• Serge E. Hallyn's avatar
    userns: add a user_namespace as creator/owner of uts_namespace · 59607db3
    Serge E. Hallyn authored
    The expected course of development for user namespaces targeted
    capabilities is laid out at https://wiki.ubuntu.com/UserNamespace.
    
    Goals:
    
    - Make it safe for an unprivileged user to unshare namespaces.  They
      will be privileged with respect to the new namespace, but this should
      only include resources which the unprivileged user already owns.
    
    - Provide separate limits and accounting for userids in different
      namespaces.
    
    Status:
    
      Currently (as of 2.6.38) you can clone with the CLONE_NEWUSER flag to
      get a new user namespace if you have the CAP_SYS_ADMIN, CAP_SETUID, and
      CAP_SETGID capabilities.  What this gets you is a whole new set of
      userids, meaning that user 500 will have a different 'struct user' in
      your namespace than in other namespaces.  So any accounting information
      stored in struct user will be unique to your namespace.
    
      However, throughout the kernel there are checks which
    
      - simply check for a capability.  Since root in a child namespace
        has all capabilities, this means that a child namespace is not
        constrained.
    
      - simply compare uid1 == uid2.  Since these are the integer uids,
        uid 500 in namespace 1 will be said to be equal to uid 500 in
        namespace 2.
    
      As a result, the lxc implementation at lxc.sf.net does not use user
      namespaces.  This is actually helpful because it leaves us free to
      develop user namespaces in such a way that, for some time, user
      namespaces may be unuseful.
    
    Bugs aside, this patchset is supposed to not at all affect systems which
    are not actively using user namespaces, and only restrict what tasks in
    child user namespace can do.  They begin to limit privilege to a user
    namespace, so that root in a container cannot kill or ptrace tasks in the
    parent user namespace, and can only get world access rights to files.
    Since all files currently belong to the initila user namespace, that means
    that child user namespaces can only get world access rights to *all*
    files.  While this temporarily makes user namespaces bad for system
    containers, it starts to get useful for some sandboxing.
    
    I've run the 'runltplite.sh' with and without this patchset and found no
    difference.
    
    This patch:
    
    copy_process() handles CLONE_NEWUSER before the rest of the namespaces.
    So in the case of clone(CLONE_NEWUSER|CLONE_NEWUTS) the new uts namespace
    will have the new user namespace as its owner.  That is what we want,
    since we want root in that new userns to be able to have privilege over
    it.
    
    Changelog:
    	Feb 15: don't set uts_ns->user_ns if we didn't create
    		a new uts_ns.
    	Feb 23: Move extern init_user_ns declaration from
    		init/version.c to utsname.h.
    Signed-off-by: 's avatarSerge E. Hallyn <serge.hallyn@canonical.com>
    Acked-by: 's avatar"Eric W. Biederman" <ebiederm@xmission.com>
    Acked-by: 's avatarDaniel Lezcano <daniel.lezcano@free.fr>
    Acked-by: 's avatarDavid Howells <dhowells@redhat.com>
    Cc: James Morris <jmorris@namei.org>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    59607db3
version.c 1.1 KB