xref: /freebsd/sys/netinet/libalias/alias_util.c (revision 6990ffd8a95caaba6858ad44ff1b3157d1efba8f)
1 /*-
2  * Copyright (c) 2001 Charles Mott <cmott@scientech.com>
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
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.
13  *
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
24  * SUCH DAMAGE.
25  *
26  * $FreeBSD$
27  */
28 
29 /*
30     Alias_util.c contains general utilities used by other functions
31     in the packet aliasing module.  At the moment, there are functions
32     for computing IP header and TCP packet checksums.
33 
34     The checksum routines are based upon example code in a Unix networking
35     text written by Stevens (sorry, I can't remember the title -- but
36     at least this is a good author).
37 
38     Initial Version:  August, 1996  (cjm)
39 
40     Version 1.7:  January 9, 1997
41          Added differential checksum update function.
42 */
43 
44 /*
45 Note: the checksum routines assume that the actual checksum word has
46 been zeroed out.  If the checksum word is filled with the proper value,
47 then these routines will give a result of zero (useful for testing
48 purposes);
49 */
50 
51 #include <sys/types.h>
52 #include <netinet/in_systm.h>
53 #include <netinet/in.h>
54 #include <netinet/ip.h>
55 #include <netinet/tcp.h>
56 
57 #include "alias.h"
58 #include "alias_local.h"
59 
60 u_short
61 PacketAliasInternetChecksum(u_short *ptr, int nbytes)
62 {
63     int sum, oddbyte;
64 
65     sum = 0;
66     while (nbytes > 1)
67     {
68         sum += *ptr++;
69         nbytes -= 2;
70     }
71     if (nbytes == 1)
72     {
73         oddbyte = 0;
74         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
75         ((u_char *) &oddbyte)[1] = 0;
76         sum += oddbyte;
77     }
78     sum = (sum >> 16) + (sum & 0xffff);
79     sum += (sum >> 16);
80     return(~sum);
81 }
82 
83 u_short
84 IpChecksum(struct ip *pip)
85 {
86     return( PacketAliasInternetChecksum((u_short *) pip,
87             (pip->ip_hl << 2)) );
88 
89 }
90 
91 u_short
92 TcpChecksum(struct ip *pip)
93 {
94     u_short *ptr;
95     struct tcphdr *tc;
96     int nhdr, ntcp, nbytes;
97     int sum, oddbyte;
98 
99     nhdr = pip->ip_hl << 2;
100     ntcp = ntohs(pip->ip_len) - nhdr;
101 
102     tc = (struct tcphdr *) ((char *) pip + nhdr);
103     ptr = (u_short *) tc;
104 
105 /* Add up TCP header and data */
106     nbytes = ntcp;
107     sum = 0;
108     while (nbytes > 1)
109     {
110         sum += *ptr++;
111         nbytes -= 2;
112     }
113     if (nbytes == 1)
114     {
115         oddbyte = 0;
116         ((u_char *) &oddbyte)[0] = *(u_char *) ptr;
117         ((u_char *) &oddbyte)[1] = 0;
118         sum += oddbyte;
119     }
120 
121 /* "Pseudo-header" data */
122     ptr = (u_short *) &(pip->ip_dst);
123     sum += *ptr++;
124     sum += *ptr;
125     ptr = (u_short *) &(pip->ip_src);
126     sum += *ptr++;
127     sum += *ptr;
128     sum += htons((u_short) ntcp);
129     sum += htons((u_short) pip->ip_p);
130 
131 /* Roll over carry bits */
132     sum = (sum >> 16) + (sum & 0xffff);
133     sum += (sum >> 16);
134 
135 /* Return checksum */
136     return((u_short) ~sum);
137 }
138 
139 
140 void
141 DifferentialChecksum(u_short *cksum, u_short *new, u_short *old, int n)
142 {
143     int i;
144     int accumulate;
145 
146     accumulate = *cksum;
147     for (i=0; i<n; i++)
148     {
149         accumulate -= *new++;
150         accumulate += *old++;
151     }
152 
153     if (accumulate < 0)
154     {
155         accumulate = -accumulate;
156         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
157         accumulate += accumulate >> 16;
158         *cksum = (u_short) ~accumulate;
159     }
160     else
161     {
162         accumulate = (accumulate >> 16) + (accumulate & 0xffff);
163         accumulate += accumulate >> 16;
164         *cksum = (u_short) accumulate;
165     }
166 }
167 
168