Re: [PATCH] media: davinci: vpif_capture: fix potential double free
From: Lad, Prabhakar
Date: Fri Jul 24 2020 - 18:06:10 EST
On Fri, Jul 24, 2020 at 9:00 PM Evgeny Novikov <novikov@xxxxxxxxx> 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()!
> 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.
> Evgeny Novikov
> Linux Verification Center, ISP RAS
> 24.07.2020, 17:17, "Lad, Prabhakar" <prabhakar.csengg@xxxxxxxxx>:
> > Hi Evgeny,
> > Thank you for the patch.
> > On Thu, Jul 23, 2020 at 6:04 PM Evgeny Novikov <novikov@xxxxxxxxx> 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@xxxxxxxxx>
> >> ---
> >> 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