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

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Message-ID: <aH4NNppbRppZojYO@lore-desk>
Date: Mon, 21 Jul 2025 11:49:42 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Florian Westphal <fw@...len.de>
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).

ack, I will fix it in v5.

> 
> > @@ -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().

I agree, I will fix it in v5.

> 
> > +		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.

nf_flow_ip4_encap_proto() is used even for plain IP traffic but I guess we can
assume the IP payload is at least 20B, right?

> 
> > +	iph = (struct iphdr *)skb_network_header(skb);
> > +	*size = iph->ihl << 2;
> 
> I think this should be sanity tested vs. sizeof(iph).

I guess this is already done in ip_has_options(), agree?

> 
> > +
> >  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) ?

ack, I will fix it in v5.

Regards,
Lorenzo


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