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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Lukasz Luba <lukasz.luba@arm.com>,
 Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linux PM <linux-pm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
 "Rafael J. Wysocki" <rafael@kernel.org>
Subject:
 [PATCH v1 3/3] thermal/debugfs: Prevent use-after-free from occurring after
 cdev removal
Date: Thu, 25 Apr 2024 15:57:12 +0200
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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);