linux-kernel - Re: Semantics of blktrace with lockdown (integrity) enabled kernel.

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Message-ID: <CAHC9VhR06pa2mDwW26XFqiry11Ubz2_3YKj+ayftu0JdYx9m9w@mail.gmail.com>
Date:   Thu, 6 Apr 2023 17:43:19 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        serge@...lyn.com, nathanl@...ux.ibm.com, junxiao.bi@...cle.com,
        joe.jin@...cle.com, Eric <eric.snowberg@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>, axboe@...nel.dk
Subject: Re: Semantics of blktrace with lockdown (integrity) enabled kernel.

On Thu, Apr 6, 2023 at 3:33 PM Konrad Rzeszutek Wilk
<konrad.wilk@...cle.com> wrote:
> On Thu, Apr 06, 2023 at 02:39:57PM -0400, Paul Moore wrote:

...

> > Before we go any further, can you please verify that your issue is
> > reproducible on a supported, upstream tree (preferably Linus')?
>
> Yes. Very much so.

Okay, in that case I suspect the issue is due to the somewhat limited
granularity in the lockdown LSM.  While there are a number of
different lockdown "levels", the reality is that the admin has to
choose from either NONE, INTEGRITY, or CONFIDENTIALITY.  Without
digging to deep into the code path that you would be hitting, we can
see that TRACEFS is blocked by the CONFIDENTIALITY (and therefore
INTEGRITY too) setting and DEBUGFS is blocked by the INTEGRITY
setting.  With DEBUGFS blocked by INTEGRITY, the only lockdown option
that would allow DEBUGFS is NONE.

Without knowing too much about blktrace beyond the manpage, it looks
like it has the ability to trace/snoop on the block device operations
so I don't think this is something we would want to allow in a
"locked" system.

Sorry.

-- 
paul-moore.com