Re: [PATCH v4 00/14] security: digest_cache LSM

Paul Moore
2024-06-20T16:08:57Z

On Thu, Jun 20, 2024 at 11:14 AM Roberto Sassu
<roberto.sassu@huaweicloud.com> wrote:
> On Thu, 2024-06-20 at 10:48 -0400, Paul Moore wrote:
> > On Thu, Jun 20, 2024 at 5:12 AM Roberto Sassu
> > <roberto.sassu@huaweicloud.com> wrote:
> > > On Wed, 2024-06-19 at 14:43 -0400, Paul Moore wrote:
> > > > On Wed, Jun 19, 2024 at 12:38 PM Roberto Sassu
> > > > <roberto.sassu@huaweicloud.com> wrote:
> > > > >
> > > > > Making it a kernel subsystem would likely mean replicating what the LSM
> > > > > infrastructure is doing, inode (security) blob and being notified about
> > > > > file/directory changes.
> > > >
> > > > Just because the LSM framework can be used for something, perhaps it
> > > > even makes the implementation easier, it doesn't mean the framework
> > > > should be used for everything.
> > >
> > > It is supporting 3 LSMs: IMA, IPE and BPF LSM.
> > >
> > > That makes it a clear target for the security subsystem, and as you
> > > suggested to start for IMA, if other kernel subsystems require them, we
> > > can make it as an independent subsystem.
> >
> > Have you discussed the file digest cache functionality with either the
> > IPE or BPF LSM maintainers? While digest_cache may support these
>
> Well, yes. I was in a discussion since long time ago with Deven and
> Fan. The digest_cache LSM is listed in the Use Case section of the IPE
> cover letter:
>
> https://lore.kernel.org/linux-integrity/1716583609-21790-1-git-send-email-wufan@linux.microsoft.com/

I would hope to see more than one sentence casually mentioning that
there might be some integration in the future.

> I also developed an IPE module back in the DIGLIM days:
>
> https://lore.kernel.org/linux-integrity/a16a628b9e21433198c490500a987121@huawei.com/

That looks like more of an fs-verity integration to me. Yes, of
course there would be IPE changes to accept a signature/digest from a
digest cache, but that should be minor.

> As for eBPF, I just need to make the digest_cache LSM API callable by
> eBPF programs, very likely not requiring any change on the eBPF
> infrastructure itself.

That's great, but it would be good to hear from KP and any other BPF
LSM devs that this would be desirable.

I still believe that this is something that should live as a service
outside of the LSM.

--
paul-moore.com