$ git clone -n https://src.fedoraproject.org/rpms/cnmatrix.git /var/lib/mock/f42-build-side-1-3587803-46935/root/chroot_tmpdir/scmroot/cnmatrix
Cloning into '/var/lib/mock/f42-build-side-1-3587803-46935/root/chroot_tmpdir/scmroot/cnmatrix'...
$ git fetch origin cb5870174d6d10abf5909bc868fa83d7668f0bfa:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/cnmatrix
 * [new ref]         cb5870174d6d10abf5909bc868fa83d7668f0bfa -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cb58701 Source is now part of libsurvive.