Fix regexp in utils.stackTraceFilter to prevent ReDoS mochajs#3416 (m…

…ochajs#3686)

When the stacktrace begins with a large `Error.message` (single or multi line), Mocha's stack prettifier method (enabled by default) takes a long time to finish due to its regular expression. Certain assertions (e.g., `contains`, `deeplyEqual`) against large objects can trigger this problem.
This PR alters the RegExp to skip over the error message portion of the stacktrace.

lib/utils.js

@@ -671,8 +671,6 @@ exports.stackTraceFilter = function() {
   function isMochaInternal(line) {
     return (
       ~line.indexOf('node_modules' + slash + 'mocha' + slash) ||
-      ~line.indexOf('node_modules' + slash + 'mocha.js') ||
-      ~line.indexOf('bower_components' + slash + 'mocha.js') ||
       ~line.indexOf(slash + 'mocha.js')
     );
   }
@@ -701,7 +699,7 @@ exports.stackTraceFilter = function() {
       }
 
       // Clean up cwd(absolute)
-      if (/\(?.+:\d+:\d+\)?$/.test(line)) {
+      if (/:\d+:\d+\)?$/.test(line)) {
         line = line.replace('(' + cwd, '(');
       }
 

test/unit/runner.spec.js

@@ -6,6 +6,7 @@ var Runner = mocha.Runner;
 var Test = mocha.Test;
 var Hook = mocha.Hook;
 var path = require('path');
+var fs = require('fs');
 var noop = mocha.utils.noop;
 
 describe('Runner', function() {
@@ -496,6 +497,62 @@ describe('Runner', function() {
         runner.failHook(hook, err);
       });
     });
+
+    describe('hugeStackTrace', function() {
+      beforeEach(function() {
+        if (path.sep !== '/') {
+          this.skip();
+        }
+      });
+
+      it('should not hang if the error message is ridiculously long single line', function(done) {
+        var hook = new Hook();
+        hook.parent = suite;
+        var data = [];
+        // mock a long message
+        for (var i = 0; i < 10000; i++) data[i] = {a: 1};
+        var message = JSON.stringify(data);
+        var err = new Error();
+        // Fake stack-trace
+        err.stack = [message].concat(stack).join('\n');
+
+        runner.on('fail', function(hook, err) {
+          expect(
+            err.stack
+              .split('\n')
+              .slice(1)
+              .join('\n'),
+            'to be',
+            stack.slice(0, 3).join('\n')
+          );
+          done();
+        });
+        runner.failHook(hook, err);
+      });
+
+      it('should not hang if error message is ridiculously long multiple lines either', function(done) {
+        var hook = new Hook();
+        hook.parent = suite;
+        var fpath = path.join(__dirname, '../../mocha.js');
+        var message = fs.readFileSync(fpath, 'utf8');
+        var err = new Error();
+        // Fake stack-trace
+        err.stack = [message].concat(stack).join('\n');
+
+        runner.on('fail', function(hook, err) {
+          expect(
+            err.stack
+              .split('\n')
+              .slice(-3)
+              .join('\n'),
+            'to be',
+            stack.slice(0, 3).join('\n')
+          );
+          done();
+        });
+        runner.failHook(hook, err);
+      });
+    });
   });
 
   describe('abort', function() {