alias/alias_util.c

   1 /*
   2  * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23 /*-
  24  * Copyright (c) 2001 Charles Mott <cmott@scientech.com>
  25  * All rights reserved.
  26  *
  27  * Redistribution and use in source and binary forms, with or without
  28  * modification, are permitted provided that the following conditions
  29  * are met:
  30  * 1. Redistributions of source code must retain the above copyright
  31  *    notice, this list of conditions and the following disclaimer.
  32  * 2. Redistributions in binary form must reproduce the above copyright
  33  *    notice, this list of conditions and the following disclaimer in the
  34  *    documentation and/or other materials provided with the distribution.
  35  *
  36  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  37  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  38  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  39  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  40  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  41  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  42  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  43  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  44  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  45  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  46  * SUCH DAMAGE.
  47  *
  48  * Based upon:
  49  * $FreeBSD: src/lib/libalias/alias_util.c,v 1.4.2.2 2001/06/04 14:59:06 brian Exp $
  50  */
  51
  52 /*
  53     Alias_util.c contains general utilities used by other functions
  54     in the packet aliasing module.  At the moment, there are functions
  55     for computing IP header and TCP packet checksums.
  56
  57     The checksum routines are based upon example code in a Unix networking
  58     text written by Stevens (sorry, I can't remember the title -- but
  59     at least this is a good author).
  60
  61     Initial Version:  August, 1996  (cjm)
  62
  63     Version 1.7:  January 9, 1997
  64          Added differential checksum update function.
  65 */
  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
  74 #include <sys/types.h>
  75 #include <netinet/in_systm.h>
  76 #include <netinet/in.h>
  77 #include <netinet/ip.h>
  78 #include <netinet/tcp.h>
  79
  80 #include "alias.h"
  81 #include "alias_local.h"
  82
  83 u_short
  84 PacketAliasInternetChecksum(u_short *ptr, int nbytes)
  85 {
  86     int sum, oddbyte;
  87
  88     sum = 0;
  89     while (nbytes > 1)
  90     {
  91         sum += *ptr++;
  92         nbytes -= 2;
  93     }
  94     if (nbytes == 1)
  95     {
  96         oddbyte = 0;
  97         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
  98         ((u_char *) &oddbyte)[1] = 0;
  99         sum += oddbyte;
 100     }
 101     sum = (sum >> 16) + (sum & 0xffff);
 102     sum += (sum >> 16);
 103     return(~sum);
 104 }
 105
 106 u_short
 107 IpChecksum(struct ip *pip)
 108 {
 109     return( PacketAliasInternetChecksum((u_short *) pip,
 110             (pip->ip_hl << 2)) );
 111
 112 }
 113
 114 u_short
 115 TcpChecksum(struct ip *pip)
 116 {
 117     u_short *ptr;
 118     struct tcphdr *tc;
 119     int nhdr, ntcp, nbytes;
 120     int sum, oddbyte;
 121
 122     nhdr = pip->ip_hl << 2;
 123     ntcp = ntohs(pip->ip_len) - nhdr;
 124
 125     tc = (struct tcphdr *) ((char *) pip + nhdr);
 126     ptr = (u_short *) tc;
 127
 128 /* Add up TCP header and data */
 129     nbytes = ntcp;
 130     sum = 0;
 131     while (nbytes > 1)
 132     {
 133         sum += *ptr++;
 134         nbytes -= 2;
 135     }
 136     if (nbytes == 1)
 137     {
 138         oddbyte = 0;
 139         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
 140         ((u_char *) &oddbyte)[1] = 0;
 141         sum += oddbyte;
 142     }
 143
 144 /* "Pseudo-header" data */
 145     ptr = (u_short *) &(pip->ip_dst);
 146     sum += *ptr++;
 147     sum += *ptr;
 148     ptr = (u_short *) &(pip->ip_src);
 149     sum += *ptr++;
 150     sum += *ptr;
 151     sum += htons((u_short) ntcp);
 152     sum += htons((u_short) pip->ip_p);
 153
 154 /* Roll over carry bits */
 155     sum = (sum >> 16) + (sum & 0xffff);
 156     sum += (sum >> 16);
 157
 158 /* Return checksum */
 159     return((u_short) ~sum);
 160 }
 161
 162
 163 void
 164 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
 165 {
 166     int i;
 167     int accumulate;
 168
 169     accumulate = *cksum;
 170     for (i=0; i<n; i++)
 171     {
 172         accumulate -= *new++;
 173         accumulate += *old++;
 174     }
 175
 176     if (accumulate < 0)
 177     {
 178         accumulate = -accumulate;
 179         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 180         accumulate += accumulate >> 16;
 181         *cksum = (u_short) ~accumulate;
 182     }
 183     else
 184     {
 185         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 186         accumulate += accumulate >> 16;
 187         *cksum = (u_short) accumulate;
 188     }
 189 }
 190