From: Rob Clark robdclark@chromium.org
commit 52531258318ed59a2dc5a43df2eaf0eb1d65438e upstream.
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@chromium.org Reviewed-by: Chia-I Wu olvaffe@gmail.com Fixes: 62fb7a5e1096 ("virtio-gpu: add 3d/virgl support") Cc: stable@vger.kernel.org Signed-off-by: Dmitry Osipenko dmitry.osipenko@collabora.com Link: https://patchwork.freedesktop.org/patch/msgid/20221216233355.542197-2-robdcl... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/virtio/virtgpu_ioctl.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c @@ -292,10 +292,18 @@ static int virtio_gpu_resource_create_io drm_gem_object_release(obj); return ret; } - drm_gem_object_put(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(obj); + return 0; }
@@ -656,11 +664,18 @@ static int virtio_gpu_resource_create_bl drm_gem_object_release(obj); return ret; } - drm_gem_object_put(obj);
rc_blob->res_handle = bo->hw_res_handle; rc_blob->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(obj); + return 0; }