2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
33 Alias_util.c contains general utilities used by other functions
34 in the packet aliasing module. At the moment, there are functions
35 for computing IP header and TCP packet checksums.
37 The checksum routines are based upon example code in a Unix networking
38 text written by Stevens (sorry, I can't remember the title -- but
39 at least this is a good author).
41 Initial Version: August, 1996 (cjm)
43 Version 1.7: January 9, 1997
44 Added differential checksum update function.
48 #include <sys/param.h>
51 #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>
61 #include <netinet/libalias/alias.h>
62 #include <netinet/libalias/alias_local.h>
65 #include "alias_local.h"
69 * Note: the checksum routines assume that the actual checksum word has
70 * been zeroed out. If the checksum word is filled with the proper value,
71 * then these routines will give a result of zero (useful for testing
75 LibAliasInternetChecksum(struct libalias *la __unused, u_short *ptr,
88 ((u_char *)&oddbyte)[0] = *(u_char *)ptr;
89 ((u_char *)&oddbyte)[1] = 0;
92 sum = (sum >> 16) + (sum & 0xffff);
100 IpChecksum(struct ip *pip)
102 return (LibAliasInternetChecksum(NULL, (u_short *)pip,
108 TcpChecksum(struct ip *pip)
112 int nhdr, ntcp, nbytes;
115 nhdr = pip->ip_hl << 2;
116 ntcp = ntohs(pip->ip_len) - nhdr;
118 tc = (struct tcphdr *)ip_next(pip);
121 /* Add up TCP header and data */
130 ((u_char *)&oddbyte)[0] = *(u_char *)ptr;
131 ((u_char *)&oddbyte)[1] = 0;
134 /* "Pseudo-header" data */
135 ptr = (void *)&pip->ip_dst;
138 ptr = (void *)&pip->ip_src;
141 sum += htons((u_short)ntcp);
142 sum += htons((u_short)pip->ip_p);
144 /* Roll over carry bits */
145 sum = (sum >> 16) + (sum & 0xffff);
148 /* Return checksum */
149 return ((u_short)~sum);
151 #endif /* not _KERNEL */
154 DifferentialChecksum(u_short *cksum, void *newp, void *oldp, int n)
162 for (i = 0; i < n; i++) {
163 accumulate -= *new++;
164 accumulate += *old++;
167 if (accumulate < 0) {
168 accumulate = -accumulate;
169 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
170 accumulate += accumulate >> 16;
171 *cksum = (u_short)~accumulate;
173 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
174 accumulate += accumulate >> 16;
175 *cksum = (u_short)accumulate;