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