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

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Message-ID: <36cfec0a-3717-4b0e-adc0-6887e6b58f44@collabora.com>
Date: Mon, 20 Oct 2025 09:11:25 +0200
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
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>,
 Hans Verkuil <hverkuil@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] media: videobuf2: forbid create_bufs/remove_bufs when
 legacy fileio is active


Le 16/10/2025 à 13:11, Marek Szyprowski a écrit :
> create_bufs and remove_bufs ioctl calls manipulate queue internal buffer
> list, potentially overwriting some pointers used by the legacy fileio
> access mode. Simply forbid those calls when fileio is active to protect
> internal queue state between subsequent read/write calls.

Hi Marek,

I may be wrong but using fileio API and create/remove API at the same time
sound incorrect from application point of view, right ? If that not the
case maybe we should also add a test in v4l2-compliance.

Regards,
Benjamin

>
> CC: stable@...r.kernel.org
> Fixes: 2d86401c2cbf ("[media] V4L: vb2: add support for buffers of different sizes on a single queue")
> Fixes: a3293a85381e ("media: v4l2: Add REMOVE_BUFS ioctl")
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>   drivers/media/common/videobuf2/videobuf2-v4l2.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> 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
> @@ -751,6 +751,11 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>   	int ret = vb2_verify_memory_type(q, create->memory, f->type);
>   	unsigned i;
>   
> +	if (vb2_fileio_is_active(q)) {
> +		dprintk(q, 1, "file io in progress\n");
> +		return -EBUSY;
> +	}
> +
>   	create->index = vb2_get_num_buffers(q);
>   	vb2_set_flags_and_caps(q, create->memory, &create->flags,
>   			       &create->capabilities, &create->max_num_buffers);
> @@ -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);