1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 Charles Mott <cm@linktel.net> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 /* 33 Alias_util.c contains general utilities used by other functions 34 in the packet aliasing module. At the moment, there are functions 35 for computing IP header and TCP packet checksums. 36 37 The checksum routines are based upon example code in a Unix networking 38 text written by Stevens (sorry, I can't remember the title -- but 39 at least this is a good author). 40 41 Initial Version: August, 1996 (cjm) 42 43 Version 1.7: January 9, 1997 44 Added differential checksum update function. 45 */ 46 47 #ifdef _KERNEL 48 #include <sys/param.h> 49 #include <sys/proc.h> 50 #else 51 #include <sys/types.h> 52 #include <stdio.h> 53 #endif 54 55 #include <netinet/in_systm.h> 56 #include <netinet/in.h> 57 #include <netinet/ip.h> 58 #include <netinet/tcp.h> 59 60 #ifdef _KERNEL 61 #include <netinet/libalias/alias.h> 62 #include <netinet/libalias/alias_local.h> 63 #else 64 #include "alias.h" 65 #include "alias_local.h" 66 #endif 67 68 /* 69 * Note: the checksum routines assume that the actual checksum word has 70 * been zeroed out. If the checksum word is filled with the proper value, 71 * then these routines will give a result of zero (useful for testing 72 * purposes); 73 */ 74 u_short 75 LibAliasInternetChecksum(struct libalias *la __unused, u_short *ptr, 76 int nbytes) 77 { 78 int sum, oddbyte; 79 80 LIBALIAS_LOCK(la); 81 sum = 0; 82 while (nbytes > 1) { 83 sum += *ptr++; 84 nbytes -= 2; 85 } 86 if (nbytes == 1) { 87 oddbyte = 0; 88 ((u_char *)&oddbyte)[0] = *(u_char *)ptr; 89 ((u_char *)&oddbyte)[1] = 0; 90 sum += oddbyte; 91 } 92 sum = (sum >> 16) + (sum & 0xffff); 93 sum += (sum >> 16); 94 LIBALIAS_UNLOCK(la); 95 return (~sum); 96 } 97 98 #ifndef _KERNEL 99 u_short 100 IpChecksum(struct ip *pip) 101 { 102 return (LibAliasInternetChecksum(NULL, (u_short *)pip, 103 (pip->ip_hl << 2))); 104 105 } 106 107 u_short 108 TcpChecksum(struct ip *pip) 109 { 110 u_short *ptr; 111 struct tcphdr *tc; 112 int nhdr, ntcp, nbytes; 113 int sum, oddbyte; 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 ptr = (void *)&pip->ip_dst; 136 sum += *ptr++; 137 sum += *ptr; 138 ptr = (void *)&pip->ip_src; 139 sum += *ptr++; 140 sum += *ptr; 141 sum += htons((u_short)ntcp); 142 sum += htons((u_short)pip->ip_p); 143 144 /* Roll over carry bits */ 145 sum = (sum >> 16) + (sum & 0xffff); 146 sum += (sum >> 16); 147 148 /* Return checksum */ 149 return ((u_short)~sum); 150 } 151 #endif /* not _KERNEL */ 152 153 void 154 DifferentialChecksum(u_short *cksum, void *newp, void *oldp, int n) 155 { 156 int i; 157 int accumulate; 158 u_short *new = newp; 159 u_short *old = oldp; 160 161 accumulate = *cksum; 162 for (i = 0; i < n; i++) { 163 accumulate -= *new++; 164 accumulate += *old++; 165 } 166 167 if (accumulate < 0) { 168 accumulate = -accumulate; 169 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 170 accumulate += accumulate >> 16; 171 *cksum = (u_short)~accumulate; 172 } else { 173 accumulate = (accumulate >> 16) + (accumulate & 0xffff); 174 accumulate += accumulate >> 16; 175 *cksum = (u_short)accumulate; 176 } 177 } 178