[ASA-202004-4] linux: privilege escalation

[Levente Polyak]

Arch Linux Security Advisory ASA-202004-4
=========================================

Severity: High
Date    : 2020-04-01
CVE-ID  : CVE-2020-8835
Package : linux
Type    : privilege escalation
Remote  : No
Link    : https://security.archlinux.org/AVG-1122

Summary
=======

The package linux before version 5.5.13.arch2-1 is vulnerable to
privilege escalation.

Resolution
==========

Upgrade to 5.5.13.arch2-1.

# pacman -Syu "linux>=5.5.13.arch2-1"

The problem has been fixed upstream in version 5.5.13.arch2.

Workaround
==========

BPF access can be restricted to privileged users by setting
kernel.unprivileged_bpf_disabled to 1:

# 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.

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

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