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1 | /* SPDX-License-Identifier: LGPL-2.1-or-later */ | |
2 | ||
3 | #include <resolv.h> | |
4 | #include <netinet/in.h> | |
5 | #include <arpa/inet.h> | |
6 | ||
7 | #include "alloc-util.h" | |
8 | #include "fd-util.h" | |
9 | #include "resolved-manager.h" | |
10 | #include "resolved-mdns.h" | |
11 | #include "sort-util.h" | |
12 | ||
13 | #define CLEAR_CACHE_FLUSH(x) (~MDNS_RR_CACHE_FLUSH & (x)) | |
14 | ||
15 | void manager_mdns_stop(Manager *m) { | |
16 | assert(m); | |
17 | ||
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); | |
20 | ||
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); | |
23 | } | |
24 | ||
25 | int manager_mdns_start(Manager *m) { | |
26 | int r; | |
27 | ||
28 | assert(m); | |
29 | ||
30 | if (m->mdns_support == RESOLVE_SUPPORT_NO) | |
31 | return 0; | |
32 | ||
33 | r = manager_mdns_ipv4_fd(m); | |
34 | if (r == -EADDRINUSE) | |
35 | goto eaddrinuse; | |
36 | if (r < 0) | |
37 | return r; | |
38 | ||
39 | if (socket_ipv6_is_supported()) { | |
40 | r = manager_mdns_ipv6_fd(m); | |
41 | if (r == -EADDRINUSE) | |
42 | goto eaddrinuse; | |
43 | if (r < 0) | |
44 | return r; | |
45 | } | |
46 | ||
47 | return 0; | |
48 | ||
49 | eaddrinuse: | |
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; | |
52 | manager_mdns_stop(m); | |
53 | ||
54 | return 0; | |
55 | } | |
56 | ||
57 | static int mdns_rr_compare(DnsResourceRecord * const *a, DnsResourceRecord * const *b) { | |
58 | DnsResourceRecord *x = *(DnsResourceRecord **) a, *y = *(DnsResourceRecord **) b; | |
59 | size_t m; | |
60 | int r; | |
61 | ||
62 | assert(x); | |
63 | assert(y); | |
64 | ||
65 | r = CMP(CLEAR_CACHE_FLUSH(x->key->class), CLEAR_CACHE_FLUSH(y->key->class)); | |
66 | if (r != 0) | |
67 | return r; | |
68 | ||
69 | r = CMP(x->key->type, y->key->type); | |
70 | if (r != 0) | |
71 | return r; | |
72 | ||
73 | r = dns_resource_record_to_wire_format(x, false); | |
74 | if (r < 0) { | |
75 | log_warning_errno(r, "Can't wire-format RR: %m"); | |
76 | return 0; | |
77 | } | |
78 | ||
79 | r = dns_resource_record_to_wire_format(y, false); | |
80 | if (r < 0) { | |
81 | log_warning_errno(r, "Can't wire-format RR: %m"); | |
82 | return 0; | |
83 | } | |
84 | ||
85 | m = MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y)); | |
86 | ||
87 | r = memcmp(DNS_RESOURCE_RECORD_RDATA(x), DNS_RESOURCE_RECORD_RDATA(y), m); | |
88 | if (r != 0) | |
89 | return r; | |
90 | ||
91 | return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y)); | |
92 | } | |
93 | ||
94 | static int proposed_rrs_cmp(DnsResourceRecord **x, unsigned x_size, DnsResourceRecord **y, unsigned y_size) { | |
95 | unsigned m; | |
96 | int r; | |
97 | ||
98 | m = MIN(x_size, y_size); | |
99 | for (unsigned i = 0; i < m; i++) { | |
100 | r = mdns_rr_compare(&x[i], &y[i]); | |
101 | if (r != 0) | |
102 | return r; | |
103 | } | |
104 | ||
105 | return CMP(x_size, y_size); | |
106 | } | |
107 | ||
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; | |
111 | int r; | |
112 | ||
113 | assert(p); | |
114 | assert(key); | |
115 | assert(ret_rrs); | |
116 | assert_return(DNS_PACKET_NSCOUNT(p) > 0, -EINVAL); | |
117 | ||
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); | |
120 | if (r < 0) | |
121 | return r; | |
122 | if (r > 0) | |
123 | size++; | |
124 | } | |
125 | ||
126 | if (size == 0) | |
127 | return 0; | |
128 | ||
129 | list = new(DnsResourceRecord *, size); | |
130 | if (!list) | |
131 | return -ENOMEM; | |
132 | ||
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); | |
135 | if (r < 0) | |
136 | return r; | |
