Messages in this thread | | | Date | Tue, 5 Apr 2022 09:21:53 -0700 | Subject | Re: [PATCH 00/18] bpf: Secure and authenticated preloading of eBPF programs | From | Casey Schaufler <> |
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On 4/5/2022 8:29 AM, Roberto Sassu wrote: >> From: Casey Schaufler [mailto:casey@schaufler-ca.com] >> Sent: Tuesday, April 5, 2022 4:50 PM >> 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. > An eBPF program could be a provider of security_ hooks > too.
No, it can't. If I look in /sys/kernel/security/lsm what you see is "bpf". The LSM is BPF. What BPF does in its hooks is up to it and its responsibility.
> The bpf LSM is an aggregator, similarly to your > infrastructure to manage built-in LSMs. Maybe, calling > it second-level LSM or secondary LSM would better > represent this new class.
It isn't an LSM, and adding a qualifier doesn't make it one and only adds to the confusion.
> The only differences are the registration method, (SEC > directive instead of DEFINE_LSM), and what the hook > implementation can access.
Those two things pretty well define what an LSM is.
> The implementation of a security_ hook via eBPF can > follow the same structure of built-in LSMs, i.e. it can be > uniquely responsible for enforcing and be policy-agnostic, > and can retrieve the decisions based on a policy from a > component implemented somewhere else.
The BPF LSM provides mechanism. The eBPF programs provide policy.
> > Hopefully, I understood the basic principles correctly. > I let the eBPF maintainers comment on this. > > Thanks > > Roberto > > HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 > Managing Director: Li Peng, Zhong Ronghua > >>> What do you think? >>> >>> Thanks >>> >>> Roberto >>> >>> HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 >>> Managing Director: Li Peng, Zhong Ronghua
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