Linux Kernel XFS Filesystem Log Roundoff Value Vulnerability

A vulnerability in the Linux kernel's handling of XFS filesystem log roundoff values can lead to filesystem corruption and unmountable filesystems. This issue occurs when the superblock does not specify a log stripe unit, causing the in-core log roundoff value to default to 512. This misconfiguration has been observed to corrupt logs and create unmountable filesystems on disks with 4K physical sectors. The problem is exacerbated by a known issue with the 'xfsprogs' package that can create flawed filesystems.

Impact

The vulnerability causes log corruption and creates unmountable filesystems, particularly on disks with 4K physical sectors.

Reproduction

The vulnerability can be reproduced by creating an XFS filesystem with the 'xfsprogs' version that includes the broken 'mkfs' command. This version will generate a filesystem that lacks a properly defined log stripe unit, leading to the incorrect log roundoff value. When this filesystem is mounted, XFS will detect a torn write due to a CRC failure, truncate the log head block, and ultimately fail to mount the log, resulting in an error.

Remediation

Users can upgrade to a patched version of the Linux kernel where this vulnerability has been addressed. The specific commit containing the fix can be downloaded as a tarball.