It was found that the cgroup limitation of system resources used by Kubernetes can be bypassed. A guest pod can be used to consume a large amount of system memory. A suggested upstream patch set: https://lore.kernel.org/netdev/20190401113110.GA20717@hmswarspite.think-freely.org/T/#u
Statement: While this issue affects the Linux Kernel in Red Hat Enterprise Linux, and not OpenShift Container Platform (OCP) 3 code directly. OCP 3 makes use of CGroups in the Kernel to measure and report on the amount of system resources used by an end user application. The default Security Context Constraints (SCC) in OpenShift Container Platform 3.x disallow an end user from running a container as root. Also a check is performed by the OCP 3 Installer to ensure SELinux is enabled, [1]. [1] https://github.com/openshift/openshift-ansible/blob/006fb14e9a28df9bd1a58ac376bbdf3eba50fa51/roles/openshift_node/tasks/main.yml#L3
Mitigation: SELinux prevents a bind of the SCTP socket by a non-root user. To mitigate this issue if not using SELinux, or if a Security Context Constraint allows running pods as the root user the 'sctp' module should be blacklisted. Please this this Knowledge Base article for more information on how to blacklist a kernel module. https://access.redhat.com/solutions/41278
Created kernel tracking bugs for this issue: Affects: fedora-all [bug 1690646]
Acknowledgments: Name: Matteo Croce (Red Hat), Natale Vinto (Red Hat), Andrea Spagnolo (Red Hat)
The Kubernetes Security team made a public announcement about this vulnerability here: https://discuss.kubernetes.io/t/kubernetes-security-announcement-linux-kernel-memory-cgroups-escape-via-sctp-cve-2019-3874/5594
External References: https://lore.kernel.org/netdev/20190401113110.GA20717@hmswarspite.think-freely.org/T/#u https://discuss.kubernetes.io/t/kubernetes-security-announcement-linux-kernel-memory-cgroups-escape-via-sctp-cve-2019-3874/5594
This was fixed for Fedora with the 5.2 kernel rebases.
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2019:3309 https://access.redhat.com/errata/RHSA-2019:3309
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2019:3517 https://access.redhat.com/errata/RHSA-2019:3517
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2019-3874