linux-kernel - Re: [PATCH] block: nbd: fix sanity check for first

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Message-ID: <ac132dff-ccde-bb14-9590-50f5b9f076e5@gmail.com>
Date:   Sat, 9 Oct 2021 11:46:23 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     "Yan, Zheng" <ukernel@...il.com>, axboe@...nel.dk,
        Christoph Hellwig <hch@....de>
Cc:     "Yan, Zheng" <yanzheng03@...ishou.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: nbd: fix sanity check for first_minor

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

+CC Christoph

> From: "Yan, Zheng" <yanzheng03@...ishou.com>
> 
> 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@...ishou.com>
> ---
>   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