Improper Locking Affecting kernel-rt-debug package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-rt-debug package and not the kernel-rt-debug package as distributed by RHEL. See How to fix? for RHEL:7 relevant fixed versions and status.

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

thermal/debugfs: Fix two locking issues with thermal zone debug

With the current thermal zone locking arrangement in the debugfs code, user space can open the "mitigations" file for a thermal zone before the zone's debugfs pointer is set which will result in a NULL pointer dereference in tze_seq_start().

Moreover, thermal_debug_tz_remove() is not called under the thermal zone lock, so it can run in parallel with the other functions accessing the thermal zone's struct thermal_debugfs object. Then, it may clear tz->debugfs after one of those functions has checked it and the struct thermal_debugfs object may be freed prematurely.

To address the first problem, pass a pointer to the thermal zone's struct thermal_debugfs object to debugfs_create_file() in thermal_debug_tz_add() and make tze_seq_start(), tze_seq_next(), tze_seq_stop(), and tze_seq_show() retrieve it from s->private instead of a pointer to the thermal zone object. This will ensure that tz_debugfs will be valid across the "mitigations" file accesses until thermal_debugfs_remove_id() called by thermal_debug_tz_remove() removes that file.

To address the second problem, use tz->lock in thermal_debug_tz_remove() around the tz->debugfs value check (in case the same thermal zone is removed at the same time in two different threads) and its reset to NULL.

Cc :6.8+ <stable@vger.kernel.org> # 6.8+

• https://access.redhat.com/security/cve/CVE-2024-36961
• https://git.kernel.org/stable/c/6c57bdd0505422d5ccd2df541d993aec978c842e
• https://git.kernel.org/stable/c/c7f7c37271787a7f77d7eedc132b0b419a76b4c8