#! /usr/bin/python3
# ----------------------------------------------------------------------
#    Copyright (C) 2018–2022 Otto Kekäläinen <otto@kekalainen.net>
#
#    This program is free software; you can redistribute it and/or
#    modify it under the terms of version 2 of the GNU General Public
#    License as published by the Free Software Foundation.
#
#    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.
#
# ----------------------------------------------------------------------
#
# /etc/apparmor/notify.conf:
# # set to 'yes' to enable AppArmor DENIED notifications
# show_notifications="yes"
#
# # only people in use_group can run this script
# use_group="admin"
#
# $HOME/.apparmor/notify.conf can have:
# # set to 'yes' to enable AppArmor DENIED notifications
# show_notifications="yes"
#
# In a typical desktop environment one would run as a service the
# command:
#   /usr/bin/aa-notify -p -w 10
#
"""Show AppArmor events on command line or as desktop notifications."""

import argparse
import atexit
import grp
import os
import pwd
import re
import sys
import time

import notify2
import psutil

import apparmor.aa as aa
import apparmor.ui as aaui
import apparmor.config as aaconfig
import LibAppArmor  # C-library to parse one log line
from apparmor.common import DebugLogger, open_file_read
from apparmor.fail import enable_aa_exception_handler
from apparmor.notify import get_last_login_timestamp
from apparmor.translations import init_translation



def get_user_login():
    """Portable function to get username.

    Should not trigger any
    "OSError: [Errno 25] Inappropriate ioctl for device" errors in Giltab-CI.
    """
    if os.name == "posix":
        username = pwd.getpwuid(os.geteuid()).pw_name
    else:
        username = os.environ.get('USER')
        if not username and hasattr(os, 'getlogin'):
            username = os.getlogin()
    return username


def format_event(event, logsource):
    """Generate the notification text contents."""
    output = []

    if 'message_body' in config['']:
        output += [config['']['message_body']]

    if event.profile:
        output += ['Profile: {}'.format(event.profile)]
    if event.operation:
        output += ['Operation: {}'.format(event.operation)]
    if event.name:
        output += ['Name: {}'.format(event.name)]
    if event.denied_mask:
        output += ['Denied: {}'.format(event.denied_mask)]
    if event.net_family and event.net_sock_type:
        output += ['Family: {}'.format(event.net_family)]
        output += ['Socket: {}'.format(event.net_sock_type)]

    output += ['Logfile: {}'.format(logsource)]

    return "\n".join(output)


def is_event_in_filter(event, filters):
    """Checks if event is in filter"""
    if filters['profile'] and event.profile and not filters['profile_re'].match(event.profile):
        return False
    if filters['operation'] and event.operation and not filters['operation_re'].match(event.operation):
        return False
    if filters['name'] and event.name and not filters['name_re'].match(event.name):
        return False
    if filters['denied_mask'] and event.denied_mask and not filters['denied_mask_re'].match(event.denied_mask):
        return False
    if filters['net_family'] and event.net_family and not filters['net_family_re'].match(event.net_family):
        return False
    if filters['net_sock_type'] and event.net_sock_type and not filters['net_sock_type_re'].match(event.net_sock_type):
        return False
    return True


def notify_about_new_entries(logfile, filters, wait=0):
    """Run the notification daemon in the background."""
    # Kill other instances of aa-notify if already running
    for process in psutil.process_iter():
        # Find the process that has the same name as this script, e.g. aa-notify.py
        if process.name() == os.path.basename(__file__) and process.pid != os.getpid():
            print(_('Killing old daemon (PID {})...').format(process.pid))
            os.kill(process.pid, 15)

