Refactored XSS filter into an asynchronous worker to better handle DOS attempts.

src/lib/Timing.js

@@ -15,7 +15,7 @@ class Timing {
   }
 
   async pause() {
-    if (this.interrupted) throw new TimingException("Interrupted");
+    if (this.interrupted) throw new TimingException("Timing: interrupted");
     let now = Date.now();
     this.calls++;
     let sinceLastCall = now - this.lastCall;
@@ -28,7 +28,7 @@ class Timing {
     if (now - this.lastPause > this.workSlot || this.calls > this.maxCalls) {
       this.tooLong = this.elapsed >= this.longTime;
       if (this.tooLong && this.fatalTimeout) {
-        throw new TimingException(`Exceeded ${this.longTime}ms timeout`);
+        throw new TimingException(`Timing: exceeded ${this.longTime}ms timeout`);
       }
       this.calls = 0;
       await Timing.sleep(this.pauseTime);

src/lib/log.js

@@ -1,6 +1,8 @@
 
 {
-  let PREFIX = `[${browser.runtime.getManifest().name}]`;
+  let PREFIX = typeof browser === "object"
+    ? `[${browser.runtime.getManifest().name}]` : '';
+
   let debugCount = 0;
 
   function log(msg, ...rest) {

src/test/XSS_test.js

@@ -1,5 +1,5 @@
 if (UA.isMozilla) {
-  let y = async (url, originUrl = '') => await XSS.maybe({originUrl, url, method: "GET"});
+  let y = async (url, originUrl = '') => await XSS.maybe(XSS.parseRequest({originUrl, url, method: "GET"}));
   let n = async (...args) => !await y(...args);
   Promise.all([
       () => y("https://noscript.net/<script"),

src/xss/Exceptions.js

@@ -52,14 +52,14 @@ XSS.Exceptions = (() => {
       // destination or @source matching legacy regexp
       if (this.legacyExceptions &&
           (this.legacyExceptions.test(unescapedDest) &&
-          !this.isBadException(destObj.hostname) ||
+          !this.isBadException(xssReq.destDomain) ||
           this.legacyExceptions.test("@" + unescape(srcUrl))
         )) {
         logEx("Legacy exception", this.legacyExceptions);
         return true;
       }
 
-      if (!srcObj && isGet) {
+      if (!srcOrigin && isGet) {
         if (/^https?:\/\/msdn\.microsoft\.com\/query\/[^<]+$/.test(unescapedDest)) {
           return true; // MSDN from Microsoft VS
         }

src/xss/InjectionCheckWorker.js

@@ -0,0 +1,81 @@
+let include = src => {
+  if (Array.isArray(src)) importScripts(...src);
+  else importScripts(src);
+}
+
+let XSS = {};
+include("/lib/log.js");
+
+for (let logType of ["log", "debug", "error"]) {
+  this[logType] = (...log) => {
+    postMessage({log, logType});
+  }
+}
+
+include("InjectionChecker.js");
+Entities = {
+  convertAll(s) { return s },
+};
+
+{
+  let timingsMap = new Map();
+
+  let Handlers = {
+    async check({xssReq, skip}) {
+      let {destUrl, unparsedRequest: request, debugging} = xssReq;
+      let {
+        skipParams,
+        skipRx
+      } = skip;
+      let ic = new (await XSS.InjectionChecker)();
+
+      if (debugging) {
+        ic.logEnabled = true;
+        debug("[XSS] InjectionCheckWorker started in %s ms (%s).",
+          Date.now() - xssReq.timestamp, destUrl);
+      } else {
+        debug = () => {};
+      }
+
+      let {timing} = ic;
+      timingsMap.set(request.requestId, timing);
+      timing.fatalTimeout = true;
+
+      let postInjection = xssReq.isPost &&
+          request.requestBody && request.requestBody.formData &&
+          await ic.checkPost(request.requestBody.formData, skipParams);
+
+      let protectName = ic.nameAssignment;
+      let urlInjection = await ic.checkUrl(destUrl, skipRx);
+      protectName = protectName || ic.nameAssignment;
+      if (timing.tooLong) {
+        log("[XSS] Long check (%s ms) - %s", timing.elapsed, JSON.stringify(xssReq));
+      } else if (debugging) {
+        debug("[XSS] InjectionCheckWorker done in %s ms (%s).",
+          Date.now() - xssReq.timestamp, destUrl);
+      }
+
+      postMessage(!(protectName || postInjection || urlInjection) ? null
+        : { protectName, postInjection, urlInjection }
+      );
+    },
+
+    requestDone({requestId}) {
+      let timing = timingsMap.get(requestId);
+      if (timing) {
+        timing.interrupted = true;
+        timingsMap.delete(requestId);
+      }
+    }
+  }
+
+  onmessage = async e => {
+    let msg = e.data;
+    if (msg.handler in Handlers) try {
+      await Handlers[msg.handler](msg);
+    } catch (e) {
+      postMessage({error: e});
+    }
+  }
+
+}

