Sysdig Falco

Host Activity Monitoring using Sysdig Event Filtering

Overview

Brief description of what, why, how, and pointer to website.

What kind of behaviors can Falco detect?

Falco can detect and alert on any behavior that involves making Linux system calls. Thanks to Sysdig's core decoding and state tracking functionality, Falco alerts can be triggered by the use of specific system calls, their arguments, and by properties of the calling process. Rules are expressed in a high-level, human-readable language.

Installing Falco

Instructions for installing via .deb, .rpm, or docker. To be filled in pre-release.

For now, local compilation and installation is the way to install (see "Building Falco" below).

Configuring Falco

Falco is primarily configured via two files: a configuration file (such as the falco.yaml in this repository) and a rules file (such as the falco_rules.conf file in rules/). These two files are written to /etc after you install the Falco package.

Rules file

The rules file is where you define the events and actions that you want to be notified on. We've provided a sample rule file ./rules/falco_rules.conf as a starting point, but you'll want to familiarize yourself with the contents, and most likely, to adapt it to your environment.

Call for contributions: If you come up with additional rules which you think should be part of this core set - PR welcome! And likewise if you have an entirely separate ruleset that may not belong in the core rule set.

A Falco rules file is comprised of two kinds of elements: rules and macro definitions.

Here's an example of a rule that alerts whenever a bash shell is run inside a container:

container.id != host and proc.name = bash | WARNING Bash run in a container (%user.name %proc.name %evt.dir %evt.type %evt.args %fd.name)

The part to the left of the pipe (|) is the condition. It is expressed using the Sysdig filter syntax. Any Sysdig filter expression is a valid Falco expression (with the caveat of certain excluded system calls, discussed below). In addition, Falco expressions can contain macro terms, which are not present in Sysdig syntax.

The part to the right of the pipe is the output. It is composed of a priority level and an output format. The priority level is case-insensitive and should be one of "emergency", "alert", "critical", "error", "warning", "notice", "informational", or "debug". The output format specifies the message that should be output if a matching event occurs, and follows the Sysdig output format syntax.

Macro definitions provide a way to define common sub-portions of rules in a reusable way. The syntax for a macro is:

macro_name: macro_definition

where macro_name is a string, and macro_definition is any valid Falco condition.

(insert example here).

Ignored system calls

For performance reasons, some system calls are currently discarded before Falco processing. The current list is: clock_getres,clock_gettime,clock_nanosleep,clock_settime,close,epoll_create,epoll_create1,epoll_ctl,epoll_pwait,epoll_wait,eventfd,fcntl,fcntl64,fstat,fstat64,getitimer,gettimeofday,nanosleep,poll,ppoll,pread64,preadv,pselect6,pwrite64,pwritev,read,readv,recv,recvfrom,recvmmsg,recvmsg,select,send,sendfile,sendfile64,sendmmsg,sendmsg,sendto,setitimer,settimeofday,shutdown,socket,splice,switch,tee,timer_create,timer_delete,timerfd_create,timerfd_gettime,timerfd_settime,timer_getoverrun,timer_gettime,timer_settime,wait4,write,writev,

Configuration file

Falco is configured via a yaml file. The sample config falco.yaml in this repo has comments describing the various options.

Running Falco

Falco is intended to be run as a service. But for experimentation and designing/testing rulesets, you will likely want to run it manually from the command-line.

Running Falco as a service

Instructions for Centos and Ubuntu.

Running Falco manually

falco --help

Building and running Falco locally from source

Building Falco requires having cmake and g++ installed.

Building Falco

Clone this repo in a directory that also contains the sysdig source repo. The result should be something like:

22:50 vagrant@vagrant-ubuntu-trusty-64:/sysdig
$ pwd
/sysdig
22:50 vagrant@vagrant-ubuntu-trusty-64:/sysdig
$ ls -l
total 20
drwxr-xr-x  1 vagrant vagrant  238 Feb 21 21:44 falco
drwxr-xr-x  1 vagrant vagrant  646 Feb 21 17:41 sysdig

create a build dir, then setup cmake and run make from that dir:

$ mkdir build
$ cd build
$ cmake ..
$ make

as a result, you should have a falco executable in build/userspace/falco/falco.

(Optional) Install sysdig kernel driver

If you have a binary version of sysdig installed, the sysdig kernel module is already loaded and can be used by falco. Otherwise, you should load the kernel module from the sysdig source directory. Assuming you are in the build dir, you can install the kernel module via:

$ insmod driver/sysdig-probe.ko

Running Falco

Assuming you are in the build dir, you can run Falco as:

$ sudo ./userspace/falco/falco -c ../falco.yaml -r ../rules/falco_rules.conf

Or instead you can try using some of the simpler rules files in rules. Or to get started, try creating a file with this:

Create a file with some Falco rules. For example:

write: (syscall.type=write and fd.typechar=f) or syscall.type=mkdir or syscall.type=creat or syscall.type=rename
interactive: proc.pname = bash or proc.pname = sshd
write and interactive and fd.name contains sysdig
write and interactive and fd.name contains .txt

And you will see an output event for any interactive process that touches a file with "sysdig" or ".txt" in its name!