CVE-2024-42149

What it actually does

Race condition in fs_bdev_thaw() and get_bdev_super() allowing NULL return and misleading warnings when a block device is frozen prior to filesystem claim and concurrent mount attempts mark the superblock dying.

Why it matters to the business

Low-severity operational noise from kernel warnings on systems using device-mapper or frozen volumes with NFS; no confirmed exploitation or data impact, but requires kernel update across Linux distributions.

How an attack unfolds

An attacker with local access triggers concurrent dm_suspend/dm_resume and mount operations on a frozen block device; the race between active reference release and passive thaw waiter causes get_bdev_super failure and spurious warnings, but yields no privilege escalation.

How to fix it

Update Linux kernel to commit 25b1e3906e050d452427bc51620bb7f0a591373a or later stable release containing the fix; rebuild and reboot affected systems.

How to confirm the fix worked

Verify presence of commit 25b1e3906e050d452427bc51620bb7f0a591373a in kernel source or running kernel version; confirm absence of the described warning pattern under concurrent freeze/mount workloads.

Typical attack path

1. Freeze block device via dm_suspend before filesystem claim
2. Initiate concurrent mount attempt that detects elevated freeze count and aborts
3. Trigger thaw via dm_resume while mount holds temporary claim
4. Release final active reference marking filesystem dying
5. Wake thaw waiter to observe NULL from get_bdev_super and emit warning

How to detect it

Search kernel logs for thaw-related warnings involving bdev_fsfreeze_count and get_bdev_super failures around mount and device-mapper resume events.

What your security team should do

• Prioritize kernel upgrade on production systems using device-mapper and NFS within standard patch windows
• Monitor vendor advisories for distribution backports of the referenced commit
• Review logs for pre-fix warning messages as part of routine kernel stability checks