1/*-
2 * Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: releng/11.0/usr.sbin/ppp/tcpmss.c 134789 2004-09-05 01:46:52Z brian $
27 */
28
29#include <sys/param.h>
30
31#include <sys/socket.h>
32#include <net/route.h>
33#include <netinet/in_systm.h>
34#include <netinet/in.h>
35#include <netinet/ip.h>
36#include <netinet/tcp.h>
37#include <sys/un.h>
38
39#include <termios.h>
40
41#include "layer.h"
42#include "defs.h"
43#include "log.h"
44#include "timer.h"
45#include "fsm.h"
46#include "mbuf.h"
47#include "throughput.h"
48#include "lqr.h"
49#include "hdlc.h"
50#include "lcp.h"
51#include "ccp.h"
52#include "link.h"
53#include "iplist.h"
54#include "slcompress.h"
55#include "ncpaddr.h"
56#include "ipcp.h"
57#include "filter.h"
58#include "descriptor.h"
59#include "mp.h"
60#include "iface.h"
61#ifndef NORADIUS
62#include "radius.h"
63#endif
64#include "ipv6cp.h"
65#include "ncp.h"
66#include "bundle.h"
67
68
69/*-
70 * We are in a liberal position about MSS
71 * (RFC 879, section 7).
72 */
73#define MAXMSS(mtu) ((mtu) - sizeof(struct ip) - sizeof(struct tcphdr) - 12)
74
75
76/*-
77 * The following macro is used to update an
78 * internet checksum.  "acc" is a 32-bit
79 * accumulation of all the changes to the
80 * checksum (adding in old 16-bit words and
81 * subtracting out new words), and "cksum"
82 * is the checksum value to be updated.
83 */
84#define ADJUST_CHECKSUM(acc, cksum) { \
85  acc += cksum; \
86  if (acc < 0) { \
87    acc = -acc; \
88    acc = (acc >> 16) + (acc & 0xffff); \
89    acc += acc >> 16; \
90    cksum = (u_short) ~acc; \
91  } else { \
92    acc = (acc >> 16) + (acc & 0xffff); \
93    acc += acc >> 16; \
94    cksum = (u_short) acc; \
95  } \
96}
97
98static void
99MSSFixup(struct tcphdr *tc, size_t pktlen, u_int16_t maxmss)
100{
101  size_t hlen, olen, optlen;
102  u_char *opt;
103  u_int16_t *mss;
104  int accumulate;
105
106  hlen = tc->th_off << 2;
107
108  /* Invalid header length or header without options. */
109  if (hlen <= sizeof(struct tcphdr) || hlen > pktlen)
110    return;
111
112  /* MSS option only allowed within SYN packets. */
113  if (!(tc->th_flags & TH_SYN))
114    return;
115
116  for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
117       olen > 0; olen -= optlen, opt += optlen) {
118    if (*opt == TCPOPT_EOL)
119      break;
120    else if (*opt == TCPOPT_NOP)
121      optlen = 1;
122    else {
123      optlen = *(opt + 1);
124      if (optlen <= 0 || optlen > olen)
125        break;
126      if (*opt == TCPOPT_MAXSEG) {
127        if (optlen != TCPOLEN_MAXSEG)
128          continue;
129        mss = (u_int16_t *)(opt + 2);
130        if (ntohs(*mss) > maxmss) {
131          log_Printf(LogDEBUG, "MSS: %u -> %u\n",
132               ntohs(*mss), maxmss);
133          accumulate = *mss;
134          *mss = htons(maxmss);
135          accumulate -= *mss;
136          ADJUST_CHECKSUM(accumulate, tc->th_sum);
137        }
138      }
139    }
140  }
141}
142
143static struct mbuf *
144tcpmss_Check(struct bundle *bundle, struct mbuf *bp)
145{
146  struct ip *pip;
147  size_t hlen, plen;
148
149  if (!Enabled(bundle, OPT_TCPMSSFIXUP))
150    return bp;
151
152  bp = m_pullup(bp);
153  plen = m_length(bp);
154  pip = (struct ip *)MBUF_CTOP(bp);
155  hlen = pip->ip_hl << 2;
156
157  /*
158   * Check for MSS option only for TCP packets with zero fragment offsets
159   * and correct total and header lengths.
160   */
161  if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 &&
162      ntohs(pip->ip_len) == plen && hlen <= plen &&
163      plen >= sizeof(struct tcphdr) + hlen)
164    MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
165             MAXMSS(bundle->iface->mtu));
166
167  return bp;
168}
169
170static struct mbuf *
171tcpmss_LayerPush(struct bundle *bundle, struct link *l __unused,
172		 struct mbuf *bp, int pri __unused, u_short *proto __unused)
173{
174	return tcpmss_Check(bundle, bp);
175}
176
177static struct mbuf *
178tcpmss_LayerPull(struct bundle *bundle, struct link *l __unused,
179		 struct mbuf *bp, u_short *proto __unused)
180{
181	return tcpmss_Check(bundle, bp);
182}
183
184struct layer tcpmsslayer =
185  { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull };
186