linux-kernel - Re: [PATCH] sched/fair: fix mul overflow on 32-bit systems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 11 Dec 2015 14:25:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	yuyang.du@...el.com, Morten Rasmussen <morten.rasmussen@....com>,
	Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>
Subject: Re: [PATCH] sched/fair: fix mul overflow on 32-bit systems

On Fri, Dec 11, 2015 at 03:55:18PM +0300, Andrey Ryabinin wrote:
> Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX'
> on 32-bit systems:
> 	UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18
> 	signed integer overflow:
> 	87950 * 47742 cannot be represented in type 'int'
> 
> Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> ---
>  kernel/sched/fair.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e3266eb..733f0b8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2780,14 +2780,14 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
>  	int decayed, removed = 0;
>  
>  	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
> -		long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
> +		s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
>  		sa->load_avg = max_t(long, sa->load_avg - r, 0);
>  		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);

This makes sense, because sched_avg::load_sum is u64.

>  		removed = 1;
>  	}
>  
>  	if (atomic_long_read(&cfs_rq->removed_util_avg)) {
> -		long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
> +		s64 r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
>  		sa->util_avg = max_t(long, sa->util_avg - r, 0);
>  		sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
>  	}

However sched_avg::util_sum is u32, so this is still wrecked.
--
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/