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Systemd/src/resolve/resolved-dns-stub.c

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <net/if_arp.h>
#include "errno-util.h"
#include "fd-util.h"
#include "missing_network.h"
#include "missing_socket.h"
#include "resolved-dns-stub.h"
#include "socket-netlink.h"
#include "socket-util.h"
#include "string-table.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)
/* On the extra stubs, use a more conservative choice */
#define ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX DNS_PACKET_UNICAST_SIZE_LARGE_MAX
static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type);
static void dns_stub_listener_extra_hash_func(const DnsStubListenerExtra *a, struct siphash *state) {
assert(a);
siphash24_compress(&a->mode, sizeof(a->mode), state);
siphash24_compress(&a->family, sizeof(a->family), state);
siphash24_compress(&a->address, FAMILY_ADDRESS_SIZE(a->family), state);
siphash24_compress(&a->port, sizeof(a->port), state);
}
static int dns_stub_listener_extra_compare_func(const DnsStubListenerExtra *a, const DnsStubListenerExtra *b) {
int r;
assert(a);
assert(b);
r = CMP(a->mode, b->mode);
if (r != 0)
return r;
r = CMP(a->family, b->family);
if (r != 0)
return r;
r = memcmp(&a->address, &b->address, FAMILY_ADDRESS_SIZE(a->family));
if (r != 0)
return r;
return CMP(a->port, b->port);
}
DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR(
dns_stub_listener_extra_hash_ops,
DnsStubListenerExtra,
dns_stub_listener_extra_hash_func,
dns_stub_listener_extra_compare_func,
dns_stub_listener_extra_free);
int dns_stub_listener_extra_new(
Manager *m,
DnsStubListenerExtra **ret) {
DnsStubListenerExtra *l;
l = new(DnsStubListenerExtra, 1);
if (!l)
return -ENOMEM;
*l = (DnsStubListenerExtra) {
.manager = m,
};
*ret = TAKE_PTR(l);
return 0;
}
DnsStubListenerExtra *dns_stub_listener_extra_free(DnsStubListenerExtra *p) {
if (!p)
return NULL;
p->udp_event_source = sd_event_source_unref(p->udp_event_source);
p->tcp_event_source = sd_event_source_unref(p->tcp_event_source);
return mfree(p);
}
static int dns_stub_make_reply_packet(
DnsPacket **p,
size_t max_size,
DnsQuestion *q,
DnsAnswer *answer,
bool *ret_truncated) {
bool truncated = false;
DnsResourceRecord *rr;
unsigned c = 0;
int r;
assert(p);
/* 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. */
if (!*p) {
r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0, max_size);
if (r < 0)
return r;
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, 0, NULL, NULL);
if (r == -EMSGSIZE) {
truncated = true;
break;
}
if (r < 0)
return r;
c++;
}
if (ret_truncated)
*ret_truncated = truncated;
else if (truncated)
return -EMSGSIZE;
DNS_PACKET_HEADER(*p)->ancount = htobe16(be16toh(DNS_PACKET_HEADER(*p)->ancount) + c);
return 0;
}
static int dns_stub_finish_reply_packet(
DnsPacket *p,
uint16_t id,
int rcode,
bool tc, /* set the Truncated bit? */
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? */
uint16_t max_udp_size) { /* The maximum UDP datagram size to advertise to clients */
int r;
assert(p);
if (add_opt) {
r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, rcode, NULL);
if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */
tc = true;
else if (r < 0)
return r;
} else {
/* If the client can't to EDNS0, don't do DO either */
edns0_do = false;
/* If the client didn't do EDNS, clamp the rcode to 4 bit */
if (rcode > 0xF)
rcode = DNS_RCODE_SERVFAIL;
}
/* Don't set the AD bit unless DO is on, too */
if (!edns0_do)
ad = false;
DNS_PACKET_HEADER(p)->id = id;
DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
1 /* qr */,
0 /* opcode */,
0 /* aa */,
tc /* tc */,
1 /* rd */,
1 /* ra */,
ad /* ad */,
0 /* cd */,
rcode));
return 0;
}
static int dns_stub_send(
Manager *m,
DnsStubListenerExtra *l,
DnsStream *s,
DnsPacket *p,
DnsPacket *reply) {
int r;
assert(m);
assert(p);
assert(reply);
if (s)
r = dns_stream_write_packet(s, reply);
else
/* 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,
manager_dns_stub_fd_extra(m, l, SOCK_DGRAM),
l ? p->ifindex : LOOPBACK_IFINDEX, /* force loopback iface if this is the main listener stub */
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,
DnsStubListenerExtra *l,
DnsStream *s,
DnsPacket *p,
int rcode,
bool authenticated) {
_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
int r;
assert(m);
assert(p);
r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL);
if (r < 0)
return log_debug_errno(r, "Failed to make failure packet: %m");
r = dns_stub_finish_reply_packet(
reply,
DNS_PACKET_ID(p),
rcode,
/* truncated = */ false,
!!p->opt,
DNS_PACKET_DO(p),
authenticated,
l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX);
if (r < 0)
return log_debug_errno(r, "Failed to build failure packet: %m");
return dns_stub_send(m, l, 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: {
bool truncated;
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);
if (r < 0) {
log_debug_errno(r, "Failed to build reply packet: %m");
break;
}
if (!truncated) {
r = dns_query_process_cname(q);
if (r == -ELOOP) {
(void) dns_stub_send_failure(q->manager, q->stub_listener_extra, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
