CVE-2024-53685

What it actually does

ceph_mdsc_build_path enters an endless retry loop when constructing a path exceeding PATH_MAX, blocking the calling task and rendering most of the system unresponsive.

Why it matters to the business

Attackers can trigger a simple denial-of-service that halts legitimate workloads on affected Linux systems, leading to operational downtime and degraded service availability; prevalence in Linux kernel deployments amplifies exposure across many environments.

How an attack unfolds

An attacker supplies or triggers a filesystem operation in the Ceph client that requests a path longer than PATH_MAX; the flawed retry logic in ceph_mdsc_build_path loops indefinitely instead of returning an error, starving the task and freezing system responsiveness. No sophisticated primitives or named threat actors are required.

How to fix it

Update the Linux kernel to a version containing commit 0f2b2d9e881c90402dbe28f9ba831775b7992e1f or later; apply the corresponding fixed package versions for affected distributions (for example jansson 2.5-2ubuntu0.1 on Ubuntu 14.04 LTS and 2.7-3ubuntu0.1 on Ubuntu 16.04 LTS). Reboot after kernel updates.

How to confirm the fix worked

Confirm the running kernel contains the referenced commit or newer; attempt to trigger a path exceeding PATH_MAX and verify that ENAMETOOLONG is returned promptly instead of an indefinite hang.

Typical attack path

1. Identify or mount a Ceph filesystem client on a vulnerable kernel
2. Issue a filesystem call that requests construction of a path exceeding PATH_MAX
3. Trigger the endless retry loop inside ceph_mdsc_build_path
4. Observe task blocking and progressive system unusability

How to detect it

Inspect kernel logs and task traces for repeated ceph_mdsc_build_path activity without progress; look for processes stuck in uninterruptible sleep while handling Ceph paths; correlate with any sudden increase in ENAMETOOLONG errors after patching.

What your security team should do

• Prioritize kernel upgrades on all Ceph client systems within the next maintenance window
• Monitor for task hangs involving ceph_mdsc_build_path
• Restrict untrusted path inputs or filesystem operations until patches are applied
• Track EPSS trend and any future KEV additions for increased urgency