alias/alias_util.c

   1 /*
   2  * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*-
  23  * Copyright (c) 2001 Charles Mott <cmott@scientech.com>
  24  * All rights reserved.
  25  *
  26  * Redistribution and use in source and binary forms, with or without
  27  * modification, are permitted provided that the following conditions
  28  * are met:
  29  * 1. Redistributions of source code must retain the above copyright
  30  *    notice, this list of conditions and the following disclaimer.
  31  * 2. Redistributions in binary form must reproduce the above copyright
  32  *    notice, this list of conditions and the following disclaimer in the
  33  *    documentation and/or other materials provided with the distribution.
  34  *
  35  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  36  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  37  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  38  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  39  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  40  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  41  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  42  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  43  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  44  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  45  * SUCH DAMAGE.
  46  *
  47  * Based upon:
  48  * $FreeBSD: src/lib/libalias/alias_util.c,v 1.4.2.2 2001/06/04 14:59:06 brian Exp $
  49  */
  50
  51 /*
  52     Alias_util.c contains general utilities used by other functions
  53     in the packet aliasing module.  At the moment, there are functions
  54     for computing IP header and TCP packet checksums.
  55
  56     The checksum routines are based upon example code in a Unix networking
  57     text written by Stevens (sorry, I can't remember the title -- but
  58     at least this is a good author).
  59
  60     Initial Version:  August, 1996  (cjm)
  61
  62     Version 1.7:  January 9, 1997
  63          Added differential checksum update function.
  64 */
  65
  66 /*
  67 Note: the checksum routines assume that the actual checksum word has
  68 been zeroed out.  If the checksum word is filled with the proper value,
  69 then these routines will give a result of zero (useful for testing
  70 purposes);
  71 */
  72
  73 #include <sys/types.h>
  74 #include <netinet/in_systm.h>
  75 #include <netinet/in.h>
  76 #include <netinet/ip.h>
  77 #include <netinet/tcp.h>
  78
  79 #include "alias.h"
  80 #include "alias_local.h"
  81
  82 u_short
  83 PacketAliasInternetChecksum(u_short *ptr, int nbytes)
  84 {
  85     int sum, oddbyte;
  86
  87     sum = 0;
  88     while (nbytes > 1)
  89     {
  90         sum += *ptr++;
  91         nbytes -= 2;
  92     }
  93     if (nbytes == 1)
  94     {
  95         oddbyte = 0;
  96         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
  97         ((u_char *) &oddbyte)[1] = 0;
  98         sum += oddbyte;
  99     }
 100     sum = (sum >> 16) + (sum & 0xffff);
 101     sum += (sum >> 16);
 102     return(~sum);
 103 }
 104
 105 u_short
 106 IpChecksum(struct ip *pip)
 107 {
 108     return( PacketAliasInternetChecksum((u_short *) pip,
 109             (pip->ip_hl << 2)) );
 110
 111 }
 112
 113 u_short
 114 TcpChecksum(struct ip *pip)
 115 {
 116     u_short *ptr;
 117     struct tcphdr *tc;
 118     int nhdr, ntcp, nbytes;
 119     int sum, oddbyte;
 120
 121     nhdr = pip->ip_hl << 2;
 122     ntcp = ntohs(pip->ip_len) - nhdr;
 123
 124     tc = (struct tcphdr *) ((char *) pip + nhdr);
 125     ptr = (u_short *) tc;
 126
 127 /* Add up TCP header and data */
 128     nbytes = ntcp;
 129     sum = 0;
 130     while (nbytes > 1)
 131     {
 132         sum += *ptr++;
 133         nbytes -= 2;
 134     }
 135     if (nbytes == 1)
 136     {
 137         oddbyte = 0;
 138         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
 139         ((u_char *) &oddbyte)[1] = 0;
 140         sum += oddbyte;
 141     }
 142
 143 /* "Pseudo-header" data */
 144     ptr = (u_short *) &(pip->ip_dst);
 145     sum += *ptr++;
 146     sum += *ptr;
 147     ptr = (u_short *) &(pip->ip_src);
 148     sum += *ptr++;
 149     sum += *ptr;
 150     sum += htons((u_short) ntcp);
 151     sum += htons((u_short) pip->ip_p);
 152
 153 /* Roll over carry bits */
 154     sum = (sum >> 16) + (sum & 0xffff);
 155     sum += (sum >> 16);
 156
 157 /* Return checksum */
 158     return((u_short) ~sum);
 159 }
 160
 161
 162 void
 163 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
 164 {
 165     int i;
 166     int accumulate;
 167
 168     accumulate = *cksum;
 169     for (i=0; i<n; i++)
 170     {
 171         accumulate -= *new++;
 172         accumulate += *old++;
 173     }
 174
 175     if (accumulate < 0)
 176     {
 177         accumulate = -accumulate;
 178         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 179         accumulate += accumulate >> 16;
 180         *cksum = (u_short) ~accumulate;
 181     }
 182     else
 183     {
 184         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 185         accumulate += accumulate >> 16;
 186         *cksum = (u_short) accumulate;
 187     }
 188 }
 189