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Message-ID: <cf03d58a-93ad-46ce-bd59-8fbae3c311b2@arm.com>
Date: Thu, 25 Apr 2024 23:05:07 +0100
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Subject: Re: [PATCH v1 3/3] thermal/debugfs: Prevent use-after-free from
 occurring after cdev removal
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linux PM <linux-pm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
 "Rafael J. Wysocki" <rafael@kernel.org>,
 Daniel Lezcano <daniel.lezcano@linaro.org>
References: <12427744.O9o76ZdvQC@kreacher> <13503555.uLZWGnKmhe@kreacher>
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From: Lukasz Luba <lukasz.luba@arm.com>
In-Reply-To: <13503555.uLZWGnKmhe@kreacher>
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On 4/25/24 14:57, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.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 differet threads) and its reset to NULL.

s/differet/different/

> 
> Fixes: 755113d76786 ("thermal/debugfs: Add thermal cooling device debugfs information")
> Cc :6.8+ <stable@vger.kernel.org> # 6.8+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>   drivers/thermal/thermal_debugfs.c |   10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_debugfs.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_debugfs.c
> +++ linux-pm/drivers/thermal/thermal_debugfs.c
> @@ -503,15 +503,21 @@ 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;
>   
> +	mutex_lock(&cdev->lock);
> +
> +	thermal_dbg = cdev->debugfs;
>   	if (!thermal_dbg)

mutex_unlock(&cdev->lock) missing here

>   		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);
>   
> 
> 
> 
>