Re: [PATCH] drm/nouveau: RCU-free the scheduler-containing nouveau_sched

[lyude@redhat.com]

Reviewed-by: Lyude Paul <lyude@redhat.com>

Will push to drm-misc-fixes in just a moment

On Wed, 2026-09-02 at 10:27 +0900, Jonghyuk Kim(MalHyuk) wrote:
> struct nouveau_sched embeds a struct drm_gpu_scheduler (base).
> nouveau_sched_destroy() calls nouveau_sched_fini() (which does
> drm_sched_fini(&sched->base)) and then frees the object with plain
> kfree(sched).
> 
> drm_sched_fence_get_timeline_name() returns fence->sched->name, and
> the
> scheduler fence keeps a .release callback so it is not ops-detached
> on
> signalling.  A finished fence exported to userspace via drm_syncobj /
> sync_file therefore keeps pointing at &sched->base after
> nouveau_sched_destroy(),
> and a later get_timeline_name() -- reachable unprivileged through
> SYNC_IOC_FILE_INFO -- dereferences freed memory (KASAN slab-use-
> after-free
> read).
> 
> Per the dma-fence lifetime contract the exporter must keep the data
> backing a
> signalled fence alive for an RCU grace period.  Free the scheduler-
> containing
> object with kfree_rcu() instead of kfree().
> 
> Fixes: 5f03a507b29e ("drm/nouveau: implement 1:1 scheduler - entity
> relationship")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jonghyuk Kim(MalHyuk) <malhyuk97@gmail.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_sched.c | 2 +-
>  drivers/gpu/drm/nouveau/nouveau_sched.h | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c
> b/drivers/gpu/drm/nouveau/nouveau_sched.c
> index 2cbae003d6de..48dbb851df2f 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
> @@ -516,7 +516,7 @@ nouveau_sched_destroy(struct nouveau_sched
> **psched)
>  	struct nouveau_sched *sched = *psched;
>  
>  	nouveau_sched_fini(sched);
> -	kfree(sched);
> +	kfree_rcu(sched, rcu);
>  
>  	*psched = NULL;
>  }
> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.h
> b/drivers/gpu/drm/nouveau/nouveau_sched.h
> index 20cd1da8db73..51ce8dcf6285 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_sched.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.h
> @@ -98,6 +98,7 @@ void nouveau_job_free(struct nouveau_job *job);
>  
>  struct nouveau_sched {
>  	struct drm_gpu_scheduler base;
> +	struct rcu_head rcu;
>  	struct drm_sched_entity entity;
>  	struct workqueue_struct *wq;
>  	struct mutex mutex;