alias_util.c revision 173874 
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 173874 2007-11-23 23:56:03Z jb $");
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#ifdef _KERNEL
47#include <sys/param.h>
48#include <sys/proc.h>
49#else
50#include <sys/types.h>
51#include <stdio.h>
52#endif
53
54#include <netinet/in_systm.h>
55#include <netinet/in.h>
56#include <netinet/ip.h>
57#include <netinet/tcp.h>
58
59#ifdef _KERNEL
60#include <netinet/libalias/alias.h>
61#include <netinet/libalias/alias_local.h>
62#else
63#include "alias.h"
64#include "alias_local.h"
65#endif
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 */
73u_short
74LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
75	int nbytes)
76{
77	int sum, oddbyte;
78
79	LIBALIAS_LOCK(la);
80	sum = 0;
81	while (nbytes > 1) {
82		sum += *ptr++;
83		nbytes -= 2;
84	}
85	if (nbytes == 1) {
86		oddbyte = 0;
87		((u_char *) & oddbyte)[0] = *(u_char *) ptr;
88		((u_char *) & oddbyte)[1] = 0;
89		sum += oddbyte;
90	}
91	sum = (sum >> 16) + (sum & 0xffff);
92	sum += (sum >> 16);
93	LIBALIAS_UNLOCK(la);
94	return (~sum);
95}
96
97#ifndef	_KERNEL
98u_short
99IpChecksum(struct ip *pip)
100{
101	return (LibAliasInternetChecksum(NULL, (u_short *) pip,
102	    (pip->ip_hl << 2)));
103
104}
105
106u_short
107TcpChecksum(struct ip *pip)
108{
109	u_short *ptr;
110	struct tcphdr *tc;
111	int nhdr, ntcp, nbytes;
112	int sum, oddbyte;
113	void *v;
114
115	nhdr = pip->ip_hl << 2;
116	ntcp = ntohs(pip->ip_len) - nhdr;
117
118	tc = (struct tcphdr *)ip_next(pip);
119	ptr = (u_short *) tc;
120
121/* Add up TCP header and data */
122	nbytes = ntcp;
123	sum = 0;
124	while (nbytes > 1) {
125		sum += *ptr++;
126		nbytes -= 2;
127	}
128	if (nbytes == 1) {
129		oddbyte = 0;
130		((u_char *) & oddbyte)[0] = *(u_char *) ptr;
131		((u_char *) & oddbyte)[1] = 0;
132		sum += oddbyte;
133	}
134/* "Pseudo-header" data */
135	v = &pip->ip_dst;
136	ptr = v;
137	sum += *ptr++;
138	sum += *ptr;
139	v = &pip->ip_src;
140	ptr = v;
141	sum += *ptr++;
142	sum += *ptr;
143	sum += htons((u_short) ntcp);
144	sum += htons((u_short) pip->ip_p);
145
146/* Roll over carry bits */
147	sum = (sum >> 16) + (sum & 0xffff);
148	sum += (sum >> 16);
149
150/* Return checksum */
151	return ((u_short) ~ sum);
152}
153#endif	/* not _KERNEL */
154
155void
156DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)
157{
158	int i;
159	int accumulate;
160	u_short *new = newp;
161	u_short *old = oldp;
162
163	accumulate = *cksum;
164	for (i = 0; i < n; i++) {
165		accumulate -= *new++;
166		accumulate += *old++;
167	}
168
169	if (accumulate < 0) {
170		accumulate = -accumulate;
171		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
172		accumulate += accumulate >> 16;
173		*cksum = (u_short) ~ accumulate;
174	} else {
175		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
176		accumulate += accumulate >> 16;
177		*cksum = (u_short) accumulate;
178	}
179}
180