RFC(V4): Audit Kernel Container IDs

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. The motivations are: - A sysadmin needs to be able to filter unwanted, irrelevant or unimportant messages before they fill the queue so that important messages don't get lost. This is a certification requirement. - Security claims need to be made about containers, requiring tracking of actions within those containers to ensure compliance with established security policies. - It will be required to route messages from events local to an audit daemon instance or host audit daemon instance. - nsIDs were considered seriously, but turns out to be insufficient for efficient filtering, routing, and tracking. 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 identifier. The registration is a u64 representing the audit container identifier. This is written to a special file in a pseudo filesystem (proc, since PID tree already exists) representing a process that will become a parent process in that 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 mount namespace. This write can only happen once per process. Note: The justification for using a u64 is that it minimizes the information printed in every audit record, reducing bandwidth and limits comparisons to a single u64 which will be faster and less error-prone. [ALT: The registration is a netlink message to the audit subsystem of type AUDIT_SET_CONTID with a data structure including a u32 representing the PID of the target process to become the parent process in that container and a u64 representing the audit container identifier. :ALT] Require CAP_AUDIT_CONTROL to be able to carry out the registration. At that time, record the target container's user-supplied audit container identifier along with a target container's parent process (which may become the target container's "init" process) process ID (referenced from the initial PID namespace) in a new record AUDIT_CONTAINER_OP with a qualifying op=$action field. Issue a new auxilliary record AUDIT_CONTAINER_ID for each valid audit container identifier present on an auditable action or event. Forked and cloned processes inherit their parent's audit container identifier, referenced from the process' task_struct indirectly in the audit pointer to a struct audit_task_info. Since the audit container identifier is inherited rather than written, it can still be written once. This will prevent tampering while allowing nesting. 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 of the target's threads and children to the new containerID. Trust the orchestrator to judiciously use and restrict CAP_AUDIT_CONTROL. The audit container identifier will be stored in a refcounted kernel object that is searchable in a hashtabled list for efficient access. This is so that multiple container orchestrators/engines can operate on one machine without danger of them trampling each other's audit container identifiers. The owner of each container will also be stored to be able to permit tasks to be injected into an existing container only by its owner. The total number of containers can be restricted by a total count. To permit nesting containers, the target container must be a descendant process of the container orchestrator and the container's parent container (if set) will be stored in the audit container identifier kernel object. Report the chain of contids back to the top level container of a process. Filters will check the chain of contids back to the top container. The total depth of container nesting can be restricted. When a container ceases to exist because the last process in that container has exited log the fact to balance the registration action. (This is likely needed for certification accountability.) At this point it appears unnecessary to add a container session identifier since this is all tracked from loginuid and sessionid to communicate with the container orchestrator to spawn an additional session into an existing container which would be logged. It can be added at a later date without breaking API should it be deemed necessary. To permit container nesting beyond the initial user namespace, add a capcontid flag per process in its audit audit_task_info struct to store this ability communicated either via /proc/PID/capcontid or an audit netlink message type AUDIT_SET_CAPCONTID. The following namespace logging actions are not needed for certification purposes at this point, but are helpful for tracking namespace activity. These are auxilliary records that are associated with namespace manipulation syscalls unshare(2), clone(2) and setns(2), so the records will only show up if explicit syscall rules have been added to document this activity. Log the creation of every namespace, inheriting/adding its spawning process' audit container identifier(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. Since a namespace can be shared by processes in different containers, the namespace will need to track all containers to which it has been assigned. Upon registration, the target process' namespace IDs (in the form of a nsfs device number and inode number tuple) will be recorded in an AUDIT_NS_INFO auxilliary record. Log the destruction of every namespace that is no longer used by any process, including 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. The audit container identifier will need to be reaped from all implicated namespaces upon the destruction of a container. This namespace information adds supporting information for tracking events not attributable to specific processes. Changelog: (Upstream V4) - Add elaborated motivations. - Switch AUDIT_CONTAINER to AUDIT_CONTAINER_OP - Switch AUDIT_CONTAINER_INFO to AUDIT_CONTAINER_ID - Add capcontid to mimic CAP_AUDIT_CONTROL in non-init user namespaces - Check for max contid depth - Check for max contid quantity - Store the contid in a refcounted kernel object filed by hashtable lists - Mediate contid registration between peer orchestrators - Allow injection of processes into an existing container by container owner (Upstream V3) - switch back to u64 (from pmoore, can be expanded to u128 in future if need arises without breaking API. u32 was originally proposed, up to c36 discussed) - write-once, but children inherit audit container identifier and can then still be written once - switch to CAP_AUDIT_CONTROL - group namespace actions together, auxilliary records to namespace operations. (Upstream 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(a)redhat.com&gt; 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