/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include "alloc-util.h" #include "fd-util.h" #include "resolved-manager.h" #include "resolved-mdns.h" #include "sort-util.h" #define CLEAR_CACHE_FLUSH(x) (~MDNS_RR_CACHE_FLUSH_OR_QU & (x)) void manager_mdns_stop(Manager *m) { assert(m); m->mdns_ipv4_event_source = sd_event_source_disable_unref(m->mdns_ipv4_event_source); m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd); m->mdns_ipv6_event_source = sd_event_source_disable_unref(m->mdns_ipv6_event_source); m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd); } int manager_mdns_start(Manager *m) { int r; assert(m); if (m->mdns_support == RESOLVE_SUPPORT_NO) return 0; r = manager_mdns_ipv4_fd(m); if (r == -EADDRINUSE) goto eaddrinuse; if (r < 0) return r; if (socket_ipv6_is_supported()) { r = manager_mdns_ipv6_fd(m); if (r == -EADDRINUSE) goto eaddrinuse; if (r < 0) return r; } return 0; eaddrinuse: log_warning("Another mDNS responder prohibits binding the socket to the same port. Turning off mDNS support."); m->mdns_support = RESOLVE_SUPPORT_NO; manager_mdns_stop(m); return 0; } static int mdns_rr_compare(DnsResourceRecord * const *a, DnsResourceRecord * const *b) { DnsResourceRecord *x = *(DnsResourceRecord **) a, *y = *(DnsResourceRecord **) b; size_t m; int r; assert(x); assert(y); r = CMP(CLEAR_CACHE_FLUSH(x->key->class), CLEAR_CACHE_FLUSH(y->key->class)); if (r != 0) return r; r = CMP(x->key->type, y->key->type); if (r != 0) return r; r = dns_resource_record_to_wire_format(x, false); if (r < 0) { log_warning_errno(r, "Can't wire-format RR: %m"); return 0; } r = dns_resource_record_to_wire_format(y, false); if (r < 0) { log_warning_errno(r, "Can't wire-format RR: %m"); return 0; } m = MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y)); r = memcmp(DNS_RESOURCE_RECORD_RDATA(x), DNS_RESOURCE_RECORD_RDATA(y), m); if (r != 0) return r; return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y)); } static int proposed_rrs_cmp(DnsResourceRecord **x, unsigned x_size, DnsResourceRecord **y, unsigned y_size) { unsigned m; int r; m = MIN(x_size, y_size); for (unsigned i = 0; i < m; i++) { r = mdns_rr_compare(&x[i], &y[i]); if (r != 0) return r; } return CMP(x_size, y_size); } static int mdns_packet_extract_matching_rrs(DnsPacket *p, DnsResourceKey *key, DnsResourceRecord ***ret_rrs) { _cleanup_free_ DnsResourceRecord **list = NULL; size_t i, n = 0, size = 0; DnsResourceRecord *rr; int r; assert(p); assert(key); assert(ret_rrs); assert_return(DNS_PACKET_NSCOUNT(p) > 0, -EINVAL); i = 0; DNS_ANSWER_FOREACH(rr, p->answer) { if (i >= DNS_PACKET_ANCOUNT(p) && i < DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)) { r = dns_resource_key_match_rr(key, rr, NULL); if (r < 0) return r; if (r > 0) size++; } i++; } if (size == 0) { *ret_rrs = NULL; return 0; } list = new(DnsResourceRecord *, size); if (!list) return -ENOMEM; i = 0; DNS_ANSWER_FOREACH(rr, p->answer) { if (i >= DNS_PACKET_ANCOUNT(p) && i < DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)) { r = dns_resource_key_match_rr(key, rr, NULL); if (r < 0) return r; if (r > 0) list[n++] = rr; } i++; } assert(n == size); typesafe_qsort(list, size, mdns_rr_compare); *ret_rrs = TAKE_PTR(list); return size; } static int mdns_do_tiebreak(DnsResourceKey *key, DnsAnswer *answer, DnsPacket *p) { _cleanup_free_ DnsResourceRecord **our = NULL, **remote = NULL; DnsResourceRecord *rr; size_t i = 0, size; int r; size = dns_answer_size(answer); our = new(DnsResourceRecord *, size); if (!our) return -ENOMEM; DNS_ANSWER_FOREACH(rr, answer) our[i++] = rr; typesafe_qsort(our, size, mdns_rr_compare); r = mdns_packet_extract_matching_rrs(p, key, &remote); if (r < 0) return r; if (proposed_rrs_cmp(remote, r, our, size) > 0) return 1; return 