1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
4 #include <netinet/in.h>
7 #include "alloc-util.h"
9 #include "resolved-manager.h"
10 #include "resolved-mdns.h"
11 #include "sort-util.h"
13 #define CLEAR_CACHE_FLUSH(x) (~MDNS_RR_CACHE_FLUSH & (x))
15 void manager_mdns_stop(Manager
*m
) {
18 m
->mdns_ipv4_event_source
= sd_event_source_disable_unref(m
->mdns_ipv4_event_source
);
19 m
->mdns_ipv4_fd
= safe_close(m
->mdns_ipv4_fd
);
21 m
->mdns_ipv6_event_source
= sd_event_source_disable_unref(m
->mdns_ipv6_event_source
);
22 m
->mdns_ipv6_fd
= safe_close(m
->mdns_ipv6_fd
);
25 int manager_mdns_start(Manager
*m
) {
30 if (m
->mdns_support
== RESOLVE_SUPPORT_NO
)
33 r
= manager_mdns_ipv4_fd(m
);
39 if (socket_ipv6_is_supported()) {
40 r
= manager_mdns_ipv6_fd(m
);
50 log_warning("Another mDNS responder prohibits binding the socket to the same port. Turning off mDNS support.");
51 m
->mdns_support
= RESOLVE_SUPPORT_NO
;
57 static int mdns_rr_compare(DnsResourceRecord
* const *a
, DnsResourceRecord
* const *b
) {
58 DnsResourceRecord
*x
= *(DnsResourceRecord
**) a
, *y
= *(DnsResourceRecord
**) b
;
65 r
= CMP(CLEAR_CACHE_FLUSH(x
->key
->class), CLEAR_CACHE_FLUSH(y
->key
->class));
69 r
= CMP(x
->key
->type
, y
->key
->type
);
73 r
= dns_resource_record_to_wire_format(x
, false);
75 log_warning_errno(r
, "Can't wire-format RR: %m");
79 r
= dns_resource_record_to_wire_format(y
, false);
81 log_warning_errno(r
, "Can't wire-format RR: %m");
85 m
= MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x
), DNS_RESOURCE_RECORD_RDATA_SIZE(y
));
87 r
= memcmp(DNS_RESOURCE_RECORD_RDATA(x
), DNS_RESOURCE_RECORD_RDATA(y
), m
);
91 return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x
), DNS_RESOURCE_RECORD_RDATA_SIZE(y
));
94 static int proposed_rrs_cmp(DnsResourceRecord
**x
, unsigned x_size
, DnsResourceRecord
**y
, unsigned y_size
) {
98 m
= MIN(x_size
, y_size
);
99 for (unsigned i
= 0; i
< m
; i
++) {
100 r
= mdns_rr_compare(&x
[i
], &y
[i
]);
105 return CMP(x_size
, y_size
);
108 static int mdns_packet_extract_matching_rrs(DnsPacket
*p
, DnsResourceKey
*key
, DnsResourceRecord
***ret_rrs
) {
109 _cleanup_free_ DnsResourceRecord
**list
= NULL
;
110 unsigned n
= 0, size
= 0;
116 assert_return(DNS_PACKET_NSCOUNT(p
) > 0, -EINVAL
);
118 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
119 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
129 list
= new(DnsResourceRecord
*, size
);
133 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
134 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
138 list
[n
++] = p
->answer
->items
[i
].rr
;
141 typesafe_qsort(list
, size
, mdns_rr_compare
);
143 *ret_rrs
= TAKE_PTR(list
);
148 static int mdns_do_tiebreak(DnsResourceKey
*key
, DnsAnswer
*answer
, DnsPacket
*p
) {
149 _cleanup_free_ DnsResourceRecord
**our
= NULL
, **remote
= NULL
;
150 DnsResourceRecord
*rr
;
154 size
= dns_answer_size(answer
);
155 our
= new(DnsResourceRecord
