common/packet.c

   1 /* packet.c
   2
   3    Packet assembly code, originally contributed by Archie Cobbs. */
   4
   5 /*
   6  * Copyright (c) 2009,2012,2014 by Internet Systems Consortium, Inc. ("ISC")
   7  * Copyright (c) 2004,2005,2007 by Internet Systems Consortium, Inc. ("ISC")
   8  * Copyright (c) 1996-2003 by Internet Software Consortium
   9  *
  10  * Permission to use, copy, modify, and distribute this software for any
  11  * purpose with or without fee is hereby granted, provided that the above
  12  * copyright notice and this permission notice appear in all copies.
  13  *
  14  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
  15  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  16  * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
  17  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  18  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  19  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  20  * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  21  *
  22  *   Internet Systems Consortium, Inc.
  23  *   950 Charter Street
  24  *   Redwood City, CA 94063
  25  *   <info@isc.org>
  26  *   https://www.isc.org/
  27  *
  28  * This code was originally contributed by Archie Cobbs, and is still
  29  * very similar to that contribution, although the packet checksum code
  30  * has been hacked significantly with the help of quite a few ISC DHCP
  31  * users, without whose gracious and thorough help the checksum code would
  32  * still be disabled.
  33  */
  34
  35 #include "dhcpd.h"
  36
  37 #if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
  38 #include "includes/netinet/ip.h"
  39 #include "includes/netinet/udp.h"
  40 #include "includes/netinet/if_ether.h"
  41 #endif /* PACKET_ASSEMBLY || PACKET_DECODING */
  42
  43 /* Compute the easy part of the checksum on a range of bytes. */
  44
  45 u_int32_t checksum (buf, nbytes, sum)
  46         unsigned char *buf;
  47         unsigned nbytes;
  48         u_int32_t sum;
  49 {
  50         unsigned i;
  51
  52 #ifdef DEBUG_CHECKSUM
  53         log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
  54 #endif
  55
  56         /* Checksum all the pairs of bytes first... */
  57         for (i = 0; i < (nbytes & ~1U); i += 2) {
  58 #ifdef DEBUG_CHECKSUM_VERBOSE
  59                 log_debug ("sum = %x", sum);
  60 #endif
  61                 sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
  62                 /* Add carry. */
  63                 if (sum > 0xFFFF)
  64                         sum -= 0xFFFF;
  65         }
  66
  67         /* If there's a single byte left over, checksum it, too.   Network
  68            byte order is big-endian, so the remaining byte is the high byte. */
  69         if (i < nbytes) {
  70 #ifdef DEBUG_CHECKSUM_VERBOSE
  71                 log_debug ("sum = %x", sum);
  72 #endif
  73                 sum += buf [i] << 8;
  74                 /* Add carry. */
  75                 if (sum > 0xFFFF)
  76                         sum -= 0xFFFF;
  77         }
  78
  79         return sum;
  80 }
  81
  82 /* Finish computing the checksum, and then put it into network byte order. */
  83
  84 u_int32_t wrapsum (sum)
  85         u_int32_t sum;
  86 {
  87 #ifdef DEBUG_CHECKSUM
  88         log_debug ("wrapsum (%x)", sum);
  89 #endif
  90
  91         sum = ~sum & 0xFFFF;
  92 #ifdef DEBUG_CHECKSUM_VERBOSE
  93         log_debug ("sum = %x", sum);
  94 #endif
  95
  96 #ifdef DEBUG_CHECKSUM
  97         log_debug ("wrapsum returns %x", htons (sum));
  98 #endif
  99         return htons(sum);
 100 }
 101
 102 #ifdef PACKET_ASSEMBLY
 103 void assemble_hw_header (interface, buf, bufix, to)
 104         struct interface_info *interface;
 105         unsigned char *buf;
 106         unsigned *bufix;
 107         struct hardware *to;
 108 {
 109         switch (interface->hw_address.hbuf[0]) {
 110 #if defined(HAVE_TR_SUPPORT)
 111         case HTYPE_IEEE802:
 112                 assemble_tr_header(interface, buf, bufix, to);
 113                 break;
 114 #endif
 115 #if defined (DEC_FDDI)
 116         case HTYPE_FDDI:
 117                 assemble_fddi_header(interface, buf, bufix, to);
 118                 break;
 119 #endif
 120         case HTYPE_INFINIBAND:
 121                 log_error("Attempt to assemble hw header for infiniband");
 122                 break;
 123         case HTYPE_ETHER:
 124         default:
 125                 assemble_ethernet_header(interface, buf, bufix, to);
 126                 break;
 127         }
 128 }
 129
 130 /* UDP header and IP header assembled together for convenience. */
 131
 132 void assemble_udp_ip_header (interface, buf, bufix,
 133                              from, to, port, data, len)
