xref: /illumos-gate/usr/src/common/net/dhcp/udp_sum.c (revision 7c478bd9)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License, Version 1.0 only
6  * (the "License").  You may not use this file except in compliance
7  * with the License.
8  *
9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10  * or http://www.opensolaris.org/os/licensing.
11  * See the License for the specific language governing permissions
12  * and limitations under the License.
13  *
14  * When distributing Covered Code, include this CDDL HEADER in each
15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16  * If applicable, add the following below this CDDL HEADER, with the
17  * fields enclosed by brackets "[]" replaced with your own identifying
18  * information: Portions Copyright [yyyy] [name of copyright owner]
19  *
20  * CDDL HEADER END
21  */
22 /*
23  * Copyright (c) 1996-2001 by Sun Microsystems, Inc.
24  * All rights reserved.
25  */
26 
27 #pragma ident	"%Z%%M%	%I%	%E% SMI"
28 
29 #include <sys/types.h>
30 #include <strings.h>
31 #include <netinet/in.h>
32 #include "v4_sum_impl.h"
33 
34 /*
35  * RFC 768 pseudo header. Used in calculating UDP checksums.
36  */
37 struct pseudo_udp {
38 	struct in_addr	src;
39 	struct in_addr	dst;
40 	uint8_t		notused;	/* always zero */
41 	uint8_t		proto;		/* protocol used */
42 	uint16_t	len;		/* UDP len */
43 };
44 
45 /*
46  * One's complement checksum of pseudo header, udp header, and data.
47  * Must be MT SAFE.
48  */
49 uint16_t
udp_chksum(struct udphdr * udph,const struct in_addr * src,const struct in_addr * dst,uint8_t proto)50 udp_chksum(struct udphdr *udph, const struct in_addr *src,
51     const struct in_addr *dst, uint8_t proto)
52 {
53 	struct pseudo_udp	ck;
54 	uint16_t		*end_pseudo_hdr = (uint16_t *)(&ck + 1);
55 	uint16_t		*sp = (uint16_t *)&ck;
56 	uint_t			sum = 0;
57 	uint16_t		cnt;
58 
59 	/*
60 	 * Start on the pseudo header. Note that pseudo_udp already takes
61 	 * acount for the udphdr...
62 	 */
63 
64 	bzero(&ck, sizeof (ck));
65 
66 	/* struct copies */
67 	ck.src	 = *src;
68 	ck.dst	 = *dst;
69 	ck.len	 = udph->uh_ulen;
70 	ck.proto = proto;
71 
72 	/*
73 	 * If the packet is an odd length, zero the pad byte for checksum
74 	 * purposes [doesn't hurt data]
75 	 */
76 
77 	cnt = ntohs(ck.len) + sizeof (ck);
78 	if (cnt & 1) {
79 		((caddr_t)udph)[ntohs(udph->uh_ulen)] = '\0';
80 		cnt++;	/* make even */
81 	}
82 
83 	for (cnt >>= 1; cnt != 0; cnt--) {
84 
85 		sum += *sp++;
86 		if (sum >= BIT_WRAP) {
87 			/* Wrap carries into low bit */
88 			sum -= BIT_WRAP;
89 			sum++;
90 		}
91 
92 		/*
93 		 * If we've finished checking the pseudo-header, move
94 		 * onto the udp header and data.
95 		 */
96 
97 		if (sp == end_pseudo_hdr)
98 			sp = (uint16_t *)udph;
99 	}
100 
101 	return (~sum == 0 ? ~0 : ~sum);
102 }
103