drm/edid: fix invalid EDID extension block filtering

[ Upstream commit 3aefc722ff52076407203b6af9713de567993adf ]

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@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220330170426.349248-1-jani.nikula@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index cc7bd58369dfef7224c4350dc0b66129c7798fb0..c5b86414873e24df62bc1b6296303f0c57605cd2 100644 (file)
--- 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;
        }