/* SPDX-License-Identifier: LGPL-2.1+ */ #include "errno-util.h" #include "fd-util.h" #include "missing_network.h" #include "resolved-dns-stub.h" #include "socket-util.h" /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet, * IP and UDP header sizes */ #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U) static int manager_dns_stub_udp_fd(Manager *m); static int manager_dns_stub_tcp_fd(Manager *m); static int dns_stub_make_reply_packet( DnsPacket **p, size_t max_size, DnsQuestion *q, DnsAnswer *answer, bool *ret_truncated) { bool truncated = false; DnsResourceRecord *rr; unsigned c = 0; int r; assert(p); /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence * roundtrips aren't expensive. */ if (!*p) { r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0, max_size); if (r < 0) return r; r = dns_packet_append_question(*p, q); if (r < 0) return r; DNS_PACKET_HEADER(*p)->qdcount = htobe16(dns_question_size(q)); } DNS_ANSWER_FOREACH(rr, answer) { r = dns_question_matches_rr(q, rr, NULL); if (r < 0) return r; if (r > 0) goto add; r = dns_question_matches_cname_or_dname(q, rr, NULL); if (r < 0) return r; if (r > 0) goto add; continue; add: r = dns_packet_append_rr(*p, rr, 0, NULL, NULL); if (r == -EMSGSIZE) { truncated = true; break; } if (r < 0) return r; c++; } if (ret_truncated) *ret_truncated = truncated; else if (truncated) return -EMSGSIZE; DNS_PACKET_HEADER(*p)->ancount = htobe16(be16toh(DNS_PACKET_HEADER(*p)->ancount) + c); return 0; } static int dns_stub_finish_reply_packet( DnsPacket *p, uint16_t id, int rcode, bool tc, /* set the Truncated bit? */ bool add_opt, /* add an OPT RR to this packet? */ bool edns0_do, /* set the EDNS0 DNSSEC OK bit? */ bool ad) { /* set the DNSSEC authenticated data bit? */ int r; assert(p); if (add_opt) { r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL); if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */ tc = true; else if (r < 0) return r; } else { /* If the client can't to EDNS0, don't do DO either */ edns0_do = false; /* If the client didn't do EDNS, clamp the rcode to 4 bit */ if (rcode > 0xF) rcode = DNS_RCODE_SERVFAIL; } /* Don't set the AD bit unless DO is on, too */ if (!edns0_do) ad = false; DNS_PACKET_HEADER(p)->id = id; DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS( 1 /* qr */, 0 /* opcode */, 0 /* aa */, tc /* tc */, 1 /* rd */, 1 /* ra */, ad /* ad */, 0 /* cd */, rcode)); return 0; } static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) { int r; assert(m); assert(p); assert(reply); if (s) r = dns_stream_write_packet(s, reply); else { int fd; fd = manager_dns_stub_udp_fd(m); if (fd < 0) return log_debug_errno(fd, "Failed to get reply socket: %m"); /* Note that it is essential here that we explicitly choose the source IP address for this packet. This * is because otherwise the kernel will choose it automatically based on the routing table and will * thus pick 127.0.0.1 rather than 127.0.0.53. */ r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply); } if (r < 0) return log_debug_errno(r, "Failed to send reply packet: %m"); return 0; } static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode, bool authenticated) { _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; int r; assert(m); assert(p); r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL); if (r < 0) return log_debug_errno(r, "Failed to make failure packet: %m"); r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, false, !!p->opt, DNS_PACKET_DO(p), authenticated); if (r < 0) return log_debug_errno(r, "Failed to build failure packet: %m"); return dns_stub_send(m, s, p, reply); } static void dns_stub_query_complete(DnsQuery *q) { int r; assert(q); assert(q->request_dns_packet); switch (q->state) { case DNS_TRANSACTION_SUCCESS: { bool truncated; r = dns_stub_make_reply_packet(&q->reply_dns_packet, DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_dns_packet), q->question_idna, q->answer, &truncated); if (r < 0) { log_debug_errno(r, "Failed to build reply packet: %m"); break; } if (!truncated) { r = dns_query_process_cname(q); if (r == -ELOOP) { (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false); break; } if (r < 0) { log_debug_errno(r, "Failed to process CNAME: %m"); break; } if (r == DNS_QUERY_RESTARTED) return; } r = dns_stub_finish_reply_packet( q->reply_dns_packet, DNS_PACKET_ID(q->request_dns_packet), q->answer_rcode, truncated, !!q->request_dns_packet->opt, DNS_PACKET_DO(q->request_dns_packet), dns_query_fully_authenticated(q)); if (r < 0) { log_debug_errno(r, "Failed to finish reply packet: %m"); break; } (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet); break; } case DNS_TRANSACTION_RCODE_FAILURE: (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q)); break; case DNS_TRANSACTION_NOT_FOUND: (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q)); break; case DNS_TRANSACTION_TIMEOUT: case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED: /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */ break; case DNS_TRANSACTION_NO_SERVERS: case DNS_TRANSACTION_INVALID_REPLY: case DNS_TRANSACTION_ERRNO: case DNS_TRANSACTION_ABORTED: case DNS_TRANSACTION_DNSSEC_FAILED: case DNS_TRANSACTION_NO_TRUST_ANCHOR: case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED: case DNS_TRANSACTION_NETWORK_DOWN: (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false); break; case DNS_TRANSACTION_NULL: case DNS_TRANSACTION_PENDING: case DNS_TRANSACTION_VALIDATING: default: assert_not_reached("Impossible state"); } dns_query_free(q); } static int dns_stub_stream_complete(DnsStream *s, int error) { assert(s); log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m"); for (;;) { DnsQuery *q; q = set_first(s->queries); if (!q) break; dns_query_free(q); } /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections * should be kept as long as the client wants to. */ dns_stream_unref(s); return 0; } static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) { DnsQuery *q = NULL; int r; assert(m); assert(p); assert(p->protocol == DNS_PROTOCOL_DNS); if (in_addr_is_localhost(p->family, &p->sender) <= 0 || in_addr_is_localhost(p->family, &p->destination) <= 0) { log_error("Got packet on unexpected IP range, refusing."); dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false); goto fail; } r = dns_packet_extract(p); if (r < 0) { log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m"); dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false); goto fail; } if (!DNS_PACKET_VERSION_SUPPORTED(p)) { log_debug("Got EDNS OPT field with unsupported version