1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 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 * $FreeBSD$ 29 */ 30 31 #include <sys/param.h> 32 33 #include <sys/socket.h> 34 #include <net/route.h> 35 #include <netinet/in_systm.h> 36 #include <netinet/in.h> 37 #include <netinet/ip.h> 38 #include <netinet/tcp.h> 39 #include <sys/un.h> 40 41 #include <termios.h> 42 43 #include "layer.h" 44 #include "defs.h" 45 #include "log.h" 46 #include "timer.h" 47 #include "fsm.h" 48 #include "mbuf.h" 49 #include "throughput.h" 50 #include "lqr.h" 51 #include "hdlc.h" 52 #include "lcp.h" 53 #include "ccp.h" 54 #include "link.h" 55 #include "iplist.h" 56 #include "slcompress.h" 57 #include "ncpaddr.h" 58 #include "ipcp.h" 59 #include "filter.h" 60 #include "descriptor.h" 61 #include "mp.h" 62 #include "iface.h" 63 #ifndef NORADIUS 64 #include "radius.h" 65 #endif 66 #include "ipv6cp.h" 67 #include "ncp.h" 68 #include "bundle.h" 69 70 71 /*- 72 * We are in a liberal position about MSS 73 * (RFC 879, section 7). 74 */ 75 #define MAXMSS(mtu) ((mtu) - sizeof(struct ip) - sizeof(struct tcphdr) - 12) 76 77 78 /*- 79 * The following macro is used to update an 80 * internet checksum. "acc" is a 32-bit 81 * accumulation of all the changes to the 82 * checksum (adding in old 16-bit words and 83 * subtracting out new words), and "cksum" 84 * is the checksum value to be updated. 85 */ 86 #define ADJUST_CHECKSUM(acc, cksum) { \ 87 acc += cksum; \ 88 if (acc < 0) { \ 89 acc = -acc; \ 90 acc = (acc >> 16) + (acc & 0xffff); \ 91 acc += acc >> 16; \ 92 cksum = (u_short) ~acc; \ 93 } else { \ 94 acc = (acc >> 16) + (acc & 0xffff); \ 95 acc += acc >> 16; \ 96 cksum = (u_short) acc; \ 97 } \ 98 } 99 100 static void 101 MSSFixup(struct tcphdr *tc, size_t pktlen, u_int16_t maxmss) 102 { 103 size_t hlen, olen, optlen; 104 u_char *opt; 105 u_int16_t *mss; 106 int accumulate; 107 108 hlen = tc->th_off << 2; 109 110 /* Invalid header length or header without options. */ 111 if (hlen <= sizeof(struct tcphdr) || hlen > pktlen) 112 return; 113 114 /* MSS option only allowed within SYN packets. */ 115 if (!(tc->th_flags & TH_SYN)) 116 return; 117 118 for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1); 119 olen > 0; olen -= optlen, opt += optlen) { 120 if (*opt == TCPOPT_EOL) 121 break; 122 else if (*opt == TCPOPT_NOP) 123 optlen = 1; 124 else { 125 optlen = *(opt + 1); 126 if (optlen <= 0 || optlen > olen) 127 break; 128 if (*opt == TCPOPT_MAXSEG) { 129 if (optlen != TCPOLEN_MAXSEG) 130 continue; 131 mss = (u_int16_t *)(opt + 2); 132 if (ntohs(*mss) > maxmss) { 133 log_Printf(LogDEBUG, "MSS: %u -> %u\n", 134 ntohs(*mss), maxmss); 135 accumulate = *mss; 136 *mss = htons(maxmss); 137 accumulate -= *mss; 138 ADJUST_CHECKSUM(accumulate, tc->th_sum); 139 } 140 } 141 } 142 } 143 } 144 145 static struct mbuf * 146 tcpmss_Check(struct bundle *bundle, struct mbuf *bp) 147 { 148 struct ip *pip; 149 size_t hlen, plen; 150 151 if (!Enabled(bundle, OPT_TCPMSSFIXUP)) 152 return bp; 153 154 bp = m_pullup(bp); 155 plen = m_length(bp); 156 pip = (struct ip *)MBUF_CTOP(bp); 157 hlen = pip->ip_hl << 2; 158 159 /* 160 * Check for MSS option only for TCP packets with zero fragment offsets 161 * and correct total and header lengths. 162 */ 163 if (pip->ip_p == IPPROTO_TCP && (ntohs(pip->ip_off) & IP_OFFMASK) == 0 && 164 ntohs(pip->ip_len) == plen && hlen <= plen && 165 plen >= sizeof(struct tcphdr) + hlen) 166 MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen, 167 MAXMSS(bundle->iface->mtu)); 168 169 return bp; 170 } 171 172 static struct mbuf * 173 tcpmss_LayerPush(struct bundle *bundle, struct link *l __unused, 174 struct mbuf *bp, int pri __unused, u_short *proto __unused) 175 { 176 return tcpmss_Check(bundle, bp); 177 } 178 179 static struct mbuf * 180 tcpmss_LayerPull(struct bundle *bundle, struct link *l __unused, 181 struct mbuf *bp, u_short *proto __unused) 182 { 183 return tcpmss_Check(bundle, bp); 184 } 185 186 struct layer tcpmsslayer = 187 { LAYER_PROTO, "tcpmss", tcpmss_LayerPush, tcpmss_LayerPull }; 188