1 /* SPDX-License-Identifier: LGPL-2.1+ */
4 #include <netinet/in.h>
7 #include "alloc-util.h"
9 #include "resolved-manager.h"
10 #include "resolved-mdns.h"
12 #define CLEAR_CACHE_FLUSH(x) (~MDNS_RR_CACHE_FLUSH & (x))
14 void manager_mdns_stop(Manager
*m
) {
17 m
->mdns_ipv4_event_source
= sd_event_source_unref(m
->mdns_ipv4_event_source
);
18 m
->mdns_ipv4_fd
= safe_close(m
->mdns_ipv4_fd
);
20 m
->mdns_ipv6_event_source
= sd_event_source_unref(m
->mdns_ipv6_event_source
);
21 m
->mdns_ipv6_fd
= safe_close(m
->mdns_ipv6_fd
);
24 int manager_mdns_start(Manager
*m
) {
29 if (m
->mdns_support
== RESOLVE_SUPPORT_NO
)
32 r
= manager_mdns_ipv4_fd(m
);
38 if (socket_ipv6_is_supported()) {
39 r
= manager_mdns_ipv6_fd(m
);
49 log_warning("Another mDNS responder prohibits binding the socket to the same port. Turning off mDNS support.");
50 m
->mdns_support
= RESOLVE_SUPPORT_NO
;
56 static int mdns_rr_compare(DnsResourceRecord
* const *a
, DnsResourceRecord
* const *b
) {
57 DnsResourceRecord
*x
= *(DnsResourceRecord
**) a
, *y
= *(DnsResourceRecord
**) b
;
64 r
= CMP(CLEAR_CACHE_FLUSH(x
->key
->class), CLEAR_CACHE_FLUSH(y
->key
->class));
68 r
= CMP(x
->key
->type
, y
->key
->type
);
72 r
= dns_resource_record_to_wire_format(x
, false);
74 log_warning_errno(r
, "Can't wire-format RR: %m");
78 r
= dns_resource_record_to_wire_format(y
, false);
80 log_warning_errno(r
, "Can't wire-format RR: %m");
84 m
= MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x
), DNS_RESOURCE_RECORD_RDATA_SIZE(y
));
86 r
= memcmp(DNS_RESOURCE_RECORD_RDATA(x
), DNS_RESOURCE_RECORD_RDATA(y
), m
);
90 return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x
), DNS_RESOURCE_RECORD_RDATA_SIZE(y
));
93 static int proposed_rrs_cmp(DnsResourceRecord
**x
, unsigned x_size
, DnsResourceRecord
**y
, unsigned y_size
) {
97 m
= MIN(x_size
, y_size
);
98 for (unsigned i
= 0; i
< m
; i
++) {
99 r
= mdns_rr_compare(&x
[i
], &y
[i
]);
104 return CMP(x_size
, y_size
);
107 static int mdns_packet_extract_matching_rrs(DnsPacket
*p
, DnsResourceKey
*key
, DnsResourceRecord
***ret_rrs
) {
108 _cleanup_free_ DnsResourceRecord
**list
= NULL
;
109 unsigned n
= 0, size
= 0;
115 assert_return(DNS_PACKET_NSCOUNT(p
) > 0, -EINVAL
);
117 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
118 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
128 list
= new(DnsResourceRecord
*, size
);
132 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
133 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
137 list
[n
++] = p
->answer
->items
[i
].rr
;
140 typesafe_qsort(list
, size
, mdns_rr_compare
);
142 *ret_rrs
= TAKE_PTR(list
);
147 static int mdns_do_tiebreak(DnsResourceKey
*key
, DnsAnswer
*answer
, DnsPacket
*p
) {
148 _cleanup_free_ DnsResourceRecord
**our
= NULL
, **remote
= NULL
;
149 DnsResourceRecord
*rr
;
153 size
= dns_answer_size(answer
);
154 our
= new(DnsResourceRecord
*, size
);
