1 /* SPDX-License-Identifier: LGPL-2.1+ */
3 #include "errno-util.h"
5 #include "missing_network.h"
6 #include "resolved-dns-stub.h"
7 #include "socket-util.h"
9 /* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
10 * IP and UDP header sizes */
11 #define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
13 static int manager_dns_stub_udp_fd(Manager
*m
);
14 static int manager_dns_stub_tcp_fd(Manager
*m
);
16 static int dns_stub_make_reply_packet(
21 bool *ret_truncated
) {
23 bool truncated
= false;
24 DnsResourceRecord
*rr
;
30 /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
31 * roundtrips aren't expensive. */
34 r
= dns_packet_new(p
, DNS_PROTOCOL_DNS
, 0, max_size
);
38 r
= dns_packet_append_question(*p
, q
);
42 DNS_PACKET_HEADER(*p
)->qdcount
= htobe16(dns_question_size(q
));
45 DNS_ANSWER_FOREACH(rr
, answer
) {
47 r
= dns_question_matches_rr(q
, rr
, NULL
);
53 r
= dns_question_matches_cname_or_dname(q
, rr
, NULL
);
61 r
= dns_packet_append_rr(*p
, rr
, 0, NULL
, NULL
);
73 *ret_truncated
= truncated
;
77 DNS_PACKET_HEADER(*p
)->ancount
= htobe16(be16toh(DNS_PACKET_HEADER(*p
)->ancount
) + c
);
82 static int dns_stub_finish_reply_packet(
86 bool tc
, /* set the Truncated bit? */
87 bool add_opt
, /* add an OPT RR to this packet? */
88 bool edns0_do
, /* set the EDNS0 DNSSEC OK bit? */
89 bool ad
) { /* set the DNSSEC authenticated data bit? */
96 r
= dns_packet_append_opt(p
, ADVERTISE_DATAGRAM_SIZE_MAX
, edns0_do
, rcode
, NULL
);
97 if (r
== -EMSGSIZE
) /* Hit the size limit? then indicate truncation */
103 /* If the client can't to EDNS0, don't do DO either */
106 /* If the client didn't do EDNS, clamp the rcode to 4 bit */
108 rcode
= DNS_RCODE_SERVFAIL
;
111 /* Don't set the AD bit unless DO is on, too */
115 DNS_PACKET_HEADER(p
)->id
= id
;
117 DNS_PACKET_HEADER(p
)->flags
= htobe16(DNS_PACKET_MAKE_FLAGS(
131 static int dns_stub_send(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, DnsPacket
*reply
) {
139 r
= dns_stream_write_packet(s
, reply
);
143 fd
= manager_dns_stub_udp_fd(m
);
145 return log_debug_errno(fd
, "Failed to get reply socket: %m");
147 /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
148 * is because otherwise the kernel will choose it automatically based on the routing table and will
149 * thus pick 127.0.0.1 rather than 127.0.0.53. */
151 r
= manager_send(m
, fd
, LOOPBACK_IFINDEX
, p
->family
, &p
->sender
, p
->sender_port
, &p
->destination
, reply
);
154 return log_debug_errno(r
, "Failed to send reply packet: %m");
159 static int dns_stub_send_failure(Manager
*m
, DnsStream
*s
, DnsPacket
*p
, int rcode
, bool authenticated
) {
160 _cleanup_(dns_packet_unrefp
) DnsPacket
*reply
= NULL
;
166 r
= dns_stub_make_reply_packet(&reply
, DNS_PACKET_PAYLOAD_SIZE_MAX(p
), p
->question
, NULL
, NULL
);
168 return log_debug_errno(r
, "Failed to make failure packet: %m");
170 r
= dns_stub_finish_reply_packet(reply
, DNS_PACKET_ID(p
), rcode
, false, !!p
->opt
, DNS_PACKET_DO(p
), authenticated
);
172 return log_debug_errno(r
, "Failed to build failure packet: %m");
174 return dns_stub_send(m
, s
, p
, reply
);
177 static void dns_stub_query_complete(DnsQuery
*q
) {
181 assert(q
->request_dns_packet
);
185 case DNS_TRANSACTION_SUCCESS
: {
188 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
);
190 log_debug_errno(r
, "Failed to build reply packet: %m");
195 r
= dns_query_process_cname(q
);
197 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
201 log_debug_errno(r
, "Failed to process CNAME: %m");
204 if (r
== DNS_QUERY_RESTARTED
)
208 r
= dns_stub_finish_reply_packet(
210 DNS_PACKET_ID(q
->request_dns_packet
),
213 !!q
->request_dns_packet
->opt
,
214 DNS_PACKET_DO(q
->request_dns_packet
),
215 dns_query_fully_authenticated(q
));
217 log_debug_errno(r
, "Failed to finish reply packet: %m");
221 (void) dns_stub_send(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->reply_dns_packet
);
225 case DNS_TRANSACTION_RCODE_FAILURE
:
226 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, q
->answer_rcode
, dns_query_fully_authenticated(q
));
229 case DNS_TRANSACTION_NOT_FOUND