 134         struct interface_info *interface;
 135         unsigned char *buf;
 136         unsigned *bufix;
 137         u_int32_t from;
 138         u_int32_t to;
 139         u_int32_t port;
 140         unsigned char *data;
 141         unsigned len;
 142 {
 143         struct ip ip;
 144         struct udphdr udp;
 145
 146         memset (&ip, 0, sizeof ip);
 147
 148         /* Fill out the IP header */
 149         IP_V_SET (&ip, 4);
 150         IP_HL_SET (&ip, 20);
 151         ip.ip_tos = IPTOS_LOWDELAY;
 152         ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
 153         ip.ip_id = 0;
 154         ip.ip_off = 0;
 155         ip.ip_ttl = 128;
 156         ip.ip_p = IPPROTO_UDP;
 157         ip.ip_sum = 0;
 158         ip.ip_src.s_addr = from;
 159         ip.ip_dst.s_addr = to;
 160
 161         /* Checksum the IP header... */
 162         ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
 163
 164         /* Copy the ip header into the buffer... */
 165         memcpy (&buf [*bufix], &ip, sizeof ip);
 166         *bufix += sizeof ip;
 167
 168         /* Fill out the UDP header */
 169         udp.uh_sport = local_port;              /* XXX */
 170         udp.uh_dport = port;                    /* XXX */
 171         udp.uh_ulen = htons(sizeof(udp) + len);
 172         memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
 173
 174         /* Compute UDP checksums, including the ``pseudo-header'', the UDP
 175            header and the data. */
 176
 177         udp.uh_sum =
 178                 wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
 179                                    checksum (data, len,
 180                                              checksum ((unsigned char *)
 181                                                        &ip.ip_src,
 182                                                        2 * sizeof ip.ip_src,
 183                                                        IPPROTO_UDP +
 184                                                        (u_int32_t)
 185                                                        ntohs (udp.uh_ulen)))));
 186
 187         /* Copy the udp header into the buffer... */
 188         memcpy (&buf [*bufix], &udp, sizeof udp);
 189         *bufix += sizeof udp;
 190 }
 191 #endif /* PACKET_ASSEMBLY */
 192
 193 #ifdef PACKET_DECODING
 194 /* Decode a hardware header... */
 195 /* Support for ethernet, TR and FDDI
 196  * Doesn't support infiniband yet as the supported oses shouldn't get here
 197  */
 198
 199 ssize_t decode_hw_header (interface, buf, bufix, from)
 200      struct interface_info *interface;
 201      unsigned char *buf;
 202      unsigned bufix;
 203      struct hardware *from;
 204 {
 205         switch(interface->hw_address.hbuf[0]) {
 206 #if defined (HAVE_TR_SUPPORT)
 207         case HTYPE_IEEE802:
 208                 return (decode_tr_header(interface, buf, bufix, from));
 209 #endif
 210 #if defined (DEC_FDDI)
 211         case HTYPE_FDDI:
 212                 return (decode_fddi_header(interface, buf, bufix, from));
 213 #endif
 214         case HTYPE_INFINIBAND:
 215                 log_error("Attempt to decode hw header for infiniband");
 216                 return (0);
 217         case HTYPE_ETHER:
 218         default:
 219                 return (decode_ethernet_header(interface, buf, bufix, from));
 220         }
 221 }
 222
 223 /* UDP header and IP header decoded together for convenience. */
 224
 225 ssize_t
 226 decode_udp_ip_header(struct interface_info *interface,
 227                      unsigned char *buf, unsigned bufix,
 228                      struct sockaddr_in *from, unsigned buflen,
 229                      unsigned *rbuflen, int csum_ready)
 230 {
 231   unsigned char *data;
 232   struct ip ip;
 233   struct udphdr udp;
 234   unsigned char *upp, *endbuf;
 235   u_int32_t ip_len, ulen, pkt_len;
 236   static unsigned int ip_packets_seen = 0;
 237   static unsigned int ip_packets_bad_checksum = 0;
 238   static unsigned int udp_packets_seen = 0;
 239   static unsigned int udp_packets_bad_checksum = 0;
 240   static unsigned int udp_packets_length_checked = 0;
 241   static unsigned int udp_packets_length_overflow = 0;
 242   unsigned len;
 243
 244   /* Designate the end of the input buffer for bounds checks. */
 245   endbuf = buf + bufix + buflen;
 246
 247   /* Assure there is at least an IP header there. */
 248   if ((buf + bufix + sizeof(ip)) > endbuf)
 249           return -1;
 250
 251   /* Copy the IP header into a stack aligned structure for inspection.
 252    * There may be bits in the IP header that we're not decoding, so we
 253    * copy out the bits we grok and skip ahead by ip.ip_hl * 4.
