Linux Kernel Memfd Preservation Vulnerability in Folio Management

A vulnerability in the Linux kernel's memory management related to the 'memfd' feature has been addressed. This issue arises when 'memfd' preservation with Live Update Option (LUO) saves the state of memory folios. A folio can be clean (not written to) or dirty (written to), and a clean folio can be reclaimed under memory pressure. The problem occurs because saving the folio state at the 'preserve' stage can lead to data loss. If a folio is clean when preserved but gets dirtied later, the serialized state will incorrectly mark it as clean. When retrieved, the kernel may attempt to reclaim it, resulting in the loss of user data. To mitigate this, all folios are now marked as dirty, ensuring they are not reclaimed, but this also means clean folios become un-reclaimable after a live update, a necessary trade-off for preserving data integrity during updates.

Impact

The vulnerability could lead to unintended data loss by allowing the kernel to reclaim folios marked as clean, after they had been dirtied, under memory pressure.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been fixed. Instructions for downloading the patched version are available on the Linux kernel official website.