[PATCH] drm/bridge: properly refcount DT nodes in aux bridge drivers

[Neil Armstrong]

On 17/12/2023 00:59, Dmitry Baryshkov wrote:
> The aux-bridge and aux-hpd-bridge drivers didn't call of_node_get() on
> the device nodes further used for dev->of_node and platform data. When
> bridge devices are released, the reference counts are decreased,
> resulting in refcount underflow / use-after-free warnings. Get
> corresponding refcounts during AUX bridge allocation.
> 
> Reported-by: Luca Weiss <luca.weiss at fairphone.com>
> Fixes: 2a04739139b2 ("drm/bridge: add transparent bridge helper")
> Fixes: 26f4bac3d884 ("drm/bridge: aux-hpd: Replace of_device.h with explicit include")
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> ---
>   drivers/gpu/drm/bridge/aux-bridge.c     | 2 +-
>   drivers/gpu/drm/bridge/aux-hpd-bridge.c | 4 ++--
>   2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/aux-bridge.c b/drivers/gpu/drm/bridge/aux-bridge.c
> index 49d7c2ab1ecc..54d721db0ea6 100644
> --- a/drivers/gpu/drm/bridge/aux-bridge.c
> +++ b/drivers/gpu/drm/bridge/aux-bridge.c
> @@ -57,7 +57,7 @@ int drm_aux_bridge_register(struct device *parent)
>   	adev->id = ret;
>   	adev->name = "aux_bridge";
>   	adev->dev.parent = parent;
> -	adev->dev.of_node = parent->of_node;
> +	adev->dev.of_node = of_node_get(parent->of_node);
>   	adev->dev.release = drm_aux_bridge_release;
>   
>   	ret = auxiliary_device_init(adev);
> diff --git a/drivers/gpu/drm/bridge/aux-hpd-bridge.c b/drivers/gpu/drm/bridge/aux-hpd-bridge.c
> index 1999a053d59b..bb55f697a181 100644
> --- a/drivers/gpu/drm/bridge/aux-hpd-bridge.c
> +++ b/drivers/gpu/drm/bridge/aux-hpd-bridge.c
> @@ -68,9 +68,9 @@ struct device *drm_dp_hpd_bridge_register(struct device *parent,
>   	adev->id = ret;
>   	adev->name = "dp_hpd_bridge";
>   	adev->dev.parent = parent;
> -	adev->dev.of_node = parent->of_node;
> +	adev->dev.of_node = of_node_get(parent->of_node);
>   	adev->dev.release = drm_aux_hpd_bridge_release;
> -	adev->dev.platform_data = np;
> +	adev->dev.platform_data = of_node_get(np);
>   
>   	ret = auxiliary_device_init(adev);
>   	if (ret) {

Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>