netfilter: synproxy: remove module dependency on IPv6 SYNPROXY

This is a prerequisite for the infrastructure module NETFILTER_SYNPROXY.
The new module is needed to avoid duplicated code for the SYNPROXY
nftables support.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter_ipv6.h

@@ -8,6 +8,7 @@
 #define __LINUX_IP6_NETFILTER_H
 
 #include <uapi/linux/netfilter_ipv6.h>
+#include <net/tcp.h>
 
 /* Extra routing may needed on local out, as the QUEUE target never returns
  * control to the table.
@@ -35,6 +36,10 @@ struct nf_ipv6_ops {
 		       struct in6_addr *saddr);
 	int (*route)(struct net *net, struct dst_entry **dst, struct flowi *fl,
 		     bool strict);
+	u32 (*cookie_init_sequence)(const struct ipv6hdr *iph,
+				    const struct tcphdr *th, u16 *mssp);
+	int (*cookie_v6_check)(const struct ipv6hdr *iph,
+			       const struct tcphdr *th, __u32 cookie);
 #endif
 	void (*route_input)(struct sk_buff *skb);
 	int (*fragment)(struct net *net, struct sock *sk, struct sk_buff *skb,
@@ -154,6 +159,37 @@ static inline int nf_ip6_route_me_harder(struct net *net, struct sk_buff *skb)
 #endif
 }
 
+static inline u32 nf_ipv6_cookie_init_sequence(const struct ipv6hdr *iph,
+					       const struct tcphdr *th,
+					       u16 *mssp)
+{
+#if IS_MODULE(CONFIG_IPV6)
+	const struct nf_ipv6_ops *v6_ops = nf_get_ipv6_ops();
+
+	if (v6_ops)
+		return v6_ops->cookie_init_sequence(iph, th, mssp);
+
+	return 0;
+#else
+	return __cookie_v6_init_sequence(iph, th, mssp);
+#endif
+}
+
+static inline int nf_cookie_v6_check(const struct ipv6hdr *iph,
+				     const struct tcphdr *th, __u32 cookie)
+{
+#if IS_MODULE(CONFIG_IPV6)
+	const struct nf_ipv6_ops *v6_ops = nf_get_ipv6_ops();
+
+	if (v6_ops)
+		return v6_ops->cookie_v6_check(iph, th, cookie);
+
+	return 0;
+#else
+	return __cookie_v6_check(iph, th, cookie);
+#endif
+}
+
 __sum16 nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
 			unsigned int dataoff, u_int8_t protocol);
 

net/ipv6/netfilter.c

@@ -234,6 +234,8 @@ static const struct nf_ipv6_ops ipv6ops = {
 	.route_me_harder	= ip6_route_me_harder,
 	.dev_get_saddr		= ipv6_dev_get_saddr,
 	.route			= __nf_ip6_route,
+	.cookie_init_sequence	= __cookie_v6_init_sequence,
+	.cookie_v6_check	= __cookie_v6_check,
 #endif
 	.route_input		= ip6_route_input,
 	.fragment		= ip6_fragment,