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Date:   Thu, 12 Aug 2021 08:18:39 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Pavel Skripkin <paskripkin@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>, Hillf Danton <hdanton@sina.com>,
        syzbot <syzbot+9937dc42271cd87d4b98@syzkaller.appspotmail.com>,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        Eric Sandeen <sandeen@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [syzbot] WARNING in internal_create_group
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On Thu, Aug 12, 2021 at 12:37:08AM +0300, Pavel Skripkin wrote:
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1725,7 +1725,17 @@ static int nbd_dev_add(int index)
>  	refcount_set(&nbd->refs, 1);
>  	INIT_LIST_HEAD(&nbd->list);
>  	disk->major = NBD_MAJOR;
> +
> +	/* Too big first_minor can cause duplicate creation of
> +	 * sysfs files/links, since first_minor will be truncated to
> +	 * byte in __device_add_disk().
> +	 */
>  	disk->first_minor = index << part_shift;
> +	if (disk->first_minor > 0xff) {
> +		err = -EINVAL;
> +		goto out_free_idr;
> +	}
> +
>  	disk->minors = 1 << part_shift;
>  	disk->fops = &nbd_fops;
>  	disk->private_data = nbd;
>
>
> What to do you think about it?

This sounds reasonable and looks good to me.