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_warning("Got LLMNR UDP packet on unknown scope. Ignoring.");
 106         else if (dns_packet_validate_reply(p) > 0) {
 107                 log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
 108
 109                 dns_scope_check_conflicts(scope, p);
 110
 111                 t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
 112                 if (t)
 113                         dns_transaction_process_reply(t, p);
 114
 115         } else if (dns_packet_validate_query(p) > 0)  {
 116                 log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
 117
 118                 dns_scope_process_query(scope, NULL, p);
 119         } else
 120                 log_debug("Invalid LLMNR UDP packet, ignoring.");
 121
 122         return 0;
 123 }
 124
 125 int manager_llmnr_ipv4_udp_fd(Manager *m) {
 126         union sockaddr_union sa = {
 127                 .in.sin_family = AF_INET,
 128                 .in.sin_port = htobe16(LLMNR_PORT),
 129         };
 130         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 131         int r;
 132
 133         assert(m);
 134
 135         if (m->llmnr_ipv4_udp_fd >= 0)
 136                 return m->llmnr_ipv4_udp_fd;
 137
 138         m->llmnr_ipv4_udp_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 139         if (m->llmnr_ipv4_udp_fd < 0)
 140                 return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
 141
 142         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 143         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 144         if (r < 0) {
 145                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_TTL: %m");
 146                 goto fail;
 147         }
 148
 149         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 150         if (r < 0) {
 151                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
 152                 goto fail;
 153         }
 154
 155         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 156         if (r < 0) {
 157                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
 158                 goto fail;
 159         }
 160
 161         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 162         if (r < 0) {
 163                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_PKTINFO: %m");
 164                 goto fail;
 165         }
 166
 167         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 168         if (r < 0) {
 169                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_RECVTTL: %m");
 170                 goto fail;
 171         }
 172
 173         /* Disable Don't-Fragment bit in the IP header */
 174         r = setsockopt(m->llmnr_ipv4_udp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 175         if (r < 0) {
 176                 r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
 177                 goto fail;
 178         }
 179
 180         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 181         r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 182         if (r < 0) {
 183                 if (errno != EADDRINUSE) {
 184                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 185                         goto fail;
 186                 }
 187
 188                 log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 189
 190                 /* try again with SO_REUSEADDR */
 191                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 192                 if (r < 0) {
 193                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 194                         goto fail;
 195                 }
 196
 197                 r = bind(m->llmnr_ipv4_udp_fd, &sa.sa, sizeof(sa.in));
 198                 if (r < 0) {
 199                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
 200                         goto fail;
 201                 }
 202         } else {
 203                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 204                 r = setsockopt(m->llmnr_ipv4_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 205                 if (r < 0) {
 206                         r = log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
 207                         goto fail;
 208                 }
 209         }
 210
 211         r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, m->llmnr_ipv4_udp_fd, EPOLLIN, on_llmnr_packet, m);
 212         if (r < 0)
 213                 goto fail;
 214
 215         (void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
 216
 217         return m->llmnr_ipv4_udp_fd;
 218
 219 fail:
 220         m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
 221         return r;
 222 }
 223
 224 int manager_llmnr_ipv6_udp_fd(Manager *m) {
 225         union sockaddr_union sa = {
 226                 .in6.sin6_family = AF_INET6,
 227                 .in6.sin6_port = htobe16(LLMNR_PORT),
 228         };
 229         static const int one = 1, ttl = 255;
 230         int r;
 231
 232         assert(m);
 233
 234         if (m->llmnr_ipv6_udp_fd >= 0)
 235                 return m->llmnr_ipv6_udp_fd;
 236
 237         m->llmnr_ipv6_udp_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 238         if (m->llmnr_ipv6_udp_fd < 0)
 239                 return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
 240
 241         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 242         if (r < 0) {
 243                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_UNICAST_HOPS: %m");
 244                 goto fail;
 245         }
 246
 247         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 248         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 249         if (r < 0) {
 250                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
