[PATCH nf-next v3 0/4] Extract SYNPROXY infrastructure

[PATCH nf-next v3 0/4] Extract SYNPROXY infrastructure

[Fernando Fernandez Mancera]

The patch series have been tested by enabling iptables and ip6tables SYNPROXY.
All the modules loaded as expected.

$ lsmod | grep synproxy
Only IPv4:
nf_synproxy            20480  1 ipt_SYNPROXY
nf_synproxy_core       16384  2 ipt_SYNPROXY,nf_synproxy
nf_conntrack          159744  5 xt_conntrack,xt_state,ipt_SYNPROXY,nf_synproxy_core,nf_synproxy

Only IPv6:
nf_synproxy            20480  1 ip6t_SYNPROXY
nf_synproxy_core       16384  2 ip6t_SYNPROXY,nf_synproxy
nf_conntrack          159744  5 ip6t_SYNPROXY,xt_conntrack,xt_state,nf_synproxy_core,nf_synproxy

IPv4 and IPv6:
nf_synproxy            20480  2 ip6t_SYNPROXY,ipt_SYNPROXY
nf_synproxy_core       16384  3 ip6t_SYNPROXY,ipt_SYNPROXY,nf_synproxy
nf_conntrack          159744  6 ip6t_SYNPROXY,xt_conntrack,xt_state,ipt_SYNPROXY,nf_synproxy_core,nf_synproxy

v1: Initial patch
v2: Unify nf_synproxy_ipv4 and nf_synproxy_ipv6 into nf_synproxy
v3: Remove synproxy_cookie dependency

Fernando Fernandez Mancera (4):
  netfilter: synproxy: add common uapi for SYNPROXY infrastructure
  netfilter: synproxy: remove module dependency on IPv6 SYNPROXY
  netfilter: synproxy: extract SYNPROXY infrastructure from
    {ipt,ip6t}_SYNPROXY
  netfilter: add NF_SYNPROXY symbol

 include/linux/netfilter_ipv6.h             |  17 +
 include/net/netfilter/nf_synproxy.h        |  46 ++
 include/uapi/linux/netfilter/nf_SYNPROXY.h |  19 +
 include/uapi/linux/netfilter/xt_SYNPROXY.h |  18 +-
 net/ipv4/netfilter/Kconfig                 |   2 +-
 net/ipv4/netfilter/ipt_SYNPROXY.c          | 394 +---------
 net/ipv6/netfilter.c                       |   1 +
 net/ipv6/netfilter/Kconfig                 |   2 +-
 net/ipv6/netfilter/ip6t_SYNPROXY.c         | 420 +----------
 net/netfilter/Kconfig                      |   4 +
 net/netfilter/Makefile                     |   1 +
 net/netfilter/nf_synproxy.c                | 836 +++++++++++++++++++++
 12 files changed, 948 insertions(+), 812 deletions(-)
 create mode 100644 include/net/netfilter/nf_synproxy.h
 create mode 100644 include/uapi/linux/netfilter/nf_SYNPROXY.h
 create mode 100644 net/netfilter/nf_synproxy.c

-- 
2.20.1

[PATCH nf-next v3 1/4] netfilter: synproxy: add common uapi for SYNPROXY infrastructure

[Fernando Fernandez Mancera]

This new UAPI file is going to be used by the xt and nft common SYNPROXY
infrastructure. It is needed to avoid duplicated code.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
---
 include/uapi/linux/netfilter/nf_SYNPROXY.h | 19 +++++++++++++++++++
 include/uapi/linux/netfilter/xt_SYNPROXY.h | 18 +++++++-----------
 2 files changed, 26 insertions(+), 11 deletions(-)
 create mode 100644 include/uapi/linux/netfilter/nf_SYNPROXY.h

