fs: dlm: check on minimum msglen size

This patch adds an additional check for minimum dlm header size which is
an invalid dlm message and signals a broken stream. A msglen field cannot
be less than the dlm header size because the field is inclusive header
lengths.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/midcomms.c

@@ -49,9 +49,10 @@ int dlm_process_incoming_buffer(int nodeid, unsigned char *buf, int len)
 		 * cannot deliver this message to upper layers
 		 */
 		msglen = get_unaligned_le16(&hd->h_length);
-		if (msglen > DEFAULT_BUFFER_SIZE) {
-			log_print("received invalid length header: %u, will abort message parsing",
-				  msglen);
+		if (msglen > DEFAULT_BUFFER_SIZE ||
+		    msglen < sizeof(struct dlm_header)) {
+			log_print("received invalid length header: %u from node %d, will abort message parsing",
+				  msglen, nodeid);
 			return -EBADMSG;
 		}