www.tinc-vpn.org Git - tinc/blob - src/net_packet.c

   1 /*
   2     net_packet.c -- Handles in- and outgoing VPN packets
   3     Copyright (C) 1998-2005 Ivo Timmermans,
   4                   2000-2011 Guus Sliepen <guus@tinc-vpn.org>
   5                   2010      Timothy Redaelli <timothy@redaelli.eu>
   6                   2010      Brandon Black <blblack@gmail.com>
   7
   8     This program is free software; you can redistribute it and/or modify
   9     it under the terms of the GNU General Public License as published by
  10     the Free Software Foundation; either version 2 of the License, or
  11     (at your option) any later version.
  12
  13     This program is distributed in the hope that it will be useful,
  14     but WITHOUT ANY WARRANTY; without even the implied warranty of
  15     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16     GNU General Public License for more details.
  17
  18     You should have received a copy of the GNU General Public License along
  19     with this program; if not, write to the Free Software Foundation, Inc.,
  20     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21 */
  22
  23 #include "system.h"
  24
  25 #include <openssl/rand.h>
  26 #include <openssl/err.h>
  27 #include <openssl/evp.h>
  28 #include <openssl/pem.h>
  29 #include <openssl/hmac.h>
  30
  31 #ifdef HAVE_ZLIB
  32 #include <zlib.h>
  33 #endif
  34
  35 #ifdef HAVE_LZO
  36 #include LZO1X_H
  37 #endif
  38
  39 #include "avl_tree.h"
  40 #include "conf.h"
  41 #include "connection.h"
  42 #include "device.h"
  43 #include "ethernet.h"
  44 #include "event.h"
  45 #include "graph.h"
  46 #include "logger.h"
  47 #include "net.h"
  48 #include "netutl.h"
  49 #include "protocol.h"
  50 #include "process.h"
  51 #include "route.h"
  52 #include "utils.h"
  53 #include "xalloc.h"
  54
  55 int keylifetime = 0;
  56 int keyexpires = 0;
  57 #ifdef HAVE_LZO
  58 static char lzo_wrkmem[LZO1X_999_MEM_COMPRESS > LZO1X_1_MEM_COMPRESS ? LZO1X_999_MEM_COMPRESS : LZO1X_1_MEM_COMPRESS];
  59 #endif
  60
  61 static void send_udppacket(node_t *, vpn_packet_t *);
  62
  63 unsigned replaywin = 16;
  64
  65 #define MAX_SEQNO 1073741824
  66
  67 // mtuprobes == 1..30: initial discovery, send bursts with 1 second interval
  68 // mtuprobes ==    31: sleep pinginterval seconds
  69 // mtuprobes ==    32: send 1 burst, sleep pingtimeout second
  70 // mtuprobes ==    33: no response from other side, restart PMTU discovery process
  71
  72 void send_mtu_probe(node_t *n) {
  73         vpn_packet_t packet;
  74         int len, i;
  75         int timeout = 1;
  76
  77         n->mtuprobes++;
  78         n->mtuevent = NULL;
  79
  80         if(!n->status.reachable || !n->status.validkey) {
  81                 ifdebug(TRAFFIC) logger(LOG_INFO, "Trying to send MTU probe to unreachable or rekeying node %s (%s)", n->name, n->hostname);
  82                 n->mtuprobes = 0;
  83                 return;
  84         }
  85
  86         if(n->mtuprobes > 32) {
  87                 if(!n->minmtu) {
  88                         n->mtuprobes = 31;
  89                         timeout = pinginterval;
  90                         goto end;
  91                 }
  92
  93                 ifdebug(TRAFFIC) logger(LOG_INFO, "%s (%s) did not respond to UDP ping, restarting PMTU discovery", n->name, n->hostname);
  94                 n->mtuprobes = 1;
  95                 n->minmtu = 0;
  96                 n->maxmtu = MTU;
  97         }
  98
  99         if(n->mtuprobes >= 10 && n->mtuprobes < 32 && !n->minmtu) {
 100                 ifdebug(TRAFFIC) logger(LOG_INFO, "No response to MTU probes from %s (%s)", n->name, n->hostname);
 101                 n->mtuprobes = 31;
 102         }
 103
 104         if(n->mtuprobes == 30 || (n->mtuprobes < 30 && n->minmtu >= n->maxmtu)) {
 105                 if(n->minmtu > n->maxmtu)
 106                         n->minmtu = n->maxmtu;
 107                 else
 108                         n->maxmtu = n->minmtu;
 109                 n->mtu = n->minmtu;
 110                 ifdebug(TRAFFIC) logger(LOG_INFO, "Fixing MTU of %s (%s) to %d after %d probes", n->name, n->hostname, n->mtu, n->mtuprobes);
 111                 n->mtuprobes = 31;
