CVE-2024-57941

What it actually does

Improper handling of cache-disabled state in netfs leads to abandoned write requests that leave folios marked with PG_private_2, preventing proper cleanup and state-machine progress.

Why it matters to the business

Systems using cached network filesystems such as ceph may experience hangs or stalled I/O when direct writes temporarily disable caching, reducing availability for storage-dependent workloads.

How an attack unfolds

An attacker or workload triggers a DIO write to disable caching on a file, then issues subsequent writes that netfslib attempts to copy to cache; the code bails early, discards the request without cancellation, and leaves folios stuck, which can be reached via normal filesystem operations or by running xfstests against ceph with fsc enabled.

How to fix it

Update to a kernel containing commit ba37bdfe59fb43e80dd79290340a21864ba4b61e or later; Red Hat users should install the listed fixed setroubleshoot packages (3.2.24-4.el7_2 or 3.0.59-2.el7_2) where applicable and reboot.

How to confirm the fix worked

Confirm the running kernel contains ba37bdfe59fb or newer; re-run generic/013 xfstest against ceph with -o fsc and verify the test completes without hanging.

Typical attack path

1. Open a file on a cached ceph filesystem
2. Perform a direct I/O write to disable caching temporarily
3. Issue follow-on writes that netfslib routes toward the cache
4. netfs_advance_write bails without creating subrequests or canceling
5. Folios remain marked and the request is dropped, stalling the state machine

How to detect it

Search kernel logs for netfs-related stalls, hung tasks mentioning folio_queue or PG_private_2, and ceph client hangs during xfstest or DIO workloads; correlate with cache-disable events.

What your security team should do

• Prioritize kernel updates on any hosts running ceph with fsc caching enabled
• Monitor for stalled I/O or hung tasks related to netfs after applying the fix
• Review and test caching configurations before re-enabling on production systems