lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/PreferenceActivityDetector.java

/*
 * Copyright (C) 2014 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.tools.lint.checks;

import static com.android.SdkConstants.ANDROID_URI;
import static com.android.SdkConstants.ATTR_NAME;
import static com.android.SdkConstants.ATTR_PACKAGE;
import static com.android.SdkConstants.TAG_ACTIVITY;
import static com.android.tools.lint.client.api.JavaParser.TYPE_STRING;

import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.android.tools.lint.client.api.JavaEvaluator;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Detector.JavaPsiScanner;
import com.android.tools.lint.detector.api.Detector.XmlScanner;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.JavaContext;
import com.android.tools.lint.detector.api.Location;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.android.tools.lint.detector.api.XmlContext;
import com.intellij.psi.PsiClass;
import com.intellij.psi.PsiMethod;

import org.w3c.dom.Element;

import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Ensures that PreferenceActivity and its subclasses are never exported.
 */
public class PreferenceActivityDetector extends Detector
        implements XmlScanner, JavaPsiScanner {
    public static final Issue ISSUE = Issue.create(
            "ExportedPreferenceActivity", //$NON-NLS-1$
            "PreferenceActivity should not be exported",
            "Fragment injection gives anyone who can send your PreferenceActivity an intent the "
                    + "ability to load any fragment, with any arguments, in your process.",
            Category.SECURITY,
            8,
            Severity.WARNING,
            new Implementation(
                    PreferenceActivityDetector.class,
                    EnumSet.of(Scope.MANIFEST, Scope.JAVA_FILE)))
            .addMoreInfo("http://securityintelligence.com/"
                    + "new-vulnerability-android-framework-fragment-injection");
    private static final String PREFERENCE_ACTIVITY = "android.preference.PreferenceActivity"; //$NON-NLS-1$
    private static final String IS_VALID_FRAGMENT = "isValidFragment"; //$NON-NLS-1$

    private final Map<String, Location.Handle> mExportedActivities =
            new HashMap<String, Location.Handle>();

    // ---- Implements XmlScanner ----

    @Override
    public Collection<String> getApplicableElements() {
        return Collections.singletonList(TAG_ACTIVITY);
    }

    @Override
    public void visitElement(@NonNull XmlContext context, @NonNull Element element) {
        if (SecurityDetector.getExported(element)) {
            String fqcn = getFqcn(element);
            if (fqcn != null) {
                if (fqcn.equals(PREFERENCE_ACTIVITY) &&
                        !context.getDriver().isSuppressed(context, ISSUE, element)) {
                    String message = "`PreferenceActivity` should not be exported";
                    context.report(ISSUE, element, context.getLocation(element), message);
                }
                mExportedActivities.put(fqcn, context.createLocationHandle(element));
            }
        }
    }

    private static String getFqcn(@NonNull Element activityElement) {
        String activityClassName = activityElement.getAttributeNS(ANDROID_URI, ATTR_NAME);

        if (activityClassName == null || activityClassName.isEmpty()) {
            return null;
        }

        // If the activity class name starts with a '.', it is shorthand for prepending the
        // package name specified in the manifest.
        if (activityClassName.startsWith(".")) {
            String pkg = activityElement.getOwnerDocument().getDocumentElement()
                    .getAttribute(ATTR_PACKAGE);
            if (pkg != null) {
                return pkg + activityClassName;
            } else {
                return null;
            }
        }

        return activityClassName;
    }

    // ---- Implements JavaScanner ----

    @Nullable
    @Override
    public List<String> applicableSuperClasses() {
        return Collections.singletonList(PREFERENCE_ACTIVITY);
    }

    @Override
    public void checkClass(@NonNull JavaContext context, @NonNull PsiClass declaration) {
        if (!context.getProject().getReportIssues()) {
            return;
        }
        JavaEvaluator evaluator = context.getEvaluator();
        String className = declaration.getQualifiedName();
        if (evaluator.extendsClass(declaration, PREFERENCE_ACTIVITY, false)
                && mExportedActivities.containsKey(className)) {
            // Ignore the issue if we target an API greater than 19 and the class in
            // question specifically overrides isValidFragment() and thus knowingly white-lists
            // valid fragments.
            if (context.getMainProject().getTargetSdk() >= 19
                    && overridesIsValidFragment(evaluator, declaration)) {
                return;
            }

            String message = String.format(
                    "`PreferenceActivity` subclass `%1$s` should not be exported",
                    className);
            Location location = mExportedActivities.get(className).resolve();
            context.report(ISSUE, declaration, location, message);
        }
    }

    private static boolean overridesIsValidFragment(
            @NonNull JavaEvaluator evaluator,
            @NonNull PsiClass resolvedClass) {
        for (PsiMethod method : resolvedClass.findMethodsByName(IS_VALID_FRAGMENT, false)) {
            if (evaluator.parametersMatch(method, TYPE_STRING)) {
                return true;
            }
        }
        return false;
    }
}