ommit 5fb252cad61f20ae5d5a8b199f6cc4faf6f418e1, a cherry-pick of
upstream commit e7cdf5c82f1773c3386b93bbcf13b9bfff29fa31, introduced a
refcount imbalance and thus a struct drm_syncobj object leak which can
be triggered with DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD.

The function drm_syncobj_handle_to_fd first calls drm_syncobj_find
which increments the refcount of the object on success. In all of the
drm_syncobj_handle_to_fd error paths, the refcount is decremented, but
in the success path the refcount should remain at +1 as the struct
drm_syncobj now belongs to the newly opened file. Instead, the
refcount was incremented again to +2.

References:

https://source.android.com/security/bulletin/pixel/2021-06-01
https://android.googlesource.com/kernel/common/+/328ec6286a78a71500b74255448e8f3c83d2b2c4