Re: [PATCH 1/1] drm: avoid exposing kernel stack in compat_drm_getstats

[Jani Nikula]

On Mon, 22 Aug 2016, Daniel Vetter <daniel@xxxxxxxx> wrote:
> On Sun, Aug 21, 2016 at 07:56:19PM +0200, Heinrich Schuchardt wrote:
>> The C standard does not specify the size of the integer used
>> to store an enum. Hence in structure drm_stats32_t alignment
>> bytes may exist.
>> 
>> To avoid exposing bytes from the kernel stack it is
>> necessary to initialize variable s32 completely.
>> 
>> Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
>
> Applied to drm-misc, thanks.
> -Daniel
>
>> ---
>>  drivers/gpu/drm/drm_ioc32.c | 1 +
>>  1 file changed, 1 insertion(+)
>> 
>> diff --git a/drivers/gpu/drm/drm_ioc32.c b/drivers/gpu/drm/drm_ioc32.c
>> index 57676f8..32a489b 100644
>> --- a/drivers/gpu/drm/drm_ioc32.c
>> +++ b/drivers/gpu/drm/drm_ioc32.c
>> @@ -346,6 +346,7 @@ static int compat_drm_getstats(struct file *file, unsigned int cmd,
>>  	struct drm_stats __user *stats;
>>  	int i, err;
>>  
>> +	memset(&s32, 0, sizeof(drm_stats32_t));

For future reference,

	memset(&s32, 0, sizeof(s32));

is the better approach, avoiding problems if the type of s32 ever
changes.

BR,
Jani.


>>  	stats = compat_alloc_user_space(sizeof(*stats));
>>  	if (!stats)
>>  		return -EFAULT;
>> -- 
>> 2.1.4
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center