#!/usr/bin/perl

#  -------------------------------------------------------
#             -=- <check_fail2ban> -=-
#  -------------------------------------------------------
#
#  Description : This plugin checks if the fail2ban server is running 
#  and how many IPs are currently banned.
#  
#
# inspired by the work of Sebastian Mueller - http://www.elchtest.eu
# 
#
#  Version : 0.1
#  -------------------------------------------------------
#  In :
#     - see the How to use section
#
#  Out :
#     - only print on the standard output 
#
#  Features :
#     - perfdata output
#     - works with only a specific jail
#
#  Fix Me/Todo :
#     - too many things ;) but let me know what do you think about it
#
# ####################################################################

# ####################################################################
# GPL v3
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
# ####################################################################

# ####################################################################
# How to use :
# ------------
#
# Just have to run the following command:
#       $ ./check_fail2ban --help
# 
# If you need to use this script with NRPE you just have to do the 
# following steps:
#
# 1 allow your user to run the script with the sudo rights. Just add
#   something like that in your /etc/sudoers (use visudo) :
#     nagios ALL=(ALL) NOPASSWD: /<path-to>/check_fail2ban
#
# 2 then just add this kind of line in your NRPE config file :
#   command[check_fail2ban]=/usr/bin/sudo /<path-to>/check_fail2ban
#
# 3 don't forget to restart your NRPE daemon
#
#	
# /!\ be careful to let no one able to update the check_fail2ban ;)
# ------------------------------------------------------------------------------
#
# ####################################################################

# ####################################################################
# Changelog :
# -----------
#
# --------------------------------------------------------------------
#   Date:12/03/2013   Version:0.1     Author:Erwan Ben Souiden
#   >> creation
# ####################################################################

# ####################################################################
#            Don't touch anything under this line!
#        You shall not pass - Gandalf is watching you
# ####################################################################

use strict;
use warnings;
use Getopt::Long qw(:config no_ignore_case);

# Generic variables
# -----------------
my $version = '0.1';
my $author = 'Erwan Labynocle Ben Souiden';
my $a_mail = 'erwan@aleikoum.net';
my $script_name = 'check_fail2ban';
my $verbose_value = 0;
my $version_value = 0;
my $more_value = 0;
my $help_value = 0;
my $perfdata_value = 0;
my %ERRORS=('OK'=>0,'WARNING'=>1,'CRITICAL'=>2,'UNKNOWN'=>3,'DEPENDENT'=>4);

# Plugin default variables
# ------------------------
my $display = 'CHECK FAIL2BAN ACTIVITY';
my ($critical,$warning) = (2,1);
my $fail2ban_client_path = '/usr/bin/fail2ban-client';
my $fail2ban_socket = '';
my $jail_specific = '';

GetOptions (
    'P=s' => \ $fail2ban_client_path,
    'path-fail2ban_client=s' => \ $fail2ban_client_path,
    'j=s' => \ $jail_specific,
    'jail=s' => \ $jail_specific,
    'w=i' => \ $warning,
    'warning=i' => \ $warning,
    'socket=s' => \ $fail2ban_socket,
    'S=s' => \ $fail2ban_socket,
    'c=i' => \ $critical,
    'critical=i' => \ $critical,
    'V' => \ $version_value,
    'version' => \ $version_value,
    'h' => \ $help_value,
    'H' => \ $help_value,
    'help' => \ $help_value,
    'display=s' => \ $display,
    'D=s' => \ $display,
    'perfdata' => \ $perfdata_value,
    'p' => \ $perfdata_value,
    'v' => \ $verbose_value,
    'verbose' => \ $verbose_value
);

print_usage() if ($help_value);
print_version() if ($version_value);


# Syntax check of your specified options
# --------------------------------------

print "DEBUG : fail2ban_client_path: $fail2ban_client_path\n" if ($verbose_value);
if (($fail2ban_client_path eq "")) {
    print $display.'- one or more following arguments are missing: fail2ban_client_path'."\n";
    exit $ERRORS{"UNKNOWN"};
}

if(! -x $fail2ban_client_path) {
    print $display.' - '.$fail2ban_client_path.' is not executable by you'."\n";
    exit $ERRORS{"UNKNOWN"};
}
print "DEBUG : $fail2ban_client_path exists and is executable\n" if ($verbose_value);

my $fail2ban_cmd = $fail2ban_client_path;
$fail2ban_cmd .= " -s $fail2ban_socket" if ($fail2ban_socket);

print "DEBUG : final fail2ban command: $fail2ban_cmd\n" if ($verbose_value);

print "DEBUG : warning threshold : $warning, critical threshold : $critical\n" if ($verbose_value);
if (($critical < 0) or ($warning < 0) or ($critical < $warning)) {
    print $display.' - the thresholds must be integers and the critical threshold higher or equal than the warning threshold'."\n";
    exit $ERRORS{"UNKNOWN"};
}

