The KEYS subsystem in the Linux kernel before 3.18 allows local users to gain privileges or cause a denial of service (NULL pointer dereference and system crash) via vectors involving a NULL value for a certain match field, related to the keyring_search_iterator function in keyring.c.
https://usn.ubuntu.com/3849-2/
https://usn.ubuntu.com/3849-1/
https://github.com/torvalds/linux/commit/c06cfb08b88dfbe13be44a69ae2fdc3a7c902d81
https://bugzilla.redhat.com/show_bug.cgi?id=1428353
https://access.redhat.com/errata/RHSA-2017:2444
https://access.redhat.com/errata/RHSA-2017:2437
https://access.redhat.com/errata/RHSA-2017:2077
https://access.redhat.com/errata/RHSA-2017:1842