Re: [PATCH v2 net 01/15] af_unix: Set sk->sk_state under unix_state_lock() for truly disconencted peer.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Michal Luczaj <mhal@rbox.co>
Date: Mon, 10 Jun 2024 14:55:08 +0200
> On 6/9/24 23:03, Kuniyuki Iwashima wrote:
> > (...)
> > Sorry, I think I was wrong and we can't use smp_store_release()
> > and smp_load_acquire(), and smp_[rw]mb() is needed.
> > 
> > Given we avoid adding code in the hotpath in the original fix
> > 8866730aed510 [0], I prefer adding unix_state_lock() in the SOCKMAP
> > path again.
> >
> > [0]: https://lore.kernel.org/bpf/6545bc9f7e443_3358c208ae@john.notmuch/
> 
> You're saying smp_wmb() in connect() is too much for the hot path, do I
> understand correctly?

Yes, and now I think WARN_ON_ONCE() would be enough because it's unlikely
that the delay happens between the two store ops and concurrent bpf()
is in progress.

If syzkaller was able to hit this on vanilla kernel, we can revisit.

Then, probably we could just do s/WARN_ON_ONCE/unlikely/ because users
who call bpf() in such a way know that the state was TCP_CLOSE while
calling bpf().

---8<---
diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c
index bd84785bf8d6..46dc747349f2 100644
--- a/net/unix/unix_bpf.c
+++ b/net/unix/unix_bpf.c
@@ -181,6 +181,9 @@ int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool r
 	 */
 	if (!psock->sk_pair) {
 		sk_pair = unix_peer(sk);
+		if (WARN_ON_ONCE(!sk_pair))
+			return -EINVAL;
+
 		sock_hold(sk_pair);
 		psock->sk_pair = sk_pair;
 	}
---8<---