tls: copy the Buffer object before using

`convertNPNProtocols` and `convertALPNProtocols' uses the `protocols`
buffer object as it is, and if it is modified outside of core, it
might have an impact. This patch makes a copy of the buffer object,
before using it.

PR-URL: nodejs#8055
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

lib/tls.js

@@ -52,7 +52,7 @@ exports.convertNPNProtocols = function convertNPNProtocols(NPNProtocols, out) {
 
   // If it's already a Buffer - store it
   if (NPNProtocols instanceof Buffer) {
-    out.NPNProtocols = NPNProtocols;
+    out.NPNProtocols = Buffer.from(NPNProtocols);
   }
 };
 

test/parallel/test-tls-basic-validations.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto) {
+  common.skip('missing crypto');
+  return;
+}
+
+const assert = require('assert');
+const tls = require('tls');
+
+{
+  const buffer = Buffer.from('abcd');
+  const out = {};
+  tls.convertNPNProtocols(buffer, out);
+  out.NPNProtocols.write('efgh');
+  assert(buffer.equals(Buffer.from('abcd')));
+  assert(out.NPNProtocols.equals(Buffer.from('efgh')));
+}