linux-kernel - Re: [PATCH v4 00/14] security: digest

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Date: Wed, 19 Jun 2024 11:49:06 -0400
From: Paul Moore <paul@...l-moore.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>
Cc: corbet@....net, jmorris@...ei.org, serge@...lyn.com, 
	akpm@...ux-foundation.org, shuah@...nel.org, mcoquelin.stm32@...il.com, 
	alexandre.torgue@...s.st.com, mic@...ikod.net, 
	linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	bpf@...r.kernel.org, zohar@...ux.ibm.com, dmitry.kasatkin@...il.com, 
	linux-integrity@...r.kernel.org, wufan@...ux.microsoft.com, 
	pbrobinson@...il.com, zbyszek@...waw.pl, hch@....de, mjg59@...f.ucam.org, 
	pmatilai@...hat.com, jannh@...gle.com, dhowells@...hat.com, jikos@...nel.org, 
	mkoutny@...e.com, ppavlu@...e.com, petr.vorel@...il.com, mzerqung@...inter.de, 
	kgold@...ux.ibm.com, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v4 00/14] security: digest_cache LSM

On Wed, Jun 19, 2024 at 3:59 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
> On Tue, 2024-06-18 at 19:20 -0400, Paul Moore wrote:
> > On Mon, Apr 15, 2024 at 10:25 AM Roberto Sassu
> > <roberto.sassu@...weicloud.com> wrote:
> > >
> > > From: Roberto Sassu <roberto.sassu@...wei.com>
> > >
> > > Integrity detection and protection has long been a desirable feature, to
> > > reach a large user base and mitigate the risk of flaws in the software
> > > and attacks.
> > >
> > > However, while solutions exist, they struggle to reach the large user
> > > base, due to requiring higher than desired constraints on performance,
> > > flexibility and configurability, that only security conscious people are
> > > willing to accept.
> > >
> > > This is where the new digest_cache LSM comes into play, it offers
> > > additional support for new and existing integrity solutions, to make
> > > them faster and easier to deploy.
> > >
> > > The full documentation with the motivation and the solution details can be
> > > found in patch 14.
> > >
> > > The IMA integration patch set will be introduced separately. Also a PoC
> > > based on the current version of IPE can be provided.
> >
> > I'm not sure we want to implement a cache as a LSM.  I'm sure it would
> > work, but historically LSMs have provided some form of access control,
> > measurement, or other traditional security service.  A digest cache,
> > while potentially useful for a variety of security related
> > applications, is not a security service by itself, it is simply a file
> > digest storage mechanism.
>
> Uhm, currently the digest_cache LSM is heavily based on the LSM
> infrastructure:

I understand that, but as I said previously, I don't believe that we
want to support a LSM which exists solely to provide a file digest
cache.  LSMs should be based around the idea of some type of access
control, security monitoring, etc.

Including a file digest cache in IMA, or implementing it as a
standalone piece of kernel functionality, are still options.  If you
want to pursue this, I would suggest that including the digest cache
as part of IMA would be the easier of the two options; if it proves to
be generally useful outside of IMA, it can always be abstracted out to
a general kernel module/subsystem.

-- 
paul-moore.com