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         if (manager_our_packet(m, p))
 104                 return 0;
 105
 106         scope = manager_find_scope(m, p);
 107         if (!scope) {
 108                 log_debug("Got LLMNR UDP packet on unknown scope. Ignoring.");
 109                 return 0;
 110         }
 111
 112         if (dns_packet_validate_reply(p) > 0) {
 113                 log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 114
 115                 dns_scope_check_conflicts(scope, p);
 116
 117                 t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
 118                 if (t)
 119                         dns_transaction_process_reply(t, p);
 120
 121         } else if (dns_packet_validate_query(p) > 0)  {
 122                 log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 123
 124                 dns_scope_process_query(scope, NULL, p);
 125         } else
 126                 log_debug("Invalid LLMNR UDP packet, ignoring.");
 127
 128         return 0;
 129 }
 130
 131 int manager_llmnr_ipv4_udp_fd(Manager *m) {
 132         union sockaddr_union sa = {
 133                 .in.sin_family = AF_INET,
 134                 .in.sin_port = htobe16(LLMNR_PORT),
 135         };
 136         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 137         int r;
 138
 139         assert(m);
 140
 141         if (m->llmnr_ipv4_udp_fd >= 0)
 142                 return m->llmnr_ipv4_udp_fd;
 143
 144         m->llmnr_ipv4_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 145         if (m->llmnr_ipv4_udp_fd < 0)
 146                 return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
 147
 148         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 149         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 150         if (r < 0) {
 151                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_TTL: %m");
 152                 goto fail;
 153         }
 154
 155         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 156         if (r < 0) {
 157                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
 158                 goto fail;
 159         }
 160
 161         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 162         if (r < 0) {
 163                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
 164                 goto fail;
 165         }
 166
 167         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 168         if (r < 0) {
 169                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_PKTINFO: %m");
 170                 goto fail;
 171         }
 172
 173         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 174         if (r < 0) {
 175                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_RECVTTL: %m");
 176                 goto fail;
 177         }
 178
 179         /* Disable Don't-Fragment bit in the IP header */
 180         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 181         if (r < 0) {
 182                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
 183                 goto fail;
 184         }
 185
 186         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 187         r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 188         if (r < 0) {
 189                 if (errno != EADDRINUSE) {
 190                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 191                         goto fail;
 192                 }
 193
 194                 log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 195
 196                 /* try again with SO_REUSEADDR */
 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                 r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 204                 if (r < 0) {
 205                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 206                         goto fail;
 207                 }
 208         } else {
 209                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 210                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 211                 if (r < 0) {
 212                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 213                         goto fail;
 214                 }
 215         }
 216
 217         r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, m->llmnr_ipv4_udp_fd, EPOLLIN, on_llmnr_packet, m);
 218         if (r < 0)
 219                 goto fail;
 220
 221         (void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
 222
 223         return m->llmnr_ipv4_udp_fd;
 224
 225 fail:
 226         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
 227         return r;
 228 }
 229
 230 int manager_llmnr_ipv6_udp_fd(Manager *m) {
 231         union sockaddr_union sa = {
 232                 .in6.sin6_family = AF_INET6,
 233                 .in6.sin6_port = htobe16(LLMNR_PORT),
 234         };
 235         static const int one = 1, ttl = 255;
 236         int r;
 237
 238         assert(m);
 239
 240         if (m->llmnr_ipv6_udp_fd >= 0)
 241                 return m->llmnr_ipv6_udp_fd;
 242
 243         m->llmnr_ipv6_udp_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 244         if (m->llmnr_ipv6_udp_fd < 0)
 245                 return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
 246
 247         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 248         if (r < 0) {
 249                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_UNICAST_HOPS: %m");
 250                 goto fail;
 251         }
 252
 253         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 254         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 255         if (r < 0) {
 256                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
 257                 goto fail;
 258         }
 259
 260         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 261         if (r < 0) {
 262                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
 263                 goto fail;
 264         }
 265
 266         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 267         if (r < 0) {
 268                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
 269                 goto fail;
 270         }
 271
 272         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 273         if (r < 0) {
 274                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVPKTINFO: %m");
 275                 goto fail;
 276         }
 277
 278         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 279         if (r < 0) {
 280                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVHOPLIMIT: %m");
 281                 goto fail;
 282         }
 283
 284         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 285         r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 286         if (r < 0) {
 287                 if (errno != EADDRINUSE) {
 288                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 289                         goto fail;
 290                 }
 291
 292                 log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 293
 294                 /* try again with SO_REUSEADDR */
 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                 r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 302                 if (r < 0) {
 303                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 304                         goto fail;
 305                 }
 306         } else {
 307                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 308                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 309                 if (r < 0) {
 310                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 311                         goto fail;
 312                 }
 313         }
 314
 315         r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, m->llmnr_ipv6_udp_fd, EPOLLIN, on_llmnr_packet, m);
 316         if (r < 0)
 317                 goto fail;
 318
 319         (void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
 320
 321         return m->llmnr_ipv6_udp_fd;
 322
 323 fail:
 324         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
