linux-kernel - [PATCH] time: Fix casting issue in timekeeping_forward

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Message-ID: <m2mx1qlk4i.fsf@igel.home>
Date:	Sun, 19 Aug 2012 22:09:01 +0200
From:	Andreas Schwab <schwab@...ux-m68k.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [PATCH] time: Fix casting issue in timekeeping_forward_now

arch_gettimeoffset returns a u32 value which when shifted by tk->shift can
overflow.  Cast it to u64 first.

Signed-off-by: Andreas Schwab <schwab@...ux-m68k.org>
---
Found this by inspection, I don't know if any existing users of
ARCH_USES_GETTIMEOFFSET are affected.  In other words, this is untested,
but looks pretty obvious.

Can tk->shift be bigger than 30?  If so then the shifts in
update_wall_time need to be adjusted as well.

Andreas.

---
 kernel/time/timekeeping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e16af19..8776d66 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -276,7 +276,7 @@ static void timekeeping_forward_now(struct timekeeper *tk)
 	tk->xtime_nsec += cycle_delta * tk->mult;
 
 	/* If arch requires, add in gettimeoffset() */
-	tk->xtime_nsec += arch_gettimeoffset() << tk->shift;
+	tk->xtime_nsec += (u64)arch_gettimeoffset() << tk->shift;
 
 	tk_normalize_xtime(tk);
 
-- 
1.7.11.5

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
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