Messages in this thread | | | Date | Tue, 5 Apr 2022 07:49:49 -0700 | Subject | Re: [PATCH 00/18] bpf: Secure and authenticated preloading of eBPF programs | From | Casey Schaufler <> |
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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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