dist/dhcp/common/packet.c

   1 /* packet.c
   2
   3    Packet assembly code, originally contributed by Archie Cobbs. */
   4
   5 /*
   6  * Copyright (c) 2004-2005 by Internet Systems Consortium, Inc. ("ISC")
   7  * Copyright (c) 1996-2003 by Internet Software Consortium
   8  *
   9  * Permission to use, copy, modify, and distribute this software for any
  10  * purpose with or without fee is hereby granted, provided that the above
  11  * copyright notice and this permission notice appear in all copies.
  12  *
  13  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
  14  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  15  * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
  16  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  17  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  18  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  19  * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  20  *
  21  *   Internet Systems Consortium, Inc.
  22  *   950 Charter Street
  23  *   Redwood City, CA 94063
  24  *   <info@isc.org>
  25  *   http://www.isc.org/
  26  *
  27  * This code was originally contributed by Archie Cobbs, and is still
  28  * very similar to that contribution, although the packet checksum code
  29  * has been hacked significantly with the help of quite a few ISC DHCP
  30  * users, without whose gracious and thorough help the checksum code would
  31  * still be disabled.
  32  */
  33
  34 #ifndef lint
  35 static char copyright[] =
  36 "$Id: packet.c,v 1.7 2005/08/11 17:13:21 drochner Exp $ Copyright (c) 2004-2005 Internet Systems Consortium.  All rights reserved.\n";
  37 #endif /* not lint */
  38
  39 #include "dhcpd.h"
  40
  41 #if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
  42 #include "includes/netinet/ip.h"
  43 #include "includes/netinet/udp.h"
  44 #include "includes/netinet/if_ether.h"
  45 #endif /* PACKET_ASSEMBLY || PACKET_DECODING */
  46
  47 /* Compute the easy part of the checksum on a range of bytes. */
  48
  49 u_int32_t checksum (buf, nbytes, sum)
  50         unsigned char *buf;
  51         unsigned nbytes;
  52         u_int32_t sum;
  53 {
  54         unsigned i;
  55
  56 #ifdef DEBUG_CHECKSUM
  57         log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
  58 #endif
  59
  60         /* Checksum all the pairs of bytes first... */
  61         for (i = 0; i < (nbytes & ~1U); i += 2) {
  62 #ifdef DEBUG_CHECKSUM_VERBOSE
  63                 log_debug ("sum = %x", sum);
  64 #endif
  65                 sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
  66                 /* Add carry. */
  67                 if (sum > 0xFFFF)
  68                         sum -= 0xFFFF;
  69         }
  70
  71         /* If there's a single byte left over, checksum it, too.   Network
  72            byte order is big-endian, so the remaining byte is the high byte. */
  73         if (i < nbytes) {
  74 #ifdef DEBUG_CHECKSUM_VERBOSE
  75                 log_debug ("sum = %x", sum);
  76 #endif
  77                 sum += buf [i] << 8;
  78                 /* Add carry. */
  79                 if (sum > 0xFFFF)
  80                         sum -= 0xFFFF;
  81         }
  82
  83         return sum;
  84 }
  85
  86 /* Finish computing the checksum, and then put it into network byte order. */
  87
  88 u_int32_t wrapsum (sum)
  89         u_int32_t sum;
  90 {
  91 #ifdef DEBUG_CHECKSUM
  92         log_debug ("wrapsum (%x)", sum);
  93 #endif
  94
  95         sum = ~sum & 0xFFFF;
  96 #ifdef DEBUG_CHECKSUM_VERBOSE
  97         log_debug ("sum = %x", sum);
  98 #endif
  99
 100 #ifdef DEBUG_CHECKSUM
 101         log_debug ("wrapsum returns %x", htons (sum));
 102 #endif
 103         return htons(sum);
 104 }
 105
 106 #ifdef PACKET_ASSEMBLY
 107 void assemble_hw_header (interface, buf, bufix, to)
 108         struct interface_info *interface;
 109         unsigned char *buf;
 110         unsigned *bufix;
 111         struct hardware *to;
 112 {
 113 #if defined (HAVE_TR_SUPPORT)
 114         if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
 115                 assemble_tr_header (interface, buf, bufix, to);
 116         else
 117 #endif
 118 #if defined (DEC_FDDI) || defined (NETBSD_FDDI)
 119              if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
