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(const void *a
, const void *b
) {
57 DnsResourceRecord
**x
= (DnsResourceRecord
**) a
, **y
= (DnsResourceRecord
**) b
;
66 if (CLEAR_CACHE_FLUSH((*x
)->key
->class) < CLEAR_CACHE_FLUSH((*y
)->key
->class))
68 else if (CLEAR_CACHE_FLUSH((*x
)->key
->class) > CLEAR_CACHE_FLUSH((*y
)->key
->class))
71 if ((*x
)->key
->type
< (*y
)->key
->type
)
73 else if ((*x
)->key
->type
> (*y
)->key
->type
)
76 r
= dns_resource_record_to_wire_format(*x
, false);
78 log_warning_errno(r
, "Can't wire-format RR: %m");
82 r
= dns_resource_record_to_wire_format(*y
, false);
84 log_warning_errno(r
, "Can't wire-format RR: %m");
88 m
= MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(*x
), DNS_RESOURCE_RECORD_RDATA_SIZE(*y
));
90 r
= memcmp(DNS_RESOURCE_RECORD_RDATA(*x
), DNS_RESOURCE_RECORD_RDATA(*y
), m
);
94 if (DNS_RESOURCE_RECORD_RDATA_SIZE(*x
) < DNS_RESOURCE_RECORD_RDATA_SIZE(*y
))
96 else if (DNS_RESOURCE_RECORD_RDATA_SIZE(*x
) > DNS_RESOURCE_RECORD_RDATA_SIZE(*y
))
102 static int proposed_rrs_cmp(DnsResourceRecord
**x
, unsigned x_size
, DnsResourceRecord
**y
, unsigned y_size
) {
106 m
= MIN(x_size
, y_size
);
107 for (unsigned i
= 0; i
< m
; i
++) {
108 r
= mdns_rr_compare(&x
[i
], &y
[i
]);
121 static int mdns_packet_extract_matching_rrs(DnsPacket
*p
, DnsResourceKey
*key
, DnsResourceRecord
***ret_rrs
) {
122 _cleanup_free_ DnsResourceRecord
**list
= NULL
;
123 unsigned n
= 0, size
= 0;
129 assert_return(DNS_PACKET_NSCOUNT(p
) > 0, -EINVAL
);
131 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
132 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
142 list
= new(DnsResourceRecord
*, size
);
146 for (size_t i
= DNS_PACKET_ANCOUNT(p
); i
< (DNS_PACKET_ANCOUNT(p
) + DNS_PACKET_NSCOUNT(p
)); i
++) {
147 r
= dns_resource_key_match_rr(key
, p
->answer
->items
[i
].rr
, NULL
);
151 list
[n
++] = p
->answer
->items
[i
].rr
;
154 qsort_safe(list
, size
, sizeof(DnsResourceRecord
*), mdns_rr_compare
);
156 *ret_rrs
= TAKE_PTR(list
);
161 static int mdns_do_tiebreak(DnsResourceKey
*key
, DnsAnswer
*answer
, DnsPacket
*p
) {
162 _cleanup_free_ DnsResourceRecord
**our
= NULL
, **remote
= NULL
;
163 DnsResourceRecord
*rr
;
167 size
= dns_answer_size(answer
);
168 our
= new(DnsResourceRecord
*, size
);
172 DNS_ANSWER_FOREACH(rr
, answer
)
174 qsort_safe(our
, size
, sizeof(DnsResourceRecord
*), mdns_rr_compare
);
176 r
= mdns_packet_extract_matching_rrs(p
, key
, &remote
);
182 if (proposed_rrs_cmp(remote
, r
, our
, size
) > 0)
188 static int mdns_scope_process_query(DnsScope
*s
, DnsPacket
*p
) {
189 _cleanup_(dns_answer_unrefp
) DnsAnswer
*full_answer
= NULL
;
190 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
191 DnsResourceKey
*key
= NULL
;
192 DnsResourceRecord
*rr
;
193 bool tentative
= false;
199 r
= dns_packet_extract(p
);
201 return log_debug_errno(r
, "Failed to extract resource records from incoming packet: %m");
203 assert_return((dns_question_size(p
->question
) > 0), -EINVAL
);
205 DNS_QUESTION_FOREACH(key
, p
->question
) {
206 _cleanup_(dns_answer_unrefp
) DnsAnswer
*answer
= NULL
, *soa
= NULL
;
208 r
= dns_zone_lookup(&s
->zone
, key
, 0, &answer
, &soa
, &tentative
);
210 return log_debug_errno(r
, "Failed to lookup key: %m");
212 if (tentative
&& DNS_PACKET_NSCOUNT(p
) > 0) {
214 * A race condition detected with the probe packet from
216 * Do simultaneous probe tiebreaking as described in
217 * RFC 6762, Section 8.2. In case we lost don't reply
218 * the question and withdraw conflicting RRs.
