[PATCH 1/2] drm: Make control nodes master-less

[Daniel Vetter]

On Wed, Feb 19, 2014 at 02:40:41PM +0100, Thomas Hellstrom wrote:
> Like for render-nodes, there is no point in maintaining the master concept
> for control nodes, so set the struct drm_file::master pointer to NULL.
> 
> At the same time, make sure DRM_MASTER | DRM_CONTROL_ALLOW ioctls are always
> allowed when called through the control node. Previously the caller also
> needed to be master.
> 
> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> ---
>  drivers/gpu/drm/drm_drv.c  |    5 +++--
>  drivers/gpu/drm/drm_fops.c |    5 +++--
>  include/drm/drmP.h         |    5 +++++
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 345be03..42af8bd 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -355,8 +355,9 @@ long drm_ioctl(struct file *filp,
>  		retcode = -EINVAL;
>  	} else if (((ioctl->flags & DRM_ROOT_ONLY) && !capable(CAP_SYS_ADMIN)) ||
>  		   ((ioctl->flags & DRM_AUTH) && !drm_is_render_client(file_priv) && !file_priv->authenticated) ||
> -		   ((ioctl->flags & DRM_MASTER) && !file_priv->is_master) ||
> -		   (!(ioctl->flags & DRM_CONTROL_ALLOW) && (file_priv->minor->type == DRM_MINOR_CONTROL)) ||
> +		   (((ioctl->flags & DRM_MASTER) && !file_priv->is_master) &&
> +		    !(drm_is_control(file_priv) && (ioctl->flags & DRM_CONTROL_ALLOW))) ||
> +		   (!(ioctl->flags & DRM_CONTROL_ALLOW) && drm_is_control(file_priv)) ||
>  		   (!(ioctl->flags & DRM_RENDER_ALLOW) && drm_is_render_client(file_priv))) {

This is hideous to review ;-) I think it would be really good to extract
this entire condition into a drm_check_ioctl_acces(ioctl, file_priv)
helper and untangle all the different cases a bit by splitting it up into
if checks with individual return false/true; statements.

With that bit of polish for the next reviewer's sanity applied both
patches are Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

I guess with this change we could move the master pointer from drm_minor
to drm_device, which would make it really clear that there's only ever one
master per device. But that's one giant sed job, so meh ;-)

One thing I'm unsure about is whether we want/need to have the master
concept on the control node, too. logind uses set/dropmaster as a
kms-specific revoke support, so if we ever want to switch to using control
nodes for display servers we'd need to shuffle this a bit again.

Otoh no one is using control nodes for real afaik, so we likely need some
interface polishing anyway. And for non-root display servers we can block
out all the awful legacy drm ioctls easily, so just keeping on using
legacy nodes isn't a security issue for that use-case.

Cheers, Daniel

>  		retcode = -EACCES;
>  	} else {
> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> index 7f2af9a..08a3196 100644
> --- a/drivers/gpu/drm/drm_fops.c
> +++ b/drivers/gpu/drm/drm_fops.c
> @@ -259,7 +259,8 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
>  	/* if there is no current master make this fd it, but do not create
>  	 * any master object for render clients */
>  	mutex_lock(&dev->struct_mutex);
> -	if (!priv->minor->master && !drm_is_render_client(priv)) {
> +	if (!priv->minor->master && !drm_is_render_client(priv) &&
> +	    !drm_is_control(priv)) {
>  		/* create a new master */
>  		priv->minor->master = drm_master_create(priv->minor);
>  		if (!priv->minor->master) {
> @@ -297,7 +298,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
>  				goto out_close;
>  			}
>  		}
> -	} else if (!drm_is_render_client(priv)) {
> +	} else if (!drm_is_render_client(priv) && !drm_is_control(priv)) {
>  		/* get a reference to the master */
>  		priv->master = drm_master_get(priv->minor->master);
>  	}
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 04a7f31..ff68e26 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -1246,6 +1246,11 @@ static inline bool drm_is_render_client(struct drm_file *file_priv)
>  	return file_priv->minor->type == DRM_MINOR_RENDER;
>  }
>  
> +static inline bool drm_is_control(struct drm_file *file_priv)
> +{
> +	return file_priv->minor->type == DRM_MINOR_CONTROL;
> +}
> +
>  /******************************************************************/
>  /** \name Internal function definitions */
>  /*@{*/
> -- 
> 1.7.10.4
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch