Re: [PATCH bpf-next v4 6/7] bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign

[Lorenz Bauer]

On Wed, Jun 28, 2023 at 7:54 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:

> > +     reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,
> > +                                       saddr, sport, daddr, ntohs(dport),
> > +                                       ehashfn);
> > +     if (!reuse_sk || reuse_sk == sk)
> > +             return sk;
> > +
> > +     /* We've chosen a new reuseport sock which is never refcounted. This
> > +      * implies that sk also isn't refcounted.
> > +      */
> > +     WARN_ON_ONCE(*refcounted);
>
> One more nit.
>
> WARN_ON_ONCE() should be tested before inet6?_lookup_reuseport() not to
> miss the !reuse_sk case.

I was just pondering that as well, but I came to the opposite
conclusion. In the !reuse_sk case we don't really know anything about
sk, except that it isn't part of a reuseport group. How can we be sure
that it's not refcounted?