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Date: Wed, 5 Jul 2017 09:37:32 -0500
From: Eric Blake <eblake@...hat.com>
To: oss-security@...ts.openwall.com, Pali Rohár
<pali.rohar@...il.com>
Cc: Daniel Skowroński <daniel@...nf.net>
Subject: Re: systemd fails to parse user that should run
service
On 07/05/2017 03:50 AM, Pali Rohár wrote:
> There are basically two problems:
>
> 1) In more Linux distributions useradd tool allow to create a new user
> which starts with digit. Also according to POSIX such user name is a
> valid. This means that valid user name (for some Linux distributions)
> from /etc/passwd specified in systemd unit file results running service
> as root user.
In fact, it is possible to create a username of '0' which is a non-root
user. GNU Coreutils has several tools that support a lookup of '+0' to
force a numeric uid interpretation (get information related to uid 0,
regardless of whether there is also a username "0"), while omitting the
leading + does a username lookup first then falls back to a uid, since
leading + is not a valid POSIX username start character.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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