linux-kernel - Re: [PATCH v2 3/3] thermal/debugfs: Prevent use-after-free from occurring after cdev removal

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Date: Fri, 26 Apr 2024 10:35:51 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 3/3] thermal/debugfs: Prevent use-after-free from
 occurring after cdev removal



On 4/26/24 10:28, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Since thermal_debug_cdev_remove() does not run under cdev->lock, it can
> run in parallel with thermal_debug_cdev_state_update() and it may free
> the struct thermal_debugfs object used by the latter after it has been
> checked against NULL.
> 
> If that happens, thermal_debug_cdev_state_update() will access memory
> that has been freed already causing the kernel to crash.
> 
> Address this by using cdev->lock in thermal_debug_cdev_remove() around
> the cdev->debugfs value check (in case the same cdev is removed at the
> same time in two different threads) and its reset to NULL.
> 
> Fixes: 755113d76786 ("thermal/debugfs: Add thermal cooling device debugfs information")
> Cc :6.8+ <stable@...r.kernel.org> # 6.8+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> v1 -> v2: Add missing mutex_unlock() (Lukasz).
> 
> ---
>   drivers/thermal/thermal_debugfs.c |   14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_debugfs.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_debugfs.c
> +++ linux-pm/drivers/thermal/thermal_debugfs.c
> @@ -505,15 +505,23 @@ void thermal_debug_cdev_add(struct therm
>    */
>   void thermal_debug_cdev_remove(struct thermal_cooling_device *cdev)
>   {
> -	struct thermal_debugfs *thermal_dbg = cdev->debugfs;
> +	struct thermal_debugfs *thermal_dbg;
>   
> -	if (!thermal_dbg)
> +	mutex_lock(&cdev->lock);
> +
> +	thermal_dbg = cdev->debugfs;
> +	if (!thermal_dbg) {
> +		mutex_unlock(&cdev->lock);
>   		return;
> +	}
> +
> +	cdev->debugfs = NULL;
> +
> +	mutex_unlock(&cdev->lock);
>   
>   	mutex_lock(&thermal_dbg->lock);
>   
>   	thermal_debugfs_cdev_clear(&thermal_dbg->cdev_dbg);
> -	cdev->debugfs = NULL;
>   
>   	mutex_unlock(&thermal_dbg->lock);
>   
> 
> 
> 
> 

It looks good now

Reviewed-by: Lukasz Luba <lukasz.luba@....com>