Mini Shell

# -*- coding: utf-8 -*-

# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2018 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT
#

import os
import re
import subprocess
import sys

CAGEFS_MP_FILENAME = '/etc/cagefs/cagefs.mp'
CAGEFSCTL_TOOL     = '/usr/sbin/cagefsctl'


class CagefsMpConflict(Exception):
    def __init__(self, new_item, existing_item):

        self._msg = (
            f"Conflict in adding '{new_item}' to {CAGEFS_MP_FILENAME} "
            f"because of pre-existing alternative specification: '{existing_item}'"
        )

    def __str__(self):
        return self._msg


class CagefsNotSupportedError(Exception):
    """Cagefs Not Supported Exception"""
    def __init__(self, message):
        Exception.__init__(self, message)


class CagefsMpItem:

    PREFIX_LIST        = '@!%*'
    _PREFIX_MOUNT_RW   = ''
    _PREFIX_MOUNT_RO   = '!'

    def __init__(self, arg):
        """Constructor

        :param arg: Is either path to add to cagefs.mp or a raw line is read from cagefs.mp
        :param prefix: The same as adding prefix '!' to arg before passing it to ctor"""

        if arg[:1] == '#':  # is a comment? then init as dummy
            self._path_spec = None
        elif arg.strip() == '':  # init as dummy for empty lines
            self._path_spec = None
        else:
            self._path_spec = arg

    def mode(self, mode):
        """Specify mode as in fluent constructor"""

        if self.prefix() == '@' and mode is not None:
            self._path_spec = f"{self._path_spec},{mode:03o}"

        return self

    def __str__(self):
        return self._path_spec

    @staticmethod
    def _add_slash(path):
        if path == '':
            return '/'
        if path[-1] != '/':
            return path + '/'
        return path

    def pre_exist_in(self, another):

        adopted = CagefsMpItem._adopt(another)

        # overkill: just to keep strictly to comparing NULL objects principle
        if self.is_dummy() or adopted.is_dummy():
            return False

        this_path = CagefsMpItem._add_slash(self.path())
        test_preexist_in_path = CagefsMpItem._add_slash(adopted.path())
        return this_path.startswith(test_preexist_in_path)

    def is_compatible_by_prefix_with(self, existing):

        adopted = CagefsMpItem._adopt(existing)

        # overkill: just to keep strictly to comparing NULL objects principle
        if self.is_dummy() or adopted.is_dummy():
            return False

        if self.prefix() == adopted.prefix():
            return True

        prefix_compatibility_map = { CagefsMpItem._PREFIX_MOUNT_RW : [CagefsMpItem._PREFIX_MOUNT_RO] }
        null_options = []

        return self.prefix() in prefix_compatibility_map.get(adopted.prefix(), null_options)

    def is_dummy(self):
        return self._path_spec is None

    @staticmethod
    def _adopt(x):
        if isinstance(x, CagefsMpItem):
            return x
        else:
            return CagefsMpItem(x)

    @staticmethod
    def _cut_off_mode(path_spec):
        """Cut off mode from path spec like @/var/run/screen,777

        Only one comma per path spec is allowed ;-)"""

        return path_spec.split(',')[0]

    @staticmethod
    def _cut_off_prefix(path_spec):
        return path_spec.lstrip(CagefsMpItem.PREFIX_LIST)

    def path(self):
        return CagefsMpItem._cut_off_prefix(CagefsMpItem._cut_off_mode(self._path_spec))

    def prefix(self):
        if self._path_spec != self.path():
            return self._path_spec[0]
        else:
            return ''


def is_cagefs_present():
    return os.path.exists(CAGEFSCTL_TOOL)


def _mk_mount_dir_setup_perm(path, mode=0o755, owner_id=None, group_id=None):
    # -1 means 'unchanged'
    if group_id is None:
        group_id = -1
    if owner_id is None:
        owner_id = -1

    if not os.path.isdir(path):
        os.mkdir(path)

    if mode is not None:
        os.chmod(path, mode)

    os.chown(path, owner_id, group_id)


def _remount_cagefs(user=None, remount_in_background=False):
    if not is_cagefs_present():
        return

    if user is None:
        command = [CAGEFSCTL_TOOL, "--wait-lock", "--remount-all"]
    else:
        command = [CAGEFSCTL_TOOL, "--remount", user]
    if remount_in_background:
        subprocess.Popen(  # pylint: disable=consider-using-with
            command,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
        )
    else:
        subprocess.run(
            command,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            check=False,
        )


def setup_mount_dir_cagefs(path, added_by=None, mode=0o755, owner_id=None, group_id=None,
                           prefix='', remount_cagefs=False, remount_in_background=False):
    """
    Add mount point to /etc/cagefs/cagefs.mp

    :param path: Directory path to be added in cagefs.mp and mounted
                 from within setup_mount_dir_cagefs().
                 If this directory does not exist, then it is created.

