Pluggable Authentication Modules (PAM)

Introduction

Before Bareos Version 18.2 authentication with a Bareos Director is done primarily by a named Console connection. Name and password are set in the regarding Bareos Console or Bareos WebUI configuration resource. Starting with Bareos Version 18.2 it is also possible to use Pluggable Authentication Modules (PAM) to authenticate a user indenpendently from the Console Resource.

As consequence a dedicated named Console or Bareos WebUI configuration must be used to establish a connection to a Bareos Director Daemon. This connection has name and password credentials, but only to establish an encrypted connection to the Director. To be able to authenticate users with PAM using this console, each user needs an additional User configuration that holds the regarding name and the Access Control List (ACL) or ACL profile. The ACL will be loaded as soon as the User is authenticated.

The credentials for user authentication comes from the PAM module which has been enabled for the Bareos Director Daemon.

For a simplified technical overview the following diagram shows the connection sequence of a Bareos Console to a Bareos Director using an interactive PAM authentication using the pam_unix.so PAM module.

More technical details can be found in the Bareos Developer Guide: PAM.

hide footbox

actor user
participant "B-Console" as console
participant "Director" as director
participant "PAM-Linux" as pam

user -> console: start a named bconsole
console <-> director: initiate TCP connection
console <-> director: initiate a secure TLS connection (cert/psk)
console <-> director: primary challenge/response authentication

== PAM user authentication ==
note left of pam: i.e. pam_unix.so\nconfigured in /etc/pam.d/bareos
autonumber
director -> pam: initialize pam module
director <- pam: request username / password via callback
console <- director: send "login:" / "password:" request encrypted via TLS
user <- console: prompt "login:" / "Password:"
user -> console: enter username / password (hidden)
console -> director: send username / password encrypted via TLS
director -> pam: give back username / password
director <- pam: return success of authentication
console <- director: send welcome message
user <- console: show welcome message
director -> pam: shutdown pam module

autonumber stop
== PAM user authentication end ==

... do something with console ...

user -> console: quit session ('q'; Ctrl + D)
console <-> director: Shutdown TLS
console <-> director: Finish TCP connection — Initiation of a Bareos Console connection using PAM authentication

Configuration

To enable PAM authentication two systems have to be configured. The PAM module in the operating system and the Bareos Console.

PAM Module

This is depending on the operating system and on the used pam module. For details read the manuals. The name of the service that has to be registered is bareos.

Fedora 28 example:

/etc/pam.d/bareos

auth       required     pam_unix.so
account    required     pam_unix.so

Warning

The Bareos Director runs as user bareos. However, some PAM modules require more priviliges. E.g. pam_unix requires access to the file /etc/shadow, which is normally not permitted. Make sure you verify your system accordingly.

Upgrading from previous versions

Previous versions of Bareos only used PAM authentication (who is the user) but not PAM authorization (what is the user allowed to do). As a result configuring the account management group in PAM had no effect in these versions so that, for example, a disabled user might still be able to log in.

If on an existing installation account is not configured at all, the login will always fail after upgrading from an affected version.

We strongly suggest that you configure proper authorization on production systems. We strictly advise against the possibility to regain the old behaviour by configuring account required pam_permit.so.

Bareos Console

For PAM authentication a dedicated named console is used. Set the directive UsePamAuthentication=yes in the regarding Director-Console resource:

bareos-dir.d/console/pam-console.conf

Console {
  Name = "PamConsole"
  Password = "Secretpassword"
  UsePamAuthentication = yes
}

In the dedicated Bareos Console config use name and password according as to the Bareos Director:

bconsole.conf

Director {
  ...
}

Console {
  Name = "PamConsole"
  Password = "Secretpassword"
}

PAM User

Users have limited access to commands and jobs. Therefore the appropriate rights should also be granted to PAM users. This is an example of a User resource (Bareos Director Configuration):

bareos-dir.d/user/a-pam-user.conf

User {
   Name = "a-pam-user"
   CommandACL = status, .status
   JobACL = *all*
}

Additional information can be found at https://github.com/bareos/bareos/tree/master/contrib/misc/bareos_pam_integration