diff --git a/include/uapi/linux/netfilter/nf_SYNPROXY.h b/include/uapi/linux/netfilter/nf_SYNPROXY.h
new file mode 100644
index 000000000000..068d1b3a6f06
--- /dev/null
+++ b/include/uapi/linux/netfilter/nf_SYNPROXY.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NF_SYNPROXY_H
+#define _NF_SYNPROXY_H
+
+#include <linux/types.h>
+
+#define NF_SYNPROXY_OPT_MSS		0x01
+#define NF_SYNPROXY_OPT_WSCALE		0x02
+#define NF_SYNPROXY_OPT_SACK_PERM	0x04
+#define NF_SYNPROXY_OPT_TIMESTAMP	0x08
+#define NF_SYNPROXY_OPT_ECN		0x10
+
+struct nf_synproxy_info {
+	__u8	options;
+	__u8	wscale;
+	__u16	mss;
+};
+
+#endif /* _NF_SYNPROXY_H */
diff --git a/include/uapi/linux/netfilter/xt_SYNPROXY.h b/include/uapi/linux/netfilter/xt_SYNPROXY.h
index ea5eba15d4c1..4d5611d647df 100644
--- a/include/uapi/linux/netfilter/xt_SYNPROXY.h
+++ b/include/uapi/linux/netfilter/xt_SYNPROXY.h
@@ -2,18 +2,14 @@
 #ifndef _XT_SYNPROXY_H
 #define _XT_SYNPROXY_H
 
-#include <linux/types.h>
+#include <linux/netfilter/nf_SYNPROXY.h>
 
-#define XT_SYNPROXY_OPT_MSS		0x01
-#define XT_SYNPROXY_OPT_WSCALE		0x02
-#define XT_SYNPROXY_OPT_SACK_PERM	0x04
-#define XT_SYNPROXY_OPT_TIMESTAMP	0x08
-#define XT_SYNPROXY_OPT_ECN		0x10
+#define XT_SYNPROXY_OPT_MSS		NF_SYNPROXY_OPT_MSS
+#define XT_SYNPROXY_OPT_WSCALE		NF_SYNPROXY_OPT_WSCALE
+#define XT_SYNPROXY_OPT_SACK_PERM	NF_SYNPROXY_OPT_SACK_PERM
+#define XT_SYNPROXY_OPT_TIMESTAMP	NF_SYNPROXY_OPT_TIMESTAMP
+#define XT_SYNPROXY_OPT_ECN		NF_SYNPROXY_OPT_ECN
 
-struct xt_synproxy_info {
-	__u8	options;
-	__u8	wscale;
-	__u16	mss;
-};
+#define xt_synproxy_info		nf_synproxy_info
 
 #endif /* _XT_SYNPROXY_H */
-- 
2.20.1

[PATCH nf-next v3 2/4] netfilter: synproxy: remove module dependency on IPv6 SYNPROXY

[Fernando Fernandez Mancera]

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

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
---
 include/linux/netfilter_ipv6.h | 17 +++++++++++++++++
 net/ipv6/netfilter.c           |  1 +
 2 files changed, 18 insertions(+)

diff --git a/include/linux/netfilter_ipv6.h b/include/linux/netfilter_ipv6.h
index 12113e502656..549a5df39cf9 100644
--- a/include/linux/netfilter_ipv6.h
+++ b/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.
@@ -34,6 +35,8 @@ 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);
 #endif
 	void (*route_input)(struct sk_buff *skb);
 	int (*fragment)(struct net *net, struct sock *sk, struct sk_buff *skb,
@@ -102,6 +105,20 @@ 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);
+#else
+	return __cookie_v6_init_sequence(iph, th, mssp);
+#endif
+}
+
 __sum16 nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
 			unsigned int dataoff, u_int8_t protocol);
 
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 1240ccd57f39..32b8b1f470f4 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -115,6 +115,7 @@ 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,
 #endif
 	.route_input		= ip6_route_input,
 	.fragment		= ip6_fragment,
-- 
2.20.1

Re: [PATCH nf-next v3 2/4] netfilter: synproxy: remove module dependency on IPv6 SYNPROXY

[Florian Westphal]

Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
> This is a prerequisite for the new infrastructure module NF_SYNPROXY. The new
> module is needed to avoid duplicated code for the SYNPROXY nftables support.
> Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
> ---
>  include/linux/netfilter_ipv6.h | 17 +++++++++++++++++
>  net/ipv6/netfilter.c           |  1 +
>  2 files changed, 18 insertions(+)
> 
> diff --git a/include/linux/netfilter_ipv6.h b/include/linux/netfilter_ipv6.h
> index 12113e502656..549a5df39cf9 100644
> --- a/include/linux/netfilter_ipv6.h
> +++ b/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.
> @@ -34,6 +35,8 @@ 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);

This is good, but not enough:

/tmp/foo/./lib/modules/5.2.0-rc1+/kernel/net/netfilter/nf_synproxy.ko needs "__cookie_v6_check": /tmp/foo/./lib/modules/5.2.0-rc1+/kernel/net/ipv6/ipv6.ko

IOW, you need to also add the same trick for __cookie_v6_check.

Otherwise, an ipv4 only rule involving synproxy will pull in ipv6.ko
module.

> +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);

This triggers a compiler warning for me, because return value is
undefined in !v6ops case.

I think you can just return 0 here for the !v6ops case.

[PATCH nf-next v3 3/4] netfilter: synproxy: extract SYNPROXY infrastructure from {ipt,ip6t}_SYNPROXY

[Fernando Fernandez Mancera]

Add common functions into nf_synproxy.c to prepare for nftables support.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
---
 include/net/netfilter/nf_synproxy.h |  46 ++
 net/ipv4/netfilter/ipt_SYNPROXY.c   | 394 +------------
 net/ipv6/netfilter/ip6t_SYNPROXY.c  | 420 +-------------
 net/netfilter/nf_synproxy.c         | 836 ++++++++++++++++++++++++++++
 4 files changed, 897 insertions(+), 799 deletions(-)
 create mode 100644 include/net/netfilter/nf_synproxy.h
 create mode 100644 net/netfilter/nf_synproxy.c

diff --git a/include/net/netfilter/nf_synproxy.h b/include/net/netfilter/nf_synproxy.h
new file mode 100644
index 000000000000..859945cabc4c
--- /dev/null
+++ b/include/net/netfilter/nf_synproxy.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NF_SYNPROXY_SHARED_H
+#define _NF_SYNPROXY_SHARED_H
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <net/ip6_checksum.h>
+#include <net/ip6_route.h>
+#include <net/tcp.h>
+
+#include <net/netfilter/nf_conntrack_seqadj.h>
+#include <net/netfilter/nf_conntrack_synproxy.h>
+
+/* IPv4 support */
+void synproxy_send_client_synack(struct net *net, const struct sk_buff *skb,
+				 const struct tcphdr *th,
+				 const struct synproxy_options *opts);
+
+bool synproxy_recv_client_ack(struct net *net,
+			      const struct sk_buff *skb,
+			      const struct tcphdr *th,
+			      struct synproxy_options *opts, u32 recv_seq);
+
+unsigned int ipv4_synproxy_hook(void *priv, struct sk_buff *skb,
+				const struct nf_hook_state *nhs);
+int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net);
+void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net);
+
+#if IS_ENABLED(CONFIG_IPV6) /* IPv6 support */
+void synproxy_send_client_synack_ipv6(struct net *net,
+				      const struct sk_buff *skb,
+				      const struct tcphdr *th,
+				      const struct synproxy_options *opts);
+
+bool synproxy_recv_client_ack_ipv6(struct net *net, const struct sk_buff *skb,
+				   const struct tcphdr *th,
+				   struct synproxy_options *opts, u32 recv_seq);
+
+unsigned int ipv6_synproxy_hook(void *priv, struct sk_buff *skb,
+				const struct nf_hook_state *nhs);
+int nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net);
+void nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net);
+
+#endif /* IPv6 support */
+
+#endif /* _NF_SYNPROXY_SHARED_H */
diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c b/net/ipv4/netfilter/ipt_SYNPROXY.c
index 690b17ef6a44..7f7979734fb4 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -6,258 +6,11 @@
  * published by the Free Software Foundation.
  */
 