    # Spawn/fork into the background and stay running
    newpid = os.fork()
    if newpid == 0:

        # Follow the logfile and stream notifications
        # Rate limit to not show too many notifications
        try:
            for event in follow_apparmor_events(logfile, wait):
                if not is_event_in_filter(event, filters):
                    continue
                debug_logger.info(format_event(event, logfile))
                yield (format_event(event, logfile))
        except PermissionError:
            sys.exit(_("ERROR: Cannot read {}. Please check permissions.".format(logfile)))

    else:
        print(_('Notification emitter started in the background'))
        # pids = (os.getpid(), newpid)
        # print("parent: %d, child: %d\n" % pids)
        os._exit(0)  # Exit child without calling exit handlers etc


def show_entries_since_epoch(logfile, epoch_since, filters):
    """Show AppArmor notifications since given timestamp."""
    count = 0
    for event in get_apparmor_events(logfile, epoch_since):
        if not is_event_in_filter(event, filters):
            continue
        count += 1
        if args.verbose:
            print(format_event(event, logfile))
            print()  # Print a newline after each entry for better readability

    aaui.UI_Info(_('AppArmor denials: {count} (since {date})').format(
            **{
                'count': count,
                'date': time.strftime(timeformat, time.localtime(epoch_since))
            }
        )
    )

    if args.verbose:
        if 'message_footer' in config['']:
            print(config['']['message_footer'])
        else:
            print(_('For more information, please see: {}').format(debug_docs_url))


def show_entries_since_last_login(logfile, filters, username=get_user_login()):
    """Show AppArmor notifications since last login of user."""
    # If running as sudo, use username of sudo user instead of root
    if 'SUDO_USER' in os.environ.keys():
        username = os.environ['SUDO_USER']

    if args.verbose:
        print(_('Showing entries since {} logged in').format(username))
        print()  # Newline
    epoch_since = get_last_login_timestamp(username)
    if epoch_since == 0:
        print(_('ERROR: Could not find last login'), file=sys.stderr)
        sys.exit(1)
    show_entries_since_epoch(logfile, epoch_since, filters)


def show_entries_since_days(logfile, since_days, filters):
    """Show AppArmor notifications since the given amount of days."""
    day_in_seconds = 60 * 60 * 24
    epoch_now = int(time.time())
    epoch_since = epoch_now - day_in_seconds * since_days
    show_entries_since_epoch(logfile, epoch_since, filters)


def follow_apparmor_events(logfile, wait=0):
    """Follow AppArmor events and yield relevant entries until process stops."""
    # If wait was given as argument but was type None (from ArgumentParser)
    # ensure it's type int and zero
    if not wait:
        wait = 0

    # Record start time here so wait can be calculated later
    start_time = int(time.time())

    # Record initial file size to detect if log rotates
    log_size = os.stat(logfile).st_size
    # Record initial file inode number to detect if log gets renamed
    log_inode = os.stat(logfile).st_ino

    # @TODO Implement more log sources in addition to just the logfile
    with open_file_read(logfile) as logdata:

        # Loop all pre-existing events in the log source once so later runs
        # will only see new events
        for discarded_event in logdata:
            pass

        # @TODO: while+sleep will cause CPU interruptions once per second,
        # so switch to epoll/inotify/etc for less resource consumption.
        while True:
            debug_logger.debug(
                'Poll AppArmor event source {} seconds since start'.
                format(int(time.time()) - start_time)
            )

            (logdata, log_inode, log_size) = reopen_logfile_if_needed(logfile, logdata, log_inode, log_size)

            for event in parse_logdata(logdata):
                # @TODO Alternatively use os.times()
                if int(time.time()) - start_time < wait:
                    debug_logger.debug('Omitted an event seen during wait time')
                    continue
                yield event

            if debug_logger.debugging and debug_logger.debug_level <= 10 and int(time.time()) - start_time > 100:
                debug_logger.debug('Debug mode detected: aborting notification emitter after 100 seconds.')
                sys.exit(0)

            time.sleep(1)


def reopen_logfile_if_needed(logfile, logdata, log_inode, log_size):
    retry = True

    while retry:
        try:
            # Reopen file if inode has changed, e.g. rename by logrotate
            if os.stat(logfile).st_ino != log_inode:
                debug_logger.debug('Logfile was renamed, reload to read the new file.')
                logdata = open(logfile, 'r')
                # Store new inode number for next comparisons
                log_inode = os.stat(logfile).st_ino

            # Start reading from the beginning if file shrank
            if os.stat(logfile).st_size < log_size:
                debug_logger.debug('Logfile shrank in size, reload from beginning.')
                logdata.seek(0)
                log_size = os.stat(logfile).st_size  # Reset file size value

            # Record new file size if grown
            if os.stat(logfile).st_size > log_size:
                log_size = os.stat(logfile).st_size

            retry = False
        except FileNotFoundError:
            # @TODO: switch to epoll/inotify/
            debug_logger.debug('Logfile not found, retrying.')
            time.sleep(1)
            # @TODO: send notification if reopening the log fails too many times

    return (logdata, log_inode, log_size)


def get_apparmor_events(logfile, since=0):
    """Read audit events from log source and yield all relevant events."""

