Re: [PATCH 19/31] net/tcp: Add TCP-AO SNE support

On 8/18/22 19:59, Dmitry Safonov wrote:

Add Sequence Number Extension (SNE) extension for TCP-AO.
This is needed to protect long-living TCP-AO connections from replaying
attacks after sequence number roll-over, see RFC5925 (6.2).

+#ifdef CONFIG_TCP_AO
+	ao = rcu_dereference_protected(tp->ao_info,
+				       lockdep_sock_is_held((struct sock *)tp));
+	if (ao) {
+		if (ack < ao->snd_sne_seq)
+			ao->snd_sne++;
+		ao->snd_sne_seq = ack;
+	}
+#endif
  	tp->snd_una = ack;
  }

... snip ...

+#ifdef CONFIG_TCP_AO
+	ao = rcu_dereference_protected(tp->ao_info,
+				       lockdep_sock_is_held((struct sock *)tp));
+	if (ao) {
+		if (seq < ao->rcv_sne_seq)
+			ao->rcv_sne++;
+		ao->rcv_sne_seq = seq;
+	}
+#endif
  	WRITE_ONCE(tp->rcv_nxt, seq);

It should always be the case that (rcv_nxt == rcv_sne_seq) and (snd_una 
== snd_sne_seq) so the _sne_seq fields are redundant. It's possible to 
avoid those extra fields.

However 8 bytes per TCP-AO socket is inconsequential.

--
Regards,
Leonard