1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <sys/cdefs.h>
30/*
31    Alias_util.c contains general utilities used by other functions
32    in the packet aliasing module.  At the moment, there are functions
33    for computing IP header and TCP packet checksums.
34
35    The checksum routines are based upon example code in a Unix networking
36    text written by Stevens (sorry, I can't remember the title -- but
37    at least this is a good author).
38
39    Initial Version:  August, 1996  (cjm)
40
41    Version 1.7:  January 9, 1997
42	 Added differential checksum update function.
43*/
44
45#ifdef _KERNEL
46#include <sys/param.h>
47#include <sys/proc.h>
48#else
49#include <sys/types.h>
50#include <stdio.h>
51#endif
52
53#include <netinet/in_systm.h>
54#include <netinet/in.h>
55#include <netinet/ip.h>
56#include <netinet/tcp.h>
57
58#ifdef _KERNEL
59#include <netinet/libalias/alias.h>
60#include <netinet/libalias/alias_local.h>
61#else
62#include "alias.h"
63#include "alias_local.h"
64#endif
65
66/*
67 * Note: the checksum routines assume that the actual checksum word has
68 * been zeroed out.  If the checksum word is filled with the proper value,
69 * then these routines will give a result of zero (useful for testing
70 * purposes);
71 */
72u_short
73LibAliasInternetChecksum(struct libalias *la __unused, u_short *ptr,
74    int nbytes)
75{
76	int sum, oddbyte;
77
78	LIBALIAS_LOCK(la);
79	sum = 0;
80	while (nbytes > 1) {
81		sum += *ptr++;
82		nbytes -= 2;
83	}
84	if (nbytes == 1) {
85		oddbyte = 0;
86		((u_char *)&oddbyte)[0] = *(u_char *)ptr;
87		((u_char *)&oddbyte)[1] = 0;
88		sum += oddbyte;
89	}
90	sum = (sum >> 16) + (sum & 0xffff);
91	sum += (sum >> 16);
92	LIBALIAS_UNLOCK(la);
93	return (~sum);
94}
95
96#ifndef _KERNEL
97u_short
98IpChecksum(struct ip *pip)
99{
100	return (LibAliasInternetChecksum(NULL, (u_short *)pip,
101	    (pip->ip_hl << 2)));
102
103}
104
105u_short
106TcpChecksum(struct ip *pip)
107{
108	u_short *ptr;
109	struct tcphdr *tc;
110	int nhdr, ntcp, nbytes;
111	int sum, oddbyte;
112
113	nhdr = pip->ip_hl << 2;
114	ntcp = ntohs(pip->ip_len) - nhdr;
115
116	tc = (struct tcphdr *)ip_next(pip);
117	ptr = (u_short *)tc;
118
119/* Add up TCP header and data */
120	nbytes = ntcp;
121	sum = 0;
122	while (nbytes > 1) {
123		sum += *ptr++;
124		nbytes -= 2;
125	}
126	if (nbytes == 1) {
127		oddbyte = 0;
128		((u_char *)&oddbyte)[0] = *(u_char *)ptr;
129		((u_char *)&oddbyte)[1] = 0;
130		sum += oddbyte;
131	}
132/* "Pseudo-header" data */
133	ptr = (void *)&pip->ip_dst;
134	sum += *ptr++;
135	sum += *ptr;
136	ptr = (void *)&pip->ip_src;
137	sum += *ptr++;
138	sum += *ptr;
139	sum += htons((u_short)ntcp);
140	sum += htons((u_short)pip->ip_p);
141
142/* Roll over carry bits */
143	sum = (sum >> 16) + (sum & 0xffff);
144	sum += (sum >> 16);
145
146/* Return checksum */
147	return ((u_short)~sum);
148}
149#endif	/* not _KERNEL */
150
151void
152DifferentialChecksum(u_short *cksum, void *newp, void *oldp, int n)
153{
154	int i;
155	int accumulate;
156	u_short *new = newp;
157	u_short *old = oldp;
158
159	accumulate = *cksum;
160	for (i = 0; i < n; i++) {
161		accumulate -= *new++;
162		accumulate += *old++;
163	}
164
165	if (accumulate < 0) {
166		accumulate = -accumulate;
167		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
168		accumulate += accumulate >> 16;
169		*cksum = (u_short)~accumulate;
170	} else {
171		accumulate = (accumulate >> 16) + (accumulate & 0xffff);
172		accumulate += accumulate >> 16;
173		*cksum = (u_short)accumulate;
174	}
175}
176