common/packet.c

   1 /* packet.c
   2
   3    Packet assembly code, originally contributed by Archie Cobbs. */
   4
   5 /*
   6  * Copyright (c) 2004-2017 by Internet Systems Consortium, Inc. ("ISC")
   7  * Copyright (c) 1996-2003 by Internet Software Consortium
   8  *
   9  * This Source Code Form is subject to the terms of the Mozilla Public
  10  * License, v. 2.0. If a copy of the MPL was not distributed with this
  11  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  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  *   PO Box 360
  23  *   Newmarket, NH 03857 USA
  24  *   <info@isc.org>
  25  *   https://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 #include "dhcpd.h"
  35
  36 #if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
  37 #include "includes/netinet/ip.h"
  38 #include "includes/netinet/udp.h"
  39 #include "includes/netinet/if_ether.h"
  40 #endif /* PACKET_ASSEMBLY || PACKET_DECODING */
  41
  42 /* Compute the easy part of the checksum on a range of bytes. */
  43
  44 u_int32_t checksum (buf, nbytes, sum)
  45         unsigned char *buf;
  46         unsigned nbytes;
  47         u_int32_t sum;
  48 {
  49         unsigned i;
  50
  51 #ifdef DEBUG_CHECKSUM
  52         log_debug ("checksum (%x %d %x)", (unsigned)buf, nbytes, sum);
  53 #endif
  54
  55         /* Checksum all the pairs of bytes first... */
  56         for (i = 0; i < (nbytes & ~1U); i += 2) {
  57 #ifdef DEBUG_CHECKSUM_VERBOSE
  58                 log_debug ("sum = %x", sum);
  59 #endif
  60                 sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
  61                 /* Add carry. */
  62                 if (sum > 0xFFFF)
  63                         sum -= 0xFFFF;
  64         }
  65
  66         /* If there's a single byte left over, checksum it, too.   Network
  67            byte order is big-endian, so the remaining byte is the high byte. */
  68         if (i < nbytes) {
  69 #ifdef DEBUG_CHECKSUM_VERBOSE
  70                 log_debug ("sum = %x", sum);
  71 #endif
  72                 sum += buf [i] << 8;
  73                 /* Add carry. */
  74                 if (sum > 0xFFFF)
  75                         sum -= 0xFFFF;
  76         }
  77
  78         return sum;
  79 }
  80
  81 /* Finish computing the checksum, and then put it into network byte order. */
  82
  83 u_int32_t wrapsum (sum)
  84         u_int32_t sum;
  85 {
  86 #ifdef DEBUG_CHECKSUM
  87         log_debug ("wrapsum (%x)", sum);
  88 #endif
  89
  90         sum = ~sum & 0xFFFF;
  91 #ifdef DEBUG_CHECKSUM_VERBOSE
  92         log_debug ("sum = %x", sum);
  93 #endif
  94
  95 #ifdef DEBUG_CHECKSUM
  96         log_debug ("wrapsum returns %x", htons (sum));
  97 #endif
  98         return htons(sum);
  99 }
 100
 101 #ifdef PACKET_ASSEMBLY
 102 void assemble_hw_header (interface, buf, bufix, to)
 103         struct interface_info *interface;
 104         unsigned char *buf;
 105         unsigned *bufix;
 106         struct hardware *to;
 107 {
 108         switch (interface->hw_address.hbuf[0]) {
 109 #if defined(HAVE_TR_SUPPORT)
 110         case HTYPE_IEEE802:
 111                 assemble_tr_header(interface, buf, bufix, to);
 112                 break;
 113 #endif
 114 #if defined (DEC_FDDI)
 115         case HTYPE_FDDI:
 116                 assemble_fddi_header(interface, buf, bufix, to);
 117                 break;
 118 #endif
 119         case HTYPE_INFINIBAND:
 120                 log_error("Attempt to assemble hw header for infiniband");
 121                 break;
 122         case HTYPE_ETHER:
 123         default:
 124                 assemble_ethernet_header(interface, buf, bufix, to);
 125                 break;
 126         }
 127 }
 128
 129 /* UDP header and IP header assembled together for convenience. */
 130
 131 void assemble_udp_ip_header (interface, buf, bufix,
 132                              from, to, port, data, len)
 133         struct interface_info *interface;
 134         unsigned char *buf;
 135         unsigned *bufix;
 136         u_int32_t from;
 137         u_int32_t to;
 138         u_int32_t port;
 139         unsigned char *data;
 140         unsigned len;
 141 {
 142         struct ip ip;
 143         struct udphdr udp;
 144
 145         memset (&ip, 0, sizeof ip);
 146
 147         /* Fill out the IP header */
 148         IP_V_SET (&ip, 4);
 149         IP_HL_SET (&ip, 20);
 150         ip.ip_tos = IPTOS_LOWDELAY;
 151         ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
 152         ip.ip_id = 0;
 153         ip.ip_off = 0;
 154         ip.ip_ttl = 128;
 155         ip.ip_p = IPPROTO_UDP;
 156         ip.ip_sum = 0;
 157         ip.ip_src.s_addr = from;
 158         ip.ip_dst.s_addr = to;
 159
 160         /* Checksum the IP header... */
 161         ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
 162
 163         /* Copy the ip header into the buffer... */
 164         memcpy (&buf [*bufix], &ip, sizeof ip);
 165         *bufix += sizeof ip;
 166
 167         /* Fill out the UDP header */
 168         udp.uh_sport = local_port;              /* XXX */
