netdev - Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown permission checks

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Date:   Sat, 5 Jun 2021 21:30:57 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        selinux@...r.kernel.org, ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown
 permission checks

On Fri, Jun 4, 2021 at 8:08 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Fri, Jun 4, 2021 at 4:34 PM Paul Moore <paul@...l-moore.com> wrote:
> >
> > > Again, the problem is not limited to BPF at all. kprobes is doing register-
> > > time hooks which are equivalent to the one of BPF. Anything in run-time
> > > trying to prevent probe_read_kernel by kprobes or BPF is broken by design.
> >
> > Not being an expert on kprobes I can't really comment on that, but
> > right now I'm focused on trying to make things work for the BPF
> > helpers.  I suspect that if we can get the SELinux lockdown
> > implementation working properly for BPF the solution for kprobes won't
> > be far off.
>
> Paul,

Hi Alexei,

> Both kprobe and bpf can call probe_read_kernel==copy_from_kernel_nofault
> from all contexts.
> Including NMI.

Thanks, that is helpful.  In hindsight it should have been obvious
that kprobe/BPF would offer to insert code into the NMI handlers, but
I don't recall it earlier in the discussion, it's possible I simply
missed the mention.

> Most of audit_log_* is not acceptable.
> Just removing a wakeup is not solving anything.

That's not really fair now is it?  Removing the wakeups in
audit_log_start() and audit_log_end() does solve some problems,
although not all of them (i.e. the NMI problem being the 800lb
gorilla).  Because of the NMI case we're not going to solve the
LSM/audit case anytime soon so it looks like we are going to have to
fall back to the patch Daniel proposed.

Acked-by: Paul Moore <paul@...l-moore.com>

--
paul moore
www.paul-moore.com