Linux Kernel Ext4 Filesystem Deadlock Vulnerability in Writeback Process

A deadlock vulnerability has been identified in the Ext4 filesystem of the Linux kernel. This issue arises from a filesystem-wide lock that protects the 'ext4_writepages()' function. The lock is intended to prevent races when switching the journaled data flag or inode format. However, it can lead to a deadlock scenario where one process blocks another, causing all readers to become stuck indefinitely. The deadlock occurs when 'ext4_writepages()' tries to acquire the write lock, which is already held by a process changing the inode journal flag, after a series of operations have left the inode dirty and ready to be written back. This vulnerability affects several versions of the Linux kernel.

Impact

Exploitation of this vulnerability leads to a deadlock condition, where the system becomes unresponsive due to processes waiting indefinitely for resources to be released.

Reproduction

The vulnerability can be reproduced by invoking 'ext4_writepages()' while simultaneously changing the inode journal flag of the same filesystem. This sequence causes a deadlock, as the writeback process waits for a lock that is being held by the flag-changing operation, which in turn is blocked by the writeback process's own lock acquisition.

Remediation

Users can upgrade to the latest stable version of the Linux kernel, where this vulnerability has been addressed.