The KEYS subsystem in the Linux kernel through 4.13.7 mishandles use of add_key for a key that already exists but is uninstantiated, which allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact via a crafted system call.
access.redhat.com/errata/RHSA-2018:0654
bugzilla.redhat.com/show_bug.cgi?id=1498016
lists.debian.org/debian-lts-announce/2017/12/msg00004.html
marc.info/?t=150654188100001&r=1&w=2
marc.info/?t=150783958600011&r=1&w=2
usn.ubuntu.com/3798-1/
usn.ubuntu.com/3798-2/
www.mail-archive.com/linux-kernel%40vger.kernel.org/msg1499828.html