CVE-2024-26772

What it actually does

Race condition in ext4_mb_find_by_goal allows block allocation from a group whose bitmap is marked corrupt because the corruption check occurs outside the group lock.

Why it matters to the business

Linux systems using ext4 may experience unexpected filesystem corruption and data loss when block allocation races with bitmap state changes; the issue affects a broad set of kernel versions and downstream distributions.

How an attack unfolds

An attacker with local access triggers concurrent operations that expose a window between bitmap corruption detection and block allocation, allowing the kernel to allocate blocks from a group whose bitmap is already known to be corrupt.

How to fix it

Upgrade the Linux kernel to a version containing commit 5a6dcc4ad0f7f7fa8e8d127b5526e7c5f2d38a43 or later; rebuild and reboot with the patched kernel. Apply vendor backports if available for distribution kernels.

How to confirm the fix worked

Confirm the running kernel Git commit or package version includes 5a6dcc4ad0f7f7fa8e8d127b5526e7c5f2d38a43; review ext4 source for the group-lock-protected bitmap check around mb_find_by_goal.

Typical attack path

1. Obtain local code execution on a system running a vulnerable ext4 kernel
2. Create or trigger filesystem activity that marks a block group bitmap as corrupt
3. Race allocation requests against the unprotected corruption check in ext4_mb_find_by_goal
4. Force the allocator to return blocks from the corrupt group
5. Continue filesystem operations that rely on the allocated blocks to induce corruption or crashes

How to detect it

Inspect kernel logs for ext4 bitmap corruption messages around allocation paths; correlate with process activity that performs heavy ext4 writes or fsck runs; no public exploitation artifacts are known.

What your security team should do

• Prioritize kernel updates on all ext4-based systems within standard patch windows
• Monitor upstream stable and distribution security feeds for the referenced commit
• Test patched kernels in staging environments before broad deployment
• Review ext4 filesystem error logs for bitmap corruption warnings as an ongoing hygiene measure