linux-kernel - Re: [PATCH] ALSA: usb-audio: Fix memory leak in __snd_usbmidi

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Date:   Mon, 28 Oct 2019 11:42:50 -0500
From:   Navid Emamdoost <navid.emamdoost@...il.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Navid Emamdoost <emamd001@....edu>, Kangjie Lu <kjlu@....edu>,
        Stephen McCamant <smccaman@....edu>,
        Clemens Ladisch <clemens@...isch.de>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: usb-audio: Fix memory leak in __snd_usbmidi_create

On Mon, Oct 28, 2019 at 11:38 AM Takashi Iwai <tiwai@...e.de> wrote:
>
> On Mon, 28 Oct 2019 17:25:41 +0100,
> Navid Emamdoost wrote:
> >
> > Thanks for the explanation,
> >
> > On Mon, Oct 28, 2019 at 1:27 AM Takashi Iwai <tiwai@...e.de> wrote:
> > >
> > > On Sun, 27 Oct 2019 23:10:06 +0100,
> > > Navid Emamdoost wrote:
> > > >
> > > > In the implementation of __snd_usbmidi_create() there is a memory leak
> > > > caused by incorrect goto destination. Go to free_midi if
> > > > snd_usbmidi_create_endpoints_midiman() or snd_usbmidi_create_endpoints()
> > > > fail.
> > >
> > > No, this will lead to double-free.  After registering the rawmidi
> > > interface at snd_usbmidi_create_rawmidi(), the common destructor will
> > > be called via rawmidi private_free callback, and this will release the
> > > all resources already.
> > Now I can see how rawmidi private_free is set up to release the
> > resources, but what concerns me is that at the moment of endpoint/port
> > creation umidi is not yet added to the midi_list.
> > In other words, what I see is that we still have just one local
> > pointer to umidi if any of snd_usbmidi_create_endpoint* fail.
> > Am I missing something?
>
> The rawmidi object that is created via snd_rawmidi_new() is managed
> via snd_device list, and it's traversed at snd_card_disconnect() and
> snd_card_free() calls.  It's something like devm-stuff (but
> implemented in a different way).  The midi_list is an explicit list
> for the USB MIDI driver, and it's an individual one from the device
> list.

Thanks for the clarification.

>
>
> Takashi
>
> >
> >
> > >
> > >
> > > thanks,
> > >
> > > Takashi
> > >
> > > >
> > > > Fixes: 731209cc0417 ("ALSA: usb-midi: Use common error handling code in __snd_usbmidi_create()")
> > > > Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> > > > ---
> > > >  sound/usb/midi.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/sound/usb/midi.c b/sound/usb/midi.c
> > > > index b737f0ec77d0..22db37fbfbbd 100644
> > > > --- a/sound/usb/midi.c
> > > > +++ b/sound/usb/midi.c
> > > > @@ -2476,7 +2476,7 @@ int __snd_usbmidi_create(struct snd_card *card,
> > > >       else
> > > >               err = snd_usbmidi_create_endpoints(umidi, endpoints);
> > > >       if (err < 0)
> > > > -             goto exit;
> > > > +             goto free_midi;
> > > >
> > > >       usb_autopm_get_interface_no_resume(umidi->iface);
> > > >
> > > > --
> > > > 2.17.1
> > > >
> >
> >
> >
> > --
> > Navid.
> >



-- 
Navid.