Re: [PATCH] videobuf2-core: avoid buffer operations while in stop_streaming

[Hans Verkuil <hverkuil-cisco@xs4all.nl>]

On 8/15/19 2:28 PM, Hans Verkuil wrote:
> The stop_streaming callback is called with the queue lock held.
> 
> But some drivers (vivid being one of them) need to stop a kernel thread
> in stop_streaming, and if that kernel thread takes the same queue lock,
> then stop_streaming may have to unlock the queue lock, stop the thread,
> and lock it again.
> 
> However, if you do that, then you must ensure that no other operations
> can take place that can change the list of buffers queued to the driver,
> specifically: QBUF, STREAMON/OFF, REQBUFS, CREATE_BUFS.
> 
> __vb2_wait_for_done_vb() also checks for this and won't try to wait for
> new buffers if in_stop_streaming is true.
> 
> This issue caused this syzbot report:
> 
> https://syzkaller.appspot.com/bug?extid=736c3aae4af7b50d9683

And also this syzbot report:

https://syzkaller.appspot.com/bug?extid=06283a66a648cd073885

> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Reported-by: syzbot+736c3aae4af7b50d9683@syzkaller.appspotmail.com

Reported-and-tested-by: syzbot+06283a66a648cd073885@syzkaller.appspotmail.com

Regards,

	Hans

> ---
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 4489744fbbd9..7c70bb9f6cb8 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -677,6 +677,11 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>  		return -EBUSY;
>  	}
> 
> +	if (q->in_stop_streaming) {
> +		dprintk(1, "reqbufs while the stream is being stopped\n");
> +		return -EBUSY;
> +	}
> +
>  	if (q->waiting_in_dqbuf && *count) {
>  		dprintk(1, "another dup()ped fd is waiting for a buffer\n");
>  		return -EBUSY;
> @@ -811,6 +816,11 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>  	unsigned plane_sizes[VB2_MAX_PLANES] = { };
>  	int ret;
> 
> +	if (q->in_stop_streaming) {
> +		dprintk(1, "create_bufs while the stream is being stopped\n");
> +		return -EBUSY;
> +	}
> +
>  	if (q->num_buffers == VB2_MAX_FRAME) {
>  		dprintk(1, "maximum number of buffers already allocated\n");
>  		return -ENOBUFS;
> @@ -1514,6 +1524,11 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
>  	struct vb2_buffer *vb;
>  	int ret;
> 
> +	if (q->in_stop_streaming) {
> +		dprintk(1, "qbuf while the stream is being stopped\n");
> +		return -EBUSY;
> +	}
> +
>  	if (q->error) {
>  		dprintk(1, "fatal error occurred on queue\n");
>  		return -EIO;
> @@ -1675,6 +1690,11 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
>  			return -EBUSY;
>  		}
> 
> +		if (q->in_stop_streaming) {
> +			dprintk(1, "the stream is being stopped, will not wait for buffers\n");
> +			return -EINVAL;
> +		}
> +
>  		if (!q->streaming) {
>  			dprintk(1, "streaming off, will not wait for buffers\n");
>  			return -EINVAL;
> @@ -1716,7 +1736,7 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
>  		dprintk(3, "will sleep waiting for buffers\n");
>  		ret = wait_event_interruptible(q->done_wq,
>  				!list_empty(&q->done_list) || !q->streaming ||
> -				q->error);
> +				q->in_stop_streaming || q->error);
> 
>  		/*
>  		 * We need to reevaluate both conditions again after reacquiring
> @@ -1866,12 +1886,18 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
>  {
>  	unsigned int i;
> 
> +	if (WARN_ON(q->in_stop_streaming))
> +		return;
> +
>  	/*
>  	 * Tell driver to stop all transactions and release all queued
>  	 * buffers.
>  	 */
> -	if (q->start_streaming_called)
> +	if (q->start_streaming_called) {
> +		q->in_stop_streaming = 1;
>  		call_void_qop(q, stop_streaming, q);
> +		q->in_stop_streaming = 0;
> +	}
> 
>  	/*
>  	 * If you see this warning, then the driver isn't cleaning up properly
> @@ -1975,6 +2001,11 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type)
>  		return -EINVAL;
>  	}
> 
> +	if (q->in_stop_streaming) {
> +		dprintk(1, "streamon while the stream is being stopped\n");
> +		return -EBUSY;
> +	}
> +
>  	if (q->streaming) {
>  		dprintk(3, "already streaming\n");
>  		return 0;
> @@ -2026,6 +2057,11 @@ int vb2_core_streamoff(struct vb2_queue *q, unsigned int type)
>  		return -EINVAL;
>  	}
> 
> +	if (q->in_stop_streaming) {
> +		dprintk(1, "streamoff while the stream is being stopped\n");
> +		return -EBUSY;
> +	}
> +
>  	/*
>  	 * Cancel will pause streaming and remove all buffers from the driver
>  	 * and videobuf, effectively returning control over them to userspace.
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 640aabe69450..c4b7edd25e13 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -535,6 +535,9 @@ struct vb2_buf_ops {
>   * @streaming:	current streaming state
>   * @start_streaming_called: @start_streaming was called successfully and we
>   *		started streaming.
> + * @in_stop_streaming: set when calling @stop_streaming. While 1, no new buffers
> + * 		can be queued or created, and neither is it possible to start or
> + * 		stop streaming.
>   * @error:	a fatal error occurred on the queue
>   * @waiting_for_buffers: used in poll() to check if vb2 is still waiting for
>   *		buffers. Only set for capture queues if qbuf has not yet been
> @@ -595,6 +598,7 @@ struct vb2_queue {
> 
>  	unsigned int			streaming:1;
>  	unsigned int			start_streaming_called:1;
> +	unsigned int			in_stop_streaming:1;
>  	unsigned int			error:1;
>  	unsigned int			waiting_for_buffers:1;
>  	unsigned int			waiting_in_dqbuf:1;
>