137 | if (r > 0) | |
138 | list[n++] = p->answer->items[i].rr; | |
139 | } | |
140 | assert(n == size); | |
141 | typesafe_qsort(list, size, mdns_rr_compare); | |
142 | ||
143 | *ret_rrs = TAKE_PTR(list); | |
144 | ||
145 | return size; | |
146 | } | |
147 | ||
148 | static int mdns_do_tiebreak(DnsResourceKey *key, DnsAnswer *answer, DnsPacket *p) { | |
149 | _cleanup_free_ DnsResourceRecord **our = NULL, **remote = NULL; | |
150 | DnsResourceRecord *rr; | |
151 | size_t i = 0, size; | |
152 | int r; | |
153 | ||
154 | size = dns_answer_size(answer); | |
155 | our = new(DnsResourceRecord *, size); | |
156 | if (!our) | |
157 | return -ENOMEM; | |
158 | ||
159 | DNS_ANSWER_FOREACH(rr, answer) | |
160 | our[i++] = rr; | |
161 | ||
162 | typesafe_qsort(our, size, mdns_rr_compare); | |
163 | ||
164 | r = mdns_packet_extract_matching_rrs(p, key, &remote); | |
165 | if (r < 0) | |
166 | return r; | |
167 | ||
168 | assert(r > 0); | |
169 | ||
170 | if (proposed_rrs_cmp(remote, r, our, size) > 0) | |
171 | return 1; | |
172 | ||
173 | return 0; | |
174 | } | |
175 | ||
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; | |
182 | int r; | |
183 | ||
184 | assert(s); | |
185 | assert(p); | |
186 | ||
187 | r = dns_packet_extract(p); | |
188 | if (r < 0) | |
189 | return log_debug_errno(r, "Failed to extract resource records from incoming packet: %m"); | |
190 | ||
191 | assert_return((dns_question_size(p->question) > 0), -EINVAL); | |
192 | ||
193 | DNS_QUESTION_FOREACH(key, p->question) { | |
194 | _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL; | |
195 | ||
196 | r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative); | |
197 | if (r < 0) | |
198 | return log_debug_errno(r, "Failed to look up key: %m"); | |
199 | ||
200 | if (tentative && DNS_PACKET_NSCOUNT(p) > 0) { | |
201 | /* | |
202 | * A race condition detected with the probe packet from | |
203 | * a remote host. | |
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. | |
207 | */ | |
208 | r = mdns_do_tiebreak(key, answer, p); | |
209 | if (r < 0) | |
210 | return log_debug_errno(r, "Failed to do tiebreaking"); | |
211 | ||
212 | if (r > 0) { /* we lost */ | |
213 | DNS_ANSWER_FOREACH(rr, answer) { | |
214 | DnsZoneItem *i; | |
215 | ||
216 | i = dns_zone_get(&s->zone, rr); | |
217 | if (i) | |
218 | dns_zone_item_conflict(i); | |
219 | } | |
220 | ||
221 | continue; | |
222 | } | |
223 | } | |
224 | ||
225 | r = dns_answer_extend(&full_answer, answer); | |
226 | if (r < 0) | |
227 | return log_debug_errno(r, "Failed to extend answer: %m"); | |
228 | } | |
229 | ||
230 | if (dns_answer_isempty(full_answer)) | |
231 | return 0; | |
232 | ||
233 | r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, NULL, full_answer, NULL, false, &reply); | |
234 | if (r < 0) | |
235 | return log_debug_errno(r, "Failed to build reply packet: %m"); | |
236 | ||
237 | if (!ratelimit_below(&s->ratelimit)) | |
238 | return 0; | |
239 | ||
240 | r = dns_scope_emit_udp(s, -1, AF_UNSPEC, reply); | |
241 | if (r < 0) | |
242 | return log_debug_errno(r, "Failed to send reply packet: %m"); | |
243 | ||
244 | return 0; | |
245 | } | |
246 | ||
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; | |
250 | DnsScope *scope; | |
251 | int r; | |
252 | ||
253 | r = manager_recv(m, fd, DNS_PROTOCOL_MDNS, &p); | |
254 | if (r <= 0) | |
255 | return r; | |
256 | ||
257 | if (manager_packet_from_local_address(m, p)) | |
258 | return 0; | |
259 | ||
260 | scope = manager_find_scope(m, p); | |
261 | if (!scope) { | |
262 | log_debug("Got mDNS UDP packet on unknown scope. Ignoring."); | |
263 | return 0; | |
264 | } | |
