| /* |
| * Copyright (C) 2019 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.android.server.integrity.engine; |
| |
| import static android.content.integrity.Rule.DENY; |
| import static android.content.integrity.Rule.FORCE_ALLOW; |
| |
| import android.annotation.NonNull; |
| import android.content.integrity.AppInstallMetadata; |
| import android.content.integrity.AtomicFormula; |
| import android.content.integrity.CompoundFormula; |
| import android.content.integrity.Formula; |
| import android.content.integrity.Rule; |
| import android.util.Slog; |
| |
| import com.android.server.integrity.model.IntegrityCheckResult; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| /** |
| * A helper class for evaluating rules against app install metadata to find if there are matching |
| * rules. |
| */ |
| final class RuleEvaluator { |
| |
| private static final String TAG = "RuleEvaluator"; |
| |
| /** |
| * Match the list of rules against an app install metadata. |
| * |
| * <p>Rules must be in disjunctive normal form (DNF). A rule should contain AND'ed formulas |
| * only. All rules are OR'ed together by default. |
| * |
| * @param rules The list of rules to evaluate. |
| * @param appInstallMetadata Metadata of the app to be installed, and to evaluate the rules |
| * against. |
| * @return result of the integrity check |
| */ |
| @NonNull |
| static IntegrityCheckResult evaluateRules( |
| List<Rule> rules, AppInstallMetadata appInstallMetadata) { |
| List<Rule> matchedRules = new ArrayList<>(); |
| for (Rule rule : rules) { |
| if (isConjunctionOfFormulas(rule.getFormula()) |
| && rule.getFormula().isSatisfied(appInstallMetadata)) { |
| matchedRules.add(rule); |
| } |
| } |
| |
| boolean denied = false; |
| Rule denyRule = null; |
| for (Rule rule : matchedRules) { |
| switch (rule.getEffect()) { |
| case DENY: |
| if (!denied) { |
| denied = true; |
| denyRule = rule; |
| } |
| break; |
| case FORCE_ALLOW: |
| return IntegrityCheckResult.allow(rule); |
| default: |
| Slog.e(TAG, "Matched an unknown effect rule: " + rule); |
| return IntegrityCheckResult.allow(); |
| } |
| } |
| return denied ? IntegrityCheckResult.deny(denyRule) : IntegrityCheckResult.allow(); |
| } |
| |
| private static boolean isConjunctionOfFormulas(Formula formula) { |
| if (formula == null) { |
| return false; |
| } |
| if (isAtomicFormula(formula)) { |
| return true; |
| } |
| CompoundFormula compoundFormula = (CompoundFormula) formula; |
| return compoundFormula.getConnector() == CompoundFormula.AND |
| && compoundFormula.getFormulas().stream().allMatch(RuleEvaluator::isAtomicFormula); |
| } |
| |
| private static boolean isAtomicFormula(Formula formula) { |
| if (formula instanceof AtomicFormula) { |
| return true; |
| } |
| CompoundFormula compoundFormula = (CompoundFormula) formula; |
| return compoundFormula.getConnector() == CompoundFormula.NOT |
| && compoundFormula.getFormulas().get(0) instanceof AtomicFormula; |
| } |
| } |