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Filename : mls.py
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# Copyright 2016, Tresys Technology, LLC
# Copyright 2018, Chris PeBenito <pebenito@ieee.org>
#
# SPDX-License-Identifier: LGPL-2.1-only
#
from collections import defaultdict
from typing import NamedTuple, Set

from ..policyrep import Category, Level, LevelDecl, Range, Sensitivity

from .descriptors import DiffResultDescriptor
from .difference import Difference, SymbolWrapper, Wrapper
from .typing import SymbolCache

_cats_cache: SymbolCache[Category] = defaultdict(dict)
_sens_cache: SymbolCache[Sensitivity] = defaultdict(dict)


class ModifiedCategory(NamedTuple):

    """Difference details for a modified category."""

    added_aliases: Set[str]
    removed_aliases: Set[str]
    matched_aliases: Set[str]


class ModifiedSensitivity(NamedTuple):

    """Difference details for a modified sensitivity."""

    added_aliases: Set[str]
    removed_aliases: Set[str]
    matched_aliases: Set[str]


class ModifiedLevelDecl(NamedTuple):

    """Difference details for a modified level declaration."""

    level: LevelDecl
    added_categories: Set[Category]
    removed_categories: Set[Category]
    matched_categories: Set[Category]


def category_wrapper_factory(category: Category) -> SymbolWrapper[Category]:
    """
    Wrap category from the specified policy.

    This caches results to prevent duplicate wrapper
    objects in memory.
    """
    try:
        return _cats_cache[category.policy][category]
    except KeyError:
        c = SymbolWrapper(category)
        _cats_cache[category.policy][category] = c
        return c


def sensitivity_wrapper_factory(sensitivity: Sensitivity) -> SymbolWrapper[Sensitivity]:
    """
    Wrap sensitivity from the specified policy.

    This caches results to prevent duplicate wrapper
    objects in memory.
    """
    try:
        return _sens_cache[sensitivity.policy][sensitivity]
    except KeyError:
        c = SymbolWrapper(sensitivity)
        _sens_cache[sensitivity.policy][sensitivity] = c
        return c


class CategoriesDifference(Difference):

    """Determine the difference in categories between two policies."""

    added_categories = DiffResultDescriptor("diff_categories")
    removed_categories = DiffResultDescriptor("diff_categories")
    modified_categories = DiffResultDescriptor("diff_categories")

    def diff_categories(self) -> None:
        """Generate the difference in categories between the policies."""

        self.log.info(
            "Generating category differences from {0.left_policy} to {0.right_policy}".format(self))

        self.added_categories, self.removed_categories, matched_categories = self._set_diff(
            (category_wrapper_factory(c) for c in self.left_policy.categories()),
            (category_wrapper_factory(c) for c in self.right_policy.categories()))

        self.modified_categories = dict()

        for left_category, right_category in matched_categories:
            # Criteria for modified categories
            # 1. change to aliases
            added_aliases, removed_aliases, matched_aliases = self._set_diff(
                left_category.aliases(), right_category.aliases(), unwrap=False)

            if added_aliases or removed_aliases:
                self.modified_categories[left_category] = ModifiedCategory(added_aliases,
                                                                           removed_aliases,
                                                                           matched_aliases)

    #
    # Internal functions
    #
    def _reset_diff(self) -> None:
        """Reset diff results on policy changes."""
        self.log.debug("Resetting category differences")
        self.added_categories = None
        self.removed_categories = None
        self.modified_categories = None


class SensitivitiesDifference(Difference):

    """Determine the difference in sensitivities between two policies."""

    added_sensitivities = DiffResultDescriptor("diff_sensitivities")
    removed_sensitivities = DiffResultDescriptor("diff_sensitivities")
    modified_sensitivities = DiffResultDescriptor("diff_sensitivities")

    def diff_sensitivities(self) -> None:
        """Generate the difference in sensitivities between the policies."""

        self.log.info(
            "Generating sensitivity differences from {0.left_policy} to {0.right_policy}".
            format(self))

        self.added_sensitivities, self.removed_sensitivities, matched_sensitivities = \
            self._set_diff(
                (sensitivity_wrapper_factory(s) for s in self.left_policy.sensitivities()),
                (sensitivity_wrapper_factory(s) for s in self.right_policy.sensitivities()))

        self.modified_sensitivities = dict()

        for left_sens, right_sens in matched_sensitivities:
            # Criteria for modified sensitivities
            # 1. change to aliases
            added_aliases, removed_aliases, matched_aliases = self._set_diff(
                left_sens.aliases(), right_sens.aliases(), unwrap=False)

            if added_aliases or removed_aliases:
                self.modified_sensitivities[left_sens] = ModifiedSensitivity(added_aliases,
                                                                             removed_aliases,
                                                                             matched_aliases)

