[PATCH 3.2 41/92] timer: Prevent overflow in apply_slack

Ben Hutchings
2014-06-07T01:26:29Z

From: Jiri Bohac <jbohac@suse.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@us.ibm.com>
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Link: http://lkml.kernel.org/r/20140418152310.GA13654@midget.suse.cz
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.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);