linux-kernel - Re: [PATCH V31 25/25] debugfs: Disable open() when kernel is locked down

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Date:   Wed, 27 Mar 2019 11:35:20 +0900
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Matthew Garrett <mjg59@...gle.com>
Cc:     James Morris <jmorris@...ei.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Linux API <linux-api@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH V31 25/25] debugfs: Disable open() when kernel is locked
 down

On Tue, Mar 26, 2019 at 07:06:36PM -0700, Matthew Garrett wrote:
> On Tue, Mar 26, 2019 at 5:31 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Tue, Mar 26, 2019 at 11:27:41AM -0700, Matthew Garrett wrote:
> > > From: Matthew Garrett <mjg59@...gle.com>
> > >
> > > debugfs has not been meaningfully audited in terms of ensuring that
> > > userland cannot trample over the kernel. At Greg's request, disable
> > > access to it entirely when the kernel is locked down. This is done at
> > > open() time rather than init time as the kernel lockdown status may be
> > > made stricter at runtime.
> 
> (snip)
> 
> > Why allow all this, why not just abort the registering of the filesystem
> > with the vfs core so it can't even be mounted?
> 
> As mentioned in the commit message, because the lockdown state can be
> made stricter at runtime - blocking at mount time would be
> inconsistent if the machine is locked down afterwards. We could
> potentially assert that it's the admin's responsibility to ensure that
> debugfs isn't mounted at the point of policy being made stricter?

Ugh, I can not read, sorry, neverind.

The patch is fine as-is.

greg k-h