On Fri, Sep 03, 2021 at 02:05:54PM +0200, Boris Brezillon wrote:

drm_sched_job_cleanup() will pass an uninitialized fence to drm_sched_fence_free(), which will cause to_drm_sched_fence() to return a NULL fence object, causing a NULL pointer deref when this NULL object is passed to kmem_cache_free().

Let's create a new drm_sched_fence_free() function that takes a drm_sched_fence pointer and suffix the old function with _rcu. While at it, complain if drm_sched_fence_free() is passed an initialized fence or if drm_sched_fence_free_rcu() is passed an uninitialized fence.

Fixes: dbe48d030b28 ("drm/sched: Split drm_sched_job_init") Signed-off-by: Boris Brezillon boris.brezillon@collabora.com

---

Found while debugging another issue in panfrost causing a failure in the submit ioctl and exercising the error path (path that calls drm_sched_job_cleanup() on an unarmed job).

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

I already provided an irc r-b, just here for the record too. -Daniel

---

drivers/gpu/drm/scheduler/sched_fence.c | 29 ++++++++++++++++--------- drivers/gpu/drm/scheduler/sched_main.c | 2 +- include/drm/gpu_scheduler.h | 2 +- 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c index db3fd1303fc4..7fd869520ef2 100644 --- a/drivers/gpu/drm/scheduler/sched_fence.c +++ b/drivers/gpu/drm/scheduler/sched_fence.c @@ -69,19 +69,28 @@ static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f) return (const char *)fence->sched->name; }

-/**

• • drm_sched_fence_free - free up the fence memory
• • @rcu: RCU callback head
• • Free up the fence memory after the RCU grace period.
• */

-void drm_sched_fence_free(struct rcu_head *rcu) +static void drm_sched_fence_free_rcu(struct rcu_head *rcu) { struct dma_fence *f = container_of(rcu, struct dma_fence, rcu); struct drm_sched_fence *fence = to_drm_sched_fence(f);

• kmem_cache_free(sched_fence_slab, fence);

• if (!WARN_ON_ONCE(!fence))

• kmem_cache_free(sched_fence_slab, fence);
  

+}

+/**

• • drm_sched_fence_free - free up an uninitialized fence
• • @fence: fence to free
• • Free up the fence memory. Should only be used if drm_sched_fence_init()
• • has not been called yet.
• */

+void drm_sched_fence_free(struct drm_sched_fence *fence) +{

• /* This function should not be called if the fence has been initialized. */
• if (!WARN_ON_ONCE(fence->sched))

• kmem_cache_free(sched_fence_slab, fence);
  

}

/** @@ -97,7 +106,7 @@ static void drm_sched_fence_release_scheduled(struct dma_fence *f) struct drm_sched_fence *fence = to_drm_sched_fence(f);

dma_fence_put(fence->parent);

• call_rcu(&fence->finished.rcu, drm_sched_fence_free);

• call_rcu(&fence->finished.rcu, drm_sched_fence_free_rcu);

}

/** diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c index fbbd3b03902f..6987d412a946 100644 --- a/drivers/gpu/drm/scheduler/sched_main.c +++ b/drivers/gpu/drm/scheduler/sched_main.c @@ -750,7 +750,7 @@ void drm_sched_job_cleanup(struct drm_sched_job *job) dma_fence_put(&job->s_fence->finished); } else { /* aborted job before committing to run it */

• drm_sched_fence_free(&job->s_fence->finished.rcu);
  

• drm_sched_fence_free(job->s_fence);
  

  }

  job->s_fence = NULL;

diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h index 7f77a455722c..f011e4c407f2 100644 --- a/include/drm/gpu_scheduler.h +++ b/include/drm/gpu_scheduler.h @@ -509,7 +509,7 @@ struct drm_sched_fence *drm_sched_fence_alloc( struct drm_sched_entity *s_entity, void *owner); void drm_sched_fence_init(struct drm_sched_fence *fence, struct drm_sched_entity *entity); -void drm_sched_fence_free(struct rcu_head *rcu); +void drm_sched_fence_free(struct drm_sched_fence *fence);

void drm_sched_fence_scheduled(struct drm_sched_fence *fence); void drm_sched_fence_finished(struct drm_sched_fence *fence); -- 2.31.1