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
103 static void
MSSFixup(struct tcphdr * tc,size_t pktlen,u_int16_t maxmss)104 MSSFixup(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
148 static struct mbuf *
tcpmss_Check(struct bundle * bundle,struct mbuf * bp)149 tcpmss_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
218 static struct mbuf *
tcpmss_LayerPush(struct bundle * bundle,struct link * l __unused,struct mbuf * bp,int pri __unused,u_short * proto __unused)219 tcpmss_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
225 static struct mbuf *
tcpmss_LayerPull(struct bundle * bundle,struct link * l __unused,struct mbuf * bp,u_short * proto __unused)226 tcpmss_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
232 struct layer tcpmsslayer =
233 { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull };
234