 251                 goto fail;
 252         }
 253
 254         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 255         if (r < 0) {
 256                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
 257                 goto fail;
 258         }
 259
 260         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 261         if (r < 0) {
 262                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
 263                 goto fail;
 264         }
 265
 266         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 267         if (r < 0) {
 268                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVPKTINFO: %m");
 269                 goto fail;
 270         }
 271
 272         r = setsockopt(m->llmnr_ipv6_udp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 273         if (r < 0) {
 274                 r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set IPV6_RECVHOPLIMIT: %m");
 275                 goto fail;
 276         }
 277
 278         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 279         r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 280         if (r < 0) {
 281                 if (errno != EADDRINUSE) {
 282                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 283                         goto fail;
 284                 }
 285
 286                 log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 287
 288                 /* try again with SO_REUSEADDR */
 289                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 290                 if (r < 0) {
 291                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 292                         goto fail;
 293                 }
 294
 295                 r = bind(m->llmnr_ipv6_udp_fd, &sa.sa, sizeof(sa.in6));
 296                 if (r < 0) {
 297                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
 298                         goto fail;
 299                 }
 300         } else {
 301                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 302                 r = setsockopt(m->llmnr_ipv6_udp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 303                 if (r < 0) {
 304                         r = log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
 305                         goto fail;
 306                 }
 307         }
 308
 309         r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, m->llmnr_ipv6_udp_fd, EPOLLIN, on_llmnr_packet, m);
 310         if (r < 0)
 311                 goto fail;
 312
 313         (void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
 314
 315         return m->llmnr_ipv6_udp_fd;
 316
 317 fail:
 318         m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
 319         return r;
 320 }
 321
 322 static int on_llmnr_stream_packet(DnsStream *s) {
 323         DnsScope *scope;
 324
 325         assert(s);
 326         assert(s->read_packet);
 327
 328         scope = manager_find_scope(s->manager, s->read_packet);
 329         if (!scope)
 330                 log_warning("Got LLMNR TCP packet on unknown scope. Ignoring.");
 331         else if (dns_packet_validate_query(s->read_packet) > 0) {
 332                 log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
 333
 334                 dns_scope_process_query(scope, s, s->read_packet);
 335         } else
 336                 log_debug("Invalid LLMNR TCP packet, ignoring.");
 337
 338         dns_stream_unref(s);
 339         return 0;
 340 }
 341
 342 static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 343         DnsStream *stream;
 344         Manager *m = userdata;
 345         int cfd, r;
 346
 347         cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
 348         if (cfd < 0) {
 349                 if (IN_SET(errno, EAGAIN, EINTR))
 350                         return 0;
 351
 352                 return -errno;
 353         }
 354
 355         r = dns_stream_new(m, &stream, DNS_PROTOCOL_LLMNR, cfd);
 356         if (r < 0) {
 357                 safe_close(cfd);
 358                 return r;
 359         }
 360
 361         stream->on_packet = on_llmnr_stream_packet;
 362         return 0;
 363 }
 364
 365 int manager_llmnr_ipv4_tcp_fd(Manager *m) {
 366         union sockaddr_union sa = {
 367                 .in.sin_family = AF_INET,
 368                 .in.sin_port = htobe16(LLMNR_PORT),
 369         };
 370         static const int one = 1, pmtu = IP_PMTUDISC_DONT;
 371         int r;
 372
 373         assert(m);
 374
 375         if (m->llmnr_ipv4_tcp_fd >= 0)
 376                 return m->llmnr_ipv4_tcp_fd;
 377
 378         m->llmnr_ipv4_tcp_fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 379         if (m->llmnr_ipv4_tcp_fd < 0)
 380                 return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
 381
 382         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 383         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_TTL, &one, sizeof(one));
 384         if (r < 0) {
 385                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_TTL: %m");
 386                 goto fail;
 387         }
 388
 389         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 390         if (r < 0) {
 391                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_PKTINFO: %m");
 392                 goto fail;
 393         }
 394
 395         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 396         if (r < 0) {
 397                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_RECVTTL: %m");
 398                 goto fail;
 399         }
 400
 401         /* Disable Don't-Fragment bit in the IP header */
 402         r = setsockopt(m->llmnr_ipv4_tcp_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 403         if (r < 0) {
