[PATCH] thermal/of: Fix double free of params during unregistration

[Mark Brown]

Unlike the other data structures provided during registration the
thermal core takes a copy of the thermal_zone_params provided to it and
stores that copy in the thermal_zone_device, taking care to free it on
unregistration.  This is done because the parameters will be modified at
runtime.

Unfortunately the thermal_of code assumes that the params structure it
provides will be used throughout the lifetime of the device and since
the params are dynamically allocated based on the bindings it attempts
to free it on unregistration.  This results in not only leaking the
original params but also double freeing the copy the core made, leading
to memory corruption.

Fix this by instead freeing the params parsed from the DT during
registration.

This issue causing instability on systems where thermal zones are
unregistered, especially visble on those systems where some zones
provided by a device have no trip points such as Allwinner systems.
For example with current mainline an arm64 defconfig is unbootable on
Pine64 Plus and LibreTech Tritium is massively unstable.  These issues
have been there for a while and have been made more prominent by recent
memory management changes.

Fixes: 3fd6d6e2b4e80 ("thermal/of: Rework the thermal device tree initialization")
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 drivers/thermal/thermal_of.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
index 6fb14e521197..0af11cdfa2c1 100644
--- a/drivers/thermal/thermal_of.c
+++ b/drivers/thermal/thermal_of.c
@@ -442,13 +442,11 @@ static int thermal_of_unbind(struct thermal_zone_device *tz,
 static void thermal_of_zone_unregister(struct thermal_zone_device *tz)
 {
 	struct thermal_trip *trips = tz->trips;
-	struct thermal_zone_params *tzp = tz->tzp;
 	struct thermal_zone_device_ops *ops = tz->ops;
 
 	thermal_zone_device_disable(tz);
 	thermal_zone_device_unregister(tz);
 	kfree(trips);
-	kfree(tzp);
 	kfree(ops);
 }
 
@@ -530,6 +528,9 @@ static struct thermal_zone_device *thermal_of_zone_register(struct device_node *
 		goto out_kfree_tzp;
 	}
 
+	/* The core will take a copy of tzp, free our copy here. */
+	kfree(tzp);
+
 	ret = thermal_zone_device_enable(tz);
 	if (ret) {
 		pr_err("Failed to enabled thermal zone '%s', id=%d: %d\n",

---
base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
change-id: 20230722-thermal-fix-of-memory-corruption-73c023f8612b

Best regards,
-- 
Mark Brown <broonie@xxxxxxxxxx>