jenkins: whitelist IPs allowed to push status changes

This is needed to ensure not everyone on the internet can push an inline
status to any PR if they know the bot URL.

README.md

@@ -18,6 +18,8 @@ See [CONTRIBUTING.md](CONTRIBUTING.md).
   The webhook secret that GitHub signs the POSTed payloads with. This is created when the webhook is defined. The default is `hush-hush`.
 - **`TRAVIS_CI_TOKEN`**<br>
   For scripts that communicate with Travis CI. Your Travis token is visible on [yourprofile](https://travis-ci.org/profile) page, by clicking the "show token" link. Also See: https://blog.travis-ci.com/2013-01-28-token-token-token
+- **`JENKINS_WORKER_IPS`**<br>
+  List of valid Jenkins worker IPs allowed to push PR status updates, split by comma: `192.168.1.100,192.168.1.101`.
 - **`JENKINS_API_CREDENTIALS`** (optional)<br>
   For scripts that communicate with Jenkins on http://ci.nodejs.org. The Jenkins API token is visible on
   your own profile page `https://ci.nodejs.org/user/<YOUR_GITHUB_USERNAME>/configure`, by clicking the

scripts/jenkins-status.js

@@ -3,6 +3,21 @@
 const pushJenkinsUpdate = require('../lib/push-jenkins-update')
 const enabledRepos = ['citgm', 'node']
 
+const jenkinsIpWhitelist = process.env.JENKINS_WORKER_IPS ? process.env.JENKINS_WORKER_IPS.split(',') : []
+
+function isJenkinsIpWhitelisted (req) {
+  const ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress
+
+  if (jenkinsIpWhitelist.length) {
+    if (!jenkinsIpWhitelist.includes(ip)) {
+      req.log.warn({ ip }, 'Ignoring, not allowed to push Jenkins updates')
+      return false
+    }
+  }
+
+  return true
+}
+
 module.exports = function (app) {
   app.post('/:repo/jenkins/start', (req, res) => {
     const isValid = pushJenkinsUpdate.validate(req.body)
@@ -16,6 +31,10 @@ module.exports = function (app) {
       return res.status(400).end('Invalid repository')
     }
 
+    if (!isJenkinsIpWhitelisted(req)) {
+      return res.status(401).end('Invalid Jenkins IP')
+    }
+
     pushJenkinsUpdate.pushStarted({
       owner: 'nodejs',
       repo,
@@ -37,6 +56,10 @@ module.exports = function (app) {
       return res.status(400).end('Invalid repository')
     }
 
+    if (!isJenkinsIpWhitelisted(req)) {
+      return res.status(401).end('Invalid Jenkins IP')
+    }
+
     req.log.debug({ payload: req.body }, 'Jenkins / Github PR end status incoming')
 
     pushJenkinsUpdate.pushEnded({