Re: [PATCH net-next 3/3] net: sched: add helper support in act_ct

[Paolo Abeni <pabeni@redhat.com>]

On Tue, 2022-10-04 at 21:19 -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.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  include/net/tc_act/tc_ct.h        |   1 +
>  include/uapi/linux/tc_act/tc_ct.h |   3 +
>  net/sched/act_ct.c                | 113 ++++++++++++++++++++++++++++--
>  3 files changed, 112 insertions(+), 5 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..f237c27079db 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;
> @@ -655,7 +656,7 @@ struct tc_ct_action_net {
>  
>  /* Determine whether skb->_nfct is equal to the result of conntrack lookup. */
>  static bool tcf_ct_skb_nfct_cached(struct net *net, struct sk_buff *skb,
> -				   u16 zone_id, bool force)
> +				   struct tcf_ct_params *p, bool force)
>  {
>  	enum ip_conntrack_info ctinfo;
>  	struct nf_conn *ct;
> @@ -665,8 +666,15 @@ static bool tcf_ct_skb_nfct_cached(struct net *net, struct sk_buff *skb,
>  		return false;
>  	if (!net_eq(net, read_pnet(&ct->ct_net)))
>  		goto drop_ct;
> -	if (nf_ct_zone(ct)->id != zone_id)
> +	if (nf_ct_zone(ct)->id != p->zone)
>  		goto drop_ct;
> +	if (p->helper) {
> +		struct nf_conn_help *help;
> +
> +		help = nf_ct_ext_find(ct, NF_CT_EXT_HELPER);
> +		if (help && rcu_access_pointer(help->helper) != p->helper)
> +			goto drop_ct;
> +	}
>  
>  	/* Force conntrack entry direction. */
>  	if (force && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
> @@ -832,6 +840,13 @@ 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);
> +	}

There is exactly the same code chunk in __ovs_ct_free_action(), I guess
you can extract a common helper here, too.

>  	if (params->ct_ft)
>  		tcf_ct_flow_table_put(params->ct_ft);
>  	if (params->tmpl)
> @@ -1033,6 +1048,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>  	struct nf_hook_state state;
>  	int nh_ofs, err, retval;
>  	struct tcf_ct_params *p;
> +	bool add_helper = false;
>  	bool skip_add = false;
>  	bool defrag = false;
>  	struct nf_conn *ct;
> @@ -1086,7 +1102,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>  	 * actually run the packet through conntrack twice unless it's for a
>  	 * different zone.
>  	 */
> -	cached = tcf_ct_skb_nfct_cached(net, skb, p->zone, force);
> +	cached = tcf_ct_skb_nfct_cached(net, skb, p, force);
>  	if (!cached) {
>  		if (tcf_ct_flow_table_lookup(p, skb, family)) {
>  			skip_add = true;
> @@ -1119,6 +1135,22 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>  	if (err != NF_ACCEPT)
>  		goto drop;
>  
> +	if (commit && p->helper && !nfct_help(ct)) {
> +		err = __nf_ct_try_assign_helper(ct, p->tmpl, GFP_ATOMIC);
> +		if (err)
> +			goto drop;
> +		add_helper = true;
> +		if (p->ct_action & TCA_CT_ACT_NAT && !nfct_seqadj(ct)) {
> +			if (!nfct_seqadj_ext_add(ct))
> +				return -EINVAL;

This return looks suspect/wrong. It will confuse the tc action
mechanism. I guess you shold do
				goto drop;

even here. 

> +		}
> +	}
> +
> +	if (nf_ct_is_confirmed(ct) ? ((!cached && !skip_add) || add_helper) : commit) {
> +		if (nf_ct_helper(skb, family) != NF_ACCEPT)
> +			goto drop;

With the above change, this chunk closely resamble

https://elixir.bootlin.com/linux/latest/source/net/openvswitch/conntrack.c#L1018
...
https://elixir.bootlin.com/linux/latest/source/net/openvswitch/conntrack.c#L1042

opening to an additional common helper;) Not strictly necessary, just
nice to have :)


Thanks!

Paolo