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

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Date:   Wed, 16 Jun 2021 13:43:39 +0000
From:   Aravind Ramesh <Aravind.Ramesh@....com>
To:     Niklas Cassel <Niklas.Cassel@....com>,
        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>
CC:     Damien Le Moal <Damien.LeMoal@....com>,
        Niklas Cassel <Niklas.Cassel@....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



> -----Original Message-----
> From: Niklas Cassel <Niklas.Cassel@....com>
> Sent: Monday, June 14, 2021 5:53 PM
> To: 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>
> Cc: Damien Le Moal <Damien.LeMoal@....com>; Niklas Cassel
> <Niklas.Cassel@....com>; stable@...r.kernel.org; Jens Axboe <axboe@...com>;
> linux-block@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: [PATCH v3 2/2] blk-zoned: allow BLKREPORTZONE without
> CAP_SYS_ADMIN
> 
> 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

Looks good,

Reviewed-by: Aravind Ramesh <aravind.ramesh@....com>