linux-hardening - Re: [PATCH v7 6/6] mm/memfd: security hook for memfd

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Message-ID: <CALmYWFvrasXnshO01YGWRyC7qKk4o0G88yAgkgjO1YBumF5zeA@mail.gmail.com>
Date:   Tue, 13 Dec 2022 07:00:00 -0800
From:   Jeff Xu <jeffxu@...gle.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     jeffxu@...omium.org, skhan@...uxfoundation.org,
        keescook@...omium.org, akpm@...ux-foundation.org,
        dmitry.torokhov@...il.com, dverkamp@...omium.org, hughd@...gle.com,
        jorgelo@...omium.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        jannh@...gle.com, linux-hardening@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v7 6/6] mm/memfd: security hook for memfd_create

On Fri, Dec 9, 2022 at 10:29 AM Paul Moore <paul@...l-moore.com> wrote:
>
> On Fri, Dec 9, 2022 at 11:05 AM <jeffxu@...omium.org> wrote:
> >
> > From: Jeff Xu <jeffxu@...gle.com>
> >
> > The new security_memfd_create allows lsm to check flags of
> > memfd_create.
> >
> > The security by default system (such as chromeos) can use this
> > to implement system wide lsm to allow only non-executable memfd
> > being created.
> >
> > Signed-off-by: Jeff Xu <jeffxu@...gle.com>
> > Reported-by: kernel test robot <lkp@...el.com>
> > ---
> >  include/linux/lsm_hook_defs.h | 1 +
> >  include/linux/lsm_hooks.h     | 4 ++++
> >  include/linux/security.h      | 6 ++++++
> >  mm/memfd.c                    | 5 +++++
> >  security/security.c           | 5 +++++
> >  5 files changed, 21 insertions(+)
>
> We typically require at least one in-tree LSM implementation to
> accompany a new LSM hook.  Beyond simply providing proof that the hook
> has value, it helps provide a functional example both for reviewers as
> well as future LSM implementations.  Also, while the BPF LSM is
> definitely "in-tree", its nature is such that the actual
> implementation lives out-of-tree; something like SELinux, AppArmor,
> Smack, etc. are much more desirable from an in-tree example
> perspective.
>
Thanks for the comments.
Would that be OK if I add a new LSM in the kernel  to block executable
memfd creation ?
Alternatively,  it might be possible to add this into SELinux or
landlock, it will be a larger change.

Thanks

Jeff


> --
> paul-moore.com