src/resolve/resolved-llmnr.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2014 Tom Gundersen <teg@jklm.no>
   6  ***/
   7
   8 #include <netinet/in.h>
   9 #include <resolv.h>
  10
  11 #include "fd-util.h"
  12 #include "resolved-llmnr.h"
  13 #include "resolved-manager.h"
  14
  15 void manager_llmnr_stop(Manager *m) {
  16         assert(m);
  17
  18         m->llmnr_ipv4_udp_event_source = sd_event_source_unref(m->llmnr_ipv4_udp_event_source);
  19         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
  20
  21         m->llmnr_ipv6_udp_event_source = sd_event_source_unref(m->llmnr_ipv6_udp_event_source);
  22         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
  23
  24         m->llmnr_ipv4_tcp_event_source = sd_event_source_unref(m->llmnr_ipv4_tcp_event_source);
  25         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
  26
  27         m->llmnr_ipv6_tcp_event_source = sd_event_source_unref(m->llmnr_ipv6_tcp_event_source);
  28         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
  29 }
  30
  31 int manager_llmnr_start(Manager *m) {
  32         int r;
  33
  34         assert(m);
  35
  36         if (m->llmnr_support == RESOLVE_SUPPORT_NO)
  37                 return 0;
  38
  39         r = manager_llmnr_ipv4_udp_fd(m);
  40         if (r == -EADDRINUSE)
  41                 goto eaddrinuse;
  42         if (r < 0)
  43                 return r;
  44
  45         r = manager_llmnr_ipv4_tcp_fd(m);
  46         if (r == -EADDRINUSE)
  47                 goto eaddrinuse;
  48         if (r < 0)
  49                 return r;
  50
  51         if (socket_ipv6_is_supported()) {
  52                 r = manager_llmnr_ipv6_udp_fd(m);
  53                 if (r == -EADDRINUSE)
  54                         goto eaddrinuse;
  55                 if (r < 0)
  56                         return r;
  57
  58                 r = manager_llmnr_ipv6_tcp_fd(m);
  59                 if (r == -EADDRINUSE)
  60                         goto eaddrinuse;
  61                 if (r < 0)
  62                         return r;
  63         }
  64
  65         return 0;
  66
  67 eaddrinuse:
  68         log_warning("Another LLMNR responder prohibits binding the socket to the same port. Turning off LLMNR support.");
  69         m->llmnr_support = RESOLVE_SUPPORT_NO;
  70         manager_llmnr_stop(m);
  71
  72         return 0;
  73 }
  74
  75 static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
  76         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
  77         DnsTransaction *t = NULL;
  78         Manager *m = userdata;
  79         DnsScope *scope;
  80         int r;
  81
  82         assert(s);
  83         assert(fd >= 0);
  84         assert(m);
  85
  86         r = manager_recv(m, fd, DNS_PROTOCOL_LLMNR, &p);
  87         if (r <= 0)
  88                 return r;
  89
  90         if (manager_our_packet(m, p))
  91                 return 0;
  92
  93         scope = manager_find_scope(m, p);
  94         if (!scope) {
  95                 log_debug("Got LLMNR UDP packet on unknown scope. Ignoring.");
  96                 return 0;
  97         }
  98
  99         if (dns_packet_validate_reply(p) > 0) {
 100                 log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 101
 102                 dns_scope_check_conflicts(scope, p);
 103
 104                 t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
 105                 if (t)
 106                         dns_transaction_process_reply(t, p);
 107
 108         } else if (dns_packet_validate_query(p) > 0)  {
 109                 log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 110
 111                 dns_scope_process_query(scope, NULL, p);
 112         } else
 113                 log_debug("Invalid LLMNR UDP packet, ignoring.");
 114
 115         return 0;
 116 }
 117
 118 int manager_llmnr_ipv4_udp_fd(Manager *m) {
 119         union sockaddr_union sa = {
 120                 .in.sin_family = AF_INET,
 121                 .in.sin_port = htobe16(LLMNR_PORT),
 122         };
 123         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 124         int r;
 125
 126         assert(m);
 127
 128         if (m->llmnr_ipv4_udp_fd >= 0)
 129                 return m->llmnr_ipv4_udp_fd;
 130
 131         m->llmnr_ipv4_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 132         if (m->llmnr_ipv4_udp_fd < 0)
 133                 return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
 134
 135         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 136         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 137         if (r < 0) {
 138                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_TTL: %m");
 139                 goto fail;
 140         }
 141
 142         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 143         if (r < 0) {
 144                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
 145                 goto fail;
 146         }
 147
 148         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 149         if (r < 0) {
 150                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
 151                 goto fail;
 152         }
 153
 154         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 155         if (r < 0) {
 156                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_PKTINFO: %m");
 157                 goto fail;
 158         }
 159
 160         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 161         if (r < 0) {
 162                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_RECVTTL: %m");
 163                 goto fail;
 164         }
 165
 166         /* Disable Don't-Fragment bit in the IP header */
 167         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 168         if (r < 0) {
 169                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
 170                 goto fail;
 171         }
 172
 173         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 174         r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 175         if (r < 0) {
 176                 if (errno != EADDRINUSE) {
 177                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 178                         goto fail;
 179                 }
 180
 181                 log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 182
 183                 /* try again with SO_REUSEADDR */
 184                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 185                 if (r < 0) {
 186                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 187                         goto fail;
 188                 }
 189