    #
    # Internal functions
    #
    def _reset_diff(self) -> None:
        """Reset diff results on policy changes."""
        self.log.debug("Resetting sensitivity differences")
        self.added_sensitivities = None
        self.removed_sensitivities = None
        self.modified_sensitivities = None


class LevelDeclsDifference(Difference):

    """Determine the difference in levels between two policies."""

    added_levels = DiffResultDescriptor("diff_levels")
    removed_levels = DiffResultDescriptor("diff_levels")
    modified_levels = DiffResultDescriptor("diff_levels")

    def diff_levels(self) -> None:
        """Generate the difference in levels between the policies."""

        self.log.info(
            "Generating level decl differences from {0.left_policy} to {0.right_policy}".
            format(self))

        self.added_levels, self.removed_levels, matched_levels = \
            self._set_diff(
                (LevelDeclWrapper(s) for s in self.left_policy.levels()),
                (LevelDeclWrapper(s) for s in self.right_policy.levels()))

        self.modified_levels = []

        for left_level, right_level in matched_levels:
            # Criteria for modified levels
            # 1. change to allowed categories
            added_categories, removed_categories, matched_categories = self._set_diff(
                (category_wrapper_factory(c) for c in left_level.categories()),
                (category_wrapper_factory(c) for c in right_level.categories()))

            if added_categories or removed_categories:
                self.modified_levels.append(ModifiedLevelDecl(
                    left_level, added_categories, removed_categories, matched_categories))

    #
    # Internal functions
    #
    def _reset_diff(self) -> None:
        """Reset diff results on policy changes."""
        self.log.debug("Resetting sensitivity differences")
        self.added_levels = None
        self.removed_levels = None
        self.modified_levels = None


class LevelDeclWrapper(Wrapper[LevelDecl]):

    """Wrap level declarations to allow comparisons."""

    __slots__ = ("sensitivity",)

    def __init__(self, level: LevelDecl) -> None:
        self.origin = level
        self.sensitivity = sensitivity_wrapper_factory(level.sensitivity)
        self.key = hash(level)

    def __hash__(self):
        return self.key

    def __eq__(self, other):
        # non-MLS policies have no level declarations so there
        # should be no AttributeError possiblity here
        return self.sensitivity == other.sensitivity

    def __lt__(self, other):
        return self.sensitivity < other.sensitivity


class LevelWrapper(Wrapper[Level]):

    """Wrap levels to allow comparisons."""

    __slots__ = ("sensitivity", "categories")

    def __init__(self, level: Level) -> None:
        self.origin = level
        self.sensitivity = sensitivity_wrapper_factory(level.sensitivity)
        self.categories = set(category_wrapper_factory(c) for c in level.categories())

    def __hash__(self):
        return hash(self.origin)

    def __eq__(self, other):
        try:
            return self.sensitivity == other.sensitivity and \
                self.categories == other.categories
        except AttributeError:
            # comparing an MLS policy to non-MLS policy will result in
            # other being None
            return False

    def __lt__(self, other):
        try:
            return self.sensitivity < other.sensitivity and \
                self.categories < other.categories
        except AttributeError:
            # comparing an MLS policy to non-MLS policy will result in
            # other being None
            return False


class RangeWrapper(Wrapper[Range]):

    """
    Wrap ranges to allow comparisons.

    This only compares the low and high levels of the range.
    It does not detect additions/removals/modifications
    to levels between the low and high levels of the range.
    """

    __slots__ = ("low", "high")

    def __init__(self, range_: Range) -> None:
        self.origin = range_
        self.low = LevelWrapper(range_.low)
        self.high = LevelWrapper(range_.high)

    def __hash__(self):
        return hash(self.origin)

    def __eq__(self, other):
        try:
            return self.low == other.low and \
                self.high == other.high
        except AttributeError:
            # comparing an MLS policy to non-MLS policy will result in
            # other being None
            return False

    def __lt__(self, other):
        try:
            return self.low < other.low and \
                self.high < other.high
        except AttributeError:
            # comparing an MLS policy to non-MLS policy will result in
            # other being None
            return False