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.
git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c06cfb08b88dfbe13be44a69ae2fdc3a7c902d81
www.securityfocus.com/bid/97258
access.redhat.com/errata/RHSA-2017:1842
access.redhat.com/errata/RHSA-2017:2077
access.redhat.com/errata/RHSA-2017:2437
access.redhat.com/errata/RHSA-2017:2444
bugzilla.redhat.com/show_bug.cgi?id=1428353
github.com/torvalds/linux/commit/c06cfb08b88dfbe13be44a69ae2fdc3a7c902d81
usn.ubuntu.com/3849-1/
usn.ubuntu.com/3849-2/