buffer: stop alloc() uninitialized memory return

CVE-2018-7166 Discovered by ChALkeR - Сковорода Никита Андреевич Prevent Buffer.alloc(size, fill, number) from returning uninitialized memory. Fixes: nodejs-private/security#202 PR-URL: nodejs-private/node-private#137 Reviewed-By: Rod Vagg <rod@vagg.org> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Evan Lucas <evanlucas@me.com> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

Author: cjihrig

lib/buffer.js

@@ -278,7 +278,8 @@ function assertSize(size) {
 Buffer.alloc = function alloc(size, fill, encoding) {
  assertSize(size);
  if (fill !== undefined && fill !== 0 && size > 0) {
- return _fill(createUnsafeBuffer(size), fill, encoding);
+ const buf = createUnsafeBuffer(size);
+ return _fill(buf, fill, 0, buf.length, encoding);
  }
  return new FastBuffer(size);
 };

test/parallel/test-buffer-alloc.js

@@ -1039,3 +1039,10 @@ common.expectsError(() => {
  code: 'ERR_INVALID_ARG_VALUE',
  type: TypeError
 });
+
+common.expectsError(() => {
+ Buffer.alloc(40, 'x', 20);
+}, {
+ code: 'ERR_INVALID_ARG_TYPE',
+ type: TypeError
+});