rn: evaluate config.js in a sandboxed environment

We are downloading code off the Internet and executing it on the user's device,
so run it sandboxed to avoid potential bad actors.

Since it's impossible to eval() safely in JS and React Native doesn't offer
something akin to Node's vm module, here we are rolling our own.

On Android it uses the Duktape JavaScript engine and on iOS the builtin
JavaScriptCore engine. The extra JS engine is *only* used for evaluating the
downloaded code and returning a JSON string which is then passed back to RN.

android/sdk/build.gradle

 
     implementation 'com.dropbox.core:dropbox-core-sdk:3.0.8'
     implementation 'com.jakewharton.timber:timber:4.7.1'
+    implementation 'com.squareup.duktape:duktape-android:1.3.0'
 
     if (!rootProject.ext.libreBuild) {
         implementation 'com.amplitude:android-sdk:2.14.1'

android/sdk/src/main/java/org/jitsi/meet/sdk/JavaScriptSandboxModule.java

+/*
+ * Copyright @ 2019-present 8x8, Inc.
+ *
+ * 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 org.jitsi.meet.sdk;
+
+import com.facebook.react.bridge.Promise;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.module.annotations.ReactModule;
+import com.squareup.duktape.Duktape;
+
+@ReactModule(name = JavaScriptSandboxModule.NAME)
+class JavaScriptSandboxModule extends ReactContextBaseJavaModule {
+    public static final String NAME = "JavaScriptSandbox";
+
+    public JavaScriptSandboxModule(ReactApplicationContext reactContext) {
+        super(reactContext);
+    }
+
+    /**
+     * Evaluates the given code in a Duktape VM.
+     * @param code - The code that needs to evaluated.
+     * @param promise - Resolved with the output in case of success or rejected with an exception
+     *                in case of failure.
+     */
+    @ReactMethod
+    public void evaluate(String code, Promise promise) {
+        Duktape vm = Duktape.create();
+        try {
+            Object res = vm.evaluate(code);
+            promise.resolve(res.toString());
+        } catch (Throwable tr) {
+            promise.reject(tr);
+        } finally {
+            vm.close();
+        }
+    }
+
+    @Override
+    public String getName() {
+        return NAME;
+    }
+}

android/sdk/src/main/java/org/jitsi/meet/sdk/ReactInstanceManagerHolder.java

                 new AudioModeModule(reactContext),
                 new DropboxModule(reactContext),
                 new ExternalAPIModule(reactContext),
+                new JavaScriptSandboxModule(reactContext),
                 new LocaleDetector(reactContext),
                 new LogBridgeModule(reactContext),
                 new PictureInPictureModule(reactContext),

