ldap_server: Terminate LDAP connections on krb ticket expiry

See RFC4511 section 4.4.1 and

https://lists.samba.org/archive/cifs-protocol/2020-August/003515.html

for details: Windows terminates LDAP connections when the krb5 ticket
expires, Samba should do the same. This patch slightly deviates from
Windows behaviour by sending a LDAP exop response with msgid 0 that is
ASN1-encoded conforming to RFC4511.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=14465

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

selftest/knownfail.d/ldap

@@ -1,4 +1,3 @@
 # the attributes too long test returns the wrong error
 ^samba4.ldap.python.+test_attribute_ranges_too_long
 samba4.ldap.python\(ad_dc_default\).*__main__.BasicTests.test_ldapSearchNoAttributes
-^samba4.ldap.session-expiry.session-expiry\(ad_dc_default\)

source4/ldap_server/ldap_backend.c

@@ -1384,11 +1384,48 @@ static NTSTATUS ldapsrv_AbandonRequest(struct ldapsrv_call *call)
 	return NT_STATUS_OK;
 }
 
+static NTSTATUS ldapsrv_expired(struct ldapsrv_call *call)
+{
+	struct ldapsrv_reply *reply = NULL;
+	struct ldap_ExtendedResponse *r = NULL;
+
+	DBG_DEBUG("Sending connection expired message\n");
+
+	reply = ldapsrv_init_reply(call, LDAP_TAG_ExtendedResponse);
+	if (reply == NULL) {
+		return NT_STATUS_NO_MEMORY;
+	}
+
+	/*
+	 * According to RFC4511 section 4.4.1 this has a msgid of 0
+	 */
+	reply->msg->messageid = 0;
+
+	r = &reply->msg->r.ExtendedResponse;
+	r->response.resultcode = LDB_ERR_UNAVAILABLE;
+	r->response.errormessage = "The server has timed out this connection";
+	r->oid = "1.3.6.1.4.1.1466.20036"; /* see rfc4511 section 4.4.1 */
+
+	ldapsrv_queue_reply(call, reply);
+	return NT_STATUS_OK;
+}
+
 NTSTATUS ldapsrv_do_call(struct ldapsrv_call *call)
 {
 	unsigned int i;
 	struct ldap_message *msg = call->request;
+	struct ldapsrv_connection *conn = call->conn;
 	NTSTATUS status;
+	bool expired;
+
+	expired = timeval_expired(&conn->limits.expire_time);
+	if (expired) {
+		status = ldapsrv_expired(call);
+		if (!NT_STATUS_IS_OK(status)) {
+			return status;
+		}
+		return NT_STATUS_NETWORK_SESSION_EXPIRED;
+	}
 
 	/* Check for undecoded critical extensions */
 	for (i=0; msg->controls && msg->controls[i]; i++) {

source4/ldap_server/ldap_server.c

@@ -69,6 +69,7 @@ static void ldapsrv_terminate_connection(struct ldapsrv_connection *conn,
 
 	tevent_queue_stop(conn->sockets.send_queue);
 	TALLOC_FREE(conn->sockets.read_req);
+	TALLOC_FREE(conn->deferred_expire_disconnect);
 	if (conn->active_call) {
 		tevent_req_cancel(conn->active_call);
 		conn->active_call = NULL;
@@ -1014,16 +1015,62 @@ static struct tevent_req *ldapsrv_process_call_send(TALLOC_CTX *mem_ctx,
 	return req;
 }
 
+static void ldapsrv_disconnect_ticket_expired(struct tevent_req *subreq);
+
 static void ldapsrv_process_call_trigger(struct tevent_req *req,
 					 void *private_data)
 {
 	struct ldapsrv_process_call_state *state =
 		tevent_req_data(req,
 		struct ldapsrv_process_call_state);
+	struct ldapsrv_connection *conn = state->call->conn;
 	NTSTATUS status;
 
+	if (conn->deferred_expire_disconnect != NULL) {
+		/*
+		 * Just drop this on the floor
+		 */
+		tevent_req_done(req);
+		return;
+	}
+
 	/* make the call */
 	status = ldapsrv_do_call(state->call);
+
+	if (NT_STATUS_EQUAL(status, NT_STATUS_NETWORK_SESSION_EXPIRED)) {
+		/*
+		 * For testing purposes, defer the TCP disconnect
+		 * after having sent the msgid 0
+		 * 1.3.6.1.4.1.1466.20036 exop response. LDAP clients
+		 * should not wait for the TCP connection to close but
+		 * handle this packet equivalent to a TCP
+		 * disconnect. This delay enables testing both cases
+		 * in LDAP client libraries.
+		 */
+
+		int defer_msec = lpcfg_parm_int(
+			conn->lp_ctx,
+			NULL,
+			"ldap_server",
+			"delay_expire_disconnect",
+			0);
+
+		conn->deferred_expire_disconnect = tevent_wakeup_send(
+			conn,
+			conn->connection->event.ctx,
+			timeval_current_ofs_msec(defer_msec));
+		if (tevent_req_nomem(conn->deferred_expire_disconnect, req)) {
+			return;
+		}
+		tevent_req_set_callback(
+			conn->deferred_expire_disconnect,
+			ldapsrv_disconnect_ticket_expired,
+			conn);
+
+		tevent_req_done(req);
+		return;
+	}
+
 	if (!NT_STATUS_IS_OK(status)) {
 		tevent_req_nterror(req, status);
 		return;
@@ -1032,6 +1079,21 @@ static void ldapsrv_process_call_trigger(struct tevent_req *req,
 	tevent_req_done(req);
 }
 
+static void ldapsrv_disconnect_ticket_expired(struct tevent_req *subreq)
+{
+	struct ldapsrv_connection *conn = tevent_req_callback_data(
+		subreq, struct ldapsrv_connection);
+	bool ok;
+
+	ok = tevent_wakeup_recv(subreq);
+	TALLOC_FREE(subreq);
+	if (!ok) {
+		DBG_WARNING("tevent_wakeup_recv failed\n");
+	}
+	conn->deferred_expire_disconnect = NULL;
+	ldapsrv_terminate_connection(conn, "network session expired");
+}
+
 static NTSTATUS ldapsrv_process_call_recv(struct tevent_req *req)
 {
 	NTSTATUS status;

source4/ldap_server/ldap_server.h

@@ -66,6 +66,7 @@ struct ldapsrv_connection {
 	} limits;
 
 	struct tevent_req *active_call;
+	struct tevent_req *deferred_expire_disconnect;
 
 	struct ldapsrv_call *pending_calls;
 };