linux-kernel - Re: [PATCH V1 2/3] rpmsg: glink: Add lock to avoid race when rpmsg device is released

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Date:   Fri, 11 Mar 2022 14:52:45 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Deepak Kumar Singh <quic_deesin@...cinc.com>
Cc:     swboyd@...omium.org, quic_clew@...cinc.com,
        mathieu.poirier@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: [PATCH V1 2/3] rpmsg: glink: Add lock to avoid race when rpmsg
 device is released

On Wed 26 Jan 13:04 CST 2022, Deepak Kumar Singh wrote:

> When remote host goes down glink char device channel is freed,
> At the same time user space apps can still try to open rpmsg_char
> device which will result in calling rpmsg_create_ept. This may cause
> reference to already freed context of glink chardev channel.
> 

Hi Deepak,

Could you please be a little bit more specific on the details of where
you're seeing this race? Perhaps I'm just missing something obvious?

> Use per ept lock to avoid race between rpmsg_destroy_ept and
> rpmsg_destory_ept.

I presume one of these should say rpmsg_eptdev_open().

Regards,
Bjorn

> ---
>  drivers/rpmsg/rpmsg_char.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 72ee101..2108ef8 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -85,6 +85,7 @@ static int rpmsg_eptdev_destroy(struct device *dev, void *data)
>  	struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
>  
>  	mutex_lock(&eptdev->ept_lock);
> +	eptdev->rpdev = NULL;
>  	if (eptdev->ept) {
>  		rpmsg_destroy_ept(eptdev->ept);
>  		eptdev->ept = NULL;
> @@ -145,15 +146,24 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
>  
>  	get_device(dev);
>  
> +	mutex_lock(&eptdev->ept_lock);
> +	if (!eptdev->rpdev) {
> +		put_device(dev);
> +		mutex_unlock(&eptdev->ept_lock);
> +		return -ENETRESET;
> +	}
> +
>  	ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
>  	if (!ept) {
>  		dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
> +		mutex_unlock(&eptdev->ept_lock);
>  		put_device(dev);
>  		return -EINVAL;
>  	}
>  
>  	ept->sig_cb = rpmsg_sigs_cb;
>  	eptdev->ept = ept;
> +	mutex_unlock(&eptdev->ept_lock);
>  	filp->private_data = eptdev;
>  
>  	return 0;
> @@ -285,7 +295,9 @@ static __poll_t rpmsg_eptdev_poll(struct file *filp, poll_table *wait)
>  	if (eptdev->sig_pending)
>  		mask |= EPOLLPRI;
>  
> +	mutex_lock(&eptdev->ept_lock);
>  	mask |= rpmsg_poll(eptdev->ept, filp, wait);
> +	mutex_unlock(&eptdev->ept_lock);
>  
>  	return mask;
>  }
> -- 
> 2.7.4
>