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   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19  ***/
  20
  21 #include <netinet/in.h>
  22 #include <resolv.h>
  23
  24 #include "fd-util.h"
  25 #include "resolved-llmnr.h"
  26 #include "resolved-manager.h"
  27
  28 void manager_llmnr_stop(Manager *m) {
  29         assert(m);
  30
  31         m->llmnr_ipv4_udp_event_source = sd_event_source_unref(m->llmnr_ipv4_udp_event_source);
  32         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
  33
  34         m->llmnr_ipv6_udp_event_source = sd_event_source_unref(m->llmnr_ipv6_udp_event_source);
  35         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
  36
  37         m->llmnr_ipv4_tcp_event_source = sd_event_source_unref(m->llmnr_ipv4_tcp_event_source);
  38         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
  39
  40         m->llmnr_ipv6_tcp_event_source = sd_event_source_unref(m->llmnr_ipv6_tcp_event_source);
  41         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
  42 }
  43
  44 int manager_llmnr_start(Manager *m) {
  45         int r;
  46
  47         assert(m);
  48
  49         if (m->llmnr_support == RESOLVE_SUPPORT_NO)
  50                 return 0;
  51
  52         r = manager_llmnr_ipv4_udp_fd(m);
  53         if (r == -EADDRINUSE)
  54                 goto eaddrinuse;
  55         if (r < 0)
  56                 return r;
  57
  58         r = manager_llmnr_ipv4_tcp_fd(m);
  59         if (r == -EADDRINUSE)
  60                 goto eaddrinuse;
  61         if (r < 0)
  62                 return r;
  63
  64         if (socket_ipv6_is_supported()) {
  65                 r = manager_llmnr_ipv6_udp_fd(m);
  66                 if (r == -EADDRINUSE)
  67                         goto eaddrinuse;
  68                 if (r < 0)
  69                         return r;
  70
  71                 r = manager_llmnr_ipv6_tcp_fd(m);
  72                 if (r == -EADDRINUSE)
  73                         goto eaddrinuse;
  74                 if (r < 0)
  75                         return r;
  76         }
  77
  78         return 0;
  79
  80 eaddrinuse:
  81         log_warning("Another LLMNR responder prohibits binding the socket to the same port. Turning off LLMNR support.");
  82         m->llmnr_support = RESOLVE_SUPPORT_NO;
  83         manager_llmnr_stop(m);
  84
  85         return 0;
  86 }
  87
  88 static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
  89         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
  90         DnsTransaction *t = NULL;
  91         Manager *m = userdata;
  92         DnsScope *scope;
  93         int r;
  94
  95         assert(s);
  96         assert(fd >= 0);
  97         assert(m);
  98
  99         r = manager_recv(m, fd, DNS_PROTOCOL_LLMNR, &p);
 100         if (r <= 0)
 101                 return r;
 102
 103         scope = manager_find_scope(m, p);
 104         if (!scope) {
 105                 log_debug("Got LLMNR UDP packet on unknown scope. Ignoring.");
 106                 return 0;
 107         }
 108
 109         if (dns_packet_validate_reply(p) > 0) {
 110                 log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 111
 112                 dns_scope_check_conflicts(scope, p);
 113
 114                 t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
 115                 if (t)
 116                         dns_transaction_process_reply(t, p);
 117
 118         } else if (dns_packet_validate_query(p) > 0)  {
 119                 log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 120
 121                 dns_scope_process_query(scope, NULL, p);
 122         } else
 123                 log_debug("Invalid LLMNR UDP packet, ignoring.");
 124
 125         return 0;
 126 }
 127
 128 int manager_llmnr_ipv4_udp_fd(Manager *m) {
 129         union sockaddr_union sa = {
 130                 .in.sin_family = AF_INET,
 131                 .in.sin_port = htobe16(LLMNR_PORT),
 132         };
 133         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 134         int r;
 135
 136         assert(m);
 137
 138         if (m->llmnr_ipv4_udp_fd >= 0)
 139                 return m->llmnr_ipv4_udp_fd;
 140
 141         m->llmnr_ipv4_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 142         if (m->llmnr_ipv4_udp_fd < 0)
 143                 return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
 144
 145         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 146         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 147         if (r < 0) {
 148                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_TTL: %m");
 149                 goto fail;
 150         }
 151
 152         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 153         if (r < 0) {
 154                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
 155                 goto fail;
 156         }
 157
 158         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 159         if (r < 0) {
 160                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
 161                 goto fail;
 162         }
 163
 164         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 165         if (r < 0) {
 166                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_PKTINFO: %m");
 167                 goto fail;
 168         }
 169
 170         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 171         if (r < 0) {
 172                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_RECVTTL: %m");
 173                 goto fail;
 174         }
 175
 176         /* Disable Don't-Fragment bit in the IP header */
 177         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 178         if (r < 0) {
 179                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
 180                 goto fail;
 181         }
 182
 183         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 184         r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 185         if (r < 0) {
 186                 if (errno != EADDRINUSE) {
 187                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 188                         goto fail;
 189                 }
 190
 191                 log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 192
 193                 /* try again with SO_REUSEADDR */
 194                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 195                 if (r < 0) {
 196                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 197                         goto fail;
 198                 }
 199
 200                 r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 201                 if (r < 0) {
