Fix #2848: avoid overflow during time calculation

1 files changed, 4 insertions, 3 deletions

diff --git a/rts/posix/Itimer.c b/rts/posix/Itimer.c
index a60f8f1295..6b4ba3bb70 100644
--- a/rts/posix/Itimer.c
+++ b/rts/posix/Itimer.c
@@ -264,7 +264,8 @@ getourtimeofday(void)
   interval = RtsFlags.MiscFlags.tickInterval;
   if (interval == 0) { interval = 50; }
   gettimeofday(&tv, (struct timezone *) NULL);
-  	// cast to lnat because nat may be 64 bit when int is only 32 bit
-  return ((lnat)tv.tv_sec * 1000 / interval +
-	  (lnat)tv.tv_usec / (interval * 1000));
+
+  // Avoid overflow when we multiply seconds by 1000.  See #2848
+  return (lnat)((StgWord64)tv.tv_sec * 1000 / interval +
+                (StgWord64)tv.tv_usec / (interval * 1000));
 }