    # Get logdata from file
    # @TODO Implement more log sources in addition to just the logfile
    try:
        with open_file_read(logfile) as logdata:
            for event in parse_logdata(logdata):
                if event.epoch > since:
                    yield event
    except PermissionError:
        sys.exit(_("ERROR: Cannot read {}. Please check permissions.".format(logfile)))


def parse_logdata(logsource):
    """Traverse any iterable log source and extract relevant AppArmor events.

    Expects log lines like:
      Feb 16 20:22:28 XPS-13-9370 kernel: [520374.926882] audit: type=1400
      audit(1581877348.868:657): apparmor="ALLOWED" operation="open"
      profile="libreoffice-soffice"
      name="/usr/share/drirc.d/00-mesa-defaults.conf" pid=22690
      comm="soffice.bin" requested_mask="r" denied_mask="r" fsuid=1001 ouid=0
    """

    re_audit_time_id = r'(msg=)?audit\([\d\.\:]+\):\s+'  # 'audit(1282626827.320:411): '
    re_kernel_time = r'\[[\d\.\s]+\]'  # '[ 1612.746129]'
    re_type_num = '1[45][0-9][0-9]'  # 1400..1599
    re_aa_or_op = '(apparmor=|operation=)'

    re_log_parts = [
        r'kernel:\s+(' + re_kernel_time + r'\s+)?(audit:\s+)?type=' + re_type_num + r'\s+' + re_audit_time_id + re_aa_or_op,  # v2_6 syslog
        r'kernel:\s+(' + re_kernel_time + r'\s+)?' + re_audit_time_id + 'type=' + re_type_num + r'\s+' + re_aa_or_op,
        'type=(AVC|APPARMOR[_A-Z]*|' + re_type_num + r')\s+' + re_audit_time_id + '(type=' + re_type_num + r'\s+)?' + re_aa_or_op,  # v2_6 audit and dmesg
        r'type=USER_AVC\s+' + re_audit_time_id + '.*apparmor=',  # dbus
        r'type=UNKNOWN\[' + re_type_num + r'\]\s+' + re_audit_time_id + re_aa_or_op,
        r'dbus\[[0-9]+\]:\s+apparmor=',  # dbus
    ]

    # Pre-filter log lines so that we hand over only relevant lines to LibAppArmor parsing
    re_log_all = re.compile('(' + '|'.join(re_log_parts) + ')')

    for entry in logsource:

        # Check the start of the log line and only process lines from AppArmor
        apparmor_entry = re_log_all.search(entry)
        if apparmor_entry:
            # Parse the line using LibAppArmor (C library)
            # See aalogparse.h for data structure
            event = LibAppArmor.parse_record(entry)
            # Only show actual events of contained programs and ignore among
            # others AppArmor profile reloads
            if event.operation and event.operation[0:8] != 'profile_':
                yield event


def drop_privileges():
    """Drop privileges of process.

    If running as root, drop privileges to USER if known, or fall-back to
    nobody_user/group.
    """
    if os.geteuid() == 0:

        if 'SUDO_USER' in os.environ.keys():
            next_username = os.environ['SUDO_USER']
            next_uid = os.environ['SUDO_UID']
            next_gid = os.environ['SUDO_GID']
        else:
            nobody_user_info = pwd.getpwnam(nobody_user)
            next_username = nobody_user_info[0]
            next_uid = nobody_user_info[2]
            next_gid = nobody_user_info[3]

        debug_logger.debug('Dropping to user "{}" privileges'.format(next_username))

        # @TODO?
        # Remove group privileges, including potential 'adm' group that might
        # have had log read access but also other accesses.
        # os.setgroups([])

        # Try setting the new uid/gid
        # Set gid first, otherwise the latter step would fail on missing permissions
        os.setegid(int(next_gid))
        os.seteuid(int(next_uid))


def raise_privileges():
    """Raise privileges of process.

