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

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

[Heinrich Schuchardt]

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@gmx.de>
---
 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));
 	stats = compat_alloc_user_space(sizeof(*stats));
 	if (!stats)
 		return -EFAULT;
-- 
2.1.4

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

[Daniel Vetter]

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@gmx.de>

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));
>  	stats = compat_alloc_user_space(sizeof(*stats));
>  	if (!stats)
>  		return -EFAULT;
> -- 
> 2.1.4
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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

[Jani Nikula]

On Mon, 22 Aug 2016, Daniel Vetter <daniel@ffwll.ch> 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@gmx.de>
>
> 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
>> 
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Jani Nikula, Intel Open Source Technology Center