From d0b2c5334f41bdd18adaa3fbc1f7b5f1daab7eac Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Thu, 15 Aug 2013 00:02:49 +0200 Subject: drm/prime: Always add exported buffers to the handle cache ... not only when the dma-buf is freshly created. In contrived examples someone else could have exported/imported the dma-buf already and handed us the gem object with a flink name. If such on object gets reexported as a dma_buf we won't have it in the handle cache already, which breaks the guarantee that for dma-buf imports we always hand back an existing handle if there is one. This is exercised by igt/prime_self_import/with_one_bo_two_files Now if we extend the locked sections just a notch more we can also plug th racy buf/handle cache setup in handle_to_fd: If evil userspace races a concurrent gem close against a prime export operation we can end up tearing down the gem handle before the dma buf handle cache is set up. When handle_to_fd gets around to adding the handle to the cache there will be no one left to clean it up, effectily leaking the bo (and the dma-buf, since the handle cache holds a ref on the dma-buf): Thread A Thread B handle_to_fd: lookup gem object from handle creates new dma_buf gem_close on the same handle obj->dma_buf is set, but file priv buf handle cache has no entry obj->handle_count drops to 0 drm_prime_add_buf_handle sets up the handle cache -> We have a dma-buf reference in the handle cache, but since the handle_count of the gem object already dropped to 0 no on will clean it up. When closing the drm device fd we'll hit the WARN_ON in drm_prime_destroy_file_private. The important change is to extend the critical section of the filp->prime.lock to cover the gem handle lookup. This serializes with a concurrent gem handle close. This leak is exercised by igt/prime_self_import/export-vs-gem_close-race Signed-off-by: Daniel Vetter Signed-off-by: Dave Airlie --- drivers/gpu/drm/drm_gem.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'drivers/gpu/drm/drm_gem.c') diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 0a5a0ca0a52e..1ce88c3301a1 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -195,10 +195,12 @@ drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp) * Note: obj->dma_buf can't disappear as long as we still hold a * handle reference in obj->handle_count. */ + mutex_lock(&filp->prime.lock); if (obj->dma_buf) { - drm_prime_remove_buf_handle(&filp->prime, - obj->dma_buf); + drm_prime_remove_buf_handle_locked(&filp->prime, + obj->dma_buf); } + mutex_unlock(&filp->prime.lock); } static void drm_gem_object_ref_bug(struct kref *list_kref) -- cgit v1.2.3