linux-kernel - Re: [PATCH] drm/exynos: fix race condition UAF in exynos_g2d_exec

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Date:   Wed, 31 May 2023 12:39:20 +0800
From:   lm0963 <lm0963hack@...il.com>
To:     Andi Shyti <andi.shyti@...nel.org>
Cc:     inki.dae@...sung.com, sw0312.kim@...sung.com,
        kyungmin.park@...sung.com, airlied@...il.com, daniel@...ll.ch,
        krzysztof.kozlowski@...aro.org, alim.akhtar@...sung.com,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/exynos: fix race condition UAF in exynos_g2d_exec_ioctl

Hi Andi,

On Wed, May 31, 2023 at 6:21 AM Andi Shyti <andi.shyti@...nel.org> wrote:
>
> Hi Min,
>
> On Fri, May 26, 2023 at 09:01:31PM +0800, Min Li wrote:
> > If it is async, runqueue_node is freed in g2d_runqueue_worker on another
> > worker thread. So in extreme cases, if g2d_runqueue_worker runs first, and
> > then executes the following if statement, there will be use-after-free.
> >
> > Signed-off-by: Min Li <lm0963hack@...il.com>
> > ---
> >  drivers/gpu/drm/exynos/exynos_drm_g2d.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> > index ec784e58da5c..414e585ec7dd 100644
> > --- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> > +++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> > @@ -1335,7 +1335,7 @@ int exynos_g2d_exec_ioctl(struct drm_device *drm_dev, void *data,
> >       /* Let the runqueue know that there is work to do. */
> >       queue_work(g2d->g2d_workq, &g2d->runqueue_work);
> >
> > -     if (runqueue_node->async)
> > +     if (req->async)
>
> did you actually hit this? If you did, then the fix is not OK.

No, I didn't actually hit this. I found it through code review. This
is only a theoretical issue that can only be triggered in extreme
cases.

>
> Andi
>
> >               goto out;
> >
> >       wait_for_completion(&runqueue_node->complete);
> > --
> > 2.34.1
> >



-- 
Min Li