Interacting via Unix Socket

Introduction

Since 1.4 version, Suricata can listen to a unix socket and accept commands from the user. The exchange protocol is JSON-based and the format of the message has been done to be generic and it is described in this commit message. An example script called suricatasc is provided in the source and installed automatically when updating Suricata.

The unix socket is disabled by default.
You need to have libjansson installed:

libjansson4 - C library for encoding, decoding and manipulating JSON data
libjansson-dev - C library for encoding, decoding and manipulating JSON data (dev)
python-simplejson - simple, fast, extensible JSON encoder/decoder for Python
apt-get install libjansson4 libjansson-dev python-simplejson

If libjansson is present on the system , unix socket will be compiled in automatically - when you use "--enable-unix-socket" in your configure line.

The creation of the socket is activated by setting enabled to yes under unix-command in Suricata YAML configuration file:

unix-command:
  enabled: yes
  #filename: custom.socket # use this to specify an alternate file

The filename variable can be used to set an alternate socket filename. The filename is always relative to the local state base directory.

Clients are implemented for some language and can be used as code example to write custom scripts:

Commands in standard running mode

The set of existing commands is the following:

  • command-list: list available commands
  • shutdown: this shutdown suricata
  • iface-list: list interfaces where Suricata is sniffing packets
  • iface-stat: list statistic for an interface
  • help: alias of command-list
  • version: display Suricata's version
  • uptime: display Suricata's uptime
  • running-mode: display running mode (workers, autofp, simple)
  • capture-mode: display capture system used
  • conf-get: get configuration item (see example below)
  • dump-counters: dump Suricata's performance counters

You can access to these commands with the provided example script which
is named suricatasc. A typical session with suricatasc will looks like:

# suricatasc
Command list: shutdown, command-list, help, version, uptime, running-mode, capture-mode, conf-get, dump-counters, iface-stat, iface-list, quit
>>> iface-list
Success: {'count': 2, 'ifaces': ['eth0', 'eth1']}
>>> iface-stat eth0
Success: {'pkts': 378, 'drop': 0, 'invalid-checksums': 0}
>>> conf-get unix-command.enabled
Success:
"yes" 

Pcap processing mode

This mode is one of main motivation behind this code. The idea is to be able to ask to Suricata to treat different pcap files without having to restart Suricata between the files. This provides you a huge gain in time as you don’t need to wait for the signature engine to initialize.

To use this mode, start suricata with your preferred YAML file and provide the option --unix-socket as argument:

suricata -c /etc/suricata-full-sigs.yaml --unix-socket

It is also possible to specify the socket filename as argument:

suricata --unix-socket=custom.socket

In this last case, you will need to provide the complete path to the socket to suricatasc. To do so, you need to pass the filename as first argument of suricatasc:

suricatasc custom.socket

Once Suricata is started, you can use the provided script suricatasc to connect to the command socket and ask for pcap treatment:

root@tiger:~# suricatasc
>>> pcap-file /home/benches/file1.pcap /tmp/file1
Success: Successfully added file to list
>>> pcap-file /home/benches/file2.pcap /tmp/file2
Success: Successfully added file to list

You can add multiple files without waiting the result: they will be sequentially processed and the generated log/alert files will be put into the directory specified as second arguments of the pcap-file command. You need to provide absolute path to the files and directory as suricata don’t know from where the script has been run.

To know how much files are waiting to get processed, you can do:

>>> pcap-file-number
Success: 3

To get the list of queued files, do:

>>> pcap-file-list
Success: {'count': 2, 'files': ['/home/benches/file1.pcap', '/home/benches/file2.pcap']}

To get current processed file:

>>> pcap-current
Success:
"/tmp/test.pcap" 

Build your own client

The protocol is documented in the following page Unix_Socket

The following session show what is send (SND) and received (RCV) by the server. Initial negotiation is the following:

# suricatasc
SND: {"version": "0.1"}
RCV: {"return": "OK"}

Once this is done, command can be issued:

>>> iface-list
SND: {"command": "iface-list"}
RCV: {"message": {"count": 1, "ifaces": ["wlan0"]}, "return": "OK"}
Success: {'count': 1, 'ifaces': ['wlan0']}
>>> iface-stat wlan0
SND: {"command": "iface-stat", "arguments": {"iface": "wlan0"}}
RCV: {"message": {"pkts": 41508, "drop": 0, "invalid-checksums": 0}, "return": "OK"}
Success: {'pkts': 41508, 'drop': 0, 'invalid-checksums': 0}

In pcap-file mode, this gives:

>>> pcap-file /home/eric/git/oisf/benches/sandnet.pcap /tmp/bench
SND: {"command": "pcap-file", "arguments": {"output-dir": "/tmp/bench", "filename": "/home/eric/git/oisf/benches/sandnet.pcap"}}
RCV: {"message": "Successfully added file to list", "return": "OK"}
Success: Successfully added file to list
>>> pcap-file-number
SND: {"command": "pcap-file-number"}
RCV: {"message": 1, "return": "OK"}
>>> pcap-file-list
SND: {"command": "pcap-file-list"}
RCV: {"message": {"count": 1, "files": ["/home/eric/git/oisf/benches/sandnet.pcap"]}, "return": "OK"}
Success: {'count': 1, 'files': ['/home/eric/git/oisf/benches/sandnet.pcap']}

There is one thing to be careful about: a suricata message is sent in multiple send operations. This result in possible incomplete read on client side. The worse workaround is to sleep a bit before trying a recv call. An other solution is to use non blocking socket and retry a recv if the previous one has failed. This method is used here: source:scripts/suricatasc/suricatasc.in#L43