CVE-2026-89934: Linux Kernel Race Condition Vulnerability

CVE-2026-89934 Overview

CVE-2026-89934 is a runtime power management (PM) reference leak in the Linux kernel's Industrial I/O (IIO) subsystem, specifically in the ltrf216a ambient light sensor driver. The ltrf216a_get_lux() function acquires a runtime PM reference through ltrf216a_set_power_state(data, true) but fails to release it when ltrf216a_read_data() returns an error. This leaves the runtime PM usage counter unbalanced and prevents the device from entering autosuspend after a failed read.

Critical Impact
The unbalanced runtime PM counter keeps the sensor powered indefinitely after read failures, causing resource retention and potential power management degradation on affected systems.

Affected Products

Linux kernel builds including the drivers/iio/light/ltrf216a.c driver
Systems using the Liteon LTRF216A ambient light sensor via IIO
Kernel versions prior to the commits referenced in the stable tree fixes

Discovery Timeline

2026-09-16 - CVE-2026-89934 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89934

Vulnerability Analysis

The defect is a resource-management error classified as a Memory/Reference Leak in the kernel IIO light sensor driver. Runtime PM in the Linux kernel uses a reference-counted usage counter to determine when a device may be autosuspended. Each pm_runtime_get-style call must be matched with a corresponding pm_runtime_put call to keep the counter balanced.

In ltrf216a_get_lux(), the driver correctly increments the runtime PM usage counter by calling ltrf216a_set_power_state(data, true) before performing a sensor read. When the subsequent call to ltrf216a_read_data() succeeds, execution flow reaches the normal exit path and drops the reference. When the read fails, the function returns the error immediately and skips the release call.

Root Cause

The root cause is a missing cleanup step on the error branch of ltrf216a_get_lux(). The function omits ltrf216a_set_power_state(data, false) in the failure path after ltrf216a_read_data() returns non-zero. Every failed lux read therefore increments the PM usage counter permanently, disabling autosuspend for the sensor.

Attack Vector

This is a local reliability and resource-consumption issue rather than a remote code execution flaw. Any workload that repeatedly triggers ltrf216a_read_data() failures — for example, through I2C bus contention, faulty hardware states, or repeated sysfs in_illuminance_input reads under error conditions — will accumulate PM references. The device remains powered, consuming energy and preventing the parent bus from suspending.

No verified proof-of-concept code is published. Technical details are available in the upstream stable kernel commits: Kernel Git Commit 0614928, Kernel Git Commit 80e7381, Kernel Git Commit c132aef, and Kernel Git Commit c4f003d.

Detection Methods for CVE-2026-89934

Indicators of Compromise

Elevated runtime_usage values reported under /sys/bus/i2c/devices/*/power/runtime_usage for the LTRF216A device that never return to zero.
The device's runtime_status remains active despite the sensor being idle for extended periods.
Kernel logs from the ltrf216a driver showing repeated read failures without corresponding suspend transitions.

Detection Strategies

Audit installed kernel versions against the fix commits listed in the upstream stable tree.
Instrument the IIO subsystem with ftrace on rpm_* tracepoints to observe unmatched get/put pairs originating from ltrf216a_get_lux.
Monitor platform power telemetry for regressions in idle residency on devices carrying the LTRF216A sensor.

Monitoring Recommendations

Track kernel package versions across managed Linux endpoints and correlate against the patched builds.
Alert on sustained non-zero power/runtime_usage counters for IIO light sensors during system idle windows.
Include IIO driver error rates in device-health dashboards to surface repeated ltrf216a_read_data() failures.

How to Mitigate CVE-2026-89934

Immediate Actions Required

Apply the upstream Linux kernel stable patches referenced in the NVD advisory for CVE-2026-89934.
Update to a distribution kernel that includes the ltrf216a runtime PM error-path fix.
Reboot affected systems after patching to reset any leaked runtime PM references.

Patch Information

The fix releases the runtime PM reference before returning from the error path in ltrf216a_get_lux(). The correction is available in the stable kernel tree via commits 0614928, 80e7381, c132aef, and c4f003d. Distribution vendors have backported these commits into their respective long-term support kernels; consult your distribution's security bulletin for exact package versions.

Workarounds

Where patching is not immediately possible, unload the ltrf216a module on systems where the light sensor is not required.
Restrict user-space access to the IIO sysfs entries that trigger ltrf216a_get_lux() to reduce exposure to error-path invocations.
Reboot systems periodically to clear accumulated runtime PM references until the patched kernel is deployed.

bash

# Configuration example: block the vulnerable driver until patched
echo "blacklist ltrf216a" | sudo tee /etc/modprobe.d/blacklist-ltrf216a.conf
sudo modprobe -r ltrf216a