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 bool *ret_truncated
) {
38 bool truncated
= false;
39 DnsResourceRecord
*rr
;
45 /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
46 * roundtrips aren't expensive. */
49 r
= dns_packet_new(p
, DNS_PROTOCOL_DNS
, 0, max_size
);
53 r
= dns_packet_append_question(*p
, q
);
57 DNS_PACKET_HEADER(*p
)->qdcount
= htobe16(dns_question_size(q
));
60 DNS_ANSWER_FOREACH(rr
, answer
) {
62 r
= dns_question_matches_rr(q
, rr
, NULL
);
68 r
= dns_question_matches_cname_or_dname(q
, rr
, NULL
);
76 r
= dns_packet_append_rr(*p
, rr
, 0, NULL
, NULL
);
88 *ret_truncated
= truncated
;
92 DNS_PACKET_HEADER(*p
)->ancount
= htobe16(be16toh(DNS_PACKET_HEADER(*p
)->ancount
) + c
);
97 static int dns_stub_finish_reply_packet(
101 bool tc
, /* set the Truncated bit? */
102 bool add_opt
, /* add an OPT RR to this packet? */
103 bool edns0_do
, /* set the EDNS0 DNSSEC OK bit? */
104 bool ad
) { /* set the DNSSEC authenticated data bit? */
111 /* If the client can't to EDNS0, don't do DO either */
114 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
116 rcode
= DNS_RCODE_SERVFAIL
;
119 /* Don't set the AD bit unless DO is on, too */
123 DNS_PACKET_HEADER(p
)->id
= id
;
125 DNS_PACKET_HEADER(p
)->flags
= htobe16(DNS_PACKET_MAKE_FLAGS(
137 r
= dns_packet_append_opt(p
, ADVERTISE_DATAGRAM_SIZE_MAX
, edns0_do
, rcode
, NULL
);
145 static void dns_stub_detach_stream(DnsStream
*s
) {
153 static int dns_stub_send(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, DnsPacket
*reply
) {
161 r
= dns_stream_write_packet(s
, reply
);
165 fd
= manager_dns_stub_udp_fd(m
);
167 return log_debug_errno(fd
, "Failed to get reply socket: %m");
169 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
170 * is because otherwise the kernel will choose it automatically based on the routing table and will
171 * thus pick 127.0.0.1 rather than 127.0.0.53. */
173 r
= manager_send(m
, fd
, LOOPBACK_IFINDEX
, p
->family
, &p
->sender
, p
->sender_port
, &p
->destination
, reply
);
176 return log_debug_errno(r
, "Failed to send reply packet: %m");
181 static int dns_stub_send_failure(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, int rcode
, bool authenticated
) {
182 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
188 r
= dns_stub_make_reply_packet(&reply
, DNS_PACKET_PAYLOAD_SIZE_MAX(p
), p
->question
, NULL
, NULL
);
190 return log_debug_errno(r
, "Failed to make failure packet: %m");
192 r
= dns_stub_finish_reply_packet(reply
, DNS_PACKET_ID(p
), rcode
, false, !!p
->opt
, DNS_PACKET_DO(p
), authenticated
);
194 return log_debug_errno(r
, "Failed to build failure packet: %m");
196 return dns_stub_send(m
, s
, p
, reply
);
199 static void dns_stub_query_complete(DnsQuery
*q
) {
203 assert(q
->request_dns_packet
);
207 case DNS_TRANSACTION_SUCCESS
: {
210 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
);
212 log_debug_errno(r
, "Failed to build reply packet: %m");
216 r
= dns_query_process_cname(q
);
218 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
222 log_debug_errno(r
, "Failed to process CNAME: %m");
225 if (r
== DNS_QUERY_RESTARTED
)
228 r
= dns_stub_finish_reply_packet(
230 DNS_PACKET_ID(q
->request_dns_packet
),
233 !!q
->request_dns_packet
->opt
,
234 DNS_PACKET_DO(q
->request_dns_packet
),
235 dns_query_fully_authenticated(q
));
237 log_debug_errno(r
, "Failed to finish reply packet: %m");
241 (void) dns_stub_send(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->reply_dns_packet
);
245 case DNS_TRANSACTION_RCODE_FAILURE
:
246 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->answer_rcode
, dns_query_fully_authenticated(q
));
249 case DNS_TRANSACTION_NOT_FOUND
:
250 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_NXDOMAIN
, dns_query_fully_authenticated(q
));
253 case DNS_TRANSACTION_TIMEOUT
:
254 case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED
:
255 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
258 case DNS_TRANSACTION_NO_SERVERS
:
259 case DNS_TRANSACTION_INVALID_REPLY
:
260 case DNS_TRANSACTION_ERRNO
:
261 case DNS_TRANSACTION_ABORTED
:
262 case DNS_TRANSACTION_DNSSEC_FAILED
