VULNERABILITY DETAILS
A use-after-free flaw was found in the way the Linux kernel's key management subsystem handled keyring object reference counting in certain error path of the join_session_keyring() function. A local, unprivileged user could use this flaw to escalate their privileges on the system.

VERSION
Operating System: ChromeOS current master branch

REPRODUCTION CASE
The join_session_keyring function in security/keys/process_keys.c in the Linux kernel before 4.4.1 mishandles object references in a certain error case, which allows local users to gain privileges or cause a denial of service (integer overflow and use-after-free) via crafted keyctl commands. 

MITIGATION
Update to kernmel 4.4.1 or higher.
Or apply this patch: https://bugzilla.redhat.com/show_bug.cgi?id=1297475#c13