/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include "errno-util.h" #include "fd-util.h" #include "missing_network.h" #include "missing_socket.h" #include "resolved-dns-stub.h" #include "socket-netlink.h" #include "socket-util.h" #include "string-table.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) /* On the extra stubs, use a more conservative choice */ #define ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX DNS_PACKET_UNICAST_SIZE_LARGE_MAX static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type); static void dns_stub_listener_extra_hash_func(const DnsStubListenerExtra *a, struct siphash *state) { assert(a); siphash24_compress(&a->mode, sizeof(a->mode), state); siphash24_compress(&a->family, sizeof(a->family), state); siphash24_compress(&a->address, FAMILY_ADDRESS_SIZE(a->family), state); siphash24_compress(&a->port, sizeof(a->port), state); } static int dns_stub_listener_extra_compare_func(const DnsStubListenerExtra *a, const DnsStubListenerExtra *b) { int r; assert(a); assert(b); r = CMP(a->mode, b->mode); if (r != 0) return r; r = CMP(a->family, b->family); if (r != 0) return r; r = memcmp(&a->address, &b->address, FAMILY_ADDRESS_SIZE(a->family)); if (r != 0) return r; return CMP(a->port, b->port); } DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR( dns_stub_listener_extra_hash_ops, DnsStubListenerExtra, dns_stub_listener_extra_hash_func, dns_stub_listener_extra_compare_func, dns_stub_listener_extra_free); int dns_stub_listener_extra_new( Manager *m, DnsStubListenerExtra **ret) { DnsStubListenerExtra *l; l = new(DnsStubListenerExtra, 1); if (!l) return -ENOMEM; *l = (DnsStubListenerExtra) { .manager = m, }; *ret = TAKE_PTR(l); return 0; } DnsStubListenerExtra *dns_stub_listener_extra_free(DnsStubListenerExtra *p) { if (!p) return NULL; p->udp_event_source = sd_event_source_unref(p->udp_event_source); p->tcp_event_source = sd_event_source_unref(p->tcp_event_source); return mfree(p); } 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? */ uint16_t max_udp_size) { /* The maximum UDP datagram size to advertise to clients */ int r; assert(p); if (add_opt) { r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, 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, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p, DnsPacket *reply) { int r; assert(m); assert(p); assert(reply); if (s) r = dns_stream_write_packet(s, reply); else /* 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, manager_dns_stub_fd_extra(m, l, SOCK_DGRAM), l ? p->ifindex : LOOPBACK_IFINDEX, /* force loopback iface if this is the main listener stub */ 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, DnsStubListenerExtra *l, 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, /* truncated = */ false, !!p->opt, DNS_PACKET_DO(p), authenticated, l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX); if (r < 0) return log_debug_errno(r, "Failed to build failure packet: %m"); return dns_stub_send(m, l, 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->stub_listener_extra, 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), q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX); if (r < 0) { log_debug_errno(r, "Failed to finish reply packet: %m"); break; } (void) dns_stub_send(q->manager, q->stub_listener_extra, 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->stub_listener_extra, 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->stub_listener_extra, 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->stub_listener_extra, 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, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) { _cleanup_(dns_query_freep) DnsQuery *q = NULL; int r; assert(m); assert(p); assert(p->protocol == DNS_PROTOCOL_DNS); if (!l && /* l == NULL if this is the main stub */ (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, l, s, p, DNS_RCODE_SERVFAIL, false); return; } 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, l, s, p, DNS_RCODE_FORMERR, false); return; } if (!DNS_PACKET_VERSION_SUPPORTED(p)) { log_debug("Got EDNS OPT field with unsupported version number."); dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false); return; } if (dns_type_is_obsolete(p->question->keys[0]->type)) { log_debug("Got message with obsolete key type, refusing."); dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false); return; } if (dns_type_is_zone_transer(p->question->keys[0]->type)) { log_debug("Got request for zone transfer, refusing."); dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false); return; } 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, l, s, p, DNS_RCODE_REFUSED, false); return; } if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) { log_debug("Got request with DNSSEC CD bit set, refusing."); dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false); return; } 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, l, s, p, DNS_RCODE_SERVFAIL, false); return; } /* 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->stub_listener_extra = l; 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_put(&s->queries, NULL, q); if (r < 0) { log_oom(); return; } assert(r > 0); } r = dns_query_go(q); if (r < 0) { log_error_errno(r, "Failed to start query: %m"); dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false); return; } log_debug("Processing query..."); TAKE_PTR(q); } static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) { _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; 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, l, NULL, p); } else log_debug("Invalid DNS stub UDP packet, ignoring."); return 