usr/src/common/net/dhcp/udp_sum.c

   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
  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 }