CVE-2023-40791

What it actually does

extract_user_to_sg in lib/scatterlist.c fails to unpin pages under specific conditions, resulting in memory management errors demonstrated by try_grab_page warnings and potential corruption or resource leaks in the Linux kernel.

Why it matters to the business

Linux systems may experience kernel warnings, instability, or crashes during scatter-gather operations, affecting service availability and requiring unplanned maintenance on servers and devices.

How an attack unfolds

A local attacker with low privileges supplies crafted data to trigger the unpin failure in extract_user_to_sg, potentially leading to memory corruption or denial of service; no widespread threat actor exploitation is associated with this issue.

How to fix it

Upgrade the Linux kernel to version 6.4.12 or later; apply commit f443fd5af5dbd531f880d3645d5dd36976cf087f from the mainline repository; rebuild and reboot with the patched kernel.

How to confirm the fix worked

Verify the running kernel version is 6.4.12 or higher; confirm presence of commit f443fd5af5dbd531f880d3645d5dd36976cf087f in the source tree; test affected scatterlist paths to ensure no try_grab_page warnings occur.

Typical attack path

1. Obtain local user access on an affected Linux system
2. Invoke operations that call extract_user_to_sg with malicious input
3. Trigger the page pinning failure to induce kernel warnings or corruption
4. Attempt to leverage resulting state for further impact such as crashes

How to detect it

Inspect kernel logs (dmesg, syslog) for WARNING messages referencing try_grab_page in conjunction with scatterlist operations; correlate with process activity invoking user-to-sg transfers.

• WARNING.*try_grab_page
• extract_user_to_sg

What your security team should do

• Apply the kernel patch or upgrade immediately on all affected systems
• Monitor kernel logs for try_grab_page warnings as a temporary detection measure
• Prioritize updates on high-value or internet-facing Linux hosts
• Review downstream package distributions for backported fixes