buffer: convert offset & length to int properly

As per ecma-262 2015's #sec-%typedarray%-buffer-byteoffset-length,
`offset` would be an integer, not a 32 bit unsigned integer. Also,
`length` would be an integer with the maximum value of 2^53 - 1, not a
32 bit unsigned integer.

This would be a problem because, if we create a buffer from an
arraybuffer, from an offset which is greater than 2^32, it would be
actually pointing to a different location in arraybuffer. For example,
if we use 2^40 as offset, then the actual value used will be 0,
because `byteOffset >>>= 0` will convert `byteOffset` to a 32 bit
unsigned int, which is based on 2^32 modulo.

PR-URL: #9492

Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

lib/buffer.js

@@ -238,7 +238,7 @@ function fromArrayLike(obj) {
 }
 
 function fromArrayBuffer(obj, byteOffset, length) {
-  byteOffset >>>= 0;
+  byteOffset = internalUtil.toInteger(byteOffset);
 
   const maxLength = obj.byteLength - byteOffset;
 
@@ -248,7 +248,7 @@ function fromArrayBuffer(obj, byteOffset, length) {
   if (length === undefined) {
     length = maxLength;
   } else {
-    length >>>= 0;
+    length = internalUtil.toLength(length);
     if (length > maxLength)
       throw new RangeError("'length' is out of bounds");
   }

lib/internal/util.js

@@ -161,3 +161,21 @@ exports.cachedResult = function cachedResult(fn) {
     return result;
   };
 };
+
+/*
+ * Implementation of ToInteger as per ECMAScript Specification
+ * Refer: http://www.ecma-international.org/ecma-262/6.0/#sec-tointeger
+ */
+const toInteger = exports.toInteger = function toInteger(argument) {
+  const number = +argument;
+  return Number.isNaN(number) ? 0 : Math.trunc(number);
+};
+
+/*
+ * Implementation of ToLength as per ECMAScript Specification
+ * Refer: http://www.ecma-international.org/ecma-262/6.0/#sec-tolength
+ */
+exports.toLength = function toLength(argument) {
+  const len = toInteger(argument);
+  return len <= 0 ? 0 : Math.min(len, Number.MAX_SAFE_INTEGER);
+};

test/parallel/test-buffer-creation-regression.js

@@ -0,0 +1,21 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+function test(size, offset, length) {
+  const arrayBuffer = new ArrayBuffer(size);
+
+  const uint8Array = new Uint8Array(arrayBuffer, offset, length);
+  for (let i = 0; i < length; i += 1) {
+    uint8Array[i] = 1;
+  }
+
+  const buffer = Buffer.from(arrayBuffer, offset, length);
+  for (let i = 0; i < length; i += 1) {
+    assert.strictEqual(buffer[i], 1);
+  }
+}
+
+test(200, 50, 100);
+test(8589934592 /* 1 << 40 */, 4294967296 /* 1 << 39 */, 1000);

test/parallel/test-internal-util-toInteger.js

@@ -0,0 +1,32 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const {toInteger} = require('internal/util');
+
+const expectZero = [
+  '0', '-0', NaN, {}, [], {'a': 'b'}, [1, 2], '0x', '0o', '0b', false,
+  '', ' ', undefined, null
+];
+expectZero.forEach(function(value) {
+  assert.strictEqual(toInteger(value), 0);
+});
+
+assert.strictEqual(toInteger(Infinity), Infinity);
+assert.strictEqual(toInteger(-Infinity), -Infinity);
+
+const expectSame = [
+  '0x100', '0o100', '0b100', 0x100, -0x100, 0o100, -0o100, 0b100, -0b100, true
+];
+expectSame.forEach(function(value) {
+  assert.strictEqual(toInteger(value), +value, `${value} is not an Integer`);
+});
+
+const expectIntegers = new Map([
+  [[1], 1], [[-1], -1], [['1'], 1], [['-1'], -1],
+  [3.14, 3], [-3.14, -3], ['3.14', 3], ['-3.14', -3],
+]);
+expectIntegers.forEach(function(expected, value) {
+  assert.strictEqual(toInteger(value), expected);
+});

test/parallel/test-internal-util-toLength.js

@@ -0,0 +1,35 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const {toLength} = require('internal/util');
+const maxValue = Number.MAX_SAFE_INTEGER;
+
+const expectZero = [
+  '0', '-0', NaN, {}, [], {'a': 'b'}, [1, 2], '0x', '0o', '0b', false,
+  '', ' ', undefined, null, -1, -1.25, -1.1, -1.9, -Infinity
+];
+expectZero.forEach(function(value) {
+  assert.strictEqual(toLength(value), 0);
+});
+
+assert.strictEqual(toLength(maxValue - 1), maxValue - 1);
+assert.strictEqual(maxValue, maxValue);
+assert.strictEqual(toLength(Infinity), maxValue);
+assert.strictEqual(toLength(maxValue + 1), maxValue);
+
+
+[
+  '0x100', '0o100', '0b100', 0x100, -0x100, 0o100, -0o100, 0b100, -0b100, true
+].forEach(function(value) {
+  assert.strictEqual(toLength(value), +value > 0 ? +value : 0);
+});
+
+const expectIntegers = new Map([
+  [[1], 1], [[-1], 0], [['1'], 1], [['-1'], 0],
+  [3.14, 3], [-3.14, 0], ['3.14', 3], ['-3.14', 0],
+]);
+expectIntegers.forEach(function(expected, value) {
+  assert.strictEqual(toLength(value), expected);
+});