Re: [PATCH v3 bpf-next 1/3] bpf: introduce new VFS based BPF kfuncs

[Matt Bobrowski <mattbobrowski@google.com>]

On Fri, Jul 26, 2024 at 01:43:45PM -0700, Alexei Starovoitov wrote:
> On Fri, Jul 26, 2024 at 1:56 AM Matt Bobrowski <mattbobrowski@google.com> wrote:
> > +
> > +static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
> > +{
> > +       if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) ||
> > +           prog->type == BPF_PROG_TYPE_LSM)
> > +               return 0;
> > +       return -EACCES;
> > +}
> > +
> > +static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
> > +       .owner = THIS_MODULE,
> > +       .set = &bpf_fs_kfunc_set_ids,
> > +       .filter = bpf_fs_kfuncs_filter,
> > +};
> > +
> > +static int __init bpf_fs_kfuncs_init(void)
> > +{
> > +       return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set);
> > +}
> 
> Aside from buf__sz <= 0 that Christian spotted

I'm going to fix this up in v2 of this patch, so don't worry about it.

> the bpf_fs_kfuncs_filter() is a watery water.
> It's doing a redundant check that is already covered by
> 
> register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM,...
> 
> I'll remove it while applying.

As discussed, this filter is currently required as without it we
inadvertently allow tracing BPF programs to also use these BPF
kfuncs.

/M