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    SubjectRe: [PATCH 00/18] bpf: Secure and authenticated preloading of eBPF programs
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    On 4/4/2022 10:20 AM, Roberto Sassu wrote:
    >> From: Djalal Harouni [mailto:tixxdz@gmail.com]
    >> Sent: Monday, April 4, 2022 9:45 AM
    >> On Sun, Apr 3, 2022 at 5:42 PM KP Singh <kpsingh@kernel.org> wrote:
    >>> On Sat, Apr 2, 2022 at 1:55 AM Alexei Starovoitov
    >>> <alexei.starovoitov@gmail.com> wrote:
    >> ...
    >>>>> Pinning
    >>>>> them to unreachable inodes intuitively looked the
    >>>>> way to go for achieving the stated goal.
    >>>> We can consider inodes in bpffs that are not unlinkable by root
    >>>> in the future, but certainly not for this use case.
    >>> Can this not be already done by adding a BPF_LSM program to the
    >>> inode_unlink LSM hook?
    >>>
    >> Also, beside of the inode_unlink... and out of curiosity: making sysfs/bpffs/
    >> readonly after pinning, then using bpf LSM hooks
    >> sb_mount|remount|unmount...
    >> family combining bpf() LSM hook... isn't this enough to:
    >> 1. Restrict who can pin to bpffs without using a full MAC
    >> 2. Restrict who can delete or unmount bpf filesystem
    >>
    >> ?
    > I'm thinking to implement something like this.
    >
    > First, I add a new program flag called
    > BPF_F_STOP_ONCONFIRM, which causes the ref count
    > of the link to increase twice at creation time. In this way,
    > user space cannot make the link disappear, unless a
    > confirmation is explicitly sent via the bpf() system call.
    >
    > Another advantage is that other LSMs can decide
    > whether or not they allow a program with this flag
    > (in the bpf security hook).
    >
    > This would work regardless of the method used to
    > load the eBPF program (user space or kernel space).
    >
    > Second, I extend the bpf() system call with a new
    > subcommand, BPF_LINK_CONFIRM_STOP, which
    > decreasres the ref count for the link of the programs
    > with the BPF_F_STOP_ONCONFIRM flag. I will also
    > introduce a new security hook (something like
    > security_link_confirm_stop), so that an LSM has the
    > opportunity to deny the stop (the bpf security hook
    > would not be sufficient to determine exactly for
    > which link the confirmation is given, an LSM should
    > be able to deny the stop for its own programs).

    Would you please stop referring to a set of eBPF programs
    loaded into the BPF LSM as an LSM? Call it a BPF security
    module (BSM) if you must use an abbreviation. An LSM is a
    provider of security_ hooks. In your case that is BPF. When
    you call the set of eBPF programs an LSM it is like calling
    an SELinux policy an LSM.

    >
    > What do you think?
    >
    > Thanks
    >
    > Roberto
    >
    > HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
    > Managing Director: Li Peng, Zhong Ronghua

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