 112         }
 113
 114         if(n->mtuprobes == 31) {
 115                 timeout = pinginterval;
 116                 goto end;
 117         } else if(n->mtuprobes == 32) {
 118                 timeout = pingtimeout;
 119         }
 120
 121         for(i = 0; i < 3; i++) {
 122                 if(n->maxmtu <= n->minmtu)
 123                         len = n->maxmtu;
 124                 else
 125                         len = n->minmtu + 1 + rand() % (n->maxmtu - n->minmtu);
 126
 127                 if(len < 64)
 128                         len = 64;
 129
 130                 memset(packet.data, 0, 14);
 131                 RAND_pseudo_bytes(packet.data + 14, len - 14);
 132                 packet.len = len;
 133                 packet.priority = 0;
 134
 135                 ifdebug(TRAFFIC) logger(LOG_INFO, "Sending MTU probe length %d to %s (%s)", len, n->name, n->hostname);
 136
 137                 send_udppacket(n, &packet);
 138         }
 139
 140 end:
 141         n->mtuevent = new_event();
 142         n->mtuevent->handler = (event_handler_t)send_mtu_probe;
 143         n->mtuevent->data = n;
 144         n->mtuevent->time = now + timeout;
 145         event_add(n->mtuevent);
 146 }
 147
 148 void mtu_probe_h(node_t *n, vpn_packet_t *packet, length_t len) {
 149         ifdebug(TRAFFIC) logger(LOG_INFO, "Got MTU probe length %d from %s (%s)", packet->len, n->name, n->hostname);
 150
 151         if(!packet->data[0]) {
 152                 packet->data[0] = 1;
 153                 send_udppacket(n, packet);
 154         } else {
 155                 if(n->mtuprobes > 30) {
 156                         if(n->minmtu)
 157                                 n->mtuprobes = 30;
 158                         else
 159                                 n->mtuprobes = 1;
 160                 }
 161
 162                 if(len > n->maxmtu)
 163                         len = n->maxmtu;
 164                 if(n->minmtu < len)
 165                         n->minmtu = len;
 166         }
 167 }
 168
 169 static length_t compress_packet(uint8_t *dest, const uint8_t *source, length_t len, int level) {
 170         if(level == 0) {
 171                 memcpy(dest, source, len);
 172                 return len;
 173         } else if(level == 10) {
 174 #ifdef HAVE_LZO
 175                 lzo_uint lzolen = MAXSIZE;
 176                 lzo1x_1_compress(source, len, dest, &lzolen, lzo_wrkmem);
 177                 return lzolen;
 178 #else
 179                 return -1;
 180 #endif
 181         } else if(level < 10) {
 182 #ifdef HAVE_ZLIB
 183                 unsigned long destlen = MAXSIZE;
 184                 if(compress2(dest, &destlen, source, len, level) == Z_OK)
 185                         return destlen;
 186                 else
 187 #endif
 188                         return -1;
 189         } else {
 190 #ifdef HAVE_LZO
 191                 lzo_uint lzolen = MAXSIZE;
 192                 lzo1x_999_compress(source, len, dest, &lzolen, lzo_wrkmem);
 193                 return lzolen;
 194 #else
 195                 return -1;
 196 #endif
 197         }
 198
 199         return -1;
 200 }
 201
 202 static length_t uncompress_packet(uint8_t *dest, const uint8_t *source, length_t len, int level) {
 203         if(level == 0) {
 204                 memcpy(dest, source, len);
 205                 return len;
 206         } else if(level > 9) {
 207 #ifdef HAVE_LZO
 208                 lzo_uint lzolen = MAXSIZE;
 209                 if(lzo1x_decompress_safe(source, len, dest, &lzolen, NULL) == LZO_E_OK)
 210                         return lzolen;
 211                 else
 212 #endif
 213                         return -1;
 214         }
 215 #ifdef HAVE_ZLIB
 216         else {
 217                 unsigned long destlen = MAXSIZE;
 218                 if(uncompress(dest, &destlen, source, len) == Z_OK)
 219                         return destlen;
 220                 else
 221                         return -1;
 222         }
 223 #endif
 224
 225         return -1;
 226 }
 227
 228 /* VPN packet I/O */
 229
 230 static void receive_packet(node_t *n, vpn_packet_t *packet) {
 231         ifdebug(TRAFFIC) logger(LOG_DEBUG, "Received packet of %d bytes from %s (%s)",
