Re: [PATCH 1/3] drivers/media/dvb-core/en50221: use kref to manage struct dvb_ca_private

[Shuah Khan <shuahkh@osg.samsung.com>]

On 06/15/2016 02:15 PM, Max Kellermann wrote:
> Don't free the object until the file handle has been closed.  Fixes
> use-after-free bug which occurs when I disconnect my DVB-S received
> while VDR is running.

Which file handle? /dev/dvb---

There seems to be a problem in the driver release routine:
dvb_ca_en50221_release() routine:

	kfree(ca->slot_info);
	dvb_unregister_device(ca->dvbdev);
	kfree(ca);

I think this should be since ioctl references slot info

	dvb_unregister_device(ca->dvbdev);
	kfree(ca->slot_info);
	kfree(ca);

I think dvb_ca_en50221_release() and dvb_ca_en50221_io_do_ioctl()
should serialize access to ca. dvb_ca_en50221_io_do_ioctl() holds
the ioctl_mutex, however, dvb_ca_en50221_release() could happen while
ioctl is in progress. Maybe you can try fixing those first.

As I mentioned in my review on your 3/3 patch, adding a kref here
adds more refcounted objects to the mix. You want to avoid that.

thanks,
-- Shuah