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Subject[PATCH v2] 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.

Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Suggested-by: Deborah Townsend <dstownse@us.ibm.com>

diff --git a/kernel/timer.c b/kernel/timer.c
index 87bd529..4c36c91 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 = (1LL << bit) - 1;

expires_limit = expires_limit & ~(mask);

--
--
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, SUSE CZ



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