linux-kernel - [PATCH 1/2] drm/mediatek: fix potential OF node use-after-free

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Message-ID: <20250829090345.21075-2-johan@kernel.org>
Date: Fri, 29 Aug 2025 11:03:44 +0200
From: Johan Hovold <johan@...nel.org>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>
Cc: David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Ma Ke <make24@...as.ac.cn>,
	dri-devel@...ts.freedesktop.org,
	linux-mediatek@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan@...nel.org>,
	stable@...r.kernel.org
Subject: [PATCH 1/2] 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@...as.ac.cn>
Cc: stable@...r.kernel.org
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 34131ae2c207..3b02ed0a16da 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -388,11 +388,11 @@ 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)
@@ -418,11 +418,10 @@ 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) {
-- 
2.49.1