break;
}
if (r < 0) {
log_debug_errno(r, "Failed to process CNAME: %m");
break;
}
if (r == DNS_QUERY_RESTARTED)
return;
}
r = dns_stub_finish_reply_packet(
q->reply_dns_packet,
DNS_PACKET_ID(q->request_dns_packet),
q->answer_rcode,
truncated,
!!q->request_dns_packet->opt,
DNS_PACKET_DO(q->request_dns_packet),
dns_query_fully_authenticated(q),
q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX);
if (r < 0) {
log_debug_errno(r, "Failed to finish reply packet: %m");
break;
}
(void) dns_stub_send(q->manager, q->stub_listener_extra, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
break;
}
case DNS_TRANSACTION_RCODE_FAILURE:
(void) dns_stub_send_failure(q->manager, q->stub_listener_extra, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
break;
case DNS_TRANSACTION_NOT_FOUND:
(void) dns_stub_send_failure(q->manager, q->stub_listener_extra, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
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->stub_listener_extra, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
break;
case DNS_TRANSACTION_NULL:
case DNS_TRANSACTION_PENDING:
case DNS_TRANSACTION_VALIDATING:
default:
assert_not_reached("Impossible state");
}
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 queries: %m");
for (;;) {
DnsQuery *q;
q = set_first(s->queries);
if (!q)
break;
dns_query_free(q);
}
/* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
* should be kept as long as the client wants to. */
dns_stream_unref(s);
return 0;
}
static void dns_stub_process_query(Manager *m, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) {
_cleanup_(dns_query_freep) DnsQuery *q = NULL;
int r;
assert(m);
assert(p);
assert(p->protocol == DNS_PROTOCOL_DNS);
if (!l && /* l == NULL if this is the main stub */
(in_addr_is_localhost(p->family, &p->sender) <= 0 ||
in_addr_is_localhost(p->family, &p->destination) <= 0)) {
log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring.");
return;
}
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, l, s, p, DNS_RCODE_FORMERR, false);
return;
}
if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
log_debug("Got EDNS OPT field with unsupported version number.");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false);
return;
}
if (dns_type_is_obsolete(p->question->keys[0]->type)) {
log_debug("Got message with obsolete key type, refusing.");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false);
return;
}
if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
log_debug("Got request for zone transfer, refusing.");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false);
return;
}
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, l, s, p, DNS_RCODE_REFUSED, false);
return;
}
if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
log_debug("Got request with DNSSEC CD bit set, refusing.");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_NOTIMP, false);
return;
}
r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH);
if (r < 0) {
log_error_errno(r, "Failed to generate query object: %m");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
return;
}
/* 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->stub_listener_extra = l;
q->complete = dns_stub_query_complete;
if (s) {
/* Remember which queries belong to this stream, so that we can cancel them when the stream
* is disconnected early */
r = set_ensure_put(&s->queries, NULL, q);
if (r < 0) {
log_oom();
return;
}
assert(r > 0);
}
r = dns_query_go(q);
if (r < 0) {
log_error_errno(r, "Failed to start query: %m");
dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false);
return;
}
log_debug("Processing query...");
TAKE_PTR(q);
}
static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
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, l, NULL, p);
} else
log_debug("Invalid DNS stub UDP packet, ignoring.");
return 0;
}
static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL);
}
static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
DnsStubListenerExtra *l = userdata;
assert(l);
return on_dns_stub_packet_internal(s, fd, revents, l->manager, l);
}
static int on_dns_stub_stream_packet(DnsStream *s) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
assert(s);
p = dns_stream_take_read_packet(s);
assert(p);
if (dns_packet_validate_query(p) > 0) {
log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
dns_stub_process_query(s->manager, s->stub_listener_extra, s, p);
} else
log_debug("Invalid DNS stub TCP packet, ignoring.");
return 0;
}
static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) {
DnsStream *stream;
int cfd, r;
cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
if (cfd < 0) {
if (ERRNO_IS_ACCEPT_AGAIN(errno))
return 0;
return -errno;
}
r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
if (r < 0) {
safe_close(cfd);
return r;
}
stream->stub_listener_extra = l;
stream->on_packet = on_dns_stub_stream_packet;
stream->complete = dns_stub_stream_complete;
/* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
return 0;
}
static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL);
}
static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
DnsStubListenerExtra *l = userdata;