    If was running as user with saved user ID 0, raise back to root privileges.
    """
    if os.geteuid() != 0 and original_effective_user == 0:

        debug_logger.debug('Rasing privileges from UID {} back to UID 0 (root)'.format(os.geteuid()))

        # os.setgid(int(next_gid))
        os.seteuid(original_effective_user)


def read_notify_conf(path, shell_config):
    """Read notify.conf."""
    try:
        shell_config.CONF_DIR = path
        conf_dict = shell_config.read_config('notify.conf')
        debug_logger.debug('Found configuration file in {}/notify.conf'.format(shell_config.CONF_DIR))
        return conf_dict
    except FileNotFoundError:
        return {}


def compile_filter_regex(filters):
    """Compile each filter regex and add it to filters"""
    if filters['profile']:
        filters['profile_re'] = re.compile(filters['profile'])
    if filters['operation']:
        filters['operation_re'] = re.compile(filters['operation'])
    if filters['name']:
        filters['name_re'] = re.compile(filters['name'])
    if filters['denied_mask']:
        filters['denied_mask_re'] = re.compile(filters['denied_mask'])
    if filters['net_family']:
        filters['net_family_re'] = re.compile(filters['net_family'])
    if filters['net_sock_type']:
        filters['net_sock_type_re'] = re.compile(filters['net_sock_type'])

    return filters


def main():
    """Run aa-notify.

    Parse command line arguments and starts the requested operations.
    """
    global _, debug_logger, config, args
    global debug_docs_url, nobody_user, original_effective_user, timeformat

    debug_docs_url = "https://wiki.ubuntu.com/DebuggingApparmor"
    nobody_user = "nobody"
    timeformat = "%c"  # Automatically using locale format
    original_effective_user = os.geteuid()

    # setup exception handling
    enable_aa_exception_handler()

    # setup module translations
    _ = init_translation()

    # Register the on_exit method with atexit
    # Takes care of closing the debug log etc
    atexit.register(aa.on_exit)

    # Set up UI logger for separate messages from UI module
    debug_logger = DebugLogger('Notify')
    debug_logger.debug("Starting aa-notify")

    parser = argparse.ArgumentParser(description=_('Display AppArmor notifications or messages for DENIED entries.'))
    parser.add_argument('-p', '--poll', action='store_true', help=_('poll AppArmor logs and display notifications'))
    parser.add_argument('--display', type=str, help=_('set the DISPLAY environment variable (might be needed if sudo resets $DISPLAY)'))
    parser.add_argument('-f', '--file', type=str, help=_('search FILE for AppArmor messages'))
    parser.add_argument('-l', '--since-last', action='store_true', help=_('display stats since last login'))
    parser.add_argument('-s', '--since-days', type=int, metavar=('NUM'), help=_('show stats for last NUM days (can be used alone or with -p)'))
    parser.add_argument('-v', '--verbose', action='store_true', help=_('show messages with stats'))
    parser.add_argument('-u', '--user', type=str, help=_('user to drop privileges to when not using sudo'))
    parser.add_argument('-w', '--wait', type=int, metavar=('NUM'), help=_('wait NUM seconds before displaying notifications (with -p)'))
    parser.add_argument('--debug', action='store_true', help=_('debug mode'))
    parser.add_argument('--configdir', type=str, help=argparse.SUPPRESS)

    filter_group = parser.add_argument_group('Filtering options',
                                             description=('Filters are used to reduce the output of information to only '
                                                          'those entries that will match the filter. Filters use Python\'s regular '
                                                          'expression syntax.'))
    filter_group.add_argument('--filter.profile', metavar='PROFILE', help=_('regular expression to match the profile'))
    filter_group.add_argument('--filter.operation', metavar='OPERATION', help=_('regular expression to match the operation'))
    filter_group.add_argument('--filter.name', metavar='NAME', help=_('regular expression to match the name'))
    filter_group.add_argument('--filter.denied', metavar='DENIED', help=_('regular expression to match the denied mask'))
    filter_group.add_argument('--filter.family', metavar='FAMILY', help=_('regular expression to match the network family'))
    filter_group.add_argument('--filter.socket', metavar='SOCKET', help=_('regular expression to match the network socket type'))