-#include <linux/module.h>
-#include <linux/skbuff.h>
-#include <net/tcp.h>
-
 #include <linux/netfilter_ipv4/ip_tables.h>
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter/xt_SYNPROXY.h>
-#include <net/netfilter/nf_conntrack.h>
-#include <net/netfilter/nf_conntrack_seqadj.h>
-#include <net/netfilter/nf_conntrack_synproxy.h>
-#include <net/netfilter/nf_conntrack_ecache.h>
-
-static struct iphdr *
-synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
-		  __be32 daddr)
-{
-	struct iphdr *iph;
-
-	skb_reset_network_header(skb);
-	iph = skb_put(skb, sizeof(*iph));
-	iph->version	= 4;
-	iph->ihl	= sizeof(*iph) / 4;
-	iph->tos	= 0;
-	iph->id		= 0;
-	iph->frag_off	= htons(IP_DF);
-	iph->ttl	= net->ipv4.sysctl_ip_default_ttl;
-	iph->protocol	= IPPROTO_TCP;
-	iph->check	= 0;
-	iph->saddr	= saddr;
-	iph->daddr	= daddr;
-
-	return iph;
-}
-
-static void
-synproxy_send_tcp(struct net *net,
-		  const struct sk_buff *skb, struct sk_buff *nskb,
-		  struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
-		  struct iphdr *niph, struct tcphdr *nth,
-		  unsigned int tcp_hdr_size)
-{
-	nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
-	nskb->ip_summed   = CHECKSUM_PARTIAL;
-	nskb->csum_start  = (unsigned char *)nth - nskb->head;
-	nskb->csum_offset = offsetof(struct tcphdr, check);
-
-	skb_dst_set_noref(nskb, skb_dst(skb));
-	nskb->protocol = htons(ETH_P_IP);
-	if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
-		goto free_nskb;
-
-	if (nfct) {
-		nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
-		nf_conntrack_get(nfct);
-	}
-
-	ip_local_out(net, nskb->sk, nskb);
-	return;
-
-free_nskb:
-	kfree_skb(nskb);
-}
-
-static void
-synproxy_send_client_synack(struct net *net,
-			    const struct sk_buff *skb, const struct tcphdr *th,
-			    const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct iphdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-	u16 mss = opts->mss;
-
-	iph = ip_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->dest;
-	nth->dest	= th->source;
-	nth->seq	= htonl(__cookie_v4_init_sequence(iph, th, &mss));
-	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
-	tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
-	if (opts->options & XT_SYNPROXY_OPT_ECN)
-		tcp_flag_word(nth) |= TCP_FLAG_ECE;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= 0;
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
-			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
-}
-
-static void
-synproxy_send_server_syn(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts, u32 recv_seq)
-{
-	struct synproxy_net *snet = synproxy_pernet(net);
-	struct sk_buff *nskb;
-	struct iphdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ip_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->source;
-	nth->dest	= th->dest;
-	nth->seq	= htonl(recv_seq - 1);
-	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
-	 * sequence number translation once a connection tracking entry exists.
-	 */
-	nth->ack_seq	= htonl(ntohl(th->ack_seq) - 1);
-	tcp_flag_word(nth) = TCP_FLAG_SYN;
-	if (opts->options & XT_SYNPROXY_OPT_ECN)
-		tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= th->window;
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
-			  niph, nth, tcp_hdr_size);
-}
-
-static void
-synproxy_send_server_ack(struct net *net,
-			 const struct ip_ct_tcp *state,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct iphdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ip_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
 
