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