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Date:   Tue, 27 Sep 2022 12:29:01 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, kuba@...nel.org,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Davide Caratti <dcaratti@...hat.com>,
        Oz Shlomo <ozsh@...dia.com>, Paul Blakey <paulb@...dia.com>,
        Ilya Maximets <i.maximets@....org>
Subject: Re: [PATCH net-next 2/2] net: sched: add helper support in act_ct

On Fri, 2022-09-23 at 11:28 -0400, Xin Long wrote:
> This patch is to add helper support in act_ct for OVS actions=ct(alg=xxx)
> offloading, which is corresponding to Commit cae3a2627520 ("openvswitch:
> Allow attaching helpers to ct action") in OVS kernel part.
> 
> The difference is when adding TC actions family and proto cannot be got
> from the filter/match, other than helper name in tb[TCA_CT_HELPER_NAME],
> we also need to send the family in tb[TCA_CT_HELPER_FAMILY] and the
> proto in tb[TCA_CT_HELPER_PROTO] to kernel.
> 
> Note when calling helper->help() in tcf_ct_act(), the packet will be
> dropped if skb's family and proto do not match the helper's.
> 
> Reported-by: Ilya Maximets <i.maximets@....org>

This tag is a bit out of place here, as it should belong to fixes. Do
you mean 'Suggested-by' ?

> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  include/net/tc_act/tc_ct.h        |   1 +
>  include/uapi/linux/tc_act/tc_ct.h |   3 +
>  net/sched/act_ct.c                | 163 +++++++++++++++++++++++++++++-
>  3 files changed, 165 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/tc_act/tc_ct.h b/include/net/tc_act/tc_ct.h
> index 8250d6f0a462..b24ea2d9400b 100644
> --- a/include/net/tc_act/tc_ct.h
> +++ b/include/net/tc_act/tc_ct.h
> @@ -10,6 +10,7 @@
>  #include <net/netfilter/nf_conntrack_labels.h>
>  
>  struct tcf_ct_params {
> +	struct nf_conntrack_helper *helper;
>  	struct nf_conn *tmpl;
>  	u16 zone;
>  
> diff --git a/include/uapi/linux/tc_act/tc_ct.h b/include/uapi/linux/tc_act/tc_ct.h
> index 5fb1d7ac1027..6c5200f0ed38 100644
> --- a/include/uapi/linux/tc_act/tc_ct.h
> +++ b/include/uapi/linux/tc_act/tc_ct.h
> @@ -22,6 +22,9 @@ enum {
>  	TCA_CT_NAT_PORT_MIN,	/* be16 */
>  	TCA_CT_NAT_PORT_MAX,	/* be16 */
>  	TCA_CT_PAD,
> +	TCA_CT_HELPER_NAME,	/* string */
> +	TCA_CT_HELPER_FAMILY,	/* u8 */
> +	TCA_CT_HELPER_PROTO,	/* u8 */
>  	__TCA_CT_MAX
>  };
>  
> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
> index 193a460a9d7f..771cf72ee9e1 100644
> --- a/net/sched/act_ct.c
> +++ b/net/sched/act_ct.c
> @@ -33,6 +33,7 @@
>  #include <net/netfilter/nf_conntrack_acct.h>
>  #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
>  #include <net/netfilter/nf_conntrack_act_ct.h>
> +#include <net/netfilter/nf_conntrack_seqadj.h>
>  #include <uapi/linux/netfilter/nf_nat.h>
>  
>  static struct workqueue_struct *act_ct_wq;
> @@ -832,6 +833,13 @@ static int tcf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
>  
>  static void tcf_ct_params_free(struct tcf_ct_params *params)
>  {
> +	if (params->helper) {
> +#if IS_ENABLED(CONFIG_NF_NAT)
> +		if (params->ct_action & TCA_CT_ACT_NAT)
> +			nf_nat_helper_put(params->helper);
> +#endif
> +		nf_conntrack_helper_put(params->helper);
> +	}
>  	if (params->ct_ft)
>  		tcf_ct_flow_table_put(params->ct_ft);
>  	if (params->tmpl)
> @@ -1022,6 +1030,69 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
>  #endif
>  }
>  
> +static int tcf_ct_helper(struct sk_buff *skb, u8 family)
> +{

This is very similar to ovs_ct_helper(), I'm wondering if a common
helper could be factored out?

> +	const struct nf_conntrack_helper *helper;
> +	const struct nf_conn_help *help;
> +	enum ip_conntrack_info ctinfo;
> +	unsigned int protoff;
> +	struct nf_conn *ct;
> +	u8 proto;
> +	int err;
> +
> +	ct = nf_ct_get(skb, &ctinfo);
> +	if (!ct || ctinfo == IP_CT_RELATED_REPLY)
> +		return NF_ACCEPT;
> +
> +	help = nfct_help(ct);
> +	if (!help)
> +		return NF_ACCEPT;
> +
> +	helper = rcu_dereference(help->helper);
> +	if (!helper)
> +		return NF_ACCEPT;
> +
> +	if (helper->tuple.src.l3num != NFPROTO_UNSPEC &&
> +	    helper->tuple.src.l3num != family)
> +		return NF_DROP;
> +
> +	switch (family) {
> +	case NFPROTO_IPV4:
> +		protoff = ip_hdrlen(skb);
> +		proto = ip_hdr(skb)->protocol;
> +		break;
> +	case NFPROTO_IPV6: {
> +		__be16 frag_off;
> +		int ofs;
> +
> +		proto = ipv6_hdr(skb)->nexthdr;
> +		ofs = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &proto, &frag_off);
> +		if (ofs < 0 || (frag_off & htons(~0x7)) != 0) {
> +			pr_debug("proto header not found\n");
> +			return NF_DROP;

Why this is returning NF_DROP while ovs_ct_helper() returns NF_ACCEPT
here?

> +		}
> +		protoff = ofs;
> +		break;
> +	}
> +	default:
> +		WARN_ONCE(1, "helper invoked on non-IP family!");
> +		return NF_DROP;
> +	}
> +
> +	if (helper->tuple.dst.protonum != proto)
> +		return NF_DROP;

I'm wondering if NF_DROP is appropriate here. This should be a 
situation similar to the above one: the current packet does not match
the helper.

Thanks!

Paolo

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