Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct 
virtio_gpu_object_array.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: David Airlie <airl...@redhat.com>
Cc: Gerd Hoffmann <kra...@redhat.com>
Cc: Gurchetan Singh <gurchetansi...@chromium.org>
Cc: Chia-I Wu <olva...@gmail.com>
Cc: Daniel Vetter <dan...@ffwll.ch>
Cc: dri-de...@lists.freedesktop.org
Cc: virtualizat...@lists.linux-foundation.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/gpu/drm/virtio/virtgpu_drv.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h 
b/drivers/gpu/drm/virtio/virtgpu_drv.h
index 8513b671f871..96365a772f77 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -119,7 +119,7 @@ struct virtio_gpu_object_array {
        struct ww_acquire_ctx ticket;
        struct list_head next;
        u32 nents, total;
-       struct drm_gem_object *objs[];
+       struct drm_gem_object *objs[] __counted_by(total);
 };
 
 struct virtio_gpu_vbuffer;
-- 
2.34.1

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