[PATCH] drm/sched: Fix UAF in drm_sched_fence_get_timeline_name()

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

The fence can outlive the sched, so it is not safe to dereference the
sched in drm_sched_fence_get_timeline_name()

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/scheduler/sched_fence.c |  3 ++-
 include/drm/gpu_scheduler.h             | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
index e971528504a5..4e529c3ba6d4 100644
--- a/drivers/gpu/drm/scheduler/sched_fence.c
+++ b/drivers/gpu/drm/scheduler/sched_fence.c
@@ -92,7 +92,7 @@ static const char *drm_sched_fence_get_driver_name(struct dma_fence *fence)
 static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f)
 {
 	struct drm_sched_fence *fence = to_drm_sched_fence(f);
-	return (const char *)fence->sched->name;
+	return fence->name;
 }
 
 static void drm_sched_fence_free_rcu(struct rcu_head *rcu)
@@ -226,6 +226,7 @@ void drm_sched_fence_init(struct drm_sched_fence *fence,
 	unsigned seq;
 
 	fence->sched = entity->rq->sched;
+	fence->name  = fence->sched->name;
 	seq = atomic_inc_return(&entity->fence_seq);
 	dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled,
 		       &fence->lock, entity->fence_context, seq);
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 0ae108f6fcaf..d830ffe083f1 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -295,6 +295,9 @@ struct drm_sched_fence {
         /**
          * @sched: the scheduler instance to which the job having this struct
          * belongs to.
+         *
+         * Some care must be taken as to where the sched is derefed, as the
+         * fence can outlive the sched.
          */
 	struct drm_gpu_scheduler	*sched;
         /**
@@ -305,6 +308,14 @@ struct drm_sched_fence {
          * @owner: job owner for debugging
          */
 	void				*owner;
+
+	/**
+	 * @name: the timeline name
+	 *
+	 * This comes from the @sched, but since the fence can outlive the
+	 * sched, we need to keep our own copy.
+	 */
+	const char			*name;
 };
 
 struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
-- 
2.49.0