In fs/ocfs2/cluster/nodemanager.c in the Linux kernel before 4.15, local users can cause a denial of service (NULL pointer dereference and BUG) because a required mutex is not used.
https://www.debian.org/security/2018/dsa-4188
https://www.debian.org/security/2018/dsa-4187
https://usn.ubuntu.com/3798-2/
https://usn.ubuntu.com/3798-1/
https://usn.ubuntu.com/3776-2/
https://usn.ubuntu.com/3776-1/
https://lists.debian.org/debian-lts-announce/2018/05/msg00000.html
https://github.com/torvalds/linux/commit/853bc26a7ea39e354b9f8889ae7ad1492ffa28d2