The (1) v9fs_create and (2) v9fs_lcreate functions in hw/9pfs/9p.c in QEMU (aka Quick Emulator) allow local guest OS privileged users to cause a denial of service (file descriptor or memory consumption) via vectors related to an already in-use fid.
https://bugzilla.redhat.com/show_bug.cgi?id=1437871
https://lists.debian.org/debian-lts-announce/2018/09/msg00007.html
https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg05449.html