netdev - Re: [PATCH bpf-next 06/11] bpf: Add reference tracking to verifier

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Date:   Thu, 13 Sep 2018 12:00:38 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Joe Stringer <joe@...d.net.nz>, daniel@...earbox.net,
        netdev <netdev@...r.kernel.org>, ast@...nel.org,
        john fastabend <john.fastabend@...il.com>, tgraf@...g.ch,
        Martin KaFai Lau <kafai@...com>,
        Nitin Hande <nitin.hande@...il.com>, mauricio.vasquez@...ito.it
Subject: Re: [PATCH bpf-next 06/11] bpf: Add reference tracking to verifier

On Wed, 12 Sep 2018 at 16:17, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Tue, Sep 11, 2018 at 05:36:35PM -0700, Joe Stringer wrote:
> > ...
> > +
> > +/* release function corresponding to acquire_reference_state(). Idempotent. */
> > +static int __release_reference_state(struct bpf_func_state *state, int ptr_id)
> > +{
> > +     int i, last_idx;
> > +
> > +     if (!ptr_id)
> > +             return 0;
>
> Is this defensive programming or this condition can actually happen?
> As far as I can see all callers suppose to pass valid ptr_id into it.
>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
>

Looks like defensive programming to me. That said, if it's being
defensive, why not return `-EFAULT`? I'll try this out locally.