 202                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 203                         goto fail;
 204                 }
 205         } else {
 206                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 207                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 208                 if (r < 0) {
 209                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 210                         goto fail;
 211                 }
 212         }
 213
 214         r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, m->llmnr_ipv4_udp_fd, EPOLLIN, on_llmnr_packet, m);
 215         if (r < 0)
 216                 goto fail;
 217
 218         (void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
 219
 220         return m->llmnr_ipv4_udp_fd;
 221
 222 fail:
 223         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
 224         return r;
 225 }
 226
 227 int manager_llmnr_ipv6_udp_fd(Manager *m) {
 228         union sockaddr_union sa = {
 229                 .in6.sin6_family = AF_INET6,
 230                 .in6.sin6_port = htobe16(LLMNR_PORT),
 231         };
 232         static const int one = 1, ttl = 255;
 233         int r;
 234
 235         assert(m);
 236
 237         if (m->llmnr_ipv6_udp_fd >= 0)
 238                 return m->llmnr_ipv6_udp_fd;
 239
 240         m->llmnr_ipv6_udp_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 241         if (m->llmnr_ipv6_udp_fd < 0)
 242                 return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
 243
 244         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 245         if (r < 0) {
 246                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_UNICAST_HOPS: %m");
 247                 goto fail;
 248         }
 249
 250         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 251         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 252         if (r < 0) {
 253                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
 254                 goto fail;
 255         }
 256
 257         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 258         if (r < 0) {
 259                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
 260                 goto fail;
 261         }
 262
 263         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 264         if (r < 0) {
 265                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
 266                 goto fail;
 267         }
 268
 269         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 270         if (r < 0) {
 271                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVPKTINFO: %m");
 272                 goto fail;
 273         }
 274
 275         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 276         if (r < 0) {
 277                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVHOPLIMIT: %m");
 278                 goto fail;
 279         }
 280
 281         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 282         r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 283         if (r < 0) {
 284                 if (errno != EADDRINUSE) {
 285                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 286                         goto fail;
 287                 }
 288
 289                 log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 290
 291                 /* try again with SO_REUSEADDR */
 292                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 293                 if (r < 0) {
 294                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 295                         goto fail;
 296                 }
 297
 298                 r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 299                 if (r < 0) {
 300                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 301                         goto fail;
 302                 }
 303         } else {
 304                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 305                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 306                 if (r < 0) {
 307                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 308                         goto fail;
 309                 }
 310         }
 311
 312         r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, m->llmnr_ipv6_udp_fd, EPOLLIN, on_llmnr_packet, m);
 313         if (r < 0)
 314                 goto fail;
 315
 316         (void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
 317
 318         return m->llmnr_ipv6_udp_fd;
 319
 320 fail:
 321         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
 322         return r;
 323 }
 324
 325 static int on_llmnr_stream_packet(DnsStream *s) {
 326         DnsScope *scope;
 327
 328         assert(s);
 329         assert(s->read_packet);
 330
 331         scope = manager_find_scope(s->manager, s->read_packet);
 332         if (!scope)
 333                 log_debug("Got LLMNR TCP packet on unknown scope. Ignoring.");
 334         else if (dns_packet_validate_query(s->read_packet) > 0) {
 335                 log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 336
 337                 dns_scope_process_query(scope, s, s->read_packet);
 338         } else
 339                 log_debug("Invalid LLMNR TCP packet, ignoring.");
 340
 341         dns_stream_unref(s);
 342         return 0;
 343 }
 344
 345 static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 346         DnsStream *stream;
 347         Manager *m = userdata;
 348         int cfd, r;
 349
 350         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 351         if (cfd < 0) {
 352                 if (IN_SET(errno, EAGAIN, EINTR))
 353                         return 0;
 354
 355                 return -errno;
 356         }
 357
 358         r = dns_stream_new(m, &stream, DNS_PROTOCOL_LLMNR, cfd);
 359         if (r < 0) {
 360                 safe_close(cfd);
 361                 return r;
 362         }
 363
 364         stream->on_packet = on_llmnr_stream_packet;
 365         return 0;
 366 }
 367
 368 int manager_llmnr_ipv4_tcp_fd(Manager *m) {
 369         union sockaddr_union sa = {
 370                 .in.sin_family = AF_INET,
 371                 .in.sin_port = htobe16(LLMNR_PORT),
 372         };
 373         static const int one = 1, pmtu = IP_PMTUDISC_DONT;
 374         int r;
 375
 376         assert(m);
 377
 378         if (m->llmnr_ipv4_tcp_fd >= 0)
 379                 return m->llmnr_ipv4_tcp_fd;
 380
 381         m->llmnr_ipv4_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 382         if (m->llmnr_ipv4_tcp_fd < 0)
