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

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Date: Tue, 18 Jun 2024 19:20:54 -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 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.

I think it's fine if an individual LSM wants to implement a file
digest cache as part of its own functionality, but a generalized file
digest cache seems like something that should be part of the general
kernel, and not implemented as a LSM.

-- 
paul-moore.com