linux-kernel - Re: [RFC PATCH] mm: create security context for memfd

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Date:   Thu, 17 Feb 2022 17:32:39 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Christian Göttsche <cgzones@...glemail.com>
Cc:     SElinux list <selinux@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: create security context for memfd_secret inodes

On Thu, Feb 17, 2022 at 9:24 AM Christian Göttsche
<cgzones@...glemail.com> wrote:
> On Thu, 27 Jan 2022 at 00:01, Paul Moore <paul@...l-moore.com> wrote:
> > On Tue, Jan 25, 2022 at 9:33 AM Christian Göttsche
> > <cgzones@...glemail.com> wrote:
> > >
> > > Create a security context for the inodes created by memfd_secret(2) via
> > > the LSM hook inode_init_security_anon to allow a fine grained control.
> > > As secret memory areas can affect hibernation and have a global shared
> > > limit access control might be desirable.
> > >
> > > Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> > > ---
> > > An alternative way of checking memfd_secret(2) is to create a new LSM
> > > hook and e.g. for SELinux check via a new process class permission.
> > > ---
> > >  mm/secretmem.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> >
> > This seems reasonable to me, and I like the idea of labeling the anon
> > inode as opposed to creating a new set of LSM hooks.  If we want to
> > apply access control policy to the memfd_secret() fds we are going to
> > need to attach some sort of LSM state to the inode, we might as well
> > use the mechanism we already have instead of inventing another one.
>
> Any further comments (on design or implementation)?
>
> Should I resend a non-rfc?

I personally would really like to see a selinux-testsuite for this so
that we can verify it works not just now but in the future too.  I
think having a test would also help demonstrate the usefulness of the
additional LSM controls.

> One naming question:
> Should the anonymous inode class be named "[secretmem]", like
> "[userfaultfd]", or "[secret_mem]" similar to "[io_uring]"?

The pr_fmt() string in mm/secretmem.c uses "secretmem" so I would
suggest sticking with "[secretmem]", although that is question best
answered by the secretmem maintainer.

-- 
paul-moore.com