 254    */
 255   upp = buf + bufix;
 256   memcpy(&ip, upp, sizeof(ip));
 257   ip_len = (*upp & 0x0f) << 2;
 258   upp += ip_len;
 259
 260   /* Check the IP packet length. */
 261   pkt_len = ntohs(ip.ip_len);
 262   if (pkt_len > buflen)
 263         return -1;
 264
 265   /* Assure after ip_len bytes that there is enough room for a UDP header. */
 266   if ((upp + sizeof(udp)) > endbuf)
 267           return -1;
 268
 269   /* Copy the UDP header into a stack aligned structure for inspection. */
 270   memcpy(&udp, upp, sizeof(udp));
 271
 272 #ifdef USERLAND_FILTER
 273   /* Is it a UDP packet? */
 274   if (ip.ip_p != IPPROTO_UDP)
 275           return -1;
 276
 277   /* Is it to the port we're serving? */
 278   if (udp.uh_dport != local_port)
 279           return -1;
 280 #endif /* USERLAND_FILTER */
 281
 282   ulen = ntohs(udp.uh_ulen);
 283   if (ulen < sizeof(udp))
 284         return -1;
 285
 286   udp_packets_length_checked++;
 287   if ((upp + ulen) > endbuf) {
 288         udp_packets_length_overflow++;
 289         if (((udp_packets_length_checked > 4) &&
 290              (udp_packets_length_overflow != 0)) &&
 291             ((udp_packets_length_checked / udp_packets_length_overflow) < 2)) {
 292                 log_info("%u udp packets in %u too long - dropped",
 293                          udp_packets_length_overflow,
 294                          udp_packets_length_checked);
 295                 udp_packets_length_overflow = 0;
 296                 udp_packets_length_checked = 0;
 297         }
 298         return -1;
 299   }
 300
 301   /* If at least 5 with less than 50% bad, start over */
 302   if (udp_packets_length_checked > 4) {
 303         udp_packets_length_overflow = 0;
 304         udp_packets_length_checked = 0;
 305   }
 306
 307   /* Check the IP header checksum - it should be zero. */
 308   ip_packets_seen++;
 309   if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
 310           ++ip_packets_bad_checksum;
 311           if (((ip_packets_seen > 4) && (ip_packets_bad_checksum != 0)) &&
 312               ((ip_packets_seen / ip_packets_bad_checksum) < 2)) {
 313                   log_info ("%u bad IP checksums seen in %u packets",
 314                             ip_packets_bad_checksum, ip_packets_seen);
 315                   ip_packets_seen = ip_packets_bad_checksum = 0;
 316           }
 317           return -1;
 318   }
 319
 320   /* If at least 5 with less than 50% bad, start over */
 321   if (ip_packets_seen > 4) {
 322         ip_packets_bad_checksum = 0;
 323         ip_packets_seen = 0;
 324   }
 325
 326   /* Copy out the IP source address... */
 327   memcpy(&from->sin_addr, &ip.ip_src, 4);
 328
 329   data = upp + sizeof(udp);
 330   len = ulen - sizeof(udp);
 331
 332   /* UDP check sum may be optional (udp.uh_sum == 0) or not ready if checksum
 333    * offloading is in use */
 334   udp_packets_seen++;
 335   if (udp.uh_sum && csum_ready) {
 336         /* Check the UDP header checksum - since the received packet header
 337          * contains the UDP checksum calculated by the transmitter, calculating
 338          * it now should come out to zero. */
 339         if (wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
 340                                checksum(data, len,
 341                                         checksum((unsigned char *)&ip.ip_src,
 342                                                  8, IPPROTO_UDP + ulen))))) {
 343                 udp_packets_bad_checksum++;
 344                 if (((udp_packets_seen > 4) && (udp_packets_bad_checksum != 0))
 345                     && ((udp_packets_seen / udp_packets_bad_checksum) < 2)) {
 346                         log_info ("%u bad udp checksums in %u packets",
 347                                   udp_packets_bad_checksum, udp_packets_seen);
 348                         udp_packets_seen = udp_packets_bad_checksum = 0;
 349                 }
 350
 351                 return -1;
 352         }
 353   }
 354
 355   /* If at least 5 with less than 50% bad, start over */
 356   if (udp_packets_seen > 4) {
 357         udp_packets_bad_checksum = 0;
 358         udp_packets_seen = 0;
 359   }
 360
 361   /* Copy out the port... */
 362   memcpy (&from -> sin_port, &udp.uh_sport, sizeof udp.uh_sport);
 363
 364   /* Save the length of the UDP payload. */
 365   if (rbuflen != NULL)
 366         *rbuflen = len;
 367
 368   /* Return the index to the UDP payload. */
 369   return ip_len + sizeof udp;
 370 }
 371 #endif /* PACKET_DECODING */