ACK/cmnt: [PATCH Trusty] drm/vmwgfx: Make sure backup_handle is always valid

[Thadeu Lima de Souza Cascardo]

On Thu, Jun 22, 2017 at 05:28:13PM +0200, Stefan Bader wrote:
> From: Sinclair Yeh <syeh at vmware.com>
> 
> When vmw_gb_surface_define_ioctl() is called with an existing buffer,
> we end up returning an uninitialized variable in the backup_handle.
> 
> The fix is to first initialize backup_handle to 0 just to be sure, and
> second, when a user-provided buffer is found, we will use the
> req->buffer_handle as the backup_handle.
> 
> Cc: <stable at vger.kernel.org>
> Reported-by: Murray McAllister <murray.mcallister at insomniasec.com>
> Signed-off-by: Sinclair Yeh <syeh at vmware.com>
> Reviewed-by: Deepak Rawat <drawat at vmware.com>
> 
> CVE-2017-9605
> 
> (backported from commit 07678eca2cf9c9a18584e546c2b2a0d0c9a3150c)
> Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> index 8a98b88..9593df6 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
> @@ -1178,7 +1178,7 @@ int vmw_gb_surface_define_ioctl(struct drm_device *dev, void *data,
>  	uint32_t size;
>  	struct vmw_master *vmaster = vmw_master(file_priv->master);
>  	const struct svga3d_surface_desc *desc;
> -	uint32_t backup_handle;
> +	uint32_t backup_handle = 0;
>  
>  	if (req->mip_levels > DRM_VMW_MAX_MIP_LEVELS)
>  		return -EINVAL;
> @@ -1247,6 +1247,17 @@ int vmw_gb_surface_define_ioctl(struct drm_device *dev, void *data,
>  	if (req->buffer_handle != SVGA3D_INVALID_ID) {
>  		ret = vmw_user_dmabuf_lookup(tfile, req->buffer_handle,
>  					     &res->backup);
> +		if (ret == 0) {
> +			if (res->backup->base.num_pages * PAGE_SIZE <
> +			    res->backup_size) {
> +				DRM_ERROR("Surface backup buffer is too small.\n");
> +				vmw_dmabuf_unreference(&res->backup);
> +				ret = -EINVAL;
> +				goto out_unlock;
> +			}
> +		} else {
> +			backup_handle = req->buffer_handle;
> +		}
>  	} else if (req->drm_surface_flags &
>  		   drm_vmw_surface_flag_create_buffer)
>  		ret = vmw_user_dmabuf_alloc(dev_priv, tfile,
> -- 
> 2.7.4

Commit d80efd5cb3dec16a8d1aea9b8a4a7921972dba65 ("drm/vmwgfx: Initial DX
support"), which introduces that check is a complex change, so I
understand that it's not included. As far as I could check whether that
test would be OK, I noticed a BUG_ON at
drivers/gpu/drm/vmwgfx/vmwgfx_resource.c:vmw_resource_buf_alloc, which
indicates it might be correct to check for that.

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>