| /*** |
| This file is part of systemd. |
| |
| Copyright 2016 Lennart Poettering |
| |
| systemd is free software; you can redistribute it and/or modify it |
| under the terms of the GNU Lesser General Public License as published by |
| the Free Software Foundation; either version 2.1 of the License, or |
| (at your option) any later version. |
| |
| systemd is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public License |
| along with systemd; If not, see <http://www.gnu.org/licenses/>. |
| ***/ |
| |
| #include "fd-util.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, |
| DnsQuestion *q, |
| DnsAnswer *answer) { |
| |
| 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); |
| 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 < 0) |
| return r; |
| |
| c++; |
| } |
| |
| 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 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) { |
| /* 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 */, |
| 0 /* tc */, |
| 1 /* rd */, |
| 1 /* ra */, |
| ad /* ad */, |
| 0 /* cd */, |
| rcode)); |
| |
| if (add_opt) { |
| r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL); |
| if (r < 0) |
| return r; |
| } |
| |
| return 0; |
| } |
| |
| static void dns_stub_detach_stream(DnsStream *s) { |
| assert(s); |
| |
| s->complete = NULL; |
| s->on_packet = NULL; |
| s->query = NULL; |
| } |
| |
| 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; |
| |
| /* Truncate the message to the right size */ |
| if (reply->size > DNS_PACKET_PAYLOAD_SIZE_MAX(p)) { |
| dns_packet_truncate(reply, DNS_PACKET_UNICAST_SIZE_MAX); |
| DNS_PACKET_HEADER(reply)->flags = htobe16(be16toh(DNS_PACKET_HEADER(reply)->flags) | DNS_PACKET_FLAG_TC); |
| } |
| |
| 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, p->question, 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, !!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: |
| |
| r = dns_stub_make_reply_packet(&q->reply_dns_packet, q->question_idna, q->answer); |
| if (r < 0) { |
| log_debug_errno(r, "Failed to build reply packet: %m"); |
| break; |
| } |
| |
| 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, |
| !!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"); |
| } |
| |
| /* If there's a packet to write set, let's leave the stream around */ |
| if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) { |
| |
| /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The |
| * default completion action of the stream will drop the reference. */ |
| |
| dns_stub_detach_stream(q->request_dns_stream); |
| q->request_dns_stream = NULL; |
| } |
| |
| 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 query: %m"); |
| |
| assert(s->query); |
| dns_query_free(s->query); |
| |
| 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); |
| |
| /* Takes ownership of the *s stream object */ |
| |
| 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) { |
| s->on_packet = NULL; |
| s->complete = dns_stub_stream_complete; |
| s->query = q; |
| } |
| |
| 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: |
| if (s && DNS_STREAM_QUEUED(s)) |
| dns_stub_detach_stream(s); |
| |
| 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) { |
| static const int one = 1; |
| 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; |
| |
| if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0) |
| return -errno; |
| |
| if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0) |
| return -errno; |
| |
| if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0) |
| return -errno; |
| |
| /* Make sure no traffic from outside the local host can leak to onto this socket */ |
| if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0) |
| return -errno; |
| |
| 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"); |
| m->dns_stub_udp_fd = fd; |
| fd = -1; |
| |
| return m->dns_stub_udp_fd; |
| } |
| |
| static int on_dns_stub_stream_packet(DnsStream *s) { |
| assert(s); |
| assert(s->read_packet); |
| |
| if (dns_packet_validate_query(s->read_packet) > 0) { |
| log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet)); |
| |
| dns_stub_process_query(s->manager, s, s->read_packet); |
| } else |
| log_debug("Invalid DNS stub TCP packet, ignoring."); |
| |
| /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now, |
| * or that didn't happen in which case we want to free the stream */ |
| dns_stream_unref(s); |
| |
| 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 == EAGAIN || errno == EINTR) |
| return 0; |
| |
| return -errno; |
| } |
| |
| r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd); |
| if (r < 0) { |
| safe_close(cfd); |
| return r; |
| } |
| |
| stream->on_packet = on_dns_stub_stream_packet; |
| |
| /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action |
| * of the stream, or by our packet callback, or when the manager is shut down. */ |
| |
| return 0; |
| } |
| |
| static int manager_dns_stub_tcp_fd(Manager *m) { |
| static const int one = 1; |
| 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; |
| |
| if (setsockopt(fd, IPPROTO_IP, IP_TTL, &one, sizeof one) < 0) |
| return -errno; |
| |
| if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0) |
| return -errno; |
| |
| if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0) |
| return -errno; |
| |
| if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0) |
| return -errno; |
| |
| /* Make sure no traffic from outside the local host can leak to onto this socket */ |
| if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0) |
| return -errno; |
| |
| 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"); |
| m->dns_stub_tcp_fd = fd; |
| fd = -1; |
| |
| return m->dns_stub_tcp_fd; |
| } |
| |
| int manager_dns_stub_start(Manager *m) { |
| const char *t = "UDP"; |
| int r = 0; |
| |
| assert(m); |
| |
| 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); |
| } |