src/resolve/resolved-llmnr.c

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