment to include data.
*
* DISCUSSION
* It has been suggested that a RST segment could contain
* ASCII text that encoded and explained the cause of the
* RST. No standard has yet been established for such
* data.
*
* If the reset segment passes the sequence number test examine
* the state:
* SYN_RECEIVED STATE:
* If passive open, return to LISTEN state.
* If active open, inform user that connection was refused.
* ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
* Inform user that connection was reset, and close tcb.
* CLOSING, LAST_ACK STATES:
* Close the tcb.
* TIME_WAIT STATE:
* Drop the segment - see Stevens, vol. 2, p. 964 and
* RFC 1337.
*/
if (thflags & TH_RST) {
if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
switch (tp->t_state) {
case TCPS_SYN_RECEIVED:
so->so_error = ECONNREFUSED;
goto close;
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
so->so_error = ECONNRESET;
close:
tp->t_state = TCPS_CLOSED;
tcpstat.tcps_drops++;
tp = tcp_close(tp);
break;
case TCPS_CLOSING:
case TCPS_LAST_ACK:
tp = tcp_close(tp);
break;
case TCPS_TIME_WAIT:
break;
}
}
goto drop;
}
/*
* RFC 1323 PAWS: If we have a timestamp reply on this segment
* and it's less than ts_recent, drop it.
*/
if ((to.to_flag & TOF_TS) != 0 && tp->ts_recent &&
TSTMP_LT(to.to_tsval, tp->ts_recent)) {
/* Check to see if ts_recent is over 24 days old. */
if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) {
/*
* Invalidate ts_recent. If this segment updates
* ts_recent, the age will be reset later and ts_recent
* will get a valid value. If it does not, setting
* ts_recent to zero will at least satisfy the
* requirement that zero be placed in the timestamp
* echo reply when ts_recent isn't valid. The
* age isn't reset until we get a valid ts_recent
* because we don't want out-of-order segments to be
* dropped when ts_recent is old.
*/
tp->ts_recent = 0;
} else {
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += tlen;
tcpstat.tcps_pawsdrop++;
goto dropafterack;
}
}
/*
* T/TCP mechanism
* If T/TCP was negotiated and the segment doesn't have CC,
* or if its CC is wrong then drop the segment.
* RST segments do not have to comply with this.
*/
if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
((to.to_flag & TOF_CC) == 0 || tp->cc_recv != to.to_cc))
goto dropafterack;
/*
* In the SYN-RECEIVED state, validate that the packet belongs to
* this connection before trimming the data to fit the receive
* window. Check the sequence number versus IRS since we know
* the sequence numbers haven't wrapped. This is a partial fix
* for the "LAND" DoS attack.
*/
if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs))
goto maybedropwithreset;
todrop = tp->rcv_nxt - th->th_seq;
if (todrop > 0) {
if (thflags & TH_SYN) {
thflags &= ~TH_SYN;
th->th_seq++;
if (th->th_urp > 1)
th->th_urp--;
else
thflags &= ~TH_URG;
todrop--;
}
/*
* Following if statement from Stevens, vol. 2, p. 960.
*/
if (todrop > tlen
|| (todrop == tlen && (thflags & TH_FIN) == 0)) {
/*
* Any valid FIN must be to the left of the window.
* At this point the FIN must be a duplicate or out
* of sequence; drop it.
*/
thflags &= ~TH_FIN;
/*
* Send an ACK to resynchronize and drop any data.
* But keep on processing for RST or ACK.
*/
tp->t_flags |= TF_ACKNOW;
todrop = tlen;
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += todrop;
} else {
tcpstat.tcps_rcvpartduppack++;
tcpstat.tcps_rcvpartdupbyte += todrop;
}
drop_hdrlen += todrop; /* drop from the top afterwards */
th->th_seq += todrop;
tlen -= todrop;
if (th->th_urp > todrop)
th->th_urp -= todrop;
else {
thflags &= ~TH_URG;
th->th_urp = 0;
}
}
/*
* If new data are received on a connection after the
* user processes are gone, then RST the other end.
*/
if ((so->so_state & SS_NOFDREF) &&
tp->t_state > TCPS_CLOSE_WAIT && tlen) {
tp = tcp_close(tp);
tcpstat.tcps_rcvafterclose++;
goto dropwithreset;
}
/*
* If segment ends after window, drop trailing data
* (and PUSH and FIN); if nothing left, just ACK.
*/
todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd);
if (todrop > 0) {
tcpstat.tcps_rcvpackafterwin++;
if (todrop >= tlen) {
tcpstat.tcps_rcvbyteafterwin += tlen;
/*
* If a new connection request is received
* while in TIME_WAIT, drop the old connection
* and start over if the sequence numbers
* are above the previous ones.
