linux-kernel - Re: [PATCH v6 07/15] digest_cache: Allow registration of digest list parsers

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Message-ID: <Z0d4vXuCqjTo_QW1@bombadil.infradead.org>
Date: Wed, 27 Nov 2024 11:53:33 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Roberto Sassu <roberto.sassu@...weicloud.com>
Cc: zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
	eric.snowberg@...cle.com, corbet@....net, petr.pavlu@...e.com,
	samitolvanen@...gle.com, da.gomez@...sung.com,
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	alexandre.torgue@...s.st.com, linux-integrity@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-modules@...r.kernel.org,
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	ppavlu@...e.com, petr.vorel@...il.com, mzerqung@...inter.de,
	kgold@...ux.ibm.com, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v6 07/15] digest_cache: Allow registration of digest list
 parsers

On Wed, Nov 27, 2024 at 10:51:11AM +0100, Roberto Sassu wrote:
> For eBPF programs we are also in a need for a better way to
> measure/appraise them.

I am confused now, I was under the impression this "Integrity Digest
Cache" is just a special thing for LSMs, and so I was under the
impression that kernel_read_file() lsm hook already would take care
of eBPF programs.

> Now, I'm trying to follow you on the additional kernel_read_file()
> calls. I agree with you, if a parser tries to open again the file that
> is being verified it would cause a deadlock in IMA (since the inode
> mutex is already locked for verifying the original file).

Just document this on the parser as a requirement.

> > > Supporting kernel modules opened the road for new deadlocks, since one
> > > can ask a digest list to verify a kernel module, but that digest list
> > > requires the same kernel module. That is why the in-kernel mechanism is
> > > 100% reliable,
> > 
> > Are users of this infrastructure really in need of modules for these
> > parsers?
> 
> I planned to postpone this to later, and introduced two parsers built-
> in (TLV and RPM). However, due to Linus's concern regarding the RPM
> parser, I moved it out in a kernel module.

OK this should be part of the commit log, ie that it is not desirable to
have an rpm parser in-kernel for some users.

  Luis