CVE-2026-89942: Linux Kernel IIO Buffer Use-After-Free

CVE-2026-89942 Overview

CVE-2026-89942 is a use-after-free vulnerability in the Linux kernel's Industrial I/O (IIO) subsystem. The flaw resides in the anonymous buffer release path, where a mutex guard held by the buffer's release function is unlocked after the underlying IIO device reference is dropped. When the anonymous buffer holds the last reference to the device, iio_device_put() can free the memory containing the mutex before the guard unlocks it. The result is a use-after-free triggered during buffer teardown following device unbind or hot-unplug.

Critical Impact
Local attackers with access to IIO device handles can trigger memory corruption in kernel context, potentially leading to privilege escalation or denial of service.

Affected Products

Linux kernel versions containing the anonymous IIO buffer handle feature
Distributions shipping the affected IIO subsystem code
Systems exposing IIO devices supporting hot-unplug or unbind

Discovery Timeline

2026-09-16 - CVE-2026-89942 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89942

Vulnerability Analysis

The Linux kernel IIO subsystem exposes anonymous buffer handles that hold references to their parent IIO device. When userspace closes an anonymous buffer, the kernel invokes the buffer's release function to tear down state and drop the device reference through iio_device_put().

The release function acquires the buffer's mutex using a scope-wide guard. The guard releases the mutex only when the function returns, meaning iio_device_put() executes while the guard is still active. If the calling context holds the final reference, dropping it frees the IIO device and the embedded buffer structure, which contains the mutex. The guard then attempts to unlock a mutex that lives in freed memory.

The fix narrows the guard's scope to cover only the dmabuf list access, ensuring the mutex is released before iio_device_put() runs. This preserves the correct ordering that version 10 of the original patch implemented, before review feedback introduced the wider guard in version 11.

Root Cause

The root cause is incorrect lock scoping in the anonymous buffer release path. A guard object was used to hold the buffer mutex across the entire release function, including the reference drop that can free the mutex itself. This is a classic ordering error between locking primitives and object lifetime.

Attack Vector

Exploitation requires local access with permissions to open an IIO device buffer. An attacker triggers device removal, either through unbind via sysfs or by removing a hot-pluggable IIO device, while holding an anonymous buffer handle. Closing the handle after the device is gone forces the release path to drop the final reference, freeing the buffer, and then unlock the mutex embedded in the freed memory.

The vulnerability requires local low-privilege access and no user interaction. Successful exploitation yields kernel memory corruption, which can be leveraged for local privilege escalation or kernel panic.

Detection Methods for CVE-2026-89942

Indicators of Compromise

Kernel oops or panic messages referencing iio buffer release paths or mutex unlock on freed memory
KASAN reports flagging use-after-free in iio_buffer_release or related anonymous buffer teardown functions
Unexpected process terminations following IIO device unbind or hot-unplug events

Detection Strategies

Enable Kernel Address Sanitizer (KASAN) on test kernels to surface use-after-free conditions during IIO stress tests
Correlate device unbind or removal events in dmesg with subsequent process crashes or kernel warnings
Audit userspace processes opening IIO character devices under /dev/iio:device* and monitor for anomalous close sequences after device removal

Monitoring Recommendations

Collect kernel logs centrally and alert on BUG: or KASAN: entries referencing the drivers/iio/industrialio-buffer.c code path
Track sysfs unbind operations against IIO drivers and correlate with kernel error output
Monitor privilege escalation indicators following IIO device removal events on systems with untrusted local users

How to Mitigate CVE-2026-89942

Immediate Actions Required

Apply the upstream Linux kernel patch that narrows the mutex guard scope in the anonymous IIO buffer release function
Rebuild and deploy kernel packages incorporating the fix commits referenced in the stable tree
Restrict local access to IIO device nodes to trusted users through group ownership and permissions on /dev/iio:device*

Patch Information

The fix is available in the upstream stable tree through the following commits: Linux Kernel Commit 6288b593, Linux Kernel Commit 6d4bdbf7, Linux Kernel Commit ab530775, and Linux Kernel Commit f1f8f0e8. Distribution vendors should backport these commits to supported kernel branches.

Workarounds

Disable IIO drivers on systems that do not require industrial sensor support until the patched kernel is deployed
Tighten permissions on /dev/iio:device* nodes to prevent unprivileged access to anonymous buffer handles
Prevent unprivileged users from triggering driver unbind by restricting write access to sysfs unbind files

bash

# Restrict IIO device node access to a trusted group
chgrp iio-users /dev/iio:device*
chmod 660 /dev/iio:device*

# Prevent unprivileged writes to sysfs unbind entries
find /sys/bus/iio/drivers -name unbind -exec chmod 600 {} \;