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/*-
* Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.org>
* 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.
*
* 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 <sys/param.h>
#include <sys/socket.h>
#include <net/route.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <sys/un.h>
#include <termios.h>
#include "layer.h"
#include "defs.h"
#include "log.h"
#include "timer.h"
#include "fsm.h"
#include "mbuf.h"
#include "throughput.h"
#include "lqr.h"
#include "hdlc.h"
#include "lcp.h"
#include "ccp.h"
#include "link.h"
#include "iplist.h"
#include "slcompress.h"
#include "ipcp.h"
#include "filter.h"
#include "descriptor.h"
#include "mp.h"
#include "iface.h"
#ifndef NORADIUS
#include "radius.h"
#endif
#include "bundle.h"
/*-
* We are in a liberal position about MSS
* (RFC 879, section 7).
*/
#define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr))
static void MSSFixup(struct tcphdr *, ssize_t, u_int16_t);
static struct mbuf *
tcpmss_LayerPush(struct bundle *bundle, struct link *l, struct mbuf *bp,
int pri, u_short *proto)
{
struct ip *pip;
int hlen, plen;
if (!Enabled(bundle, OPT_TCPMSSFIXUP))
return bp;
bp = m_pullup(bp);
plen = m_length(bp);
pip = (struct ip *)MBUF_CTOP(bp);
hlen = pip->ip_hl << 2;
/*
* Check for MSS option only for TCP packets with zero fragment offsets
* and correct total and header lengths.
*/
if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 &&
ntohs(pip->ip_len) == plen && hlen <= plen &&
plen - hlen >= sizeof(struct tcphdr))
MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
MAXMSS(bundle->iface->mtu));
return bp;
}
/*-
* The following macro is used to update an
* internet checksum. "acc" is a 32-bit
* accumulation of all the changes to the
* checksum (adding in old 16-bit words and
* subtracting out new words), and "cksum"
* is the checksum value to be updated.
*/
#define ADJUST_CHECKSUM(acc, cksum) { \
acc += cksum; \
if (acc < 0) { \
acc = -acc; \
acc = (acc >> 16) + (acc & 0xffff); \
acc += acc >> 16; \
cksum = (u_short) ~acc; \
} else { \
acc = (acc >> 16) + (acc & 0xffff); \
acc += acc >> 16; \
cksum = (u_short) acc; \
} \
}
static void
MSSFixup(struct tcphdr *tc, ssize_t pktlen, u_int16_t maxmss)
{
int hlen, olen, optlen;
u_char *opt;
u_int16_t *mss;
int accumulate;
hlen = tc->th_off << 2;
/* Invalid header length or header without options. */
if (hlen <= sizeof(struct tcphdr) || hlen > pktlen)
return;
/* MSS option only allowed within SYN packets. */
if (!(tc->th_flags & TH_SYN))
return;
for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
olen > 0; olen -= optlen, opt += optlen) {
if (*opt == TCPOPT_EOL)
break;
else if (*opt == TCPOPT_NOP)
optlen = 1;
else {
optlen = *(opt + 1);
if (optlen <= 0 || optlen > olen)
break;
if (*opt == TCPOPT_MAXSEG) {
if (optlen != TCPOLEN_MAXSEG)
continue;
mss = (u_int16_t *)(opt + 2);
if (ntohs(*mss) > maxmss) {
log_Printf(LogDEBUG, "MSS: %u -> %u\n",
ntohs(*mss), maxmss);
accumulate = *mss;
*mss = htons(maxmss);
accumulate -= *mss;
ADJUST_CHECKSUM(accumulate, tc->th_sum);
}
}
}
}
}
struct layer tcpmsslayer = { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, NULL };
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