linux-kernel - Re: [PATCH v3] media: videobuf2: forbid remove

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Message-ID: <c081ec16-adb0-41b9-8ad6-5db9ccd6242c@kernel.org>
Date: Thu, 23 Oct 2025 14:25:48 +0200
From: Hans Verkuil <hverkuil+cisco@...nel.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Tomasz Figa <tfiga@...omium.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Guennadi Liakhovetski <g.liakhovetski@....de>,
 Benjamin Gaignard <benjamin.gaignard@...labora.com>,
 Hans Verkuil <hverkuil@...nel.org>, stable@...r.kernel.org,
 Shuangpeng Bai <SJB7183@....edu>
Subject: Re: [PATCH v3] media: videobuf2: forbid remove_bufs when legacy
 fileio is active

On 23/10/2025 13:55, Marek Szyprowski wrote:
> On 23.10.2025 13:36, Hans Verkuil wrote:
>> On 23/10/2025 13:30, Marek Szyprowski wrote:
>>> vb2_ioctl_remove_bufs() call manipulates queue internal buffer list,
>>> potentially overwriting some pointers used by the legacy fileio access
>>> mode. Add a vb2_verify_memory_type() check symmetrical to
>>> vb2_ioctl_create_bufs() to forbid that ioctl when fileio is active to
>>> protect internal queue state between subsequent read/write calls.
>>>
>>> CC: stable@...r.kernel.org
>>> Fixes: a3293a85381e ("media: v4l2: Add REMOVE_BUFS ioctl")
>>> Reported-by: Shuangpeng Bai<SJB7183@....edu>
>>> Suggested-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>>> ---
>>>   drivers/media/common/videobuf2/videobuf2-v4l2.c | 8 +++++---
>>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>> index d911021c1bb0..a8a5b42a42d0 100644
>>> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>> @@ -1000,13 +1000,15 @@ int vb2_ioctl_remove_bufs(struct file *file, void *priv,
>>>   			  struct v4l2_remove_buffers *d)
>>>   {
>>>   	struct video_device *vdev = video_devdata(file);
>>> -
>>> -	if (vdev->queue->type != d->type)
>>> -		return -EINVAL;
>>> +	int res;
>>>   
>>>   	if (d->count == 0)
>>>   		return 0;
>> Ah, no. This should still check d->type. So:
>>
>> 	if (d->count == 0)
>> 		return d->type == vdev->queue->type ? 0 : -EINVAL;
> 
> Then frankly speaking lets get back to v1 limited to 
> vb2_ioctl_remove_bufs(), as using vb2_verify_memory_type() in this 
> context only makes things harder to understand:
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c 
> b/drivers/media/common/videobuf2/videobuf2-v4l2.c index 
> d911021c1bb0..f4104d5971dd 100644 --- 
> a/drivers/media/common/videobuf2/videobuf2-v4l2.c +++ 
> b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> 
> @@ -1010,6 +1015,11 @@ int vb2_ioctl_remove_bufs(struct file *file, void 
> *priv, if (vb2_queue_is_busy(vdev->queue, file)) return -EBUSY; + if 
> (vb2_fileio_is_active(vdev->queue)) { + dprintk(vdev->queue, 1, "file io 
> in progress\n"); + return -EBUSY; + } + return 
> vb2_core_remove_bufs(vdev->queue, d->index, d->count); } 
> EXPORT_SYMBOL_GPL(vb2_ioctl_remove_bufs);

I agree. Can you post a v4?

Regards,

	Hans

> 
> 
>> Regards,
>>
>> 	Hans
>>
>>>   
>>> +	res = vb2_verify_memory_type(vdev->queue, vdev->queue->memory, d->type);
>>> +	if (res)
>>> +		return res;
>>> +
>>>   	if (vb2_queue_is_busy(vdev->queue, file))
>>>   		return -EBUSY;
>>>
> Best regards