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 --- include/drm/drmP.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/drm') diff --git a/include/drm/drmP.h b/include/drm/drmP.h index 5914cc5c3fa6..90833dccc919 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -1508,7 +1508,7 @@ int drm_gem_dumb_destroy(struct drm_file *file, void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv); void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv); -void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf); +void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf); #if DRM_DEBUG_CODE extern int drm_vma_info(struct seq_file *m, void *data); -- cgit v1.2.3-59-g8ed1b