On Mon, 2025-10-06 at 11:39 +0200, Johan Hovold wrote:
> 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 80805b62ea5b ("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.
Thanks for correcting my "fix". This looks better and i can confirm it fixes
the issue :)
Reviewed-By: Sjoerd Simons <[email protected]>
Tested-By: Sjoerd Simons <[email protected]>
>
> Fixes: 1f403699c40f ("drm/mediatek: Fix device/node reference count leaks in
> mtk_drm_get_all_drm_priv")
> Reported-by: Sjoerd Simons <[email protected]>
> Link:
> https://lore.kernel.org/r/[email protected]
> Cc: [email protected]
> Cc: Ma Ke <[email protected]>
> Cc: AngeloGioacchino Del Regno <[email protected]>
> Signed-off-by: Johan Hovold <[email protected]>
> ---
> drivers/gpu/drm/mediatek/mtk_drm_drv.c | 10 ----------
> 1 file changed, 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index 384b0510272c..a94c51a83261 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -686,10 +686,6 @@ static int mtk_drm_bind(struct device *dev)
> 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 @@ static int mtk_drm_bind(struct device *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;