*, size
);
159 DNS_ANSWER_FOREACH(rr
, answer
)
162 typesafe_qsort(our
, size
, mdns_rr_compare
);
164 r
= mdns_packet_extract_matching_rrs(p
, key
, &remote
);
170 if (proposed_rrs_cmp(remote
, r
, our
, size
) > 0)
176 static int mdns_scope_process_query(DnsScope
*s
, DnsPacket
*p
) {
177 _cleanup_(dns_answer_unrefp
) DnsAnswer
*full_answer
= NULL
;
178 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
179 DnsResourceKey
*key
= NULL
;
180 DnsResourceRecord
*rr
;
181 bool tentative
= false;
187 r
= dns_packet_extract(p
);
189 return log_debug_errno(r
, "Failed to extract resource records from incoming packet: %m");
191 assert_return((dns_question_size(p
->question
) > 0), -EINVAL
);
193 DNS_QUESTION_FOREACH(key
, p
->question
) {
194 _cleanup_(dns_answer_unrefp
) DnsAnswer
*answer
= NULL
, *soa
= NULL
;
196 r
= dns_zone_lookup(&s
->zone
, key
, 0, &answer
, &soa
, &tentative
);
198 return log_debug_errno(r
, "Failed to look up key: %m");
200 if (tentative
&& DNS_PACKET_NSCOUNT(p
) > 0) {
202 * A race condition detected with the probe packet from
204 * Do simultaneous probe tiebreaking as described in
205 * RFC 6762, Section 8.2. In case we lost don't reply
206 * the question and withdraw conflicting RRs.
208 r
= mdns_do_tiebreak(key
, answer
, p
);
210 return log_debug_errno(r
, "Failed to do tiebreaking");
212 if (r
> 0) { /* we lost */
213 DNS_ANSWER_FOREACH(rr
, answer
) {
216 i
= dns_zone_get(&s
->zone
, rr
);
218 dns_zone_item_conflict(i
);
225 r
= dns_answer_extend(&full_answer
, answer
);
227 return log_debug_errno(r
, "Failed to extend answer: %m");
230 if (dns_answer_isempty(full_answer
))
233 r
= dns_scope_make_reply_packet(s
, DNS_PACKET_ID(p
), DNS_RCODE_SUCCESS
, NULL
, full_answer
, NULL
, false, &reply
);
235 return log_debug_errno(r
, "Failed to build reply packet: %m");
237 if (!ratelimit_below(&s
->ratelimit
))
240 r
= dns_scope_emit_udp(s
, -1, AF_UNSPEC
, reply
);
242 return log_debug_errno(r
, "Failed to send reply packet: %m");
247 static int on_mdns_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
248 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
249 Manager
*m
= userdata
;
253 r
= manager_recv(m
, fd
, DNS_PROTOCOL_MDNS
, &p
);
257 if (manager_packet_from_local_address(m
, p
))
260 scope
= manager_find_scope(m
, p
);
262 log_debug("Got mDNS UDP packet on unknown scope. Ignoring.");
266 if (dns_packet_validate_reply(p
) > 0) {
267 DnsResourceRecord
*rr
;
269 log_debug("Got mDNS reply packet");
272 * mDNS is different from regular DNS and LLMNR with regard to handling responses.
273 * While on other protocols, we can ignore every answer that doesn't match a question
274 * we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
275 * incoming information, regardless of the DNS packet ID.
277 * Hence, extract the packet here, and try to find a transaction for answer the we got
278 * and complete it. Also store the new information in scope's cache.
