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 #ifdef _KERNEL 47 #include <sys/param.h> 48 #else 49 #include <sys/types.h> 50 #include <stdio.h> 51 #endif 52 53 #include <netinet/in_systm.h> 54 #include <netinet/in.h> 55 #include <netinet/ip.h> 56 #include <netinet/tcp.h> 57 58 #ifdef _KERNEL 59 #include <netinet/libalias/alias.h> 60 #include <netinet/libalias/alias_local.h> 61 #else 62 #include "alias.h" 63 #include "alias_local.h" 64 #endif 65 66 /* 67 * Note: the checksum routines assume that the actual checksum word has 68 * been zeroed out. If the checksum word is filled with the proper value, 69 * then these routines will give a result of zero (useful for testing 70 * purposes); 71 */ 72 u_short 73 LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr, 74 int nbytes) 75 { 76 int sum, oddbyte; 77 78 sum = 0; 79 while (nbytes > 1) { 80 sum += *ptr++; 81 nbytes -= 2; 82 } 83 if (nbytes == 1) { 84 oddbyte = 0; 85 ((u_char *) & oddbyte)[0] = *(u_char *) ptr; 86 ((u_char *) & oddbyte)[1] = 0; 87 sum += oddbyte; 88 } 89 sum = (sum >> 16) + (sum & 0xffff); 90 sum += (sum >> 16); 91 return (~sum); 92 } 93 94 #ifndef _KERNEL 95 u_short 96 IpChecksum(struct ip *pip) 97 { 98 return (LibAliasInternetChecksum(NULL, (u_short *) pip, 99 (pip->ip_hl << 2))); 100 101 } 102 103 u_short 104 TcpChecksum(struct ip *pip) 105 { 106 u_short *ptr; 107 struct tcphdr *tc; 108 int nhdr, ntcp, nbytes; 109 int sum, oddbyte; 110 111 nhdr = pip->ip_hl << 2; 112 ntcp = ntohs(pip->ip_len) - nhdr; 113 114 tc = (struct tcphdr *)ip_next(pip); 115 ptr = (u_short *) tc; 116 117 /* Add up TCP header and data */ 118 nbytes = ntcp; 119 sum = 0; 120 while (nbytes > 1) { 121 sum += *ptr++; 122 nbytes -= 2; 123 } 124 if (nbytes == 1) { 125 oddbyte = 0; 126 ((u_char *) & oddbyte)[0] = *(u_char *) ptr; 127 ((u_char *) & oddbyte)[1] = 0; 128 sum += oddbyte; 129 } 130 /* "Pseudo-header" data */ 131 ptr = (u_short *) & (pip->ip_dst); 132 sum += *ptr++; 133 sum += *ptr; 134 ptr = (u_short *) & (pip->ip_src); 135 sum += *ptr++; 136 sum += *ptr; 137 sum += htons((u_short) ntcp); 138 sum += htons((u_short) pip->ip_p); 139 140 /* Roll over carry bits */ 141 sum = (sum >> 16) + (sum & 0xffff); 142 sum += (sum >> 16); 143 144 /* Return checksum */ 145 return ((u_short) ~ sum); 146 } 147 #endif /* not _KERNEL */ 148 149 void 150 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n) 151 { 152 int i; 153 int accumulate; 154 u_short *new = newp; 155 u_short *old = oldp; 156 157 accumulate = *cksum; 158 for (i = 0; i < n; i++) { 159 accumulate -= *new++; 160 accumulate += *old++; 161 } 162 163 if (accumulate < 0) { 164 accumulate = -accumulate; 165 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 166 accumulate += accumulate >> 16; 167 *cksum = (u_short) ~ accumulate; 168 } else { 169 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 170 accumulate += accumulate >> 16; 171 *cksum = (u_short) accumulate; 172 } 173 } 174