1 /* SPDX-License-Identifier: LGPL-2.1+ */
3 Copyright 2016 Lennart Poettering
7 #include "resolved-dns-stub.h"
8 #include "socket-util.h"
10 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
11 * IP and UDP header sizes */
12 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
14 static int manager_dns_stub_udp_fd(Manager
*m
);
15 static int manager_dns_stub_tcp_fd(Manager
*m
);
17 static int dns_stub_make_reply_packet(
22 bool *ret_truncated
) {
24 bool truncated
= false;
25 DnsResourceRecord
*rr
;
31 /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
32 * roundtrips aren't expensive. */
35 r
= dns_packet_new(p
, DNS_PROTOCOL_DNS
, 0, max_size
);
39 r
= dns_packet_append_question(*p
, q
);
43 DNS_PACKET_HEADER(*p
)->qdcount
= htobe16(dns_question_size(q
));
46 DNS_ANSWER_FOREACH(rr
, answer
) {
48 r
= dns_question_matches_rr(q
, rr
, NULL
);
54 r
= dns_question_matches_cname_or_dname(q
, rr
, NULL
);
62 r
= dns_packet_append_rr(*p
, rr
, 0, NULL
, NULL
);
74 *ret_truncated
= truncated
;
78 DNS_PACKET_HEADER(*p
)->ancount
= htobe16(be16toh(DNS_PACKET_HEADER(*p
)->ancount
) + c
);
83 static int dns_stub_finish_reply_packet(
87 bool tc
, /* set the Truncated bit? */
88 bool add_opt
, /* add an OPT RR to this packet? */
89 bool edns0_do
, /* set the EDNS0 DNSSEC OK bit? */
90 bool ad
) { /* set the DNSSEC authenticated data bit? */
97 /* If the client can't to EDNS0, don't do DO either */
100 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
102 rcode
= DNS_RCODE_SERVFAIL
;
105 /* Don't set the AD bit unless DO is on, too */
109 DNS_PACKET_HEADER(p
)->id
= id
;
111 DNS_PACKET_HEADER(p
)->flags
= htobe16(DNS_PACKET_MAKE_FLAGS(
123 r
= dns_packet_append_opt(p
, ADVERTISE_DATAGRAM_SIZE_MAX
, edns0_do
, rcode
, NULL
);
131 static void dns_stub_detach_stream(DnsStream
*s
) {
139 static int dns_stub_send(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, DnsPacket
*reply
) {
147 r
= dns_stream_write_packet(s
, reply
);
151 fd
= manager_dns_stub_udp_fd(m
);
153 return log_debug_errno(fd
, "Failed to get reply socket: %m");
155 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
156 * is because otherwise the kernel will choose it automatically based on the routing table and will
157 * thus pick 127.0.0.1 rather than 127.0.0.53. */
159 r
= manager_send(m
, fd
, LOOPBACK_IFINDEX
, p
->family
, &p
->sender
, p
->sender_port
, &p
->destination
, reply
);
162 return log_debug_errno(r
, "Failed to send reply packet: %m");
167 static int dns_stub_send_failure(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, int rcode
, bool authenticated
) {
168 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
174 r
= dns_stub_make_reply_packet(&reply
, DNS_PACKET_PAYLOAD_SIZE_MAX(p
), p
->question
, NULL
, NULL
);
176 return log_debug_errno(r
, "Failed to make failure packet: %m");
178 r
= dns_stub_finish_reply_packet(reply
, DNS_PACKET_ID(p
), rcode
, false, !!p
->opt
, DNS_PACKET_DO(p
), authenticated
);
180 return log_debug_errno(r
, "Failed to build failure packet: %m");
182 return dns_stub_send(m
, s
, p
, reply
);
185 static void dns_stub_query_complete(DnsQuery
*q
) {
189 assert(q
->request_dns_packet
);
193 case DNS_TRANSACTION_SUCCESS
: {
196 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
);
198 log_debug_errno(r
, "Failed to build reply packet: %m");
202 r
= dns_query_process_cname(q
);
204 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
208 log_debug_errno(r
, "Failed to process CNAME: %m");
211 if (r
== DNS_QUERY_RESTARTED
)
214 r
= dns_stub_finish_reply_packet(
216 DNS_PACKET_ID(q
->request_dns_packet
),
219 !!q
->request_dns_packet
->opt
,
220 DNS_PACKET_DO(q
->request_dns_packet
),
221 dns_query_fully_authenticated(q
));
223 log_debug_errno(r
, "Failed to finish reply packet: %m");
227 (void) dns_stub_send(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->reply_dns_packet
);
231 case DNS_TRANSACTION_RCODE_FAILURE
:
232 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->answer_rcode
