Re: [PATCH] block: nbd: fix sanity check for first_minor

[Pavel Skripkin]

On 10/9/21 08:35, Yan, Zheng wrote:

+CC Christoph

> From: "Yan, Zheng" <yanzheng03@xxxxxxxxxxxx>
>
> Device's minor is a 20-bits number, max value is 0xfffff.
>
> Fixes: b1a811633f ("block: nbd: add sanity check for first_minor").
> Signed-off-by: "Yan, Zheng" <yanzheng03@xxxxxxxxxxxx>
> ---
>   drivers/block/nbd.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 1183f7872b71..53cd038c96e9 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1753,7 +1753,7 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
>   	 * byte in __device_add_disk().
>   	 */
>   	disk->first_minor = index << part_shift;
> -	if (disk->first_minor > 0xff) {
> +	if (disk->first_minor > MINORMASK) {
>   		err = -EINVAL;
>   		goto out_free_idr;
>   	}

I've looked into what confused me with 0xff and I found that uapi's 
kdev_t.h has following MINOR definition:

#define MINOR(dev)	((dev) & 0xff)


But kernel's kdev_t.h is really allows 20 bit minor number :)

Also, can you, please, fix up comment above this check, since it 
contains info about max minor 0xff and it can confuse readers.




With regards,
Pavel Skripkin