alias_util.c revision 77701 
1/*-
2 * Copyright (c) 2001 Charles Mott <cmott@scientech.com>
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: head/sys/netinet/libalias/alias_util.c 77701 2001-06-04 15:09:51Z brian $
27 */
28
29/*
30    Alias_util.c contains general utilities used by other functions
31    in the packet aliasing module.  At the moment, there are functions
32    for computing IP header and TCP packet checksums.
33
34    The checksum routines are based upon example code in a Unix networking
35    text written by Stevens (sorry, I can't remember the title -- but
36    at least this is a good author).
37
38    Initial Version:  August, 1996  (cjm)
39
40    Version 1.7:  January 9, 1997
41         Added differential checksum update function.
42*/
43
44/*
45Note: the checksum routines assume that the actual checksum word has
46been zeroed out.  If the checksum word is filled with the proper value,
47then these routines will give a result of zero (useful for testing
48purposes);
49*/
50
51#include <sys/types.h>
52#include <netinet/in_systm.h>
53#include <netinet/in.h>
54#include <netinet/ip.h>
55#include <netinet/tcp.h>
56
57#include "alias.h"
58#include "alias_local.h"
59
60u_short
61PacketAliasInternetChecksum(u_short *ptr, int nbytes)
62{
63    int sum, oddbyte;
64
65    sum = 0;
66    while (nbytes > 1)
67    {
68        sum += *ptr++;
69        nbytes -= 2;
70    }
71    if (nbytes == 1)
72    {
73        oddbyte = 0;
74        ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
75        ((u_char *) &oddbyte)[1] = 0;
76        sum += oddbyte;
77    }
78    sum = (sum >> 16) + (sum & 0xffff);
79    sum += (sum >> 16);
80    return(~sum);
81}
82
83u_short
84IpChecksum(struct ip *pip)
85{
86    return( PacketAliasInternetChecksum((u_short *) pip,
87            (pip->ip_hl << 2)) );
88
89}
90
91u_short
92TcpChecksum(struct ip *pip)
93{
94    u_short *ptr;
95    struct tcphdr *tc;
96    int nhdr, ntcp, nbytes;
97    int sum, oddbyte;
98
99    nhdr = pip->ip_hl << 2;
100    ntcp = ntohs(pip->ip_len) - nhdr;
101
102    tc = (struct tcphdr *) ((char *) pip + nhdr);
103    ptr = (u_short *) tc;
104
105/* Add up TCP header and data */
106    nbytes = ntcp;
107    sum = 0;
108    while (nbytes > 1)
109    {
110        sum += *ptr++;
111        nbytes -= 2;
112    }
113    if (nbytes == 1)
114    {
115        oddbyte = 0;
116        ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
117        ((u_char *) &oddbyte)[1] = 0;
118        sum += oddbyte;
119    }
120
121/* "Pseudo-header" data */
122    ptr = (u_short *) &(pip->ip_dst);
123    sum += *ptr++;
124    sum += *ptr;
125    ptr = (u_short *) &(pip->ip_src);
126    sum += *ptr++;
127    sum += *ptr;
128    sum += htons((u_short) ntcp);
129    sum += htons((u_short) pip->ip_p);
130
131/* Roll over carry bits */
132    sum = (sum >> 16) + (sum & 0xffff);
133    sum += (sum >> 16);
134
135/* Return checksum */
136    return((u_short) ~sum);
137}
138
139
140void
141DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
142{
143    int i;
144    int accumulate;
145
146    accumulate = *cksum;
147    for (i=0; i<n; i++)
148    {
149        accumulate -= *new++;
150        accumulate += *old++;
151    }
152
153    if (accumulate < 0)
154    {
155        accumulate = -accumulate;
156        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
157        accumulate += accumulate >> 16;
158        *cksum = (u_short) ~accumulate;
159    }
160    else
161    {
162        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
163        accumulate += accumulate >> 16;
164        *cksum = (u_short) accumulate;
165    }
166}
167
168