src/resolve/resolved-llmnr.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2014 Tom Gundersen <teg@jklm.no>
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18  ***/
  19
  20 #include <netinet/in.h>
  21 #include <resolv.h>
  22
  23 #include "fd-util.h"
  24 #include "resolved-llmnr.h"
  25 #include "resolved-manager.h"
  26
  27 void manager_llmnr_stop(Manager *m) {
  28         assert(m);
  29
  30         m->llmnr_ipv4_udp_event_source = sd_event_source_unref(m->llmnr_ipv4_udp_event_source);
  31         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
  32
  33         m->llmnr_ipv6_udp_event_source = sd_event_source_unref(m->llmnr_ipv6_udp_event_source);
  34         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
  35
  36         m->llmnr_ipv4_tcp_event_source = sd_event_source_unref(m->llmnr_ipv4_tcp_event_source);
  37         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
  38
  39         m->llmnr_ipv6_tcp_event_source = sd_event_source_unref(m->llmnr_ipv6_tcp_event_source);
  40         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
  41 }
  42
  43 int manager_llmnr_start(Manager *m) {
  44         int r;
  45
  46         assert(m);
  47
  48         if (m->llmnr_support == RESOLVE_SUPPORT_NO)
  49                 return 0;
  50
  51         r = manager_llmnr_ipv4_udp_fd(m);
  52         if (r == -EADDRINUSE)
  53                 goto eaddrinuse;
  54         if (r < 0)
  55                 return r;
  56
  57         r = manager_llmnr_ipv4_tcp_fd(m);
  58         if (r == -EADDRINUSE)
  59                 goto eaddrinuse;
  60         if (r < 0)
  61                 return r;
  62
  63         if (socket_ipv6_is_supported()) {
  64                 r = manager_llmnr_ipv6_udp_fd(m);
  65                 if (r == -EADDRINUSE)
  66                         goto eaddrinuse;
  67                 if (r < 0)
  68                         return r;
  69
  70                 r = manager_llmnr_ipv6_tcp_fd(m);
  71                 if (r == -EADDRINUSE)
  72                         goto eaddrinuse;
  73                 if (r < 0)
  74                         return r;
  75         }
  76
  77         return 0;
  78
  79 eaddrinuse:
  80         log_warning("Another LLMNR responder prohibits binding the socket to the same port. Turning off LLMNR support.");
  81         m->llmnr_support = RESOLVE_SUPPORT_NO;
  82         manager_llmnr_stop(m);
  83
  84         return 0;
  85 }
  86
  87 static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
  88         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
  89         DnsTransaction *t = NULL;
  90         Manager *m = userdata;
  91         DnsScope *scope;
  92         int r;
  93
  94         assert(s);
  95         assert(fd >= 0);
  96         assert(m);
  97
  98         r = manager_recv(m, fd, DNS_PROTOCOL_LLMNR, &p);
  99         if (r <= 0)
 100                 return r;
 101
 102         scope = manager_find_scope(m, p);
 103         if (!scope)
 104                 log_warning("Got LLMNR UDP packet on unknown scope. Ignoring.");
 105         else if (dns_packet_validate_reply(p) > 0) {
 106                 log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 107
 108                 dns_scope_check_conflicts(scope, p);
 109
 110                 t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
 111                 if (t)
 112                         dns_transaction_process_reply(t, p);
 113
 114         } else if (dns_packet_validate_query(p) > 0)  {
 115                 log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 116
 117                 dns_scope_process_query(scope, NULL, p);
 118         } else
 119                 log_debug("Invalid LLMNR UDP packet, ignoring.");
 120
 121         return 0;
 122 }
 123
 124 int manager_llmnr_ipv4_udp_fd(Manager *m) {
 125         union sockaddr_union sa = {
 126                 .in.sin_family = AF_INET,
 127                 .in.sin_port = htobe16(LLMNR_PORT),
 128         };
 129         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 130         int r;
 131
 132         assert(m);
 133
 134         if (m->llmnr_ipv4_udp_fd >= 0)
 135                 return m->llmnr_ipv4_udp_fd;
 136
 137         m->llmnr_ipv4_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 138         if (m->llmnr_ipv4_udp_fd < 0)
 139                 return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
 140
 141         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 142         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 143         if (r < 0) {
 144                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_TTL: %m");
 145                 goto fail;
 146         }
 147
 148         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 149         if (r < 0) {
 150                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
 151                 goto fail;
 152         }
 153
 154         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 155         if (r < 0) {
 156                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
 157                 goto fail;
 158         }
 159
 160         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 161         if (r < 0) {
 162                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_PKTINFO: %m");
 163                 goto fail;
 164         }
 165
 166         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 167         if (r < 0) {
 168                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_RECVTTL: %m");
 169                 goto fail;
 170         }
 171
 172         /* Disable Don't-Fragment bit in the IP header */
 173         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 174         if (r < 0) {
 175                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
 176                 goto fail;
 177         }
 178
 179         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 180         r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 181         if (r < 0) {
 182                 if (errno != EADDRINUSE) {
 183                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 184                         goto fail;
 185                 }
 186
 187                 log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 188
 189                 /* try again with SO_REUSEADDR */
 190                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 191                 if (r < 0) {
 192                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 193                         goto fail;
 194                 }
 195
 196                 r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 197                 if (r < 0) {
