#!/usr/bin/env python3

# written by sqall
# twitter: https://twitter.com/sqall01
# blog: https://h4des.org
# github: https://github.com/sqall01
#
# Licensed under the MIT License.

"""
Short summary:
Monitor /etc/passwd for changes to detect malicious attempts to hijack/change users.

Requirements:
None
"""

import os
from typing import Dict

from lib.state import load_state, store_state
from lib.util import output_error, output_finding

# Read configuration.
try:
    from config.config import ALERTR_FIFO, FROM_ADDR, TO_ADDR, STATE_DIR
    from config.monitor_passwd import ACTIVATED
    STATE_DIR = os.path.join(os.path.dirname(__file__), STATE_DIR, os.path.basename(__file__))
except:
    ALERTR_FIFO = None
    FROM_ADDR = None
    TO_ADDR = None
    ACTIVATED = True
    STATE_DIR = os.path.join("/tmp", os.path.basename(__file__))


def _get_passwd() -> Dict[str, str]:

    passwd_data = {}
    with open("/etc/passwd", 'rt') as fp:
        for line in fp:
            line = line.strip()

            if line == "":
                continue

            entry = line.strip().split(":")

            user = entry[0]
            passwd_data[user] = line

    return passwd_data


def monitor_passwd():

    # Decide where to output results.
    print_output = False
    if ALERTR_FIFO is None and FROM_ADDR is None and TO_ADDR is None:
        print_output = True

    if not ACTIVATED:
        if print_output:
            print("Module deactivated.")
        return

    stored_passwd_data = {}
    try:
        stored_passwd_data = load_state(STATE_DIR)

    except Exception as e:
        output_error(__file__, str(e))
        return

    curr_passwd_data = {}
    try:
        curr_passwd_data = _get_passwd()

    except Exception as e:
        output_error(__file__, str(e))
        return

    # Compare stored data with current one.
    for stored_entry_user in stored_passwd_data.keys():

        # Extract current entry belonging to the same user.
        if stored_entry_user not in curr_passwd_data.keys():
            message = "User '%s' was deleted." % stored_entry_user

            output_finding(__file__, message)

            continue

        # Check entry was modified.
        if stored_passwd_data[stored_entry_user] != curr_passwd_data[stored_entry_user]:
            message = "Passwd entry for user '%s' was modified.\n\n" % stored_entry_user
            message += "Old entry: %s\n" % stored_passwd_data[stored_entry_user]
            message += "New entry: %s" % curr_passwd_data[stored_entry_user]

            output_finding(__file__, message)

    # Check new data was added.
    for curr_entry_user in curr_passwd_data.keys():
        if curr_entry_user not in stored_passwd_data.keys():
            message = "User '%s' was added.\n\n" % curr_entry_user
            message += "Entry: %s" % curr_passwd_data[curr_entry_user]

            output_finding(__file__, message)

    try:
        store_state(STATE_DIR, curr_passwd_data)

    except Exception as e:
        output_error(__file__, str(e))


if __name__ == '__main__':
    monitor_passwd()