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

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Date:   Tue, 13 Nov 2018 12:56:18 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Myungho Jung <mhjungk@...il.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 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

> 
> 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
>