 198                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 199                         goto fail;
 200                 }
 201         } else {
 202                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 203                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 204                 if (r < 0) {
 205                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 206                         goto fail;
 207                 }
 208         }
 209
 210         r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, m->llmnr_ipv4_udp_fd, EPOLLIN, on_llmnr_packet, m);
 211         if (r < 0)
 212                 goto fail;
 213
 214         (void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
 215
 216         return m->llmnr_ipv4_udp_fd;
 217
 218 fail:
 219         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
 220         return r;
 221 }
 222
 223 int manager_llmnr_ipv6_udp_fd(Manager *m) {
 224         union sockaddr_union sa = {
 225                 .in6.sin6_family = AF_INET6,
 226                 .in6.sin6_port = htobe16(LLMNR_PORT),
 227         };
 228         static const int one = 1, ttl = 255;
 229         int r;
 230
 231         assert(m);
 232
 233         if (m->llmnr_ipv6_udp_fd >= 0)
 234                 return m->llmnr_ipv6_udp_fd;
 235
 236         m->llmnr_ipv6_udp_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 237         if (m->llmnr_ipv6_udp_fd < 0)
 238                 return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
 239
 240         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 241         if (r < 0) {
 242                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_UNICAST_HOPS: %m");
 243                 goto fail;
 244         }
 245
 246         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 247         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 248         if (r < 0) {
 249                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
 250                 goto fail;
 251         }
 252
 253         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 254         if (r < 0) {
 255                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
 256                 goto fail;
 257         }
 258
 259         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 260         if (r < 0) {
 261                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
 262                 goto fail;
 263         }
 264
 265         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 266         if (r < 0) {
 267                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVPKTINFO: %m");
 268                 goto fail;
 269         }
 270
 271         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 272         if (r < 0) {
 273                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVHOPLIMIT: %m");
 274                 goto fail;
 275         }
 276
 277         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 278         r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 279         if (r < 0) {
 280                 if (errno != EADDRINUSE) {
 281                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 282                         goto fail;
 283                 }
 284
 285                 log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 286
 287                 /* try again with SO_REUSEADDR */
 288                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 289                 if (r < 0) {
 290                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 291                         goto fail;
 292                 }
 293
 294                 r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 295                 if (r < 0) {
 296                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 297                         goto fail;
 298                 }
 299         } else {
 300                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 301                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 302                 if (r < 0) {
 303                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 304                         goto fail;
 305                 }
 306         }
 307
 308         r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, m->llmnr_ipv6_udp_fd, EPOLLIN, on_llmnr_packet, m);
 309         if (r < 0)
 310                 goto fail;
 311
 312         (void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
 313
 314         return m->llmnr_ipv6_udp_fd;
 315
 316 fail:
 317         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
 318         return r;
 319 }
 320
 321 static int on_llmnr_stream_packet(DnsStream *s) {
 322         DnsScope *scope;
 323
 324         assert(s);
 325         assert(s->read_packet);
 326
 327         scope = manager_find_scope(s->manager, s->read_packet);
 328         if (!scope)
 329                 log_warning("Got LLMNR TCP packet on unknown scope. Ignoring.");
 330         else if (dns_packet_validate_query(s->read_packet) > 0) {
 331                 log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 332
 333                 dns_scope_process_query(scope, s, s->read_packet);
 334         } else
 335                 log_debug("Invalid LLMNR TCP packet, ignoring.");
 336
 337         dns_stream_unref(s);
 338         return 0;
 339 }
 340
 341 static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 342         DnsStream *stream;
 343         Manager *m = userdata;
 344         int cfd, r;
 345
 346         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 347         if (cfd < 0) {
 348                 if (IN_SET(errno, EAGAIN, EINTR))
 349                         return 0;
 350
 351                 return -errno;
 352         }
 353
 354         r = dns_stream_new(m, &stream, DNS_PROTOCOL_LLMNR, cfd);
 355         if (r < 0) {
 356                 safe_close(cfd);
 357                 return r;
 358         }
 359
 360         stream->on_packet = on_llmnr_stream_packet;
 361         return 0;
 362 }
 363
 364 int manager_llmnr_ipv4_tcp_fd(Manager *m) {
 365         union sockaddr_union sa = {
 366                 .in.sin_family = AF_INET,
 367                 .in.sin_port = htobe16(LLMNR_PORT),
 368         };
 369         static const int one = 1, pmtu = IP_PMTUDISC_DONT;
 370         int r;
 371
 372         assert(m);
 373
 374         if (m->llmnr_ipv4_tcp_fd >= 0)
 375                 return m->llmnr_ipv4_tcp_fd;
 376
 377         m->llmnr_ipv4_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 378         if (m->llmnr_ipv4_tcp_fd < 0)