:
263 case DNS_TRANSACTION_NO_TRUST_ANCHOR
:
264 case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED
:
265 case DNS_TRANSACTION_NETWORK_DOWN
:
266 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
269 case DNS_TRANSACTION_NULL
:
270 case DNS_TRANSACTION_PENDING
:
271 case DNS_TRANSACTION_VALIDATING
:
273 assert_not_reached("Impossible state");
276 /* If there's a packet to write set, let's leave the stream around */
277 if (q
->request_dns_stream
&& DNS_STREAM_QUEUED(q
->request_dns_stream
)) {
279 /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
280 * default completion action of the stream will drop the reference. */
282 dns_stub_detach_stream(q
->request_dns_stream
);
283 q
->request_dns_stream
= NULL
;
289 static int dns_stub_stream_complete(DnsStream
*s
, int error
) {
292 log_debug_errno(error
, "DNS TCP connection terminated, destroying query: %m");
295 dns_query_free(s
->query
);
300 static void dns_stub_process_query(Manager
*m
, DnsStream
*s
, DnsPacket
*p
) {
306 assert(p
->protocol
== DNS_PROTOCOL_DNS
);
308 /* Takes ownership of the *s stream object */
310 if (in_addr_is_localhost(p
->family
, &p
->sender
) <= 0 ||
311 in_addr_is_localhost(p
->family
, &p
->destination
) <= 0) {
312 log_error("Got packet on unexpected IP range, refusing.");
313 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
317 r
= dns_packet_extract(p
);
319 log_debug_errno(r
, "Failed to extract resources from incoming packet, ignoring packet: %m");
320 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_FORMERR
, false);
324 if (!DNS_PACKET_VERSION_SUPPORTED(p
)) {
325 log_debug("Got EDNS OPT field with unsupported version number.");
326 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_BADVERS
, false);
330 if (dns_type_is_obsolete(p
->question
->keys
[0]->type
)) {
331 log_debug("Got message with obsolete key type, refusing.");
332 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
336 if (dns_type_is_zone_transer(p
->question
->keys
[0]->type
)) {
337 log_debug("Got request for zone transfer, refusing.");
338 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
342 if (!DNS_PACKET_RD(p
)) {
343 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
344 log_debug("Got request with recursion disabled, refusing.");
345 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_REFUSED
, false);
349 if (DNS_PACKET_DO(p
) && DNS_PACKET_CD(p
)) {
350 log_debug("Got request with DNSSEC CD bit set, refusing.");
351 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
355 r
= dns_query_new(m
, &q
, p
->question
, p
->question
, 0, SD_RESOLVED_PROTOCOLS_ALL
|SD_RESOLVED_NO_SEARCH
);
357 log_error_errno(r
, "Failed to generate query object: %m");
358 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
362 /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
365 q
->request_dns_packet
= dns_packet_ref(p
);
366 q
->request_dns_stream
= dns_stream_ref(s
); /* make sure the stream stays around until we can send a reply through it */
367 q
->complete
= dns_stub_query_complete
;
371 s
->complete
= dns_stub_stream_complete
;
377 log_error_errno(r
, "Failed to start query: %m");
378 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
382 log_debug("Processing query...");
386 if (s
&& DNS_STREAM_QUEUED(s
))
387 dns_stub_detach_stream(s
);
392 static int on_dns_stub_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
393 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
394 Manager
*m
= userdata
;
397 r
= manager_recv(m
, fd
, DNS_PROTOCOL_DNS
, &p
);
401 if (dns_packet_validate_query(p
) > 0) {
402 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p
));
404 dns_stub_process_query(m
, NULL
, p
);
406 log_debug("Invalid DNS stub UDP packet, ignoring.");
411 static int manager_dns_stub_udp_fd(Manager
*m
) {
412 static const int one
= 1;
413 union sockaddr_union sa
= {
414 .in
.sin_family
= AF_INET
,
415 .in
.sin_port
= htobe16(53),
416 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
418 _cleanup_close_
int fd
= -1;
421 if (m
->dns_stub_udp_fd
>= 0)
422 return m
->dns_stub_udp_fd
;
424 fd
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
