[tip:timers/urgent] timer: Prevent overflow in apply_slack

[tip-bot for Jiri Bohac]

Commit-ID:  98a01e779f3c66b0b11cd7e64d531c0e41c95762
Gitweb:     http://git.kernel.org/tip/98a01e779f3c66b0b11cd7e64d531c0e41c95762
Author:     Jiri Bohac <jbohac@xxxxxxx>
AuthorDate: Fri, 18 Apr 2014 17:23:11 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 30 Apr 2014 13:46:17 +0200

timer: Prevent overflow in apply_slack

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>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20140418152310.GA13654@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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

diff --git a/kernel/timer.c b/kernel/timer.c
index 87bd529..3bb01a3 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -838,7 +838,7 @@ 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);
 
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