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

Leonard Crestez
2022-08-23T16:34:17Z

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