158 DNS_ANSWER_FOREACH(rr
, answer
)
161 typesafe_qsort(our
, size
, mdns_rr_compare
);
163 r
= mdns_packet_extract_matching_rrs(p
, key
, &remote
);
169 if (proposed_rrs_cmp(remote
, r
, our
, size
) > 0)
175 static int mdns_scope_process_query(DnsScope
*s
, DnsPacket
*p
) {
176 _cleanup_(dns_answer_unrefp
) DnsAnswer
*full_answer
= NULL
;
177 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
178 DnsResourceKey
*key
= NULL
;
179 DnsResourceRecord
*rr
;
180 bool tentative
= false;
186 r
= dns_packet_extract(p
);
188 return log_debug_errno(r
, "Failed to extract resource records from incoming packet: %m");
190 assert_return((dns_question_size(p
->question
) > 0), -EINVAL
);
192 DNS_QUESTION_FOREACH(key
, p
->question
) {
193 _cleanup_(dns_answer_unrefp
) DnsAnswer
*answer
= NULL
, *soa
= NULL
;
195 r
= dns_zone_lookup(&s
->zone
, key
, 0, &answer
, &soa
, &tentative
);
197 return log_debug_errno(r
, "Failed to lookup key: %m");
199 if (tentative
&& DNS_PACKET_NSCOUNT(p
) > 0) {
201 * A race condition detected with the probe packet from
203 * Do simultaneous probe tiebreaking as described in
204 * RFC 6762, Section 8.2. In case we lost don't reply
205 * the question and withdraw conflicting RRs.
207 r
= mdns_do_tiebreak(key
, answer
, p
);
209 return log_debug_errno(r
, "Failed to do tiebreaking");
211 if (r
> 0) { /* we lost */
212 DNS_ANSWER_FOREACH(rr
, answer
) {
215 i
= dns_zone_get(&s
->zone
, rr
);
217 dns_zone_item_conflict(i
);
224 r
= dns_answer_extend(&full_answer
, answer
);
226 return log_debug_errno(r
, "Failed to extend answer: %m");
229 if (dns_answer_isempty(full_answer
))
232 r
= dns_scope_make_reply_packet(s
, DNS_PACKET_ID(p
), DNS_RCODE_SUCCESS
, NULL
, full_answer
, NULL
, false, &reply
);
234 return log_debug_errno(r
, "Failed to build reply packet: %m");
236 if (!ratelimit_below(&s
->ratelimit
))
239 r
= dns_scope_emit_udp(s
, -1, reply
);
241 return log_debug_errno(r
, "Failed to send reply packet: %m");
246 static int on_mdns_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
247 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
248 Manager
*m
= userdata
;
252 r
= manager_recv(m
, fd
, DNS_PROTOCOL_MDNS
, &p
);
256 if (manager_our_packet(m
, p
))
259 scope
= manager_find_scope(m
, p
);
261 log_debug("Got mDNS UDP packet on unknown scope. Ignoring.");
265 if (dns_packet_validate_reply(p
) > 0) {
266 DnsResourceRecord
*rr
;
268 log_debug("Got mDNS reply packet");
271 * mDNS is different from regular DNS and LLMNR with regard to handling responses.
272 * While on other protocols, we can ignore every answer that doesn't match a question
273 * we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
274 * incoming information, regardless of the DNS packet ID.
276 * Hence, extract the packet here, and try to find a transaction for answer the we got
277 * and complete it. Also store the new information in scope's cache.
