Linux Kernel F2FS Deadlock Vulnerability in Compression Overwrite Preparation

A potential deadlock vulnerability has been identified in the Linux kernel's F2FS file system, specifically in the function responsible for preparing compressed data overwrites. This issue can cause a kernel hang, as observed during the execution of the xfstests suite on Linux kernel versions 6.14.0-rc3 and 6.12. The problem arises when the F2FS write data pages function gets blocked, disrupting the writeback process. The deadlock occurs because the compression overwrite preparation function loops indefinitely reading compressed cluster pages due to I/O errors, while simultaneously holding a lock that prevents other writeback tasks from proceeding.

Impact

Exploitation of this vulnerability leads to a kernel hang, causing the system to become unresponsive for an extended period.

Reproduction

The vulnerability can be reproduced by running the generic/475 test from the xfstests suite on a Linux kernel version 6.14.0-rc3 or 6.12, with a F2FS file system that has compression enabled. The test will hang as the F2FS write data pages function gets blocked, creating a deadlock situation.

Remediation

Users can apply the latest patches available in the Linux kernel Git repository to address this vulnerability.