RFC(v2): Audit Kernel Container IDs

Casey Schaufler casey at schaufler-ca.com
Thu Oct 12 16:33:49 UTC 2017

On 10/12/2017 7:14 AM, Richard Guy Briggs wrote:
> Containers are a userspace concept.  The kernel knows nothing of them.
> The Linux audit system needs a way to be able to track the container
> provenance of events and actions.  Audit needs the kernel's help to do
> this.
> Since the concept of a container is entirely a userspace concept, a
> registration from the userspace container orchestration system initiates
> this.  This will define a point in time and a set of resources
> associated with a particular container with an audit container ID.
> The registration is a pseudo filesystem (proc, since PID tree already
> exists) write of a u8[16] UUID representing the container ID to a file
> representing a process that will become the first process in a new
> container.  This write might place restrictions on mount namespaces
> required to define a container, or at least careful checking of
> namespaces in the kernel to verify permissions of the orchestrator so it
> can't change its own container ID.  A bind mount of nsfs may be
> necessary in the container orchestrator's mntNS.
> Note: Use a 128-bit scalar rather than a string to make compares faster
> and simpler.
> Require a new CAP_CONTAINER_ADMIN to be able to carry out the
> registration.

Hang on. If containers are a user space concept, how can
you want CAP_CONTAINER_ANYTHING? If there's not such thing as
a container, how can you be asking for a capability to manage

>   At that time, record the target container's user-supplied
> container identifier along with the target container's first process
> (which may become the target container's "init" process) process ID
> (referenced from the initial PID namespace), all namespace IDs (in the
> form of a nsfs device number and inode number tuple) in a new auxilliary
> record AUDIT_CONTAINER with a qualifying op=$action field.
> Issue a new auxilliary record AUDIT_CONTAINER_INFO for each valid
> container ID present on an auditable action or event.
> Forked and cloned processes inherit their parent's container ID,
> referenced in the process' task_struct.
> Mimic setns(2) and return an error if the process has already initiated
> threading or forked since this registration should happen before the
> process execution is started by the orchestrator and hence should not
> yet have any threads or children.  If this is deemed overly restrictive,
> switch all threads and children to the new containerID.
> Trust the orchestrator to judiciously use and restrict CAP_CONTAINER_ADMIN.
> Log the creation of every namespace, inheriting/adding its spawning
> process' containerID(s), if applicable.  Include the spawning and
> spawned namespace IDs (device and inode number tuples).
> [AUDIT_NS_CREATE, AUDIT_NS_DESTROY] [clone(2), unshare(2), setns(2)]
> Note: At this point it appears only network namespaces may need to track
> container IDs apart from processes since incoming packets may cause an
> auditable event before being associated with a process.
> Log the destruction of every namespace when it is no longer used by any
> process, include the namespace IDs (device and inode number tuples).
> [AUDIT_NS_DESTROY] [process exit, unshare(2), setns(2)]
> Issue a new auxilliary record AUDIT_NS_CHANGE listing (opt: op=$action)
> the parent and child namespace IDs for any changes to a process'
> namespaces. [setns(2)]
> Note: It may be possible to combine AUDIT_NS_* record formats and
> distinguish them with an op=$action field depending on the fields
> required for each message type.
> When a container ceases to exist because the last process in that
> container has exited and hence the last namespace has been destroyed and
> its refcount dropping to zero, log the fact.
> (This latter is likely needed for certification accountability.)  A
> container object may need a list of processes and/or namespaces.
> A namespace cannot directly migrate from one container to another but
> could be assigned to a newly spawned container.  A namespace can be
> moved from one container to another indirectly by having that namespace
> used in a second process in another container and then ending all the
> processes in the first container.
> (v2)
> - switch from u64 to u128 UUID
> - switch from "signal" and "trigger" to "register"
> - restrict registration to single process or force all threads and children into same container
> - RGB
> --
> Richard Guy Briggs <rgb at redhat.com>
> Sr. S/W Engineer, Kernel Security, Base Operating Systems
> Remote, Ottawa, Red Hat Canada
> IRC: rgb, SunRaycer
> Voice: +1.647.777.2635, Internal: (81) 32635
> --
> Linux-audit mailing list
> Linux-audit at redhat.com
> https://www.redhat.com/mailman/listinfo/linux-audit

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