CVE-2026-53222: Linux Kernel Use-After-Free Vulnerability

CVE-2026-53222 Overview

CVE-2026-53222 is a use-after-free vulnerability in the Linux kernel's PTP (Precision Time Protocol) OCP driver. The flaw exists in the ptp_ocp_detach() function, which frees pin resources before calling ptp_clock_unregister(). A prior change introduced ptp_disable_all_events() inside the unregister path, which subsequently accesses pin configuration for EXTTS-capable pins. Accessing those already-freed structures during driver removal results in a use-after-free condition. The issue has been resolved in upstream kernel commits.

Critical Impact
Triggering the use-after-free during driver removal can corrupt kernel memory and destabilize the system. Concurrent IRQ handlers on other cores compound the race window.

Affected Products

Linux kernel versions containing commit a60fc3294a37 ("ptp: rework ptp_clock_unregister() to disable events") and using the ptp_ocp driver
Systems with PTP OCP timing hardware (e.g., Open Compute Project time appliance cards)
Stable kernel branches prior to the fixes in commits 627366c51145 and aa03698bb28d

Discovery Timeline

2026-06-25 - CVE-2026-53222 published to NVD
2026-06-25 - Last updated in NVD database

Technical Details for CVE-2026-53222

Vulnerability Analysis

The vulnerability resides in the ptp_ocp driver, which supports Open Compute Project timing hardware that exposes EXTTS (external timestamp) pins through the Linux PTP subsystem. During driver removal, ptp_ocp_detach() is responsible for tearing down hardware resources and unregistering the PTP clock device with the kernel.

An earlier kernel change reworked ptp_clock_unregister() to call ptp_disable_all_events(). This helper inspects and rewrites pin configuration for pins that support EXTTS events. The intent was a clean shutdown of event sources before the clock device disappears.

In ptp_ocp_detach(), however, pin resources were freed prior to the ptp_clock_unregister() call. When the unregister path reached ptp_disable_all_events(), it dereferenced pin structures that had already been released, producing a use-after-free [CWE-416].

A secondary concern involves IRQ handling. While the PTP device is being unregistered, an interrupt handler can still run on another core and touch driver state during teardown, widening the race window.

Root Cause

The root cause is incorrect resource teardown ordering. The driver released pin-related allocations before invoking ptp_clock_unregister(), but the unregister routine now depends on those allocations remaining valid to disable EXTTS events. The original ordering was safe before the rework, making this a latent ordering bug exposed by the new unregister semantics.

Attack Vector

Triggering the condition requires the ptp_ocp driver to be unloaded or the underlying device to be removed on a system with affected hardware. This is a local kernel-state issue typically reached by a privileged operator performing module removal or device hot-unplug. There is no known network-reachable trigger, and no public proof-of-concept exploit is referenced.

The vulnerability manifests in the driver detach path. See the upstream kernel commits referenced below for the exact code changes that reorder the unregister and free operations and add synchronize_irq().

Detection Methods for CVE-2026-53222

Indicators of Compromise

Kernel oops, panic, or KASAN reports referencing ptp_ocp_detach, ptp_clock_unregister, or ptp_disable_all_events during module unload
Slab-use-after-free or general protection fault messages in dmesg coinciding with rmmod ptp_ocp or PCI hot-unplug events
Unexpected system instability on hosts using OCP timing cards after driver reload cycles

Detection Strategies

Enable KASAN (Kernel Address Sanitizer) on test kernels to surface use-after-free accesses in the PTP detach path
Monitor /var/log/kern.log and journald for stack traces involving the ptp_ocp driver during shutdown or maintenance operations
Inventory hosts running the ptp_ocp module against fixed kernel versions to identify exposed systems

Monitoring Recommendations

Forward kernel logs to a centralized logging or SIEM platform and alert on ptp_ocp stack traces and KASAN reports
Track module load and unload events using auditd rules on init_module and delete_module syscalls
Correlate device hot-plug events with kernel error reports to identify race conditions in production

How to Mitigate CVE-2026-53222

Immediate Actions Required

Apply the upstream stable kernel updates containing commits 627366c51145a07f675b1800fb5ea2ec960bd900 and aa03698bb28d3be5ee180adb185395054b342b04
Restrict module unload and device hot-unplug operations on systems with the ptp_ocp driver until patched
Identify hosts using OCP timing hardware and prioritize them for kernel updates

Patch Information

The fix reorders operations in ptp_ocp_detach() so that ptp_clock_unregister() is called before pin resources are freed. It also adds synchronize_irq() after hardware is configured to stop producing interrupts, ensuring no IRQ handlers are in flight during teardown. Patch details are available in the kernel.org commit 627366c5 and kernel.org commit aa03698b.

Workarounds

Avoid unloading the ptp_ocp module on running systems until the patched kernel is deployed
Restrict root and CAP_SYS_MODULE privileges to a minimal set of administrators to reduce accidental triggering
Blacklist the ptp_ocp module on hosts that do not require PTP OCP hardware support

bash

# Blacklist the ptp_ocp module if PTP OCP hardware is not in use
echo "blacklist ptp_ocp" | sudo tee /etc/modprobe.d/blacklist-ptp-ocp.conf
sudo update-initramfs -u

# Verify installed kernel version against fixed stable releases
uname -r