linux-kernel - Re: [PATCH] sound/usb: fix to release stream resources from media_snd_device

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Date:	Sat, 19 Mar 2016 07:25:23 -0600
From:	Shuah Khan <shuahkh@....samsung.com>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	tiwai@...e.com, perex@...ex.cz, linux-media@...r.kernel.org,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH] sound/usb: fix to release stream resources from
 media_snd_device_delete()

On 03/19/2016 04:39 AM, Mauro Carvalho Chehab wrote:
> Em Fri, 18 Mar 2016 23:57:08 -0300
> Mauro Carvalho Chehab <mchehab@....samsung.com> escreveu:
> 
>> Em Fri, 18 Mar 2016 20:50:31 -0600
>> Shuah Khan <shuahkh@....samsung.com> escreveu:
>>
>>> Fix to release stream resources from media_snd_device_delete() before
>>> media device is unregistered. Without this change, stream resource free
>>> is attempted after the media device is unregistered which would result
>>> in use-after-free errors.
>>>
>>> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
>>> ---
>>>
>>> - Ran bind/unbind loop (1000 iteration) test on snd-usb-audio
>>>   while running mc_nextgen_test loop (1000 iterations) in parallel.
>>> - Ran bind/unbind and rmmod/modprobe tests on both drivers. Also
>>>   generated graphs when after bind/unbind, rmmod/modprobe. Graphs
>>>   look good.
>>> - Note: Please apply the following patch to fix memory leak:
>>>   sound/usb: Fix memory leak in media_snd_stream_delete() during unbind
>>>   https://lkml.org/lkml/2016/3/16/1050
>>>
>>>  sound/usb/media.c | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/sound/usb/media.c b/sound/usb/media.c
>>> index de4a815..e35af88 100644
>>> --- a/sound/usb/media.c
>>> +++ b/sound/usb/media.c
>>> @@ -301,6 +301,13 @@ int media_snd_device_create(struct snd_usb_audio *chip,
>>>  void media_snd_device_delete(struct snd_usb_audio *chip)
>>>  {
>>>  	struct media_device *mdev = chip->media_dev;
>>> +	struct snd_usb_stream *stream;
>>> +
>>> +	/* release resources */
>>> +	list_for_each_entry(stream, &chip->pcm_list, list) {
>>> +		media_snd_stream_delete(&stream->substream[0]);
>>> +		media_snd_stream_delete(&stream->substream[1]);  
>>
>> I'll look on it better tomorrow, but it sounds weird to hardcode
>> substream[0] and [1] here... are you sure that this is valid for
>> *all* devices supported by snd-usb-audio?
> 
> After looking at pcm.c and finding this:
> 
> static void snd_usb_audio_stream_free(struct snd_usb_stream *stream)
> {
> 	free_substream(&stream->substream[0]);
> 	free_substream(&stream->substream[1]);
> 	list_del(&stream->list);
> 	kfree(stream);
> }
> 
> It seems that assuming that substream is always an array with size 2
> is right.
> 
> I'll do some tests with it today with your patch.
> 

Right. snd-usb-audio uses this in several places like the one above you found.

thanks,
-- Shuah


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@....samsung.com | (970) 217-8978