From: Johan Hovold Date: Mon, 6 Oct 2025 09:39:37 +0000 (+0200) Subject: drm/mediatek: Fix device use-after-free on unbind X-Git-Tag: v6.18-rc4~10^2~5^2 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=926d002e6d7e2f1fd5c1b53cf6208153ee7d380d;p=thirdparty%2Fkernel%2Fstable.git drm/mediatek: Fix device use-after-free on unbind 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. Fixes: 1f403699c40f ("drm/mediatek: Fix device/node reference count leaks in mtk_drm_get_all_drm_priv") Reported-by: Sjoerd Simons Closes: https://lore.kernel.org/r/20251003-mtk-drm-refcount-v1-1-3b3f2813b0db@collabora.com Cc: stable@vger.kernel.org Cc: Ma Ke Cc: AngeloGioacchino Del Regno Signed-off-by: Johan Hovold Reviewed-by: AngeloGioacchino Del Regno Reviewed-by: Sjoerd Simons Tested-by: Sjoerd Simons Tested-by: Ritesh Raj Sarraf Reviewed-by: CK Hu Link: https://patchwork.kernel.org/project/dri-devel/patch/20251006093937.27869-1-johan@kernel.org/ Signed-off-by: Chun-Kuang Hu --- diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c index eb5537f0ac90..31ff2922758a 100644 --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c @@ -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;