:
230 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_NXDOMAIN
, dns_query_fully_authenticated(q
));
233 case DNS_TRANSACTION_TIMEOUT
:
234 case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED
:
235 /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
238 case DNS_TRANSACTION_NO_SERVERS
:
239 case DNS_TRANSACTION_INVALID_REPLY
:
240 case DNS_TRANSACTION_ERRNO
:
241 case DNS_TRANSACTION_ABORTED
:
242 case DNS_TRANSACTION_DNSSEC_FAILED
:
243 case DNS_TRANSACTION_NO_TRUST_ANCHOR
:
244 case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED
:
245 case DNS_TRANSACTION_NETWORK_DOWN
:
246 (void) dns_stub_send_failure(q
->manager
, q
->request_dns_stream
, q
->request_dns_packet
, DNS_RCODE_SERVFAIL
, false);
249 case DNS_TRANSACTION_NULL
:
250 case DNS_TRANSACTION_PENDING
:
251 case DNS_TRANSACTION_VALIDATING
:
253 assert_not_reached("Impossible state");
259 static int dns_stub_stream_complete(DnsStream
*s
, int error
) {
262 log_debug_errno(error
, "DNS TCP connection terminated, destroying queries: %m");
267 q
= set_first(s
->queries
);
274 /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
275 * should be kept as long as the client wants to. */
280 static void dns_stub_process_query(Manager
*m
, DnsStream
*s
, DnsPacket
*p
) {
286 assert(p
->protocol
== DNS_PROTOCOL_DNS
);
288 if (in_addr_is_localhost(p
->family
, &p
->sender
) <= 0 ||
289 in_addr_is_localhost(p
->family
, &p
->destination
) <= 0) {
290 log_error("Got packet on unexpected IP range, refusing.");
291 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
295 r
= dns_packet_extract(p
);
297 log_debug_errno(r
, "Failed to extract resources from incoming packet, ignoring packet: %m");
298 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_FORMERR
, false);
302 if (!DNS_PACKET_VERSION_SUPPORTED(p
)) {
303 log_debug("Got EDNS OPT field with unsupported version number.");
304 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_BADVERS
, false);
308 if (dns_type_is_obsolete(p
->question
->keys
[0]->type
)) {
309 log_debug("Got message with obsolete key type, refusing.");
310 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
314 if (dns_type_is_zone_transer(p
->question
->keys
[0]->type
)) {
315 log_debug("Got request for zone transfer, refusing.");
316 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
320 if (!DNS_PACKET_RD(p
)) {
321 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
322 log_debug("Got request with recursion disabled, refusing.");
323 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_REFUSED
, false);
327 if (DNS_PACKET_DO(p
) && DNS_PACKET_CD(p
)) {
328 log_debug("Got request with DNSSEC CD bit set, refusing.");
329 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_NOTIMP
, false);
333 r
= dns_query_new(m
, &q
, p
->question
, p
->question
, 0, SD_RESOLVED_PROTOCOLS_ALL
|SD_RESOLVED_NO_SEARCH
);
335 log_error_errno(r
, "Failed to generate query object: %m");
336 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
340 /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
343 q
->request_dns_packet
= dns_packet_ref(p
);
344 q
->request_dns_stream
= dns_stream_ref(s
); /* make sure the stream stays around until we can send a reply through it */
345 q
->complete
= dns_stub_query_complete
;
348 /* Remember which queries belong to this stream, so that we can cancel them when the stream
349 * is disconnected early */
351 r
= set_ensure_allocated(&s
->queries
, &trivial_hash_ops
);
357 if (set_put(s
->queries
, q
) < 0) {
365 log_error_errno(r
, "Failed to start query: %m");
366 dns_stub_send_failure(m
, s
, p
, DNS_RCODE_SERVFAIL
, false);
370 log_debug("Processing query...");
377 static int on_dns_stub_packet(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
378 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
379 Manager
*m
= userdata
;
382 r
= manager_recv(m
, fd
, DNS_PROTOCOL_DNS
, &p
);
386 if (dns_packet_validate_query(p
) > 0) {
387 log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p
));
389 dns_stub_process_query(m
, NULL
, p
);
391 log_debug("Invalid DNS stub UDP packet, ignoring.");