, dns_query_fully_authenticated(q
));
235 case DNS_TRANSACTION_NOT_FOUND
:
236 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_NXDOMAIN
, dns_query_fully_authenticated(q
));
239 case DNS_TRANSACTION_TIMEOUT
:
240 case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED
:
241 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
244 case DNS_TRANSACTION_NO_SERVERS
:
245 case DNS_TRANSACTION_INVALID_REPLY
:
246 case DNS_TRANSACTION_ERRNO
:
247 case DNS_TRANSACTION_ABORTED
:
248 case DNS_TRANSACTION_DNSSEC_FAILED
:
249 case DNS_TRANSACTION_NO_TRUST_ANCHOR
:
250 case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED
:
251 case DNS_TRANSACTION_NETWORK_DOWN
:
252 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
255 case DNS_TRANSACTION_NULL
:
256 case DNS_TRANSACTION_PENDING
:
257 case DNS_TRANSACTION_VALIDATING
:
259 assert_not_reached("Impossible state");
262 /* If there's a packet to write set, let's leave the stream around */
263 if (q
->request_dns_stream
&& DNS_STREAM_QUEUED(q
->request_dns_stream
)) {
265 /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
266 * default completion action of the stream will drop the reference. */
268 dns_stub_detach_stream(q
->request_dns_stream
);
269 q
->request_dns_stream
= NULL
;
275 static int dns_stub_stream_complete(DnsStream
*s
, int error
) {
278 log_debug_errno(error
, "DNS TCP connection terminated, destroying query: %m");
281 dns_query_free(s
->query
);
286 static void dns_stub_process_query(Manager
*m
, DnsStream
*s
, DnsPacket
*p
) {
292 assert(p
->protocol
== DNS_PROTOCOL_DNS
);
294 /* Takes ownership of the *s stream object */
296 if (in_addr_is_localhost(p
->family
, &p
->sender
) <= 0 ||
297 in_addr_is_localhost(p
->family
, &p
->destination
) <= 0) {
298 log_error("Got packet on unexpected IP range, refusing.");
299 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
303 r
= dns_packet_extract(p
);
305 log_debug_errno(r
, "Failed to extract resources from incoming packet, ignoring packet: %m");
306 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_FORMERR
, false);
310 if (!DNS_PACKET_VERSION_SUPPORTED(p
)) {
311 log_debug("Got EDNS OPT field with unsupported version number.");
312 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_BADVERS
, false);
316 if (dns_type_is_obsolete(p
->question
->keys
[0]->type
)) {
317 log_debug("Got message with obsolete key type, refusing.");
318 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
322 if (dns_type_is_zone_transer(p
->question
->keys
[0]->type
)) {
323 log_debug("Got request for zone transfer, refusing.");
324 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
328 if (!DNS_PACKET_RD(p
)) {
329 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
330 log_debug("Got request with recursion disabled, refusing.");
331 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_REFUSED
, false);
335 if (DNS_PACKET_DO(p
) && DNS_PACKET_CD(p
)) {
336 log_debug("Got request with DNSSEC CD bit set, refusing.");
337 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
341 r
= dns_query_new(m
, &q
, p
->question
, p
->question
, 0, SD_RESOLVED_PROTOCOLS_ALL
|SD_RESOLVED_NO_SEARCH
);
343 log_error_errno(r
, "Failed to generate query object: %m");
344 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
348 /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
351 q
->request_dns_packet
= dns_packet_ref(p
);
352 q
->request_dns_stream
= dns_stream_ref(s
); /* make sure the stream stays around until we can send a reply through it */
353 q
->complete
= dns_stub_query_complete
;
357 s
->complete
= dns_stub_stream_complete
;
363 log_error_errno(r
, "Failed to start query: %m");
364 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
368 log_debug("Processing query...");
372 if (s
&& DNS_STREAM_QUEUED(s
))
373 dns_stub_detach_stream(s
);
378 static int on_dns_stub_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
379 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
