linux-kernel - Re: [RFC PATCH v14 15/19] fsverity: consume builtin signature via LSM hook

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Date: Mon, 11 Mar 2024 20:07:12 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Fan Wu <wufan@...ux.microsoft.com>
Cc: corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org,
	serge@...lyn.com, tytso@....edu, axboe@...nel.dk, agk@...hat.com,
	snitzer@...nel.org, eparis@...hat.com, paul@...l-moore.com,
	linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
	dm-devel@...ts.linux.dev, audit@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Deven Bowers <deven.desai@...ux.microsoft.com>
Subject: Re: [RFC PATCH v14 15/19] fsverity: consume builtin signature via
 LSM hook

On Mon, Mar 11, 2024 at 07:57:12PM -0700, Eric Biggers wrote:
> 
> As I've said before, this commit message needs some work.  It currently doesn't
> say anything about what the patch actually does.
> 
> BTW, please make sure you're Cc'ing the fsverity mailing list
> (fsverity@...ts.linux.dev), not fscrypt (linux-fscrypt@...r.kernel.org).

Also, I thought this patch was using a new LSM hook, but I now see that you're
actually abusing the existing security_inode_setsecurity() LSM hook.  Currently
that hook is called when an xattr is set.  I don't see any precedent for
overloading it for other purposes.  This seems problematic, as it means that a
request to set an xattr with the name you chose ("fsverity.builtin-sig") will be
interpreted by LSMs as the fsverity builtin signature.  A dedicated LSM hook may
be necessary to avoid issues with overloading the existing xattr hook like this.

- Eric