280 r
= dns_packet_extract(p
);
282 log_debug("mDNS packet extraction failed.");
286 dns_scope_check_conflicts(scope
, p
);
288 DNS_ANSWER_FOREACH(rr
, p
->answer
) {
289 const char *name
= dns_resource_key_name(rr
->key
);
292 /* If the received reply packet contains ANY record that is not .local
293 * or .in-addr.arpa or .ip6.arpa, we assume someone's playing tricks on
294 * us and discard the packet completely. */
295 if (!(dns_name_endswith(name
, "in-addr.arpa") > 0 ||
296 dns_name_endswith(name
, "ip6.arpa") > 0 ||
297 dns_name_endswith(name
, "local") > 0))
301 log_debug("Got a goodbye packet");
302 /* See the section 10.1 of RFC6762 */
306 t
= dns_scope_find_transaction(scope
, rr
->key
, SD_RESOLVED_NO_CACHE
|SD_RESOLVED_NO_ZONE
);
308 dns_transaction_process_reply(t
, p
, false);
310 /* Also look for the various types of ANY transactions */
311 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(rr
->key
->class, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), SD_RESOLVED_NO_CACHE
|SD_RESOLVED_NO_ZONE
);
313 dns_transaction_process_reply(t
, p
, false);
315 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, rr
->key
->type
, dns_resource_key_name(rr
->key
)), SD_RESOLVED_NO_CACHE
|SD_RESOLVED_NO_ZONE
);
317 dns_transaction_process_reply(t
, p
, false);
319 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), SD_RESOLVED_NO_CACHE
|SD_RESOLVED_NO_ZONE
);
321 dns_transaction_process_reply(t
, p
, false);
324 dns_cache_put(&scope
->cache
, scope
->manager
->enable_cache
, NULL
, DNS_PACKET_RCODE(p
), p
->answer
, NULL
, false, _DNSSEC_RESULT_INVALID
, UINT32_MAX
, p
->family
, &p
->sender
);
326 } else if (dns_packet_validate_query(p
) > 0) {
327 log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p
));
329 r
= mdns_scope_process_query(scope
, p
);
331 log_debug_errno(r
, "mDNS query processing failed: %m");
335 log_debug("Invalid mDNS UDP packet.");
340 int manager_mdns_ipv4_fd(Manager
*m
) {
341 union sockaddr_union sa
= {
342 .in
.sin_family
= AF_INET
,
343 .in
.sin_port
= htobe16(MDNS_PORT
),
345 _cleanup_close_
int s
= -1;
350 if (m
->mdns_ipv4_fd
>= 0)
351 return m
->mdns_ipv4_fd
;
353 s
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
355 return log_error_errno(errno
, "mDNS-IPv4: Failed to create socket: %m");
357 r
= setsockopt_int(s
, IPPROTO_IP
, IP_TTL
, 255);
359 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_TTL: %m");
361 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_TTL
, 255);
363 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
365 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_LOOP
, true);
367 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
369 r
= setsockopt_int(s
, IPPROTO_IP
, IP_PKTINFO
, true);
371 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
373 r
= setsockopt_int(s
, IPPROTO_IP
, IP_RECVTTL
, true);
375 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
377 /* Disable Don't-Fragment bit in the IP header */
378 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MTU_DISCOVER
, IP_PMTUDISC_DONT
);
380 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
382 /* See the section 15.1 of RFC6762 */
383 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
384 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
386 if (errno
!= EADDRINUSE
)
387 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
389 log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
391 /* try again with SO_REUSEADDR */
392 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
394 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
396 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
398 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
400 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
401 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
403 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
406 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv4_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
408 return log_error_errno(r
, "mDNS-IPv4: Failed to create event source: %m");
410 return m
->mdns_ipv4_fd
= TAKE_FD(s
);
413 int manager_mdns_ipv6_fd(Manager
*m
) {
414 union sockaddr_union sa
= {
415 .in6
.sin6_family
= AF_INET6
,
416 .in6
.sin6_port
= htobe16(MDNS_PORT
),
418 _cleanup_close_
int s
= -1;
423 if (m
->mdns_ipv6_fd
>= 0)
424 return m
->mdns_ipv6_fd
;
426 s
= socket(AF_INET6
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
428 return log_error_errno(errno
, "mDNS-IPv6: Failed to create socket: %m");
430 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_UNICAST_HOPS
, 255);
432 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
434 /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
435 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_HOPS
, 255);
437 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
439 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_LOOP
, true);
441 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
443 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_V6ONLY
, true);
445 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
447 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVPKTINFO
, true);
449 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
451 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVHOPLIMIT
, true);
453 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
455 /* See the section 15.1 of RFC6762 */
456 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
457 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
459 if (errno
!= EADDRINUSE
)
460 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
462 log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
464 /* try again with SO_REUSEADDR */
465 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
467 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
469 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
471 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
473 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
474 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
476 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
479 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv6_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
481 return log_error_errno(r
, "mDNS-IPv6: Failed to create event source: %m");
483 return m
->mdns_ipv6_fd
= TAKE_FD(s
);