In the Linux kernel, the following vulnerability has been resolved: thermal: hwmon: Remove hwmon class device along with its parent The current code creates one hwmon device per thermal zone type and that device is registered under the…

Overview

In the Linux kernel, the following vulnerability has been resolved:

thermal: hwmon: Remove hwmon class device along with its parent

The current code creates one hwmon device per thermal zone type and that device is registered under the first thermal zone of the given type.

That turns out to be problematic when the thermal zone holding the hwmon device is removed.

For example, say that there are two ACPI thermal zones on a system

/sys/devices/virtual/thermal/thermal_zone0/ /sys/devices/virtual/thermal/thermal_zone1/

The current code registers a hwmon class device for thermal_zone0 only:

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/

because the type is "acpitz" for both of them, but it adds a sysfs attribute that belongs to thermal_zone1 under it:

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/temp2_input

There is also

/sys/devices/virtual/thermal/thermal_zone0/hwmon0/temp1_input

which belongs to thermal_zone0.

When thermal_zone0 is removed, say because the ACPI thermal driver is unbound from the underlying platform device, thermal_remove_hwmon_sysfs() skips the removal of hwmon0 because of the temp2_input attribute belonging to thermal_zone1 which effectively prevents thermal_zone0 removal from making progress.

Address this by making thermal_remove_hwmon_sysfs() remove the entire hwmon class device interface for the given thermal zone type when the thermal zone device holding it is removed.

To prevent races with thermal_add_hwmon_sysfs() that may interfere with this, carry out the entire addition and removal of hwmon sysfs interfaces for thermal zones under thermal_hwmon_list_lock.

Also adjust the layout of the labels in thermal_add_hwmon_sysfs() to the current kernel coding style to align with the new "unlock" label.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.