src/xss/InjectionChecker.js

@@ -1,6 +1,6 @@
-debug("Initializing InjectionChecker");
 XSS.InjectionChecker = (async () => {
   await include([
+    "/common/SyntaxChecker.js",
     "/lib/Base64.js",
     "/lib/Timing.js",
     "/xss/FlashIdiocy.js",
@@ -1031,7 +1031,7 @@ XSS.InjectionChecker = (async () => {
         return true;
 
       if (s.indexOf("&") !== -1) {
-        let unent = Entities.convertAll(s);
+        let unent = await Entities.convertAll(s);
         if (unent !== s && await this._checkRecursive(unent, depth)) return true;
       }
 
@@ -1050,7 +1050,7 @@ XSS.InjectionChecker = (async () => {
         return true;
 
       if (/[\u0000-\u001f]|&#/.test(unescaped)) {
-        let unent = Entities.convertAll(unescaped.replace(/[\u0000-\u001f]+/g, ''));
+        let unent = await Entities.convertAll(unescaped.replace(/[\u0000-\u001f]+/g, ''));
         if (unescaped != unent && await this._checkRecursive(unent, depth)) {
           this.log("Trash-stripped nested URL match!");
           return true;

src/xss/XSS.js

@@ -4,8 +4,8 @@ var XSS = (() => {
 
   const ABORT = {cancel: true}, ALLOW = {};
 
+  let workersMap = new Map();
   let promptsMap = new Map();
-  let timingsMap = new Map();
 
   async function getUserResponse(xssReq) {
     let {originKey} = xssReq;
@@ -23,10 +23,11 @@ var XSS = (() => {
   }
 
   function doneListener(request) {
-    let timing = timingsMap.get(request.id);
-    if (timing) {
-      timing.interrupted = true;
-      timingsMap.delete(request.id);
+    let {requestId} = request;
+    let worker = workersMap.get(requestId);
+    if (worker) {
+      worker.terminate();
+      workersMap.delete(requestId);
     }
   }
 
@@ -58,7 +59,7 @@ var XSS = (() => {
       data = [];
     } catch (e) {
       error(e, "XSS filter processing %o", xssReq);
-      if (e instanceof TimingException) {
+      if (/^Timing:/.test(e.message)  && !/\btimeout\b/i.test(e.message)) {
         // we don't want prompts if the request expired / errored first
         return ABORT;
       }
@@ -125,6 +126,21 @@ var XSS = (() => {
     }
   };
 
+  function parseUrl(url) {
+    let u = new URL(url);
+    // make it cloneable
+    return {
+      href: u.href,
+      protocol: u.protocol,
+      hostname: u.hostname,
+      port: u.port,
+      origin: u.origin,
+      pathname: u.pathname,
+      search: u.search,
+      hash: u.hash,
+    };
+  }
+
   return {
     async start() {
       if (!UA.isMozilla) return; // async webRequest is supported on Mozilla only
@@ -166,7 +182,6 @@ var XSS = (() => {
       }
     },
 
