It was discovered in the Linux kernel before 4.11-rc8 that root can gain direct access to an internal keyring, such as ‘.dns_resolver’ in RHEL-7 or ‘.builtin_trusted_keys’ upstream, by joining it as its session keyring. This allows root to bypass module signature verification by adding a new public key of its own devising to the keyring.
people.canonical.com/~ubuntu-security/cve/2016/CVE-2016-9604.html
www.securityfocus.com/bid/102135
access.redhat.com/errata/RHSA-2017:1842
access.redhat.com/errata/RHSA-2017:2077
access.redhat.com/errata/RHSA-2017:2669
bugzilla.novell.com/show_bug.cgi?id=1035576
bugzilla.redhat.com/show_bug.cgi?id=CVE-2016-9604
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ee8f844e3c5a73b999edf733df1c529d6503ec2f