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 <stdio.h> 54 #include <sys/types.h> 55 #include <netinet/in_systm.h> 56 #include <netinet/in.h> 57 #include <netinet/ip.h> 58 #include <netinet/tcp.h> 59 60 #include "alias.h" 61 #include "alias_local.h" 62 63 u_short 64 LibAliasInternetChecksum(struct libalias *la, u_short *ptr, int nbytes) 65 { 66 int sum, oddbyte; 67 68 sum = 0; 69 while (nbytes > 1) 70 { 71 sum += *ptr++; 72 nbytes -= 2; 73 } 74 if (nbytes == 1) 75 { 76 oddbyte = 0; 77 ((u_char *) &oddbyte)[0] = *(u_char *) ptr; 78 ((u_char *) &oddbyte)[1] = 0; 79 sum += oddbyte; 80 } 81 sum = (sum >> 16) + (sum & 0xffff); 82 sum += (sum >> 16); 83 return(~sum); 84 } 85 86 u_short 87 IpChecksum(struct ip *pip) 88 { 89 return( PacketAliasInternetChecksum((u_short *) pip, 90 (pip->ip_hl << 2)) ); 91 92 } 93 94 u_short 95 TcpChecksum(struct ip *pip) 96 { 97 u_short *ptr; 98 struct tcphdr *tc; 99 int nhdr, ntcp, nbytes; 100 int sum, oddbyte; 101 102 nhdr = pip->ip_hl << 2; 103 ntcp = ntohs(pip->ip_len) - nhdr; 104 105 tc = (struct tcphdr *) ((char *) pip + nhdr); 106 ptr = (u_short *) tc; 107 108 /* Add up TCP header and data */ 109 nbytes = ntcp; 110 sum = 0; 111 while (nbytes > 1) 112 { 113 sum += *ptr++; 114 nbytes -= 2; 115 } 116 if (nbytes == 1) 117 { 118 oddbyte = 0; 119 ((u_char *) &oddbyte)[0] = *(u_char *) ptr; 120 ((u_char *) &oddbyte)[1] = 0; 121 sum += oddbyte; 122 } 123 124 /* "Pseudo-header" data */ 125 ptr = (u_short *) &(pip->ip_dst); 126 sum += *ptr++; 127 sum += *ptr; 128 ptr = (u_short *) &(pip->ip_src); 129 sum += *ptr++; 130 sum += *ptr; 131 sum += htons((u_short) ntcp); 132 sum += htons((u_short) pip->ip_p); 133 134 /* Roll over carry bits */ 135 sum = (sum >> 16) + (sum & 0xffff); 136 sum += (sum >> 16); 137 138 /* Return checksum */ 139 return((u_short) ~sum); 140 } 141 142 143 void 144 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n) 145 { 146 int i; 147 int accumulate; 148 149 accumulate = *cksum; 150 for (i=0; i<n; i++) 151 { 152 accumulate -= *new++; 153 accumulate += *old++; 154 } 155 156 if (accumulate < 0) 157 { 158 accumulate = -accumulate; 159 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 160 accumulate += accumulate >> 16; 161 *cksum = (u_short) ~accumulate; 162 } 163 else 164 { 165 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 166 accumulate += accumulate >> 16; 167 *cksum = (u_short) accumulate; 168 } 169 } 170 171