*/
if (thflags & TH_SYN &&
tp->t_state == TCPS_TIME_WAIT &&
SEQ_GT(th->th_seq, tp->rcv_nxt)) {
iss = tp->snd_nxt + TCP_ISSINCR;
tp = tcp_close(tp);
goto findpcb;
}
/*
* If window is closed can only take segments at
* window edge, and have to drop data and PUSH from
* incoming segments. Continue processing, but
* remember to ack. Otherwise, drop segment
* and ack.
*/
if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
tp->t_flags |= TF_ACKNOW;
tcpstat.tcps_rcvwinprobe++;
} else
goto dropafterack;
} else
tcpstat.tcps_rcvbyteafterwin += todrop;
m_adj(m, -todrop);
tlen -= todrop;
thflags &= ~(TH_PUSH|TH_FIN);
}
/*
* If last ACK falls within this segment's sequence numbers,
* record its timestamp.
* NOTE that the test is modified according to the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
*/
if ((to.to_flag & TOF_TS) != 0 &&
SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
tp->ts_recent_age = ticks;
tp->ts_recent = to.to_tsval;
}
/*
* If a SYN is in the window, then this is an
* error and we send an RST and drop the connection.
*/
if (thflags & TH_SYN) {
tp = tcp_drop(tp, ECONNRESET);
goto dropwithreset;
}
/*
* If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
* flag is on (half-synchronized state), then queue data for
* later processing; else drop segment and return.
*/
if ((thflags & TH_ACK) == 0) {
if (tp->t_state == TCPS_SYN_RECEIVED ||
(tp->t_flags & TF_NEEDSYN))
goto step6;
else
goto drop;
}
/*
* Ack processing.
*/
switch (tp->t_state) {
/*
* In SYN_RECEIVED state, the ack ACKs our SYN, so enter
* ESTABLISHED state and continue processing.
* The ACK was checked above.
*/
case TCPS_SYN_RECEIVED:
tcpstat.tcps_connects++;
soisconnected(so);
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
/*
* Upon successful completion of 3-way handshake,
* update cache.CC if it was undefined, pass any queued
* data to the user, and advance state appropriately.
*/
if ((taop = tcp_gettaocache(inp)) != NULL &&
taop->tao_cc == 0)
taop->tao_cc = tp->cc_recv;
/*
* Make transitions:
* SYN-RECEIVED -> ESTABLISHED
* SYN-RECEIVED* -> FIN-WAIT-1
*/
tp->t_starttime = ticks;
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
} else {
tp->t_state = TCPS_ESTABLISHED;
callout_reset(tp->tt_keep, tcp_keepidle,
tcp_timer_keep, tp);
}
/*
* If segment contains data or ACK, will call tcp_reass()
* later; if not, do so now to pass queued data to user.
*/
if (tlen == 0 && (thflags & TH_FIN) == 0)
(void) tcp_reass(tp, (struct tcphdr *)0, 0,
(struct mbuf *)0);
tp->snd_wl1 = th->th_seq - 1;
/* fall into ... */
/*
* In ESTABLISHED state: drop duplicate ACKs; ACK out of range
* ACKs. If the ack is in the range
* tp->snd_una < th->th_ack <= tp->snd_max
* then advance tp->snd_una to th->th_ack and drop
* data from the retransmission queue. If this ACK reflects
* more up to date window information we update our window information.
*/
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
case TCPS_CLOSING:
case TCPS_LAST_ACK:
case TCPS_TIME_WAIT:
if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
if (tlen == 0 && tiwin == tp->snd_wnd) {
tcpstat.tcps_rcvdupack++;
/*
* If we have outstanding data (other than
* a window probe), this is a completely
* duplicate ack (ie, window info didn't
* change), the ack is the biggest we've
* seen and we've seen exactly our rexmt
* threshhold of them, assume a packet
* has been dropped and retransmit it.
* Kludge snd_nxt & the congestion
* window so we send only this one
* packet.
*
* We know we're losing at the current
* window size so do congestion avoidance
* (set ssthresh to half the current window
* and pull our congestion window back to
* the new ssthresh).
*
* Dup acks mean that packets have left the
* network (they're now cached at the receiver)
* so bump cwnd by the amount in the receiver
* to keep a constant cwnd packets in the
* network.