assert(l);
return on_dns_stub_stream_internal(s, fd, revents, l->manager, l);
}
static int set_dns_stub_common_socket_options(int fd, int family) {
int r;
assert(fd >= 0);
assert(IN_SET(family, AF_INET, AF_INET6));
r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return r;
r = socket_set_recvpktinfo(fd, family, true);
if (r < 0)
return r;
r = socket_set_recvttl(fd, family, true);
if (r < 0)
return r;
return 0;
}
static int manager_dns_stub_fd(Manager *m, int type) {
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;
assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
sd_event_source **event_source = type == SOCK_DGRAM ? &m->dns_stub_udp_event_source : &m->dns_stub_tcp_event_source;
if (*event_source)
return sd_event_source_get_io_fd(*event_source);
fd = socket(AF_INET, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
if (fd < 0)
return -errno;
r = set_dns_stub_common_socket_options(fd, AF_INET);
if (r < 0)
return r;
/* Make sure no traffic from outside the local host can leak to onto this socket */
r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, 1);
if (r < 0)
return r;
if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
return -errno;
if (type == SOCK_STREAM &&
listen(fd, SOMAXCONN) < 0)
return -errno;
r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream,
m);
if (r < 0)
return r;
r = sd_event_source_set_io_fd_own(*event_source, true);
if (r < 0)
return r;
(void) sd_event_source_set_description(*event_source,
type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp");
return TAKE_FD(fd);
}
static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) {
_cleanup_free_ char *pretty = NULL;
_cleanup_close_ int fd = -1;
union sockaddr_union sa;
int r;
assert(m);
assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM));
if (!l)
return manager_dns_stub_fd(m, type);
sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source;
if (*event_source)
return sd_event_source_get_io_fd(*event_source);
if (l->family == AF_INET)
sa = (union sockaddr_union) {
.in.sin_family = l->family,
.in.sin_port = htobe16(l->port != 0 ? l->port : 53U),
.in.sin_addr = l->address.in,
};
else
sa = (union sockaddr_union) {
.in6.sin6_family = l->family,
.in6.sin6_port = htobe16(l->port != 0 ? l->port : 53U),
.in6.sin6_addr = l->address.in6,
};
fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
if (fd < 0) {
r = -errno;
goto fail;
}
r = set_dns_stub_common_socket_options(fd, l->family);
if (r < 0)
goto fail;
/* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case
* people may want ttl > 1. */
r = socket_set_freebind(fd, l->family, true);
if (r < 0)
goto fail;
if (bind(fd, &sa.sa, SOCKADDR_LEN(sa)) < 0) {
r = -errno;
goto fail;
}
if (type == SOCK_STREAM &&
listen(fd, SOMAXCONN) < 0) {
r = -errno;
goto fail;
}
r = sd_event_add_io(m->event, event_source, fd, EPOLLIN,
type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra,
l);
if (r < 0)
goto fail;
r = sd_event_source_set_io_fd_own(*event_source, true);
if (r < 0)
goto fail;
(void) sd_event_source_set_description(*event_source,
type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra");
if (DEBUG_LOGGING) {
(void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
log_debug("Listening on %s socket %s.",
type == SOCK_DGRAM ? "UDP" : "TCP",
strnull(pretty));
}
return TAKE_FD(fd);
fail:
assert(r < 0);
(void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty);
return log_warning_errno(r,
r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" :
"Failed to listen on %s socket %s: %m",
type == SOCK_DGRAM ? "UDP" : "TCP",
strnull(pretty));
}
int manager_dns_stub_start(Manager *m) {
const char *t = "UDP";
int r = 0;
assert(m);
if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
log_debug("Not creating stub listener.");
else
log_debug("Creating stub listener using %s.",
m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
"UDP/TCP");
if (FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_UDP))
r = manager_dns_stub_fd(m, SOCK_DGRAM);
if (r >= 0 &&
FLAGS_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_TCP)) {
t = "TCP";
r = manager_dns_stub_fd(m, SOCK_STREAM);
}
if (IN_SET(r, -EADDRINUSE, -EPERM)) {
log_warning_errno(r,
r == -EADDRINUSE ? "Another process is already listening on %s socket 127.0.0.53:53.\n"
"Turning off local DNS stub support." :
"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);
if (!ordered_set_isempty(m->dns_extra_stub_listeners)) {
DnsStubListenerExtra *l;
log_debug("Creating extra stub listeners.");
ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) {
if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP))
(void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM);
if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP))
(void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM);
}
}
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);
}
static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = {
[DNS_STUB_LISTENER_NO] = "no",
[DNS_STUB_LISTENER_UDP] = "udp",
[DNS_STUB_LISTENER_TCP] = "tcp",
[DNS_STUB_LISTENER_YES] = "yes",
};
DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES);
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