CVE-2023-52704

What it actually does

Race condition in Linux kernel freezer logic causing improper handling of SIGKILL during call_usermode_helper_exec(), leading to on-stack completion variable being used after going out of scope.

Why it matters to the business

Potential kernel crashes or instability on Linux systems, impacting availability of services running on affected kernels, especially those using user-mode helpers.

How an attack unfolds

An attacker sends SIGKILL to a process executing a user-mode helper, exploiting the missing wait_for_completion to cause memory corruption or panic before the completion is properly waited upon.

How to fix it

Upgrade the Linux kernel to a version including commit 7f9f6c54da876b3f0bece2b569456ceb96965ed7 or later stable releases.

How to confirm the fix worked

Verify the presence of the fix commit in the kernel source or check for updated kernel packages from the distribution.

Typical attack path

1. Identify a process using call_usermodehelper_exec with KILLABLE flag
2. Send SIGKILL signal to the process
3. Trigger the race condition leading to use-after-scope of completion variable

How to detect it

Look for kernel logs indicating crashes or warnings related to freezer or usermodehelper execution around the time of potential exploitation.

What your security team should do

• Apply the kernel patch immediately
• Monitor for kernel oops or panics related to usermode helpers
• Test in staging environments before production deployment