*/
if (!callout_active(tp->tt_rexmt) ||
th->th_ack != tp->snd_una)
tp->t_dupacks = 0;
else if (++tp->t_dupacks == tcprexmtthresh) {
tcp_seq onxt = tp->snd_nxt;
u_int win =
min(tp->snd_wnd, tp->snd_cwnd) / 2 /
tp->t_maxseg;
if (win < 2)
win = 2;
tp->snd_ssthresh = win * tp->t_maxseg;
callout_stop(tp->tt_rexmt);
tp->t_rtttime = 0;
tp->snd_nxt = th->th_ack;
tp->snd_cwnd = tp->t_maxseg;
(void) tcp_output(tp);
tp->snd_cwnd = tp->snd_ssthresh +
tp->t_maxseg * tp->t_dupacks;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
goto drop;
} else if (tp->t_dupacks > tcprexmtthresh) {
tp->snd_cwnd += tp->t_maxseg;
(void) tcp_output(tp);
goto drop;
}
} else
tp->t_dupacks = 0;
break;
}
/*
* If the congestion window was inflated to account
* for the other side's cached packets, retract it.
*/
if (tp->t_dupacks >= tcprexmtthresh &&
tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_dupacks = 0;
if (SEQ_GT(th->th_ack, tp->snd_max)) {
tcpstat.tcps_rcvacktoomuch++;
goto dropafterack;
}
/*
* If we reach this point, ACK is not a duplicate,
* i.e., it ACKs something we sent.
*/
if (tp->t_flags & TF_NEEDSYN) {
/*
* T/TCP: Connection was half-synchronized, and our
* SYN has been ACK'd (so connection is now fully
* synchronized). Go to non-starred state,
* increment snd_una for ACK of SYN, and check if
* we can do window scaling.
*/
tp->t_flags &= ~TF_NEEDSYN;
tp->snd_una++;
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
}
process_ACK:
acked = th->th_ack - tp->snd_una;
tcpstat.tcps_rcvackpack++;
tcpstat.tcps_rcvackbyte += acked;
/*
* If we just performed our first retransmit, and the ACK
* arrives within our recovery window, then it was a mistake
* to do the retransmit in the first place. Recover our
* original cwnd and ssthresh, and proceed to transmit where
* we left off.
*/
if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) {
tp->snd_cwnd = tp->snd_cwnd_prev;
tp->snd_ssthresh = tp->snd_ssthresh_prev;
tp->snd_nxt = tp->snd_max;
tp->t_badrxtwin = 0; /* XXX probably not required */
}
/*
* If we have a timestamp reply, update smoothed
* round trip time. If no timestamp is present but
* transmit timer is running and timed sequence
* number was acked, update smoothed round trip time.
* Since we now have an rtt measurement, cancel the
* timer backoff (cf., Phil Karn's retransmit alg.).
* Recompute the initial retransmit timer.
*/
if (to.to_flag & TOF_TS)
tcp_xmit_timer(tp, ticks - to.to_tsecr + 1);
else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
tcp_xmit_timer(tp, ticks - tp->t_rtttime);
/*
* If all outstanding data is acked, stop retransmit
* timer and remember to restart (more output or persist).
* If there is more data to be acked, restart retransmit
* timer, using current (possibly backed-off) value.
*/
if (th->th_ack == tp->snd_max) {
callout_stop(tp->tt_rexmt);
needoutput = 1;
} else if (!callout_active(tp->tt_persist))
callout_reset(tp->tt_rexmt, tp->t_rxtcur,
tcp_timer_rexmt, tp);
/*
* If no data (only SYN) was ACK'd,
* skip rest of ACK processing.
*/
if (acked == 0)
goto step6;
/*
* When new data is acked, open the congestion window.
* If the window gives us less than ssthresh packets
* in flight, open exponentially (maxseg per packet).
* Otherwise open linearly: maxseg per window
* (maxseg^2 / cwnd per packet).
*/
{
register u_int cw = tp->snd_cwnd;
register u_int incr = tp->t_maxseg;
if (cw > tp->snd_ssthresh)
incr = incr * incr / cw;
tp->snd_cwnd = min(cw + incr, TCP_MAXWIN << tp->snd_scale);
}
if (acked > so->so_snd.sb_cc) {
tp->snd_wnd -= so->so_snd.sb_cc;
sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
ourfinisacked = 1;
} else {
sbdrop(&so->so_snd, acked);
tp->snd_wnd -= acked;
ourfinisacked = 0;
}
sowwakeup(so);
tp->snd_una = th->th_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
switch (tp->t_state) {
/*
* In FIN_WAIT_1 STATE in addition to the processing
* for the ESTABLISHED state if our FIN is now acknowledged
* then enter FIN_WAIT_2.
*/
case TCPS_FIN_WAIT_1:
if (ourfinisacked) {
/*
* If we can't receive any more
* data, then closing user can proceed.
* Starting the timer is contrary to the
* specification, but if we don't get a FIN
* we'll hang forever.
