linux-kernel - Re: [PATCH] drm/scheduler: Fix UAF race in drm_sched_entity_push

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Date:   Wed, 5 Apr 2023 14:23:32 -0400
From:   Luben Tuikov <luben.tuikov@....com>
To:     Asahi Lina <lina@...hilina.net>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH] drm/scheduler: Fix UAF race in
 drm_sched_entity_push_job()

On 2023-04-05 12:37, Asahi Lina wrote:
> After a job is pushed into the queue, it is owned by the scheduler core
> and may be freed at any time, so we can't write nor read the submit
> timestamp after that point.
> 
> Fixes oopses observed with the drm/asahi driver, found with kASAN.
> 
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---

That's a good fix! Thanks for fixing this. I'll push
this through drm-misc-next and drm-misc-fixes, if there
are no objections.

Reviewed-by: Luben Tuikov <luben.tuikov@....com>

Regards,
Luben

>  drivers/gpu/drm/scheduler/sched_entity.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 15d04a0ec623..e0a8890a62e2 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -507,12 +507,19 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
>  {
>  	struct drm_sched_entity *entity = sched_job->entity;
>  	bool first;
> +	ktime_t submit_ts;
>  
>  	trace_drm_sched_job(sched_job, entity);
>  	atomic_inc(entity->rq->sched->score);
>  	WRITE_ONCE(entity->last_user, current->group_leader);
> +
> +	/*
> +	 * After the sched_job is pushed into the entity queue, it may be
> +	 * completed and freed up at any time. We can no longer access it.
> +	 * Make sure to set the submit_ts first, to avoid a race.
> +	 */
> +	sched_job->submit_ts = submit_ts = ktime_get();
>  	first = spsc_queue_push(&entity->job_queue, &sched_job->queue_node);
> -	sched_job->submit_ts = ktime_get();
>  
>  	/* first job wakes up scheduler */
>  	if (first) {
> @@ -529,7 +536,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
>  		spin_unlock(&entity->rq_lock);
>  
>  		if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> -			drm_sched_rq_update_fifo(entity, sched_job->submit_ts);
> +			drm_sched_rq_update_fifo(entity, submit_ts);
>  
>  		drm_sched_wakeup(entity->rq->sched);
>  	}
> 
> ---
> base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6
> change-id: 20230406-scheduler-uaf-2-44cf8faed245
> 
> Thank you,
> ~~ Lina
>