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
53 #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 "alias_local.h"
63 PacketAliasInternetChecksum(u_short *ptr, int nbytes)
76 ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
77 ((u_char *) &oddbyte)[1] = 0;
80 sum = (sum >> 16) + (sum & 0xffff);
86 IpChecksum(struct ip *pip)
88 return( PacketAliasInternetChecksum((u_short *) pip,
94 TcpChecksum(struct ip *pip)
98 int nhdr, ntcp, nbytes;
101 nhdr = pip->ip_hl << 2;
102 ntcp = ntohs(pip->ip_len) - nhdr;
104 tc = (struct tcphdr *) ((char *) pip + nhdr);
105 ptr = (u_short *) tc;
107 /* Add up TCP header and data */
118 ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
119 ((u_char *) &oddbyte)[1] = 0;
123 /* "Pseudo-header" data */
124 ptr = (u_short *) &(pip->ip_dst);
127 ptr = (u_short *) &(pip->ip_src);
130 sum += htons((u_short) ntcp);
131 sum += htons((u_short) pip->ip_p);
133 /* Roll over carry bits */
134 sum = (sum >> 16) + (sum & 0xffff);
137 /* Return checksum */
138 return((u_short) ~sum);
143 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
151 accumulate -= *new++;
152 accumulate += *old++;
157 accumulate = -accumulate;
158 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
159 accumulate += accumulate >> 16;
160 *cksum = (u_short) ~accumulate;
164 accumulate = (accumulate >> 16) + (accumulate & 0xffff);
165 accumulate += accumulate >> 16;
166 *cksum = (u_short) accumulate;