linux-kernel - Re: [PATCH] ALSA: usx2y: fix a memory leak bug

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Message-ID: <s5h4l6hl3ca.wl-tiwai@suse.de>
Date:   Mon, 29 Apr 2019 08:42:29 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Wenwen Wang <wang6495@....edu>
Cc:     "moderated list:SOUND" <alsa-devel@...a-project.org>,
        Kees Cook <keescook@...omium.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: usx2y: fix a memory leak bug

On Mon, 29 Apr 2019 07:50:11 +0200,
Wenwen Wang wrote:
> 
> On Mon, Apr 29, 2019 at 12:36 AM Takashi Iwai <tiwai@...e.de> wrote:
> >
> > On Sun, 28 Apr 2019 09:18:40 +0200,
> > Takashi Iwai wrote:
> > >
> > > On Sun, 28 Apr 2019 08:42:32 +0200,
> > > Wenwen Wang wrote:
> > > >
> > > > In usX2Y_In04_init(), a new urb is firstly created through usb_alloc_urb()
> > > > and saved to 'usX2Y->In04urb'. Then, a buffer is allocated through
> > > > kmalloc() and saved to 'usX2Y->In04Buf'. After the urb is initialized, a
> > > > sanity check is performed for the endpoint in the urb by invoking
> > > > usb_urb_ep_type_check(). If the check fails, the error code EINVAL will be
> > > > returned. In that case, however, the created urb and the allocated buffer
> > > > are not freed, leading to memory leaks.
> > > >
> > > > To fix the above issue, free the urb and the buffer if the check fails.
> > > >
> > > > Signed-off-by: Wenwen Wang <wang6495@....edu>
> > >
> > > Applied now, thanks.
> >
> > ... and looking at the code again, this patch turned out to be wrong.
> > The in04 urb and transfer buffer are freed at card->private_free
> > callback (snd_usX2Y_card_private_free()) later, so this patch would
> > lead to double-free.
> 
> Thanks for your comment! Does that mean we should remove
> usb_free_urb() in the if statement of allocating 'usX2Y->In04Buf',
> because it may also lead to double free?

Yes, that's another superfluous code.


Takashi