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Message-ID: <01f8616c-2904-42f1-1e59-ca4c71f7a9bd@gmail.com>
Date:   Tue, 23 Aug 2022 17:50:43 +0300
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Subject: Re: [PATCH 19/31] net/tcp: Add TCP-AO SNE support
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To:     Dmitry Safonov <dima@arista.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Ard Biesheuvel <ardb@kernel.org>,
        Bob Gilligan <gilligan@arista.com>,
        David Ahern <dsahern@kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Eric Biggers <ebiggers@kernel.org>,
        Francesco Ruggeri <fruggeri@arista.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Ivan Delalande <colona@arista.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Salam Noureddine <noureddine@arista.com>,
        Shuah Khan <shuah@kernel.org>, netdev@vger.kernel.org,
        linux-crypto@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-kernel@vger.kernel.org
References: <20220818170005.747015-1-dima@arista.com>
 <20220818170005.747015-20-dima@arista.com>
From:   Leonard Crestez <cdleonard@gmail.com>
In-Reply-To: <20220818170005.747015-20-dima@arista.com>
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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