linux-kernel - Re: [RFC][PATCH 3/4] lsm: Redefine LSM_HOOK() macro to add return value flags as argument

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Date:   Wed, 16 Nov 2022 17:04:05 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, revest@...omium.org,
        jackmanb@...omium.org, jmorris@...ei.org, serge@...lyn.com,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [RFC][PATCH 3/4] lsm: Redefine LSM_HOOK() macro to add return
 value flags as argument

On Wed, Nov 16, 2022 at 3:11 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
> On Tue, 2022-11-15 at 21:27 -0500, Paul Moore wrote:
> > On Tue, Nov 15, 2022 at 12:58 PM Roberto Sassu
> > <roberto.sassu@...weicloud.com> wrote:
> > > From: Roberto Sassu <roberto.sassu@...wei.com>
> > >
> > > Define four return value flags (LSM_RET_NEG, LSM_RET_ZERO, LSM_RET_ONE,
> > > LSM_RET_GT_ONE), one for each interval of interest (< 0, = 0, = 1, > 1).
> > >
> > > Redefine the LSM_HOOK() macro to add return value flags as argument, and
> > > set the correct flags for each LSM hook.
> > >
> > > Implementors of new LSM hooks should do the same as well.
> > >
> > > Cc: stable@...r.kernel.org # 5.7.x
> > > Fixes: 9d3fdea789c8 ("bpf: lsm: Provide attachment points for BPF LSM programs")
> > > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > > ---
> > >  include/linux/bpf_lsm.h       |   2 +-
> > >  include/linux/lsm_hook_defs.h | 779 ++++++++++++++++++++--------------
> > >  include/linux/lsm_hooks.h     |   9 +-
> > >  kernel/bpf/bpf_lsm.c          |   5 +-
> > >  security/bpf/hooks.c          |   2 +-
> > >  security/security.c           |   4 +-
> > >  6 files changed, 466 insertions(+), 335 deletions(-)
> >
> > Just a quick note here that even if we wanted to do something like
> > this, it is absolutely not -stable kernel material.  No way.
>
> I was unsure about that. We need a proper fix for this issue that needs
> to be backported to some kernels. I saw this more like a dependency.
> But I agree with you that it would be unlikely that this patch is
> applied to stable kernels.
>
> For stable kernels, what it would be the proper way? We still need to
> maintain an allow list of functions that allow a positive return value,
> at least. Should it be in the eBPF code only?

Ideally the fix for -stable is the same as what is done for Linus'
kernel (ignoring backport fuzzing), so I would wait and see how that
ends up first.  However, if the patchset for Linus' tree is
particularly large and touches a lot of code, you may need to work on
something a bit more targeted to the specific problem.  I tend to be
more conservative than most kernel devs when it comes to -stable
patches, but if you can't backport the main upstream patchset, smaller
(both in terms of impact and lines changed) is almost always better.

-- 
paul-moore.com