*/
if (so->so_state & SS_CANTRCVMORE) {
soisdisconnected(so);
callout_reset(tp->tt_2msl, tcp_maxidle,
tcp_timer_2msl, tp);
}
tp->t_state = TCPS_FIN_WAIT_2;
}
break;
/*
* In CLOSING STATE in addition to the processing for
* the ESTABLISHED state if the ACK acknowledges our FIN
* then enter the TIME-WAIT state, otherwise ignore
* the segment.
*/
case TCPS_CLOSING:
if (ourfinisacked) {
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
/* Shorten TIME_WAIT [RFC-1644, p.28] */
if (tp->cc_recv != 0 &&
(ticks - tp->t_starttime) < tcp_msl)
callout_reset(tp->tt_2msl,
tp->t_rxtcur *
TCPTV_TWTRUNC,
tcp_timer_2msl, tp);
else
callout_reset(tp->tt_2msl, 2 * tcp_msl,
tcp_timer_2msl, tp);
soisdisconnected(so);
}
break;
/*
* In LAST_ACK, we may still be waiting for data to drain
* and/or to be acked, as well as for the ack of our FIN.
* If our FIN is now acknowledged, delete the TCB,
* enter the closed state and return.
*/
case TCPS_LAST_ACK:
if (ourfinisacked) {
tp = tcp_close(tp);
goto drop;
}
break;
/*
* In TIME_WAIT state the only thing that should arrive
* is a retransmission of the remote FIN. Acknowledge
* it and restart the finack timer.
*/
case TCPS_TIME_WAIT:
callout_reset(tp->tt_2msl, 2 * tcp_msl,
tcp_timer_2msl, tp);
goto dropafterack;
}
}
step6:
/*
* Update window information.
* Don't look at window if no ACK: TAC's send garbage on first SYN.
*/
if ((thflags & TH_ACK) &&
(SEQ_LT(tp->snd_wl1, th->th_seq) ||
(tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
(tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
/* keep track of pure window updates */
if (tlen == 0 &&
tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
tcpstat.tcps_rcvwinupd++;
tp->snd_wnd = tiwin;
tp->snd_wl1 = th->th_seq;
tp->snd_wl2 = th->th_ack;
if (tp->snd_wnd > tp->max_sndwnd)
tp->max_sndwnd = tp->snd_wnd;
needoutput = 1;
}
/*
* Process segments with URG.
*/
if ((thflags & TH_URG) && th->th_urp &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
/*
* This is a kludge, but if we receive and accept
* random urgent pointers, we'll crash in
* soreceive. It's hard to imagine someone
* actually wanting to send this much urgent data.
*/
if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
th->th_urp = 0; /* XXX */
thflags &= ~TH_URG; /* XXX */
goto dodata; /* XXX */
}
/*
* If this segment advances the known urgent pointer,
* then mark the data stream. This should not happen
* in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
* a FIN has been received from the remote side.
* In these states we ignore the URG.
*
* According to RFC961 (Assigned Protocols),
* the urgent pointer points to the last octet
* of urgent data. We continue, however,
* to consider it to indicate the first octet
* of data past the urgent section as the original
* spec states (in one of two places).
*/
if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
tp->rcv_up = th->th_seq + th->th_urp;
so->so_oobmark = so->so_rcv.sb_cc +
(tp->rcv_up - tp->rcv_nxt) - 1;
if (so->so_oobmark == 0)
so->so_state |= SS_RCVATMARK;
sohasoutofband(so);
tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
}
/*
* Remove out of band data so doesn't get presented to user.
* This can happen independent of advancing the URG pointer,
* but if two URG's are pending at once, some out-of-band
* data may creep in... ick.
*/
if (th->th_urp <= (u_long)tlen
#ifdef SO_OOBINLINE
&& (so->so_options & SO_OOBINLINE) == 0
#endif
)
tcp_pulloutofband(so, th, m,
drop_hdrlen); /* hdr drop is delayed */
} else
/*
* If no out of band data is expected,
* pull receive urgent pointer along
* with the receive window.
*/
if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
tp->rcv_up = tp->rcv_nxt;
dodata: /* XXX */
/*
* Process the segment text, merging it into the TCP sequencing queue,
* and arranging for acknowledgment of receipt if necessary.
* This process logically involves adjusting tp->rcv_wnd as data
* is presented to the user (this happens in tcp_usrreq.c,
* case PRU_RCVD). If a FIN has already been received on this
* connection then we just ignore the text.
*/
if ((tlen || (thflags&TH_FIN)) &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
m_adj(m, drop_hdrlen); /* delayed header drop */
TCP_REASS(tp, th, &tlen, m, so, thflags);
/*
* Note the amount of data that peer has sent into
* our window, in order to estimate the sender's
* buffer size.