 169         udp.uh_dport = port;                    /* XXX */
 170 #if defined(RELAY_PORT)
 171         /* Change to relay port defined if sending to server */
 172         if (relay_port && (port == htons(67))) {
 173                 udp.uh_sport = relay_port;
 174         }
 175 #endif
 176         udp.uh_ulen = htons(sizeof(udp) + len);
 177         memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 178
 179         /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 180            header and the data. */
 181
 182         udp.uh_sum =
 183                 wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
 184                                    checksum (data, len,
 185                                              checksum ((unsigned char *)
 186                                                        &ip.ip_src,
 187                                                        2 * sizeof ip.ip_src,
 188                                                        IPPROTO_UDP +
 189                                                        (u_int32_t)
 190                                                        ntohs (udp.uh_ulen)))));
 191
 192         /* Copy the udp header into the buffer... */
 193         memcpy (&buf [*bufix], &udp, sizeof udp);
 194         *bufix += sizeof udp;
 195 }
 196 #endif /* PACKET_ASSEMBLY */
 197
 198 #ifdef PACKET_DECODING
 199 /* Decode a hardware header... */
 200 /* Support for ethernet, TR and FDDI
 201  * Doesn't support infiniband yet as the supported oses shouldn't get here
 202  */
 203
 204 ssize_t decode_hw_header (interface, buf, bufix, from)
 205      struct interface_info *interface;
 206      unsigned char *buf;
 207      unsigned bufix;
 208      struct hardware *from;
 209 {
 210         switch(interface->hw_address.hbuf[0]) {
 211 #if defined (HAVE_TR_SUPPORT)
 212         case HTYPE_IEEE802:
 213                 return (decode_tr_header(interface, buf, bufix, from));
 214 #endif
 215 #if defined (DEC_FDDI)
 216         case HTYPE_FDDI:
 217                 return (decode_fddi_header(interface, buf, bufix, from));
 218 #endif
 219         case HTYPE_INFINIBAND:
 220                 log_error("Attempt to decode hw header for infiniband");
 221                 return (0);
 222         case HTYPE_ETHER:
 223         default:
 224                 return (decode_ethernet_header(interface, buf, bufix, from));
 225         }
 226 }
 227
 228 /*!
 229  *
 230  * \brief UDP header and IP header decoded together for convenience.
 231  *
 232  * Attempt to decode the UDP and IP headers and, if necessary, checksum
 233  * the packet.
 234  *
 235  * \param inteface - the interface on which the packet was recevied
 236  * \param buf - a pointer to the buffer for the received packet
 237  * \param bufix - where to start processing the buffer, previous
 238  *                routines may have processed parts of the buffer already
 239  * \param from - space to return the address of the packet sender
 240  * \param buflen - remaining length of the buffer, this will have been
 241  *                 decremented by bufix by the caller
 242  * \param rbuflen - space to return the length of the payload from the udp
 243  *                  header
 244  * \param csum_ready - indication if the checksum is valid for use
 245  *                     non-zero indicates the checksum should be validated
 246  *
 247  * \return - the index to the first byte of the udp payload (that is the
 248  *           start of the DHCP packet
 249  */
 250
 251 ssize_t
 252 decode_udp_ip_header(struct interface_info *interface,
 253                      unsigned char *buf, unsigned bufix,
 254                      struct sockaddr_in *from, unsigned buflen,
 255                      unsigned *rbuflen, int csum_ready)
 256 {
 257   unsigned char *data;
 258   struct ip ip;
 259   struct udphdr udp;
 260   unsigned char *upp;
 261   u_int32_t ip_len, ulen, pkt_len;
 262   static unsigned int ip_packets_seen = 0;
 263   static unsigned int ip_packets_bad_checksum = 0;
 264   static unsigned int udp_packets_seen = 0;
 265   static unsigned int udp_packets_bad_checksum = 0;
 266   static unsigned int udp_packets_length_checked = 0;
 267   static unsigned int udp_packets_length_overflow = 0;
 268   unsigned len;
 269
 270   /* Assure there is at least an IP header there. */
 271   if (sizeof(ip) > buflen)
 272           return -1;
 273
 274   /* Copy the IP header into a stack aligned structure for inspection.
 275    * There may be bits in the IP header that we're not decoding, so we
 276    * copy out the bits we grok and skip ahead by ip.ip_hl * 4.
 277    */
 278   upp = buf + bufix;
 279   memcpy(&ip, upp, sizeof(ip));
 280   ip_len = (*upp & 0x0f) << 2;
 281   upp += ip_len;
 282
 283   /* Check packet lengths are within the buffer:
 284    * first the ip header (ip_len)
 285    * then the packet length from the ip header (pkt_len)
 286    * then the udp header (ip_len + sizeof(udp)
 287    * We are liberal in what we accept, the udp payload should fit within
 288    * pkt_len, but we only check against the full buffer size.
