linux-kernel - Re: [PATCH 1/3] ALSA: timer: fix NULL pointer dereference in read()/ioctl() race

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Message-ID: <s5hzinqe96e.wl-tiwai@suse.de>
Date:   Fri, 02 Sep 2016 15:13:45 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Vegard Nossum <vegard.nossum@...cle.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
        syzkaller <syzkaller@...glegroups.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ALSA: timer: fix NULL pointer dereference in read()/ioctl() race

On Fri, 02 Sep 2016 14:34:47 +0200,
Vegard Nossum wrote:
> 
> On 08/29/2016 09:14 AM, Vegard Nossum wrote:
> > On 08/29/2016 09:02 AM, Takashi Iwai wrote:
> >> On Mon, 29 Aug 2016 00:33:49 +0200,
> >> Vegard Nossum wrote:
> >>> @@ -1602,15 +1602,25 @@ static int snd_timer_user_tselect(struct file
> >>> *file,
> >>>      kfree(tu->tqueue);
> >>>      tu->tqueue = NULL;
> >>>      if (tu->tread) {
> >>> -        tu->tqueue = kmalloc(tu->queue_size * sizeof(struct
> >>> snd_timer_tread),
> >>> +        struct snd_timer_tread *ttr;
> >>> +        ttr = kmalloc(tu->queue_size * sizeof(struct snd_timer_tread),
> >>>                       GFP_KERNEL);
> >>> -        if (tu->tqueue == NULL)
> >>> +        if (ttr) {
> >>> +            kfree(tu->tqueue);
> >>> +            tu->tqueue = ttr;
> >>
> >> This looks like the double-tree, as you didn't remove the kfree() call
> >> in the above.  But, I guess this change is superfluous when you
> >> introduce the mutex at...
> >
> > You're right, this hunk is garbage.
> >
> > Please see the new patch (attached), I also changed the patch
> > description slightly to match the changes.
> >
> > I'll start running some tests on the new patch.
> 
> I tested the new patch (from the email I'm replying to). It seems to
> work for me.

OK, queued now.  Thanks!


Takashi