This is a note to let you know that I've just added the patch titled drm/virtio: Fix GEM handle creation UAF to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-virtio-fix-gem-handle-creation-uaf.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 6319e14464835581a7794d16e25de12156f55272 Author: Rob Clark <robdclark@xxxxxxxxxxxx> Date: Fri Dec 16 15:33:55 2022 -0800 drm/virtio: Fix GEM handle creation UAF [ Upstream commit 52531258318ed59a2dc5a43df2eaf0eb1d65438e ] Userspace can guess the handle value and try to race GEM object creation with handle close, resulting in a use-after-free if we dereference the object after dropping the handle's reference. For that reason, dropping the handle's reference must be done *after* we are done dereferencing the object. Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx> Reviewed-by: Chia-I Wu <olvaffe@xxxxxxxxx> Fixes: 62fb7a5e1096 ("virtio-gpu: add 3d/virgl support") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20221216233355.542197-2-robdclark@xxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c index 0a88ef11b9d3..5ae132e37277 100644 --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c @@ -327,10 +327,18 @@ static int virtio_gpu_resource_create_ioctl(struct drm_device *dev, void *data, drm_gem_object_release(obj); return ret; } - drm_gem_object_put_unlocked(obj); rc->res_handle = qobj->hw_res_handle; /* similiar to a VM address */ rc->bo_handle = handle; + + /* + * The handle owns the reference now. But we must drop our + * remaining reference *after* we no longer need to dereference + * the obj. Otherwise userspace could guess the handle and + * race closing it from another thread. + */ + drm_gem_object_put_unlocked(obj); + return 0; }