Re: [RFC bpf-next] lsm: bpf: Remove lsm_prop_bpf

[Paul Moore <paul@paul-moore.com>]

On Mon, Oct 27, 2025 at 6:45 PM Song Liu <song@kernel.org> wrote:
> On Mon, Oct 27, 2025 at 2:14 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Fri, Oct 24, 2025 at 8:10 PM Song Liu <song@kernel.org> wrote:
> > >
> > > lsm_prop_bpf is not used in any code. Remove it.
> > >
> > > Signed-off-by: Song Liu <song@kernel.org>
> > >
> > > ---
> > >
> > > Or did I miss any user of it?
> > > ---
> > >  include/linux/lsm/bpf.h  | 16 ----------------
> > >  include/linux/security.h |  2 --
> > >  2 files changed, 18 deletions(-)
> > >  delete mode 100644 include/linux/lsm/bpf.h
> >
> > You probably didn't miss any direct reference to lsm_prop_bpf, but the
> > data type you really should look for when deciding on this is
> > lsm_prop.  There are a number of LSM hooks that operate on a lsm_prop
> > struct instead of secid tokens, and without a lsm_prop_bpf
> > struct/field in the lsm_prop struct a BPF LSM will be limited compared
> > to other LSMs.  Perhaps that limitation is okay, but it is something
>
> I think audit is the only user of lsm_prop (via audit_names and
> audit_context). For BPF based LSM or audit, I don't think we need
> specific lsm_prop. If anything is needed, we can implement it with
> task local storage or inode local storage.
>
> CC audit@ and Eric Paris for more comments on audit side.

You might not want to wait on a comment from Eric :)

> > that should be discussed; I see you've added KP to the To/CC line, I
> > would want to see an ACK from him before I merge anything removing
> > lsm_prop_bpf.
>
> Matt Bobrowski is the co-maintainer of BPF LSM. I think we are OK
> with his Reviewed-by?

Good to know, I wasn't aware that Matt was also listed as a maintainer
for the BPF LSM.  In that case as long as there is an ACK, not just a
reviewed tag, I think that should be sufficient.

> > I haven't checked to see if the LSM hooks associated with a lsm_prop
> > struct are currently allowed for a BPF LSM, but I would expect a patch
> > removing the lsm_prop_bpf struct/field to also disable those LSM hooks
> > for BPF LSM use.
>
> I don't think we need to disable anything here. When lsm_prop was
> first introduced in [1], nothing was added to handle BPF.

If the BPF LSM isn't going to maintain any state in the lsm_prop
struct, I'd rather see the associated LSM interfaces disabled from
being used in a BPF LSM just so we don't run into odd expectations in
the future.  Maybe they are already disabled, I haven't checked.

If you want to keep those interfaces/hooks enabled for a BPF LSM, just
keep the lsm_prop_bpf struct/field.

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