 383                 return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
 384
 385         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 386         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
 387         if (r < 0) {
 388                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_TTL: %m");
 389                 goto fail;
 390         }
 391
 392         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 393         if (r < 0) {
 394                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_PKTINFO: %m");
 395                 goto fail;
 396         }
 397
 398         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 399         if (r < 0) {
 400                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_RECVTTL: %m");
 401                 goto fail;
 402         }
 403
 404         /* Disable Don't-Fragment bit in the IP header */
 405         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 406         if (r < 0) {
 407                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
 408                 goto fail;
 409         }
 410
 411         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 412         r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 413         if (r < 0) {
 414                 if (errno != EADDRINUSE) {
 415                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 416                         goto fail;
 417                 }
 418
 419                 log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 420
 421                 /* try again with SO_REUSEADDR */
 422                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 423                 if (r < 0) {
 424                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 425                         goto fail;
 426                 }
 427
 428                 r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 429                 if (r < 0) {
 430                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 431                         goto fail;
 432                 }
 433         } else {
 434                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 435                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 436                 if (r < 0) {
 437                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 438                         goto fail;
 439                 }
 440         }
 441
 442         r = listen(m->llmnr_ipv4_tcp_fd, SOMAXCONN);
 443         if (r < 0) {
 444                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
 445                 goto fail;
 446         }
 447
 448         r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, m->llmnr_ipv4_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 449         if (r < 0)
 450                 goto fail;
 451
 452         (void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
 453
 454         return m->llmnr_ipv4_tcp_fd;
 455
 456 fail:
 457         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
 458         return r;
 459 }
 460
 461 int manager_llmnr_ipv6_tcp_fd(Manager *m) {
 462         union sockaddr_union sa = {
 463                 .in6.sin6_family = AF_INET6,
 464                 .in6.sin6_port = htobe16(LLMNR_PORT),
 465         };
 466         static const int one = 1;
 467         int r;
 468
 469         assert(m);
 470
 471         if (m->llmnr_ipv6_tcp_fd >= 0)
 472                 return m->llmnr_ipv6_tcp_fd;
 473
 474         m->llmnr_ipv6_tcp_fd = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 475         if (m->llmnr_ipv6_tcp_fd < 0)
 476                 return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
 477
 478         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 479         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &one, sizeof(one));
 480         if (r < 0) {
 481                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_UNICAST_HOPS: %m");
 482                 goto fail;
 483         }
 484
 485         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 486         if (r < 0) {
 487                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
 488                 goto fail;
 489         }
 490
 491         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 492         if (r < 0) {
 493                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVPKTINFO: %m");
 494                 goto fail;
 495         }
 496
 497         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 498         if (r < 0) {
 499                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVHOPLIMIT: %m");
 500                 goto fail;
 501         }
 502
 503         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 504         r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 505         if (r < 0) {
 506                 if (errno != EADDRINUSE) {
 507                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 508                         goto fail;
 509                 }
 510
 511                 log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 512
 513                 /* try again with SO_REUSEADDR */
 514                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 515                 if (r < 0) {
 516                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 517                         goto fail;
 518                 }
 519
 520                 r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 521                 if (r < 0) {
 522                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 523                         goto fail;
 524                 }
 525         } else {
 526                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 527                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 528                 if (r < 0) {
 529                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 530                         goto fail;
 531                 }
 532         }
 533
 534         r = listen(m->llmnr_ipv6_tcp_fd, SOMAXCONN);
 535         if (r < 0) {
 536                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
 537                 goto fail;
 538         }
 539
 540         r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, m->llmnr_ipv6_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 541         if (r < 0)
 542                 goto fail;
 543
 544         (void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
 545
 546         return m->llmnr_ipv6_tcp_fd;
 547
 548 fail:
 549         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 550         return r;
 551 }