Journald plugin for Falco

This plugin lets you match Falco rules against journald messages (effectively, all your system logs).

Installation

Prerequisites

1. The Rust toolchain: https://rustup.rs/
2. libsystemd headers, e.g. sudo apt install libsystemd-dev for Debian-like systems.

Building

Run cargo build --release in the source directory.

git clone https://github.com/gnosek/falco-journald-plugin
cd falco-journald-plugin
cargo build --release

Installation

Copy the compiled file into your Falco plugin directory

sudo cp target/release/libfalco_journald_plugin.so /usr/share/falco/plugins

Usage

Enabling the plugin

First, enable the plugin in your falco.yaml, for example:

plugins:
  - name: journald
    library_path: libfalco_journald_plugin.so
    init_config:
      filter:
        - _TRANSPORT=kernel
load_plugins:
  - journald

Then, configure filtering. In the example above, the plugin will only receive messages from the kernel. For more information about filtering, please see the systemd documentation.

Note: specifying a filter item as AND or OR will insert a conjunction/disjunction respectively, as described in the linked docs. This enables construction of complex filters.

Writing rules

The plugin returns all events matching the journal filter as JSON objects, but also provides some helpers to extract individual fields:

Field	Contents
journal.message	the actual log message
journal.priority	message priority, as an integer (0 is emergency, 7 is debug)
journal.priority_str	message priority as a string
journal.facility	syslog facility as an integer
journal.facility_str	syslog facility as a string
journal.transport	the transport which received the message
journal.field[NAME]	the raw NAME field from the message as a string

For example, to match messages about interfaces entering/leaving promiscuous mode, you could use a rule like:

- rule: promiscuous mode changed
  desc: match whenever an interface enters/leaves promiscuous mode
  condition: journal.priority == 6 and journal.transport == "kernel" and journal.message contains "promiscuous"
  output: "%journal.field[_HOSTNAME]: %journal.message"
  priority: INFO
  source: journal

Note: to dump the whole JSON event (e.g. to inspect additional fields), use %evt.plugininfo as an output field