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.

It was discovered that the keyring implementation in the Linux kernel in
some situations did not prevent special internal keyrings from being joined
by userspace keyrings. A privileged local attacker could use this to bypass
module verification.

 jdstrand> android kernels (flo, goldfish, grouper, maguro, mako and manta) are
  not supported on the Ubuntu Touch 14.10 and earlier preview kernels
 jdstrand> linux-lts-saucy no longer receives official support
 jdstrand> linux-lts-quantal no longer receives official support