The KEYS subsystem in the Linux kernel before 4.14.6 omitted an access-control check when adding a key to the current task's "default request-key keyring" via the request_key() system call, allowing a local user to use a sequence of crafted system calls to add keys to a keyring with only Search permission (not Write permission) to that keyring, related to construct_get_dest_keyring() in security/keys/request_key.c.
https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.6
https://www.debian.org/security/2018/dsa-4082
https://www.debian.org/security/2017/dsa-4073
https://usn.ubuntu.com/3632-1/
https://usn.ubuntu.com/3620-2/
https://usn.ubuntu.com/3620-1/
https://usn.ubuntu.com/3619-2/
https://usn.ubuntu.com/3619-1/
https://usn.ubuntu.com/3617-3/
https://usn.ubuntu.com/3617-2/
https://usn.ubuntu.com/3617-1/
https://lists.debian.org/debian-lts-announce/2018/01/msg00004.html
https://github.com/torvalds/linux/commit/4dca6ea1d9432052afb06baf2e3ae78188a4410b