picnoir
/
Systemd
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity
Systemd/src/resolve/resolved-dns-stub.c

581 lines
20 KiB
C
Raw Blame History

/* SPDX-License-Identifier: LGPL-2.1+ */
#include "errno-util.h"
#include "fd-util.h"
#include "missing_network.h"
#include "resolved-dns-stub.h"
#include "socket-util.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)
static int manager_dns_stub_udp_fd(Manager *m);
static int manager_dns_stub_tcp_fd(Manager *m);
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? */
int r;
assert(p);
if (add_opt) {
r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, 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, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
int r;
assert(m);
assert(p);
assert(reply);
if (s)
r = dns_stream_write_packet(s, reply);
else {
int fd;
fd = manager_dns_stub_udp_fd(m);
if (fd < 0)
return log_debug_errno(fd, "Failed to get reply socket: %m");
/* 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, fd, LOOPBACK_IFINDEX, 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, 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, false, !!p->opt, DNS_PACKET_DO(p), authenticated);
if (r < 0)
return log_debug_errno(r, "Failed to build failure packet: %m");
return dns_stub_send(m, 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->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));
if (r < 0) {
log_debug_errno(r, "Failed to finish reply packet: %m");
break;
}
(void) dns_stub_send(q->manager, 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->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->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->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, DnsStream *s, DnsPacket *p) {
DnsQuery *q = NULL;
int r;
assert(m);
assert(p);
assert(p->protocol == DNS_PROTOCOL_DNS);
if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
in_addr_is_localhost(p->family, &p->destination) <= 0) {
log_error("Got packet on unexpected IP range, refusing.");
dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
goto fail;
}
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, s, p, DNS_RCODE_FORMERR, false);
goto fail;
}
if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
log_debug("Got EDNS OPT field with unsupported version number.");
dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
goto fail;
}
if (dns_type_is_obsolete(p->question->keys[0]->type)) {
log_debug("Got message with obsolete key type, refusing.");
dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
goto fail;
}
if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
log_debug("Got request for zone transfer, refusing.");
dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
goto fail;
}
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, s, p, DNS_RCODE_REFUSED, false);
goto fail;
}
if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
log_debug("Got request with DNSSEC CD bit set, refusing.");
dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
goto fail;
}
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, s, p, DNS_RCODE_SERVFAIL, false);
goto fail;
}
/* 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->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, &trivial_hash_ops, q);
if (r < 0) {
log_oom();
goto fail;
}
}
r = dns_query_go(q);
if (r < 0) {
log_error_errno(r, "Failed to start query: %m");
dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
goto fail;
}
log_debug("Processing query...");
return;
fail:
dns_query_free(q);
}
static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
Manager *m = userdata;
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, NULL, p);
} else
log_debug("Invalid DNS stub UDP packet, ignoring.");
return 0;
}
static int manager_dns_stub_udp_fd(Manager *m) {
union sockaddr_union sa = {
.in.sin_family = AF_INET,
.in.sin_port = htobe16(53),
.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
};
_cleanup_close_ int fd = -1;
int r;
if (m->dns_stub_udp_fd >= 0)
return m->dns_stub_udp_fd;
fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (fd < 0)
return -errno;
r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
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;
if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
return -errno;
r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
if (r < 0)
return r;
(void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
return m->dns_stub_udp_fd = TAKE_FD(fd);
}
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, p);
} else
log_debug("Invalid DNS stub TCP packet, ignoring.");
return 0;
}
static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
DnsStream *stream;
Manager *m = userdata;
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->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 manager_dns_stub_tcp_fd(Manager *m) {
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;
if (m->dns_stub_tcp_fd >= 0)
return m->dns_stub_tcp_fd;
fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (fd < 0)
return -errno;
r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, true);
if (r < 0)
return r;
r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
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;
if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
return -errno;
if (listen(fd, SOMAXCONN) < 0)
return -errno;
r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
if (r < 0)
return r;
(void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
return m->dns_stub_tcp_fd = TAKE_FD(fd);
}
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 (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
r = manager_dns_stub_udp_fd(m);
if (r >= 0 &&
IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
t = "TCP";
r = manager_dns_stub_tcp_fd(m);
}
if (IN_SET(r, -EADDRINUSE, -EPERM)) {
if (r == -EADDRINUSE)
log_warning_errno(r,
"Another process is already listening on %s socket 127.0.0.53:53.\n"
"Turning off local DNS stub support.", t);
else
log_warning_errno(r,
"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);
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);
m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
}
Reference in New Issue View Git Blame Copy Permalink