CVE-2019-15538 : Security Advisory and Response

A problem was found in the function xfs_setattr_nonsize located in fs/xfs/xfs_iops.c in the Linux kernel versions up to 5.2.9. The issue can lead to a Denial-of-Service (DoS) situation, primarily exploitable locally but with potential for remote attacks if the XFS filesystem is exported.

Understanding CVE-2019-15538

What is CVE-2019-15538?

An issue in xfs_setattr_nonsize in the Linux kernel through version 5.2.9 can cause the XFS file system to partially freeze under specific conditions, potentially leading to a DoS scenario.

The Impact of CVE-2019-15538

The vulnerability allows for local exploitation to trigger a DoS situation. If the XFS filesystem is exported, remote DoS attacks are also possible, such as through NFS.

Technical Details of CVE-2019-15538

Vulnerability Description

The problem arises from xfs_setattr_nonsize failing to release the ILOCK after an unsuccessful xfs_qm_vop_chown_reserve call, resulting in a partial system freeze.

Affected Systems and Versions

Linux kernel versions up to 5.2.9

Exploitation Mechanism

Local exploitation through a chgrp operation failure due to disk quota limit
Remote DoS attacks if the XFS filesystem is exported, e.g., via NFS

Mitigation and Prevention

Immediate Steps to Take

Apply patches provided by the Linux kernel maintainers
Monitor system logs for any unusual behavior

Long-Term Security Practices

Regularly update the Linux kernel to the latest stable version
Implement proper disk quota management to prevent quota-related issues

Patching and Updates

Keep the Linux kernel up to date with the latest security patches