-
     parseRequest(request) {
       let {
         url: destUrl,
@@ -175,7 +190,7 @@ var XSS = (() => {
       } = request;
       let destObj;
       try {
-        destObj = new URL(destUrl);
+        destObj = parseUrl(destUrl);
       } catch (e) {
         error(e, "Cannot create URL object for %s", destUrl);
         return null;
@@ -183,7 +198,7 @@ var XSS = (() => {
       let srcObj = null;
       if (srcUrl) {
         try {
-          srcObj = new URL(srcUrl);
+          srcObj = parseUrl(srcUrl);
         } catch (e) {}
       } else {
         srcUrl = "";
@@ -198,28 +213,21 @@ var XSS = (() => {
 
       let isGet = method === "GET";
       return {
-        xssUnparsed: request,
+        unparsedRequest: request,
         srcUrl,
         destUrl,
         srcObj,
         destObj,
         srcOrigin,
         destOrigin,
-        get srcDomain() {
-          delete this.srcDomain;
-          return this.srcDomain = srcObj && srcObj.hostname && tld.getDomain(srcObj.hostname) || "";
-        },
-        get destDomain() {
-          delete this.destDomain;
-          return this.destDomain = tld.getDomain(destObj.hostname);
-        },
-        get originKey() {
-          delete this.originKey;
-          return this.originKey = `${srcOrigin}>${destOrigin}`;
-        },
+        srcDomain: srcObj && srcObj.hostname && tld.getDomain(srcObj.hostname) || "",
+        destDomain: tld.getDomain(destObj.hostname),
+        originKey: `${srcOrigin}>${destOrigin}`,
         unescapedDest,
         isGet,
         isPost: !isGet && method === "POST",
+        timestamp: Date.now(),
+        debugging: ns.local.debug,
       }
     },
 
@@ -237,42 +245,46 @@ var XSS = (() => {
       return this._userChoices[originKey];
     },
 
-    async maybe(request) { // return reason or null if everything seems fine
-      let xssReq = request.xssUnparsed ? request : this.parseRequest(request);
-      request = xssReq.xssUnparsed;
-
+    async maybe(xssReq) { // return reason or null if everything seems fine
       if (await this.Exceptions.shouldIgnore(xssReq)) {
         return null;
       }
 
-      let {
-        skipParams,
-        skipRx
-      } = this.Exceptions.partial(xssReq);
-
-      let {destUrl} = xssReq;
-
-      await include("/xss/InjectionChecker.js");
-      let ic = new (await this.InjectionChecker)();
-      ic.logEnabled = ns.local.debug;
-      let {timing} = ic;
-      timingsMap.set(request.id, timing);
-      timing.fatalTimeout = true;
-
-      let postInjection = xssReq.isPost &&
-          request.requestBody && request.requestBody.formData &&
-          await ic.checkPost(request.requestBody.formData, skipParams);
-
-      if (timing.tooLong) {
-        log("[XSS] Long check (%s ms) - %s", timing.elapsed, JSON.stringify(xssReq));
-      }
-
-      let protectName = ic.nameAssignment;
-      let urlInjection = await ic.checkUrl(destUrl, skipRx);
-      protectName = protectName || ic.nameAssignment;
-
-      return !(protectName || postInjection || urlInjection) ? null
-        : { protectName, postInjection, urlInjection };
+      let skip = this.Exceptions.partial(xssReq);
+      let worker = new Worker(browser.runtime.getURL("/xss/InjectionCheckWorker.js"));
+      let {requestId} = xssReq.unparsedRequest;
+      workersMap.set(requestId, worker)
+      return await new Promise((resolve, reject) => {
+        let cleanup = () => {
+          workersMap.delete(requestId);
+          worker.terminate();
+        };
+        worker.onmessage = e => {
+          let {data} = e;
+          if (data) {
+            if (data.logType) {
+              window[data.logType](...data.log);
+              return;
+            }
+            if (data.error) {
+              reject(data.error);
+              cleanup();
+              return;
+            }
+          }
+          resolve(e.data);
+          cleanup();
+        }
+        worker.onerror = worker.onmessageerror = e => {
+          reject(e);
+          cleanup();
+        }
+        worker.postMessage({handler: "check", xssReq, skip});
+        setTimeout(() => {
+          reject(new Error("Timeout! DOS attack attempt?"));
+          cleanup();
+        }, 20000)
+      });
     }
   };
 })();