396 static int manager_dns_stub_udp_fd(Manager
*m
) {
397 union sockaddr_union sa
= {
398 .in
.sin_family
= AF_INET
,
399 .in
.sin_port
= htobe16(53),
400 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
402 _cleanup_close_
int fd
= -1;
405 if (m
->dns_stub_udp_fd
>= 0)
406 return m
->dns_stub_udp_fd
;
408 fd
= socket(AF_INET
, SOCK_DGRAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
412 r
= setsockopt_int(fd
, SOL_SOCKET
, SO_REUSEADDR
, true);
416 r
= setsockopt_int(fd
, IPPROTO_IP
, IP_PKTINFO
, true);
420 r
= setsockopt_int(fd
, IPPROTO_IP
, IP_RECVTTL
, true);
424 /* Make sure no traffic from outside the local host can leak to onto this socket */
425 r
= socket_bind_to_ifindex(fd
, LOOPBACK_IFINDEX
);
429 if (bind(fd
, &sa
.sa
, sizeof(sa
.in
)) < 0)
432 r
= sd_event_add_io(m
->event
, &m
->dns_stub_udp_event_source
, fd
, EPOLLIN
, on_dns_stub_packet
, m
);
436 (void) sd_event_source_set_description(m
->dns_stub_udp_event_source
, "dns-stub-udp");
438 return m
->dns_stub_udp_fd
= TAKE_FD(fd
);
441 static int on_dns_stub_stream_packet(DnsStream
*s
) {
442 _cleanup_(dns_packet_unrefp
) DnsPacket
*p
= NULL
;
446 p
= dns_stream_take_read_packet(s
);
449 if (dns_packet_validate_query(p
) > 0) {
450 log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p
));
452 dns_stub_process_query(s
->manager
, s
, p
);
454 log_debug("Invalid DNS stub TCP packet, ignoring.");
459 static int on_dns_stub_stream(sd_event_source
*s
, int fd
, uint32_t revents
, void *userdata
) {
461 Manager
*m
= userdata
;
464 cfd
= accept4(fd
, NULL
, NULL
, SOCK_NONBLOCK
|SOCK_CLOEXEC
);
466 if (ERRNO_IS_ACCEPT_AGAIN(errno
))
472 r
= dns_stream_new(m
, &stream
, DNS_STREAM_STUB
, DNS_PROTOCOL_DNS
, cfd
, NULL
);
478 stream
->on_packet
= on_dns_stub_stream_packet
;
479 stream
->complete
= dns_stub_stream_complete
;
481 /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
486 static int manager_dns_stub_tcp_fd(Manager
*m
) {
487 union sockaddr_union sa
= {
488 .in
.sin_family
= AF_INET
,
489 .in
.sin_addr
.s_addr
= htobe32(INADDR_DNS_STUB
),
490 .in
.sin_port
= htobe16(53),
492 _cleanup_close_
int fd
= -1;
495 if (m
->dns_stub_tcp_fd
>= 0)
496 return m
->dns_stub_tcp_fd
;
498 fd
= socket(AF_INET
, SOCK_STREAM
|SOCK_CLOEXEC
|SOCK_NONBLOCK
, 0);
502 r
= setsockopt_int(fd
, IPPROTO_IP
, IP_TTL
, true);
506 r
= setsockopt_int(fd
, SOL_SOCKET
, SO_REUSEADDR
, true);
510 r
= setsockopt_int(fd
, IPPROTO_IP
, IP_PKTINFO
, true);
514 r
= setsockopt_int(fd
, IPPROTO_IP
, IP_RECVTTL
, true);
518 /* Make sure no traffic from outside the local host can leak to onto this socket */
519 r
= socket_bind_to_ifindex(fd
, LOOPBACK_IFINDEX
);
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");
535 return m
->dns_stub_tcp_fd
= TAKE_FD(fd
);
538 int manager_dns_stub_start(Manager
*m
) {
539 const char *t
= "UDP";
544 if (m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_NO
)
545 log_debug("Not creating stub listener.");
547 log_debug("Creating stub listener using %s.",
548 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_UDP
? "UDP" :
549 m
->dns_stub_listener_mode
== DNS_STUB_LISTENER_TCP
? "TCP" :
552 if (IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_UDP
))
553 r
= manager_dns_stub_udp_fd(m
);
556 IN_SET(m
->dns_stub_listener_mode
, DNS_STUB_LISTENER_YES
, DNS_STUB_LISTENER_TCP
)) {
558 r
= manager_dns_stub_tcp_fd(m
);
561 if (IN_SET(r
, -EADDRINUSE
, -EPERM
)) {
562 if (r
== -EADDRINUSE
)
564 "Another process is already listening on %s socket 127.0.0.53:53.\n"
565 "Turning off local DNS stub support.", t
);
568 "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
569 "Turning off local DNS stub support.", t
);
570 manager_dns_stub_stop(m
);
572 return log_error_errno(r
, "Failed to listen on %s socket 127.0.0.53:53: %m", t
);
577 void manager_dns_stub_stop(Manager
*m
) {
580 m
->dns_stub_udp_event_source
= sd_event_source_unref(m
->dns_stub_udp_event_source
);
581 m
->dns_stub_tcp_event_source
= sd_event_source_unref(m
->dns_stub_tcp_event_source
);
583 m
->dns_stub_udp_fd
= safe_close(m
->dns_stub_udp_fd
);
584 m
->dns_stub_tcp_fd
= safe_close(m
->dns_stub_tcp_fd
);