linux-kernel - Re: [PATCH] media: videobuf2-core: Fix error handling when fileio is deallocated

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Date:   Tue, 13 Nov 2018 09:38:22 -0800
From:   Myungho Jung <mhjungk@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>,
        Marek Szyprowski <m.szyprowski@...sung.com>, pawel@...iak.com,
        kyungmin.park@...sung.com, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: videobuf2-core: Fix error handling when fileio is
 deallocated

On Tue, Nov 13, 2018 at 12:56:18PM +0100, Hans Verkuil wrote:
> On 11/13/18 11:27, Marek Szyprowski wrote:
> > Hi Myungho,
> > 
> > On 2018-11-12 01:49, Myungho Jung wrote:
> >> The mutex that is held from vb2_fop_read() can be unlocked while waiting
> >> for a buffer if the queue is streaming and blocking. Meanwhile, fileio
> >> can be released. So, it should return an error if the fileio address is
> >> changed.
> >>
> >> Signed-off-by: Myungho Jung <mhjungk@...il.com>
> >> Reported-by: syzbot+4180ff9ca6810b06c1e9@...kaller.appspotmail.com
> > 
> > Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>
> 
> Sorry:
> 
> Nacked-by: Hans Verkuil <hans.verkuil@...co.com>
> 
> This addresses the symptom, not the underlying cause.
> 
> I have a patch that fixes the actual cause that I plan to post soon
> after I review it a bit more.
> 
> Regards,
> 
> 	Hans
> 

Hi Hans,

Thanks for explaining the root cause. I was also thinking a similar
patch with your second one. It looks like the reported syzbot is needed
to be added to your first patch.

Regards,
Myungho

> > 
> > Thanks for analyzing the code and fixing this issue!
> > 
> >> ---
> >>  drivers/media/common/videobuf2/videobuf2-core.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> >> index 975ff5669f72..bff94752eb27 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> >> @@ -2564,6 +2564,10 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
> >>  		dprintk(5, "vb2_dqbuf result: %d\n", ret);
> >>  		if (ret)
> >>  			return ret;
> >> +		if (fileio != q->fileio) {
> >> +			dprintk(3, "fileio deallocated\n");
> >> +			return -EFAULT;
> >> +		}
> >>  		fileio->dq_count += 1;
> >>  
> >>  		fileio->cur_index = index;
> > 
> > Best regards
> > 
>