380 Manager
*m
= userdata
;
383 r
= manager_recv(m
, fd
, DNS_PROTOCOL_DNS
, &p
);
387 if (dns_packet_validate_query(p
) > 0) {
388 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p
));
390 dns_stub_process_query(m
, NULL
, p
);
392 log_debug("Invalid DNS stub UDP packet, ignoring.");
397 static int manager_dns_stub_udp_fd(Manager
*m
) {
398 static const int one
= 1;
399 union sockaddr_union sa
= {
400 .in
.sin_family
= AF_INET
,
401 .in
.sin_port
= htobe16(53),
402 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
404 _cleanup_close_
int fd
= -1;
407 if (m
->dns_stub_udp_fd
>= 0)
408 return m
->dns_stub_udp_fd
;
410 fd
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
414 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
417 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
420 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
423 /* Make sure no traffic from outside the local host can leak to onto this socket */
424 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
427 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
430 r
= sd_event_add_io(m
->event
, &m
->dns_stub_udp_event_source
, fd
, EPOLLIN
, on_dns_stub_packet
, m
);
434 (void) sd_event_source_set_description(m
->dns_stub_udp_event_source
, "dns-stub-udp");
436 return m
->dns_stub_udp_fd
= TAKE_FD(fd
);
439 static int on_dns_stub_stream_packet(DnsStream
*s
) {
441 assert(s
->read_packet
);
443 if (dns_packet_validate_query(s
->read_packet
) > 0) {
444 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s
->read_packet
));
446 dns_stub_process_query(s
->manager
, s
, s
->read_packet
);
448 log_debug("Invalid DNS stub TCP packet, ignoring.");
450 /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
451 * or that didn't happen in which case we want to free the stream */
457 static int on_dns_stub_stream(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
459 Manager
*m
= userdata
;
462 cfd
= accept4(fd
, NULL
, NULL
, SOCK_NONBLOCK
|SOCK_CLOEXEC
);
464 if (IN_SET(errno
, EAGAIN
, EINTR
))
470 r
= dns_stream_new(m
, &stream
, DNS_PROTOCOL_DNS
, cfd
, NULL
);
476 stream
->on_packet
= on_dns_stub_stream_packet
;
478 /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
479 * of the stream, or by our packet callback, or when the manager is shut down. */
484 static int manager_dns_stub_tcp_fd(Manager
*m
) {
485 static const int one
= 1;
486 union sockaddr_union sa
= {
487 .in
.sin_family
= AF_INET
,
488 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
489 .in
.sin_port
= htobe16(53),
491 _cleanup_close_
int fd
= -1;
494 if (m
->dns_stub_tcp_fd
>= 0)
495 return m
->dns_stub_tcp_fd
;
497 fd
= socket(AF_INET
, SOCK_STREAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
501 if (setsockopt(fd
, IPPROTO_IP
, IP_TTL
, &one
, sizeof one
) < 0)
504 if (setsockopt(fd
, SOL_SOCKET
, SO_REUSEADDR
, &one
, sizeof one
) < 0)
507 if (setsockopt(fd
, IPPROTO_IP
, IP_PKTINFO
, &one
, sizeof one
) < 0)
510 if (setsockopt(fd
, IPPROTO_IP
, IP_RECVTTL
, &one
, sizeof one
) < 0)
513 /* Make sure no traffic from outside the local host can leak to onto this socket */
514 if (setsockopt(fd
, SOL_SOCKET
, SO_BINDTODEVICE
, "lo", 3) < 0)
517 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
520 if (listen(fd
, SOMAXCONN
) < 0)
523 r
= sd_event_add_io(m
->event
, &m
->dns_stub_tcp_event_source
, fd
, EPOLLIN
, on_dns_stub_stream
, m
);
527 (void) sd_event_source_set_description(m
->dns_stub_tcp_event_source
, "dns-stub-tcp");
529 return m
->dns_stub_tcp_fd
= TAKE_FD(fd
);
532 int manager_dns_stub_start(Manager
*m
) {
533 const char *t
= "UDP";
538 if (m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_NO
)
539 log_debug("Not creating stub listener.");
541 log_debug("Creating stub listener using %s.",
542 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_UDP
? "UDP" :
543 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_TCP
? "TCP" :
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
);