Linux Kernel DAX Entry Scanning Vulnerability

A vulnerability in the Linux kernel's DAX (Direct Access) filesystem handling has been identified. The issue arises from a change introduced in a recent commit, which added a function to wait for locked entries to become unlocked. This new function requires dropping the XArray lock, but doing so without properly pausing the iterator can cause entries to be skipped during scanning. This flaw has led to intermittent warnings when running specific filesystem tests on XFS with DAX enabled.

Impact

Exploitation of this vulnerability can cause skipped entries during the scanning process, leading to incomplete or incorrect filesystem operations. This was observed as an intermittent warning when running XFS filesystem tests with DAX enabled.

Reproduction

The vulnerability can be reproduced by running the XFS filesystem test suite with FS DAX enabled. The issue will manifest as an intermittent warning related to the truncation of folios, indicating that the vulnerability has been successfully triggered.