netdev - Re: [PATCH v2 06/25] tcp: authopt: Compute packet signatures

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Date:   Fri, 5 Nov 2021 01:53:31 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Leonard Crestez <cdleonard@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Ivan Delalande <colona@...sta.com>,
        Priyaranjan Jha <priyarjha@...gle.com>, netdev@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 06/25] tcp: authopt: Compute packet signatures

On 11/1/21 16:34, Leonard Crestez wrote:
[..]
> +static int skb_shash_frags(struct shash_desc *desc,
> +			   struct sk_buff *skb)
> +{
> +	struct sk_buff *frag_iter;
> +	int err, i;
> +
> +	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> +		skb_frag_t *f = &skb_shinfo(skb)->frags[i];
> +		u32 p_off, p_len, copied;
> +		struct page *p;
> +		u8 *vaddr;
> +
> +		skb_frag_foreach_page(f, skb_frag_off(f), skb_frag_size(f),
> +				      p, p_off, p_len, copied) {
> +			vaddr = kmap_atomic(p);
> +			err = crypto_shash_update(desc, vaddr + p_off, p_len);
> +			kunmap_atomic(vaddr);
> +			if (err)
> +				return err;
> +		}
> +	}
> +
> +	skb_walk_frags(skb, frag_iter) {
> +		err = skb_shash_frags(desc, frag_iter);
> +		if (err)
> +			return err;
> +	}
> +
> +	return 0;
> +}

This seems quite sub-optimal: IIUC, shash should only be used for small
amount of hashing. That's why tcp-md5 uses ahash with scatterlists.
Which drives me to the question: why not reuse tcp_md5sig_pool code?

And it seems that you can avoid TCP_AUTHOPT_ALG_* enum and just supply
to crypto the string from socket option (like xfrm does).

Here is my idea:
https://lore.kernel.org/all/20211105014953.972946-6-dima@arista.com/T/#u

Thanks,
          Dmitry