ios/sdk/sdk.xcodeproj/project.pbxproj

 		C69EFA0E209A0F660027712B /* JMCallKitListener.swift in Sources */ = {isa = PBXBuildFile; fileRef = C69EFA0B209A0F660027712B /* JMCallKitListener.swift */; };
 		C6A34261204EF76800E062DD /* DragGestureController.swift in Sources */ = {isa = PBXBuildFile; fileRef = C6A3425E204EF76800E062DD /* DragGestureController.swift */; };
 		C6CC49AF207412CF000DFA42 /* PiPViewCoordinator.swift in Sources */ = {isa = PBXBuildFile; fileRef = C6CC49AE207412CF000DFA42 /* PiPViewCoordinator.swift */; };
+		DE438CDA2350934700DD541D /* JavaScriptSandbox.m in Sources */ = {isa = PBXBuildFile; fileRef = DE438CD82350934700DD541D /* JavaScriptSandbox.m */; };
 		DE65AACA2317FFCD00290BEC /* LogUtils.h in Headers */ = {isa = PBXBuildFile; fileRef = DE65AAC92317FFCD00290BEC /* LogUtils.h */; };
 		DE65AACC2318028300290BEC /* JitsiMeetBaseLogHandler+Private.h in Headers */ = {isa = PBXBuildFile; fileRef = DE65AACB2318028300290BEC /* JitsiMeetBaseLogHandler+Private.h */; };
 		DE762DB422AFDE76000DEBD6 /* JitsiMeetUserInfo.h in Headers */ = {isa = PBXBuildFile; fileRef = DE762DB322AFDE76000DEBD6 /* JitsiMeetUserInfo.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		C6A3425E204EF76800E062DD /* DragGestureController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DragGestureController.swift; sourceTree = "<group>"; };
 		C6CC49AE207412CF000DFA42 /* PiPViewCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PiPViewCoordinator.swift; sourceTree = "<group>"; };
 		C6F99C13204DB63D0001F710 /* JitsiMeetView+Private.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "JitsiMeetView+Private.h"; sourceTree = "<group>"; };
+		DE438CD82350934700DD541D /* JavaScriptSandbox.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = JavaScriptSandbox.m; sourceTree = "<group>"; };
 		DE65AAC92317FFCD00290BEC /* LogUtils.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = LogUtils.h; sourceTree = "<group>"; };
 		DE65AACB2318028300290BEC /* JitsiMeetBaseLogHandler+Private.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "JitsiMeetBaseLogHandler+Private.h"; sourceTree = "<group>"; };
 		DE762DB322AFDE76000DEBD6 /* JitsiMeetUserInfo.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = JitsiMeetUserInfo.h; sourceTree = "<group>"; };
 				A4A934E7212F3AB8001E9388 /* dropbox */,
 				0BA13D301EE83FF8007BEF7F /* ExternalAPI.m */,
 				0BD906E91EC0C00300C8C18E /* Info.plist */,
+				DE438CD82350934700DD541D /* JavaScriptSandbox.m */,
 				0BD906E81EC0C00300C8C18E /* JitsiMeet.h */,
 				DEFE535821FB311F00011A3A /* JitsiMeet+Private.h */,
 				DEFE535321FB1BF800011A3A /* JitsiMeet.m */,
 				C69EFA0E209A0F660027712B /* JMCallKitListener.swift in Sources */,
 				0B412F191EDEC65D00B1A0A6 /* JitsiMeetView.m in Sources */,
 				DEFE535421FB1BF800011A3A /* JitsiMeet.m in Sources */,
+				DE438CDA2350934700DD541D /* JavaScriptSandbox.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
 				INFOPLIST_FILE = src/Info.plist;
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
 				IPHONEOS_DEPLOYMENT_TARGET = 10.0;
-				LD_RUNPATH_SEARCH_PATHS = (
-					"$(inherited)",
-					"@executable_path/Frameworks",
-					"@loader_path/Frameworks",
-				);
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = org.jitsi.JitsiMeetSDK.ios;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				INFOPLIST_FILE = src/Info.plist;
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
 				IPHONEOS_DEPLOYMENT_TARGET = 10.0;
-				LD_RUNPATH_SEARCH_PATHS = (
-					"$(inherited)",
-					"@executable_path/Frameworks",
-					"@loader_path/Frameworks",
-				);
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = org.jitsi.JitsiMeetSDK.ios;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";

ios/sdk/src/JavaScriptSandbox.m

+/*
+ * Copyright @ 2019-present 8x8, Inc.
+ *
+ * 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.
+ */
+
+@import JavaScriptCore;
+
+#import <React/RCTBridgeModule.h>
+
+
+@interface JavaScriptSandbox : NSObject<RCTBridgeModule>
+@end
+
+@implementation JavaScriptSandbox
+
+RCT_EXPORT_MODULE();
+
++ (BOOL)requiresMainQueueSetup {
+    return NO;
+}
+
+#pragma mark - Exported methods
+
+RCT_EXPORT_METHOD(evaluate:(NSString *)code
+                  resolve:(RCTPromiseResolveBlock)resolve
+                   reject:(RCTPromiseRejectBlock)reject) {
+    __block BOOL hasError = NO;
+    JSContext *ctx = [[JSContext alloc] init];
+    ctx.exceptionHandler = ^(JSContext *context, JSValue *exception) {
+        hasError = YES;
+        reject(@"evaluate", [exception toString], nil);
+    };
+    JSValue *ret = [ctx evaluateScript:code];
+    if (!hasError) {
+        NSString *result = [ret toString];
+        if (result == nil) {
+            reject(@"evaluate", @"Error in string coercion", nil);
+        } else {
+            resolve(result);
+        }
+    }
+}
+
+@end

