[PATCH 30/30] fbdev: Make support for userspace interfaces configurable

[Greg KH]

On Mon, Jun 05, 2023 at 04:48:12PM +0200, Thomas Zimmermann wrote:
> Add Kconfig option CONFIG_FB_DEVICE and make the virtual fbdev
> device optional. If the new option has not been selected, fbdev
> does not create a files in devfs or sysfs.
> 
> Most modern Linux systems run a DRM-based graphics stack that uses
> the kernel's framebuffer console, but has otherwise deprecated fbdev
> support. Yet fbdev userspace interfaces are still present.
> 
> The option makes it possible to use the fbdev subsystem as console
> implementation without support for userspace. This closes potential
> entry points to manipulate kernel or I/O memory via framebuffers. It
> also prevents the execution of driver code via ioctl or sysfs, both
> of which might allow malicious software to exploit bugs in the fbdev
> code.
> 
> A small number of fbdev drivers require struct fbinfo.dev to be
> initialized, usually for the support of sysfs interface. Make these
> drivers depend on FB_DEVICE. They can later be fixed if necessary.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>

Acked-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>