netfilter: move tee_active to core

This prepares for a TEE like expression in nftables.
We want to ensure only one duplicate is sent, so both will
use the same percpu variable to detect duplication.

The other use case is detection of recursive call to xtables, but since
we don't want dependency from nft to xtables core its put into core.c
instead of the x_tables core.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter.h

@@ -390,4 +390,15 @@ extern struct nfq_ct_hook __rcu *nfq_ct_hook;
 static inline void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb) {}
 #endif
 
+/**
+ * nf_skb_duplicated - TEE target has sent a packet
+ *
+ * When a xtables target sends a packet, the OUTPUT and POSTROUTING
+ * hooks are traversed again, i.e. nft and xtables are invoked recursively.
+ *
+ * This is used by xtables TEE target to prevent the duplicated skb from
+ * being duplicated again.
+ */
+DECLARE_PER_CPU(bool, nf_skb_duplicated);
+
 #endif /*__LINUX_NETFILTER_H*/

net/netfilter/core.c

@@ -34,6 +34,9 @@ EXPORT_SYMBOL(nf_afinfo);
 const struct nf_ipv6_ops __rcu *nf_ipv6_ops __read_mostly;
 EXPORT_SYMBOL_GPL(nf_ipv6_ops);
 
+DEFINE_PER_CPU(bool, nf_skb_duplicated);
+EXPORT_SYMBOL_GPL(nf_skb_duplicated);
+
 int nf_register_afinfo(const struct nf_afinfo *afinfo)
 {
 	mutex_lock(&afinfo_mutex);

net/netfilter/xt_TEE.c

@@ -37,7 +37,6 @@ struct xt_tee_priv {
 };
 
 static const union nf_inet_addr tee_zero_address;
-static DEFINE_PER_CPU(bool, tee_active);
 
 static struct net *pick_net(struct sk_buff *skb)
 {
@@ -88,7 +87,7 @@ tee_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 	const struct xt_tee_tginfo *info = par->targinfo;
 	struct iphdr *iph;
 
-	if (__this_cpu_read(tee_active))
+	if (__this_cpu_read(nf_skb_duplicated))
 		return XT_CONTINUE;
 	/*
 	 * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
@@ -125,9 +124,9 @@ tee_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 	ip_send_check(iph);
 
 	if (tee_tg_route4(skb, info)) {
-		__this_cpu_write(tee_active, true);
+		__this_cpu_write(nf_skb_duplicated, true);
 		ip_local_out(skb);
-		__this_cpu_write(tee_active, false);
+		__this_cpu_write(nf_skb_duplicated, false);
 	} else {
 		kfree_skb(skb);
 	}
@@ -170,7 +169,7 @@ tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct xt_tee_tginfo *info = par->targinfo;
 
-	if (__this_cpu_read(tee_active))
+	if (__this_cpu_read(nf_skb_duplicated))
 		return XT_CONTINUE;
 	skb = pskb_copy(skb, GFP_ATOMIC);
 	if (skb == NULL)
@@ -188,9 +187,9 @@ tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 		--iph->hop_limit;
 	}
 	if (tee_tg_route6(skb, info)) {
-		__this_cpu_write(tee_active, true);
+		__this_cpu_write(nf_skb_duplicated, true);
 		ip6_local_out(skb);
-		__this_cpu_write(tee_active, false);
+		__this_cpu_write(nf_skb_duplicated, false);
 	} else {
 		kfree_skb(skb);
 	}