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-rw-r--r--src/resolve/resolved-mdns.c613
1 files changed, 613 insertions, 0 deletions
diff --git a/src/resolve/resolved-mdns.c b/src/resolve/resolved-mdns.c
new file mode 100644
index 0000000..f5f1560
--- /dev/null
+++ b/src/resolve/resolved-mdns.c
@@ -0,0 +1,613 @@
+/* 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_enabled()) {
+ 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");
+
+ /* TODO: Support Known-Answers only packets gracefully. */
+ if (dns_question_size(p->question) <= 0)
+ return 0;
+
+ 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 = -1;
+ 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 = -1;
+ 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);
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-19 14:29:13 +0000