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