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-rw-r--r--src/resolve/resolved-dns-stub.c586
1 files changed, 586 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-stub.c b/src/resolve/resolved-dns-stub.c
new file mode 100644
index 0000000..a00716c
--- /dev/null
+++ b/src/resolve/resolved-dns-stub.c
@@ -0,0 +1,586 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#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) {
+ /* 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));
+
+ if (add_opt) {
+ r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
+ if (r < 0)
+ return r;
+ }
+
+ return 0;
+}
+
+static void dns_stub_detach_stream(DnsStream *s) {
+ assert(s);
+
+ s->complete = NULL;
+ s->on_packet = NULL;
+ s->query = NULL;
+}
+
+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;
+ }
+
+ 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");
+ }
+
+ /* If there's a packet to write set, let's leave the stream around */
+ if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
+
+ /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
+ * default completion action of the stream will drop the reference. */
+
+ dns_stub_detach_stream(q->request_dns_stream);
+ q->request_dns_stream = NULL;
+ }
+
+ 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 query: %m");
+
+ assert(s->query);
+ dns_query_free(s->query);
+
+ 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);
+
+ /* Takes ownership of the *s stream object */
+
+ 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) {
+ s->on_packet = NULL;
+ s->complete = dns_stub_stream_complete;
+ s->query = q;
+ }
+
+ 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:
+ if (s && DNS_STREAM_QUEUED(s))
+ dns_stub_detach_stream(s);
+
+ 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 */
+ if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
+ return -errno;
+
+ 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.");
+
+ /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
+ * or that didn't happen in which case we want to free the stream */
+ dns_stream_unref(s);
+
+ 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 (IN_SET(errno, EAGAIN, EINTR))
+ return 0;
+
+ return -errno;
+ }
+
+ r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd, NULL);
+ if (r < 0) {
+ safe_close(cfd);
+ return r;
+ }
+
+ stream->on_packet = on_dns_stub_stream_packet;
+
+ /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
+ * of the stream, or by our packet callback, or when the manager is shut down. */
+
+ 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 */
+ if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
+ return -errno;
+
+ 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);
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-08-13 11:34:52 +0000