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

mlxsw: thermal: Fix out-of-bounds memory accesses

Currently, mlxsw allows cooling states to be set above the maximum cooling state supported by the driver:

cat /sys/class/thermal/thermal_zone2/cdev0/type

mlxsw_fan

cat /sys/class/thermal/thermal_zone2/cdev0/max_state

10

echo 18 > /sys/class/thermal/thermal_zone2/cdev0/cur_state

echo $?

0

This results in out-of-bounds memory accesses when thermal state transition statistics are enabled (CONFIG_THERMAL_STATISTICS=y), as the transition table is accessed with a too large index (state) [1].

According to the thermal maintainer, it is the responsibility of the driver to reject such operations [2].

Therefore, return an error when the state to be set exceeds the maximum cooling state supported by the driver.

To avoid dead code, as suggested by the thermal maintainer [3], partially revert commit a421ce088ac8 ("mlxsw: core: Extend cooling device with cooling levels") that tried to interpret these invalid cooling states (above the maximum) in a special way. The cooling levels array is not removed in order to prevent the fans going below 20% PWM, which would cause them to get stuck at 0% PWM.

[1] BUG: KASAN: slab-out-of-bounds in thermal_cooling_device_stats_update+0x271/0x290 Read of size 4 at addr ffff8881052f7bf8 by task kworker/0:0/5

CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.15.0-rc3-custom-45935-gce1adf704b14 #122 Hardware name: Mellanox Technologies Ltd. "MSN2410-CB2FO"/"SA000874", BIOS 4.6.5 03/08/2016 Workqueue: events_freezable_power_ thermal_zone_device_check Call Trace: dump_stack_lvl+0x8b/0xb3 print_address_description.constprop.0+0x1f/0x140 kasan_report.cold+0x7f/0x11b thermal_cooling_device_stats_update+0x271/0x290 __thermal_cdev_update+0x15e/0x4e0 thermal_cdev_update+0x9f/0xe0 step_wise_throttle+0x770/0xee0 thermal_zone_device_update+0x3f6/0xdf0 process_one_work+0xa42/0x1770 worker_thread+0x62f/0x13e0...