    :param added_by: package or component, mount dir relates to, or whatever will
                     stay in cagefs.mp with "# added by..." comment

    :param mode: If is not None: Regardless of whether directory exists or not prior this call,
                 it's permissions will be set to mode.

    :param owner_id: Regardless of whether directory exists or not prior this call,
                     it's owner id will be set to.
                     If None, the owner won't be changed.

    :param group_id: Regardless of whether directory exists or not prior this call,
                     it's group id will be set to.
                     If None, the group won't be changed.

    :param prefix: Mount point prefix. Default is mount as RW.
                   Pass '!' to add read-only mount point.
                   Refer CageFS section at http://docs.cloudlinux.com/ for more options.

    :param remount_cagefs: If True, cagefs skeleton will be automatically
                           remounted to apply changes.

    :param remount_in_background: If True, cagefs remount will be done in separate
                    background process, without waiting for completion

    :returns: None

    Propagates native EnvironmentError if no CageFS installed or something else goes wrong.

    Raises CagefsMpConflict if path is already specified in cagefs.mp, but in a way which is opposite
    to mount_as_readonly param.
    """

    _mk_mount_dir_setup_perm(path, mode, owner_id, group_id)

    if not is_cagefs_present():
        return

    # Create cagefs.mp if absent. It will be merged when cagefsctl --init.
    if not os.path.exists(CAGEFS_MP_FILENAME):
        subprocess.run(
            [CAGEFSCTL_TOOL, "--create-mp"],
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            check=False,
        )

    add_new_line_to_cagefs_mp()
    # ^^
    # Hereafter we will not care if there was
    # 'no newline at the end of file'

    with open(CAGEFS_MP_FILENAME, "r+", encoding="utf-8") as f:
        new_item = CagefsMpItem(prefix + path).mode(mode)

        trim_nl_iter = (file_line.rstrip() for file_line in f)
        pre_exist_option = [x for x in trim_nl_iter if new_item.pre_exist_in(x)]

        if not pre_exist_option:
            f.seek(0, 2)  # 2: seek to the end of file

            if added_by is not None:
                # no newline is allowed
                added_by = added_by.strip()
                print("# next line is added by ", added_by, file=f)
            print(new_item, file=f)

            if remount_cagefs:
                _remount_cagefs(remount_in_background=remount_in_background)

        elif not new_item.is_compatible_by_prefix_with(pre_exist_option[-1]):
            raise CagefsMpConflict(new_item, pre_exist_option[-1])


def _get_cagefs_mp_lines():
    with open(CAGEFS_MP_FILENAME, "r", encoding="utf-8") as f:
        return f.readlines()


def _write_cagefs_mp_lines(lines):
    with open(CAGEFS_MP_FILENAME, "w", encoding="utf-8") as f:
        return f.writelines(lines)

# next line is added by
def add_new_line_to_cagefs_mp():
    """
    Add new line to the end of /etc/cagefs/cagefs.mp file if it is not there
    """
    lines = _get_cagefs_mp_lines()
    # file is not empty and last line in the file does not end with new line symbol ?
    if lines and lines[0] != '' and lines[-1][-1] != '\n':
        lines[-1] += '\n'
        _write_cagefs_mp_lines(lines)


def remove_mount_dir_cagefs(path, remount_cagefs=False, remount_in_background=False):
    """
    Remove mount points matching given path from cagefs.mp file
    :param str path: Path that should be removed from file.
    :param bool remount_cagefs: Remount cagefs skeleton or not
    :param remount_in_background: If True, cagefs remount will be done in separate
           background process, without waiting for completion
    :return: Nothing
    """
    lines = _get_cagefs_mp_lines()

    r = re.compile(rf'^[{CagefsMpItem.PREFIX_LIST}]?{re.escape(path)}(,\d+)?$')
    lines_with_excluded_path = [line for line in lines if not r.match(line)]

    # nothing to do if nothing found by pattern
    if len(lines) == len(lines_with_excluded_path):
        return

    _write_cagefs_mp_lines(lines_with_excluded_path)
    if remount_cagefs:
        _remount_cagefs(remount_in_background=remount_in_background)


def in_cagefs():
    """If this folder /var/.cagefs exists, it means process is inside cagefs"""
    return os.path.isdir('/var/.cagefs')


def _is_cagefs_enabled(user):
    """
    Check that cagefs enabled for user
    """
    try:
        cagefs_lib_dir = '/usr/share/cagefs/'
        if cagefs_lib_dir not in sys.path:
            sys.path.append(cagefs_lib_dir)
        import cagefsctl  # pylint: disable=import-outside-toplevel
    except ImportError:
        return False
    try:
        if not cagefsctl.is_user_enabled(user):
            return False
    except AttributeError as e:
        raise CagefsNotSupportedError(
            'ERROR: CageFS version is unsupported. Please update CageFS.'
        ) from e

    return True