common/packet.c

   1 /* packet.c
   2
   3    Packet assembly code, originally contributed by Archie Cobbs. */
   4
   5 /*
   6  * Copyright (c) 1996-2001 Internet Software Consortium.
   7  * All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  *
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of The Internet Software Consortium nor the names
  19  *    of its contributors may be used to endorse or promote products derived
  20  *    from this software without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
  23  * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
  24  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  25  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  26  * DISCLAIMED.  IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
  27  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  28  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  29  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  30  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  31  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  32  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  33  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * This code was originally contributed by Archie Cobbs, and is still
  37  * very similar to that contribution, although the packet checksum code
  38  * has been hacked significantly with the help of quite a few ISC DHCP
  39  * users, without whose gracious and thorough help the checksum code would
  40  * still be disabled.
  41  */
  42
  43 #ifndef lint
  44 static char copyright[] =
  45 "$Id: packet.c,v 1.41 2001/06/27 00:29:55 mellon Exp $ Copyright (c) 1996-2001 The Internet Software Consortium.  All rights reserved.\n";
  46 #endif /* not lint */
  47
  48 #include "dhcpd.h"
  49
  50 #if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
  51 #include "includes/netinet/ip.h"
  52 #include "includes/netinet/udp.h"
  53 #include "includes/netinet/if_ether.h"
  54 #endif /* PACKET_ASSEMBLY || PACKET_DECODING */
  55
  56 /* Compute the easy part of the checksum on a range of bytes. */
  57
  58 u_int32_t checksum (buf, nbytes, sum)
  59         unsigned char *buf;
  60         unsigned nbytes;
  61         u_int32_t sum;
  62 {
  63         unsigned i;
  64
  65 #ifdef DEBUG_CHECKSUM
  66         log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
  67 #endif
  68
  69         /* Checksum all the pairs of bytes first... */
  70         for (i = 0; i < (nbytes & ~1U); i += 2) {
  71 #ifdef DEBUG_CHECKSUM_VERBOSE
  72                 log_debug ("sum = %x", sum);
  73 #endif
  74                 sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
  75                 /* Add carry. */
  76                 if (sum > 0xFFFF)
  77                         sum -= 0xFFFF;
  78         }
  79
  80         /* If there's a single byte left over, checksum it, too.   Network
  81            byte order is big-endian, so the remaining byte is the high byte. */
  82         if (i < nbytes) {
  83 #ifdef DEBUG_CHECKSUM_VERBOSE
  84                 log_debug ("sum = %x", sum);
  85 #endif
  86                 sum += buf [i] << 8;
  87                 /* Add carry. */
  88                 if (sum > 0xFFFF)
  89                         sum -= 0xFFFF;
  90         }
  91
  92         return sum;
  93 }
  94
  95 /* Finish computing the checksum, and then put it into network byte order. */
  96
  97 u_int32_t wrapsum (sum)
  98         u_int32_t sum;
  99 {
 100 #ifdef DEBUG_CHECKSUM
 101         log_debug ("wrapsum (%x)", sum);
 102 #endif
 103
 104         sum = ~sum & 0xFFFF;
 105 #ifdef DEBUG_CHECKSUM_VERBOSE
 106         log_debug ("sum = %x", sum);
 107 #endif
 108
 109 #ifdef DEBUG_CHECKSUM
 110         log_debug ("wrapsum returns %x", htons (sum));
 111 #endif
 112         return htons(sum);
 113 }
 114
 115 #ifdef PACKET_ASSEMBLY
 116 void assemble_hw_header (interface, buf, bufix, to)
 117         struct interface_info *interface;
 118         unsigned char *buf;
 119         unsigned *bufix;
 120         struct hardware *to;
 121 {
 122 #if defined (HAVE_TR_SUPPORT)
 123         if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
 124                 assemble_tr_header (interface, buf, bufix, to);
 125         else
 126 #endif
 127 #if defined (DEC_FDDI)
 128              if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