 120                      assemble_fddi_header (interface, buf, bufix, to);
 121         else
 122 #endif
 123                 assemble_ethernet_header (interface, buf, bufix, to);
 124
 125 }
 126
 127 /* UDP header and IP header assembled together for convenience. */
 128
 129 void assemble_udp_ip_header (interface, buf, bufix,
 130                              from, to, port, data, len)
 131         struct interface_info *interface;
 132         unsigned char *buf;
 133         unsigned *bufix;
 134         u_int32_t from;
 135         u_int32_t to;
 136         u_int32_t port;
 137         unsigned char *data;
 138         unsigned len;
 139 {
 140         struct ip ip;
 141         struct udphdr udp;
 142
 143         /* Fill out the IP header */
 144         IP_V_SET (&ip, 4);
 145         IP_HL_SET (&ip, 20);
 146         ip.ip_tos = IPTOS_LOWDELAY;
 147         ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
 148         ip.ip_id = 0;
 149         ip.ip_off = 0;
 150         ip.ip_ttl = 32;
 151         ip.ip_p = IPPROTO_UDP;
 152         ip.ip_sum = 0;
 153         ip.ip_src.s_addr = from;
 154         ip.ip_dst.s_addr = to;
 155
 156         /* Checksum the IP header... */
 157         ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
 158
 159         /* Copy the ip header into the buffer... */
 160         memcpy (&buf [*bufix], &ip, sizeof ip);
 161         *bufix += sizeof ip;
 162
 163         /* Fill out the UDP header */
 164         udp.uh_sport = local_port;              /* XXX */
 165         udp.uh_dport = port;                    /* XXX */
 166         udp.uh_ulen = htons(sizeof(udp) + len);
 167         memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 168
 169         /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 170            header and the data. */
 171
 172         udp.uh_sum =
 173                 wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
 174                                    checksum (data, len,
 175                                              checksum ((unsigned char *)
 176                                                        &ip.ip_src,
 177                                                        2 * sizeof ip.ip_src,
 178                                                        IPPROTO_UDP +
 179                                                        (u_int32_t)
 180                                                        ntohs (udp.uh_ulen)))));
 181
 182         /* Copy the udp header into the buffer... */
 183         memcpy (&buf [*bufix], &udp, sizeof udp);
 184         *bufix += sizeof udp;
 185 }
 186 #endif /* PACKET_ASSEMBLY */
 187
 188 #ifdef PACKET_DECODING
 189 /* Decode a hardware header... */
 190 /* XXX currently only supports ethernet; doesn't check for other types. */
 191
 192 ssize_t decode_hw_header (interface, buf, bufix, from)
 193      struct interface_info *interface;
 194      unsigned char *buf;
 195      unsigned bufix;
 196      struct hardware *from;
 197 {
 198 #if defined (HAVE_TR_SUPPORT)
 199         if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
 200                 return decode_tr_header (interface, buf, bufix, from);
 201         else
 202 #endif
 203 #if defined (DEC_FDDI) || defined (NETBSD_FDDI)
 204              if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
 205                      return decode_fddi_header (interface, buf, bufix, from);
 206         else
 207 #endif
 208                 return decode_ethernet_header (interface, buf, bufix, from);
 209 }
 210
 211 /* UDP header and IP header decoded together for convenience. */
 212
 213 ssize_t decode_udp_ip_header (interface, buf, bufix, from, buflen, rbuflen)
 214         struct interface_info *interface;
 215         unsigned char *buf;
 216         unsigned bufix;
 217         struct sockaddr_in *from;
 218         unsigned buflen;
 219         unsigned *rbuflen;
 220 {
 221   unsigned char *data;
 222   struct ip ip;
 223   struct udphdr *udp;
 224   u_int32_t ip_len = (buf [bufix] & 0xf) << 2;
 225   u_int32_t sum, usum;
 226   static int ip_packets_seen;
 227   static int ip_packets_bad_checksum;
 228   static int udp_packets_seen;
 229   static int udp_packets_bad_checksum;
 230   static int udp_packets_length_checked;
 231   static int udp_packets_length_overflow;
 232   unsigned len;
 233   unsigned ulen;