    # If a TTY then assume running in test mode and fix output width
    if not sys.stdout.isatty():
        parser.formatter_class = lambda prog: argparse.HelpFormatter(prog, width=80)

    args = parser.parse_args()

    # Debug mode can be invoked directly with --debug or env LOGPROF_DEBUG=3
    if args.debug:
        debug_logger.activateStderr()
        debug_logger.debug('Logging level: {}'.format(debug_logger.debug_level))
        debug_logger.debug('Running as uid: {0[0]}, euid: {0[1]}, suid: {0[2]}'.format(os.getresuid()))
        if args.poll:
            debug_logger.debug('Running with --debug and --poll. Will exit in 100s')
    # Sanity checks
    user_ids = os.getresuid()
    groups_ids = os.getresgid()
    if user_ids[1] != user_ids[2]:
        sys.exit("ERROR: Cannot be started with suid set!")
    if groups_ids[1] != groups_ids[2]:
        sys.exit("ERROR: Cannot be started with sgid set!")

    # Define global variables that will be populated by init_aa()
    # conf = None
    logfile = None

    if args.configdir:  # prefer --configdir if given
        confdir = args.configdir
    else:  # fallback to env variable (or None if not set)
        confdir = os.getenv('__AA_CONFDIR')

    aa.init_aa(confdir=confdir)

    # Initialize aa.logfile
    aa.set_logfile(args.file)

    # Load global config reader
    shell_config = aaconfig.Config('shell')

    # Load system's notify.conf
    # By default aa.CONFDIR is /etc/apparmor on most production systems
    system_config = read_notify_conf(aa.CONFDIR, shell_config)
    # Set default is no system notify.conf was found
    if not system_config:
        system_config = {'': {'show_notifications': 'yes'}}

    # Load user's notify.conf
    if os.path.isfile(os.environ['HOME'] + '/.apparmor/notify.conf'):
        # Use legacy path if the conf file is there
        user_config = read_notify_conf(os.environ['HOME'] + '/.apparmor', shell_config)
    elif 'XDG_CONFIG_HOME' in os.environ and os.path.isfile(os.environ['XDG_CONFIG_HOME'] + '/apparmor/notify.conf'):
        # Use XDG_CONFIG_HOME if it is defined
        user_config = read_notify_conf(os.environ['XDG_CONFIG_HOME'] + '/apparmor', shell_config)
    else:
        # Fallback to the default value of XDG_CONFIG_HOME
        user_config = read_notify_conf(os.environ['HOME'] + '/.config/apparmor', shell_config)

    # Merge the two config dicts in an accurate and idiomatic way (requires Python 3.5)
    config = {**system_config, **user_config}

    """
    Possible configuration options:
    - show_notifications
    - message_body
    - message_footer
    - use_group
    - filter.profile,
    - filter.operation,
    - filter.name,
    - filter.denied,
    - filter.family,
    - filter.socket,
    """

    # # Config checks

    # Warn about unknown keys in the config
    allowed_config_keys = [
        'use_group',
        'show_notifications',
        'message_body',
        'message_footer',
        'filter.profile',
        'filter.operation',
        'filter.name',
        'filter.denied',
        'filter.family',
        'filter.socket',
    ]
    found_config_keys = config[''].keys()
    unknown_keys = [
        item for item in found_config_keys if item not in allowed_config_keys
    ]
    for item in unknown_keys:
        print(_('Warning! Configuration item "{}" is unknown!').format(item))

    filters = {
        'profile': '',
        'operation': '',
        'name': '',
        'denied_mask': '',
        'net_family': '',
        'net_sock_type': '',
    }

    if 'filter.profile' in config['']:
        filters['profile'] = config['']['filter.profile']
    if 'filter.operation' in config['']:
        filters['operation'] = config['']['filter.operation']
    if 'filter.name' in config['']:
        filters['name'] = config['']['filter.name']
    if 'filter.denied' in config['']:
        filters['denied_mask'] = config['']['filter.denied']
    if 'filter.family' in config['']:
        filters['net_family'] = config['']['filter.family']
    if 'filter.socket' in config['']:
        filters['net_sock_type'] = config['']['filter.socket']

