[PATCH v1 3/3] thermal/debugfs: Prevent use-after-free from occurring after cdev removal

Rafael J. Wysocki
2024-04-25T13:57:36Z

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.

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)
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);