220 r
= mdns_do_tiebreak(key
, answer
, p
);
222 return log_debug_errno(r
, "Failed to do tiebreaking");
224 if (r
> 0) { /* we lost */
225 DNS_ANSWER_FOREACH(rr
, answer
) {
228 i
= dns_zone_get(&s
->zone
, rr
);
230 dns_zone_item_conflict(i
);
237 r
= dns_answer_extend(&full_answer
, answer
);
239 return log_debug_errno(r
, "Failed to extend answer: %m");
242 if (dns_answer_isempty(full_answer
))
245 r
= dns_scope_make_reply_packet(s
, DNS_PACKET_ID(p
), DNS_RCODE_SUCCESS
, NULL
, full_answer
, NULL
, false, &reply
);
247 return log_debug_errno(r
, "Failed to build reply packet: %m");
249 if (!ratelimit_below(&s
->ratelimit
))
252 r
= dns_scope_emit_udp(s
, -1, reply
);
254 return log_debug_errno(r
, "Failed to send reply packet: %m");
259 static int on_mdns_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
260 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
261 Manager
*m
= userdata
;
265 r
= manager_recv(m
, fd
, DNS_PROTOCOL_MDNS
, &p
);
269 if (manager_our_packet(m
, p
))
272 scope
= manager_find_scope(m
, p
);
274 log_debug("Got mDNS UDP packet on unknown scope. Ignoring.");
278 if (dns_packet_validate_reply(p
) > 0) {
279 DnsResourceRecord
*rr
;
281 log_debug("Got mDNS reply packet");
284 * mDNS is different from regular DNS and LLMNR with regard to handling responses.
285 * While on other protocols, we can ignore every answer that doesn't match a question
286 * we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
287 * incoming information, regardless of the DNS packet ID.
289 * Hence, extract the packet here, and try to find a transaction for answer the we got
290 * and complete it. Also store the new information in scope's cache.
292 r
= dns_packet_extract(p
);
294 log_debug("mDNS packet extraction failed.");
298 dns_scope_check_conflicts(scope
, p
);
300 DNS_ANSWER_FOREACH(rr
, p
->answer
) {
301 const char *name
= dns_resource_key_name(rr
->key
);
304 /* If the received reply packet contains ANY record that is not .local or .in-addr.arpa,
305 * we assume someone's playing tricks on us and discard the packet completely. */
306 if (!(dns_name_endswith(name
, "in-addr.arpa") > 0 ||
307 dns_name_endswith(name
, "local") > 0))
311 log_debug("Got a goodbye packet");
312 /* See the section 10.1 of RFC6762 */
316 t
= dns_scope_find_transaction(scope
, rr
->key
, false);
318 dns_transaction_process_reply(t
, p
);
320 /* Also look for the various types of ANY transactions */
321 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(rr
->key
->class, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
323 dns_transaction_process_reply(t
, p
);
325 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, rr
->key
->type
, dns_resource_key_name(rr
->key
)), false);
327 dns_transaction_process_reply(t
, p
);
329 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
331 dns_transaction_process_reply(t
, p
);
334 dns_cache_put(&scope
->cache
, NULL
, DNS_PACKET_RCODE(p
), p
->answer
, false, (uint32_t) -1, 0, p
->family
, &p
->sender
);
336 } else if (dns_packet_validate_query(p
) > 0) {
337 log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p
));
339 r
= mdns_scope_process_query(scope
, p
);
341 log_debug_errno(r
, "mDNS query processing failed: %m");
345 log_debug("Invalid mDNS UDP packet.");
350 int manager_mdns_ipv4_fd(Manager
*m
) {
351 union sockaddr_union sa
= {
352 .in
.sin_family
= AF_INET
,
353 .in
.sin_port
= htobe16(MDNS_PORT
),
355 static const int one
= 1, pmtu
= IP_PMTUDISC_DONT
, ttl
= 255;
360 if (m
->mdns_ipv4_fd
>= 0)
361 return m
->mdns_ipv4_fd
;
363 m
->mdns_ipv4_fd
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
364 if (m
->mdns_ipv4_fd
< 0)
365 return log_error_errno(errno
, "mDNS-IPv4: Failed to create socket: %m");
367 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_TTL
, &ttl
, sizeof(ttl
));
369 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_TTL: %m");
373 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_MULTICAST_TTL
, &ttl
, sizeof(ttl
));
375 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
379 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_MULTICAST_LOOP
