src/resolve/resolved-mdns.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2015 Daniel Mack
   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 <resolv.h>
  21 #include <netinet/in.h>
  22 #include <arpa/inet.h>
  23
  24 #include "fd-util.h"
  25 #include "resolved-manager.h"
  26 #include "resolved-mdns.h"
  27
  28 void manager_mdns_stop(Manager *m) {
  29         assert(m);
  30
  31         m->mdns_ipv4_event_source = sd_event_source_unref(m->mdns_ipv4_event_source);
  32         m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd);
  33
  34         m->mdns_ipv6_event_source = sd_event_source_unref(m->mdns_ipv6_event_source);
  35         m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
  36 }
  37
  38 int manager_mdns_start(Manager *m) {
  39         int r;
  40
  41         assert(m);
  42
  43         if (m->mdns_support == RESOLVE_SUPPORT_NO)
  44                 return 0;
  45
  46         r = manager_mdns_ipv4_fd(m);
  47         if (r == -EADDRINUSE)
  48                 goto eaddrinuse;
  49         if (r < 0)
  50                 return r;
  51
  52         if (socket_ipv6_is_supported()) {
  53                 r = manager_mdns_ipv6_fd(m);
  54                 if (r == -EADDRINUSE)
  55                         goto eaddrinuse;
  56                 if (r < 0)
  57                         return r;
  58         }
  59
  60         return 0;
  61
  62 eaddrinuse:
  63         log_warning("There appears to be another mDNS responder running. Turning off mDNS support.");
  64         m->mdns_support = RESOLVE_SUPPORT_NO;
  65         manager_mdns_stop(m);
  66
  67         return 0;
  68 }
  69
  70 static int mdns_scope_process_query(DnsScope *s, DnsPacket *p) {
  71         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL;
  72         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
  73         DnsResourceKey *key = NULL;
  74         bool tentative = false;
  75         int r;
  76
  77         assert(s);
  78         assert(p);
  79
  80         r = dns_packet_extract(p);
  81         if (r < 0)
  82                 return log_debug_errno(r, "Failed to extract resource records from incoming packet: %m");
  83
  84         /* TODO: there might be more than one question in mDNS queries. */
  85         assert_return((dns_question_size(p->question) > 0), -EINVAL);
  86         key = p->question->keys[0];
  87
  88         r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative);
  89         if (r < 0) {
  90                 log_debug_errno(r, "Failed to lookup key: %m");
  91                 return r;
  92         }
  93         if (r == 0)
  94                 return 0;
  95
  96         r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, NULL, answer, NULL, false, &reply);
  97         if (r < 0) {
  98                 log_debug_errno(r, "Failed to build reply packet: %m");
  99                 return r;
 100         }
 101
 102         if (!ratelimit_test(&s->ratelimit))
 103                 return 0;
 104
 105         r = dns_scope_emit_udp(s, -1, reply);
 106         if (r < 0) {
 107                 log_debug_errno(r, "Failed to send reply packet: %m");
 108                 return r;
 109         }
 110
 111         return 0;
 112 }
 113
 114 static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
 115         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
 116         Manager *m = userdata;
 117         DnsScope *scope;
 118         int r;
 119
 120         r = manager_recv(m, fd, DNS_PROTOCOL_MDNS, &p);
 121         if (r <= 0)
 122                 return r;
 123
 124         if (manager_our_packet(m, p))
 125                 return 0;
 126
 127         scope = manager_find_scope(m, p);
 128         if (!scope) {
 129                 log_warning("Got mDNS UDP packet on unknown scope. Ignoring.");
 130                 return 0;
 131         }
 132
 133         if (dns_packet_validate_reply(p) > 0) {
 134                 DnsResourceRecord *rr;
 135
 136                 log_debug("Got mDNS reply packet");
 137
 138                 /*
 139                  * mDNS is different from regular DNS and LLMNR with regard to handling responses.
 140                  * While on other protocols, we can ignore every answer that doesn't match a question
 141                  * we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
 142                  * incoming information, regardless of the DNS packet ID.
 143                  *
 144                  * Hence, extract the packet here, and try to find a transaction for answer the we got
 145                  * and complete it. Also store the new information in scope's cache.
