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("$FreeBSD$");
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
114	nhdr = pip->ip_hl << 2;
115	ntcp = ntohs(pip->ip_len) - nhdr;
116
117	tc = (struct tcphdr *)ip_next(pip);
118	ptr = (u_short *) tc;
119
120/* Add up TCP header and data */
121	nbytes = ntcp;
122	sum = 0;
123	while (nbytes > 1) {
124		sum += *ptr++;
125		nbytes -= 2;
126	}
127	if (nbytes == 1) {
128		oddbyte = 0;
129		((u_char *) & oddbyte)[0] = *(u_char *) ptr;
130		((u_char *) & oddbyte)[1] = 0;
131		sum += oddbyte;
132	}
133/* "Pseudo-header" data */
134	ptr = (void *)&pip->ip_dst;
135	sum += *ptr++;
136	sum += *ptr;
137	ptr = (void *)&pip->ip_src;
138	sum += *ptr++;
139	sum += *ptr;
140	sum += htons((u_short) ntcp);
141	sum += htons((u_short) pip->ip_p);
142
143/* Roll over carry bits */
144	sum = (sum >> 16) + (sum & 0xffff);
145	sum += (sum >> 16);
146
147/* Return checksum */
148	return ((u_short) ~ sum);
149}
150#endif	/* not _KERNEL */
151
152void
153DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)
154{
155	int i;
156	int accumulate;
157	u_short *new = newp;
158	u_short *old = oldp;
159
160	accumulate = *cksum;
161	for (i = 0; i < n; i++) {
162		accumulate -= *new++;
163		accumulate += *old++;
164	}
165
166	if (accumulate < 0) {
167		accumulate = -accumulate;
168		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
169		accumulate += accumulate >> 16;
170		*cksum = (u_short) ~ accumulate;
171	} else {
172		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
173		accumulate += accumulate >> 16;
174		*cksum = (u_short) accumulate;
175	}
176}
177