[PATCH 3/4] drm/modes: Introduce a whitelist for the named modes

[Thomas Graichen]

hi maxime,

On Tue, Aug 27, 2019 at 1:59 PM Maxime Ripard <mripard at kernel.org> wrote:
>
> From: Maxime Ripard <maxime.ripard at bootlin.com>
>
> The named modes support has introduced a number of glitches that were in
> part due to the fact that the parser will take any string as a named mode.
>
> Since we shouldn't have a lot of options there (and they should be pretty
> standard), let's introduce a whitelist of the available named modes so that
> the kernel can differentiate between a poorly formed command line and a
> named mode.
>
> Signed-off-by: Maxime Ripard <maxime.ripard at bootlin.com>

Tested-by: thomas graichen <thomas.graichen at gmail.com>

BEFORE (only "[PATCH v5 05/12] drm/modes: Rewrite the command line
parser " applied):
my eachlink h6 mini tv box (which requires the video=HDMI-A-1:e
cmdline option to give any output on hdmi) did not show any hdmi
output any more (in 5.2 it still worked)

AFTER (the above patch plus this patch set here applied):
my eachlink h6 mini tv box gives output on hdmi again. i also did
check it the other way around: if i remove the video=HDMI-A-1:e option
i no longer get any hdmi output as expected. as a result this patch
series fixes the problem/regression for me.

best wishes - thomas

> ---
>  drivers/gpu/drm/drm_modes.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index ea7e6c8c8318..988797d8080a 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1677,6 +1677,22 @@ static int drm_mode_parse_cmdline_options(char *str, size_t len,
>         return 0;
>  }
>
> +const char *drm_named_modes_whitelist[] = {
> +       "NTSC",
> +       "PAL",
> +};
> +
> +static bool drm_named_mode_is_in_whitelist(const char *mode, unsigned int size)
> +{
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++)
> +               if (!strncmp(mode, drm_named_modes_whitelist[i], size))
> +                       return true;
> +
> +       return false;
> +}
> +
>  /**
>   * drm_mode_parse_command_line_for_connector - parse command line modeline for connector
>   * @mode_option: optional per connector mode option
> @@ -1794,6 +1810,10 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>         if (named_mode) {
>                 if (mode_end + 1 > DRM_DISPLAY_MODE_LEN)
>                         return false;
> +
> +               if (!drm_named_mode_is_in_whitelist(name, mode_end))
> +                       return false;
> +
>                 strscpy(mode->name, name, mode_end + 1);
>         } else {
>                 ret = drm_mode_parse_cmdline_res_mode(name, mode_end,
> --
> 2.21.0
>