 129                      assemble_fddi_header (interface, buf, bufix, to);
 130         else
 131 #endif
 132                 assemble_ethernet_header (interface, buf, bufix, to);
 133
 134 }
 135
 136 /* UDP header and IP header assembled together for convenience. */
 137
 138 void assemble_udp_ip_header (interface, buf, bufix,
 139                              from, to, port, data, len)
 140         struct interface_info *interface;
 141         unsigned char *buf;
 142         unsigned *bufix;
 143         u_int32_t from;
 144         u_int32_t to;
 145         u_int32_t port;
 146         unsigned char *data;
 147         unsigned len;
 148 {
 149         struct ip ip;
 150         struct udphdr udp;
 151
 152         /* Fill out the IP header */
 153         IP_V_SET (&ip, 4);
 154         IP_HL_SET (&ip, 20);
 155         ip.ip_tos = IPTOS_LOWDELAY;
 156         ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
 157         ip.ip_id = 0;
 158         ip.ip_off = 0;
 159         ip.ip_ttl = 16;
 160         ip.ip_p = IPPROTO_UDP;
 161         ip.ip_sum = 0;
 162         ip.ip_src.s_addr = from;
 163         ip.ip_dst.s_addr = to;
 164
 165         /* Checksum the IP header... */
 166         ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
 167
 168         /* Copy the ip header into the buffer... */
 169         memcpy (&buf [*bufix], &ip, sizeof ip);
 170         *bufix += sizeof ip;
 171
 172         /* Fill out the UDP header */
 173         udp.uh_sport = local_port;              /* XXX */
 174         udp.uh_dport = port;                    /* XXX */
 175         udp.uh_ulen = htons(sizeof(udp) + len);
 176         memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 177
 178         /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 179            header and the data. */
 180
 181         udp.uh_sum =
 182                 wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
 183                                    checksum (data, len,
 184                                              checksum ((unsigned char *)
 185                                                        &ip.ip_src,
 186                                                        2 * sizeof ip.ip_src,
 187                                                        IPPROTO_UDP +
 188                                                        (u_int32_t)
 189                                                        ntohs (udp.uh_ulen)))));
 190
 191         /* Copy the udp header into the buffer... */
 192         memcpy (&buf [*bufix], &udp, sizeof udp);
 193         *bufix += sizeof udp;
 194 }
 195 #endif /* PACKET_ASSEMBLY */
 196
 197 #ifdef PACKET_DECODING
 198 /* Decode a hardware header... */
 199 /* XXX currently only supports ethernet; doesn't check for other types. */
 200
 201 ssize_t decode_hw_header (interface, buf, bufix, from)
 202      struct interface_info *interface;
 203      unsigned char *buf;
 204      unsigned bufix;
 205      struct hardware *from;
 206 {
 207 #if defined (HAVE_TR_SUPPORT)
 208         if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
 209                 return decode_tr_header (interface, buf, bufix, from);
 210         else
 211 #endif
 212 #if defined (DEC_FDDI)
 213              if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
 214                      return decode_fddi_header (interface, buf, bufix, from);
 215         else
 216 #endif
 217                 return decode_ethernet_header (interface, buf, bufix, from);
 218 }
 219
 220 /* UDP header and IP header decoded together for convenience. */
 221
 222 ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
 223         struct interface_info *interface;
 224         unsigned char *buf;
 225         unsigned bufix;
 226         struct sockaddr_in *from;
 227         unsigned char *data;
 228         unsigned buflen;
 229 {
 230   struct ip *ip;
 231   struct udphdr *udp;
 232   u_int32_t ip_len = (buf [bufix] & 0xf) << 2;
 233   u_int32_t sum, usum;
 234   static int ip_packets_seen;
 235   static int ip_packets_bad_checksum;
 236   static int udp_packets_seen;
 237   static int udp_packets_bad_checksum;
 238   static int udp_packets_length_checked;
 239   static int udp_packets_length_overflow;
 240   unsigned len;
 241   unsigned ulen;
 242   int ignore = 0;
 243
 244   ip = (struct ip *)(buf + bufix);