265 | ||
266 | if (dns_packet_validate_reply(p) > 0) { | |
267 | DnsResourceRecord *rr; | |
268 | ||
269 | log_debug("Got mDNS reply packet"); | |
270 | ||
271 | /* | |
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. | |
276 | * | |
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. | |
279 | */ | |
280 | r = dns_packet_extract(p); | |
281 | if (r < 0) { | |
282 | log_debug("mDNS packet extraction failed."); | |
283 | return 0; | |
284 | } | |
285 | ||
286 | dns_scope_check_conflicts(scope, p); | |
287 | ||
288 | DNS_ANSWER_FOREACH(rr, p->answer) { | |
289 | const char *name = dns_resource_key_name(rr->key); | |
290 | DnsTransaction *t; | |
291 | ||
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)) | |
298 | return 0; | |
299 | ||
300 | if (rr->ttl == 0) { | |
301 | log_debug("Got a goodbye packet"); | |
302 | /* See the section 10.1 of RFC6762 */ | |
303 | rr->ttl = 1; | |
304 | } | |
305 | ||
306 | t = dns_scope_find_transaction(scope, rr->key, SD_RESOLVED_NO_CACHE|SD_RESOLVED_NO_ZONE); | |
307 | if (t) | |
308 | dns_transaction_process_reply(t, p, false); | |
309 | ||
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); | |
312 | if (t) | |
313 | dns_transaction_process_reply(t, p, false); | |
314 | ||
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); | |
316 | if (t) | |
317 | dns_transaction_process_reply(t, p, false); | |
318 | ||
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); | |
320 | if (t) | |
321 | dns_transaction_process_reply(t, p, false); | |
322 | } | |
323 | ||
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); | |
325 | ||
326 | } else if (dns_packet_validate_query(p) > 0) { | |
327 | log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p)); | |
328 | ||
329 | r = mdns_scope_process_query(scope, p); | |
330 | if (r < 0) { | |
331 | log_debug_errno(r, "mDNS query processing failed: %m"); | |
332 | return 0; | |
333 | } | |
334 | } else | |
335 | log_debug("Invalid mDNS UDP packet."); | |
336 | ||
337 | return 0; | |
338 | } | |
339 | ||
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), | |
344 | }; | |
345 | _cleanup_close_ int s = -1; | |
346 | int r; | |
347 | ||
348 | assert(m); | |
349 | ||
350 | if (m->mdns_ipv4_fd >= 0) | |
351 | return m->mdns_ipv4_fd; | |
352 | ||
353 | s = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); | |
354 | if (s < 0) | |
355 | return log_error_errno(errno, "mDNS-IPv4: Failed to create socket: %m"); | |
356 | ||
357 | r = setsockopt_int(s, IPPROTO_IP, IP_TTL, 255); | |
358 | if (r < 0) | |
359 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_TTL: %m"); | |
360 | ||
361 | r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_TTL, 255); | |
362 | if (r < 0) | |
363 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m"); | |
364 | ||
365 | r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_LOOP, true); | |
366 | if (r < 0) | |
367 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m"); | |
368 | ||
369 | r = setsockopt_int(s, IPPROTO_IP, IP_PKTINFO, true); | |
370 | if (r < 0) | |
371 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_PKTINFO: %m"); | |
372 | ||
373 | r = setsockopt_int(s, IPPROTO_IP, IP_RECVTTL, true); | |
374 | if (r < 0) | |
375 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_RECVTTL: %m"); | |
376 | ||
377 | /* Disable Don't-Fragment bit in the IP header */ | |
378 | r = setsockopt_int(s, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DONT); | |
379 | if (r < 0) | |
380 | return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m"); | |
381 | ||
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)); | |
