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

[Jani Nikula]

On Wed, 30 Mar 2022, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> 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>

Thanks, pushed to drm-misc-next. I didn't bother with -fixes, because
the bug is ancient and rare, and that would only cause conflicts for me.

BR,
Jani.

>
>> ---
>>  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

-- 
Jani Nikula, Intel Open Source Graphics Center