Re: [PATCH RESEND v2 06/32] drm/vkms: Introduce configfs for plane name

["José Expósito" <jose.exposito89@gmail.com>]

On Wed, Oct 29, 2025 at 03:36:43PM +0100, Louis Chauvet wrote:
> Planes can have name, create a plane attribute to configure it. Currently
> plane name is mainly used in logs.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  Documentation/gpu/vkms.rst           |  3 ++-
>  drivers/gpu/drm/vkms/vkms_configfs.c | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 3574e01b928d..1fe6e420c963 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,10 +87,11 @@ Start by creating one or more planes::
>  
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>  
> -Planes have 1 configurable attribute:
> +Planes have 2 configurable attributes:
>  
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> +- name: Name of the plane

I'd like to mention again my comment on limiting the name to a set of
well-known characters [1].

The reason is that, in libinput, we had a format string vulnerability
due to the kernel exposing devices with names containing strings like
"%s" in the name (CVE-2022-1215):
https://gitlab.freedesktop.org/libinput/libinput/-/issues/752

In my opinion, we should avoid surprising user-space too much and allow
only a set of "safe" characters.

Maybe I'm too cautious, as this is valid code, but I'd like to bring up
the discussion again to see if someone else agrees or disagrees.

[1] https://lore.kernel.org/all/aPtgCUX5kixTh2ua@fedora/
  
>  Continue by creating one or more CRTCs::
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 07ab794e1052..be6c3ba998b9 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -322,10 +322,42 @@ static ssize_t plane_type_store(struct config_item *item, const char *page,
>  	return (ssize_t)count;
>  }
>  
> +static ssize_t plane_name_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	const char *name;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock)
> +		name = vkms_config_plane_get_name(plane->config);
> +
> +	return sprintf(page, "%s\n", name);
> +}
> +
> +static ssize_t plane_name_store(struct config_item *item, const char *page,
> +				size_t count)
> +{
> +	struct vkms_configfs_plane *plane;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		if (plane->dev->enabled)
> +			return -EBUSY;
> +
> +		vkms_config_plane_set_name(plane->config, page);
> +	}
> +
> +	return (ssize_t)count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
> +CONFIGFS_ATTR(plane_, name);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> +	&plane_attr_name,
>  	NULL,
>  };
>  
> 
> -- 
> 2.51.0
>