[PATCH 5.17 233/772] drm/edid: fix invalid EDID extension block filtering

[Greg Kroah-Hartman]

From: Jani Nikula <jani.nikula@xxxxxxxxx>

[ 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@xxxxxxxxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20220330170426.349248-1-jani.nikula@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 83e5c115e754..502ef71dac68 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -2029,9 +2029,6 @@ 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)
@@ -2048,6 +2045,9 @@ 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;
 	}
-- 
2.35.1