    # command line filters override notify.conf
    if getattr(args, 'filter.profile'):
        filters['profile'] = getattr(args, 'filter.profile')
    if getattr(args, 'filter.operation'):
        filters['operation'] = getattr(args, 'filter.operation')
    if getattr(args, 'filter.name'):
        filters['name'] = getattr(args, 'filter.name')
    if getattr(args, 'filter.denied'):
        filters['denied_mask'] = getattr(args, 'filter.denied')
    if getattr(args, 'filter.family'):
        filters['net_family'] = getattr(args, 'filter.family')
    if getattr(args, 'filter.socket'):
        filters['net_sock_type'] = getattr(args, 'filter.socket')

    filters = compile_filter_regex(filters)

    # Warn if use_group is defined and current group does not match defined
    if 'use_group' in config['']:
        user = pwd.getpwuid(os.geteuid())[0]
        user_groups = [g.gr_name for g in grp.getgrall() if user in g.gr_mem]
        gid = pwd.getpwnam(user).pw_gid
        user_groups.append(grp.getgrgid(gid).gr_name)

        if config['']['use_group'] not in user_groups:
            print(
                _('ERROR! User {user} not member of {group} group!').format(
                    user=user,
                    group=config['']['use_group']
                ),
                file=sys.stderr
            )
            sys.exit(1)
            # @TODO: Extend UI lib to have warning and error functions that
            # can be used in an uniform way with both text and JSON output.

    if args.file:
        logfile = args.file
    elif os.path.isfile('/var/run/auditd.pid') and os.path.isfile('/var/log/audit/audit.log'):
        # If auditd is running, look at /var/log/audit/audit.log
        logfile = '/var/log/audit/audit.log'
    elif os.path.isfile('/var/log/kern.log'):
        # For aa-notify, the fallback is kern.log, not syslog from aa.logfile
        logfile = '/var/log/kern.log'
    else:
        # If all above failed, use aa cfg
        logfile = aa.logfile

    if args.verbose:
        print(_('Using log file'), logfile)

    if args.display:
        os.environ['DISPLAY'] = args.display

    if args.poll:
        # Exit immediately if show_notifications is no or any of the options below
        if config['']['show_notifications'] in [False, 'no', 'false', '0']:
            print(_('Showing notifications forbidden in notify.conf, aborting..'))
            sys.exit(0)

        # Don't allow usage of aa-notify by root, must be some user. Desktop
        # logins as root are not recommended and certainly not a use case for
        # aa-notify notifications.
        if not args.user and os.getuid() == 0 and 'SUDO_USER' not in os.environ.keys():
            sys.exit("ERROR: Cannot be started a real root user. Use --user to define what user to use.")

        # At this point this script needs to be able to read 'logfile' but once
        # the for loop starts, privileges can be dropped since the file descriptor
        # has been opened and access granted. Further reads of the file will not
        # trigger any new permission checks.
        # @TODO Plan to catch PermissionError here or..?
        for message in notify_about_new_entries(logfile, filters, args.wait):

            # Notifications should not be run as root, since root probably is
            # the wrong desktop user and not the one getting the notifications.
            drop_privileges()

            # sudo does not preserve DBUS address, so we need to guess it based on UID
            if 'DBUS_SESSION_BUS_ADDRESS' not in os.environ:
                os.environ['DBUS_SESSION_BUS_ADDRESS'] = 'unix:path=/run/user/{}/bus'.format(os.geteuid())

            # Before use, notify2 must be initialized and the DBUS channel
            # should be opened using the non-root user. This step needs to
            # be executed after the drop_privileges().
            notify2.init('AppArmor')

            n = notify2.Notification(
                _('AppArmor notification'),
                message,
                'gtk-dialog-warning'
            )
            n.show()

            # When notification is sent, raise privileged back to root if the
            # original effective user id was zero (to be able to read AppArmor logs)
            raise_privileges()

    elif args.since_last:
        show_entries_since_last_login(logfile, filters)
    elif args.since_days:
        show_entries_since_days(logfile, args.since_days, filters)
    else:
        parser.print_help()

    sys.exit(0)


if __name__ == '__main__':
    main()