 232                            packet->len, n->name, n->hostname);
 233
 234         route(n, packet);
 235 }
 236
 237 static bool try_mac(const node_t *n, const vpn_packet_t *inpkt) {
 238         unsigned char hmac[EVP_MAX_MD_SIZE];
 239
 240         if(!n->indigest || !n->inmaclength || !n->inkey || inpkt->len < sizeof inpkt->seqno + n->inmaclength)
 241                 return false;
 242
 243         HMAC(n->indigest, n->inkey, n->inkeylength, (unsigned char *) &inpkt->seqno, inpkt->len - n->inmaclength, (unsigned char *)hmac, NULL);
 244
 245         return !memcmp(hmac, (char *) &inpkt->seqno + inpkt->len - n->inmaclength, n->inmaclength);
 246 }
 247
 248 static void receive_udppacket(node_t *n, vpn_packet_t *inpkt) {
 249         vpn_packet_t pkt1, pkt2;
 250         vpn_packet_t *pkt[] = { &pkt1, &pkt2, &pkt1, &pkt2 };
 251         int nextpkt = 0;
 252         vpn_packet_t *outpkt = pkt[0];
 253         int outlen, outpad;
 254         unsigned char hmac[EVP_MAX_MD_SIZE];
 255         int i;
 256
 257         if(!n->inkey) {
 258                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Got packet from %s (%s) but he hasn't got our key yet",
 259                                         n->name, n->hostname);
 260                 return;
 261         }
 262
 263         /* Check packet length */
 264
 265         if(inpkt->len < sizeof(inpkt->seqno) + n->inmaclength) {
 266                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Got too short packet from %s (%s)",
 267                                         n->name, n->hostname);
 268                 return;
 269         }
 270
 271         /* Check the message authentication code */
 272
 273         if(n->indigest && n->inmaclength) {
 274                 inpkt->len -= n->inmaclength;
 275                 HMAC(n->indigest, n->inkey, n->inkeylength,
 276                          (unsigned char *) &inpkt->seqno, inpkt->len, (unsigned char *)hmac, NULL);
 277
 278                 if(memcmp(hmac, (char *) &inpkt->seqno + inpkt->len, n->inmaclength)) {
 279                         ifdebug(TRAFFIC) logger(LOG_DEBUG, "Got unauthenticated packet from %s (%s)",
 280                                            n->name, n->hostname);
 281                         return;
 282                 }
 283         }
 284
 285         /* Decrypt the packet */
 286
 287         if(n->incipher) {
 288                 outpkt = pkt[nextpkt++];
 289
 290                 if(!EVP_DecryptInit_ex(&n->inctx, NULL, NULL, NULL, NULL)
 291                                 || !EVP_DecryptUpdate(&n->inctx, (unsigned char *) &outpkt->seqno, &outlen,
 292                                         (unsigned char *) &inpkt->seqno, inpkt->len)
 293                                 || !EVP_DecryptFinal_ex(&n->inctx, (unsigned char *) &outpkt->seqno + outlen, &outpad)) {
 294                         ifdebug(TRAFFIC) logger(LOG_DEBUG, "Error decrypting packet from %s (%s): %s",
 295                                                 n->name, n->hostname, ERR_error_string(ERR_get_error(), NULL));
 296                         return;
 297                 }
 298
 299                 outpkt->len = outlen + outpad;
 300                 inpkt = outpkt;
 301         }
 302
 303         /* Check the sequence number */
 304
 305         inpkt->len -= sizeof(inpkt->seqno);
 306         inpkt->seqno = ntohl(inpkt->seqno);
 307
 308         if(replaywin) {
 309                 if(inpkt->seqno != n->received_seqno + 1) {
 310                         if(inpkt->seqno >= n->received_seqno + replaywin * 8) {
 311                                 if(n->farfuture++ < replaywin >> 2) {
 312                                         logger(LOG_WARNING, "Packet from %s (%s) is %d seqs in the future, dropped (%u)",
 313                                                 n->name, n->hostname, inpkt->seqno - n->received_seqno - 1, n->farfuture);
 314                                         return;
 315                                 }
 316                                 logger(LOG_WARNING, "Lost %d packets from %s (%s)",
 317                                                 inpkt->seqno - n->received_seqno - 1, n->name, n->hostname);