*/
len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
} else {
m_freem(m);
thflags &= ~TH_FIN;
}
/*
* If FIN is received ACK the FIN and let the user know
* that the connection is closing.
*/
if (thflags & TH_FIN) {
if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
socantrcvmore(so);
/*
* If connection is half-synchronized
* (ie NEEDSYN flag on) then delay ACK,
* so it may be piggybacked when SYN is sent.
* Otherwise, since we received a FIN then no
* more input can be expected, send ACK now.
*/
if (tcp_delack_enabled && (tp->t_flags & TF_NEEDSYN))
callout_reset(tp->tt_delack, tcp_delacktime,
tcp_timer_delack, tp);
else
tp->t_flags |= TF_ACKNOW;
tp->rcv_nxt++;
}
switch (tp->t_state) {
/*
* In SYN_RECEIVED and ESTABLISHED STATES
* enter the CLOSE_WAIT state.
*/
case TCPS_SYN_RECEIVED:
tp->t_starttime = ticks;
/*FALLTHROUGH*/
case TCPS_ESTABLISHED:
tp->t_state = TCPS_CLOSE_WAIT;
break;
/*
* If still in FIN_WAIT_1 STATE FIN has not been acked so
* enter the CLOSING state.
*/
case TCPS_FIN_WAIT_1:
tp->t_state = TCPS_CLOSING;
break;
/*
* In FIN_WAIT_2 state enter the TIME_WAIT state,
* starting the time-wait timer, turning off the other
* standard timers.
*/
case TCPS_FIN_WAIT_2:
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
/* Shorten TIME_WAIT [RFC-1644, p.28] */
if (tp->cc_recv != 0 &&
(ticks - tp->t_starttime) < tcp_msl) {
callout_reset(tp->tt_2msl,
tp->t_rxtcur * TCPTV_TWTRUNC,
tcp_timer_2msl, tp);
/* For transaction client, force ACK now. */
tp->t_flags |= TF_ACKNOW;
}
else
callout_reset(tp->tt_2msl, 2 * tcp_msl,
tcp_timer_2msl, tp);
soisdisconnected(so);
break;
/*
* In TIME_WAIT state restart the 2 MSL time_wait timer.
*/
case TCPS_TIME_WAIT:
callout_reset(tp->tt_2msl, 2 * tcp_msl,
tcp_timer_2msl, tp);
break;
}
}
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
/*
* Return any desired output.
*/
if (needoutput || (tp->t_flags & TF_ACKNOW))
(void) tcp_output(tp);
return;
dropafterack:
/*
* Generate an ACK dropping incoming segment if it occupies
* sequence space, where the ACK reflects our state.
*
* We can now skip the test for the RST flag since all
* paths to this code happen after packets containing
* RST have been dropped.
*
* In the SYN-RECEIVED state, don't send an ACK unless the
* segment we received passes the SYN-RECEIVED ACK test.
* If it fails send a RST. This breaks the loop in the
* "LAND" DoS attack, and also prevents an ACK storm
* between two listening ports that have been sent forged
* SYN segments, each with the source address of the other.
*/
if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
(SEQ_GT(tp->snd_una, th->th_ack) ||
SEQ_GT(th->th_ack, tp->snd_max)) )
goto maybedropwithreset;
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
m_freem(m);
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
return;
/*
* Conditionally drop with reset or just drop depending on whether
* we think we are under attack or not.
*/
maybedropwithreset:
#ifdef ICMP_BANDLIM
if (badport_bandlim(1) < 0)
goto drop;
#endif
/* fall through */
dropwithreset:
#ifdef TCP_RESTRICT_RST
if (restrict_rst)
goto drop;
#endif
/*
* Generate a RST, dropping incoming segment.
* Make ACK acceptable to originator of segment.
* Don't bother to respond if destination was broadcast/multicast.
*/
if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
goto drop;
#ifdef INET6
if (isipv6) {
if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
goto drop;
} else
#endif /* INET6 */
if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
ip->ip_src.s_addr == htonl(INADDR_BROADCAST))
goto drop;
/* IPv6 anycast check is done at tcp6_input() */
#ifdef TCPDEBUG
if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
if (thflags & TH_ACK)
/* mtod() below is safe as long as hdr dropping is delayed */
tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
TH_RST);
else {
if (thflags & TH_SYN)
tlen++;
/* mtod() below is safe as long as hdr dropping is delayed */
tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
(tcp_seq)0, TH_RST|TH_ACK);
}
/* destroy temporarily created socket */
if (dropsocket)
(void) soabort(so);
return;
drop:
/*
* Drop space held by incoming segment and return.