0; } static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) { return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL); } static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) { DnsStubListenerExtra *l = userdata; assert(l); return on_dns_stub_packet_internal(s, fd, revents, l->manager, l); } 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->stub_listener_extra, s, p); } else log_debug("Invalid DNS stub TCP packet, ignoring."); return 0; } static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) { DnsStream *stream; 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->stub_listener_extra = l; 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 on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) { return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL); } static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) { DnsStubListenerExtra *l = userdata; assert(l); return on_dns_stub_stream_internal(s, fd, revents, l->manager, l); } static int set_dns_stub_common_socket_options(int fd, int family) { int r; assert(fd >= 0); assert(IN_SET(family, AF_INET, AF_INET6)); r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true); if (r < 0) return r; r = socket_set_recvpktinfo(fd, family, true); if (r < 0) return r; r = socket_set_recvttl(fd, family, true); if (r < 0) return r; return 0; } static int manager_dns_stub_fd(Manager *m, int type) { 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; assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM)); sd_event_source **event_source = type == SOCK_DGRAM ? &m->dns_stub_udp_event_source : &m->dns_stub_tcp_event_source; if (*event_source) return sd_event_source_get_io_fd(*event_source); fd = socket(AF_INET, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0); if (fd < 0) return -errno; r = set_dns_stub_common_socket_options(fd, AF_INET); 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; r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, 1); if (r < 0) return r; if (bind(fd, &sa.sa, sizeof(sa.in)) < 0) return -errno; if (type == SOCK_STREAM && listen(fd, SOMAXCONN) < 0) return -errno; r = sd_event_add_io(m->event, event_source, fd, EPOLLIN, type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream, m); if (r < 0) return r; r = sd_event_source_set_io_fd_own(*event_source, true); if (r < 0) return r; (void) sd_event_source_set_description(*event_source, type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp"); return TAKE_FD(fd); } static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) { _cleanup_free_ char *pretty = NULL; _cleanup_close_ int fd = -1; union sockaddr_union sa; int r; assert(m); assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM)); if (!l) return manager_dns_stub_fd(m, type); sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source; if (*event_source) return sd_event_source_get_io_fd(*event_source); if (l->family == AF_INET) sa = (union sockaddr_union) { .in.sin_family = l->family, .in.sin_port = htobe16(l->port != 0 ? l->port : 53U), .in.sin_addr = l->address.in, }; else sa = (union sockaddr_union) { .in6.sin6_family = l->family, .in6.sin6_port = htobe16(l->port != 0 ? l->port : 53U), .in6.sin6_addr = l->address.in6, }; fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0); if (fd < 0) { r = -errno; goto fail; } r = set_dns_stub_common_socket_options(fd, l->family); if (r < 0) goto fail; /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case * people may want ttl > 1. */ r = socket_set_freebind(fd, l->family, true); if (r < 0) goto fail; if (bind(fd, &sa.sa, SOCKADDR_LEN(sa)) < 0) { r = -errno; goto fail; } if (type == SOCK_STREAM && listen(fd, SOMAXCONN) < 0) { r = -errno; goto fail; } r = sd_event_add_io(m->event, event_source, fd, EPOLLIN, type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra, l); if (r < 0) goto fail; r = sd_event_source_set_io_fd_own(*event_source, true); if (r < 0) goto fail; (void) sd_event_source_set_description(*event_source, type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra"); if (DEBUG_LOGGING) { (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty); log_debug("Listening on %s socket %s.", type == SOCK_DGRAM ? "UDP" : "TCP", strnull(pretty)); } return TAKE_FD(fd); fail: assert(r < 0); (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty); return log_warning_errno(r, r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" : "Failed to listen on %s socket %s: %m", type == SOCK_DGRAM ? "UDP" : "TCP", strnull(pretty)); } 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 (FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_UDP)) r = manager_dns_stub_fd(m, SOCK_DGRAM); if (r >= 0 && FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_TCP)) { t = "TCP"; r = manager_dns_stub_fd(m, SOCK_STREAM); } if (IN_SET(r, -EADDRINUSE, -EPERM)) { log_warning_errno(r, r == -EADDRINUSE ? "Another process is already listening on %s socket 127.0.0.53:53.\n" "Turning off local DNS stub support." : "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); if (!ordered_set_isempty(m->dns_extra_stub_listeners)) { DnsStubListenerExtra *l; log_debug("Creating extra stub listeners."); ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) { if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP)) (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM); if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP)) (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM); } } 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); } static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = { [DNS_STUB_LISTENER_NO] = "no", [DNS_STUB_LISTENER_UDP] = "udp", [DNS_STUB_LISTENER_TCP] = "tcp", [DNS_STUB_LISTENER_YES] = "yes", }; DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);