2 This file is part of systemd.
4 Copyright 2016 Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
21 #include "resolved-dns-stub.h"
22 #include "socket-util.h"
24 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
25 * IP and UDP header sizes */
26 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
28 static int manager_dns_stub_udp_fd(Manager
*m
);
29 static int manager_dns_stub_tcp_fd(Manager
*m
);
31 static int dns_stub_make_reply_packet(
36 DnsResourceRecord
*rr
;
42 /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
43 * roundtrips aren't expensive. */
46 r
= dns_packet_new(p
, DNS_PROTOCOL_DNS
, 0);
50 r
= dns_packet_append_question(*p
, q
);
54 DNS_PACKET_HEADER(*p
)->qdcount
= htobe16(dns_question_size(q
));
57 DNS_ANSWER_FOREACH(rr
, answer
) {
59 r
= dns_question_matches_rr(q
, rr
, NULL
);
65 r
= dns_question_matches_cname_or_dname(q
, rr
, NULL
);
73 r
= dns_packet_append_rr(*p
, rr
, 0, NULL
, NULL
);
80 DNS_PACKET_HEADER(*p
)->ancount
= htobe16(be16toh(DNS_PACKET_HEADER(*p
)->ancount
) + c
);
85 static int dns_stub_finish_reply_packet(
89 bool add_opt
, /* add an OPT RR to this packet? */
90 bool edns0_do
, /* set the EDNS0 DNSSEC OK bit? */
91 bool ad
) { /* set the DNSSEC authenticated data bit? */
98 /* If the client can't to EDNS0, don't do DO either */
101 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
103 rcode
= DNS_RCODE_SERVFAIL
;
106 /* Don't set the AD bit unless DO is on, too */
110 DNS_PACKET_HEADER(p
)->id
= id
;
112 DNS_PACKET_HEADER(p
)->flags
= htobe16(DNS_PACKET_MAKE_FLAGS(
124 r
= dns_packet_append_opt(p
, ADVERTISE_DATAGRAM_SIZE_MAX
, edns0_do
, rcode
, NULL
);
132 static void dns_stub_detach_stream(DnsStream
*s
) {
140 static int dns_stub_send(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, DnsPacket
*reply
) {
148 r
= dns_stream_write_packet(s
, reply
);
152 /* Truncate the message to the right size */
153 if (reply
->size
> DNS_PACKET_PAYLOAD_SIZE_MAX(p
)) {
154 dns_packet_truncate(reply
, DNS_PACKET_UNICAST_SIZE_MAX
);
155 DNS_PACKET_HEADER(reply
)->flags
= htobe16(be16toh(DNS_PACKET_HEADER(reply
)->flags
) | DNS_PACKET_FLAG_TC
);
158 fd
= manager_dns_stub_udp_fd(m
);
160 return log_debug_errno(fd
, "Failed to get reply socket: %m");
162 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
163 * is because otherwise the kernel will choose it automatically based on the routing table and will
164 * thus pick 127.0.0.1 rather than 127.0.0.53. */
166 r
= manager_send(m
, fd
, LOOPBACK_IFINDEX
, p
->family
, &p
->sender
, p
->sender_port
, &p
->destination
, reply
);
169 return log_debug_errno(r
, "Failed to send reply packet: %m");
174 static int dns_stub_send_failure(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, int rcode
, bool authenticated
) {
175 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
181 r
= dns_stub_make_reply_packet(&reply
, p
->question
, NULL
);
183 return log_debug_errno(r
, "Failed to make failure packet: %m");
185 r
= dns_stub_finish_reply_packet(reply
, DNS_PACKET_ID(p
), rcode
, !!p
->opt
, DNS_PACKET_DO(p
), authenticated
);
187 return log_debug_errno(r
, "Failed to build failure packet: %m");
189 return dns_stub_send(m
, s
, p
, reply
);
192 static void dns_stub_query_complete(DnsQuery
*q
) {
196 assert(q
->request_dns_packet
);
200 case DNS_TRANSACTION_SUCCESS
:
202 r
= dns_stub_make_reply_packet(&q
->reply_dns_packet
, q
->question_idna
, q
->answer
);
204 log_debug_errno(r
, "Failed to build reply packet: %m");
208 r
= dns_query_process_cname(q
);
210 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
214 log_debug_errno(r
, "Failed to process CNAME: %m");
217 if (r
== DNS_QUERY_RESTARTED
)
220 r
= dns_stub_finish_reply_packet(
222 DNS_PACKET_ID(q
->request_dns_packet
),
224 !!q
->request_dns_packet
->opt
,
225 DNS_PACKET_DO(q
->request_dns_packet
),
226 dns_query_fully_authenticated(q
));
228 log_debug_errno(r
, "Failed to finish reply packet: %m");
232 (void) dns_stub_send(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->reply_dns_packet
);
235 case DNS_TRANSACTION_RCODE_FAILURE
:
236 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->answer_rcode
, dns_query_fully_authenticated(q
));
239 case DNS_TRANSACTION_NOT_FOUND
