AddJavascriptInterfaceDetector.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.klint.checks;


import static com.android.tools.klint.client.api.JavaParser.TYPE_OBJECT;
import static com.android.tools.klint.client.api.JavaParser.TYPE_STRING;

import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.android.tools.klint.client.api.JavaEvaluator;
import com.android.tools.klint.detector.api.Category;
import com.android.tools.klint.detector.api.Detector;
import com.android.tools.klint.detector.api.Implementation;
import com.android.tools.klint.detector.api.Issue;
import com.android.tools.klint.detector.api.JavaContext;
import com.android.tools.klint.detector.api.Scope;
import com.android.tools.klint.detector.api.Severity;

import org.jetbrains.uast.UCallExpression;
import org.jetbrains.uast.UElement;
import org.jetbrains.uast.UMethod;
import org.jetbrains.uast.visitor.UastVisitor;

import java.util.Collections;
import java.util.List;

/**
 * Ensures that addJavascriptInterface is not called for API levels below 17.
 */
public class AddJavascriptInterfaceDetector extends Detector implements Detector.UastScanner {
    public static final Issue ISSUE = Issue.create(
            "AddJavascriptInterface", //$NON-NLS-1$
            "addJavascriptInterface Called",
            "For applications built for API levels below 17, `WebView#addJavascriptInterface` "
                    + "presents a security hazard as JavaScript on the target web page has the "
                    + "ability to use reflection to access the injected object's public fields and "
                    + "thus manipulate the host application in unintended ways.",
            Category.SECURITY,
            9,
            Severity.WARNING,
            new Implementation(
                    AddJavascriptInterfaceDetector.class,
                    Scope.JAVA_FILE_SCOPE)).
            addMoreInfo(
                    "https://labs.mwrinfosecurity.com/blog/2013/09/24/webview-addjavascriptinterface-remote-code-execution/");

    private static final String WEB_VIEW = "android.webkit.WebView"; //$NON-NLS-1$
    private static final String ADD_JAVASCRIPT_INTERFACE = "addJavascriptInterface"; //$NON-NLS-1$

    // ---- Implements UastScanner ----

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

    @Override
    public void visitMethod(@NonNull JavaContext context, @Nullable UastVisitor visitor,
            @NonNull UCallExpression call, @NonNull UMethod method) {
        // Ignore the issue if we never build for any API less than 17.
        if (context.getMainProject().getMinSdk() >= 17) {
            return;
        }

        JavaEvaluator evaluator = context.getEvaluator();
        if (!evaluator.methodMatches(method, WEB_VIEW, true, TYPE_OBJECT, TYPE_STRING)) {
            return;
        }

        String message = "`WebView.addJavascriptInterface` should not be called with minSdkVersion < 17 for security reasons: " +
                "JavaScript can use reflection to manipulate application";
        UElement reportElement = call.getMethodIdentifier();
        if (reportElement == null) {
            reportElement = call;
        }
        context.reportUast(ISSUE, reportElement, context.getUastNameLocation(reportElement), message);
    }
}