 146                  */
 147                 r = dns_packet_extract(p);
 148                 if (r < 0) {
 149                         log_debug("mDNS packet extraction failed.");
 150                         return 0;
 151                 }
 152
 153                 dns_scope_check_conflicts(scope, p);
 154
 155                 DNS_ANSWER_FOREACH(rr, p->answer) {
 156                         const char *name = dns_resource_key_name(rr->key);
 157                         DnsTransaction *t;
 158
 159                         /* If the received reply packet contains ANY record that is not .local or .in-addr.arpa,
 160                          * we assume someone's playing tricks on us and discard the packet completely. */
 161                         if (!(dns_name_endswith(name, "in-addr.arpa") > 0 ||
 162                               dns_name_endswith(name, "local") > 0))
 163                                 return 0;
 164
 165                         if (rr->ttl == 0) {
 166                                 log_debug("Got a goodbye packet");
 167                                 /* See the section 10.1 of RFC6762 */
 168                                 rr->ttl = 1;
 169                         }
 170
 171                         t = dns_scope_find_transaction(scope, rr->key, false);
 172                         if (t)
 173                                 dns_transaction_process_reply(t, p);
 174                 }
 175
 176                 dns_cache_put(&scope->cache, NULL, DNS_PACKET_RCODE(p), p->answer, false, (uint32_t) -1, 0, p->family, &p->sender);
 177
 178         } else if (dns_packet_validate_query(p) > 0)  {
 179                 log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p));
 180
 181                 r = mdns_scope_process_query(scope, p);
 182                 if (r < 0) {
 183                         log_debug_errno(r, "mDNS query processing failed: %m");
 184                         return 0;
 185                 }
 186         } else
 187                 log_debug("Invalid mDNS UDP packet.");
 188
 189         return 0;
 190 }
 191
 192 int manager_mdns_ipv4_fd(Manager *m) {
 193         union sockaddr_union sa = {
 194                 .in.sin_family = AF_INET,
 195                 .in.sin_port = htobe16(MDNS_PORT),
 196         };
 197         static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
 198         int r;
 199
 200         assert(m);
 201
 202         if (m->mdns_ipv4_fd >= 0)
 203                 return m->mdns_ipv4_fd;
 204
 205         m->mdns_ipv4_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 206         if (m->mdns_ipv4_fd < 0)
 207                 return -errno;
 208
 209         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
 210         if (r < 0) {
 211                 r = -errno;
 212                 goto fail;
 213         }
 214
 215         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
 216         if (r < 0) {
 217                 r = -errno;
 218                 goto fail;
 219         }
 220
 221         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
 222         if (r < 0) {
 223                 r = -errno;
 224                 goto fail;
 225         }
 226
 227         r = setsockopt(m->mdns_ipv4_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 228         if (r < 0) {
 229                 r = -errno;
 230                 goto fail;
 231         }
 232
 233         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
 234         if (r < 0) {
 235                 r = -errno;
 236                 goto fail;
 237         }
 238
 239         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
 240         if (r < 0) {
 241                 r = -errno;
 242                 goto fail;
 243         }
 244
 245         /* Disable Don't-Fragment bit in the IP header */
 246         r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
 247         if (r < 0) {
 248                 r = -errno;
 249                 goto fail;
 250         }
 251
 252         r = bind(m->mdns_ipv4_fd, &sa.sa, sizeof(sa.in));
 253         if (r < 0) {
 254                 r = -errno;
 255                 goto fail;
 256         }
 257
 258         r = sd_event_add_io(m->event, &m->mdns_ipv4_event_source, m->mdns_ipv4_fd, EPOLLIN, on_mdns_packet, m);
 259         if (r < 0)
 260                 goto fail;
 261
 262         return m->mdns_ipv4_fd;
 263
 264 fail:
 265         m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd);
 266         return r;
 267 }
 268
 269 int manager_mdns_ipv6_fd(Manager *m) {
 270         union sockaddr_union sa = {
 271                 .in6.sin6_family = AF_INET6,
 272                 .in6.sin6_port = htobe16(MDNS_PORT),
 273         };
 274         static const int one = 1, ttl = 255;
 275         int r;
 276
 277         assert(m);
 278
 279         if (m->mdns_ipv6_fd >= 0)
 280                 return m->mdns_ipv6_fd;
 281
 282         m->mdns_ipv6_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
 283         if (m->mdns_ipv6_fd < 0)
 284                 return -errno;
 285
 286         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
 287         if (r < 0) {
 288                 r = -errno;
 289                 goto fail;
 290         }
 291
 292         /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
 293         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 294         if (r < 0) {
 295                 r = -errno;
 296                 goto fail;
 297         }
 298
 299         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 300         if (r < 0) {
 301                 r = -errno;
 302                 goto fail;
 303         }
 304
 305         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 306         if (r < 0) {
 307                 r = -errno;
 308                 goto fail;
 309         }
 310
 311         r = setsockopt(m->mdns_ipv6_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
 312         if (r < 0) {
 313                 r = -errno;
 314                 goto fail;
 315         }
 316
 317         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
 318         if (r < 0) {
 319                 r = -errno;
 320                 goto fail;
 321         }
 322
 323         r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
 324         if (r < 0) {
 325                 r = -errno;
 326                 goto fail;
 327         }
 328
 329         r = bind(m->mdns_ipv6_fd, &sa.sa, sizeof(sa.in6));
 330         if (r < 0) {
 331                 r = -errno;
 332                 goto fail;
 333         }
 334
 335         r = sd_event_add_io(m->event, &m->mdns_ipv6_event_source, m->mdns_ipv6_fd, EPOLLIN, on_mdns_packet, m);
 336         if (r < 0)
 337                 goto fail;
 338
 339         return m->mdns_ipv6_fd;
 340
 341 fail:
 342         m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
 343         return r;
 344 }