In the Linux kernel, the following vulnerability has been resolved:
platform/x86: x86-android-tablets: Unregister devices in reverse order
Not all subsystems support a device getting removed while there are still consumers of the device with a reference to the device.
One example of this is the regulator subsystem. If a regulator gets unregistered while there are still drivers holding a reference a WARN() at drivers/regulator/core.c:5829 triggers, e.g.:
WARNING: CPU: 1 PID: 1587 at drivers/regulator/core.c:5829 regulator_unregister Hardware name: Intel Corp. VALLEYVIEW C0 PLATFORM/BYT-T FFD8, BIOS BLADE_21.X64.0005.R00.1504101516 FFD8_X64_R_2015_04_10_1516 04/10/2015 RIP: 0010:regulator_unregister Call Trace: regulator_unregister devres_release_group i2c_device_remove device_release_driver_internal bus_remove_device device_del device_unregister x86_android_tablet_remove
On the Lenovo Yoga Tablet 2 series the bq24190 charger chip also provides a 5V boost converter output for powering USB devices connected to the micro USB port, the bq24190-charger driver exports this as a Vbus regulator.
On the 830 (8") and 1050 ("10") models this regulator is controlled by a platform_device and x86_android_tablet_remove() removes platform_device-s before i2c_clients so the consumer gets removed first.
But on the 1380 (13") model there is a lc824206xa micro-USB switch connected over I2C and the extcon driver for that controls the regulator. The bq24190 i2c-client *must* be registered first, because that creates the regulator with the lc824206xa listed as its consumer. If the regulator has not been registered yet the lc824206xa driver will end up getting a dummy regulator.
Since in this case both the regulator provider and consumer are I2C devices, the only way to ensure that the consumer is unregistered first is to unregister the I2C devices in reverse order of in which they were created.
For consistency and to avoid similar problems in the future change x86_android_tablet_remove() to unregister all device types in reverse order.