| /* |
| * 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 android.util.Slog; |
| |
| import com.android.server.integrity.model.AppInstallMetadata; |
| import com.android.server.integrity.model.AtomicFormula; |
| import com.android.server.integrity.model.Formula; |
| import com.android.server.integrity.model.OpenFormula; |
| import com.android.server.integrity.model.Rule; |
| |
| 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 A rule matching the metadata. If there are multiple matching rules, returns any. If |
| * no rules are matching, returns {@link Rule#EMPTY}. |
| */ |
| static Rule evaluateRules(List<Rule> rules, AppInstallMetadata appInstallMetadata) { |
| for (Rule rule : rules) { |
| if (isConjunctionOfFormulas(rule.getFormula()) && isMatch(rule, appInstallMetadata)) { |
| return rule; |
| } |
| } |
| return Rule.EMPTY; |
| } |
| |
| /** |
| * Match a rule against app install metadata. |
| */ |
| private static boolean isMatch(Rule rule, AppInstallMetadata appInstallMetadata) { |
| return isMatch(rule.getFormula(), appInstallMetadata); |
| } |
| |
| private static boolean isMatch(Formula formula, AppInstallMetadata appInstallMetadata) { |
| if (formula instanceof AtomicFormula) { |
| AtomicFormula atomicFormula = (AtomicFormula) formula; |
| switch (atomicFormula.getKey()) { |
| case PACKAGE_NAME: |
| return atomicFormula.isMatch(appInstallMetadata.getPackageName()); |
| case APP_CERTIFICATE: |
| return atomicFormula.isMatch(appInstallMetadata.getAppCertificate()); |
| case INSTALLER_NAME: |
| return atomicFormula.isMatch(appInstallMetadata.getInstallerName()); |
| case INSTALLER_CERTIFICATE: |
| return atomicFormula.isMatch(appInstallMetadata.getInstallerCertificate()); |
| case VERSION_CODE: |
| return atomicFormula.isMatch(appInstallMetadata.getVersionCode()); |
| case PRE_INSTALLED: |
| return atomicFormula.isMatch(appInstallMetadata.isPreInstalled()); |
| default: |
| Slog.i(TAG, String.format("Returned no match for unknown key %s", |
| atomicFormula.getKey())); |
| return false; |
| } |
| } else if (formula instanceof OpenFormula) { |
| OpenFormula openFormula = (OpenFormula) formula; |
| // A rule is in disjunctive normal form, so there are no OR connectors. |
| switch (openFormula.getConnector()) { |
| case NOT: |
| // NOT connector has only 1 formula attached. |
| return !isMatch(openFormula.getFormulas().get(0), appInstallMetadata); |
| case AND: |
| return openFormula.getFormulas().stream().allMatch( |
| subFormula -> isMatch(subFormula, appInstallMetadata)); |
| default: |
| Slog.i(TAG, String.format("Returned no match for unknown connector %s", |
| openFormula.getConnector())); |
| return false; |
| } |
| } |
| |
| return false; |
| } |
| |
| private static boolean isConjunctionOfFormulas(Formula formula) { |
| if (formula == null) { |
| return false; |
| } |
| if (isAtomicFormula(formula)) { |
| return true; |
| } |
| OpenFormula openFormula = (OpenFormula) formula; |
| return openFormula.getConnector() == OpenFormula.Connector.AND |
| && openFormula.getFormulas().stream().allMatch(RuleEvaluator::isAtomicFormula); |
| } |
| |
| private static boolean isAtomicFormula(Formula formula) { |
| if (formula instanceof AtomicFormula) { |
| return true; |
| } |
| OpenFormula openFormula = (OpenFormula) formula; |
| return openFormula.getConnector() == OpenFormula.Connector.NOT |
| && openFormula.getFormulas().get(0) instanceof AtomicFormula; |
| } |
| } |