 318                                 memset(n->late, 0, replaywin);
 319                         } else if (inpkt->seqno <= n->received_seqno) {
 320                                 if((n->received_seqno >= replaywin * 8 && inpkt->seqno <= n->received_seqno - replaywin * 8) || !(n->late[(inpkt->seqno / 8) % replaywin] & (1 << inpkt->seqno % 8))) {
 321                                         logger(LOG_WARNING, "Got late or replayed packet from %s (%s), seqno %d, last received %d",
 322                                                 n->name, n->hostname, inpkt->seqno, n->received_seqno);
 323                                         return;
 324                                 }
 325                         } else {
 326                                 for(i = n->received_seqno + 1; i < inpkt->seqno; i++)
 327                                         n->late[(i / 8) % replaywin] |= 1 << i % 8;
 328                         }
 329                 }
 330
 331                 n->farfuture = 0;
 332                 n->late[(inpkt->seqno / 8) % replaywin] &= ~(1 << inpkt->seqno % 8);
 333         }
 334
 335         if(inpkt->seqno > n->received_seqno)
 336                 n->received_seqno = inpkt->seqno;
 337
 338         if(n->received_seqno > MAX_SEQNO)
 339                 keyexpires = 0;
 340
 341         /* Decompress the packet */
 342
 343         length_t origlen = inpkt->len;
 344
 345         if(n->incompression) {
 346                 outpkt = pkt[nextpkt++];
 347
 348                 if((outpkt->len = uncompress_packet(outpkt->data, inpkt->data, inpkt->len, n->incompression)) < 0) {
 349                         ifdebug(TRAFFIC) logger(LOG_ERR, "Error while uncompressing packet from %s (%s)",
 350                                                  n->name, n->hostname);
 351                         return;
 352                 }
 353
 354                 inpkt = outpkt;
 355
 356                 origlen -= MTU/64 + 20;
 357         }
 358
 359         inpkt->priority = 0;
 360
 361         if(!inpkt->data[12] && !inpkt->data[13])
 362                 mtu_probe_h(n, inpkt, origlen);
 363         else
 364                 receive_packet(n, inpkt);
 365 }
 366
 367 void receive_tcppacket(connection_t *c, const char *buffer, int len) {
 368         vpn_packet_t outpkt;
 369
 370         outpkt.len = len;
 371         if(c->options & OPTION_TCPONLY)
 372                 outpkt.priority = 0;
 373         else
 374                 outpkt.priority = -1;
 375         memcpy(outpkt.data, buffer, len);
 376
 377         receive_packet(c->node, &outpkt);
 378 }
 379
 380 static void send_udppacket(node_t *n, vpn_packet_t *origpkt) {
 381         vpn_packet_t pkt1, pkt2;
 382         vpn_packet_t *pkt[] = { &pkt1, &pkt2, &pkt1, &pkt2 };
 383         vpn_packet_t *inpkt = origpkt;
 384         int nextpkt = 0;
 385         vpn_packet_t *outpkt;
 386         int origlen;
 387         int outlen, outpad;
 388 #if defined(SOL_IP) && defined(IP_TOS)
 389         static int priority = 0;
 390 #endif
 391         int origpriority;
 392         int sock;
 393
 394         if(!n->status.reachable) {
 395                 ifdebug(TRAFFIC) logger(LOG_INFO, "Trying to send UDP packet to unreachable node %s (%s)", n->name, n->hostname);
 396                 return;
 397         }
 398
 399         /* Make sure we have a valid key */
 400
 401         if(!n->status.validkey) {
 402                 ifdebug(TRAFFIC) logger(LOG_INFO,
 403                                    "No valid key known yet for %s (%s), forwarding via TCP",
 404                                    n->name, n->hostname);
 405
 406                 if(n->last_req_key + 10 <= now) {
 407                         send_req_key(n);
 408                         n->last_req_key = now;
 409                 }
 410
 411                 send_tcppacket(n->nexthop->connection, origpkt);
 412
 413                 return;
 414         }
 415
 416         if(n->options & OPTION_PMTU_DISCOVERY && inpkt->len > n->minmtu && (inpkt->data[12] | inpkt->data[13])) {
 417                 ifdebug(TRAFFIC) logger(LOG_INFO,
 418                                 "Packet for %s (%s) larger than minimum MTU, forwarding via %s",
 419                                 n->name, n->hostname, n != n->nexthop ? n->nexthop->name : "TCP");
