linux-kernel - Re: [PATCH] driver core: class: mark the struct class for sysfs callbacks as constant

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Date:   Mon, 17 Apr 2023 17:53:17 +0400
From:   "Denis Efremov (Oracle)" <efremov@...ux.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, Minchan Kim <minchan@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Wade Mealing <wmealing@...hat.com>
Subject: Re: [PATCH] driver core: class: mark the struct class for sysfs
 callbacks as constant

Hello,

On 3/25/23 12:45, Greg Kroah-Hartman wrote:
> struct class should never be modified in a sysfs callback as there is
> nothing in the structure to modify, and frankly, the structure is almost
> never used in a sysfs callback, so mark it as constant to allow struct
> class to be moved to read-only memory.
> 
> While we are touching all class sysfs callbacks also mark the attribute
> as constant as it can not be modified.  The bonding code still uses this
> structure so it can not be removed from the function callbacks.
>

...

> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b7bb52f8dfbd..3feadfb96114 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -2424,8 +2424,8 @@ static int zram_remove(struct zram *zram)
>   * 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 ssize_t hot_add_show(struct class *class,
> -			struct class_attribute *attr,
> +static ssize_t hot_add_show(const struct class *class,
> +			const struct class_attribute *attr,
>  			char *buf)
>  {
>  	int ret;
> @@ -2438,11 +2438,10 @@ static ssize_t hot_add_show(struct class *class,
>  		return ret;
>  	return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
>  }
> -static struct class_attribute class_attr_hot_add =
> -	__ATTR(hot_add, 0400, hot_add_show, NULL);
> +static CLASS_ATTR_RO(hot_add);
>  
> -static ssize_t hot_remove_store(struct class *class,
> -			struct class_attribute *attr,
> +static ssize_t hot_remove_store(const struct class *class,
> +			const struct class_attribute *attr,
>  			const char *buf,
>  			size_t count)
>  {

This looks like a security regression (CVE-2020-10781).
Previous fix 853eab68afc80f59f36bbdeb715e5c88c501e680.

Thanks,
Denis Efremov