, &one
, sizeof(one
));
381 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
385 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof(one
));
387 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
391 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof(one
));
393 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
397 /* Disable Don't-Fragment bit in the IP header */
398 r
= setsockopt(m
->mdns_ipv4_fd
, IPPROTO_IP
, IP_MTU_DISCOVER
, &pmtu
, sizeof(pmtu
));
400 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
404 /* See the section 15.1 of RFC6762 */
405 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
406 r
= bind(m
->mdns_ipv4_fd
, &sa
.sa
, sizeof(sa
.in
));
408 if (errno
!= EADDRINUSE
) {
409 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
413 log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
415 /* try again with SO_REUSEADDR */
416 r
= setsockopt(m
->mdns_ipv4_fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof(one
));
418 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
422 r
= bind(m
->mdns_ipv4_fd
, &sa
.sa
, sizeof(sa
.in
));
424 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
428 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
429 r
= setsockopt(m
->mdns_ipv4_fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof(one
));
431 r
= log_error_errno(errno
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
436 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv4_event_source
, m
->mdns_ipv4_fd
, EPOLLIN
, on_mdns_packet
, m
);
440 return m
->mdns_ipv4_fd
;
443 m
->mdns_ipv4_fd
= safe_close(m
->mdns_ipv4_fd
);
447 int manager_mdns_ipv6_fd(Manager
*m
) {
448 union sockaddr_union sa
= {
449 .in6
.sin6_family
= AF_INET6
,
450 .in6
.sin6_port
= htobe16(MDNS_PORT
),
452 static const int one
= 1, ttl
= 255;
457 if (m
->mdns_ipv6_fd
>= 0)
458 return m
->mdns_ipv6_fd
;
460 m
->mdns_ipv6_fd
= socket(AF_INET6
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
461 if (m
->mdns_ipv6_fd
< 0)
462 return log_error_errno(errno
, "mDNS-IPv6: Failed to create socket: %m");
464 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_UNICAST_HOPS
, &ttl
, sizeof(ttl
));
466 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
470 /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
471 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_MULTICAST_HOPS
, &ttl
, sizeof(ttl
));
473 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
477 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_MULTICAST_LOOP
, &one
, sizeof(one
));
479 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
483 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_V6ONLY
, &one
, sizeof(one
));
485 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
489 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_RECVPKTINFO
, &one
, sizeof(one
));
491 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
495 r
= setsockopt(m
->mdns_ipv6_fd
, IPPROTO_IPV6
, IPV6_RECVHOPLIMIT
, &one
, sizeof(one
));
497 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
501 /* See the section 15.1 of RFC6762 */
502 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
503 r
= bind(m
->mdns_ipv6_fd
, &sa
.sa
, sizeof(sa
.in6
));
505 if (errno
!= EADDRINUSE
) {
506 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
510 log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
512 /* try again with SO_REUSEADDR */
513 r
= setsockopt(m
->mdns_ipv6_fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof(one
));
515 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
519 r
= bind(m
->mdns_ipv6_fd
, &sa
.sa
, sizeof(sa
.in6
));
521 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
525 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
526 r
= setsockopt(m
->mdns_ipv6_fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof(one
));
528 r
= log_error_errno(errno
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
533 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv6_event_source
, m
->mdns_ipv6_fd
, EPOLLIN
, on_mdns_packet
, m
);
537 return m
->mdns_ipv6_fd
;
540 m
->mdns_ipv6_fd
= safe_close(m
->mdns_ipv6_fd
);