netdev - Re: [PATCH net-next 1/3] netfilter: flowtable: Support GRE

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Message-ID: <YgOQ6a0itcJjQJqx@salvia>
Date:   Wed, 9 Feb 2022 11:01:13 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Toshiaki Makita <toshiaki.makita1@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        Paul Blakey <paulb@...dia.com>
Subject: Re: [PATCH net-next 1/3] netfilter: flowtable: Support GRE

On Tue, Feb 08, 2022 at 11:30:03PM +0900, Toshiaki Makita wrote:
> On 2022/02/08 2:56, Pablo Neira Ayuso wrote:
> > On Thu, Feb 03, 2022 at 08:59:39PM +0900, Toshiaki Makita wrote:
[...]
> > > diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
> > > index 889cf88..48e2f58 100644
> > > --- a/net/netfilter/nf_flow_table_ip.c
> > > +++ b/net/netfilter/nf_flow_table_ip.c
[...]
> > > @@ -202,15 +209,25 @@ static int nf_flow_tuple_ip(struct sk_buff *skb, const struct net_device *dev,
> > >   	if (!pskb_may_pull(skb, thoff + *hdrsize))
> > >   		return -1;
> > > +	if (ipproto == IPPROTO_GRE) {
> > 
> > No ifdef here? Maybe remove these ifdef everywhere?
> 
> I wanted to avoid adding many ifdefs and I expect this to be compiled out
> when CONFIG_NF_CT_PROTO_GRE=n as this block is unreachable anyway. It rather
> may have been unintuitive though.
> 
> Removing all of these ifdefs will cause inconsistent behavior between
> CONFIG_NF_CT_PROTO_GRE=n/y.
> When CONFIG_NF_CT_PROTO_GRE=n, conntrack cannot determine GRE version, thus
> it will track GREv1 without key infomation, and the flow will be offloaded.
> When CONFIG_NF_CT_PROTO_GRE=y, GREv1 will have key information and will not
> be offloaded.
> I wanted to just refuse offloading of GRE to avoid this inconsistency.
> Anyway this kind of inconsistency seems to happen in software conntrack, so
> if you'd like to remove ifdefs, I will do.

Good point, thanks for explaining. LGTM.

[...]
> > > diff --git a/net/netfilter/nft_flow_offload.c b/net/netfilter/nft_flow_offload.c
> > > index 0af34ad..731b5d8 100644
> > > --- a/net/netfilter/nft_flow_offload.c
> > > +++ b/net/netfilter/nft_flow_offload.c
> > > @@ -298,6 +298,19 @@ static void nft_flow_offload_eval(const struct nft_expr *expr,
> > >   		break;
> > >   	case IPPROTO_UDP:
> > >   		break;
> > > +#ifdef CONFIG_NF_CT_PROTO_GRE
> > > +	case IPPROTO_GRE: {
> > > +		struct nf_conntrack_tuple *tuple;
> > > +
> > > +		if (ct->status & IPS_NAT_MASK)
> > > +			goto out;
> > 
> > Why this NAT check?
> 
> NAT requires more work. I'd like to start with a minimal GRE support.
> Maybe we can add NAT support later.

Oh well, yes, no problem.