 190                 r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 191                 if (r < 0) {
 192                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 193                         goto fail;
 194                 }
 195         } else {
 196                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 197                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 198                 if (r < 0) {
 199                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 200                         goto fail;
 201                 }
 202         }
 203
 204         r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, m->llmnr_ipv4_udp_fd, EPOLLIN, on_llmnr_packet, m);
 205         if (r < 0)
 206                 goto fail;
 207
 208         (void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
 209
 210         return m->llmnr_ipv4_udp_fd;
 211
 212 fail:
 213         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
 214         return r;
 215 }
 216
 217 int manager_llmnr_ipv6_udp_fd(Manager *m) {
 218         union sockaddr_union sa = {
 219                 .in6.sin6_family = AF_INET6,
 220                 .in6.sin6_port = htobe16(LLMNR_PORT),
 221         };
 222         static const int one = 1, ttl = 255;
 223         int r;
 224
 225         assert(m);
 226
 227         if (m->llmnr_ipv6_udp_fd >= 0)
 228                 return m->llmnr_ipv6_udp_fd;
 229
 230         m->llmnr_ipv6_udp_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 231         if (m->llmnr_ipv6_udp_fd < 0)
 232                 return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
 233
 234         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 235         if (r < 0) {
 236                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_UNICAST_HOPS: %m");
 237                 goto fail;
 238         }
 239
 240         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 241         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 242         if (r < 0) {
 243                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
 244                 goto fail;
 245         }
 246
 247         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 248         if (r < 0) {
 249                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
 250                 goto fail;
 251         }
 252
 253         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 254         if (r < 0) {
 255                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
 256                 goto fail;
 257         }
 258
 259         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 260         if (r < 0) {
 261                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVPKTINFO: %m");
 262                 goto fail;
 263         }
 264
 265         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 266         if (r < 0) {
 267                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVHOPLIMIT: %m");
 268                 goto fail;
 269         }
 270
 271         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 272         r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 273         if (r < 0) {
 274                 if (errno != EADDRINUSE) {
 275                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 276                         goto fail;
 277                 }
 278
 279                 log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 280
 281                 /* try again with SO_REUSEADDR */
 282                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 283                 if (r < 0) {
 284                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 285                         goto fail;
 286                 }
 287
 288                 r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 289                 if (r < 0) {
 290                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 291                         goto fail;
 292                 }
 293         } else {
 294                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 295                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 296                 if (r < 0) {
 297                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 298                         goto fail;
 299                 }
 300         }
 301
 302         r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, m->llmnr_ipv6_udp_fd, EPOLLIN, on_llmnr_packet, m);
 303         if (r < 0)
 304                 goto fail;
 305
 306         (void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
 307
 308         return m->llmnr_ipv6_udp_fd;
 309
 310 fail:
 311         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
 312         return r;
 313 }
 314
 315 static int on_llmnr_stream_packet(DnsStream *s) {
 316         DnsScope *scope;
 317
 318         assert(s);
 319         assert(s->read_packet);
 320
 321         scope = manager_find_scope(s->manager, s->read_packet);
 322         if (!scope)
 323                 log_debug("Got LLMNR TCP packet on unknown scope. Ignoring.");
 324         else if (dns_packet_validate_query(s->read_packet) > 0) {
 325                 log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 326
 327                 dns_scope_process_query(scope, s, s->read_packet);
 328         } else
 329                 log_debug("Invalid LLMNR TCP packet, ignoring.");
 330
 331         dns_stream_unref(s);
 332         return 0;
 333 }
 334
 335 static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 336         DnsStream *stream;
 337         Manager *m = userdata;
 338         int cfd, r;
 339
 340         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 341         if (cfd < 0) {
 342                 if (IN_SET(errno, EAGAIN, EINTR))
 343                         return 0;
 344
 345                 return -errno;
 346         }
 347
 348         r = dns_stream_new(m, &stream, DNS_PROTOCOL_LLMNR, cfd, NULL);
 349         if (r < 0) {
 350                 safe_close(cfd);
 351                 return r;
 352         }
 353
 354         stream->on_packet = on_llmnr_stream_packet;
 355         return 0;
 356 }
 357
 358 int manager_llmnr_ipv4_tcp_fd(Manager *m) {
 359         union sockaddr_union sa = {
 360                 .in.sin_family = AF_INET,
 361                 .in.sin_port = htobe16(LLMNR_PORT),
 362         };
 363         static const int one = 1, pmtu = IP_PMTUDISC_DONT;
 364         int r;
 365
 366         assert(m);
 367
 368         if (m->llmnr_ipv4_tcp_fd >= 0)
 369                 return m->llmnr_ipv4_tcp_fd;
 370
 371         m->llmnr_ipv4_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 372         if (m->llmnr_ipv4_tcp_fd < 0)
