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

[Evgeny Novikov]

Hi Lad,

25.07.2020, 01:06, "Lad, Prabhakar" <prabhakar.csengg@xxxxxxxxx>:
> Hi Evgeny,
>
> On Fri, Jul 24, 2020 at 9:00 PM Evgeny Novikov <novikov@xxxxxxxxx> wrote:
>> ÂHi Lad,
>>
>> ÂYet 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.
>>
>> ÂWhen 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.
>
>> ÂDo 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.

vpif_remove() from vpif_capture.ko already both frees vpif_obj.sd and unregisters the V4L2 device. So, there is no need to fix the patch.

BTW, other drivers, e.g. drivers/media/platform/renesas-ceu.c, do not clean up memory allocated by probe within v4l2_async_notifier_operations.complete as well. 

--
Best regards,
Evgeny Novikov

> Cheers,
> --Prabhakar
>
>> Â--
>> ÂEvgeny Novikov
>> ÂLinux Verification Center, ISP RAS
>> Âhttp://linuxtesting.org
>>
>> Â24.07.2020, 17:17, "Lad, Prabhakar" <prabhakar.csengg@xxxxxxxxx>:
>> Â> Hi Evgeny,
>> Â>
>> Â> Thank you for the patch.
>> Â>
>> Â> On Thu, Jul 23, 2020 at 6:04 PM Evgeny Novikov <novikov@xxxxxxxxx> wrote:
>> Â>> In case of errors vpif_probe_complete() releases memory for vpif_obj.sd
>> Â>> and unregisters the V4L2 device. But then this is done again by
>> Â>> vpif_probe() itself. The patch removes the cleaning from
>> Â>> vpif_probe_complete().
>> Â>>
>> Â>> Found by Linux Driver Verification project (linuxtesting.org).
>> Â>>
>> Â>> Signed-off-by: Evgeny Novikov <novikov@xxxxxxxxx>
>> Â>> ---
>> Â>> drivers/media/platform/davinci/vpif_capture.c | 2 --
>> Â>> 1 file changed, 2 deletions(-)
>> Â>>
>> Â>> diff --git a/drivers/media/platform/davinci/vpif_capture.c b/drivers/media/platform/davinci/vpif_capture.c
>> Â>> index d9ec439faefa..72a0e94e2e21 100644
>> Â>> --- a/drivers/media/platform/davinci/vpif_capture.c
>> Â>> +++ b/drivers/media/platform/davinci/vpif_capture.c
>> Â>> @@ -1482,8 +1482,6 @@ static int vpif_probe_complete(void)
>> Â>> /* Unregister video device */
>> Â>> video_unregister_device(&ch->video_dev);
>> Â>> }
>> Â>> - kfree(vpif_obj.sd);
>> Â>> - v4l2_device_unregister(&vpif_obj.v4l2_dev);
>> Â>
>> Â> vpif_probe_complete() is a async callback and probe() should have
>> Â> already completed by then.
>> Â>
>> Â> Cheers,
>> Â> --Prabhakar
>> Â>
>> Â>> return err;
>> Â>> }
>> Â>> --
>> Â>> 2.16.4