Re: [PATCH] sound/usb: fix to release stream resources from media_snd_device_delete()

Mauro Carvalho Chehab
2016-03-19T10:39:53Z

Em Fri, 18 Mar 2016 23:57:08 -0300
Mauro Carvalho Chehab <mchehab@osg.samsung.com> escreveu:

> Em Fri, 18 Mar 2016 20:50:31 -0600
> Shuah Khan <shuahkh@osg.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@osg.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.

Regards,
Mauro

>
> Regards,
> Mauro
>
> > + }
> >
> > media_snd_mixer_delete(chip);
> >
>
>

--
Thanks,
Mauro