From e0269cd0a646953a5bd3b10f2760b43c3478cc69 Mon Sep 17 00:00:00 2001
From: Karl Wiberg <kwiberg@webrtc.org>
Date: Mon, 26 Feb 2018 23:44:19 +0100
Subject: [PATCH] SystemTimeNanos() on Mac: DCHECK that multiplication doesn't
 overflow
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Bug: webrtc:6149
Change-Id: I1a58b60838d924e40e89126110cc19e16c953e80
Reviewed-on: https://webrtc-review.googlesource.com/56701
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22194}
---
 rtc_base/timeutils.cc | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/rtc_base/timeutils.cc b/rtc_base/timeutils.cc
index f924d5fddc..35c25c762c 100644
--- a/rtc_base/timeutils.cc
+++ b/rtc_base/timeutils.cc
@@ -27,6 +27,7 @@
 #endif
 
 #include "rtc_base/checks.h"
+#include "rtc_base/numerics/safe_conversions.h"
 #include "rtc_base/timeutils.h"
 
 namespace rtc {
@@ -55,7 +56,13 @@ int64_t SystemTimeNanos() {
     }
   }
   // Use timebase to convert absolute time tick units into nanoseconds.
-  ticks = mach_absolute_time() * timebase.numer / timebase.denom;
+  const auto mul = [](uint64_t a, uint32_t b) -> int64_t {
+    RTC_DCHECK_NE(b, 0);
+    RTC_DCHECK_LE(a, std::numeric_limits<int64_t>::max() / b)
+        << "The multiplication " << a << " * " << b << " overflows";
+    return rtc::dchecked_cast<int64_t>(a * b);
+  };
+  ticks = mul(mach_absolute_time(), timebase.numer) / timebase.denom;
 #elif defined(WEBRTC_POSIX)
   struct timespec ts;
   // TODO(deadbeef): Do we need to handle the case when CLOCK_MONOTONIC is not