| /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
| |
| #include <resolv.h> |
| #include <netinet/in.h> |
| #include <arpa/inet.h> |
| |
| #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); |
| } |