:
240 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_NXDOMAIN
, dns_query_fully_authenticated(q
));
243 case DNS_TRANSACTION_TIMEOUT
:
244 case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED
:
245 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
248 case DNS_TRANSACTION_NO_SERVERS
:
249 case DNS_TRANSACTION_INVALID_REPLY
:
250 case DNS_TRANSACTION_ERRNO
:
251 case DNS_TRANSACTION_ABORTED
:
252 case DNS_TRANSACTION_DNSSEC_FAILED
:
253 case DNS_TRANSACTION_NO_TRUST_ANCHOR
:
254 case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED
:
255 case DNS_TRANSACTION_NETWORK_DOWN
:
256 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
259 case DNS_TRANSACTION_NULL
:
260 case DNS_TRANSACTION_PENDING
:
261 case DNS_TRANSACTION_VALIDATING
:
263 assert_not_reached("Impossible state");
266 /* If there's a packet to write set, let's leave the stream around */
267 if (q
->request_dns_stream
&& DNS_STREAM_QUEUED(q
->request_dns_stream
)) {
269 /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
270 * default completion action of the stream will drop the reference. */
272 dns_stub_detach_stream(q
->request_dns_stream
);
273 q
->request_dns_stream
= NULL
;
279 static int dns_stub_stream_complete(DnsStream
*s
, int error
) {
282 log_debug_errno(error
, "DNS TCP connection terminated, destroying query: %m");
285 dns_query_free(s
->query
);
290 static void dns_stub_process_query(Manager
*m
, DnsStream
*s
, DnsPacket
*p
) {
296 assert(p
->protocol
== DNS_PROTOCOL_DNS
);
298 /* Takes ownership of the *s stream object */
300 if (in_addr_is_localhost(p
->family
, &p
->sender
) <= 0 ||
301 in_addr_is_localhost(p
->family
, &p
->destination
) <= 0) {
302 log_error("Got packet on unexpected IP range, refusing.");
303 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
307 r
= dns_packet_extract(p
);
309 log_debug_errno(r
, "Failed to extract resources from incoming packet, ignoring packet: %m");
310 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_FORMERR
, false);
314 if (!DNS_PACKET_VERSION_SUPPORTED(p
)) {
315 log_debug("Got EDNS OPT field with unsupported version number.");
316 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_BADVERS
, false);
320 if (dns_type_is_obsolete(p
->question
->keys
[0]->type
)) {
321 log_debug("Got message with obsolete key type, refusing.");
322 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
326 if (dns_type_is_zone_transer(p
->question
->keys
[0]->type
)) {
327 log_debug("Got request for zone transfer, refusing.");
328 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
332 if (!DNS_PACKET_RD(p
)) {
333 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
334 log_debug("Got request with recursion disabled, refusing.");
335 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_REFUSED
, false);
339 if (DNS_PACKET_DO(p
) && DNS_PACKET_CD(p
)) {
340 log_debug("Got request with DNSSEC CD bit set, refusing.");
341 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
345 r
= dns_query_new(m
, &q
, p
->question
, p
->question
, 0, SD_RESOLVED_PROTOCOLS_ALL
|SD_RESOLVED_NO_SEARCH
);
347 log_error_errno(r
, "Failed to generate query object: %m");
348 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
352 /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
355 q
->request_dns_packet
= dns_packet_ref(p
);
356 q
->request_dns_stream
= dns_stream_ref(s
); /* make sure the stream stays around until we can send a reply through it */
357 q
->complete
= dns_stub_query_complete
;
361 s
->complete
= dns_stub_stream_complete
;
367 log_error_errno(r
, "Failed to start query: %m");
368 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
372 log_debug("Processing query...");
376 if (s
&& DNS_STREAM_QUEUED(s
))
377 dns_stub_detach_stream(s
);
382 static int on_dns_stub_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
383 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
384 Manager
*m
= userdata
;
387 r
= manager_recv(m
, fd
, DNS_PROTOCOL_DNS
, &p
);
391 if (dns_packet_validate_query(p
) > 0) {
392 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p
));
394 dns_stub_process_query(m
, NULL
, p
);
396 log_debug("Invalid DNS stub UDP packet, ignoring.");
401 static int manager_dns_stub_udp_fd(Manager
