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

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Message-ID: <4efe960a-83e3-4c0b-a7e1-1d467ea94962@samsung.com>
Date: Thu, 23 Oct 2025 13:44:16 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: 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 13:30, 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>
> ---

History:

v3:
- moved vb2_verify_memory_type() check after (d->count == 0) check to 
pass v4l2
  compliance

v2: 
https://lore.kernel.org/all/20251020160121.1985354-1-m.szyprowski@samsung.com/
- dropped a change to vb2_ioctl_create_bufs(), as it is already handled
   by the vb2_verify_memory_type() call
- replaced queue->type check in vb2_ioctl_remove_bufs() by a call to
   vb2_verify_memory_type() which covers all cases

v1: 
https://lore.kernel.org/all/20251016111154.993949-1-m.szyprowski@samsung.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;
>   
> +	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
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland