vfs - fix dentry ref count in do_lookup()

There is a ref count problem in fs/namei.c:do_lookup().

When walking in ref-walk mode, if follow_managed() returns a fail we
need to drop dentry and possibly vfsmount. Clean up properly,
as we do in the other caller of follow_managed().

Signed-off-by: Ian Kent <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/namei.c

···
 	path->mnt = mnt;
 	path->dentry = dentry;
 	err = follow_managed(path, nd->flags);
-	if (unlikely(err < 0))
+	if (unlikely(err < 0)) {
+		path_put_conditional(path, nd);
 		return err;
+	}
 	*inode = path->dentry->d_inode;
 	return 0;