react/features/base/lib-jitsi-meet/functions.js → react/features/base/lib-jitsi-meet/functions.any.js

 // @flow
 
 import { toState } from '../redux';
-import { loadScript } from '../util';
-
 import JitsiMeetJS from './_';
-import logger from './logger';
-
-declare var APP: Object;
 
 const JitsiConferenceErrors = JitsiMeetJS.errors.conference;
 const JitsiConnectionErrors = JitsiMeetJS.errors.connection;
             || error === JitsiConnectionErrors.OTHER_ERROR
             || error === JitsiConnectionErrors.SERVER_ERROR);
 }
-
-/**
- * Loads config.js from a specific remote server.
- *
- * @param {string} url - The URL to load.
- * @returns {Promise<Object>}
- */
-export function loadConfig(url: string): Promise<Object> {
-    let promise;
-
-    if (typeof APP === 'undefined') {
-        promise
-            = loadScript(url, 2.5 * 1000 /* Timeout in ms */)
-                .then(() => {
-                    const { config } = window;
-
-                    // We don't want to pollute the global scope.
-                    window.config = undefined;
-
-                    if (typeof config !== 'object') {
-                        throw new Error('window.config is not an object');
-                    }
-
-                    return config;
-                })
-                .catch(err => {
-                    logger.error(`Failed to load config from ${url}`, err);
-
-                    throw err;
-                });
-    } else {
-        // Return "the config.js file" from the global scope - that is how the
-        // Web app on both the client and the server was implemented before the
-        // React Native app was even conceived.
-        promise = Promise.resolve(window.config);
-    }
-
-    return promise;
-}

react/features/base/lib-jitsi-meet/functions.native.js

+// @flow
+
+import { NativeModules } from 'react-native';
+
+import { loadScript } from '../util';
+import logger from './logger';
+
+export * from './functions.any';
+
+const { JavaScriptSandbox } = NativeModules;
+
+/**
+ * Loads config.js from a specific remote server.
+ *
+ * @param {string} url - The URL to load.
+ * @returns {Promise<Object>}
+ */
+export async function loadConfig(url: string): Promise<Object> {
+    try {
+        const configTxt = await loadScript(url, 2.5 * 1000 /* Timeout in ms */, true /* skipeval */);
+        const configJson = await JavaScriptSandbox.evaluate(`${configTxt}\nJSON.stringify(config);`);
+        const config = JSON.parse(configJson);
+
+        if (typeof config !== 'object') {
+            throw new Error('config is not an object');
+        }
+
+        logger.info(`Config loaded from ${url}`);
+
+        return config;
+    } catch (err) {
+        logger.error(`Failed to load config from ${url}`, err);
+
+        throw err;
+    }
+}

react/features/base/lib-jitsi-meet/functions.web.js

+// @flow
+
+export * from './functions.any';
+
+/**
+ * Loads config.js from a specific remote server.
+ *
+ * @param {string} url - The URL to load.
+ * @returns {Promise<Object>}
+ */
+export async function loadConfig(url: string): Promise<Object> { // eslint-disable-line no-unused-vars
+    // Return "the config.js file" from the global scope - that is how the
+    // Web app on both the client and the server was implemented before the
+    // React Native app was even conceived.
+    return window.config;
+}