 379                 return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
 380
 381         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 382         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
 383         if (r < 0) {
 384                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_TTL: %m");
 385                 goto fail;
 386         }
 387
 388         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 389         if (r < 0) {
 390                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_PKTINFO: %m");
 391                 goto fail;
 392         }
 393
 394         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 395         if (r < 0) {
 396                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_RECVTTL: %m");
 397                 goto fail;
 398         }
 399
 400         /* Disable Don't-Fragment bit in the IP header */
 401         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 402         if (r < 0) {
 403                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
 404                 goto fail;
 405         }
 406
 407         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 408         r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 409         if (r < 0) {
 410                 if (errno != EADDRINUSE) {
 411                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 412                         goto fail;
 413                 }
 414
 415                 log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 416
 417                 /* try again with SO_REUSEADDR */
 418                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 419                 if (r < 0) {
 420                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 421                         goto fail;
 422                 }
 423
 424                 r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 425                 if (r < 0) {
 426                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 427                         goto fail;
 428                 }
 429         } else {
 430                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 431                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 432                 if (r < 0) {
 433                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 434                         goto fail;
 435                 }
 436         }
 437
 438         r = listen(m->llmnr_ipv4_tcp_fd, SOMAXCONN);
 439         if (r < 0) {
 440                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
 441                 goto fail;
 442         }
 443
 444         r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, m->llmnr_ipv4_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 445         if (r < 0)
 446                 goto fail;
 447
 448         (void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
 449
 450         return m->llmnr_ipv4_tcp_fd;
 451
 452 fail:
 453         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
 454         return r;
 455 }
 456
 457 int manager_llmnr_ipv6_tcp_fd(Manager *m) {
 458         union sockaddr_union sa = {
 459                 .in6.sin6_family = AF_INET6,
 460                 .in6.sin6_port = htobe16(LLMNR_PORT),
 461         };
 462         static const int one = 1;
 463         int r;
 464
 465         assert(m);
 466
 467         if (m->llmnr_ipv6_tcp_fd >= 0)
 468                 return m->llmnr_ipv6_tcp_fd;
 469
 470         m->llmnr_ipv6_tcp_fd = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 471         if (m->llmnr_ipv6_tcp_fd < 0)
 472                 return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
 473
 474         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 475         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &one, sizeof(one));
 476         if (r < 0) {
 477                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_UNICAST_HOPS: %m");
 478                 goto fail;
 479         }
 480
 481         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 482         if (r < 0) {
 483                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
 484                 goto fail;
 485         }
 486
 487         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 488         if (r < 0) {
 489                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVPKTINFO: %m");
 490                 goto fail;
 491         }
 492
 493         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 494         if (r < 0) {
 495                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVHOPLIMIT: %m");
 496                 goto fail;
 497         }
 498
 499         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 500         r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 501         if (r < 0) {
 502                 if (errno != EADDRINUSE) {
 503                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 504                         goto fail;
 505                 }
 506
 507                 log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 508
 509                 /* try again with SO_REUSEADDR */
 510                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 511                 if (r < 0) {
 512                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 513                         goto fail;
 514                 }
 515
 516                 r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 517                 if (r < 0) {
 518                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 519                         goto fail;
 520                 }
 521         } else {
 522                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 523                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 524                 if (r < 0) {
 525                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 526                         goto fail;
 527                 }
 528         }
 529
 530         r = listen(m->llmnr_ipv6_tcp_fd, SOMAXCONN);
 531         if (r < 0) {
 532                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
 533                 goto fail;
 534         }
 535
 536         r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, m->llmnr_ipv6_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 537         if (r < 0)
 538                 goto fail;
 539
 540         (void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
 541
 542         return m->llmnr_ipv6_tcp_fd;
 543
 544 fail:
 545         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 546         return r;
 547 }