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

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Date:   Tue, 23 Aug 2022 17:50:43 +0300
From:   Leonard Crestez <cdleonard@...il.com>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        David Ahern <dsahern@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ivan Delalande <colona@...sta.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Salam Noureddine <noureddine@...sta.com>,
        Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
        linux-crypto@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: 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