From 0a1a26cc73b0d449d2b51f12536c7c13bf15fbd9 Mon Sep 17 00:00:00 2001 From: Rob Clark Date: Fri, 16 Dec 2022 15:33:55 -0800 Subject: [PATCH] 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 Reviewed-by: Chia-I Wu Fixes: 02e398c17c39 ("virtio-gpu: add 3d/virgl support") Cc: stable@vger.kernel.org Signed-off-by: Dmitry Osipenko Link: https://patchwork.freedesktop.org/patch/msgid/20221216233355.542197-2-robdclark@gmail.com Signed-off-by: Sasha Levin --- drivers/gpu/drm/virtio/virtgpu_ioctl.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c index 0a88ef11b9d3f..5ae132e37277d 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; } -- 2.39.5