Commit 6ea565a9 authored Aug 21, 2012 by John Stultz Committed by Thomas Gleixner Aug 22, 2012

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 1e75fa8b (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>

parent 85dc8f05

kernel/time/timekeeping.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;

		/*

Admin message