Re: [PATCH] kernel: drm/vmwgfx: limit the number of mip levels in vmw_gb_surface_define_ioctl()

[Vladis Dronov]

Hello, Sinclair!

> Here, the check should be "> DRM_VMW_MAX_MIP_LEVELS" because req->mip_levels
> is only for one layer.

Got it, thanks!

> Also, as long as we can doing a check, I would suggest we check for 0 as
> well.

Do you mean a check for "req->mip_levels > 0" or for "req->mip_levels >= 0" ?

I glimpsed thru the code and I do not see problems with req->mip_levels being 0,
surely I may be mistaking.

Best regards,
Vladis Dronov | Red Hat, Inc. | Product Security Engineer


----- Original Message -----
From: "Sinclair Yeh" <syeh@xxxxxxxxxx>
To: "Vladis Dronov" <vdronov@xxxxxxxxxx>
Cc: "VMware Graphics" <linux-graphics-maintainer@xxxxxxxxxx>, "Thomas Hellstrom" <thellstrom@xxxxxxxxxx>, "David Airlie" <airlied@xxxxxxxx>, dri-devel@xxxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
Sent: Friday, March 31, 2017 5:07:12 PM
Subject: Re: [PATCH] kernel: drm/vmwgfx: limit the number of mip levels in vmw_gb_surface_define_ioctl()

Hi Vladis,


On Thu, Mar 30, 2017 at 12:27:12PM +0200, Vladis Dronov wrote:
> The 'req->mip_levels' parameter in vmw_gb_surface_define_ioctl() is
> a user-controlled 'uint32_t' value which is used as a loop count limit.
> This can lead to a kernel lockup and DoS. Add check for 'req->mip_levels'.
> 
> References:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.redhat.com_show-5Fbug.cgi-3Fid-3D1437431&d=DwIBAg&c=uilaK90D4TOVoH58JNXRgQ&r=HaJ2a6NYExoV0cntAYcoqA&m=5yR87BuuU86aoAjCveInxh6jvgOyumqIHQhTs0xLo38&s=tWQs7vwNLgD_b2RWMddVtusEKh9FQTIF5rKFOWudslE&e= 
> Signed-off-by: Vladis Dronov <vdronov@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> index b445ce9..b30824b 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> @@ -1281,6 +1281,10 @@ int vmw_gb_surface_define_ioctl(struct drm_device *dev, void *data,
>  	if (req->multisample_count != 0)
>  		return -EINVAL;
>  
> +	if (req->mip_levels > DRM_VMW_MAX_SURFACE_FACES *
> +	    DRM_VMW_MAX_MIP_LEVELS)
> +		return -EINVAL;
> +

Here, the check should be "> DRM_VMW_MAX_MIP_LEVELS" because req->mip_levels
is only for one layer.

Also, as long as we can doing a check, I would suggest we check for 0 as
well.

Sinclair