linux-kernel - Re: [PATCH] sched/topology: check variable group before dereferenced

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Message-ID: <20180723083702.GW2494@hirez.programming.kicks-ass.net>
Date:   Mon, 23 Jul 2018 10:37:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yi Wang <wang.yi59@....com.cn>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        jiang.biao2@....com.cn, zhong.weidong@....com.cn
Subject: Re: [PATCH] sched/topology: check variable group before dereferenced

On Mon, Jul 23, 2018 at 12:19:07PM +0800, Yi Wang wrote:
> The variable group in sched_domain_debug_one() is not checked
> when firstly used in cpumask_test_cpu(cpu, sched_group_span(group)),
> but it maybe NULL(checked later in the following while loop) and may
> cause NULL pointer dereference without checking. We need to check it
> before using to avoid NULL dereference.

It being NULL really is a fairly severe error in construction; but sure.
This patch won't hurt.

> Signed-off-by: Yi Wang <wang.yi59@....com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
> ---
>  kernel/sched/topology.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 5ac724b..c7cf87c 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -53,7 +53,7 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
>  		printk(KERN_ERR "ERROR: domain->span does not contain "
>  				"CPU%d\n", cpu);
>  	}
> -	if (!cpumask_test_cpu(cpu, sched_group_span(group))) {
> +	if (group && !cpumask_test_cpu(cpu, sched_group_span(group))) {
>  		printk(KERN_ERR "ERROR: domain->groups does not contain"
>  				" CPU%d\n", cpu);
>  	}
> -- 
> 1.8.3.1
>