A flaw was found in the Linux kernels SELinux LSM hook implementation
before version 5.7, where it incorrectly assumed that an skb would only
contain a single netlink message. The hook would incorrectly only validate
the first netlink message in the skb and allow or deny the rest of the
messages within the skb with the granted permission without further
processing.

Dmitry Vyukov discovered that the SELinux netlink security hook in the
Linux kernel did not validate messages in some situations. A privileged
attacker could use this to bypass SELinux netlink restrictions.

sbeattie

SELinux specific, not the default LSM in Ubuntu.