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"
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_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_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 lookup 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, 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_our_packet(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 or .in-addr.arpa,
293 * we assume someone's playing tricks on us and discard the packet completely. */
294 if (!(dns_name_endswith(name
, "in-addr.arpa") > 0 ||
295 dns_name_endswith(name
, "local") > 0))
299 log_debug("Got a goodbye packet");
300 /* See the section 10.1 of RFC6762 */
304 t
= dns_scope_find_transaction(scope
, rr
->key
, false);
306 dns_transaction_process_reply(t
, p
);
308 /* Also look for the various types of ANY transactions */
309 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(rr
->key
->class, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
311 dns_transaction_process_reply(t
, p
);
313 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, rr
->key
->type
, dns_resource_key_name(rr
->key
)), false);
315 dns_transaction_process_reply(t
, p
);
317 t
= dns_scope_find_transaction(scope
, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY
, DNS_TYPE_ANY
, dns_resource_key_name(rr
->key
)), false);
319 dns_transaction_process_reply(t
, p
);
322 dns_cache_put(&scope
->cache
, scope
->manager
->enable_cache
, NULL
, DNS_PACKET_RCODE(p
), p
->answer
, false, (uint32_t) -1, 0, p
->family
, &p
->sender
);
324 } else if (dns_packet_validate_query(p
) > 0) {
325 log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p
));
327 r
= mdns_scope_process_query(scope
, p
);
329 log_debug_errno(r
, "mDNS query processing failed: %m");
333 log_debug("Invalid mDNS UDP packet.");
338 int manager_mdns_ipv4_fd(Manager
*m
) {
339 union sockaddr_union sa
= {
340 .in
.sin_family
= AF_INET
,
341 .in
.sin_port
= htobe16(MDNS_PORT
),
343 _cleanup_close_
int s
= -1;
348 if (m
->mdns_ipv4_fd
>= 0)
349 return m
->mdns_ipv4_fd
;
351 s
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
353 return log_error_errno(errno
, "mDNS-IPv4: Failed to create socket: %m");
355 r
= setsockopt_int(s
, IPPROTO_IP
, IP_TTL
, 255);
357 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_TTL: %m");
359 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_TTL
, 255);
361 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
363 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MULTICAST_LOOP
, true);
365 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
367 r
= setsockopt_int(s
, IPPROTO_IP
, IP_PKTINFO
, true);
369 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
371 r
= setsockopt_int(s
, IPPROTO_IP
, IP_RECVTTL
, true);
373 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
375 /* Disable Don't-Fragment bit in the IP header */
376 r
= setsockopt_int(s
, IPPROTO_IP
, IP_MTU_DISCOVER
, IP_PMTUDISC_DONT
);
378 return log_error_errno(r
, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
380 /* See the section 15.1 of RFC6762 */
381 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
382 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
384 if (errno
!= EADDRINUSE
)
385 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
387 log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
389 /* try again with SO_REUSEADDR */
390 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
392 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
394 r
= bind(s
, &sa
.sa
, sizeof(sa
.in
));
396 return log_error_errno(errno
, "mDNS-IPv4: Failed to bind socket: %m");
398 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
399 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
401 return log_error_errno(r
, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
404 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv4_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
406 return log_error_errno(r
, "mDNS-IPv4: Failed to create event source: %m");
408 return m
->mdns_ipv4_fd
= TAKE_FD(s
);
411 int manager_mdns_ipv6_fd(Manager
*m
) {
412 union sockaddr_union sa
= {
413 .in6
.sin6_family
= AF_INET6
,
414 .in6
.sin6_port
= htobe16(MDNS_PORT
),
416 _cleanup_close_
int s
= -1;
421 if (m
->mdns_ipv6_fd
>= 0)
422 return m
->mdns_ipv6_fd
;
424 s
= socket(AF_INET6
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
426 return log_error_errno(errno
, "mDNS-IPv6: Failed to create socket: %m");
428 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_UNICAST_HOPS
, 255);
430 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
432 /* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
433 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_HOPS
, 255);
435 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
437 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_MULTICAST_LOOP
, true);
439 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
441 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_V6ONLY
, true);
443 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
445 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVPKTINFO
, true);
447 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
449 r
= setsockopt_int(s
, IPPROTO_IPV6
, IPV6_RECVHOPLIMIT
, true);
451 return log_error_errno(r
, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
453 /* See the section 15.1 of RFC6762 */
454 /* first try to bind without SO_REUSEADDR to detect another mDNS responder */
455 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
457 if (errno
!= EADDRINUSE
)
458 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
460 log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
462 /* try again with SO_REUSEADDR */
463 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
465 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
467 r
= bind(s
, &sa
.sa
, sizeof(sa
.in6
));
469 return log_error_errno(errno
, "mDNS-IPv6: Failed to bind socket: %m");
471 /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
472 r
= setsockopt_int(s
, SOL_SOCKET
, SO_REUSEADDR
, true);
474 return log_error_errno(r
, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
477 r
= sd_event_add_io(m
->event
, &m
->mdns_ipv6_event_source
, s
, EPOLLIN
, on_mdns_packet
, m
);
479 return log_error_errno(r
, "mDNS-IPv6: Failed to create event source: %m");
481 return m
->mdns_ipv6_fd
= TAKE_FD(s
);