 245   udp = (struct udphdr *)(buf + bufix + ip_len);
 246
 247 #ifdef USERLAND_FILTER
 248   /* Is it a UDP packet? */
 249   if (ip -> ip_p != IPPROTO_UDP)
 250           return -1;
 251
 252   /* Is it to the port we're serving? */
 253   if (udp -> uh_dport != local_port)
 254           return -1;
 255 #endif /* USERLAND_FILTER */
 256
 257   ulen = ntohs (udp -> uh_ulen);
 258   if (ulen < sizeof *udp ||
 259       ((unsigned char *)udp) + ulen > buf + bufix + buflen) {
 260           log_info ("bogus UDP packet length: %d", ulen);
 261           return -1;
 262   }
 263
 264   /* Check the IP header checksum - it should be zero. */
 265   ++ip_packets_seen;
 266   if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
 267           ++ip_packets_bad_checksum;
 268           if (ip_packets_seen > 4 &&
 269               (ip_packets_seen / ip_packets_bad_checksum) < 2) {
 270                   log_info ("%d bad IP checksums seen in %d packets",
 271                             ip_packets_bad_checksum, ip_packets_seen);
 272                   ip_packets_seen = ip_packets_bad_checksum = 0;
 273           }
 274           return -1;
 275   }
 276
 277   /* Check the IP packet length. */
 278   if (ntohs (ip -> ip_len) != buflen) {
 279           if ((ntohs (ip -> ip_len + 2) & ~1) == buflen)
 280                   ignore = 1;
 281           else
 282                   log_debug ("ip length %d disagrees with bytes received %d.",
 283                              ntohs (ip -> ip_len), buflen);
 284   }
 285
 286   /* Copy out the IP source address... */
 287   memcpy (&from -> sin_addr, &ip -> ip_src, 4);
 288
 289   /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 290      header and the data.   If the UDP checksum field is zero, we're
 291      not supposed to do a checksum. */
 292
 293   if (!data) {
 294           data = buf + bufix + ip_len + sizeof *udp;
 295           len = ulen - sizeof *udp;
 296           ++udp_packets_length_checked;
 297           if (len + data > buf + bufix + buflen) {
 298                   ++udp_packets_length_overflow;
 299                   if (udp_packets_length_checked > 4 &&
 300                       (udp_packets_length_checked /
 301                        udp_packets_length_overflow) < 2) {
 302                           log_info ("%d udp packets in %d too long - dropped",
 303                                     udp_packets_length_overflow,
 304                                     udp_packets_length_checked);
 305                           udp_packets_length_overflow =
 306                                   udp_packets_length_checked = 0;
 307                   }
 308                   return -1;
 309           }
 310           if (len + data < buf + bufix + buflen &&
 311               len + data != buf + bufix + buflen && !ignore)
 312                   log_debug ("accepting packet with data after udp payload.");
 313           if (len + data > buf + bufix + buflen) {
 314                   log_debug ("dropping packet with bogus uh_ulen %ld",
 315                              (long)(len + sizeof *udp));
 316                   return -1;
 317           }
 318   }
 319
 320   usum = udp -> uh_sum;
 321   udp -> uh_sum = 0;
 322
 323   sum = wrapsum (checksum ((unsigned char *)udp, sizeof *udp,
 324                            checksum (data, len,
 325                                      checksum ((unsigned char *)
 326                                                &ip -> ip_src,
 327                                                2 * sizeof ip -> ip_src,
 328                                                IPPROTO_UDP +
 329                                                (u_int32_t)ulen))));
 330
 331   udp_packets_seen++;
 332   if (usum && usum != sum) {
 333           udp_packets_bad_checksum++;
 334           if (udp_packets_seen > 4 &&
 335               (udp_packets_seen / udp_packets_bad_checksum) < 2) {
 336                   log_info ("%d bad udp checksums in %d packets",
 337                             udp_packets_bad_checksum, udp_packets_seen);
 338                   udp_packets_seen = udp_packets_bad_checksum = 0;
 339           }
 340           return -1;
 341   }
 342
 343   /* Copy out the port... */
 344   memcpy (&from -> sin_port, &udp -> uh_sport, sizeof udp -> uh_sport);
 345
 346   return ip_len + sizeof *udp;
 347 }
 348 #endif /* PACKET_DECODING */