• Eric W. Biederman's avatar
    userns,pidns: Verify the userns for new pid namespaces · a2b42626
    Eric W. Biederman authored
    It is pointless and confusing to allow a pid namespace hierarchy and
    the user namespace hierarchy to get out of sync.  The owner of a child
    pid namespace should be the owner of the parent pid namespace or
    a descendant of the owner of the parent pid namespace.
    
    Otherwise it is possible to construct scenarios where a process has a
    capability over a parent pid namespace but does not have the
    capability over a child pid namespace.  Which confusingly makes
    permission checks non-transitive.
    
    It requires use of setns into a pid namespace (but not into a user
    namespace) to create such a scenario.
    
    Add the function in_userns to help in making this determination.
    
    v2: Optimized in_userns by using level as suggested
        by: Kirill Tkhai <ktkhai@virtuozzo.com>
    
    Ref: 49f4d8b9 ("pidns: Capture the user namespace and filter ns_last_pid")
    Signed-off-by: 's avatar"Eric W. Biederman" <ebiederm@xmission.com>
    a2b42626