linux-kernel - Re: [PATCH 2/3] security: add symbol namespace for reading file data

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Date:   Wed, 13 May 2020 11:07:46 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        viro@...iv.linux.org.uk, gregkh@...uxfoundation.org,
        rafael@...nel.org, jeyu@...nel.org, jmorris@...ei.org,
        keescook@...omium.org, paul@...l-moore.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        nayna@...ux.ibm.com, zohar@...ux.ibm.com,
        scott.branden@...adcom.com, dan.carpenter@...cle.com,
        skhan@...uxfoundation.org, geert@...ux-m68k.org,
        tglx@...utronix.de, bauerman@...ux.ibm.com, dhowells@...hat.com,
        linux-integrity@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
        selinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] security: add symbol namespace for reading file data

On Wed, May 13, 2020 at 04:16:22PM +0000, Luis Chamberlain wrote:
> On Wed, May 13, 2020 at 10:40:31AM -0500, Eric W. Biederman wrote:
> > Luis Chamberlain <mcgrof@...nel.org> writes:
> > 
> > > Certain symbols are not meant to be used by everybody, the security
> > > helpers for reading files directly is one such case. Use a symbol
> > > namespace for them.
> > >
> > > This will prevent abuse of use of these symbols in places they were
> > > not inteded to be used, and provides an easy way to audit where these
> > > types of operations happen as a whole.
> > 
> > Why not just remove the ability for the firmware loader to be a module?
> > 
> > Is there some important use case that requires the firmware loader
> > to be a module?
> > 
> > We already compile the code in by default.  So it is probably just
> > easier to remove the modular support all together.  Which would allow
> > the export of the security hooks to be removed as well.
> 
> Yeah, that's a better solution. The only constaint I am aware of is
> we *cannot* change the name of the module from firmware_class since the
> old fallback sysfs loader depends on the module name. So, so long as we
> take care with that on built-in and document this very well, I think
> we should be good.
> 
> I checked the commit logs and this was tristate since the code was added
> upstream, so I cannot see any good reason it was enabled as modular.
> 
> Speaking with a *backports experience* hat on, we did have a use case
> to use a module for it in case a new feature was added upstream which
> was not present on older kernels. However I think that using a separate
> symbol prefix would help with that.
> 
> Would any Android stakeholders / small / embedded folks whave any issue
> with this?

As long as you can still *completely* compile out firmware loading, I
don't think there's a huge use case for making it modular. y/n seems
fine.