0; } static bool mdns_should_reply_using_unicast(DnsPacket *p) { DnsQuestionItem *item; /* Work out if we should respond using multicast or unicast. */ /* The query was a legacy "one-shot mDNS query", RFC 6762, sections 5.1 and 6.7 */ if (p->sender_port != MDNS_PORT) return true; /* The query was a "direct unicast query", RFC 6762, section 5.5 */ switch (p->family) { case AF_INET: if (!in4_addr_equal(&p->destination.in, &MDNS_MULTICAST_IPV4_ADDRESS)) return true; break; case AF_INET6: if (!in6_addr_equal(&p->destination.in6, &MDNS_MULTICAST_IPV6_ADDRESS)) return true; break; } /* All the questions in the query had a QU bit set, RFC 6762, section 5.4 */ DNS_QUESTION_FOREACH_ITEM(item, p->question) if (!FLAGS_SET(item->flags, DNS_QUESTION_WANTS_UNICAST_REPLY)) return false; return true; } static bool sender_on_local_subnet(DnsScope *s, DnsPacket *p) { int r; /* Check whether the sender is on a local subnet. */ if (!s->link) return false; LIST_FOREACH(addresses, a, s->link->addresses) { if (a->family != p->family) continue; if (a->prefixlen == UCHAR_MAX) /* don't know subnet mask */ continue; r = in_addr_prefix_covers(a->family, &a->in_addr, a->prefixlen, &p->sender); if (r < 0) log_debug_errno(r, "Failed to determine whether link address covers sender address: %m"); if (r > 0) return true; } return false; } static int mdns_scope_process_query(DnsScope *s, DnsPacket *p) { _cleanup_(dns_answer_unrefp) DnsAnswer *full_answer = NULL; _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; DnsResourceKey *key = NULL; DnsResourceRecord *rr; bool tentative = false; bool legacy_query = p->sender_port != MDNS_PORT; bool unicast_reply; int r; assert(s); assert(p); r = dns_packet_extract(p); if (r < 0) return log_debug_errno(r, "Failed to extract resource records from incoming packet: %m"); if (dns_question_size(p->question) <= 0) return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "Received mDNS query without question, ignoring."); unicast_reply = mdns_should_reply_using_unicast(p); if (unicast_reply && !sender_on_local_subnet(s, p)) { /* RFC 6762, section 5.5 recommends silently ignoring unicast queries * from senders outside the local network, so that we don't reveal our * internal network structure to outsiders. */ log_debug("Sender wants a unicast reply, but is not on a local subnet. Ignoring."); return 0; } DNS_QUESTION_FOREACH(key, p->question) { _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL; DnsAnswerItem *item; r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative); if (r < 0) return log_debug_errno(r, "Failed to look up key: %m"); if (tentative && DNS_PACKET_NSCOUNT(p) > 0) { /* * A race condition detected with the probe packet from * a remote host. * Do simultaneous probe tiebreaking as described in * RFC 6762, Section 8.2. In case we lost don't reply * the question and withdraw conflicting RRs. */ r = mdns_do_tiebreak(key, answer, p); if (r < 0) return log_debug_errno(r, "Failed to do tiebreaking"); if (r > 0) { /* we lost */ DNS_ANSWER_FOREACH(rr, answer) { DnsZoneItem *i; i = dns_zone_get(&s->zone, rr); if (i) dns_zone_item_conflict(i); } continue; } } if (dns_answer_isempty(answer)) continue; /* Copy answer items from full_answer to answer, tweaking them if needed. */ if (full_answer) { r = dns_answer_reserve(&full_answer, dns_answer_size(answer)); if (r < 0) return log_debug_errno(r, "Failed to reserve space in answer"); } else { full_answer = dns_answer_new(dns_answer_size(answer)); if (!full_answer) return log_oom(); } DNS_ANSWER_FOREACH_ITEM(item, answer) { DnsAnswerFlags flags = item->flags; /* The cache-flush bit must not be set in legacy unicast responses. * See section 6.7 of RFC 6762. */ if (legacy_query) flags &= ~DNS_ANSWER_CACHE_FLUSH; r = dns_answer_add(full_answer, item->rr, item->ifindex, flags, item->rrsig); if (r < 0) return log_debug_errno(r, "Failed to extend answer: %m"); } } if (dns_answer_isempty(full_answer)) return 0; r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, legacy_query ? p->question : NULL, full_answer, NULL, false, &reply); if (r < 0) return log_debug_errno(r, "Failed to build reply packet: %m"); if (!ratelimit_below(&s->ratelimit)) return 0; if (unicast_reply) { reply->destination = p->sender; reply->destination_port = p->sender_port; } r = dns_scope_emit_udp(s, -1, AF_UNSPEC, reply); if (r < 0) return log_debug_errno(r, "Failed to send reply packet: %m"); return 0; } static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) { _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; Manager *m = userdata; DnsScope *scope; int r; r = manager_recv(m, fd, DNS_PROTOCOL_MDNS, &p); if (r <= 0) return r; if (manager_packet_from_local_address(m, p)) return 0; scope = manager_find_scope(m, p); if (!scope) { log_debug("Got mDNS UDP packet on unknown scope. Ignoring."); return 0; } if (dns_packet_validate_reply(p) > 0) { DnsResourceRecord *rr; log_debug("Got mDNS reply packet"); /* * mDNS is different from regular DNS and LLMNR with regard to handling responses. * While on other protocols, we can ignore every answer that doesn't match a question * we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all * incoming information, regardless of the DNS packet ID. * * Hence, extract the packet here, and try to find a transaction for answer the we got * and complete it. Also store the new information in scope's cache. */ r = dns_packet_extract(p); if (r < 0) { log_debug("mDNS packet extraction failed."); return 0; } dns_scope_check_conflicts(scope, p); DNS_ANSWER_FOREACH(rr, p->answer) { const char *name; name = dns_resource_key_name(rr->key); /* If the received reply packet contains ANY record that is not .local * or .in-addr.arpa or .ip6.arpa, we assume someone's playing tricks on * us and discard the packet completely. */ if (!(dns_name_endswith(name, "in-addr.arpa") > 0 || dns_name_endswith(name, "ip6.arpa") > 0 || dns_name_endswith(name, "local") > 0)) return 0; if (rr->ttl == 0) { log_debug("Got a goodbye packet"); /* See the section 10.1 of RFC6762 */ rr->ttl = 1; } } for (bool match = true; match;) { match = false; LIST_FOREACH(transactions_by_scope, t, scope->transactions) { if (t->state != DNS_TRANSACTION_PENDING) continue; r = dns_answer_match_key(p->answer, dns_transaction_key(t), NULL); if (r <= 0) { if (r < 0) log_debug_errno(r, "Failed to match resource key, ignoring: %m"); continue; } /* This packet matches the transaction, let's pass it on as reply */ dns_transaction_process_reply(t, p, false); /* The dns_transaction_process_reply() -> dns_transaction_complete() -> * dns_query_candidate_stop() may free multiple transactions. Hence, restart * the loop. */ match = true; break; } } dns_cache_put( &scope->cache, scope->manager->enable_cache, DNS_PROTOCOL_MDNS, NULL, DNS_PACKET_RCODE(p), p->answer, NULL, false, _DNSSEC_RESULT_INVALID, UINT32_MAX, p->family, &p->sender); } else if (dns_packet_validate_query(p) > 0) { log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p)); r = mdns_scope_process_query(scope, p); if (r < 0) { log_debug_errno(r, "mDNS query processing failed: %m"); return 0; } } else log_debug("Invalid mDNS UDP packet."); return 0; } int manager_mdns_ipv4_fd(Manager *m) { union sockaddr_union sa = { .in.sin_family = AF_INET, .in.sin_port = htobe16(MDNS_PORT), }; _cleanup_close_ int s = -EBADF; int r; assert(m); if (m->mdns_ipv4_fd >= 0) return m->mdns_ipv4_fd; s = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); if (s < 0) return log_error_errno(errno, "mDNS-IPv4: Failed to