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

    Serge E. Hallyn wrote:
    > Quoting Oren Laadan (orenl@cs.columbia.edu):
    >> 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 ?
    >
    > Miklos' user mount patches enforced that if !capable(CAP_MKNOD),
    > then mnt->mnt_flags |= MNT_NODEV. So that's no problem.

    Yes, that works to disallow all device files from a mounted file system.

    But it's a black and white thing: either they are all banned or allowed;
    you can't have some devices allowed and others not, depending on type
    A scenario where this may be useful is, for instance, if we some apps in
    the container to execute withing a pre-made chroot (sub)tree within that
    container.

    >
    > But that's been pulled out of -mm! ? Crap.
    >
    >> 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.
    >
    > By that you mean more along the lines of Pavel's patch than my whitelist
    > LSM, or you actually mean Tetsuo's filesystem (i assume you don't mean that
    > by 'vfs layer' :), or something different entirely?

    :)

    By 'vfs' I mean at open() time, and not at mount(), or mknod() time.
    Either yours or Pavel's; I tend to prefer not to use LSM as it may
    collide with future security modules.

    Oren.

    >
    > thanks,
    > -serge


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