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

On Wed, Jun 28, 2023 at 7:54 PM Kuniyuki Iwashima kuniyu@amazon.com 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?