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    Subject[RFC 0/5] user namespaces: start clamping down
    Following is the next version of the user namespace patchset.

    The core of the set is patch 2, originally conceived of and
    implemented by Eric Biederman. The concept is to target
    capabilities at user namespaces. A task's capabilities are
    now contextualized as follows (previously, capabilities had
    no context):

    1. For a task in the initial user namespace, the calculated
    capabilities (pi, pe, pp) are available to act upon any
    user namespace.

    2. For a task in a child user namespace, the calculated
    capabilities are available to act only on its own or any
    descendent user namespace. It has no capabilities to any
    parent or unrelated user namespaces.

    3. If a user A creates a new user namespace, that user has
    all capabilities to that new user namespace and any of its
    descendents. (Contrast this with a user namespace created
    by another user B in the same user namespace, to which this
    user A has only his calculated capabilities)

    All existing 'capable' checks are automatically converted to
    checks against the initial user namespace. This means that
    by default, root in a child user namespace is powerless.
    Patches 3-5 begin to enable capabilities in child user
    namespaces to set hostnames, kill tasks, and do ptrace.

    My near-term next goals will be to enable setuid and setgid,
    and to provide a way for the filesystem to be usable in child
    user namespaces. At the very least I'd like a fresh loopback
    or LVM mount and proc mounts to be supported.


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