 404                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
 405                 goto fail;
 406         }
 407
 408         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 409         r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 410         if (r < 0) {
 411                 if (errno != EADDRINUSE) {
 412                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 413                         goto fail;
 414                 }
 415
 416                 log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 417
 418                 /* try again with SO_REUSEADDR */
 419                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 420                 if (r < 0) {
 421                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 422                         goto fail;
 423                 }
 424
 425                 r = bind(m->llmnr_ipv4_tcp_fd, &sa.sa, sizeof(sa.in));
 426                 if (r < 0) {
 427                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
 428                         goto fail;
 429                 }
 430         } else {
 431                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 432                 r = setsockopt(m->llmnr_ipv4_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 433                 if (r < 0) {
 434                         r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
 435                         goto fail;
 436                 }
 437         }
 438
 439         r = listen(m->llmnr_ipv4_tcp_fd, SOMAXCONN);
 440         if (r < 0) {
 441                 r = log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
 442                 goto fail;
 443         }
 444
 445         r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, m->llmnr_ipv4_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 446         if (r < 0)
 447                 goto fail;
 448
 449         (void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
 450
 451         return m->llmnr_ipv4_tcp_fd;
 452
 453 fail:
 454         m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
 455         return r;
 456 }
 457
 458 int manager_llmnr_ipv6_tcp_fd(Manager *m) {
 459         union sockaddr_union sa = {
 460                 .in6.sin6_family = AF_INET6,
 461                 .in6.sin6_port = htobe16(LLMNR_PORT),
 462         };
 463         static const int one = 1;
 464         int r;
 465
 466         assert(m);
 467
 468         if (m->llmnr_ipv6_tcp_fd >= 0)
 469                 return m->llmnr_ipv6_tcp_fd;
 470
 471         m->llmnr_ipv6_tcp_fd = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 472         if (m->llmnr_ipv6_tcp_fd < 0)
 473                 return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
 474
 475         /* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
 476         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &one, sizeof(one));
 477         if (r < 0) {
 478                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_UNICAST_HOPS: %m");
 479                 goto fail;
 480         }
 481
 482         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 483         if (r < 0) {
 484                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
 485                 goto fail;
 486         }
 487
 488         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 489         if (r < 0) {
 490                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVPKTINFO: %m");
 491                 goto fail;
 492         }
 493
 494         r = setsockopt(m->llmnr_ipv6_tcp_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 495         if (r < 0) {
 496                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set IPV6_RECVHOPLIMIT: %m");
 497                 goto fail;
 498         }
 499
 500         /* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
 501         r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 502         if (r < 0) {
 503                 if (errno != EADDRINUSE) {
 504                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 505                         goto fail;
 506                 }
 507
 508                 log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
 509
 510                 /* try again with SO_REUSEADDR */
 511                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 512                 if (r < 0) {
 513                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 514                         goto fail;
 515                 }
 516
 517                 r = bind(m->llmnr_ipv6_tcp_fd, &sa.sa, sizeof(sa.in6));
 518                 if (r < 0) {
 519                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
 520                         goto fail;
 521                 }
 522         } else {
 523                 /* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
 524                 r = setsockopt(m->llmnr_ipv6_tcp_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 525                 if (r < 0) {
 526                         r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
 527                         goto fail;
 528                 }
 529         }
 530
 531         r = listen(m->llmnr_ipv6_tcp_fd, SOMAXCONN);
 532         if (r < 0) {
 533                 r = log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
 534                 goto fail;
 535         }
 536
 537         r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, m->llmnr_ipv6_tcp_fd, EPOLLIN, on_llmnr_stream, m);
 538         if (r < 0)
 539                 goto fail;
 540
 541         (void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
 542
 543         return m->llmnr_ipv6_tcp_fd;
 544
 545 fail:
 546         m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
 547         return r;
 548 }