man
5 auditd-plugins
AUDITD-PLUGINS(5) System Administration Utilities AUDITD-PLUGINS(5)
NAME
auditd-plugins - realtime event receivers
DESCRIPTION
auditd can multiplex audit events in realtime. It takes audit events
and distributes them to child programs that want to analyze events in
realtime. When the audit daemon receives a SIGTERM or SIGHUP, it passes
that signal to its child processes so that can reload the configuration
or terminate.
The child programs install a configuration file in a plugins directory
which defaults to /etc/audit/plugins.d. This can be controlled by a au-
ditd.conf config option plugin_dir if the admin wished to locate plug-
ins somewhere else. But auditd will install its plugins in the default
location.
The plugin directory will be scanned and every plugin that is active
will be started. If the plugin has a problem and exits, it will be
started a maximum of max_restarts times as found in auditd.conf.
Config file names are not allowed to have more than one '.' in the name
or it will be treated as a backup copy and skipped. Config file options
are given one per line with an equal sign between the keyword and its
value. The available options are as follows:
active The options for this are yes or no.
direction
The option is dictated by the plugin. In or out are the only
choices. You cannot make a plugin operate in a way it wasn't de-
signed just by changing this option. This option is to give a
clue to the event dispatcher about which direction events flow.
NOTE: inbound events are not supported yet.
path This is the absolute path to the plugin executable. In the case
of internal plugins, it would be the name of the plugin.
type This tells the dispatcher how the plugin wants to be run. There
is only one valid option, always , which means the plugin is ex-
ternal and should always be run. The default is always since
there are no more builtin plugins.
args This allows you to pass arguments to the child program. Gener-
ally plugins do not take arguments and have their own config
file that instructs them how they should be configured. At the
moment, there is a limit of 2 args.
format The valid options for this are binary and string. Binary passes
the data exactly as the audit event dispatcher gets it from the
audit daemon. The string option tells the dispatcher to com-
pletely change the event into a string suitable for parsing with
the audit parsing library. The default value is string.
NOTE
auditd has an internal queue to hold events for plugins. (See the
q_depth setting in auditd.conf.) Plugins have to watch for and dequeue
events as fast as possible and queue them internally if they can't be
immediately processed. If the plugin is not able to dequeue records,
the auditd internal queue will get filled. At any time, as root, you
can run the following to check auditd's metrics:
auditctl --signal cont ; sleep 1 ; cat /var/run/auditd.state
If auditd's internal queue fills, it cannot dequeue any events from the
kernel backlog. If the kernel's backlog fills, it looks at the value of
backlog_wait_time to delay all processes that generate an event to see
if there is eventually room to add the event. This will likely be no-
ticed as slowing down various processes on the machine. The kernel's
audit subsystem can be checked by running:
auditctl -s
When tuning the audit system's performance, you'd want to check both
kernel and auditd metrics and adjust accordingly.
NOTES FOR DEVELOPERS
When the audit daemon starts your plugin, you will be running as root.
If you do not need root privileges, you should change uid/gid to lower
chances of being a target for exploit. If you need to retain capabili-
ties, using libcap-ng is the simplest way.
Your environment is not going to be clean. You are inheriting many at-
tributes from auditd itself. You will need to adjust your signal mask,
sigaction, umask, and environmental variables. Look at the auditd man
page to see which signals auditd used. Plugins are expected to handle
SIGTERM and SIGHUP. You will also inherit the resource limits of au-
ditd. Note that some of these resource limits, such as maximum number
of open descriptors, are controlled by systemd. You also inherit au-
ditd's nice value. You might want to adjust that to be sure to keep up
with incoming audit events.
Auditd will send events to the plugin on it's stdin. The plugin has to
keep this descriptor empty so that events don't back up. If you do sig-
nificant processing of each event, you should add an internal queue to
your design in order to keep events flowing. The auparse_feed function
is the preferred way to examine whole events if you need to analyze the
contents of the events.
FILES
/etc/auditd/auditd.conf /etc/audit/plugins.d
SEE ALSO
auditd.conf(5), auditd(8), execve(2), auparse_feed(3).
AUTHOR
Steve Grubb
Red Hat Jan 2024 AUDITD-PLUGINS(5)