[3.11.y.z extended stable] Patch "timer: Prevent overflow in apply_slack" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    timer: Prevent overflow in apply_slack

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f326bbfe70d8fe4de5243d9291927cc36ed9a6af Mon Sep 17 00:00:00 2001
From: Jiri Bohac <jbohac at suse.cz>
Date: Fri, 18 Apr 2014 17:23:11 +0200
Subject: timer: Prevent overflow in apply_slack

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 at us.ibm.com>
Signed-off-by: Jiri Bohac <jbohac at suse.cz>
Link: http://lkml.kernel.org/r/20140418152310.GA13654@midget.suse.cz
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index 4296d13..4addfa2 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -822,7 +822,7 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires)

 	bit = find_last_bit(&mask, BITS_PER_LONG);

-	mask = (1 << bit) - 1;
+	mask = (1UL << bit) - 1;

 	expires_limit = expires_limit & ~(mask);

--
1.9.1