*/
#ifdef TCPDEBUG
if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
m_freem(m);
/* destroy temporarily created socket */
if (dropsocket)
(void) soabort(so);
return;
}
static void
tcp_dooptions(tp, cp, cnt, th, to)
struct tcpcb *tp;
u_char *cp;
int cnt;
struct tcphdr *th;
struct tcpopt *to;
{
u_short mss = 0;
int opt, optlen;
for (; cnt > 0; cnt -= optlen, cp += optlen) {
opt = cp[0];
if (opt == TCPOPT_EOL)
break;
if (opt == TCPOPT_NOP)
optlen = 1;
else {
optlen = cp[1];
if (optlen <= 0)
break;
}
switch (opt) {
default:
continue;
case TCPOPT_MAXSEG:
if (optlen != TCPOLEN_MAXSEG)
continue;
if (!(th->th_flags & TH_SYN))
continue;
bcopy((char *) cp + 2, (char *) &mss, sizeof(mss));
NTOHS(mss);
break;
case TCPOPT_WINDOW:
if (optlen != TCPOLEN_WINDOW)
continue;
if (!(th->th_flags & TH_SYN))
continue;
tp->t_flags |= TF_RCVD_SCALE;
tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
break;
case TCPOPT_TIMESTAMP:
if (optlen != TCPOLEN_TIMESTAMP)
continue;
to->to_flag |= TOF_TS;
bcopy((char *)cp + 2,
(char *)&to->to_tsval, sizeof(to->to_tsval));
NTOHL(to->to_tsval);
bcopy((char *)cp + 6,
(char *)&to->to_tsecr, sizeof(to->to_tsecr));
NTOHL(to->to_tsecr);
/*
* A timestamp received in a SYN makes
* it ok to send timestamp requests and replies.
*/
if (th->th_flags & TH_SYN) {
tp->t_flags |= TF_RCVD_TSTMP;
tp->ts_recent = to->to_tsval;
tp->ts_recent_age = ticks;
}
break;
case TCPOPT_CC:
if (optlen != TCPOLEN_CC)
continue;
to->to_flag |= TOF_CC;
bcopy((char *)cp + 2,
(char *)&to->to_cc, sizeof(to->to_cc));
NTOHL(to->to_cc);
/*
* A CC or CC.new option received in a SYN makes
* it ok to send CC in subsequent segments.
*/
if (th->th_flags & TH_SYN)
tp->t_flags |= TF_RCVD_CC;
break;
case TCPOPT_CCNEW:
if (optlen != TCPOLEN_CC)
continue;
if (!(th->th_flags & TH_SYN))
continue;
to->to_flag |= TOF_CCNEW;
bcopy((char *)cp + 2,
(char *)&to->to_cc, sizeof(to->to_cc));
NTOHL(to->to_cc);
/*
* A CC or CC.new option received in a SYN makes
* it ok to send CC in subsequent segments.
*/
tp->t_flags |= TF_RCVD_CC;
break;
case TCPOPT_CCECHO:
if (optlen != TCPOLEN_CC)
continue;
if (!(th->th_flags & TH_SYN))
continue;
to->to_flag |= TOF_CCECHO;
bcopy((char *)cp + 2,
(char *)&to->to_ccecho, sizeof(to->to_ccecho));
NTOHL(to->to_ccecho);
break;
}
}
if (th->th_flags & TH_SYN)
tcp_mss(tp, mss); /* sets t_maxseg */
}
/*
* Pull out of band byte out of a segment so
* it doesn't appear in the user's data queue.
* It is still reflected in the segment length for
* sequencing purposes.
*/
static void
tcp_pulloutofband(so, th, m, off)
struct socket *so;
struct tcphdr *th;
register struct mbuf *m;
int off; /* delayed to be droped hdrlen */
{
int cnt = off + th->th_urp - 1;
while (cnt >= 0) {
if (m->m_len > cnt) {
char *cp = mtod(m, caddr_t) + cnt;
struct tcpcb *tp = sototcpcb(so);
tp->t_iobc = *cp;
tp->t_oobflags |= TCPOOB_HAVEDATA;
bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
m->m_len--;
if (m->m_flags & M_PKTHDR)
m->m_pkthdr.len--;
return;
}
cnt -= m->m_len;
m = m->m_next;
if (m == 0)
break;
}
panic("tcp_pulloutofband");
}
/*
* Collect new round-trip time estimate
* and update averages and current timeout.
*/
static void
tcp_xmit_timer(tp, rtt)
register struct tcpcb *tp;
int rtt;
{
register int delta;
tcpstat.tcps_rttupdated++;
tp->t_rttupdated++;
if (tp->t_srtt != 0) {
/*
* srtt is stored as fixed point with 5 bits after the
* binary point (i.e., scaled by 8). The following magic
* is equivalent to the smoothing algorithm in rfc793 with
* an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
* point). Adjust rtt to origin 0.
