diff options
Diffstat (limited to 'src/grp-resolve/systemd-resolved/resolved-dns-stub.c')
| -rw-r--r-- | src/grp-resolve/systemd-resolved/resolved-dns-stub.c | 539 |
1 files changed, 539 insertions, 0 deletions
diff --git a/src/grp-resolve/systemd-resolved/resolved-dns-stub.c b/src/grp-resolve/systemd-resolved/resolved-dns-stub.c new file mode 100644 index 0000000000..ad49862a70 --- /dev/null +++ b/src/grp-resolve/systemd-resolved/resolved-dns-stub.c @@ -0,0 +1,539 @@ +/*** + 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 "systemd-basic/fd-util.h" +#include "systemd-basic/socket-util.h" + +#include "resolved-dns-stub.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( + uint16_t id, + int rcode, + DnsQuestion *q, + DnsAnswer *answer, + 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 */ + DnsPacket **ret) { + + _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; + DnsResourceRecord *rr; + unsigned c = 0; + int r; + + /* 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. */ + + r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0); + if (r < 0) + return r; + + /* If the client didn't do EDNS, clamp the rcode to 4 bit */ + if (!add_opt && rcode > 0xF) + rcode = DNS_RCODE_SERVFAIL; + + 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)); + + 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, NULL, NULL); + if (r < 0) + return r; + + c++; + } + DNS_PACKET_HEADER(p)->ancount = htobe16(c); + + if (add_opt) { + r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL); + if (r < 0) + return r; + } + + *ret = p; + p = NULL; + + 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) { + _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; + int r; + + assert(m); + assert(p); + + r = dns_stub_make_reply_packet(DNS_PACKET_ID(p), rcode, p->question, NULL, !!p->opt, DNS_PACKET_DO(p), false, &reply); + 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: { + _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; + + r = dns_stub_make_reply_packet( + DNS_PACKET_ID(q->request_dns_packet), + q->answer_rcode, + q->question_idna, + q->answer, + !!q->request_dns_packet->opt, + DNS_PACKET_DO(q->request_dns_packet), + DNS_PACKET_DO(q->request_dns_packet) && q->answer_authenticated, + &reply); + if (r < 0) { + log_debug_errno(r, "Failed to build reply packet: %m"); + break; + } + + (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, reply); + break; + } + + case DNS_TRANSACTION_RCODE_FAILURE: + (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode); + break; + + case DNS_TRANSACTION_NOT_FOUND: + (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN); + 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); + 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); + 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); + 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); + 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); + 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); + 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); + 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); + goto fail; + } + + r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH|SD_RESOLVED_NO_CNAME); + if (r < 0) { + log_error_errno(r, "Failed to generate query object: %m"); + dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL); + 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); + goto fail; + } + + log_info("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); +} |