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 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 * 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 * 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 * 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