linux-kernel - Re: [PATCH] sched/fair: Add null pointer check to pick_next

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Message-ID: <72cb8df7-42e7-4266-b014-7d43796b14d8@arm.com>
Date: Thu, 20 Mar 2025 22:42:44 +0000
From: Christian Loehle <christian.loehle@....com>
To: Pat Cody <pat@...cody.io>, mingo@...hat.com
Cc: peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
 riel@...riel.com, patcody@...a.com, kernel-team@...a.com,
 stable@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity()

On 3/20/25 20:53, Pat Cody wrote:
> pick_eevdf() can return null, resulting in a null pointer dereference
> crash in pick_next_entity()
> 
> The other call site of pick_eevdf() can already handle a null pointer,
> and pick_next_entity() can already return null as well. Add an extra
> check to handle the null return here.
> 
> Cc: stable@...r.kernel.org
> Fixes: f12e148892ed ("sched/fair: Prepare pick_next_task() for delayed dequeue")
> Signed-off-by: Pat Cody <pat@...cody.io>

Did this happen on mainline? Any chance it's reproducible?

> ---
>  kernel/sched/fair.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a553181dc764..f2157298cbce 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5560,6 +5560,8 @@ pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
>  	}
>  
>  	struct sched_entity *se = pick_eevdf(cfs_rq);
> +	if (!se)
> +		return NULL;
>  	if (se->sched_delayed) {
>  		dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
>  		/*