 373                 return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
 374
 375         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 376         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
 377         if (r < 0) {
 378                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_TTL: %m");
 379                 goto fail;
 380         }
 381
 382         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 383         if (r < 0) {
 384                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_PKTINFO: %m");
 385                 goto fail;
 386         }
 387
 388         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 389         if (r < 0) {
 390                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_RECVTTL: %m");
 391                 goto fail;
 392         }
 393
 394         /* Disable Don't-Fragment bit in the IP header */
 395         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 396         if (r < 0) {
 397                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
 398                 goto fail;
 399         }
 400
 401         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 402         r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 403         if (r < 0) {
 404                 if (errno != EADDRINUSE) {
 405                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 406                         goto fail;
 407                 }
 408
 409                 log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 410
 411                 /* try again with SO_REUSEADDR */
 412                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 413                 if (r < 0) {
 414                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 415                         goto fail;
 416                 }
 417
 418                 r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 419                 if (r < 0) {
 420                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 421                         goto fail;
 422                 }
 423         } else {
 424                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 425                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 426                 if (r < 0) {
 427                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 428                         goto fail;
 429                 }
 430         }
 431
 432         r = listen(m->llmnr_ipv4_tcp_fd, SOMAXCONN);
 433         if (r < 0) {
 434                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
 435                 goto fail;
 436         }
 437
 438         r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, m->llmnr_ipv4_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 439         if (r < 0)
 440                 goto fail;
 441
 442         (void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
 443
 444         return m->llmnr_ipv4_tcp_fd;
 445
 446 fail:
 447         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
 448         return r;
 449 }
 450
 451 int manager_llmnr_ipv6_tcp_fd(Manager *m) {
 452         union sockaddr_union sa = {
 453                 .in6.sin6_family = AF_INET6,
 454                 .in6.sin6_port = htobe16(LLMNR_PORT),
 455         };
 456         static const int one = 1;
 457         int r;
 458
 459         assert(m);
 460
 461         if (m->llmnr_ipv6_tcp_fd >= 0)
 462                 return m->llmnr_ipv6_tcp_fd;
 463
 464         m->llmnr_ipv6_tcp_fd = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 465         if (m->llmnr_ipv6_tcp_fd < 0)
 466                 return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
 467
 468         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 469         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &one, sizeof(one));
 470         if (r < 0) {
 471                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_UNICAST_HOPS: %m");
 472                 goto fail;
 473         }
 474
 475         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 476         if (r < 0) {
 477                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
 478                 goto fail;
 479         }
 480
 481         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 482         if (r < 0) {
 483                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVPKTINFO: %m");
 484                 goto fail;
 485         }
 486
 487         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 488         if (r < 0) {
 489                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVHOPLIMIT: %m");
 490                 goto fail;
 491         }
 492
 493         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 494         r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 495         if (r < 0) {
 496                 if (errno != EADDRINUSE) {
 497                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 498                         goto fail;
 499                 }
 500
 501                 log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 502
 503                 /* try again with SO_REUSEADDR */
 504                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 505                 if (r < 0) {
 506                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 507                         goto fail;
 508                 }
 509
 510                 r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 511                 if (r < 0) {
 512                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 513                         goto fail;
 514                 }
 515         } else {
 516                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 517                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 518                 if (r < 0) {
 519                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 520                         goto fail;
 521                 }
 522         }
 523
 524         r = listen(m->llmnr_ipv6_tcp_fd, SOMAXCONN);
 525         if (r < 0) {
 526                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
 527                 goto fail;
 528         }
 529
 530         r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, m->llmnr_ipv6_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 531         if (r < 0)
 532                 goto fail;
 533
 534         (void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
 535
 536         return m->llmnr_ipv6_tcp_fd;
 537
 538 fail:
 539         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 540         return r;
 541 }