 420
 421                 if(n != n->nexthop)
 422                         send_packet(n->nexthop, origpkt);
 423                 else
 424                         send_tcppacket(n->nexthop->connection, origpkt);
 425
 426                 return;
 427         }
 428
 429         origlen = inpkt->len;
 430         origpriority = inpkt->priority;
 431
 432         /* Compress the packet */
 433
 434         if(n->outcompression) {
 435                 outpkt = pkt[nextpkt++];
 436
 437                 if((outpkt->len = compress_packet(outpkt->data, inpkt->data, inpkt->len, n->outcompression)) < 0) {
 438                         ifdebug(TRAFFIC) logger(LOG_ERR, "Error while compressing packet to %s (%s)",
 439                                    n->name, n->hostname);
 440                         return;
 441                 }
 442
 443                 inpkt = outpkt;
 444         }
 445
 446         /* Add sequence number */
 447
 448         inpkt->seqno = htonl(++(n->sent_seqno));
 449         inpkt->len += sizeof(inpkt->seqno);
 450
 451         /* Encrypt the packet */
 452
 453         if(n->outcipher) {
 454                 outpkt = pkt[nextpkt++];
 455
 456                 if(!EVP_EncryptInit_ex(&n->outctx, NULL, NULL, NULL, NULL)
 457                                 || !EVP_EncryptUpdate(&n->outctx, (unsigned char *) &outpkt->seqno, &outlen,
 458                                         (unsigned char *) &inpkt->seqno, inpkt->len)
 459                                 || !EVP_EncryptFinal_ex(&n->outctx, (unsigned char *) &outpkt->seqno + outlen, &outpad)) {
 460                         ifdebug(TRAFFIC) logger(LOG_ERR, "Error while encrypting packet to %s (%s): %s",
 461                                                 n->name, n->hostname, ERR_error_string(ERR_get_error(), NULL));
 462                         goto end;
 463                 }
 464
 465                 outpkt->len = outlen + outpad;
 466                 inpkt = outpkt;
 467         }
 468
 469         /* Add the message authentication code */
 470
 471         if(n->outdigest && n->outmaclength) {
 472                 HMAC(n->outdigest, n->outkey, n->outkeylength, (unsigned char *) &inpkt->seqno,
 473                          inpkt->len, (unsigned char *) &inpkt->seqno + inpkt->len, NULL);
 474                 inpkt->len += n->outmaclength;
 475         }
 476
 477         /* Determine which socket we have to use */
 478
 479         for(sock = 0; sock < listen_sockets; sock++)
 480                 if(n->address.sa.sa_family == listen_socket[sock].sa.sa.sa_family)
 481                         break;
 482
 483         if(sock >= listen_sockets)
 484                 sock = 0;                               /* If none is available, just use the first and hope for the best. */
 485
 486         /* Send the packet */
 487
 488 #if defined(SOL_IP) && defined(IP_TOS)
 489         if(priorityinheritance && origpriority != priority
 490            && listen_socket[sock].sa.sa.sa_family == AF_INET) {
 491                 priority = origpriority;
 492                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Setting outgoing packet priority to %d", priority);
 493                 if(setsockopt(listen_socket[sock].udp, SOL_IP, IP_TOS, &priority, sizeof(priority)))    /* SO_PRIORITY doesn't seem to work */
 494                         logger(LOG_ERR, "System call `%s' failed: %s", "setsockopt", strerror(errno));
 495         }
 496 #endif
 497
 498         if(sendto(listen_socket[sock].udp, (char *) &inpkt->seqno, inpkt->len, 0, &(n->address.sa), SALEN(n->address.sa)) < 0 && !sockwouldblock(sockerrno)) {
 499                 if(sockmsgsize(sockerrno)) {
 500                         if(n->maxmtu >= origlen)
 501                                 n->maxmtu = origlen - 1;
 502                         if(n->mtu >= origlen)
 503                                 n->mtu = origlen - 1;
 504                 } else
 505                         logger(LOG_ERR, "Error sending packet to %s (%s): %s", n->name, n->hostname, sockstrerror(sockerrno));
 506         }
 507
 508 end:
 509         origpkt->len = origlen;
 510 }
 511
 512 /*
 513   send a packet to the given vpn ip.
