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📁 ..
📄 Makefile(1.66 KB)
📄 Makefile.depend(435 B)
📄 README.changes(7.26 KB)
📄 README.nat(14.85 KB)
📄 acf.c(3.51 KB)
📄 acf.h(1.5 KB)
📄 arp.c(8.24 KB)
📄 arp.h(1.76 KB)
📄 async.c(5.39 KB)
📄 async.h(1.9 KB)
📄 auth.c(12.02 KB)
📄 auth.h(2.69 KB)
📄 bundle.c(56.37 KB)
📄 bundle.h(7.7 KB)
📄 cbcp.c(22.53 KB)
📄 cbcp.h(2.51 KB)
📄 ccp.c(23.33 KB)
📄 ccp.h(5.53 KB)
📄 chap.c(27 KB)
📄 chap.h(2.69 KB)
📄 chap_ms.c(12.22 KB)
📄 chap_ms.h(2.48 KB)
📄 chat.c(20.41 KB)
📄 chat.h(2.92 KB)
📄 command.c(101.76 KB)
📄 command.h(3.02 KB)
📄 datalink.c(42.89 KB)
📄 datalink.h(6.11 KB)
📄 deflate.c(15.89 KB)
📄 deflate.h(1.52 KB)
📄 defs.c(8.61 KB)
📄 defs.h(5.41 KB)
📄 descriptor.h(2.24 KB)
📄 ether.c(20.81 KB)
📄 ether.h(1.73 KB)
📄 exec.c(11.47 KB)
📄 exec.h(1.67 KB)
📄 filter.c(15.76 KB)
📄 filter.h(3.8 KB)
📄 fsm.c(31.01 KB)
📄 fsm.h(7.02 KB)
📄 hdlc.c(15.17 KB)
📄 hdlc.h(3.9 KB)
📄 i4b.h(1.73 KB)
📄 id.c(6.05 KB)
📄 id.h(3.01 KB)
📄 iface.c(22.41 KB)
📄 iface.h(2.97 KB)
📄 ip.c(30.21 KB)
📄 ip.h(2.09 KB)
📄 ipcp.c(42.99 KB)
📄 ipcp.h(5.14 KB)
📄 iplist.c(5.54 KB)
📄 iplist.h(1.99 KB)
📄 ipv6cp.c(21.9 KB)
📄 ipv6cp.h(3.26 KB)
📄 layer.h(1.97 KB)
📄 lcp.c(39.22 KB)
📄 lcp.h(6.3 KB)
📄 link.c(10.36 KB)
📄 link.h(3.42 KB)
📄 log.c(11.33 KB)
📄 log.h(4.14 KB)
📄 lqr.c(17.5 KB)
📄 lqr.h(3.31 KB)
📄 main.c(17.93 KB)
📄 main.h(1.6 KB)
📄 mbuf.c(10.02 KB)
📄 mbuf.h(4 KB)
📄 mp.c(33.66 KB)
📄 mp.h(4.87 KB)
📄 mppe.c(20.27 KB)
📄 mppe.h(1.57 KB)
📄 nat_cmd.c(15.37 KB)
📄 nat_cmd.h(1.88 KB)
📄 ncp.c(13.17 KB)
📄 ncp.h(4.36 KB)
📄 ncpaddr.c(23.06 KB)
📄 ncpaddr.h(4.63 KB)
📄 netgraph.c(20.65 KB)
📄 netgraph.h(1.72 KB)
📄 pap.c(8.83 KB)
📄 pap.h(1.78 KB)
📄 physical.c(29.01 KB)
📄 physical.h(6.5 KB)
📄 ppp.8(149.48 KB)
📄 ppp.conf(1.23 KB)
📄 pred.c(8.83 KB)
📄 pred.h(1.59 KB)
📄 probe.c(2.29 KB)
📄 probe.h(1.57 KB)
📄 prompt.c(12.92 KB)
📄 prompt.h(3.87 KB)
📄 proto.c(3.22 KB)
📄 proto.h(2.4 KB)
📄 radius.c(39.38 KB)
📄 radius.h(4.6 KB)
📄 route.c(25.91 KB)
📄 route.h(3.3 KB)
📄 server.c(10.9 KB)
📄 server.h(2.26 KB)
📄 sig.c(3.45 KB)
📄 sig.h(1.6 KB)
📄 slcompress.c(17.2 KB)
📄 slcompress.h(6.48 KB)
📄 sync.c(2.7 KB)
📄 sync.h(1.44 KB)
📄 systems.c(11.45 KB)
📄 systems.h(2.02 KB)
📄 tcp.c(5.63 KB)
📄 tcp.h(1.66 KB)
📄 tcpmss.c(5.06 KB)
📄 tcpmss.h(1.44 KB)
📄 throughput.c(8.84 KB)
📄 throughput.h(2.91 KB)
📄 timer.c(8.14 KB)
📄 timer.h(2.31 KB)
📄 tty.c(20.63 KB)
📄 tty.h(1.73 KB)
📄 tun.c(3.27 KB)
📄 tun.h(1.58 KB)
📄 ua.h(2.98 KB)
📄 udp.c(8.7 KB)
📄 udp.h(1.67 KB)
📄 vjcomp.c(5.68 KB)
📄 vjcomp.h(1.53 KB)

Editing: tcpmss.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * 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 "ncpaddr.h"
#include "ipcp.h"
#include "filter.h"
#include "descriptor.h"
#include "mp.h"
#include "iface.h"
#ifndef NORADIUS
#include "radius.h"
#endif
#include "ipv6cp.h"
#include "ncp.h"
#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) - 12)

/*-
 * 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, size_t pktlen, u_int16_t maxmss)
{
  size_t 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);
        }
      }
    }
  }
}

static struct mbuf *
tcpmss_Check(struct bundle *bundle, struct mbuf *bp)
{
  struct ip *pip;
  size_t 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 >= sizeof(struct tcphdr) + hlen)
    MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
             MAXMSS(bundle->iface->mtu));

return bp;
}

static struct mbuf *
tcpmss_LayerPush(struct bundle *bundle, struct link *l __unused,
		 struct mbuf *bp, int pri __unused, u_short *proto __unused)
{
	return tcpmss_Check(bundle, bp);
}

static struct mbuf *
tcpmss_LayerPull(struct bundle *bundle, struct link *l __unused,
		 struct mbuf *bp, u_short *proto __unused)
{
	return tcpmss_Check(bundle, bp);
}

struct layer tcpmsslayer =
  { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull };

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Editing: tcpmss.c

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