 325         return r;
 326 }
 327
 328 static int on_llmnr_stream_packet(DnsStream *s) {
 329         DnsScope *scope;
 330
 331         assert(s);
 332         assert(s->read_packet);
 333
 334         scope = manager_find_scope(s->manager, s->read_packet);
 335         if (!scope)
 336                 log_debug("Got LLMNR TCP packet on unknown scope. Ignoring.");
 337         else if (dns_packet_validate_query(s->read_packet) > 0) {
 338                 log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 339
 340                 dns_scope_process_query(scope, s, s->read_packet);
 341         } else
 342                 log_debug("Invalid LLMNR TCP packet, ignoring.");
 343
 344         dns_stream_unref(s);
 345         return 0;
 346 }
 347
 348 static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 349         DnsStream *stream;
 350         Manager *m = userdata;
 351         int cfd, r;
 352
 353         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 354         if (cfd < 0) {
 355                 if (IN_SET(errno, EAGAIN, EINTR))
 356                         return 0;
 357
 358                 return -errno;
 359         }
 360
 361         r = dns_stream_new(m, &stream, DNS_PROTOCOL_LLMNR, cfd);
 362         if (r < 0) {
 363                 safe_close(cfd);
 364                 return r;
 365         }
 366
 367         stream->on_packet = on_llmnr_stream_packet;
 368         return 0;
 369 }
 370
 371 int manager_llmnr_ipv4_tcp_fd(Manager *m) {
 372         union sockaddr_union sa = {
 373                 .in.sin_family = AF_INET,
 374                 .in.sin_port = htobe16(LLMNR_PORT),
 375         };
 376         static const int one = 1, pmtu = IP_PMTUDISC_DONT;
 377         int r;
 378
 379         assert(m);
 380
 381         if (m->llmnr_ipv4_tcp_fd >= 0)
 382                 return m->llmnr_ipv4_tcp_fd;
 383
 384         m->llmnr_ipv4_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 385         if (m->llmnr_ipv4_tcp_fd < 0)
 386                 return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
 387
 388         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 389         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
 390         if (r < 0) {
 391                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_TTL: %m");
 392                 goto fail;
 393         }
 394
 395         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 396         if (r < 0) {
 397                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_PKTINFO: %m");
 398                 goto fail;
 399         }
 400
 401         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 402         if (r < 0) {
 403                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_RECVTTL: %m");
 404                 goto fail;
 405         }
 406
 407         /* Disable Don't-Fragment bit in the IP header */
 408         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 409         if (r < 0) {
 410                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
 411                 goto fail;
 412         }
 413
 414         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 415         r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 416         if (r < 0) {
 417                 if (errno != EADDRINUSE) {
 418                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 419                         goto fail;
 420                 }
 421
 422                 log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 423
 424                 /* try again with SO_REUSEADDR */
 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                 r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 432                 if (r < 0) {
 433                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 434                         goto fail;
 435                 }
 436         } else {
 437                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 438                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 439                 if (r < 0) {
 440                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 441                         goto fail;
 442                 }
 443         }
 444
 445         r = listen(m->llmnr_ipv4_tcp_fd, SOMAXCONN);
 446         if (r < 0) {
 447                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
 448                 goto fail;
 449         }
 450
 451         r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, m->llmnr_ipv4_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 452         if (r < 0)
 453                 goto fail;
 454
 455         (void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
 456
 457         return m->llmnr_ipv4_tcp_fd;
 458
 459 fail:
 460         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
 461         return r;
 462 }
 463
 464 int manager_llmnr_ipv6_tcp_fd(Manager *m) {
 465         union sockaddr_union sa = {
 466                 .in6.sin6_family = AF_INET6,
 467                 .in6.sin6_port = htobe16(LLMNR_PORT),
 468         };
 469         static const int one = 1;
 470         int r;
 471
 472         assert(m);
 473
 474         if (m->llmnr_ipv6_tcp_fd >= 0)
 475                 return m->llmnr_ipv6_tcp_fd;
 476
 477         m->llmnr_ipv6_tcp_fd = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 478         if (m->llmnr_ipv6_tcp_fd < 0)
 479                 return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
 480
 481         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 482         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &one, sizeof(one));
 483         if (r < 0) {
 484                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_UNICAST_HOPS: %m");
 485                 goto fail;
 486         }
 487
 488         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 489         if (r < 0) {
 490                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
 491                 goto fail;
 492         }
 493
 494         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 495         if (r < 0) {
 496                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVPKTINFO: %m");
 497                 goto fail;
 498         }
 499
 500         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 501         if (r < 0) {
 502                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVHOPLIMIT: %m");
 503                 goto fail;
 504         }
 505
 506         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 507         r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 508         if (r < 0) {
 509                 if (errno != EADDRINUSE) {
 510                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 511                         goto fail;
 512                 }
 513
 514                 log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 515
 516                 /* try again with SO_REUSEADDR */
 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                 r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 524                 if (r < 0) {
 525                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 526                         goto fail;
 527                 }
 528         } else {
 529                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 530                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 531                 if (r < 0) {
 532                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 533                         goto fail;
 534                 }
 535         }
 536
 537         r = listen(m->llmnr_ipv6_tcp_fd, SOMAXCONN);
 538         if (r < 0) {
 539                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
 540                 goto fail;
 541         }
 542
 543         r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, m->llmnr_ipv6_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 544         if (r < 0)
 545                 goto fail;
 546
 547         (void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
 548
 549         return m->llmnr_ipv6_tcp_fd;
 550
 551 fail:
 552         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 553         return r;
 554 }