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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Apr 17, 2023 at 05:53:17PM +0400, Denis Efremov (Oracle) wrote:
> 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.

{sigh}  You would have thought I would have insisted on a big comment
here about this.  I'll do so this time, thanks for letting me know.

greg k-h