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    SubjectRe: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

    I hate to bring this again, but what if the admin in the container
    mounts an external file system (eg. nfs, usb, loop mount from a file,
    or via fuse), and that file system already has a device that we would
    like to ban inside that container ?

    Since anyway we will have to keep a white- (or black-) list of devices
    that are permitted in a container, and that list may change even change
    per container -- why not enforce the access control at the VFS layer ?
    It's safer in the long run.

    Oren.

    Serge E. Hallyn wrote:
    > Quoting Tetsuo Handa (penguin-kernel@i-love.sakura.ne.jp):
    >> Hello.
    >>
    >> Serge E. Hallyn wrote:
    >>> CAP_MKNOD will be removed from its capability
    >> I think it is not enough because the root can rename/unlink device files
    >> (mv /dev/sda1 /dev/tmp; mv /dev/sda2 /dev/sda1; mv /dev/tmp /dev/sda2).
    >
    > Sure but that doesn't bother us :)
    >
    > The admin in the container has his own /dev directory and can do what he
    > likes with the devices he's allowed to have. He just shouldn't have
    > access to others. If he wants to rename /dev/sda1 to /dev/sda5 that's
    > his choice.
    >
    >>> To use your approach, i guess we would have to use selinux (or tomoyo)
    >>> to enforce that devices may only be created under /dev?
    >> Everyone can use this filesystem alone.
    >
    > Sure but it is worthless alone.
    >
    > No?
    >
    > What will keep the container admin from doing 'mknod /root/hda1 b 3 1'?
    >
    >> But use with MAC (or whatever access control mechanisms that prevent
    >> attackers from unmounting/overlaying this filesystem) is recomennded.
    >
    > -serge
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    > Containers@lists.linux-foundation.org
    > https://lists.linux-foundation.org/mailman/listinfo/containers


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