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->dest;
-	nth->dest	= th->source;
-	nth->seq	= htonl(ntohl(th->ack_seq));
-	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
-	tcp_flag_word(nth) = TCP_FLAG_ACK;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
-}
-
-static void
-synproxy_send_client_ack(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct iphdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ip_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->source;
-	nth->dest	= th->dest;
-	nth->seq	= htonl(ntohl(th->seq) + 1);
-	nth->ack_seq	= th->ack_seq;
-	tcp_flag_word(nth) = TCP_FLAG_ACK;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= htons(ntohs(th->window) >> opts->wscale);
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
-			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
-}
-
-static bool
-synproxy_recv_client_ack(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 struct synproxy_options *opts, u32 recv_seq)
-{
-	struct synproxy_net *snet = synproxy_pernet(net);
-	int mss;
-
-	mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
-	if (mss == 0) {
-		this_cpu_inc(snet->stats->cookie_invalid);
-		return false;
-	}
-
-	this_cpu_inc(snet->stats->cookie_valid);
-	opts->mss = mss;
-	opts->options |= XT_SYNPROXY_OPT_MSS;
-
-	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
-		synproxy_check_timestamp_cookie(opts);
-
-	synproxy_send_server_syn(net, skb, th, opts, recv_seq);
-	return true;
-}
+#include <net/netfilter/nf_synproxy.h>
 
 static unsigned int
 synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
@@ -309,135 +62,6 @@ synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 	return XT_CONTINUE;
 }
 
-static unsigned int ipv4_synproxy_hook(void *priv,
-				       struct sk_buff *skb,
-				       const struct nf_hook_state *nhs)
-{
-	struct net *net = nhs->net;
-	struct synproxy_net *snet = synproxy_pernet(net);
-	enum ip_conntrack_info ctinfo;
-	struct nf_conn *ct;
-	struct nf_conn_synproxy *synproxy;
-	struct synproxy_options opts = {};
-	const struct ip_ct_tcp *state;
-	struct tcphdr *th, _th;
-	unsigned int thoff;
-
-	ct = nf_ct_get(skb, &ctinfo);
-	if (ct == NULL)
-		return NF_ACCEPT;
-
-	synproxy = nfct_synproxy(ct);
-	if (synproxy == NULL)
-		return NF_ACCEPT;
-
-	if (nf_is_loopback_packet(skb) ||
-	    ip_hdr(skb)->protocol != IPPROTO_TCP)
-		return NF_ACCEPT;
-
-	thoff = ip_hdrlen(skb);
-	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
-	if (th == NULL)
-		return NF_DROP;
-
-	state = &ct->proto.tcp;
-	switch (state->state) {
-	case TCP_CONNTRACK_CLOSE:
-		if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
-			nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
-						      ntohl(th->seq) + 1);
-			break;
-		}
-
-		if (!th->syn || th->ack ||
-		    CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
-			break;
-
-		/* Reopened connection - reset the sequence number and timestamp
-		 * adjustments, they will get initialized once the connection is
-		 * reestablished.
-		 */
-		nf_ct_seqadj_init(ct, ctinfo, 0);
-		synproxy->tsoff = 0;
-		this_cpu_inc(snet->stats->conn_reopened);
-
-		/* fall through */
-	case TCP_CONNTRACK_SYN_SENT:
-		if (!synproxy_parse_options(skb, thoff, th, &opts))
-			return NF_DROP;
-
-		if (!th->syn && th->ack &&
-		    CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
-			/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
-			 * therefore we need to add 1 to make the SYN sequence
-			 * number match the one of first SYN.
-			 */
-			if (synproxy_recv_client_ack(net, skb, th, &opts,
-						     ntohl(th->seq) + 1)) {
-				this_cpu_inc(snet->stats->cookie_retrans);
-				consume_skb(skb);
-				return NF_STOLEN;
-			} else {
-				return NF_DROP;
-			}
-		}
-
-		synproxy->isn = ntohl(th->ack_seq);
-		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
-			synproxy->its = opts.tsecr;
-
-		nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
-		break;
-	case TCP_CONNTRACK_SYN_RECV:
-		if (!th->syn || !th->ack)
-			break;
-
-		if (!synproxy_parse_options(skb, thoff, th, &opts))
-			return NF_DROP;
-
-		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) {
-			synproxy->tsoff = opts.tsval - synproxy->its;
-			nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
-		}
-
-		opts.options &= ~(XT_SYNPROXY_OPT_MSS |
-				  XT_SYNPROXY_OPT_WSCALE |
-				  XT_SYNPROXY_OPT_SACK_PERM);
-
-		swap(opts.tsval, opts.tsecr);
-		synproxy_send_server_ack(net, state, skb, th, &opts);
-
-		nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
-		nf_conntrack_event_cache(IPCT_SEQADJ, ct);
-
-		swap(opts.tsval, opts.tsecr);
-		synproxy_send_client_ack(net, skb, th, &opts);
-
-		consume_skb(skb);
-		return NF_STOLEN;
-	default:
-		break;
-	}
-
-	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
-	return NF_ACCEPT;
-}
-
-static const struct nf_hook_ops ipv4_synproxy_ops[] = {
-	{
-		.hook		= ipv4_synproxy_hook,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_LOCAL_IN,
-		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
-	},
-	{
-		.hook		= ipv4_synproxy_hook,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_POST_ROUTING,
-		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
-	},
-};
-
 static int synproxy_tg4_check(const struct xt_tgchk_param *par)
 {
 	struct synproxy_net *snet = synproxy_pernet(par->net);
@@ -452,13 +76,10 @@ static int synproxy_tg4_check(const struct xt_tgchk_param *par)
 	if (err)
 		return err;
 
