Return HTTP status code for small/malformed requests

This commit makes BIND return HTTP status codes for malformed or too
small requests.

DNS request processing code would ignore such requests. Such an
approach works well for other DNS transport but does not make much
sense for HTTP, not allowing it to complete the request/response
sequence.

Suppose execution has reached the point where DNS message handling
code has been called. In that case, it means that the HTTP request has
been successfully processed, and, thus, we are expected to respond to
it either with a message containing some DNS payload or at least to
return an error status code. This commit ensures that BIND behaves
this way.

lib/isc/include/isc/netmgr.h

@@ -509,6 +509,18 @@ isc_nm_http_endpoint(isc_nmsocket_t *sock, const char *uri, isc_nm_recv_cb_t cb,
 bool
 isc_nm_is_http_handle(isc_nmhandle_t *handle);
 
+void
+isc_nm_bad_request(isc_nmhandle_t *handle);
+/*%<
+ * Perform a transport protocol specific action on the handle in case of a
+ * bad/malformed incoming DNS message.
+ *
+ * NOTE: The function currently is no-op for any protocol except HTTP/2.
+ *
+ * Requires:
+ *  \li 'handle' is a valid netmgr handle object.
+ */
+
 void
 isc_nm_task_enqueue(isc_nm_t *mgr, isc_task_t *task, int threadid);
 /*%<

lib/isc/netmgr/http.c

@@ -2001,6 +2001,21 @@ server_call_cb(isc_nmsocket_t *socket, isc_nm_http_session_t *session,
 	isc_nmhandle_detach(&handle);
 }
 
+void
+isc__nm_http_bad_request(isc_nmhandle_t *handle) {
+	isc_nmsocket_t *sock = NULL;
+
+	REQUIRE(VALID_NMHANDLE(handle));
+	REQUIRE(VALID_NMSOCK(handle->sock));
+	sock = handle->sock;
+	REQUIRE(sock->type == isc_nm_httpsocket);
+	REQUIRE(!atomic_load(&sock->client));
+	REQUIRE(VALID_HTTP2_SESSION(sock->h2.session));
+
+	(void)server_send_error_response(ISC_HTTP_ERROR_BAD_REQUEST,
+					 sock->h2.session->ngsession, sock);
+}
+
 static int
 server_on_request_recv(nghttp2_session *ngsession,
 		       isc_nm_http_session_t *session, isc_nmsocket_t *socket) {

lib/isc/netmgr/netmgr-int.h

@@ -1654,6 +1654,16 @@ isc__nm_http_read(isc_nmhandle_t *handle, isc_nm_recv_cb_t cb, void *cbarg);
 void
 isc__nm_http_close(isc_nmsocket_t *sock);
 
+void
+isc__nm_http_bad_request(isc_nmhandle_t *handle);
+/*%<
+ * Respond to the request with 400 "Bad Request" status.
+ *
+ * Requires:
+ * \li 'handle' is a valid HTTP netmgr handle object, referencing a server-side
+ * socket
+ */
+
 void
 isc__nm_async_httpsend(isc__networker_t *worker, isc__netievent_t *ev0);
 

lib/isc/netmgr/netmgr.c

@@ -3301,6 +3301,38 @@ isc_nm_sequential(isc_nmhandle_t *handle) {
 	atomic_store(&sock->sequential, true);
 }
 
+void
+isc_nm_bad_request(isc_nmhandle_t *handle) {
+	isc_nmsocket_t *sock;
+
+	REQUIRE(VALID_NMHANDLE(handle));
+	REQUIRE(VALID_NMSOCK(handle->sock));
+
+	sock = handle->sock;
+	switch (sock->type) {
+#if HAVE_LIBNGHTTP2
+	case isc_nm_httpsocket:
+		isc__nm_http_bad_request(handle);
+		break;
+#endif /* HAVE_LIBNGHTTP2 */
+
+	case isc_nm_udpsocket:
+	case isc_nm_tcpdnssocket:
+	case isc_nm_tlsdnssocket:
+		return;
+		break;
+
+	case isc_nm_tcpsocket:
+#if HAVE_LIBNGHTTP2
+	case isc_nm_tlssocket:
+#endif /* HAVE_LIBNGHTTP2 */
+	default:
+		INSIST(0);
+		ISC_UNREACHABLE();
+		break;
+	}
+}
+
 #ifdef NETMGR_TRACE
 /*
  * Dump all active sockets in netmgr. We output to stderr

lib/ns/client.c

@@ -1724,6 +1724,7 @@ ns__client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		ns_client_log(client, DNS_LOGCATEGORY_SECURITY,
 			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(10),
 			      "dropped request: suspicious port");
+		isc_nm_bad_request(handle);
 		return;
 	}
 #endif /* if NS_CLIENT_DROPPORT */
@@ -1737,6 +1738,7 @@ ns__client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		ns_client_log(client, DNS_LOGCATEGORY_SECURITY,
 			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(10),
 			      "dropped request: blackholed peer");
+		isc_nm_bad_request(handle);
 		return;
 	}
 
@@ -1750,6 +1752,7 @@ ns__client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		 * There isn't enough header to determine whether
 		 * this was a request or a response.  Drop it.
 		 */
+		isc_nm_bad_request(handle);
 		return;
 	}
 
@@ -1766,6 +1769,7 @@ ns__client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 	 */
 	if ((flags & DNS_MESSAGEFLAG_QR) != 0) {
 		CTRACE("unexpected response");
+		isc_nm_bad_request(handle);
 		return;
 	}