279 r
= dns_packet_extract(p
);
281 log_debug("mDNS packet extraction failed.");
285 dns_scope_check_conflicts(scope
, p
);
287 DNS_ANSWER_FOREACH(rr
, p
->answer
) {
288 const char *name
= dns_resource_key_name(rr
->key
);
291 /* If the received reply packet contains ANY record that is not .local or .in-addr.arpa,
292 * we assume someone's playing tricks on us and discard the packet completely. */
293 if (!(dns_name_endswith(name
, "in-addr.arpa") > 0 ||
294 dns_name_endswith(name
, "local") > 0))
298 log_debug("Got a goodbye packet");
299 /* See the section 10.1 of RFC6762 */
303 t
= dns_scope_find_transaction(scope
, rr
->key
, false);
305 dns_transaction_process_reply(t
, p
);
307 /* Also look for the various types of ANY transactions */
308 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(rr
->key
->class, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
310 dns_transaction_process_reply(t
, p
);
312 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, rr
->key
->type
, dns_resource_key_name(rr
->key
)), false);
314 dns_transaction_process_reply(t
, p
);
316 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
318 dns_transaction_process_reply(t
, p
);
321 dns_cache_put(&scope
->cache
, NULL
, DNS_PACKET_RCODE(p
), p
->answer
, false, (uint32_t) -1, 0, p
->family
, &p
->sender
);
323 } else if (dns_packet_validate_query(p
) > 0) {
324 log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p
));
326 r
= mdns_scope_process_query(scope
, p
);
328 log_debug_errno(r
, "mDNS query processing failed: %m");
332 log_debug("Invalid mDNS UDP packet.");
337 int manager_mdns_ipv4_fd(Manager
*m
) {
338 union sockaddr_union sa
= {
339 .in
.sin_family
= AF_INET
,
340 .in
.sin_port
= htobe16(MDNS_PORT
),
342 _cleanup_close_
int s
= -1;
347 if (m
->mdns_ipv4_fd
>= 0)
348 return m
->mdns_ipv4_fd
;
350 s
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
352 return log_error_errno(errno
, "mDNS-IPv4: Failed to create socket: %m");
354 r
= setsockopt_int(s
, IPPROTO_IP
, IP_TTL
, 255);
356 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_TTL: %m");
358 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_TTL
, 255);
360 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
362 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_LOOP
, true);
364 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
366 r
= setsockopt_int(s
, IPPROTO_IP
, IP_PKTINFO
, true);
368 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
370 r
= setsockopt_int(s
, IPPROTO_IP
, IP_RECVTTL
, true);
372 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
374 /* Disable Don't-Fragment bit in the IP header */
375 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MTU_DISCOVER
, IP_PMTUDISC_DONT
);
377 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
379 /* See the section 15.1 of RFC6762 */
380 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
381 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
383 if (errno
!= EADDRINUSE
)
384 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
386 log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
388 /* try again with SO_REUSEADDR */
389 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
391 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
393 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
395 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
397 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
398 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
400 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
403 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv4_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
405 return log_error_errno(r
, "mDNS-IPv4: Failed to create event source: %m");
407 return m
->mdns_ipv4_fd
= TAKE_FD(s
);
410 int manager_mdns_ipv6_fd(Manager
*m
) {
411 union sockaddr_union sa
= {
412 .in6
.sin6_family
= AF_INET6
,
413 .in6
.sin6_port
= htobe16(MDNS_PORT
),
415 _cleanup_close_
int s
= -1;
420 if (m
->mdns_ipv6_fd
>= 0)
421 return m
->mdns_ipv6_fd
;
423 s
= socket(AF_INET6
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
425 return log_error_errno(errno
, "mDNS-IPv6: Failed to create socket: %m");
427 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_UNICAST_HOPS
, 255);
429 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
431 /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
432 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_HOPS
, 255);
434 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
436 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_LOOP
, true);
438 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
440 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_V6ONLY
, true);
442 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
444 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVPKTINFO
, true);
446 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
448 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVHOPLIMIT
, true);
450 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
452 /* See the section 15.1 of RFC6762 */
453 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
454 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
456 if (errno
!= EADDRINUSE
)
457 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
459 log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
461 /* try again with SO_REUSEADDR */
462 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
464 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
466 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
468 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
470 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
471 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
473 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
476 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv6_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
478 return log_error_errno(r
, "mDNS-IPv6: Failed to create event source: %m");
480 return m
->mdns_ipv6_fd
= TAKE_FD(s
);