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

Lukasz Luba
2024-04-26T09:35:59Z

On 4/26/24 10:28, 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 different threads) and its reset to NULL.
>
> 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>
> ---
>
> 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@arm.com>