drm/mediatek: fix potential OF node use-after-free

The for_each_child_of_node() helper drops the reference it takes to each
node as it iterates over children and an explicit of_node_put() is only
needed when exiting the loop early.

Drop the recently introduced bogus additional reference count decrement
at each iteration that could potentially lead to a use-after-free.

Fixes: 1f40369 ("drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv")
Cc: Ma Ke <[email protected]>
Cc: [email protected]
Signed-off-by: Johan Hovold <[email protected]>
Reviewed-by: CK Hu <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Link: https://patchwork.kernel.org/project/dri-devel/patch/[email protected]/
Signed-off-by: Chun-Kuang Hu <[email protected]>

Author: jhovold

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -387,11 +387,11 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 
 		of_id = of_match_node(mtk_drm_of_ids, node);
 		if (!of_id)
-			goto next_put_node;
+			continue;
 
 		pdev = of_find_device_by_node(node);
 		if (!pdev)
-			goto next_put_node;
+			continue;
 
 		drm_dev = device_find_child(&pdev->dev, NULL, mtk_drm_match);
 		if (!drm_dev)
@@ -417,11 +417,10 @@ static bool mtk_drm_get_all_drm_priv(struct device *dev)
 next_put_device_pdev_dev:
 		put_device(&pdev->dev);
 
-next_put_node:
-		of_node_put(node);
-
-		if (cnt == MAX_CRTC)
+		if (cnt == MAX_CRTC) {
+			of_node_put(node);
 			break;
+		}
 	}
 
 	if (drm_priv->data->mmsys_dev_num == cnt) {