lib/libalias/alias_util.c

   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  * $FreeBSD: src/lib/libalias/alias_util.c,v 1.4.2.3 2001/11/03 11:34:33 brian Exp $
  27  * $DragonFly: src/lib/libalias/alias_util.c,v 1.3 2004/08/20 00:08:17 joerg Exp $
  28  */
  29
  30 /*
  31     Alias_util.c contains general utilities used by other functions
  32     in the packet aliasing module.  At the moment, there are functions
  33     for computing IP header and TCP packet checksums.
  34
  35     The checksum routines are based upon example code in a Unix networking
  36     text written by Stevens (sorry, I can't remember the title -- but
  37     at least this is a good author).
  38
  39     Initial Version:  August, 1996  (cjm)
  40
  41     Version 1.7:  January 9, 1997
  42          Added differential checksum update function.
  43 */
  44
  45 /*
  46 Note: the checksum routines assume that the actual checksum word has
  47 been zeroed out.  If the checksum word is filled with the proper value,
  48 then these routines will give a result of zero (useful for testing
  49 purposes);
  50 */
  51
  52 #include <sys/param.h>
  53 #include <netinet/in_systm.h>
  54 #include <netinet/in.h>
  55 #include <netinet/ip.h>
  56 #include <netinet/tcp.h>
  57
  58 #include "alias.h"
  59 #include "alias_local.h"
  60
  61 u_short
  62 PacketAliasInternetChecksum(u_short *ptr, int nbytes)
  63 {
  64     int sum, oddbyte;
  65
  66     sum = 0;
  67     while (nbytes > 1)
  68     {
  69         sum += *ptr++;
  70         nbytes -= 2;
  71     }
  72     if (nbytes == 1)
  73     {
  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     {
 111         sum += *ptr++;
 112         nbytes -= 2;
 113     }
 114     if (nbytes == 1)
 115     {
 116         oddbyte = 0;
 117         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
 118         ((u_char *) &oddbyte)[1] = 0;
 119         sum += oddbyte;
 120     }
 121
 122 /* "Pseudo-header" data */
 123     ptr = (u_short *) &(pip->ip_dst);
 124     sum += *ptr++;
 125     sum += *ptr;
 126     ptr = (u_short *) &(pip->ip_src);
 127     sum += *ptr++;
 128     sum += *ptr;
 129     sum += htons((u_short) ntcp);
 130     sum += htons((u_short) pip->ip_p);
 131
 132 /* Roll over carry bits */
 133     sum = (sum >> 16) + (sum & 0xffff);
 134     sum += (sum >> 16);
 135
 136 /* Return checksum */
 137     return((u_short) ~sum);
 138 }
 139
 140
 141 void
 142 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
 143 {
 144     int i;
 145     int accumulate;
 146
 147     accumulate = *cksum;
 148     for (i=0; i<n; i++)
 149     {
 150         accumulate -= *new++;
 151         accumulate += *old++;
 152     }
 153
 154     if (accumulate < 0)
 155     {
 156         accumulate = -accumulate;
 157         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 158         accumulate += accumulate >> 16;
 159         *cksum = (u_short) ~accumulate;
 160     }
 161     else
 162     {
 163         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
 164         accumulate += accumulate >> 16;
 165         *cksum = (u_short) accumulate;
 166     }
 167 }
 168