Subject: [ASA-202004-2] linux-hardened: privilege escalation

Arch Linux Security Advisory ASA-202004-2
=========================================

Severity: High
Date    : 2020-04-01
CVE-ID  : CVE-2020-8835
Package : linux-hardened
Type    : privilege escalation
Remote  : No
Link    : https://security.archlinux.org/AVG-1120

Summary
=======

The package linux-hardened before version 5.5.13.b-1 is vulnerable to
privilege escalation.

Resolution
==========

Upgrade to 5.5.13.b-1.

# pacman -Syu "linux-hardened>=5.5.13.b-1"

The problem has been fixed upstream in version 5.5.13.b.

Workaround
==========

By default linux-hardened is safe as it restricts BPF access to
privileged users. In case the kernel.unprivileged_bpf_disabled setting
has been explicitly changed, it can be restricted again:

# sysctl -w kernel.unprivileged_bpf_disabled=1

Description
===========

An out-of-bounds access flaw was found in the Linux kernel’s
implementation of the eBPF code verifier, where an incorrect register
bounds calculation while checking 32-bit instructions in an eBPF
program occurs. This flaw allows an unprivileged user or process to
execute eBPF programs to crash the kernel, resulting in a denial of
service or potentially gaining root privileges on the system.

Impact
======

An unprivileged local user or process can crash the kernel, resulting
in a denial of service, or potentially gain root privileges on the
system in case the default BPF access has been changed to allow
unprivileged users.

References
==========

https://www.thezdi.com/blog/2020/3/19/pwn2own-2020-day-one-results
https://lore.kernel.org/bpf/20200330160324.15259-1-daniel@iogearbox.net/T/
https://www.openwall.com/lists/oss-security/2020/03/30/3
https://security.archlinux.org/CVE-2020-8835