 289    */
 290   pkt_len = ntohs(ip.ip_len);
 291   if ((ip_len > buflen) ||
 292       (pkt_len > buflen) ||
 293       ((ip_len + sizeof(udp)) > buflen))
 294           return -1;
 295
 296   /* Copy the UDP header into a stack aligned structure for inspection. */
 297   memcpy(&udp, upp, sizeof(udp));
 298
 299 #ifdef USERLAND_FILTER
 300   /* Is it a UDP packet? */
 301   if (ip.ip_p != IPPROTO_UDP)
 302           return -1;
 303
 304   /* Is it to the port we're serving? */
 305 #if defined(RELAY_PORT)
 306   if ((udp.uh_dport != local_port) &&
 307       ((relay_port == 0) || (udp.uh_dport != relay_port)))
 308 #else
 309   if (udp.uh_dport != local_port)
 310 #endif
 311           return -1;
 312 #endif /* USERLAND_FILTER */
 313
 314   ulen = ntohs(udp.uh_ulen);
 315   if (ulen < sizeof(udp))
 316         return -1;
 317
 318   udp_packets_length_checked++;
 319   /* verify that the payload length from the udp packet fits in the buffer */
 320   if ((ip_len + ulen) > buflen) {
 321         udp_packets_length_overflow++;
 322         if (((udp_packets_length_checked > 4) &&
 323              (udp_packets_length_overflow != 0)) &&
 324             ((udp_packets_length_checked / udp_packets_length_overflow) < 2)) {
 325                 log_info("%u udp packets in %u too long - dropped",
 326                          udp_packets_length_overflow,
 327                          udp_packets_length_checked);
 328                 udp_packets_length_overflow = 0;
 329                 udp_packets_length_checked = 0;
 330         }
 331         return -1;
 332   }
 333
 334   /* If at least 5 with less than 50% bad, start over */
 335   if (udp_packets_length_checked > 4) {
 336         udp_packets_length_overflow = 0;
 337         udp_packets_length_checked = 0;
 338   }
 339
 340   /* Check the IP header checksum - it should be zero. */
 341   ip_packets_seen++;
 342   if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
 343           ++ip_packets_bad_checksum;
 344           if (((ip_packets_seen > 4) && (ip_packets_bad_checksum != 0)) &&
 345               ((ip_packets_seen / ip_packets_bad_checksum) < 2)) {
 346                   log_info ("%u bad IP checksums seen in %u packets",
 347                             ip_packets_bad_checksum, ip_packets_seen);
 348                   ip_packets_seen = ip_packets_bad_checksum = 0;
 349           }
 350           return -1;
 351   }
 352
 353   /* If at least 5 with less than 50% bad, start over */
 354   if (ip_packets_seen > 4) {
 355         ip_packets_bad_checksum = 0;
 356         ip_packets_seen = 0;
 357   }
 358
 359   /* Copy out the IP source address... */
 360   memcpy(&from->sin_addr, &ip.ip_src, 4);
 361
 362   data = upp + sizeof(udp);
 363   len = ulen - sizeof(udp);
 364
 365   /* UDP check sum may be optional (udp.uh_sum == 0) or not ready if checksum
 366    * offloading is in use */
 367   udp_packets_seen++;
 368   if (udp.uh_sum && csum_ready) {
 369         /* Check the UDP header checksum - since the received packet header
 370          * contains the UDP checksum calculated by the transmitter, calculating
 371          * it now should come out to zero. */
 372         if (wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
 373                                checksum(data, len,
 374                                         checksum((unsigned char *)&ip.ip_src,
 375                                                  8, IPPROTO_UDP + ulen))))) {
 376                 udp_packets_bad_checksum++;
 377                 if (((udp_packets_seen > 4) && (udp_packets_bad_checksum != 0))
 378                     && ((udp_packets_seen / udp_packets_bad_checksum) < 2)) {
 379                         log_debug ("%u bad udp checksums in %u packets",
 380                                    udp_packets_bad_checksum, udp_packets_seen);
 381                         udp_packets_seen = udp_packets_bad_checksum = 0;
 382                 }
 383
 384                 return -1;
 385         }
 386   }
 387
 388   /* If at least 5 with less than 50% bad, start over */
 389   if (udp_packets_seen > 4) {
 390         udp_packets_bad_checksum = 0;
 391         udp_packets_seen = 0;
 392   }
 393
 394   /* Copy out the port... */
 395   memcpy (&from -> sin_port, &udp.uh_sport, sizeof udp.uh_sport);
 396
 397   /* Save the length of the UDP payload. */
 398   if (rbuflen != NULL)
 399         *rbuflen = len;
 400
 401   /* Return the index to the UDP payload. */
 402   return ip_len + sizeof udp;
 403 }
 404 #endif /* PACKET_DECODING */