alias_util.c revision 131699 
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 131699 2004-07-06 12:13:28Z des $");
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 <stdio.h>
54#include <sys/types.h>
55#include <netinet/in_systm.h>
56#include <netinet/in.h>
57#include <netinet/ip.h>
58#include <netinet/tcp.h>
59
60#include "alias.h"
61#include "alias_local.h"
62
63u_short
64LibAliasInternetChecksum(struct libalias *la, u_short * ptr, int nbytes)
65{
66	int sum, oddbyte;
67
68	(void)la;
69
70	sum = 0;
71	while (nbytes > 1) {
72		sum += *ptr++;
73		nbytes -= 2;
74	}
75	if (nbytes == 1) {
76		oddbyte = 0;
77		((u_char *) & oddbyte)[0] = *(u_char *) ptr;
78		((u_char *) & oddbyte)[1] = 0;
79		sum += oddbyte;
80	}
81	sum = (sum >> 16) + (sum & 0xffff);
82	sum += (sum >> 16);
83	return (~sum);
84}
85
86u_short
87IpChecksum(struct ip *pip)
88{
89	return (PacketAliasInternetChecksum((u_short *) pip,
90	    (pip->ip_hl << 2)));
91
92}
93
94u_short
95TcpChecksum(struct ip *pip)
96{
97	u_short *ptr;
98	struct tcphdr *tc;
99	int nhdr, ntcp, nbytes;
100	int sum, oddbyte;
101
102	nhdr = pip->ip_hl << 2;
103	ntcp = ntohs(pip->ip_len) - nhdr;
104
105	tc = (struct tcphdr *)ip_next(pip);
106	ptr = (u_short *) tc;
107
108/* Add up TCP header and data */
109	nbytes = ntcp;
110	sum = 0;
111	while (nbytes > 1) {
112		sum += *ptr++;
113		nbytes -= 2;
114	}
115	if (nbytes == 1) {
116		oddbyte = 0;
117		((u_char *) & oddbyte)[0] = *(u_char *) ptr;
118		((u_char *) & oddbyte)[1] = 0;
119		sum += oddbyte;
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, void *newp, void *oldp, int n)
142{
143	int i;
144	int accumulate;
145	u_short *new = newp;
146	u_short *old = oldp;
147
148	accumulate = *cksum;
149	for (i = 0; i < n; i++) {
150		accumulate -= *new++;
151		accumulate += *old++;
152	}
153
154	if (accumulate < 0) {
155		accumulate = -accumulate;
156		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
157		accumulate += accumulate >> 16;
158		*cksum = (u_short) ~ accumulate;
159	} else {
160		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
161		accumulate += accumulate >> 16;
162		*cksum = (u_short) accumulate;
163	}
164}
165