From $URL: Race condition in fs/timerfd.c in the Linux kernel before 4.10.15 allows local users to gain privileges or cause a denial of service (list corruption or use-after-free) via simultaneous file-descriptor operations that leverage improper might_cancel queueing.
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=1e38da300e1e395a15048b0af1e5305bd91402f6
Fix in 4.9.27, 4.11