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

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Date:   Mon, 2 May 2022 15:45:35 +0200
From:   Christian Göttsche <cgzones@...glemail.com>
To:     Paul Moore <paul@...l-moore.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 mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm: create security context for memfd_secret inodes

On Thu, 17 Feb 2022 at 23:32, Paul Moore <paul@...l-moore.com> wrote:
>
> 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.
>

Any comments (especially from the mm people)?

Draft SELinux testsuite patch:
https://github.com/SELinuxProject/selinux-testsuite/pull/80

> > 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