Bacula Security Issues

Backward Compatibility

One of the major goals of Bacula is to ensure that you can restore tapes (I'll use the word tape to include disk Volumes) that you wrote years ago. This means that each new version of Bacula should be able to read old format tapes. The first problem you will have is to ensure that the hardware is still working some years down the road, and the second problem will be to ensure that the media will still be good, then your OS must be able to interface to the device, and finally Bacula must be able to recognize old formats. All the problems except the last are ones that we cannot solve, but by careful planning you can.

Since the very beginning of Bacula (January 2000) until today (December 2005), there have been two major Bacula tape formats. The second format was introduced in version 1.27 in November of 2002, and it has not changed since then. In principle, Bacula can still read the original format, but I haven't tried it lately so who knows ...

Though the tape format is fixed, the kinds of data that we can put on the tapes are extensible, and that is how we added new features such as ACLs, Win32 data, encrypted data, ... Obviously, an older version of Bacula would not know how to read these newer data streams, but each newer version of Bacula should know how to read all the older streams.

If you want to be 100should:

1. Try reading old tapes from time to time - e.g. at least once a year.

2. Keep statically linked copies of every version of Bacula that you use in production then if for some reason, we botch up old tape compatibility, you can always pull out an old copy of Bacula ...

The second point is probably overkill but if you want to be sure, it may save you someday.

Configuring and Testing TCP Wrappers

TCP Wrappers are implemented if you turn them on when configuring (./configure --with-tcp-wrappers). With this code enabled, you may control who may access your daemons. This control is done by modifying the file: /etc/hosts.allow. The program name that Bacula uses when applying these access restrictions is the name you specify in the daemon configuration file (see below for examples). You must not use the twist option in your /etc/hosts.allow or it will terminate the Bacula daemon when a connection is refused.

The exact name of the package you need loaded to build with TCP wrappers depends on the system. For example, on SuSE, the TCP wrappers libraries needed to link Bacula are contained in the tcpd-devel package. On Red Hat, the package is named tcp_wrappers.

Dan Langille has provided the following information on configuring and testing TCP wrappers with Bacula.

If you read hosts_options(5), you will see an option called twist. This option replaces the current process by an instance of the specified shell command. Typically, something like this is used:

 : severity \
 : twist /bin/echo "You are not welcome to use %d from %h."

The libwrap code tries to avoid twist if it runs in a resident process, but that test will not protect the first hosts_access() call. This will result in the process (e.g. bacula-fd, bacula-sd, bacula-dir) being terminated if the first connection to their port results in the twist option being invoked. The potential, and I stress potential, exists for an attacker to prevent the daemons from running. This situation is eliminated if your /etc/hosts.allow file contains an appropriate rule set. The following example is sufficient:

undef-fd : localhost : allow
undef-sd : localhost : allow
undef-dir : localhost : allow
undef-fd : ALL : deny
undef-sd : ALL : deny
undef-dir : ALL : deny

You must adjust the names to be the same as the Name directives found in each of the daemon configuration files. They are, in general, not the same as the binary daemon names. It is not possible to use the daemon names because multiple daemons may be running on the same machine but with different configurations.

In these examples, the Director is undef-dir, the Storage Daemon is undef-sd, and the File Daemon is undef-fd. Adjust to suit your situation. The above example rules assume that the SD, FD, and DIR all reside on the same box. If you have a remote FD client, then the following rule set on the remote client will suffice:

undef-fd : : allow
undef-fd : ALL : deny

where is the host which will be contacting the client (ie. the box on which the Bacula Director daemon runs). The use of "ALL : deny" ensures that the twist option (if present) is not invoked. To properly test your configuration, start the daemon(s), then attempt to connect from an IP address which should be able to connect. You should see something like this:

$ telnet undef 9103
Connected to
Escape character is '^]'.
Connection closed by foreign host.

This is the correct response. If you see this:

$ telnet undef 9103
Connected to
Escape character is '^]'.
You are not welcome to use undef-sd from
Connection closed by foreign host.

then twist has been invoked and your configuration is not correct and you need to add the deny statement. It is important to note that your testing must include restarting the daemons after each connection attempt. You can also tcpdchk(8) and tcpdmatch(8) to validate your /etc/hosts.allow rules. Here is a simple test using tcpdmatch:

$ tcpdmatch undef-dir
warning: undef-dir: no such process name in /etc/inetd.conf
client: hostname
client: address
server: process undef-dir
matched: /etc/hosts.allow line 40
option: allow
access: granted

If you are running Bacula as a standalone daemon, the warning above can be safely ignored. Here is an example which indicates that your rules are missing a deny statement and the twist option has been invoked.

$ tcpdmatch undef-dir
warning: undef-dir: no such process name in /etc/inetd.conf
client: address
server: process undef-dir
matched: /etc/hosts.allow line 91
option: severity
option: twist /bin/echo "You are not welcome to use
  undef-dir from"
access: delegated

Running as non-root

Security advice from Dan Langille:

It is a good idea to run daemons with the lowest possible privileges. In other words, if you can, don't run applications as root which do not have to be root. The Storage Daemon and the Director Daemon do not need to be root. The File Daemon needs to be root in order to access all files on your system. In order to run as non-root, you need to create a user and a group. Choosing bacula as both the user name and the group name sounds like a good idea to me.

The FreeBSD port creates this user and group for you. Here is what those entries looked like on my FreeBSD laptop:

bacula:*:1002:1002::0:0:Bacula Daemon:/var/db/bacula:/sbin/nologin

I used vipw to create this entry. I selected a User ID and Group ID of 1002 as they were unused on my system.

I also created a group in /etc/group:


The bacula user (as opposed to the Bacula daemon) will have a home directory of /var/db/bacula which is the default location for the Bacula database.

Now that you have both a bacula user and a bacula group, you can secure the bacula home directory by issuing this command:

chown -R bacula:bacula /var/db/bacula/

This ensures that only the bacula user can access this directory. It also means that if we run the Director and the Storage daemon as bacula, those daemons also have restricted access. This would not be the case if they were running as root.

It is important to note that the storage daemon actually needs to be in the operator group for normal access to tape drives etc (at least on a FreeBSD system, that's how things are set up by default) Such devices are normally chown root:operator. It is easier and less error prone to make Bacula a member of that group than it is to play around with system permissions.

Starting the Bacula daemons

To start the bacula daemons on a FreeBSD system, issue the following command:

/usr/local/etc/rc.d/bacula-dir start
/usr/local/etc/rc.d/bacula-sd  start
/usr/local/etc/rc.d/bacula-fd  start

To confirm they are all running:

$ ps auwx | grep bacula
root   63418 0.0 0.3 1856 1036 ?? Ss 4:09PM 0:00.00
    /usr/local/sbin/bacula-fd -v -c /usr/local/etc/bacula-fd.conf
bacula 63416 0.0 0.3 2040 1172 ?? Ss 4:09PM 0:00.01
    /usr/local/sbin/bacula-sd -v -c /usr/local/etc/bacula-sd.conf
bacula 63422 0.0 0.4 2360 1440 ?? Ss 4:09PM 0:00.00
    /usr/local/sbin/bacula-dir -v -c /usr/local/etc/bacula-dir.conf

Kern Sibbald 2015-07-04