CVE-2021-47455

What it actually does

Memory leak in ptp_clock_register() when posix_clock_register() returns an error: the kobject name allocated via dev_set_name() is not freed because put_device() is not called, leaving the allocation unreferenced until kobject_cleanup.

Why it matters to the business

Systems relying on PTP clock devices (common in networking and industrial timing hardware) can experience gradual kernel memory exhaustion under repeated probe or registration failures, potentially causing performance degradation or instability.

How an attack unfolds

An attacker with local access or control over hardware/driver initialization triggers error paths in ptp_clock_register (for example via fault injection or malformed device registration) to repeatedly leak small kernel allocations without requiring code execution.

How to fix it

Update the Linux kernel to include commit 8fe28cb58bcb235034b64cbbb7550a8a43fd88be which adds the missing put_device() call on the error path in ptp_clock_register(). Rebuild and deploy the fixed kernel image.

How to confirm the fix worked

Confirm the patch is present in the running kernel source, reproduce the original fault-injection scenario, and verify that no unreferenced kobject allocations remain after the error path executes.

Typical attack path

1. Gain ability to trigger PTP device probe or registration (local, driver load, or hardware attach)
2. Force posix_clock_register to fail after dev_set_name allocates the name string
3. Repeat the failing registration to accumulate unreferenced kernel memory
4. Monitor until memory pressure leads to system impact

How to detect it

Inspect kernel logs for repeated ptp_clock_register failures or i2c/ptp device probe errors; use slabinfo or kmemleak to look for unreferenced ptp kobject allocations; correlate with device driver load attempts such as idt82p33_probe.

• ptp_clock_register
• kobject_set_name_vargs
• unreferenced object.*ptp
• idt82p33_probe

What your security team should do

• Prioritize kernel upgrade on systems exposing PTP interfaces or using ptp_idt82p33 and similar drivers
• Monitor kernel memory usage and slab allocations for ptp-related objects
• Apply the fix commit or latest stable kernel branch containing 8fe28cb58bcb235034b64cbbb7550a8a43fd88be