#!/usr/local/bin/python3

"""
    Copyright (c) 2020 Ad Schellevis <ad@opnsense.org>
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice,
     this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
    INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
    AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.

"""
import sys
import re
import argparse
import datetime
import ipaddress
import syslog
import subprocess
import time
from select import select

all_rules = {
    '.*Accepted.*': True,
    '.*Successful login.*': True,
    '.*Web GUI authentication error.*': False,
    '.*Invalid user.*': False,
    '.*Illegal user.*': False,
    '.*Postponed keyboard-interactive for invalid user.*': False,
    '.*authentication error for illegal user.*': False,
    '.*Authentication error for .*': False
}

if __name__ == '__main__':
    # handle parameters
    parser = argparse.ArgumentParser()
    parser.add_argument('--attempts', help='maximum number of attempts', type=int, default=5)
    parser.add_argument('--grace_period', help='keep stats for max number of seconds', type=int, default=3600)
    parser.add_argument('--pf_table' ,help='pf table to add failed attempts in', default='sshlockout')
    inputargs = parser.parse_args()

    suspects = dict()
    suspects_lastseen = dict()

    while True:
        rlist, _, _ = select([sys.stdin], [], [], 0.5)
        if rlist:
            line = sys.stdin.readline()
            if line == '':
                break

            ip = None
            for part in line.split():
                if re.match('^[0-9.]+$', part) or re.match('^[a-fA-F0-9:]+$', part):
                    try:
                        ip = ipaddress.ip_address(part)
                        break
                    except ValueError:
                        ip = None
            if ip:
                # cleanup entries after grace period
                for cleanup_ip in list(suspects_lastseen):
                    if time.time() - suspects_lastseen[cleanup_ip] > inputargs.grace_period:
                        del suspects_lastseen[cleanup_ip]
                        del suspects[cleanup_ip]

                allowed = None
                for rule in all_rules:
                    if re.match(rule, line):
                        allowed = all_rules[rule]
                        break

                if allowed is True:
                    # reset counter when login was successful
                    if ip in suspects:
                        del suspects[ip]
                        del suspects_lastseen[ip]
                elif allowed is False:
                    suspects_lastseen[ip] = time.time()
                    if ip not in suspects:
                        suspects[ip] = list()

                    ts = datetime.datetime.strptime(line[line.find(':')-2:][:8], "%H:%M:%S")
                    if len(suspects[ip]) == 0 or abs((ts - suspects[ip][-1]).total_seconds()) > 2:
                        # a single attempt can lead to multiple log entries, suppress likely duplicates
                        suspects[ip].append(ts)
                    if len(suspects[ip]) > inputargs.attempts:
                        syslog.syslog(syslog.LOG_NOTICE, "lockout %s [using table %s] after %d attempts" % (
                            ip, inputargs.pf_table, len(suspects[ip])
                        ))
                        subprocess.run(['/sbin/pfctl', '-t', inputargs.pf_table, '-T', 'add', str(ip)],
                                         capture_output=True)
                        # kill active state(s) for this ip address as well.
                        subprocess.run(['/sbin/pfctl', '-k', ip], capture_output=True)
