Re: [PATCH 1/4] media: cec-notifier: fix possible object reference leak

[Hans Verkuil (hansverk)]

On 11/02/2019 11:38, Hans Verkuil (hansverk) wrote:
> On 09/02/2019 03:48, Wen Yang wrote:
>> put_device() should be called in cec_notifier_release(),
>> since the dev is being passed down to cec_notifier_get_conn(),
>> which holds reference. On cec_notifier destruction, it
>> should drop the reference to the device.
>>
>> Fixes: 6917a7b77413 ("[media] media: add CEC notifier support")
>> Signed-off-by: Wen Yang <yellowriver2010@xxxxxxxxxxx>
>> ---
>>  drivers/media/cec/cec-notifier.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/media/cec/cec-notifier.c b/drivers/media/cec/cec-notifier.c
>> index dd2078b..621d4ae 100644
>> --- a/drivers/media/cec/cec-notifier.c
>> +++ b/drivers/media/cec/cec-notifier.c
>> @@ -66,6 +66,7 @@ static void cec_notifier_release(struct kref *kref)
>>  		container_of(kref, struct cec_notifier, kref);
>>  
>>  	list_del(&n->head);
>> +	put_device(n->dev);
>>  	kfree(n->conn);
>>  	kfree(n);
>>  }
>>
> 
> Sorry, no. The dev pointer is just a search key that the notifier code looks
> for. It is not the notifier's responsibility to take a reference, that would
> be the responsibility of the hdmi and cec drivers.

Correction: the cec driver should never take a reference of the hdmi device.
It never accesses the HDMI device, it only needs the HDMI device pointer as
a key in the notifier list.

The real problem is that several CEC drivers take a reference of the HDMI device
and never release it. So those drivers need to be fixed.

Regards,

	Hans

> 
> If you can demonstrate that there is an object reference leak, then please
> provide the details: it is likely a bug elsewhere and not in the notifier
> code.
> 
> BTW, your patch series didn't arrive on the linux-media mailinglist for
> some reason.
> 
> Regards,
> 
> 	Hans
>