385 | if (r < 0) { | |
386 | if (errno != EADDRINUSE) | |
387 | return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m"); | |
388 | ||
389 | log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers."); | |
390 | ||
391 | /* try again with SO_REUSEADDR */ | |
392 | r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); | |
393 | if (r < 0) | |
394 | return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m"); | |
395 | ||
396 | r = bind(s, &sa.sa, sizeof(sa.in)); | |
397 | if (r < 0) | |
398 | return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m"); | |
399 | } else { | |
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); | |
402 | if (r < 0) | |
403 | return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m"); | |
404 | } | |
405 | ||
406 | r = sd_event_add_io(m->event, &m->mdns_ipv4_event_source, s, EPOLLIN, on_mdns_packet, m); | |
407 | if (r < 0) | |
408 | return log_error_errno(r, "mDNS-IPv4: Failed to create event source: %m"); | |
409 | ||
410 | return m->mdns_ipv4_fd = TAKE_FD(s); | |
411 | } | |
412 | ||
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), | |
417 | }; | |
418 | _cleanup_close_ int s = -1; | |
419 | int r; | |
420 | ||
421 | assert(m); | |
422 | ||
423 | if (m->mdns_ipv6_fd >= 0) | |
424 | return m->mdns_ipv6_fd; | |
425 | ||
426 | s = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); | |
427 | if (s < 0) | |
428 | return log_error_errno(errno, "mDNS-IPv6: Failed to create socket: %m"); | |
429 | ||
430 | r = setsockopt_int(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, 255); | |
431 | if (r < 0) | |
432 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m"); | |
433 | ||
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); | |
436 | if (r < 0) | |
437 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m"); | |
438 | ||
439 | r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, true); | |
440 | if (r < 0) | |
441 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m"); | |
442 | ||
443 | r = setsockopt_int(s, IPPROTO_IPV6, IPV6_V6ONLY, true); | |
444 | if (r < 0) | |
445 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m"); | |
446 | ||
447 | r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVPKTINFO, true); | |
448 | if (r < 0) | |
449 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m"); | |
450 | ||
451 | r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, true); | |
452 | if (r < 0) | |
453 | return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m"); | |
454 | ||
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)); | |
458 | if (r < 0) { | |
459 | if (errno != EADDRINUSE) | |
460 | return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m"); | |
461 | ||
462 | log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers."); | |
463 | ||
464 | /* try again with SO_REUSEADDR */ | |
465 | r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); | |
466 | if (r < 0) | |
467 | return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m"); | |
468 | ||
469 | r = bind(s, &sa.sa, sizeof(sa.in6)); | |
470 | if (r < 0) | |
471 | return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m"); | |
472 | } else { | |
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); | |
475 | if (r < 0) | |
476 | return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m"); | |
477 | } | |
478 | ||
479 | r = sd_event_add_io(m->event, &m->mdns_ipv6_event_source, s, EPOLLIN, on_mdns_packet, m); | |
480 | if (r < 0) | |
481 | return log_error_errno(r, "mDNS-IPv6: Failed to create event source: %m"); | |
482 | ||
483 | return m->mdns_ipv6_fd = TAKE_FD(s); | |
484 | } |