From 55944e5e40b1be2afc4855d8d2baf4b73d1876b5 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 10 Apr 2024 22:49:52 +0200 Subject: Adding upstream version 255.4. Signed-off-by: Daniel Baumann --- src/resolve/resolved-mdns.c | 614 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 614 insertions(+) create mode 100644 src/resolve/resolved-mdns.c (limited to 'src/resolve/resolved-mdns.c') diff --git a/src/resolve/resolved-mdns.c b/src/resolve/resolved-mdns.c new file mode 100644 index 0000000..3e6e83f --- /dev/null +++ b/src/resolve/resolved-mdns.c @@ -0,0 +1,614 @@ +/* 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_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 | DNS_ANSWER_REFUSE_TTL_NO_MATCH; + /* 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, + scope->manager->stale_retention_usec); + + } 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); +} -- cgit v1.2.3