*m
) {
402 static const int one
= 1;
403 union sockaddr_union sa
= {
404 .in
.sin_family
= AF_INET
,
405 .in
.sin_port
= htobe16(53),
406 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
408 _cleanup_close_
int fd
= -1;
411 if (m
->dns_stub_udp_fd
>= 0)
412 return m
->dns_stub_udp_fd
;
414 fd
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
418 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
421 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
424 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
427 /* Make sure no traffic from outside the local host can leak to onto this socket */
428 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
431 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
434 r
= sd_event_add_io(m
->event
, &m
->dns_stub_udp_event_source
, fd
, EPOLLIN
, on_dns_stub_packet
, m
);
438 (void) sd_event_source_set_description(m
->dns_stub_udp_event_source
, "dns-stub-udp");
439 m
->dns_stub_udp_fd
= fd
;
442 return m
->dns_stub_udp_fd
;
445 static int on_dns_stub_stream_packet(DnsStream
*s
) {
447 assert(s
->read_packet
);
449 if (dns_packet_validate_query(s
->read_packet
) > 0) {
450 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s
->read_packet
));
452 dns_stub_process_query(s
->manager
, s
, s
->read_packet
);
454 log_debug("Invalid DNS stub TCP packet, ignoring.");
456 /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
457 * or that didn't happen in which case we want to free the stream */
463 static int on_dns_stub_stream(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
465 Manager
*m
= userdata
;
468 cfd
= accept4(fd
, NULL
, NULL
, SOCK_NONBLOCK
|SOCK_CLOEXEC
);
470 if (errno
== EAGAIN
|| errno
== EINTR
)
476 r
= dns_stream_new(m
, &stream
, DNS_PROTOCOL_DNS
, cfd
);
482 stream
->on_packet
= on_dns_stub_stream_packet
;
484 /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
485 * of the stream, or by our packet callback, or when the manager is shut down. */
490 static int manager_dns_stub_tcp_fd(Manager
*m
) {
491 static const int one
= 1;
492 union sockaddr_union sa
= {
493 .in
.sin_family
= AF_INET
,
494 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
495 .in
.sin_port
= htobe16(53),
497 _cleanup_close_
int fd
= -1;
500 if (m
->dns_stub_tcp_fd
>= 0)
501 return m
->dns_stub_tcp_fd
;
503 fd
= socket(AF_INET
, SOCK_STREAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
507 if (setsockopt(fd
, IPPROTO_IP
, IP_TTL
, &one
, sizeof one
) < 0)
510 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
513 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
516 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
519 /* Make sure no traffic from outside the local host can leak to onto this socket */
520 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
523 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
526 if (listen(fd
, SOMAXCONN
) < 0)
529 r
= sd_event_add_io(m
->event
, &m
->dns_stub_tcp_event_source
, fd
, EPOLLIN
, on_dns_stub_stream
, m
);
533 (void) sd_event_source_set_description(m
->dns_stub_tcp_event_source
, "dns-stub-tcp");
534 m
->dns_stub_tcp_fd
= fd
;
537 return m
->dns_stub_tcp_fd
;
540 int manager_dns_stub_start(Manager
*m
) {
541 const char *t
= "UDP";
546 if (IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_UDP
))
547 r
= manager_dns_stub_udp_fd(m
);
550 IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_TCP
)) {
552 r
= manager_dns_stub_tcp_fd(m
);
555 if (IN_SET(r
, -EADDRINUSE
, -EPERM
)) {
556 if (r
== -EADDRINUSE
)
558 "Another process is already listening on %s socket 127.0.0.53:53.\n"
559 "Turning off local DNS stub support.", t
);
562 "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
563 "Turning off local DNS stub support.", t
);
564 manager_dns_stub_stop(m
);
566 return log_error_errno(r
, "Failed to listen on %s socket 127.0.0.53:53: %m", t
);
571 void manager_dns_stub_stop(Manager
*m
) {
574 m
->dns_stub_udp_event_source
= sd_event_source_unref(m
->dns_stub_udp_event_source
);
575 m
->dns_stub_tcp_event_source
= sd_event_source_unref(m
->dns_stub_tcp_event_source
);
577 m
->dns_stub_udp_fd
= safe_close(m
->dns_stub_udp_fd
);
578 m
->dns_stub_tcp_fd
= safe_close(m
->dns_stub_tcp_fd
);