[PATCH 3.12 025/146] timer: Prevent overflow in apply_slack

From: Jiri Slaby
Date: Mon Jun 09 2014 - 04:51:30 EST


From: Jiri Bohac <jbohac@xxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

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@xxxxxxxxxx>
Signed-off-by: Jiri Bohac <jbohac@xxxxxxx>
Link: http://lkml.kernel.org/r/20140418152310.GA13654@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
kernel/timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index 4296d13db3d1..4addfa27f67d 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);

--
1.9.3

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