linux-kernel - Re: [PATCH] media: venus: fix use after free for registeredbufs

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Date:   Fri, 6 Mar 2020 11:03:17 +0200
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Jeffrey Kardatzke <jkardatzke@...gle.com>,
        linux-media@...r.kernel.org
Cc:     Andy Gross <agross@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: venus: fix use after free for registeredbufs

Hi Jeff,

Thanks for the patch!

On 3/6/20 2:23 AM, Jeffrey Kardatzke wrote:
> In dynamic bufmode we do not manage the buffers in the registeredbufs
> list, so do not add them there when they are initialized. Adding them
> there was causing a use after free of the list_head struct in the buffer
> when new buffers were allocated after existing buffers were freed.

Is this fixing a real issue? How you come to it?

> 
> Signed-off-by: Jeffrey Kardatzke <jkardatzke@...gle.com>
> ---
>  drivers/media/platform/qcom/venus/helpers.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/helpers.c b/drivers/media/platform/qcom/venus/helpers.c
> index bcc603804041..688a3593b49b 100644
> --- a/drivers/media/platform/qcom/venus/helpers.c
> +++ b/drivers/media/platform/qcom/venus/helpers.c
> @@ -1054,8 +1054,10 @@ int venus_helper_vb2_buf_init(struct vb2_buffer *vb)
>  	buf->size = vb2_plane_size(vb, 0);
>  	buf->dma_addr = sg_dma_address(sgt->sgl);
>  
> -	if (vb->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE)
> +	if (vb->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE &&
> +	    !is_dynamic_bufmode(inst)) {

If you add !is_dynamic_bufmode here, we will loose the reference frames
mechanism (see venus_helper_release_buf_ref()) which is not good.

Thus, I wonder (depending on when you observe the use-after-free issue)
does this is the correct resolution of the problem.

>  		list_add_tail(&buf->reg_list, &inst->registeredbufs);
> +	}
>  
>  	return 0;
>  }
> 

-- 
regards,
Stan