[PATCH] drm: Check for lessee in DROP_MASTER ioctl

[Daniel Vetter]

On Thu, Jan 18, 2018 at 05:51:59PM -0800, Keith Packard wrote:
> Don't let a lessee control what the current DRM master is set to;
> that's the job of the "real" master. Otherwise, the lessee would
> disable all access to master operations for the owner and all lessees
> under it.
> 
> This matches the same check made in the SET_MASTER ioctl.
> 
> Signed-off-by: Keith Packard <keithp at keithp.com>

Similar check for setmaster already exists, so looks all good. Do we have
an igt for all this? Iirc there was one floating around, but no idea
what's the status. Might also be good to resubmit them so i915 CI can run
the tests (now that the code has landed).

On the patch itself, minus lack of testcases:

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> ---
>  drivers/gpu/drm/drm_auth.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> index aad468d170a7..d9c0f7573905 100644
> --- a/drivers/gpu/drm/drm_auth.c
> +++ b/drivers/gpu/drm/drm_auth.c
> @@ -230,6 +230,12 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
>  	if (!dev->master)
>  		goto out_unlock;
>  
> +	if (file_priv->master->lessor != NULL) {
> +		DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id);
> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +
>  	ret = 0;
>  	drm_drop_master(dev, file_priv);
>  out_unlock:
> -- 
> 2.15.1
> 

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