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drm/mediatek: Fix device use-after-free on unbind

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A recent change fixed device reference leaks when looking up drm
platform device driver data during bind() but failed to remove a partial
fix which had been added by commit 80805b62ea ("drm/mediatek: Fix
kobject put for component sub-drivers").

This results in a reference imbalance on component bind() failures and
on unbind() which could lead to a user-after-free.

Make sure to only drop the references after retrieving the driver data
by effectively reverting the previous partial fix.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

Fixes: 1f403699c4 ("drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv")
Reported-by: Sjoerd Simons <sjoerd@collabora.com>
Closes: https://lore.kernel.org/r/20251003-mtk-drm-refcount-v1-1-3b3f2813b0db@collabora.com
Cc: stable@vger.kernel.org
Cc: Ma Ke <make24@iscas.ac.cn>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Sjoerd Simons <sjoerd@collabora.com>
Tested-by: Sjoerd Simons <sjoerd@collabora.com>
Tested-by: Ritesh Raj Sarraf <ritesh.sarraf@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20251006093937.27869-1-johan@kernel.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
This commit is contained in:
Johan Hovold
2025-10-06 11:39:37 +02:00
committed by Chun-Kuang Hu
parent 3a86608788
commit 926d002e6d
1 changed files with 0 additions and 10 deletions
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10
drivers/gpu/drm/mediatek/mtk_drm_drv.c
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@@ -686,10 +686,6 @@ err_free:
for (i = 0; i < private->data->mmsys_dev_num; i++)
private->all_drm_private[i]->drm = NULL;
err_put_dev:
for (i = 0; i < private->data->mmsys_dev_num; i++) {
/* For device_find_child in mtk_drm_get_all_priv() */
put_device(private->all_drm_private[i]->dev);
}
put_device(private->mutex_dev);
return ret;
}
@@ -697,18 +693,12 @@ err_put_dev:
static void mtk_drm_unbind(struct device *dev)
{
struct mtk_drm_private *private = dev_get_drvdata(dev);
int i;
/* for multi mmsys dev, unregister drm dev in mmsys master */
if (private->drm_master) {
drm_dev_unregister(private->drm);
mtk_drm_kms_deinit(private->drm);
drm_dev_put(private->drm);
for (i = 0; i < private->data->mmsys_dev_num; i++) {
/* For device_find_child in mtk_drm_get_all_priv() */
put_device(private->all_drm_private[i]->dev);
}
put_device(private->mutex_dev);
}
private->mtk_drm_bound = false;