CVE-2021-46945

What it actually does

Inconsistent panic behavior in ext4 when the errors=panic mount option is specified; operations such as remount abort or writing to trigger_fs_error in sysfs do not cause a kernel panic as intended.

Why it matters to the business

Systems configured to halt on ext4 filesystem errors may continue operating after encountering errors, increasing risk of data corruption, instability, or undetected integrity failures.

How an attack unfolds

An attacker with local access mounts an ext4 volume using errors=panic, then issues a remount abort or writes to the sysfs trigger to induce an error condition; the kernel fails to panic, allowing the system to remain available for further activity.

How to fix it

Update the Linux kernel to a version containing the fix that restores consistent panic behavior for ext4 when errors=panic is specified.

How to confirm the fix worked

Confirm the running kernel includes the commit restoring panic on remount abort and sysfs error triggers; test the documented mount/remount and sysfs sequences in a non-production environment to verify panic occurs.

Typical attack path

1. Mount ext4 filesystem with errors=panic option
2. Remount the volume using the abort option or trigger a filesystem error via sysfs
3. Confirm absence of kernel panic and continued operation

How to detect it

Review kernel and audit logs for ext4 mount and remount events followed by error triggers without associated panic or oops entries; inspect sysfs interactions and mount option persistence.

What your security team should do

• Prioritize kernel updates to restore intended error-handling behavior
• Audit ext4 mount options across fleets for reliance on errors=panic
• Incorporate filesystem error injection tests into hardening validation procedures