time: Avoid potential shift overflow with large shift values

Andreas Schwab noticed that the 1 << tk->shift could overflow if the
shift value was greater than 30, since 1 would be a 32bit long on
32bit architectures. This issue was introduced by 1e75fa8be (time:
Condense timekeeper.xtime into xtime_sec)

Use 1ULL instead to ensure we don't overflow on the shift.

Reported-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1345595449-34965-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1dbf80ec7696467c2260296fec31262e2a3c50d7..a5a9389c4c3090221d1b31bb89512cba5b36af0c 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1184,9 +1184,9 @@ static void update_wall_time(void)
        * the vsyscall implementations are converted to use xtime_nsec
        * (shifted nanoseconds), this can be killed.
        */
-       remainder = tk->xtime_nsec & ((1 << tk->shift) - 1);
+       remainder = tk->xtime_nsec & ((1ULL << tk->shift) - 1);
        tk->xtime_nsec -= remainder;
-       tk->xtime_nsec += 1 << tk->shift;
+       tk->xtime_nsec += 1ULL << tk->shift;
        tk->ntp_error += remainder << tk->ntp_error_shift;
 
        /*