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 #include <sys/proc.h> 49 #else 50 #include <sys/types.h> 51 #include <stdio.h> 52 #endif 53 54 #include <netinet/in_systm.h> 55 #include <netinet/in.h> 56 #include <netinet/ip.h> 57 #include <netinet/tcp.h> 58 59 #ifdef _KERNEL 60 #include <netinet/libalias/alias.h> 61 #include <netinet/libalias/alias_local.h> 62 #else 63 #include "alias.h" 64 #include "alias_local.h" 65 #endif 66 67 /* 68 * Note: the checksum routines assume that the actual checksum word has 69 * been zeroed out. If the checksum word is filled with the proper value, 70 * then these routines will give a result of zero (useful for testing 71 * purposes); 72 */ 73 u_short 74 LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr, 75 int nbytes) 76 { 77 int sum, oddbyte; 78 79 LIBALIAS_LOCK(la); 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 LIBALIAS_UNLOCK(la); 94 return (~sum); 95 } 96 97 #ifndef _KERNEL 98 u_short 99 IpChecksum(struct ip *pip) 100 { 101 return (LibAliasInternetChecksum(NULL, (u_short *) pip, 102 (pip->ip_hl << 2))); 103 104 } 105 106 u_short 107 TcpChecksum(struct ip *pip) 108 { 109 u_short *ptr; 110 struct tcphdr *tc; 111 int nhdr, ntcp, nbytes; 112 int sum, oddbyte; 113 void *v; 114 115 nhdr = pip->ip_hl << 2; 116 ntcp = ntohs(pip->ip_len) - nhdr; 117 118 tc = (struct tcphdr *)ip_next(pip); 119 ptr = (u_short *) tc; 120 121 /* Add up TCP header and data */ 122 nbytes = ntcp; 123 sum = 0; 124 while (nbytes > 1) { 125 sum += *ptr++; 126 nbytes -= 2; 127 } 128 if (nbytes == 1) { 129 oddbyte = 0; 130 ((u_char *) & oddbyte)[0] = *(u_char *) ptr; 131 ((u_char *) & oddbyte)[1] = 0; 132 sum += oddbyte; 133 } 134 /* "Pseudo-header" data */ 135 v = &pip->ip_dst; 136 ptr = v; 137 sum += *ptr++; 138 sum += *ptr; 139 v = &pip->ip_src; 140 ptr = v; 141 sum += *ptr++; 142 sum += *ptr; 143 sum += htons((u_short) ntcp); 144 sum += htons((u_short) pip->ip_p); 145 146 /* Roll over carry bits */ 147 sum = (sum >> 16) + (sum & 0xffff); 148 sum += (sum >> 16); 149 150 /* Return checksum */ 151 return ((u_short) ~ sum); 152 } 153 #endif /* not _KERNEL */ 154 155 void 156 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n) 157 { 158 int i; 159 int accumulate; 160 u_short *new = newp; 161 u_short *old = oldp; 162 163 accumulate = *cksum; 164 for (i = 0; i < n; i++) { 165 accumulate -= *new++; 166 accumulate += *old++; 167 } 168 169 if (accumulate < 0) { 170 accumulate = -accumulate; 171 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 172 accumulate += accumulate >> 16; 173 *cksum = (u_short) ~ accumulate; 174 } else { 175 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 176 accumulate += accumulate >> 16; 177 *cksum = (u_short) accumulate; 178 } 179 } 180