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 Note: the checksum routines assume that the actual checksum word has
48 been zeroed out. If the checksum word is filled with the proper value,
49 then these routines will give a result of zero (useful for testing
54 #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 "alias_local.h"
64 LibAliasInternetChecksum(struct libalias *la, u_short * ptr, int nbytes)
77 ((u_char *) & oddbyte)[0] = *(u_char *) ptr;
78 ((u_char *) & oddbyte)[1] = 0;
81 sum = (sum >> 16) + (sum & 0xffff);
87 IpChecksum(struct ip *pip)
89 return (PacketAliasInternetChecksum((u_short *) pip,
95 TcpChecksum(struct ip *pip)
99 int nhdr, ntcp, nbytes;
102 nhdr = pip->ip_hl << 2;
103 ntcp = ntohs(pip->ip_len) - nhdr;
105 tc = (struct tcphdr *)ip_next(pip);
106 ptr = (u_short *) tc;
108 /* Add up TCP header and data */
117 ((u_char *) & oddbyte)[0] = *(u_char *) ptr;
118 ((u_char *) & oddbyte)[1] = 0;
121 /* "Pseudo-header" data */
122 ptr = (u_short *) & (pip->ip_dst);
125 ptr = (u_short *) & (pip->ip_src);
128 sum += htons((u_short) ntcp);
129 sum += htons((u_short) pip->ip_p);
131 /* Roll over carry bits */
132 sum = (sum >> 16) + (sum & 0xffff);
135 /* Return checksum */
136 return ((u_short) ~ sum);
141 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)
149 for (i = 0; i < n; i++) {
150 accumulate -= *new++;
151 accumulate += *old++;
154 if (accumulate < 0) {
155 accumulate = -accumulate;
156 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
157 accumulate += accumulate >> 16;
158 *cksum = (u_short) ~ accumulate;
160 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
161 accumulate += accumulate >> 16;
162 *cksum = (u_short) accumulate;