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    SubjectRe: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution
    On 27-Mär 08:27, Stephen Smalley wrote:
    > On 3/26/20 8:24 PM, James Morris wrote:
    > > On Thu, 26 Mar 2020, KP Singh wrote:
    > >
    > > > +int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
    > > > + const struct bpf_prog *prog)
    > > > +{
    > > > + /* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks
    > > > + */
    > > > + if (!capable(CAP_MAC_ADMIN))
    > > > + return -EPERM;
    > > > +
    > >
    > > Stephen, can you confirm that your concerns around this are resolved
    > > (IIRC, by SELinux implementing a bpf_prog callback) ?
    >
    > I guess the only residual concern I have is that CAP_MAC_ADMIN means
    > something different to SELinux (ability to get/set file security contexts
    > unknown to the currently loaded policy), so leaving the CAP_MAC_ADMIN check
    > here (versus calling a new security hook here and checking CAP_MAC_ADMIN in
    > the implementation of that hook for the modules that want that) conflates
    > two very different things. Prior to this patch, there are no users of
    > CAP_MAC_ADMIN outside of individual security modules; it is only checked in
    > module-specific logic within apparmor, safesetid, selinux, and smack, so the
    > meaning was module-specific.

    As we had discussed, We do have a security hook as well:

    https://lore.kernel.org/bpf/20200324180652.GA11855@chromium.org/

    The bpf_prog hook which can check for BPF_PROG_TYPE_LSM and implement
    module specific logic for LSM programs. I thougt that was okay?

    Kees was in favor of keeping the CAP_MAC_ADMIN check here:

    https://lore.kernel.org/bpf/202003241133.16C02BE5B@keescook

    If you feel strongly and Kees agrees, we can remove the CAP_MAC_ADMIN
    check here, but given that we already have a security hook that meets
    the requirements, we probably don't need another one.

    - KP


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