create socket: %m"); r = setsockopt_int(s, IPPROTO_IP, IP_TTL, 255); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_TTL: %m"); r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_TTL, 255); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m"); r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_LOOP, true); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m"); r = setsockopt_int(s, IPPROTO_IP, IP_PKTINFO, true); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_PKTINFO: %m"); r = setsockopt_int(s, IPPROTO_IP, IP_RECVTTL, true); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_RECVTTL: %m"); /* Disable Don't-Fragment bit in the IP header */ r = setsockopt_int(s, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DONT); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m"); /* See the section 15.1 of RFC6762 */ /* first try to bind without SO_REUSEADDR to detect another mDNS responder */ r = bind(s, &sa.sa, sizeof(sa.in)); if (r < 0) { if (errno != EADDRINUSE) return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m"); log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers."); /* try again with SO_REUSEADDR */ r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m"); r = bind(s, &sa.sa, sizeof(sa.in)); if (r < 0) return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m"); } else { /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */ r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m"); } r = sd_event_add_io(m->event, &m->mdns_ipv4_event_source, s, EPOLLIN, on_mdns_packet, m); if (r < 0) return log_error_errno(r, "mDNS-IPv4: Failed to create event source: %m"); (void) sd_event_source_set_description(m->mdns_ipv4_event_source, "mdns-ipv4"); return m->mdns_ipv4_fd = TAKE_FD(s); } int manager_mdns_ipv6_fd(Manager *m) { union sockaddr_union sa = { .in6.sin6_family = AF_INET6, .in6.sin6_port = htobe16(MDNS_PORT), }; _cleanup_close_ int s = -EBADF; int r; assert(m); if (m->mdns_ipv6_fd >= 0) return m->mdns_ipv6_fd; s = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); if (s < 0) return log_error_errno(errno, "mDNS-IPv6: Failed to create socket: %m"); r = setsockopt_int(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, 255); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m"); /* RFC 6762, section 11 recommends setting the TTL of UDP packets to 255. */ r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, 255); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m"); r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m"); r = setsockopt_int(s, IPPROTO_IPV6, IPV6_V6ONLY, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m"); r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVPKTINFO, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m"); r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m"); /* See the section 15.1 of RFC6762 */ /* first try to bind without SO_REUSEADDR to detect another mDNS responder */ r = bind(s, &sa.sa, sizeof(sa.in6)); if (r < 0) { if (errno != EADDRINUSE) return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m"); log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers."); /* try again with SO_REUSEADDR */ r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m"); r = bind(s, &sa.sa, sizeof(sa.in6)); if (r < 0) return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m"); } else { /* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */ r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m"); } r = sd_event_add_io(m->event, &m->mdns_ipv6_event_source, s, EPOLLIN, on_mdns_packet, m); if (r < 0) return log_error_errno(r, "mDNS-IPv6: Failed to create event source: %m"); (void) sd_event_source_set_description(m->mdns_ipv6_event_source, "mdns-ipv6"); return m->mdns_ipv6_fd = TAKE_FD(s); }