sbin/dhclient/packet.c

   1 /*      $OpenBSD: packet.c,v 1.12 2006/12/28 01:10:46 stevesk Exp $     */
   2 /*      $DragonFly: src/sbin/dhclient/packet.c,v 1.1 2008/08/30 16:07:58 hasso Exp $    */
   3
   4 /* Packet assembly code, originally contributed by Archie Cobbs. */
   5
   6 /*
   7  * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
   8  * All rights reserved.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  *
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions and the following disclaimer.
  16  * 2. Redistributions in binary form must reproduce the above copyright
  17  *    notice, this list of conditions and the following disclaimer in the
  18  *    documentation and/or other materials provided with the distribution.
  19  * 3. Neither the name of The Internet Software Consortium nor the names
  20  *    of its contributors may be used to endorse or promote products derived
  21  *    from this software without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
  24  * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
  25  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  26  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  27  * DISCLAIMED.  IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
  28  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  29  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  30  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  31  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  32  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  33  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  34  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  *
  37  * This software has been written for the Internet Software Consortium
  38  * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
  39  * Enterprises.  To learn more about the Internet Software Consortium,
  40  * see ``http://www.vix.com/isc''.  To learn more about Vixie
  41  * Enterprises, see ``http://www.vix.com''.
  42  */
  43
  44 #include "dhcpd.h"
  45
  46 #include <netinet/if_ether.h>
  47 #include <netinet/in_systm.h>
  48 #include <netinet/ip.h>
  49 #include <netinet/udp.h>
  50
  51 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
  52
  53 u_int32_t       checksum(unsigned char *, unsigned, u_int32_t);
  54 u_int32_t       wrapsum(u_int32_t);
  55
  56 u_int32_t
  57 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
  58 {
  59         uint i;
  60
  61         /* Checksum all the pairs of bytes first... */
  62         for (i = 0; i < (nbytes & ~1U); i += 2) {
  63                 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
  64                 if (sum > 0xFFFF)
  65                         sum -= 0xFFFF;
  66         }
  67
  68         /*
  69          * If there's a single byte left over, checksum it, too.
  70          * Network byte order is big-endian, so the remaining byte is
  71          * the high byte.
  72          */
  73         if (i < nbytes) {
  74                 sum += buf[i] << 8;
  75                 if (sum > 0xFFFF)
  76                         sum -= 0xFFFF;
  77         }
  78
  79         return (sum);
  80 }
  81
  82 u_int32_t
  83 wrapsum(u_int32_t sum)
  84 {
  85         sum = ~sum & 0xFFFF;
  86         return (htons(sum));
  87 }
  88
  89 void
  90 assemble_hw_header(unsigned char *buf, int *bufix, struct hardware *to)
  91 {
  92         struct ether_header eh;
  93
  94         if (to != NULL && to->hlen == 6) /* XXX */
  95                 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost));
  96         else
  97                 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
  98         if (ifi->hw_address.hlen == sizeof(eh.ether_shost))
  99                 memcpy(eh.ether_shost, ifi->hw_address.haddr,
 100                     sizeof(eh.ether_shost));
 101         else
 102                 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
 103
 104         eh.ether_type = htons(ETHERTYPE_IP);
 105
 106         memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
 107         *bufix += ETHER_HEADER_SIZE;
 108 }
 109
 110 void
 111 assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
 112     u_int32_t to, unsigned int port, unsigned char *data, int len)
 113 {
 114         struct ip ip;
 115         struct udphdr udp;
 116
 117         ip.ip_v = 4;
 118         ip.ip_hl = 5;
 119         ip.ip_tos = IPTOS_LOWDELAY;
 120         ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
 121         ip.ip_id = 0;
 122         ip.ip_off = 0;
 123         ip.ip_ttl = 16;
 124         ip.ip_p = IPPROTO_UDP;
 125         ip.ip_sum = 0;
 126         ip.ip_src.s_addr = from;
 127         ip.ip_dst.s_addr = to;
 128
 129         ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
 130         memcpy(&buf[*bufix], &ip, sizeof(ip));
 131         *bufix += sizeof(ip);
 132
 133         udp.uh_sport = htons(LOCAL_PORT);       /* XXX */
