[PATCH] drm/edid: fix invalid EDID extension block filtering

[Ville Syrjälä]

On Wed, Mar 30, 2022 at 08:04:26PM +0300, Jani Nikula wrote:
> The invalid EDID block filtering uses the number of valid EDID
> extensions instead of all EDID extensions for looping the extensions in
> the copy. This is fine, by coincidence, if all the invalid blocks are at
> the end of the EDID. However, it's completely broken if there are
> invalid extensions in the middle; the invalid blocks are included and
> valid blocks are excluded.
> 
> Fix it by modifying the base block after, not before, the copy.
> 
> Fixes: 14544d0937bf ("drm/edid: Only print the bad edid when aborting")
> Reported-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> ---
>  drivers/gpu/drm/drm_edid.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index d79b06f7f34c..8829120470ab 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -2031,9 +2031,6 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
>  
>  		connector_bad_edid(connector, edid, edid[0x7e] + 1);
>  
> -		edid[EDID_LENGTH-1] += edid[0x7e] - valid_extensions;
> -		edid[0x7e] = valid_extensions;
> -
>  		new = kmalloc_array(valid_extensions + 1, EDID_LENGTH,
>  				    GFP_KERNEL);
>  		if (!new)
> @@ -2050,6 +2047,9 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
>  			base += EDID_LENGTH;
>  		}
>  
> +		new[EDID_LENGTH - 1] += new[0x7e] - valid_extensions;
> +		new[0x7e] = valid_extensions;
> +
>  		kfree(edid);
>  		edid = new;
>  	}
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel