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: 1f403699c40f ("drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv")
Cc: Ma Ke <make24@iscas.ac.cn>
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250829090345.21075-2-johan@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index f8a817689e1626fe06a753c9e522114bc6b7fd28..76719eb5db09c0883a413560c574908f1ecaf012 100644 (file)
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/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 @@ next_put_device_drm_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) {