[PATCH] drm/vmwgfx: Check check that number of mip levels is above zero in vmw_surface_define_ioctl()

[Sinclair Yeh]

Hi,

thank you for this patch.  Murray McAllister reported this one a couple
of months ago, and this is already in our queue.

Sinclair

On Fri, Mar 24, 2017 at 04:37:10PM +0100, Vladis Dronov wrote:
> In vmw_surface_define_ioctl(), a num_sizes parameter is assigned a
> user-controlled value which is not checked for zero. It is used in
> a call to kmalloc() which returns ZERO_SIZE_PTR. Later ZERO_SIZE_PTR
> is dereferenced which leads to a GPF and possibly to a kernel panic.
> Add the check for zero to avoid this.
> 
> Reference: https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.redhat.com_show-5Fbug.cgi-3Fid-3D1435719&d=DwIBAg&c=uilaK90D4TOVoH58JNXRgQ&r=HaJ2a6NYExoV0cntAYcoqA&m=OW9cIAAez9eRIxEYMaToDu2szuR_YrfQcOzAH6L8dXo&s=-3P2pG3n1YW6-8NG6mLC7kyxmx7mMxJmXgY79ZgQeo4&e= 
> Signed-off-by: Vladis Dronov <vdronov at redhat.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> index b445ce9..42840cc 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> @@ -716,8 +716,8 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data,
>  	for (i = 0; i < DRM_VMW_MAX_SURFACE_FACES; ++i)
>  		num_sizes += req->mip_levels[i];
>  
> -	if (num_sizes > DRM_VMW_MAX_SURFACE_FACES *
> -	    DRM_VMW_MAX_MIP_LEVELS)
> +	if (num_sizes <= 0 ||
> +	    num_sizes > DRM_VMW_MAX_SURFACE_FACES * DRM_VMW_MAX_MIP_LEVELS)
>  		return -EINVAL;
>  
>  	size = vmw_user_surface_size + 128 +
> -- 
> 2.9.3
>