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 sjoerd@collabora.com Tested-By: Sjoerd Simons sjoerd@collabora.com

Fixes: 1f403699c40f ("drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv") Reported-by: Sjoerd Simons sjoerd@collabora.com Link: https://lore.kernel.org/r/20251003-mtk-drm-refcount-v1-1-3b3f2813b0db@collab... 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

---

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;