linux-kernel - Re: [PATCH v3 2/2] blk-zoned: allow BLKREPORTZONE without CAP_SYS

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Date:   Fri, 18 Jun 2021 14:49:56 +0000
From:   Adam Manzanares <a.manzanares@...sung.com>
To:     Niklas Cassel <Niklas.Cassel@....com>
CC:     Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Shaun Tancheff <shaun@...cheff.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jens Axboe <axboe@...com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] blk-zoned: allow BLKREPORTZONE without
 CAP_SYS_ADMIN

On Mon, Jun 14, 2021 at 12:23:21PM +0000, Niklas Cassel wrote:
> From: Niklas Cassel <niklas.cassel@....com>
> 
> A user space process should not need the CAP_SYS_ADMIN capability set
> in order to perform a BLKREPORTZONE ioctl.
> 
> Getting the zone report is required in order to get the write pointer.
> Neither read() nor write() requires CAP_SYS_ADMIN, so it is reasonable
> that a user space process that can read/write from/to the device, also
> can get the write pointer. (Since e.g. writes have to be at the write
> pointer.)
> 
> Fixes: 3ed05a987e0f ("blk-zoned: implement ioctls")
> Signed-off-by: Niklas Cassel <niklas.cassel@....com>
> Cc: stable@...r.kernel.org # v4.10+
> ---
> Changes since v2:
> -Drop the FMODE_READ check. Right now it is possible to open() the device with
> O_WRONLY and get the zone report from that fd. Therefore adding a FMODE_READ
> check on BLKREPORTZONE would break existing applications. Instead, just remove
> the existing CAP_SYS_ADMIN check.
> 
>  block/blk-zoned.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index 0789e6e9f7db..457eceabed2e 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -288,9 +288,6 @@ int blkdev_report_zones_ioctl(struct block_device *bdev, fmode_t mode,
>  	if (!blk_queue_is_zoned(q))
>  		return -ENOTTY;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> -		return -EACCES;
> -
>  	if (copy_from_user(&rep, argp, sizeof(struct blk_zone_report)))
>  		return -EFAULT;
>  
> -- 
> 2.31.1

LGTM

Reviewed-by: Adam Manzanares <a.manzanares@...sung.com>