netdev - Re: [PATCH nf-next v4 1/2] net: netfilter: Add IPIP flowtable SW acceleration

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Message-ID: <aHpIuOiEaoewEQxm@strlen.de>
Date: Fri, 18 Jul 2025 15:14:32 +0200
From: Florian Westphal <fw@...len.de>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Shuah Khan <shuah@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH nf-next v4 1/2] net: netfilter: Add IPIP flowtable SW
 acceleration

Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> +	path->type = DEV_PATH_IPENCAP;
> +	path->dev = ctx->dev;
> +	path->encap.proto = htons(ETH_P_IP);
> +	path->encap.id = jhash_3words(ntohl(tiph->saddr), ntohl(tiph->daddr),
> +				      IPPROTO_IPIP, 0);

I think it would be better to have a helper.  Else I think this needs a
comment that explains it must be kept in sync with nf_flow_tuple_encap().

Or use __ipv4_addr_hash(tiph->saddr, (__force __u32)tiph->daddr).
(loses IPPROTO_IPIP though).

> @@ -165,6 +166,19 @@ static void nf_flow_tuple_encap(struct sk_buff *skb,
>  		tuple->encap[i].id = ntohs(phdr->sid);
>  		tuple->encap[i].proto = skb->protocol;
>  		break;
> +	case htons(ETH_P_IP):
> +		if (!pskb_may_pull(skb, sizeof(*iph)))
> +			break;

Is this needed?  Caller does:

        if (!pskb_may_pull(skb, thoff + ctx->hdrsize))
                return -1;

and then populates the inner header:
        iph = (struct iphdr *)(skb_network_header(skb) + ctx->offset);
	tuple->src_v4.s_addr    = iph->saddr;


.... so I think this can rely on the outer header being available
via skb_network_header().

> +		tuple->encap[i].proto = htons(ETH_P_IP);
> +		tuple->encap[i].id = jhash_3words(ntohl(iph->daddr),
> +						  ntohl(iph->saddr),
> +						  IPPROTO_IPIP, 0);

See above, I think this desevers a helper or a comment, or both.

> +static bool nf_flow_ip4_encap_proto(struct sk_buff *skb, u16 *size)
> +{
> +	struct iphdr *iph;
> +
> +	if (!pskb_may_pull(skb, sizeof(*iph)))
> +		return false;

Nit: I think this could be 2 * sizeof() and a comment that we will
also need the inner ip header later, might save one reallocation.

> +	iph = (struct iphdr *)skb_network_header(skb);
> +	*size = iph->ihl << 2;

I think this should be sanity tested vs. sizeof(iph).

> +
>  static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
>  				       u32 *offset)
>  {
>  	struct vlan_ethhdr *veth;
>  	__be16 inner_proto;
> +	u16 size;
>  
>  	switch (skb->protocol) {
> +	case htons(ETH_P_IP):
> +		if (nf_flow_ip4_encap_proto(skb, &size))
> +			*offset += size;

Nit: return nf_flow_ip4_encap_proto(skb, &offset) ?