 134         udp.uh_dport = port;                    /* XXX */
 135         udp.uh_ulen = htons(sizeof(udp) + len);
 136         memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
 137
 138         udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
 139             checksum(data, len, checksum((unsigned char *)&ip.ip_src,
 140             2 * sizeof(ip.ip_src),
 141             IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
 142
 143         memcpy(&buf[*bufix], &udp, sizeof(udp));
 144         *bufix += sizeof(udp);
 145 }
 146
 147 ssize_t
 148 decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
 149 {
 150         struct ether_header eh;
 151
 152         memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
 153
 154         memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
 155         from->htype = ARPHRD_ETHER;
 156         from->hlen = sizeof(eh.ether_shost);
 157
 158         return (sizeof(eh));
 159 }
 160
 161 ssize_t
 162 decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
 163     unsigned char *data, int buflen)
 164 {
 165         struct ip *ip;
 166         struct udphdr *udp;
 167         u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
 168         u_int32_t sum, usum;
 169         static int ip_packets_seen;
 170         static int ip_packets_bad_checksum;
 171         static int udp_packets_seen;
 172         static int udp_packets_bad_checksum;
 173         static int udp_packets_length_checked;
 174         static int udp_packets_length_overflow;
 175         int len = 0;
 176
 177         ip = (struct ip *)(buf + bufix);
 178         udp = (struct udphdr *)(buf + bufix + ip_len);
 179
 180         /* Check the IP header checksum - it should be zero. */
 181         ip_packets_seen++;
 182         if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
 183                 ip_packets_bad_checksum++;
 184                 if (ip_packets_seen > 4 &&
 185                     (ip_packets_seen / ip_packets_bad_checksum) < 2) {
 186                         note("%d bad IP checksums seen in %d packets",
 187                             ip_packets_bad_checksum, ip_packets_seen);
 188                         ip_packets_seen = ip_packets_bad_checksum = 0;
 189                 }
 190                 return (-1);
 191         }
 192
 193         if (ntohs(ip->ip_len) != buflen)
 194                 debug("ip length %d disagrees with bytes received %d.",
 195                     ntohs(ip->ip_len), buflen);
 196
 197         memcpy(&from->sin_addr, &ip->ip_src, 4);
 198
 199         /*
 200          * Compute UDP checksums, including the ``pseudo-header'', the
 201          * UDP header and the data.   If the UDP checksum field is zero,
 202          * we're not supposed to do a checksum.
 203          */
 204         if (!data) {
 205                 data = buf + bufix + ip_len + sizeof(*udp);
 206                 len = ntohs(udp->uh_ulen) - sizeof(*udp);
 207                 udp_packets_length_checked++;
 208                 if (len + data > buf + bufix + buflen) {
 209                         udp_packets_length_overflow++;
 210                         if (udp_packets_length_checked > 4 &&
 211                             (udp_packets_length_checked /
 212                             udp_packets_length_overflow) < 2) {
 213                                 note("%d udp packets in %d too long - dropped",
 214                                     udp_packets_length_overflow,
 215                                     udp_packets_length_checked);
 216                                 udp_packets_length_overflow =
 217                                     udp_packets_length_checked = 0;
 218                         }
 219                         return (-1);
 220                 }
 221                 if (len + data != buf + bufix + buflen)
 222                         debug("accepting packet with data after udp payload.");
 223         }
 224
 225         usum = udp->uh_sum;
 226         udp->uh_sum = 0;
 227
 228         sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
 229             checksum(data, len, checksum((unsigned char *)&ip->ip_src,
 230             2 * sizeof(ip->ip_src),
 231             IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
 232
 233         udp_packets_seen++;
 234         if (usum && usum != sum) {
 235                 udp_packets_bad_checksum++;
 236                 if (udp_packets_seen > 4 &&
 237                     (udp_packets_seen / udp_packets_bad_checksum) < 2) {
 238                         note("%d bad udp checksums in %d packets",
 239                             udp_packets_bad_checksum, udp_packets_seen);
 240                         udp_packets_seen = udp_packets_bad_checksum = 0;
 241                 }
 242                 return (-1);
 243         }
 244
 245         memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
 246
 247         return (ip_len + sizeof(*udp));
 248 }