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    SubjectRe: [PATCH resend 1/2] capability: introduce sysctl for controlled user-ns capability whitelist
    Quoting Mahesh Bandewar (mahesh@bandewar.net):
    > From: Mahesh Bandewar <maheshb@google.com>
    >
    > Add a sysctl variable kernel.controlled_userns_caps_whitelist. This

    I understand the arguments in favor of whitelists in most cases for
    security purposes. But given that you've said the goal here is to
    prevent use of a capability in a user namespace when a CVE has been
    found, a whitelist seems the wrong choice, since

    1. it means that an attacker may through some other means be able
    to add a capability back into the whitelist when you specifically
    wanted to drop it. With a blacklist, you could say "once a cap has
    been dropped it can never be re-added without rebooting".
    2. it means by default all capabilities will be denied once the
    switch is pulled which is specifically not what you want in this
    case.
    3. the admin can't just say "drop CAP_NET_ADMIN", but needs to
    know to echo ~CAP_NET_ADMIN.

    Why not make it a blacklist, and once a cap is dropped it can
    never be re-added?

    -serge

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