number."); dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false); goto fail; } if (dns_type_is_obsolete(p->question->keys[0]->type)) { log_debug("Got message with obsolete key type, refusing."); dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false); goto fail; } if (dns_type_is_zone_transer(p->question->keys[0]->type)) { log_debug("Got request for zone transfer, refusing."); dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false); goto fail; } if (!DNS_PACKET_RD(p)) { /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */ log_debug("Got request with recursion disabled, refusing."); dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false); goto fail; } if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) { log_debug("Got request with DNSSEC CD bit set, refusing."); dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false); goto fail; } r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH); if (r < 0) { log_error_errno(r, "Failed to generate query object: %m"); dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false); goto fail; } /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */ q->clamp_ttl = true; q->request_dns_packet = dns_packet_ref(p); q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */ q->complete = dns_stub_query_complete; if (s) { /* Remember which queries belong to this stream, so that we can cancel them when the stream * is disconnected early */ r = set_ensure_allocated(&s->queries, &trivial_hash_ops); if (r < 0) { log_oom(); goto fail; } if (set_put(s->queries, q) < 0) { log_oom(); goto fail; } } r = dns_query_go(q); if (r < 0) { log_error_errno(r, "Failed to start query: %m"); dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false); goto fail; } log_debug("Processing query..."); return; fail: dns_query_free(q); } static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) { _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; Manager *m = userdata; int r; r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p); if (r <= 0) return r; if (dns_packet_validate_query(p) > 0) { log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p)); dns_stub_process_query(m, NULL, p); } else log_debug("Invalid DNS stub UDP packet, ignoring."); return 0; } static int manager_dns_stub_udp_fd(Manager *m) { union sockaddr_union sa = { .in.sin_family = AF_INET, .in.sin_port = htobe16(53), .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB), }; _cleanup_close_ int fd = -1; int r; if (m->dns_stub_udp_fd >= 0) return m->dns_stub_udp_fd; fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); if (fd < 0) return -errno; r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return r; r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true); if (r < 0) return r; r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true); if (r < 0) return r; /* Make sure no traffic from outside the local host can leak to onto this socket */ r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX); if (r < 0) return r; if (bind(fd, &sa.sa, sizeof(sa.in)) < 0) return -errno; r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m); if (r < 0) return r; (void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp"); return m->dns_stub_udp_fd = TAKE_FD(fd); } static int on_dns_stub_stream_packet(DnsStream *s) { _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; assert(s); p = dns_stream_take_read_packet(s); assert(p); if (dns_packet_validate_query(p) > 0) { log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p)); dns_stub_process_query(s->manager, s, p); } else log_debug("Invalid DNS stub TCP packet, ignoring."); return 0; } static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) { DnsStream *stream; Manager *m = userdata; int cfd, r; cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC); if (cfd < 0) { if (ERRNO_IS_ACCEPT_AGAIN(errno)) return 0; return -errno; } r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL); if (r < 0) { safe_close(cfd); return r; } stream->on_packet = on_dns_stub_stream_packet; stream->complete = dns_stub_stream_complete; /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */ return 0; } static int manager_dns_stub_tcp_fd(Manager *m) { union sockaddr_union sa = { .in.sin_family = AF_INET, .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB), .in.sin_port = htobe16(53), }; _cleanup_close_ int fd = -1; int r; if (m->dns_stub_tcp_fd >= 0) return m->dns_stub_tcp_fd; fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0); if (fd < 0) return -errno; r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, true); if (r < 0) return r; r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return r; r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true); if (r < 0) return r; r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true); if (r < 0) return r; /* Make sure no traffic from outside the local host can leak to onto this socket */ r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX); if (r < 0) return r; if (bind(fd, &sa.sa, sizeof(sa.in)) < 0) return -errno; if (listen(fd, SOMAXCONN) < 0) return -errno; r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m); if (r < 0) return r; (void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp"); return m->dns_stub_tcp_fd = TAKE_FD(fd); } int manager_dns_stub_start(Manager *m) { const char *t = "UDP"; int r = 0; assert(m); if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO) log_debug("Not creating stub listener."); else log_debug("Creating stub listener using %s.", m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" : m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" : "UDP/TCP"); if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP)) r = manager_dns_stub_udp_fd(m); if (r >= 0 && IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) { t = "TCP"; r = manager_dns_stub_tcp_fd(m); } if (IN_SET(r, -EADDRINUSE, -EPERM)) { if (r == -EADDRINUSE) log_warning_errno(r, "Another process is already listening on %s socket 127.0.0.53:53.\n" "Turning off local DNS stub support.", t); else log_warning_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m.\n" "Turning off local DNS stub support.", t); manager_dns_stub_stop(m); } else if (r < 0) return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t); return 0; } void manager_dns_stub_stop(Manager *m) { assert(m); m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source); m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source); m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd); m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd); }