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