From 33c7b45378777ddff6dad1a74095d0d8d155f56d Mon Sep 17 00:00:00 2001
From: cjihrig <cjihrig@gmail.com>
Date: Fri, 20 May 2016 15:05:02 -0400
Subject: [PATCH] cluster: guard against undefined message handlers

cluster's internal message handling includes a cache of callback
functions. Once the message for that callback is received, it is
removed from the cache. If, for any reason, the same message ID
is processed twice, the callback will be missing from the cache
and cluster will try to call undefined as a function. This commit
guards against this scenario.

Refs: https://github.com/nodejs/node/issues/6561
PR-URL: https://github.com/nodejs/node/pull/6902
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
---
 lib/cluster.js                                |  2 +-
 test/parallel/test-cluster-invalid-message.js | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/parallel/test-cluster-invalid-message.js

diff --git a/lib/cluster.js b/lib/cluster.js
index 175645f713f701..68a772a74a9b59 100644
--- a/lib/cluster.js
+++ b/lib/cluster.js
@@ -749,7 +749,7 @@ function internal(worker, cb) {
   return function(message, handle) {
     if (message.cmd !== 'NODE_CLUSTER') return;
     var fn = cb;
-    if (message.ack !== undefined) {
+    if (message.ack !== undefined && callbacks[message.ack] !== undefined) {
       fn = callbacks[message.ack];
       delete callbacks[message.ack];
     }
diff --git a/test/parallel/test-cluster-invalid-message.js b/test/parallel/test-cluster-invalid-message.js
new file mode 100644
index 00000000000000..006c80a7aae8fc
--- /dev/null
+++ b/test/parallel/test-cluster-invalid-message.js
@@ -0,0 +1,22 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cluster = require('cluster');
+
+if (cluster.isMaster) {
+  const worker = cluster.fork();
+
+  worker.on('exit', common.mustCall((code, signal) => {
+    assert.strictEqual(code, 0);
+    assert.strictEqual(signal, null);
+  }));
+
+  worker.on('online', () => {
+    worker.send({
+      cmd: 'NODE_CLUSTER',
+      ack: -1
+    }, () => {
+      worker.disconnect();
+    });
+  });
+}