Re: [PATCHv2] zram: restrict add/remove attributes to root only

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Dec 04, 2016 at 09:44:13PM +0900, Sergey Senozhatsky wrote:
> zram hot_add sysfs attribute is a very 'special' attribute - reading
> from it creates a new uninitialized zram device. This file, by a mistake,
> can be read by a 'normal' user at the moment, while only root must be
> able to create a new zram device, therefore hot_add attribute must have
> S_IRUSR mode, not S_IRUGO.
> 
> Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
> Reported-by: Steven Allen <steven@stebalien.com>
> Cc: <stable@vger.kernel.org>    [4.2+]
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>  drivers/block/zram/zram_drv.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 5163c8f..3a0576f 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1413,9 +1413,16 @@ static ssize_t hot_remove_store(struct class *class,
>  	return ret ? ret : count;
>  }
>  
> +/*
> + * NOTE: hot_add attribute is not the usual read-only sysfs
> + * attribute. In a sence that reading from this file does alter
> + * the state of your system -- it creates a new un-initialized
> + * zram device and returns back this device's device_id (or an
> + * error code if it fails to create a new device).
> + */
>  static struct class_attribute zram_control_class_attrs[] = {
> -	__ATTR_RO(hot_add),
> -	__ATTR_WO(hot_remove),
> +	__ATTR(hot_add, 0400, hot_add_show, NULL),
> +	__ATTR(hot_remove, 0200, NULL, hot_remove_store),

You can leave hot_remove as __ATTR_WO(), right?  Please do so if at all
possible.

thanks,

greg k-h