1 /*- 2 * Copyright (c) 2001 Charles Mott <cm@linktel.net> 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 27 #include <sys/cdefs.h> 28 __FBSDID("$FreeBSD$"); 29 30 31 /* 32 Alias_util.c contains general utilities used by other functions 33 in the packet aliasing module. At the moment, there are functions 34 for computing IP header and TCP packet checksums. 35 36 The checksum routines are based upon example code in a Unix networking 37 text written by Stevens (sorry, I can't remember the title -- but 38 at least this is a good author). 39 40 Initial Version: August, 1996 (cjm) 41 42 Version 1.7: January 9, 1997 43 Added differential checksum update function. 44 */ 45 46 /* 47 Note: the checksum routines assume that the actual checksum word has 48 been zeroed out. If the checksum word is filled with the proper value, 49 then these routines will give a result of zero (useful for testing 50 purposes); 51 */ 52 53 #ifdef _KERNEL 54 #include <sys/param.h> 55 #else 56 #include <sys/types.h> 57 #include <stdio.h> 58 #endif 59 60 #include <netinet/in_systm.h> 61 #include <netinet/in.h> 62 #include <netinet/ip.h> 63 #include <netinet/tcp.h> 64 65 #ifdef _KERNEL 66 #include <netinet/libalias/alias.h> 67 #include <netinet/libalias/alias_local.h> 68 #else 69 #include "alias.h" 70 #include "alias_local.h" 71 #endif 72 73 u_short 74 LibAliasInternetChecksum(struct libalias *la, u_short * ptr, int nbytes) 75 { 76 int sum, oddbyte; 77 78 (void)la; 79 80 sum = 0; 81 while (nbytes > 1) { 82 sum += *ptr++; 83 nbytes -= 2; 84 } 85 if (nbytes == 1) { 86 oddbyte = 0; 87 ((u_char *) & oddbyte)[0] = *(u_char *) ptr; 88 ((u_char *) & oddbyte)[1] = 0; 89 sum += oddbyte; 90 } 91 sum = (sum >> 16) + (sum & 0xffff); 92 sum += (sum >> 16); 93 return (~sum); 94 } 95 96 u_short 97 IpChecksum(struct ip *pip) 98 { 99 return (PacketAliasInternetChecksum((u_short *) pip, 100 (pip->ip_hl << 2))); 101 102 } 103 104 u_short 105 TcpChecksum(struct ip *pip) 106 { 107 u_short *ptr; 108 struct tcphdr *tc; 109 int nhdr, ntcp, nbytes; 110 int sum, oddbyte; 111 112 nhdr = pip->ip_hl << 2; 113 ntcp = ntohs(pip->ip_len) - nhdr; 114 115 tc = (struct tcphdr *)ip_next(pip); 116 ptr = (u_short *) tc; 117 118 /* Add up TCP header and data */ 119 nbytes = ntcp; 120 sum = 0; 121 while (nbytes > 1) { 122 sum += *ptr++; 123 nbytes -= 2; 124 } 125 if (nbytes == 1) { 126 oddbyte = 0; 127 ((u_char *) & oddbyte)[0] = *(u_char *) ptr; 128 ((u_char *) & oddbyte)[1] = 0; 129 sum += oddbyte; 130 } 131 /* "Pseudo-header" data */ 132 ptr = (u_short *) & (pip->ip_dst); 133 sum += *ptr++; 134 sum += *ptr; 135 ptr = (u_short *) & (pip->ip_src); 136 sum += *ptr++; 137 sum += *ptr; 138 sum += htons((u_short) ntcp); 139 sum += htons((u_short) pip->ip_p); 140 141 /* Roll over carry bits */ 142 sum = (sum >> 16) + (sum & 0xffff); 143 sum += (sum >> 16); 144 145 /* Return checksum */ 146 return ((u_short) ~ sum); 147 } 148 149 150 void 151 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n) 152 { 153 int i; 154 int accumulate; 155 u_short *new = newp; 156 u_short *old = oldp; 157 158 accumulate = *cksum; 159 for (i = 0; i < n; i++) { 160 accumulate -= *new++; 161 accumulate += *old++; 162 } 163 164 if (accumulate < 0) { 165 accumulate = -accumulate; 166 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 167 accumulate += accumulate >> 16; 168 *cksum = (u_short) ~ accumulate; 169 } else { 170 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 171 accumulate += accumulate >> 16; 172 *cksum = (u_short) accumulate; 173 } 174 } 175