linux-kernel - [PATCH 3.2 41/92] timer: Prevent overflow in apply

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Message-ID: <lsq.1402104389.514324212@decadent.org.uk>
Date:	Sat, 07 Jun 2014 02:26:29 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
	"Deborah Townsend" <dstownse@...ibm.com>,
	"Jiri Bohac" <jbohac@...e.cz>
Subject: [PATCH 3.2 41/92] timer: Prevent overflow in apply_slack

3.2.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Bohac <jbohac@...e.cz>

commit 98a01e779f3c66b0b11cd7e64d531c0e41c95762 upstream.

On architectures with sizeof(int) < sizeof (long), the
computation of mask inside apply_slack() can be undefined if the
computed bit is > 32.

E.g. with: expires = 0xffffe6f5 and slack = 25, we get:

expires_limit = 0x20000000e
bit = 33
mask = (1 << 33) - 1  /* undefined */

On x86, mask becomes 1 and and the slack is not applied properly.
On s390, mask is -1, expires is set to 0 and the timer fires immediately.

Use 1UL << bit to solve that issue.

Suggested-by: Deborah Townsend <dstownse@...ibm.com>
Signed-off-by: Jiri Bohac <jbohac@...e.cz>
Link: http://lkml.kernel.org/r/20140418152310.GA13654@midget.suse.cz
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -769,7 +769,7 @@ unsigned long apply_slack(struct timer_l
 
 	bit = find_last_bit(&mask, BITS_PER_LONG);
 
-	mask = (1 << bit) - 1;
+	mask = (1UL << bit) - 1;
 
 	expires_limit = expires_limit & ~(mask);
 

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