cifs: handle errors from coalesce_t2

cifs_demultiplex_thread calls coalesce_t2 to try and merge follow-on t2
responses into the original mid buffer. coalesce_t2 however can return
errors, but the caller doesn't handle that situation properly. Fix the
thread to treat such a case as it would a malformed packet. Mark the
mid as being malformed and issue the callback.

Cc: stable@kernel.org
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -630,12 +630,16 @@ cifs_demultiplex_thread(struct TCP_Server_Info *server)
 				isMultiRsp = true;
 				if (mid_entry->resp_buf) {
 					/* merge response - fix up 1st*/
-					if (coalesce_t2(smb_buffer,
-							mid_entry->resp_buf)) {
+					length = coalesce_t2(smb_buffer,
+							mid_entry->resp_buf);
+					if (length > 0) {
+						length = 0;
 						mid_entry->multiRsp = true;
 						break;
 					} else {
-						/* all parts received */
+						/* all parts received or
+						 * packet is malformed
+						 */
 						mid_entry->multiEnd = true;
 						goto multi_t2_fnd;
 					}