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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@us.ibm.com>
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20140418152310.GA13654@midget.suse.cz
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jiri Bohac 2014-04-18 17:23:11 +02:00 committed by Thomas Gleixner
parent 012a45e3f4
commit 98a01e779f
1 changed files with 1 additions and 1 deletions
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kernel/timer.c
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@ -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);