2 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD$");
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.
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).
40 Initial Version: August, 1996 (cjm)
42 Version 1.7: January 9, 1997
43 Added differential checksum update function.
47 #include <sys/param.h>
50 #include <sys/types.h>
54 #include <netinet/in_systm.h>
55 #include <netinet/in.h>
56 #include <netinet/ip.h>
57 #include <netinet/tcp.h>
60 #include <netinet/libalias/alias.h>
61 #include <netinet/libalias/alias_local.h>
64 #include "alias_local.h"
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
74 LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
87 ((u_char *) & oddbyte)[0] = *(u_char *) ptr;
88 ((u_char *) & oddbyte)[1] = 0;
91 sum = (sum >> 16) + (sum & 0xffff);
99 IpChecksum(struct ip *pip)
101 return (LibAliasInternetChecksum(NULL, (u_short *) pip,
107 TcpChecksum(struct ip *pip)
111 int nhdr, ntcp, nbytes;
115 nhdr = pip->ip_hl << 2;
116 ntcp = ntohs(pip->ip_len) - nhdr;
118 tc = (struct tcphdr *)ip_next(pip);
119 ptr = (u_short *) tc;
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 */
143 sum += htons((u_short) ntcp);
144 sum += htons((u_short) pip->ip_p);
146 /* Roll over carry bits */
147 sum = (sum >> 16) + (sum & 0xffff);
150 /* Return checksum */
151 return ((u_short) ~ sum);
153 #endif /* not _KERNEL */
156 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)
164 for (i = 0; i < n; i++) {
165 accumulate -= *new++;
166 accumulate += *old++;
169 if (accumulate < 0) {
170 accumulate = -accumulate;
171 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
172 accumulate += accumulate >> 16;
173 *cksum = (u_short) ~ accumulate;
175 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
176 accumulate += accumulate >> 16;
177 *cksum = (u_short) accumulate;