 514 */
 515 void send_packet(const node_t *n, vpn_packet_t *packet) {
 516         node_t *via;
 517
 518         if(n == myself) {
 519                 if(overwrite_mac)
 520                          memcpy(packet->data, mymac.x, ETH_ALEN);
 521                 write_packet(packet);
 522                 return;
 523         }
 524
 525         ifdebug(TRAFFIC) logger(LOG_ERR, "Sending packet of %d bytes to %s (%s)",
 526                            packet->len, n->name, n->hostname);
 527
 528         if(!n->status.reachable) {
 529                 ifdebug(TRAFFIC) logger(LOG_INFO, "Node %s (%s) is not reachable",
 530                                    n->name, n->hostname);
 531                 return;
 532         }
 533
 534         via = (packet->priority == -1 || n->via == myself) ? n->nexthop : n->via;
 535
 536         if(via != n)
 537                 ifdebug(TRAFFIC) logger(LOG_INFO, "Sending packet to %s via %s (%s)",
 538                            n->name, via->name, n->via->hostname);
 539
 540         if(packet->priority == -1 || ((myself->options | via->options) & OPTION_TCPONLY)) {
 541                 if(!send_tcppacket(via->connection, packet))
 542                         terminate_connection(via->connection, true);
 543         } else
 544                 send_udppacket(via, packet);
 545 }
 546
 547 /* Broadcast a packet using the minimum spanning tree */
 548
 549 void broadcast_packet(const node_t *from, vpn_packet_t *packet) {
 550         avl_node_t *node;
 551         connection_t *c;
 552
 553         ifdebug(TRAFFIC) logger(LOG_INFO, "Broadcasting packet of %d bytes from %s (%s)",
 554                            packet->len, from->name, from->hostname);
 555
 556         if(from != myself) {
 557                 send_packet(myself, packet);
 558
 559                 // In TunnelServer mode, do not forward broadcast packets.
 560                 // The MST might not be valid and create loops.
 561                 if(tunnelserver)
 562                         return;
 563         }
 564
 565         for(node = connection_tree->head; node; node = node->next) {
 566                 c = node->data;
 567
 568                 if(c->status.active && c->status.mst && c != from->nexthop->connection)
 569                         send_packet(c->node, packet);
 570         }
 571 }
 572
 573 static node_t *try_harder(const sockaddr_t *from, const vpn_packet_t *pkt) {
 574         avl_node_t *node;
 575         edge_t *e;
 576         node_t *n = NULL;
 577         bool hard = false;
 578         static time_t last_hard_try = 0;
 579
 580         for(node = edge_weight_tree->head; node; node = node->next) {
 581                 e = node->data;
 582
 583                 if(e->to == myself)
 584                         continue;
 585
 586                 if(sockaddrcmp_noport(from, &e->address)) {
 587                         if(last_hard_try == now)
 588                                 continue;
 589                         hard = true;
 590                 }
 591
 592                 if(!try_mac(e->to, pkt))
 593                         continue;
 594
 595                 n = e->to;
 596                 break;
 597         }
 598
 599         if(hard)
 600                 last_hard_try = now;
 601
 602         return n;
 603 }
 604
 605 void handle_incoming_vpn_data(int sock) {
 606         vpn_packet_t pkt;
 607         char *hostname;
 608         sockaddr_t from;
 609         socklen_t fromlen = sizeof(from);
 610         node_t *n;
 611
 612         pkt.len = recvfrom(sock, (char *) &pkt.seqno, MAXSIZE, 0, &from.sa, &fromlen);
 613
 614         if(pkt.len < 0) {
 615                 if(!sockwouldblock(sockerrno))
 616                         logger(LOG_ERR, "Receiving packet failed: %s", sockstrerror(sockerrno));
 617                 return;
 618         }
 619
 620         sockaddrunmap(&from);           /* Some braindead IPv6 implementations do stupid things. */
 621
 622         n = lookup_node_udp(&from);
 623
 624         if(!n) {
 625                 n = try_harder(&from, &pkt);
 626                 if(n)
 627                         update_node_udp(n, &from);
 628                 else ifdebug(PROTOCOL) {
 629                         hostname = sockaddr2hostname(&from);
 630                         logger(LOG_WARNING, "Received UDP packet from unknown source %s", hostname);
 631                         free(hostname);
 632                         return;
 633                 }
 634                 else
 635                         return;
 636         }
 637
 638         receive_udppacket(n, &pkt);
 639 }