linux-kernel - Re: [PATCH V3 2/2] rpmsg: glink: Add lock to rpmsg_ctrldev

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Message-ID: <37d5a6e0-4b98-55c0-8209-98c032eaf646@foss.st.com>
Date:   Wed, 14 Sep 2022 09:57:29 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Deepak Kumar Singh <quic_deesin@...cinc.com>,
        <bjorn.andersson@...aro.org>, <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 V3 2/2] rpmsg: glink: Add lock to rpmsg_ctrldev_remove

replace "glink" by "ctrl" in subject

On 9/12/22 19:05, 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
> 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.
> 
> 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);