linux-kernel - Re: [PATCH] media: davinci: vpif_capture: fix potential double free

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Date:   Fri, 24 Jul 2020 23:05:40 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Evgeny Novikov <novikov@...ras.ru>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "ldv-project@...uxtesting.org" <ldv-project@...uxtesting.org>
Subject: Re: [PATCH] media: davinci: vpif_capture: fix potential double free

Hi Evgeny,

On Fri, Jul 24, 2020 at 9:00 PM Evgeny Novikov <novikov@...ras.ru> wrote:
>
> Hi Lad,
>
> Yet again I can not demonstrate you a nice error trace corresponding to the bug fixed by the patch. Indeed, there is a branch in vpif_probe() that explicitly invokes vpif_probe_complete() and the patch targets the possible issue that can happen during this.
>
> When I developed the patch I saw on vpif_display.ko. It looks very similar regarding things touched by the patch. In particular, it does not free vpif_obj.sd in its vpif_probe_complete(). But now I see that it does this in vpif_remove()!
>
Makes sense.

> Do you think that vpif_capture.ko should do the same? If so, I guess that I should fix the patch appropriately since likely it just replaces one (very rare) bug with another one (on a typical execution path).
>
Yes it should.

Cheers,
--Prabhakar

> --
> Evgeny Novikov
> Linux Verification Center, ISP RAS
> http://linuxtesting.org
>
>
>
> 24.07.2020, 17:17, "Lad, Prabhakar" <prabhakar.csengg@...il.com>:
> > Hi Evgeny,
> >
> > Thank you for the patch.
> >
> > On Thu, Jul 23, 2020 at 6:04 PM Evgeny Novikov <novikov@...ras.ru> wrote:
> >>  In case of errors vpif_probe_complete() releases memory for vpif_obj.sd
> >>  and unregisters the V4L2 device. But then this is done again by
> >>  vpif_probe() itself. The patch removes the cleaning from
> >>  vpif_probe_complete().
> >>
> >>  Found by Linux Driver Verification project (linuxtesting.org).
> >>
> >>  Signed-off-by: Evgeny Novikov <novikov@...ras.ru>
> >>  ---
> >>   drivers/media/platform/davinci/vpif_capture.c | 2 --
> >>   1 file changed, 2 deletions(-)
> >>
> >>  diff --git a/drivers/media/platform/davinci/vpif_capture.c b/drivers/media/platform/davinci/vpif_capture.c
> >>  index d9ec439faefa..72a0e94e2e21 100644
> >>  --- a/drivers/media/platform/davinci/vpif_capture.c
> >>  +++ b/drivers/media/platform/davinci/vpif_capture.c
> >>  @@ -1482,8 +1482,6 @@ static int vpif_probe_complete(void)
> >>                  /* Unregister video device */
> >>                  video_unregister_device(&ch->video_dev);
> >>          }
> >>  - kfree(vpif_obj.sd);
> >>  - v4l2_device_unregister(&vpif_obj.v4l2_dev);
> >
> > vpif_probe_complete() is a async callback and probe() should have
> > already completed by then.
> >
> > Cheers,
> > --Prabhakar
> >
> >>          return err;
> >>   }
> >>  --
> >>  2.16.4