*/
delta = ((rtt - 1) << TCP_DELTA_SHIFT)
- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
if ((tp->t_srtt += delta) <= 0)
tp->t_srtt = 1;
/*
* We accumulate a smoothed rtt variance (actually, a
* smoothed mean difference), then set the retransmit
* timer to smoothed rtt + 4 times the smoothed variance.
* rttvar is stored as fixed point with 4 bits after the
* binary point (scaled by 16). The following is
* equivalent to rfc793 smoothing with an alpha of .75
* (rttvar = rttvar*3/4 + |delta| / 4). This replaces
* rfc793's wired-in beta.
*/
if (delta < 0)
delta = -delta;
delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
if ((tp->t_rttvar += delta) <= 0)
tp->t_rttvar = 1;
} else {
/*
* No rtt measurement yet - use the unsmoothed rtt.
* Set the variance to half the rtt (so our first
* retransmit happens at 3*rtt).
*/
tp->t_srtt = rtt << TCP_RTT_SHIFT;
tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
}
tp->t_rtttime = 0;
tp->t_rxtshift = 0;
/*
* the retransmit should happen at rtt + 4 * rttvar.
* Because of the way we do the smoothing, srtt and rttvar
* will each average +1/2 tick of bias. When we compute
* the retransmit timer, we want 1/2 tick of rounding and
* 1 extra tick because of +-1/2 tick uncertainty in the
* firing of the timer. The bias will give us exactly the
* 1.5 tick we need. But, because the bias is
* statistical, we have to test that we don't drop below
* the minimum feasible timer (which is 2 ticks).
*/
TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
/*
* We received an ack for a packet that wasn't retransmitted;
* it is probably safe to discard any error indications we've
* received recently. This isn't quite right, but close enough
* for now (a route might have failed after we sent a segment,
* and the return path might not be symmetrical).
*/
tp->t_softerror = 0;
}
/*
* Determine a reasonable value for maxseg size.
* If the route is known, check route for mtu.
* If none, use an mss that can be handled on the outgoing
* interface without forcing IP to fragment; if bigger than
* an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
* to utilize large mbufs. If no route is found, route has no mtu,
* or the destination isn't local, use a default, hopefully conservative
* size (usually 512 or the default IP max size, but no more than the mtu
* of the interface), as we can't discover anything about intervening
* gateways or networks. We also initialize the congestion/slow start
* window to be a single segment if the destination isn't local.
* While looking at the routing entry, we also initialize other path-dependent
* parameters from pre-set or cached values in the routing entry.
*
* Also take into account the space needed for options that we
* send regularly. Make maxseg shorter by that amount to assure
* that we can send maxseg amount of data even when the options
* are present. Store the upper limit of the length of options plus
* data in maxopd.
*
* NOTE that this routine is only called when we process an incoming
* segment, for outgoing segments only tcp_mssopt is called.
*
* In case of T/TCP, we call this routine during implicit connection
* setup as well (offer = -1), to initialize maxseg from the cached
* MSS of our peer.
*/
void
tcp_mss(tp, offer)
struct tcpcb *tp;
int offer;
{
register struct rtentry *rt;
struct ifnet *ifp;
register int rtt, mss;
u_long bufsize;
struct inpcb *inp;
struct socket *so;
struct rmxp_tao *taop;
int origoffer = offer;
#ifdef INET6
int isipv6;
int min_protoh;
#endif
inp = tp->t_inpcb;
#ifdef INET6
isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
: sizeof (struct tcpiphdr);
#else
#define min_protoh (sizeof (struct tcpiphdr))
#endif
#ifdef INET6
if (isipv6)
rt = tcp_rtlookup6(inp);
else
#endif
rt = tcp_rtlookup(inp);
if (rt == NULL) {
tp->t_maxopd = tp->t_maxseg =
#ifdef INET6
isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
tcp_mssdflt;
return;
}
ifp = rt->rt_ifp;
so = inp->inp_socket;
taop = rmx_taop(rt->rt_rmx);
/*
* Offer == -1 means that we didn't receive SYN yet,
* use cached value in that case;
*/
if (offer == -1)
offer = taop->tao_mssopt;
/*
* Offer == 0 means that there was no MSS on the SYN segment,
* in this case we use tcp_mssdflt.
*/
if (offer == 0)
offer =
#ifdef INET6
isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
tcp_mssdflt;
else
/*
* Sanity check: make sure that maxopd will be large
* enough to allow some data on segments even is the
* all the option space is used (40bytes). Otherwise
* funny things may happen in tcp_output.
