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 #include <sys/types.h> 54 #include <netinet/in_systm.h> 55 #include <netinet/in.h> 56 #include <netinet/ip.h> 57 #include <netinet/tcp.h> 58 59 #include "alias.h" 60 #include "alias_local.h" 61 62 u_short 63 PacketAliasInternetChecksum(u_short *ptr, int nbytes) 64 { 65 int sum, oddbyte; 66 67 sum = 0; 68 while (nbytes > 1) 69 { 70 sum += *ptr++; 71 nbytes -= 2; 72 } 73 if (nbytes == 1) 74 { 75 oddbyte = 0; 76 ((u_char *) &oddbyte)[0] = *(u_char *) ptr; 77 ((u_char *) &oddbyte)[1] = 0; 78 sum += oddbyte; 79 } 80 sum = (sum >> 16) + (sum & 0xffff); 81 sum += (sum >> 16); 82 return(~sum); 83 } 84 85 u_short 86 IpChecksum(struct ip *pip) 87 { 88 return( PacketAliasInternetChecksum((u_short *) pip, 89 (pip->ip_hl << 2)) ); 90 91 } 92 93 u_short 94 TcpChecksum(struct ip *pip) 95 { 96 u_short *ptr; 97 struct tcphdr *tc; 98 int nhdr, ntcp, nbytes; 99 int sum, oddbyte; 100 101 nhdr = pip->ip_hl << 2; 102 ntcp = ntohs(pip->ip_len) - nhdr; 103 104 tc = (struct tcphdr *) ((char *) pip + nhdr); 105 ptr = (u_short *) tc; 106 107 /* Add up TCP header and data */ 108 nbytes = ntcp; 109 sum = 0; 110 while (nbytes > 1) 111 { 112 sum += *ptr++; 113 nbytes -= 2; 114 } 115 if (nbytes == 1) 116 { 117 oddbyte = 0; 118 ((u_char *) &oddbyte)[0] = *(u_char *) ptr; 119 ((u_char *) &oddbyte)[1] = 0; 120 sum += oddbyte; 121 } 122 123 /* "Pseudo-header" data */ 124 ptr = (u_short *) &(pip->ip_dst); 125 sum += *ptr++; 126 sum += *ptr; 127 ptr = (u_short *) &(pip->ip_src); 128 sum += *ptr++; 129 sum += *ptr; 130 sum += htons((u_short) ntcp); 131 sum += htons((u_short) pip->ip_p); 132 133 /* Roll over carry bits */ 134 sum = (sum >> 16) + (sum & 0xffff); 135 sum += (sum >> 16); 136 137 /* Return checksum */ 138 return((u_short) ~sum); 139 } 140 141 142 void 143 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n) 144 { 145 int i; 146 int accumulate; 147 148 accumulate = *cksum; 149 for (i=0; i<n; i++) 150 { 151 accumulate -= *new++; 152 accumulate += *old++; 153 } 154 155 if (accumulate < 0) 156 { 157 accumulate = -accumulate; 158 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 159 accumulate += accumulate >> 16; 160 *cksum = (u_short) ~accumulate; 161 } 162 else 163 { 164 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 165 accumulate += accumulate >> 16; 166 *cksum = (u_short) accumulate; 167 } 168 } 169 170