CVE-2026-53222: Linux Kernel PTP OCP Use-After-Free Resource Cleanup Vulnerability

Technical summary

CVE-2026-53222 is a use-after-free vulnerability in the Linux kernel's ptp_ocp driver (arch/drivers/ptp/). The issue arises from incorrect resource cleanup sequencing in ptp_ocp_detach(). Commit a60fc3294a37 modified ptp_clock_unregister() to invoke ptp_disable_all_events(), which modifies pin configuration for pins supporting EXTTS (external timestamp) events. However, ptp_ocp_detach() was freeing pin resources before calling ptp_clock_unregister(), causing the unregister function to access already-freed memory. The vulnerability is classified as CWE-401 (Missing Release of Memory after Effective Lifetime). Remediation involves reordering the cleanup sequence to unregister the PTP clock before freeing pins, and adding synchronize_irq() calls to prevent interrupt handlers from accessing freed structures.

Business impact

This vulnerability can cause kernel panics during PTP OCP driver removal on affected systems. The impact is localized to systems using the PTP OCP hardware and driver, but affects availability by forcing unexpected system downtime. Since exploitation requires local access and occurs only during driver unload, the practical risk is moderate but important for systems that frequently reload kernel modules or perform system maintenance.

Affected systems

The Linux kernel is affected across multiple versions that include the vulnerable ptp_ocp driver code. Affected configurations are primarily enterprise and embedded systems using OpenCompute (OCP) PTP-capable network hardware for precision time synchronization. The vulnerability requires local access to trigger (via driver removal), limiting exposure to systems where local module management is possible.

Exploitability

Exploitation requires local access and involves triggering the vulnerable code path during PTP OCP driver unload. No remote exploitation vector exists. The vulnerability manifests as a kernel panic rather than privilege escalation or data exfiltration. An unprivileged local user with module unload capability (or a privileged administrator) can trigger the crash, making it a localized denial-of-service condition rather than a high-severity privilege escalation.

Remediation

The vulnerability is fixed by reordering operations in ptp_ocp_detach(): call ptp_clock_unregister() before freeing pin resources. Additionally, synchronize_irq() must be invoked after hardware is configured to stop producing interrupts, ensuring in-flight interrupt handlers complete before memory is freed. Verify the fix is included in your kernel version by checking the ptp_ocp driver code and consulting the Linux kernel git repository or your distribution's advisory.

Patch guidance

Apply the latest stable kernel version from your distribution that includes fixes for the ptp_ocp driver resource cleanup. For systems running stable-track kernels (e.g., RHEL, Ubuntu LTS, Debian stable), check your vendor's security advisory for the patched kernel version and apply it via your standard kernel update process. If you maintain a custom kernel, backport the fix from the mainline Linux kernel repository, specifically the change that reorders ptp_clock_unregister() to occur before pin resource deallocation and adds synchronize_irq() synchronization. Test the update in a non-production environment first to ensure PTP clock functionality remains stable after the patch.

Detection guidance

Monitor system logs and kernel messages for use-after-free warnings or kernel oops related to ptp_ocp during driver unload. Systems may log BUG messages or WARNING lines mentioning 'ptp' or 'ocp' in dmesg or syslog. Check running kernel version and compare against patched versions from your Linux distribution. For active detection, kernel address sanitizer (KASAN) builds will reliably catch the use-after-free at runtime if enabled in your environment. Code review of ptp_ocp driver source can confirm whether the vulnerable sequencing remains present.

Why prioritize this

Assign medium priority. While the CVSS score of 5.5 reflects local-only access requirements and denial-of-service impact, the vulnerability affects a niche but important hardware/driver combination used in precision time infrastructure. Organizations using OCP PTP hardware should patch promptly to prevent unexpected outages during maintenance windows. Organizations not using PTP OCP hardware can deprioritize unless they have broad kernel patching cadences that cover this area.

Risk score, explained

CVSS v3.1 score of 5.5 (MEDIUM) reflects: Attack Vector Local (limited to local access only), Attack Complexity Low (straightforward trigger via driver unload), Privileges Required Low (standard user can trigger unload in some configurations), User Interaction None (automatic on unload), and Availability Impact High (kernel panic). Confidentiality and Integrity impacts are None because the vulnerability does not leak data or modify system state maliciously. The score appropriately reflects a reliability/availability issue rather than a security-boundary bypass.

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