[PATCH] drm: Reject unknown legacy bpp and depth for drm_mode_addfb ioctl

[Chris Wilson]

Quoting Chris Wilson (2018-09-05 11:22:05)
> Since this is handling user provided bpp and depth, we need to sanity
> check and propagate the EINVAL back rather than assume what the insane
> client intended and fill the logs with DRM_ERROR.
> 
> v2: Check both bpp and depth match the builtin pixel format, and
> introduce a canonical DRM_FORMAT_INVALID to reserve 0 against any future
> fourcc.
> 
> Testcase: igt/kms_addfb_basic/legacy-format
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_fourcc.c      | 33 +++++++++++++++++++++----------
>  drivers/gpu/drm/drm_framebuffer.c |  7 ++++++-
>  include/uapi/drm/drm_fourcc.h     |  3 +++
>  3 files changed, 32 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
> index 35c1e2742c27..d9dadbc43327 100644
> --- a/drivers/gpu/drm/drm_fourcc.c
> +++ b/drivers/gpu/drm/drm_fourcc.c
> @@ -45,32 +45,45 @@ static char printable_char(int c)
>   */
>  uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth)
>  {
> -       uint32_t fmt;
> +       uint32_t fmt = DRM_FORMAT_INVALID;
>  
>         switch (bpp) {
>         case 8:
> -               fmt = DRM_FORMAT_C8;
> +               if (depth == 0)
> +                       fmt = DRM_FORMAT_C8;

Of course the downside with increasing specificity is if any userspace
was already feeding in garbage depth that just happens to work :(
-Chris