 234   int ignore = 0;
 235
 236   memcpy(&ip, buf + bufix, sizeof (struct ip));
 237   udp = (struct udphdr *)(buf + bufix + ip_len);
 238   len = 0;      /* XXXGCC -Wuninitialized */
 239
 240 #ifdef USERLAND_FILTER
 241   /* Is it a UDP packet? */
 242   if (ip.ip_p != IPPROTO_UDP)
 243           return -1;
 244
 245   /* Is it to the port we're serving? */
 246   if (udp -> uh_dport != local_port)
 247           return -1;
 248 #endif /* USERLAND_FILTER */
 249
 250   ulen = ntohs (udp -> uh_ulen);
 251   if (ulen < sizeof *udp ||
 252       ((unsigned char *)udp) + ulen > buf + bufix + buflen) {
 253           log_info ("bogus UDP packet length: %d", ulen);
 254           return -1;
 255   }
 256
 257   /* Check the IP header checksum - it should be zero. */
 258   ++ip_packets_seen;
 259   if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
 260           ++ip_packets_bad_checksum;
 261           if (ip_packets_seen > 4 &&
 262               (ip_packets_seen / ip_packets_bad_checksum) < 2) {
 263                   log_info ("%d bad IP checksums seen in %d packets",
 264                             ip_packets_bad_checksum, ip_packets_seen);
 265                   ip_packets_seen = ip_packets_bad_checksum = 0;
 266           }
 267           return -1;
 268   }
 269
 270   /* Check the IP packet length. */
 271   if (ntohs (ip.ip_len) != buflen) {
 272           if ((ntohs (ip.ip_len + 2) & ~1) == buflen)
 273                   ignore = 1;
 274           else
 275                   log_debug ("ip length %d disagrees with bytes received %d.",
 276                              ntohs (ip.ip_len), buflen);
 277   }
 278
 279   /* Copy out the IP source address... */
 280   memcpy (&from -> sin_addr, &ip.ip_src, 4);
 281
 282   /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 283      header and the data.   If the UDP checksum field is zero, we're
 284      not supposed to do a checksum. */
 285
 286   data = buf + bufix + ip_len + sizeof *udp;
 287   len = ulen - sizeof *udp;
 288   ++udp_packets_length_checked;
 289   if (len + data > buf + bufix + buflen) {
 290           ++udp_packets_length_overflow;
 291           if (udp_packets_length_checked > 4 &&
 292               (udp_packets_length_checked /
 293                udp_packets_length_overflow) < 2) {
 294                   log_info ("%d udp packets in %d too long - dropped",
 295                             udp_packets_length_overflow,
 296                             udp_packets_length_checked);
 297                   udp_packets_length_overflow =
 298                           udp_packets_length_checked = 0;
 299           }
 300           return -1;
 301   }
 302   if (len + data < buf + bufix + buflen &&
 303       len + data != buf + bufix + buflen && !ignore)
 304           log_debug ("accepting packet with data after udp payload.");
 305   if (len + data > buf + bufix + buflen) {
 306           log_debug ("dropping packet with bogus uh_ulen %ld",
 307                      (long)(len + sizeof *udp));
 308           return -1;
 309   }
 310
 311   usum = udp -> uh_sum;
 312   udp -> uh_sum = 0;
 313
 314   sum = wrapsum (checksum ((unsigned char *)udp, sizeof *udp,
 315                            checksum (data, len,
 316                                      checksum ((unsigned char *)
 317                                                &ip.ip_src,
 318                                                2 * sizeof ip.ip_src,
 319                                                IPPROTO_UDP +
 320                                                (u_int32_t)ulen))));
 321
 322   udp_packets_seen++;
 323   if (usum && usum != sum) {
 324           udp_packets_bad_checksum++;
 325           if (udp_packets_seen > 4 &&
 326               (udp_packets_seen / udp_packets_bad_checksum) < 2) {
 327                   log_info ("%d bad udp checksums in %d packets",
 328                             udp_packets_bad_checksum, udp_packets_seen);
 329                   udp_packets_seen = udp_packets_bad_checksum = 0;
 330           }
 331           return -1;
 332   }
 333
 334   /* Copy out the port... */
 335   memcpy (&from -> sin_port, &udp -> uh_sport, sizeof udp -> uh_sport);
 336
 337   *rbuflen = ntohs (ip.ip_len) - ip_len - sizeof *udp;
 338   return ip_len + sizeof *udp;
 339 }
 340 #endif /* PACKET_DECODING */