1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2000 Ruslan Ermilov and Brian Somers <brian@Awfulhak.org>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
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#ifndef NOINET6
37#include <netinet/ip6.h>
38#endif
39#include <netinet/tcp.h>
40#include <sys/un.h>
41
42#include <termios.h>
43
44#include "layer.h"
45#include "defs.h"
46#include "log.h"
47#include "timer.h"
48#include "fsm.h"
49#include "mbuf.h"
50#include "throughput.h"
51#include "lqr.h"
52#include "hdlc.h"
53#include "lcp.h"
54#include "ccp.h"
55#include "link.h"
56#include "iplist.h"
57#include "slcompress.h"
58#include "ncpaddr.h"
59#include "ipcp.h"
60#include "filter.h"
61#include "descriptor.h"
62#include "mp.h"
63#include "iface.h"
64#ifndef NORADIUS
65#include "radius.h"
66#endif
67#include "ipv6cp.h"
68#include "ncp.h"
69#include "bundle.h"
70
71
72/*-
73 * Compute the MSS as described in RFC 6691.
74 */
75#define MAXMSS4(mtu) ((mtu) - sizeof(struct ip) - sizeof(struct tcphdr))
76#ifndef NOINET6
77#define MAXMSS6(mtu) ((mtu) - sizeof(struct ip6_hdr) - sizeof(struct tcphdr))
78#endif
79
80
81/*-
82 * The following macro is used to update an
83 * internet checksum.  "acc" is a 32-bit
84 * accumulation of all the changes to the
85 * checksum (adding in old 16-bit words and
86 * subtracting out new words), and "cksum"
87 * is the checksum value to be updated.
88 */
89#define ADJUST_CHECKSUM(acc, cksum) { \
90  acc += cksum; \
91  if (acc < 0) { \
92    acc = -acc; \
93    acc = (acc >> 16) + (acc & 0xffff); \
94    acc += acc >> 16; \
95    cksum = (u_short) ~acc; \
96  } else { \
97    acc = (acc >> 16) + (acc & 0xffff); \
98    acc += acc >> 16; \
99    cksum = (u_short) acc; \
100  } \
101}
102
103static void
104MSSFixup(struct tcphdr *tc, size_t pktlen, u_int16_t maxmss)
105{
106  size_t hlen, olen, optlen;
107  u_char *opt;
108  u_int16_t *mss;
109  int accumulate;
110
111  hlen = tc->th_off << 2;
112
113  /* Invalid header length or header without options. */
114  if (hlen <= sizeof(struct tcphdr) || hlen > pktlen)
115    return;
116
117  /* MSS option only allowed within SYN packets. */
118  if (!(tc->th_flags & TH_SYN))
119    return;
120
121  for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
122       olen > 0; olen -= optlen, opt += optlen) {
123    if (*opt == TCPOPT_EOL)
124      break;
125    else if (*opt == TCPOPT_NOP)
126      optlen = 1;
127    else {
128      optlen = *(opt + 1);
129      if (optlen <= 0 || optlen > olen)
130        break;
131      if (*opt == TCPOPT_MAXSEG) {
132        if (optlen != TCPOLEN_MAXSEG)
133          continue;
134        mss = (u_int16_t *)(opt + 2);
135        if (ntohs(*mss) > maxmss) {
136          log_Printf(LogDEBUG, "MSS: %u -> %u\n",
137               ntohs(*mss), maxmss);
138          accumulate = *mss;
139          *mss = htons(maxmss);
140          accumulate -= *mss;
141          ADJUST_CHECKSUM(accumulate, tc->th_sum);
142        }
143      }
144    }
145  }
146}
147
148static struct mbuf *
149tcpmss_Check(struct bundle *bundle, struct mbuf *bp)
150{
151  struct ip *pip;
152#ifndef NOINET6
153  struct ip6_hdr *pip6;
154  struct ip6_frag *pfrag;
155#endif
156  size_t hlen, plen;
157
158  if (!Enabled(bundle, OPT_TCPMSSFIXUP))
159    return bp;
160
161  bp = m_pullup(bp);
162  plen = m_length(bp);
163  if (plen < sizeof(struct ip))
164    return bp;
165  pip = (struct ip *)MBUF_CTOP(bp);
166
167  switch (pip->ip_v) {
168  case IPVERSION:
169    /*
170     * Check for MSS option only for TCP packets with zero fragment offsets
171     * and correct total and header lengths.
172     */
173    hlen = pip->ip_hl << 2;
174    if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 &&
175        ntohs(pip->ip_len) == plen && hlen <= plen &&
176        plen >= sizeof(struct tcphdr) + hlen)
177      MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
178               MAXMSS4(bundle->iface->mtu));
179    break;
180#ifndef NOINET6
181  case IPV6_VERSION >> 4:
182    /*
183     * Check for MSS option only for TCP packets with no extension headers
184     * or a single extension header which is a fragmentation header with
185     * offset 0. Furthermore require that the length field is correct.
186     */
187    if (plen < sizeof(struct ip6_hdr))
188      break;
189    pip6 = (struct ip6_hdr *)MBUF_CTOP(bp);
190    if (ntohs(pip6->ip6_plen) + sizeof(struct ip6_hdr) != plen)
191      break;
192    hlen = 0;
193    switch (pip6->ip6_nxt) {
194    case IPPROTO_TCP:
195      hlen = sizeof(struct ip6_hdr);
196      break;
197    case IPPROTO_FRAGMENT:
198      if (plen >= sizeof(struct ip6_frag) + sizeof(struct ip6_hdr)) {
199        pfrag = (struct ip6_frag *)(MBUF_CTOP(bp) + sizeof(struct ip6_hdr));
200        if (pfrag->ip6f_nxt == IPPROTO_TCP &&
201            ntohs(pfrag->ip6f_offlg & IP6F_OFF_MASK) == 0)
202          hlen = sizeof(struct ip6_hdr)+ sizeof(struct ip6_frag);
203      }
204      break;
205    }
206    if (hlen > 0 && plen >= sizeof(struct tcphdr) + hlen)
207      MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
208               MAXMSS6(bundle->iface->mtu));
209    break;
210#endif
211  default:
212    log_Printf(LogDEBUG, "tcpmss_Check: Unknown IP family %u\n", pip->ip_v);
213    break;
214  }
215  return bp;
216}
217
218static struct mbuf *
219tcpmss_LayerPush(struct bundle *bundle, struct link *l __unused,
220		 struct mbuf *bp, int pri __unused, u_short *proto __unused)
221{
222	return tcpmss_Check(bundle, bp);
223}
224
225static struct mbuf *
226tcpmss_LayerPull(struct bundle *bundle, struct link *l __unused,
227		 struct mbuf *bp, u_short *proto __unused)
228{
229	return tcpmss_Check(bundle, bp);
230}
231
232struct layer tcpmsslayer =
233  { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull };
234