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Message-ID: <20140430093345.GA18623@midget.suse.cz> Date: Wed, 30 Apr 2014 11:33:45 +0200 From: Jiri Bohac <jbohac@...e.cz> To: Thomas Gleixner <tglx@...utronix.de> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH v3] timer: prevent overflow in apply_slack On Tue, Apr 29, 2014 at 07:22:25PM +0200, Thomas Gleixner wrote: > > > + mask = (1LL << bit) - 1; > > This should be 1UL, shouldn't it? yes, good catch, thanks! 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@...e.cz> Suggested-by: Deborah Townsend <dstownse@...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 = (1UL << bit) - 1; expires_limit = expires_limit & ~(mask); -- Jiri Bohac <jbohac@...e.cz> SUSE Labs, SUSE CZ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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