linux-kernel - [tip:timers/urgent] time: Avoid potential shift overflow with large shift values

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Message-ID: <tip-6ea565a9be32a3c8d1092017686f183b6d8c4514@git.kernel.org>
Date:	Wed, 22 Aug 2012 01:52:04 -0700
From:	tip-bot for John Stultz <john.stultz@...aro.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org,
	hpa@...or.com, mingo@...nel.org, schwab@...ux-m68k.org,
	tglx@...utronix.de, prarit@...hat.com
Subject: [tip:timers/urgent] time:
  Avoid potential shift overflow with large shift values

Commit-ID:  6ea565a9be32a3c8d1092017686f183b6d8c4514
Gitweb:     http://git.kernel.org/tip/6ea565a9be32a3c8d1092017686f183b6d8c4514
Author:     John Stultz <john.stultz@...aro.org>
AuthorDate: Tue, 21 Aug 2012 20:30:48 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 22 Aug 2012 10:42:13 +0200

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@...ux-m68k.org>
Signed-off-by: John Stultz <john.stultz@...aro.org>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Link: http://lkml.kernel.org/r/1345595449-34965-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/timekeeping.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1dbf80e..a5a9389 100644
--- 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;
 
 	/*
--
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