[media] dvbdev: split dvb_unregister_device()

dvb_unregister_device() has a major problem: it combines unregistering
with memory disposal.  Sometimes, it is necessary to unregister a
device, but no memory can be freed yet, because a process still has a
(stale) file handle.  Therefore, we need to split
dvb_unregister_device().  This will allow sanitizing a few callers.

With my new design, dvb_unregister_device() appears misnamed, but to
reduce patch noise, I'm not renaming it just yet.

Signed-off-by: Max Kellermann <max.kellermann@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/media/dvb-core/dvbdev.h b/drivers/media/dvb-core/dvbdev.h
index 4aff7bd..576bbd4 100644
--- a/drivers/media/dvb-core/dvbdev.h
+++ b/drivers/media/dvb-core/dvbdev.h
@@ -212,8 +212,31 @@ int dvb_register_device(struct dvb_adapter *adap,
 			int demux_sink_pads);
 
 /**
+ * dvb_remove_device - Remove a registered DVB device
+ *
+ * This does not free memory.  To do that, call dvb_free_device().
+ *
+ * @dvbdev:	pointer to struct dvb_device
+ */
+void dvb_remove_device(struct dvb_device *dvbdev);
+
+/**
+ * dvb_free_device - Free memory occupied by a DVB device.
+ *
+ * Call dvb_unregister_device() before calling this function.
+ *
+ * @dvbdev:	pointer to struct dvb_device
+ */
+void dvb_free_device(struct dvb_device *dvbdev);
+
+/**
  * dvb_unregister_device - Unregisters a DVB device
  *
+ * This is a combination of dvb_remove_device() and dvb_free_device().
+ * Using this function is usually a mistake, and is often an indicator
+ * for a use-after-free bug (when a userspace process keeps a file
+ * handle to a detached device).
+ *
  * @dvbdev:	pointer to struct dvb_device
  */
 void dvb_unregister_device(struct dvb_device *dvbdev);