linux-kernel - Re: [PATCH V4 2/2] rpmsg: ctrl: Add lock to rpmsg_ctrldev

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Date:   Thu, 15 Sep 2022 07:34:00 -0700
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     Deepak Kumar Singh <quic_deesin@...cinc.com>,
        <bjorn.andersson@...aro.org>, <arnaud.pouliquen@...s.st.com>,
        <swboyd@...omium.org>, <quic_clew@...cinc.com>,
        <mathieu.poirier@...aro.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-remoteproc@...r.kernel.org>
Subject: Re: [PATCH V4 2/2] rpmsg: ctrl: Add lock to rpmsg_ctrldev_remove

On 9/15/2022 2:44 AM, Deepak Kumar Singh wrote:
> Call to rpmsg_ctrldev_ioctl() and rpmsg_ctrldev_remove() must be synchronized.
> In present code rpmsg_ctrldev_remove() is not protected with lock, therefore
> new char device creation can succeed through rpmsg_ctrldev_ioctl() call. At the
> same time call to rpmsg_ctrldev_remove() funtion for ctrl device removal will

nit: s/funtion/function/

> free associated rpdev device. As char device creation already succeeded, user
> space is free to issue open() call which maps to rpmsg_create_ept() in kernel.
> rpmsg_create_ept() function tries to reference rpdev which has already been
> freed through rpmsg_ctrldev_remove(). Issue is predominantly seen in aggressive
> reboot tests where rpmsg_ctrldev_ioctl() and rpmsg_ctrldev_remove() can race with
> each other.
> 
> Adding lock in rpmsg_ctrldev_remove() avoids any new char device creation
> throught rpmsg_ctrldev_ioctl() while remove call is already in progress.

nit: s/throught/through/
> 
> Signed-off-by: Deepak Kumar Singh <quic_deesin@...cinc.com>
> ---
>   drivers/rpmsg/rpmsg_ctrl.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> index 107da70..4332538 100644
> --- a/drivers/rpmsg/rpmsg_ctrl.c
> +++ b/drivers/rpmsg/rpmsg_ctrl.c
> @@ -194,10 +194,12 @@ static void rpmsg_ctrldev_remove(struct rpmsg_device *rpdev)
>   	struct rpmsg_ctrldev *ctrldev = dev_get_drvdata(&rpdev->dev);
>   	int ret;
>   
> +	mutex_lock(&ctrldev->ctrl_lock);
>   	/* Destroy all endpoints */
>   	ret = device_for_each_child(&ctrldev->dev, NULL, rpmsg_chrdev_eptdev_destroy);
>   	if (ret)
>   		dev_warn(&rpdev->dev, "failed to nuke endpoints: %d\n", ret);
> +	mutex_unlock(&ctrldev->ctrl_lock);
>   
>   	cdev_device_del(&ctrldev->cdev, &ctrldev->dev);
>   	put_device(&ctrldev->dev);