[PATCH 4/4] drm/ttm: Always and only destroy bo->ttm_resv in ttm_bo_release_list

[Lyude Paul]

From: Michel Dänzer <michel.daen...@amd.com>

Fixes a use-after-free due to a race condition in
ttm_bo_cleanup_refs_and_unlock, which allows one task to reserve a BO
and destroy its ttm_resv while another task is waiting for it to signal
in reservation_object_wait_timeout_rcu.

commit e1fc12c5d9ad06a2a74e97a91f1b0c5f4c723b50 upstream

v2:
* Always initialize bo->ttm_resv in ttm_bo_init_reserved
 (Christian König)

Fixes: 0d2bd2ae045d "drm/ttm: fix memory leak while individualizing BOs"
Reviewed-by: Chunming Zhou <david1.z...@amd.com> # v1
Reviewed-by: Christian König <christian.koe...@amd.com>
Signed-off-by: Michel Dänzer <michel.daen...@amd.com>
Signed-off-by: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Lyude Paul <ly...@redhat.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bee77d31895b..c088703777e2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -150,8 +150,7 @@ static void ttm_bo_release_list(struct kref *list_kref)
        ttm_tt_destroy(bo->ttm);
        atomic_dec(&bo->glob->bo_count);
        dma_fence_put(bo->moving);
-       if (bo->resv == &bo->ttm_resv)
-               reservation_object_fini(&bo->ttm_resv);
+       reservation_object_fini(&bo->ttm_resv);
        mutex_destroy(&bo->wu_mutex);
        if (bo->destroy)
                bo->destroy(bo);
@@ -402,14 +401,11 @@ static int ttm_bo_individualize_resv(struct 
ttm_buffer_object *bo)
        if (bo->resv == &bo->ttm_resv)
                return 0;
 
-       reservation_object_init(&bo->ttm_resv);
        BUG_ON(!reservation_object_trylock(&bo->ttm_resv));
 
        r = reservation_object_copy_fences(&bo->ttm_resv, bo->resv);
-       if (r) {
+       if (r)
                reservation_object_unlock(&bo->ttm_resv);
-               reservation_object_fini(&bo->ttm_resv);
-       }
 
        return r;
 }
@@ -459,6 +455,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct 
ttm_buffer_object *bo)
                        spin_unlock(&glob->lru_lock);
                        if (bo->resv != &bo->ttm_resv)
                                reservation_object_unlock(&bo->ttm_resv);
+
                        ttm_bo_cleanup_memtype_use(bo);
                        return;
                }
@@ -1205,8 +1202,8 @@ int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
                lockdep_assert_held(&bo->resv->lock.base);
        } else {
                bo->resv = &bo->ttm_resv;
-               reservation_object_init(&bo->ttm_resv);
        }
+       reservation_object_init(&bo->ttm_resv);
        atomic_inc(&bo->glob->bo_count);
        drm_vma_node_reset(&bo->vma_node);
        bo->priority = 0;
-- 
2.14.3