cuse: prevent clone

For cloned connections cuse_channel_release() will be called more than
once, resulting in use after free.

Prevent device cloning for CUSE, which does not make sense at this point,
and highly unlikely to be used in real life.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/cuse.c

@@ -627,6 +627,8 @@ static int __init cuse_init(void)
 	cuse_channel_fops.owner		= THIS_MODULE;
 	cuse_channel_fops.open		= cuse_channel_open;
 	cuse_channel_fops.release	= cuse_channel_release;
+	/* CUSE is not prepared for FUSE_DEV_IOC_CLONE */
+	cuse_channel_fops.unlocked_ioctl	= NULL;
 
 	cuse_class = class_create(THIS_MODULE, "cuse");
 	if (IS_ERR(cuse_class))