[PATCH] timers: Fix overflow in get_next_timer_interrupt

[PATCH] timers: Fix overflow in get_next_timer_interrupt

[Matija Glavinic Pecotic]

For e.g. HZ=100, timer being 430 jiffies in the future, and 32 bit
unsigned int, there is an overflow on unsigned int right-hand side
of the expression which results with wrong values being returned.

Problem was observed on tickless core and with following applied:

	sched/nohz: add debugfs control over sched_tick_max_deferment
	https://lkml.org/lkml/2013/9/16/499

Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>
---
 kernel/time/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 71ce3f4..8f5d1bf 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1495,7 +1495,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 		base->is_idle = false;
 	} else {
 		if (!is_max_delta)
-			expires = basem + (nextevt - basej) * TICK_NSEC;
+			expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
 		/*
 		 * If we expect to sleep more than a tick, mark the base idle:
 		 */
-- 
2.1.4

Re: [PATCH] timers: Fix overflow in get_next_timer_interrupt

[Alexander Sverdlin]

On 01/08/17 09:11, Matija Glavinic Pecotic wrote:
> For e.g. HZ=100, timer being 430 jiffies in the future, and 32 bit
> unsigned int, there is an overflow on unsigned int right-hand side
> of the expression which results with wrong values being returned.
> 
> Problem was observed on tickless core and with following applied:
> 
> 	sched/nohz: add debugfs control over sched_tick_max_deferment
> 	https://lkml.org/lkml/2013/9/16/499
> 
> Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>

> ---
>  kernel/time/timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 71ce3f4..8f5d1bf 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1495,7 +1495,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
>  		base->is_idle = false;
>  	} else {
>  		if (!is_max_delta)
> -			expires = basem + (nextevt - basej) * TICK_NSEC;
> +			expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
>  		/*
>  		 * If we expect to sleep more than a tick, mark the base idle:
>  		 */

-- 
Best regards,
Alexander Sverdlin.

[tip:timers/urgent] timers: Fix overflow in get_next_timer_interrupt

[tip-bot for Matija Glavinic Pecotic]

Commit-ID:  34f41c0316ed52b0b44542491d89278efdaa70e4
Gitweb:     http://git.kernel.org/tip/34f41c0316ed52b0b44542491d89278efdaa70e4
Author:     Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>
AuthorDate: Tue, 1 Aug 2017 09:11:52 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 1 Aug 2017 14:20:53 +0200

timers: Fix overflow in get_next_timer_interrupt

For e.g. HZ=100, timer being 430 jiffies in the future, and 32 bit
unsigned int, there is an overflow on unsigned int right-hand side
of the expression which results with wrong values being returned.

Type cast the multiplier to 64bit to avoid that issue.

Fixes: 46c8f0b077a8 ("timers: Fix get_next_timer_interrupt() computation")
Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Cc: khilman@baylibre.com
Cc: akpm@linux-foundation.org
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/a7900f04-2a21-c9fd-67be-ab334d459ee5@nokia.com
---
 kernel/time/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 71ce3f4..8f5d1bf 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1495,7 +1495,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 		base->is_idle = false;
 	} else {
 		if (!is_max_delta)
-			expires = basem + (nextevt - basej) * TICK_NSEC;
+			expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
 		/*
 		 * If we expect to sleep more than a tick, mark the base idle:
 		 */