*/
offer = max(offer, 64);
taop->tao_mssopt = offer;
/*
* While we're here, check if there's an initial rtt
* or rttvar. Convert from the route-table units
* to scaled multiples of the slow timeout timer.
*/
if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
/*
* XXX the lock bit for RTT indicates that the value
* is also a minimum value; this is subject to time.
*/
if (rt->rt_rmx.rmx_locks & RTV_RTT)
tp->t_rttmin = rtt / (RTM_RTTUNIT / hz);
tp->t_srtt = rtt / (RTM_RTTUNIT / (hz * TCP_RTT_SCALE));
tcpstat.tcps_usedrtt++;
if (rt->rt_rmx.rmx_rttvar) {
tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
(RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE));
tcpstat.tcps_usedrttvar++;
} else {
/* default variation is +- 1 rtt */
tp->t_rttvar =
tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
}
TCPT_RANGESET(tp->t_rxtcur,
((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
tp->t_rttmin, TCPTV_REXMTMAX);
}
/*
* if there's an mtu associated with the route, use it
* else, use the link mtu.
*/
if (rt->rt_rmx.rmx_mtu)
mss = rt->rt_rmx.rmx_mtu - min_protoh;
else
{
mss =
#ifdef INET6
(isipv6 ? nd_ifinfo[rt->rt_ifp->if_index].linkmtu :
#endif
ifp->if_mtu
#ifdef INET6
)
#endif
- min_protoh;
#ifdef INET6
if (isipv6) {
if (!in6_localaddr(&inp->in6p_faddr))
mss = min(mss, tcp_v6mssdflt);
} else
#endif
if (!in_localaddr(inp->inp_faddr))
mss = min(mss, tcp_mssdflt);
}
mss = min(mss, offer);
/*
* maxopd stores the maximum length of data AND options
* in a segment; maxseg is the amount of data in a normal
* segment. We need to store this value (maxopd) apart
* from maxseg, because now every segment carries options
* and thus we normally have somewhat less data in segments.
*/
tp->t_maxopd = mss;
/*
* In case of T/TCP, origoffer==-1 indicates, that no segments
* were received yet. In this case we just guess, otherwise
* we do the same as before T/TCP.
*/
if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
(origoffer == -1 ||
(tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
mss -= TCPOLEN_TSTAMP_APPA;
if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
(origoffer == -1 ||
(tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
mss -= TCPOLEN_CC_APPA;
#if (MCLBYTES & (MCLBYTES - 1)) == 0
if (mss > MCLBYTES)
mss &= ~(MCLBYTES-1);
#else
if (mss > MCLBYTES)
mss = mss / MCLBYTES * MCLBYTES;
#endif
/*
* If there's a pipesize, change the socket buffer
* to that size. Make the socket buffers an integral
* number of mss units; if the mss is larger than
* the socket buffer, decrease the mss.
*/
#ifdef RTV_SPIPE
if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
#endif
bufsize = so->so_snd.sb_hiwat;
if (bufsize < mss)
mss = bufsize;
else {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
(void)sbreserve(&so->so_snd, bufsize, so, NULL);
}
tp->t_maxseg = mss;
#ifdef RTV_RPIPE
if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
#endif
bufsize = so->so_rcv.sb_hiwat;
if (bufsize > mss) {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
(void)sbreserve(&so->so_rcv, bufsize, so, NULL);
}
/*
* Set the slow-start flight size depending on whether this
* is a local network or not.
*/
if (
#ifdef INET6
(isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
(!isipv6 &&
#endif
in_localaddr(inp->inp_faddr)
#ifdef INET6
)
#endif
)
tp->snd_cwnd = mss * ss_fltsz_local;
else
tp->snd_cwnd = mss * ss_fltsz;
if (rt->rt_rmx.rmx_ssthresh) {
/*
* There's some sort of gateway or interface
* buffer limit on the path. Use this to set
* the slow start threshhold, but set the
* threshold to no less than 2*mss.
*/
tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
tcpstat.tcps_usedssthresh++;
}
}
/*
* Determine the MSS option to send on an outgoing SYN.
*/
int
tcp_mssopt(tp)
struct tcpcb *tp;
{
struct rtentry *rt;
#ifdef INET6
int isipv6;
int min_protoh;
#endif
#ifdef INET6
isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
: sizeof (struct tcpiphdr);
#else
#define min_protoh (sizeof (struct tcpiphdr))
#endif
#ifdef INET6
if (isipv6)
rt = tcp_rtlookup6(tp->t_inpcb);
else
#endif /* INET6 */
rt = tcp_rtlookup(tp->t_inpcb);
if (rt == NULL)
return
#ifdef INET6
isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
tcp_mssdflt;
return rt->rt_ifp->if_mtu - min_protoh;
}
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