From: Martin KaFai Lau <kafai@xxxxxx>
Date: Thu, 20 May 2021 14:22:01 -0700
> On Thu, May 20, 2021 at 05:51:17PM +0900, Kuniyuki Iwashima wrote:
> > From: Martin KaFai Lau <kafai@xxxxxx>
> > Date: Wed, 19 May 2021 23:26:48 -0700
> > > On Mon, May 17, 2021 at 09:22:50AM +0900, Kuniyuki Iwashima wrote:
> > >
> > > > +static int reuseport_resurrect(struct sock *sk, struct sock_reuseport *old_reuse,
> > > > + struct sock_reuseport *reuse, bool bind_inany)
> > > > +{
> > > > + if (old_reuse == reuse) {
> > > > + /* If sk was in the same reuseport group, just pop sk out of
> > > > + * the closed section and push sk into the listening section.
> > > > + */
> > > > + __reuseport_detach_closed_sock(sk, old_reuse);
> > > > + __reuseport_add_sock(sk, old_reuse);
> > > > + return 0;
> > > > + }
> > > > +
> > > > + if (!reuse) {
> > > > + /* In bind()/listen() path, we cannot carry over the eBPF prog
> > > > + * for the shutdown()ed socket. In setsockopt() path, we should
> > > > + * not change the eBPF prog of listening sockets by attaching a
> > > > + * prog to the shutdown()ed socket. Thus, we will allocate a new
> > > > + * reuseport group and detach sk from the old group.
> > > > + */
> > > For the reuseport_attach_prog() path, I think it needs to consider
> > > the reuse->num_closed_socks != 0 case also and that should belong
> > > to the resurrect case. For example, when
> > > sk_unhashed(sk) but sk->sk_reuseport == 0.
> >
> > In the path, reuseport_resurrect() is called from reuseport_alloc() only
> > if reuse->num_closed_socks != 0.
> >
> >
> > > @@ -92,6 +117,14 @@ int reuseport_alloc(struct sock *sk, bool bind_inany)
> > > reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
> > > lockdep_is_held(&reuseport_lock));
> > > if (reuse) {
> > > + if (reuse->num_closed_socks) {
> >
> > But, should this be
> >
> > if (sk->sk_state == TCP_CLOSE && reuse->num_closed_socks)
> >
> > because we need not allocate a new group when we attach a bpf prog to
> > listeners?
> The reuseport_alloc() is fine as is. No need to change.
I missed sk_unhashed(sk) prevents calling reuseport_alloc()
if sk_state == TCP_LISTEN. I'll keep it as is.
>
> I should have copied reuseport_attach_prog() in the last reply and
> commented there instead.
>
> I meant reuseport_attach_prog() needs a change. In reuseport_attach_prog(),
> iiuc, currently passing the "else if (!rcu_access_pointer(sk->sk_reuseport_cb))"
> check implies the sk was (and still is) hashed with sk_reuseport enabled
> because the current behavior would have set sk_reuseport_cb to NULL during
> unhash but it is no longer true now. For example, this will break:
>
> 1. shutdown(lsk); /* lsk was bound with sk_reuseport enabled */
> 2. setsockopt(lsk, ..., SO_REUSEPORT, &zero, ...); /* disable sk_reuseport */
> 3. setsockopt(lsk, ..., SO_ATTACH_REUSEPORT_EBPF, &prog_fd, ...);
> ^---- /* This will work now because sk_reuseport_cb is not NULL.
> * However, it shouldn't be allowed.
> */
Thank you for explanation, I understood the case.
Exactly, I've confirmed that the case succeeded in the setsockopt() and I
could change the active listeners' prog via a shutdowned socket.
>
> I am thinking something like this (uncompiled code):
>
> int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
> {
> struct sock_reuseport *reuse;
> struct bpf_prog *old_prog;
>
> if (sk_unhashed(sk)) {
> int err;
>
> if (!sk->sk_reuseport)
> return -EINVAL;
>
> err = reuseport_alloc(sk, false);
> if (err)
> return err;
> } else if (!rcu_access_pointer(sk->sk_reuseport_cb)) {
> /* The socket wasn't bound with SO_REUSEPORT */
> return -EINVAL;
> }
>
> /* ... */
> }
>
> WDYT?
I tested this change worked fine. I think this change should be added in
reuseport_detach_prog() also.
---8<---
int reuseport_detach_prog(struct sock *sk)
{
struct sock_reuseport *reuse;
struct bpf_prog *old_prog;
if (!rcu_access_pointer(sk->sk_reuseport_cb))
return sk->sk_reuseport ? -ENOENT : -EINVAL;
---8<---
Another option is to add the check in sock_setsockopt():
SO_ATTACH_REUSEPORT_[CE]BPF, SO_DETACH_REUSEPORT_BPF.
Which do you think is better ?
