From: Rob Clark Date: Fri, 16 Dec 2022 23:33:55 +0000 (-0800) Subject: drm/virtio: Fix GEM handle creation UAF X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=011ecdbcd520c90c344b872ca6b4821f7783b2f8;p=linux.git drm/virtio: Fix GEM handle creation UAF 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 Reviewed-by: Chia-I Wu Fixes: 62fb7a5e1096 ("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: Greg Kroah-Hartman --- diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c index 15c3e63db396d..3c750ba6ba1fe 100644 --- 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_ioctl(struct drm_device *dev, void *data, 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_blob_ioctl(struct drm_device *dev, 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; }