fs/smb: Fix inconsistent refcnt update

commit ab529e6 upstream.

A possible inconsistent update of refcount was identified in `smb2_compound_op`.
Such inconsistent update could lead to possible resource leaks.

Why it is a possible bug:
1. In the comment section of the function, it clearly states that the
reference to `cfile` should be dropped after calling this function.
2. Every control flow path would check and drop the reference to
`cfile`, except the patched one.
3. Existing callers would not handle refcount update of `cfile` if
-ENOMEM is returned.

To fix the bug, an extra goto label "out" is added, to make sure that the
cleanup logic would always be respected. As the problem is caused by the
allocation failure of `vars`, the cleanup logic between label "finished"
and "out" can be safely ignored. According to the definition of function
`is_replayable_error`, the error code of "-ENOMEM" is not recoverable.
Therefore, the replay logic also gets ignored.

Signed-off-by: Shuhao Fu <sfual@cse.ust.hk>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Shuhao Fu

fs/smb/client/smb2inode.c

@@ -207,8 +207,10 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 	server = cifs_pick_channel(ses);
 
 	vars = kzalloc(sizeof(*vars), GFP_ATOMIC);
-	if (vars == NULL)
-		return -ENOMEM;
+	if (vars == NULL) {
+		rc = -ENOMEM;
+		goto out;
+	}
 	rqst = &vars->rqst[0];
 	rsp_iov = &vars->rsp_iov[0];
 
@@ -864,6 +866,7 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 	    smb2_should_replay(tcon, &retries, &cur_sleep))
 		goto replay_again;
 
+out:
 	if (cfile)
 		cifsFileInfo_put(cfile);