Fix UTC offset computation in date parser.

BUG=chromium:561973
LOG=N

Review URL: https://codereview.chromium.org/1532573003

Cr-Commit-Position: refs/heads/master@{#32956}

src/dateparser.cc

@@ -100,8 +100,15 @@ bool DateParser::TimeZoneComposer::Write(FixedArray* output) {
   if (sign_ != kNone) {
     if (hour_ == kNone) hour_ = 0;
     if (minute_ == kNone) minute_ = 0;
-    int total_seconds = sign_ * (hour_ * 3600 + minute_ * 60);
-    if (!Smi::IsValid(total_seconds)) return false;
+    // Avoid signed integer overflow (undefined behavior) by doing unsigned
+    // arithmetic.
+    unsigned total_seconds_unsigned = hour_ * 3600U + minute_ * 60U;
+    if (total_seconds_unsigned > Smi::kMaxValue) return false;
+    int total_seconds = static_cast<int>(total_seconds_unsigned);
+    if (sign_ < 0) {
+      total_seconds = -total_seconds;
+    }
+    DCHECK(Smi::IsValid(total_seconds));
     output->set(UTC_OFFSET, Smi::FromInt(total_seconds));
   } else {
     output->set_null(UTC_OFFSET);

test/mjsunit/regress/regress-crbug-561973.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+Date.parse('Sat, 01 Jan 100 08:00:00 UT-59011430400000');