# Core script
# -----------
my ($how_many_jail,$how_many_banned,$return_print,$plugstate) = (0,0,"","OK");


### Test the connection to the fail2ban server
my @command_output = `$fail2ban_cmd ping`;
my $return_code = $?;
if ($return_code) {
    print $display.'CRITICAL - non-zero exit code during testing fail2ban-client ping, check if the server is running and if you have the good permissions';
    exit $ERRORS{"CRITICAL"};
}
else {
    print "DEBUG : it seems the connection with the fail2ban server is ok\n" if ($verbose_value);
}


### Only if you specify one jail
if ($jail_specific) {
    my $current_ban_number = currently_ban("$fail2ban_cmd","$jail_specific");
    if ($current_ban_number == -1) {
        print $display.' - CRITICAL - impossible to retrieve info about the jail '.$jail_specific;
        exit $ERRORS{"CRITICAL"};
    }
    else {
        $how_many_banned = int($current_ban_number);
        $return_print = $how_many_banned.' current banned IP(s) for the specific jail '.$jail_specific;
    }
}
### To analyze all the jail
else {
    # Retrieve the jails list
    my @jail_list = obtain_jail_list("$fail2ban_cmd");
    if ($jail_list[0] eq "-1") {
        print $display.' - CRITICAL - impossible to retrieve the jail list'."\n";
        exit $ERRORS{"CRITICAL"};
    }

    foreach (@jail_list) {
        $how_many_jail ++;

        my $jail_name = $_;
        $jail_name =~ tr/ //ds;

        my $current_ban_number = currently_ban("$fail2ban_cmd","$jail_name");
        if ($current_ban_number == -1) {
            print "DEBUG : problem to parse the current banned IPs for jail $jail_name\n" if ($verbose_value);
        }
        else {
            print "DEBUG : the jail $jail_name has currently $current_ban_number banned IPs\n" if ($verbose_value);
            $how_many_banned += int($current_ban_number);
        }
    }
    $return_print = $how_many_jail.' detected jails with '.$how_many_banned.' current banned IP(s)';
}

### Final
$plugstate = "CRITICAL" if ($how_many_banned >= $critical);
$plugstate = "WARNING" if (($how_many_banned >= $warning) && ($how_many_banned < $critical));

$return_print = $display." - ".$plugstate." - ".$return_print;
$return_print .= " | currentBannedIP=$how_many_banned" if ($perfdata_value);

print $return_print;
exit $ERRORS{"$plugstate"};


# ####################################################################
# function 1 : display the help
# -----------------------------
sub print_usage {
    print <<EOT;
$script_name version $version by $author

This plugin checks if the fail2ban server is running and how many IPs are currently banned.
You can use this plugin to monitor all the jails or just a specific jail.

Usage: /<path-to>/$script_name [-p] [-D "$display"] [-v] [-c 2] [-w 1] [-s /<path-to>/socket] [-P /usr/bin/fail2ban-client]

Options:
 -h, --help
    Print detailed help screen
 -V, --version
    Print version information
 -D, --display=STRING
    To modify the output display 
    default is "CHECK FAIL2BAN ACTIVITY"
 -P, --path-fail2ban_client=STRING
    Specify the path to the tw_cli binary
    default value is /usr/bin/fail2ban-client
 -c, --critical=INT
    Specify a critical threshold
    default is 2
 -w, --warning=INT
    Specify a warning threshold
    default is 1
 -s, --socket=STRING
    Specify a socket path
    default is unset
 -p, --perfdata
    If you want to activate the perfdata output
 -v, --verbose
    Show details for command-line debugging (Nagios may truncate the output)
    
Send email to $a_mail if you have questions
regarding use of this software. To submit patches or suggest improvements,
send email to $a_mail
This plugin has been created by $author

Hope you will enjoy it ;)

Remember :
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.


EOT
    exit $ERRORS{"UNKNOWN"};
}

# function 2 : display version information
# ----------------------------------------
sub print_version {
    print <<EOT;
$script_name version $version
EOT
    exit $ERRORS{"UNKNOWN"};
}

# function 3 : return the jail list
# ---------------------------------
sub obtain_jail_list {
    my ($fail2ban_client_path) = @_;

    my @command_output = `$fail2ban_client_path status`;
    my $return_code = $?;
    if ($return_code) {
        return -1;
    }
    
    my @jail_list;
    foreach (@command_output) {
        if ($_=~/^.*Jail list:\t+(.*)/) {
            print "DEBUG : jails list: $1\n" if ($verbose_value);
            @jail_list = split(/,/, $1);
        }
    }
    
    return @jail_list;
}

# function 4 : return how many IP are currently ban for a given jail
# ------------------------------------------------------------------
sub currently_ban {
    my ($fail2ban_client_path,$jail_name) = @_;

    my @command_output = `$fail2ban_client_path status $jail_name`;
    my $return_code = $?;
    if ($return_code) {
        return -1;
    }

    foreach (@command_output) {
        if ($_=~/^.*Currently banned:\t+(.*)/) {
            my $current_count = $1;
            $current_count =~ tr/ //ds;
            return $current_count;
        }
    }
    return -1;
}