drm/bridge: properly refcount DT nodes in aux bridge drivers

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@fairphone.com>
Fixes: 2a047391 ("drm/bridge: add transparent bridge helper")
Fixes: 26f4bac3 ("drm/bridge: aux-hpd: Replace of_device.h with explicit include")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231216235910.911958-1-dmitry.baryshkov@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/bridge/aux-bridge.c

@@ -6,6 +6,7 @@
  */
 #include <linux/auxiliary_bus.h>
 #include <linux/module.h>
+#include <linux/of.h>
 
 #include <drm/drm_bridge.h>
 #include <drm/bridge/aux-bridge.h>
@@ -57,7 +58,7 @@ 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);

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) {