428 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
431 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
434 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
437 /* Make sure no traffic from outside the local host can leak to onto this socket */
438 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
441 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
444 r
= sd_event_add_io(m
->event
, &m
->dns_stub_udp_event_source
, fd
, EPOLLIN
, on_dns_stub_packet
, m
);
448 (void) sd_event_source_set_description(m
->dns_stub_udp_event_source
, "dns-stub-udp");
449 m
->dns_stub_udp_fd
= fd
;
452 return m
->dns_stub_udp_fd
;
455 static int on_dns_stub_stream_packet(DnsStream
*s
) {
457 assert(s
->read_packet
);
459 if (dns_packet_validate_query(s
->read_packet
) > 0) {
460 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s
->read_packet
));
462 dns_stub_process_query(s
->manager
, s
, s
->read_packet
);
464 log_debug("Invalid DNS stub TCP packet, ignoring.");
466 /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
467 * or that didn't happen in which case we want to free the stream */
473 static int on_dns_stub_stream(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
475 Manager
*m
= userdata
;
478 cfd
= accept4(fd
, NULL
, NULL
, SOCK_NONBLOCK
|SOCK_CLOEXEC
);
480 if (IN_SET(errno
, EAGAIN
, EINTR
))
486 r
= dns_stream_new(m
, &stream
, DNS_PROTOCOL_DNS
, cfd
);
492 stream
->on_packet
= on_dns_stub_stream_packet
;
494 /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
495 * of the stream, or by our packet callback, or when the manager is shut down. */
500 static int manager_dns_stub_tcp_fd(Manager
*m
) {
501 static const int one
= 1;
502 union sockaddr_union sa
= {
503 .in
.sin_family
= AF_INET
,
504 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
505 .in
.sin_port
= htobe16(53),
507 _cleanup_close_
int fd
= -1;
510 if (m
->dns_stub_tcp_fd
>= 0)
511 return m
->dns_stub_tcp_fd
;
513 fd
= socket(AF_INET
, SOCK_STREAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
517 if (setsockopt(fd
, IPPROTO_IP
, IP_TTL
, &one
, sizeof one
) < 0)
520 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
523 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
526 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
529 /* Make sure no traffic from outside the local host can leak to onto this socket */
530 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
533 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
536 if (listen(fd
, SOMAXCONN
) < 0)
539 r
= sd_event_add_io(m
->event
, &m
->dns_stub_tcp_event_source
, fd
, EPOLLIN
, on_dns_stub_stream
, m
);
543 (void) sd_event_source_set_description(m
->dns_stub_tcp_event_source
, "dns-stub-tcp");
544 m
->dns_stub_tcp_fd
= fd
;
547 return m
->dns_stub_tcp_fd
;
550 int manager_dns_stub_start(Manager
*m
) {
551 const char *t
= "UDP";
556 if (m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_NO
)
557 log_debug("Not creating stub listener.");
559 log_debug("Creating stub listener using %s.",
560 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_UDP
? "UDP" :
561 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_TCP
? "TCP" :
564 if (IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_UDP
))
565 r
= manager_dns_stub_udp_fd(m
);
568 IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_TCP
)) {
570 r
= manager_dns_stub_tcp_fd(m
);
573 if (IN_SET(r
, -EADDRINUSE
, -EPERM
)) {
574 if (r
== -EADDRINUSE
)
576 "Another process is already listening on %s socket 127.0.0.53:53.\n"
577 "Turning off local DNS stub support.", t
);
580 "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
581 "Turning off local DNS stub support.", t
);
582 manager_dns_stub_stop(m
);
584 return log_error_errno(r
, "Failed to listen on %s socket 127.0.0.53:53: %m", t
);
589 void manager_dns_stub_stop(Manager
*m
) {
592 m
->dns_stub_udp_event_source
= sd_event_source_unref(m
->dns_stub_udp_event_source
);
593 m
->dns_stub_tcp_event_source
= sd_event_source_unref(m
->dns_stub_tcp_event_source
);
595 m
->dns_stub_udp_fd
= safe_close(m
->dns_stub_udp_fd
);
596 m
->dns_stub_tcp_fd
= safe_close(m
->dns_stub_tcp_fd
);