linux-kernel - Re: [PATCH 10/10] LSM: Blob sharing support for S.A.R.A and LandLock

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Date:   Thu, 13 Sep 2018 17:50:48 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Golden_Miller83@...tonmail.ch
Cc:     keescook@...omium.org, casey@...aufler-ca.com,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
        selinux@...ho.nsa.gov, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp,
        Stephen Smalley <sds@...ho.nsa.gov>,
        linux-fsdevel@...r.kernel.org, casey.schaufler@...el.com
Subject: Re: [PATCH 10/10] LSM: Blob sharing support for S.A.R.A and LandLock

On Thu, Sep 13, 2018 at 4:58 PM Jordan Glover
<Golden_Miller83@...tonmail.ch> wrote:
>
> On Thursday, September 13, 2018 9:12 PM, Paul Moore <paul@...l-moore.com> wrote:
>
> > On Thu, Sep 13, 2018 at 11:19 AM Kees Cook keescook@...omium.org wrote:
> >
> > > On Thu, Sep 13, 2018 at 6:16 AM, Paul Moore paul@...l-moore.com wrote:
> > >
> > > > On Thu, Sep 13, 2018 at 12:19 AM Kees Cook keescook@...omium.org wrote:

...

> > > > > I don't see a good reason to make this a config. Why shouldn't this
> > > > > always be enabled?
> > > >
> > > > I do. From a user perspective it is sometimes difficult to determine
> > > > the reason behind a failed operation; its is a DAC based denial, the
> > > > LSM, or some other failure? Stacking additional LSMs has the
> > > > potential to make this worse. The boot time configuration adds to the
> > > > complexity.
> > >
> > > Let me try to convince you otherwise. :) The reason I think there's no
> > > need for this is because the only functional change here is how
> > > TOMOYO gets stacked. And in my proposal, we can convert TOMOYO to be
> > > enabled/disabled like LoadPin. Given the configs I showed, stacking
> > > TOMOYO with the other major LSMs becomes a config (and/or boottime)
> > > option.
> > > The changes for TOMOYO are still needed even with SECURITY_STACKING,
> > > and I argue that the other major LSMs remain the same. It's only
> > > infrastructure that has changed. So, I think having SECURITY_STACKING
> > > actually makes things more complex internally (all the ifdefs, weird
> > > enable logic) and for distros ("what's this stacking option", etc?)
> >
> > None of the above deals with the user experience or support burden a
> > distro would have by forcing stacking on. If we make it an option the
> > distros can choose for themselves; picking a kernel build config is
> > not something new to distros, and I think Casey's text adequately
> > explains CONFIG_SECURITY_STACKING in terms that would be sufficient.
>
> CONFIG_SECURITY_STACKING doesn't make any user visible changes on
> itself as it doesn't automatically enable any new LSM. The LSM
> specific configs are place where users/distros make decisions. If
> there is only one LSM enabled to run then there's nothing to stack.
> If someone choose to run two or more LSM in config/boot cmdline
> then we can assume having it stacked is what they wanted. As Kees
> pointed there is already CONFIG_SECURITY_DEFAULT_XXX. In both cases
> CONFIG_SECURITY_STACKING is redundant and only adds burden instead
> of removing it.

See my last response to Kees.

> > I currently have a neutral stance on stacking, making it mandatory
> > pushes me more towards a "no".
>
> This implies that your real concern is something else than
> CONFIG_SECURITY_STACKING which only allows you to ignore the whole
> thing. Please reveal it. There are a lot of people waiting for LSM
> stacking which is several years late and it would be great to
> resolve potential issues earlier  rather later.

What?  I resent the implication that I'm hiding anything; there are a
lot of fair criticisms you could level at me, but I take offense at
the idea that I'm not being honest here.  I've been speaking with
Casey, John, and others about stacking for years, both on-list and
in-person at conferences, and my
neutral-opinion-just-make-it-work-for-everything-and-make-it-optional
stance has been pretty consistent and isn't new.

Also, let's be really clear here: I'm only asking that stacking be
made a build time option (as it is in Casey's patchset).  That seems
like a pretty modest ask for something so significant and "several
years late" as you put it.

-- 
paul moore
www.paul-moore.com