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

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Message-ID: <CAEkB2ESwKEQYQx75BnaHf4aUQHObx4jf0hreQx_KTeZ+QCjL4g@mail.gmail.com>
Date:   Mon, 28 Oct 2019 11:25:41 -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

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?


>
>
> 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.