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    SubjectRe: [RESEND][RFC][PATCH 2/7] implementation of LSM hooks
    Date
    On Apr 18, 2006, at 21:48:56, Casey Schaufler wrote:
    > --- James Morris <jmorris@namei.org> wrote:
    >> With pathnames, there is an unbounded and unknown number of
    >> effective security policies on the system, as there are an
    >> unbounded and unknown number of ways of viewing the files via
    >> pathnames.
    >
    > I agree that for traditional DAC and MAC (including the flavors
    > supported by SELinux) inodes is the only way to go. SELinux is a
    > traditional Trusted OS architecture and addresses the traditional
    > Trusted OS issues.

    Perhaps the SELinux model should be extended to handle (dir-inode,
    path-entry) pairs. For example, if I want to protect the /etc/shadow
    file regardless of what tool is used to safely modify it, I would set
    up security as follows:

    o Protect the "/" and "/etc" directory inodes as usual under SELinux
    (with attributes on directory inodes).
    o Create pairs with (etc_inode,"shadow") and (etc_inode,"gshadow")
    and apply security attributes to those potentially nonexistent pairs.

    I'm not terribly familiar with the exact internal semantics of
    SELinux, but that should provide a 90% solution (it fixes bind mounts
    and namespaces). The remaining 2 issues are hardlinks and fd-
    passing. For hardlinks you don't care about other links to that
    data, you're concerned with protecting a particular filesystem
    location, not particular contents, so you just need to prevent _new_
    hardlinks to a protected (dir_inode, path_elem) pair, which doesn't
    seem very hard. For fd-passing, I don't know what to do. Perhaps
    nothing.

    Anyways, just a few ideas for consideration

    Cheers,
    Kyle Moffett

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