alias_util.c revision 85964 
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
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: head/sys/netinet/libalias/alias_util.c 85964 2001-11-03 11:34:09Z brian $");
29
30
31/*
32    Alias_util.c contains general utilities used by other functions
33    in the packet aliasing module.  At the moment, there are functions
34    for computing IP header and TCP packet checksums.
35
36    The checksum routines are based upon example code in a Unix networking
37    text written by Stevens (sorry, I can't remember the title -- but
38    at least this is a good author).
39
40    Initial Version:  August, 1996  (cjm)
41
42    Version 1.7:  January 9, 1997
43         Added differential checksum update function.
44*/
45
46/*
47Note: the checksum routines assume that the actual checksum word has
48been zeroed out.  If the checksum word is filled with the proper value,
49then these routines will give a result of zero (useful for testing
50purposes);
51*/
52
53#include <sys/types.h>
54#include <netinet/in_systm.h>
55#include <netinet/in.h>
56#include <netinet/ip.h>
57#include <netinet/tcp.h>
58
59#include "alias.h"
60#include "alias_local.h"
61
62u_short
63PacketAliasInternetChecksum(u_short *ptr, int nbytes)
64{
65    int sum, oddbyte;
66
67    sum = 0;
68    while (nbytes > 1)
69    {
70        sum += *ptr++;
71        nbytes -= 2;
72    }
73    if (nbytes == 1)
74    {
75        oddbyte = 0;
76        ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
77        ((u_char *) &oddbyte)[1] = 0;
78        sum += oddbyte;
79    }
80    sum = (sum >> 16) + (sum & 0xffff);
81    sum += (sum >> 16);
82    return(~sum);
83}
84
85u_short
86IpChecksum(struct ip *pip)
87{
88    return( PacketAliasInternetChecksum((u_short *) pip,
89            (pip->ip_hl << 2)) );
90
91}
92
93u_short
94TcpChecksum(struct ip *pip)
95{
96    u_short *ptr;
97    struct tcphdr *tc;
98    int nhdr, ntcp, nbytes;
99    int sum, oddbyte;
100
101    nhdr = pip->ip_hl << 2;
102    ntcp = ntohs(pip->ip_len) - nhdr;
103
104    tc = (struct tcphdr *) ((char *) pip + nhdr);
105    ptr = (u_short *) tc;
106
107/* Add up TCP header and data */
108    nbytes = ntcp;
109    sum = 0;
110    while (nbytes > 1)
111    {
112        sum += *ptr++;
113        nbytes -= 2;
114    }
115    if (nbytes == 1)
116    {
117        oddbyte = 0;
118        ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
119        ((u_char *) &oddbyte)[1] = 0;
120        sum += oddbyte;
121    }
122
123/* "Pseudo-header" data */
124    ptr = (u_short *) &(pip->ip_dst);
125    sum += *ptr++;
126    sum += *ptr;
127    ptr = (u_short *) &(pip->ip_src);
128    sum += *ptr++;
129    sum += *ptr;
130    sum += htons((u_short) ntcp);
131    sum += htons((u_short) pip->ip_p);
132
133/* Roll over carry bits */
134    sum = (sum >> 16) + (sum & 0xffff);
135    sum += (sum >> 16);
136
137/* Return checksum */
138    return((u_short) ~sum);
139}
140
141
142void
143DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
144{
145    int i;
146    int accumulate;
147
148    accumulate = *cksum;
149    for (i=0; i<n; i++)
150    {
151        accumulate -= *new++;
152        accumulate += *old++;
153    }
154
155    if (accumulate < 0)
156    {
157        accumulate = -accumulate;
158        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
159        accumulate += accumulate >> 16;
160        *cksum = (u_short) ~accumulate;
161    }
162    else
163    {
164        accumulate = (accumulate >> 16) + (accumulate & 0xffff);
165        accumulate += accumulate >> 16;
166        *cksum = (u_short) accumulate;
167    }
168}
169
170