-	if (snet->hook_ref4 == 0) {
-		err = nf_register_net_hooks(par->net, ipv4_synproxy_ops,
-					    ARRAY_SIZE(ipv4_synproxy_ops));
-		if (err) {
-			nf_ct_netns_put(par->net, par->family);
-			return err;
-		}
+	err = nf_synproxy_ipv4_init(snet, par->net);
+	if (err) {
+		nf_ct_netns_put(par->net, par->family);
+		return err;
 	}
 
 	snet->hook_ref4++;
@@ -469,10 +90,7 @@ static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
 {
 	struct synproxy_net *snet = synproxy_pernet(par->net);
 
-	snet->hook_ref4--;
-	if (snet->hook_ref4 == 0)
-		nf_unregister_net_hooks(par->net, ipv4_synproxy_ops,
-					ARRAY_SIZE(ipv4_synproxy_ops));
+	nf_synproxy_ipv4_fini(snet, par->net);
 	nf_ct_netns_put(par->net, par->family);
 }
 
diff --git a/net/ipv6/netfilter/ip6t_SYNPROXY.c b/net/ipv6/netfilter/ip6t_SYNPROXY.c
index cb6d42b03cb5..55a9b92d0a1f 100644
--- a/net/ipv6/netfilter/ip6t_SYNPROXY.c
+++ b/net/ipv6/netfilter/ip6t_SYNPROXY.c
@@ -6,272 +6,11 @@
  * published by the Free Software Foundation.
  */
 
-#include <linux/module.h>
-#include <linux/skbuff.h>
-#include <net/ip6_checksum.h>
-#include <net/ip6_route.h>
-#include <net/tcp.h>
-
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter/xt_SYNPROXY.h>
-#include <net/netfilter/nf_conntrack.h>
-#include <net/netfilter/nf_conntrack_seqadj.h>
-#include <net/netfilter/nf_conntrack_synproxy.h>
-#include <net/netfilter/nf_conntrack_ecache.h>
-
-static struct ipv6hdr *
-synproxy_build_ip(struct net *net, struct sk_buff *skb,
-		  const struct in6_addr *saddr,
-		  const struct in6_addr *daddr)
-{
-	struct ipv6hdr *iph;
-
-	skb_reset_network_header(skb);
-	iph = skb_put(skb, sizeof(*iph));
-	ip6_flow_hdr(iph, 0, 0);
-	iph->hop_limit	= net->ipv6.devconf_all->hop_limit;
-	iph->nexthdr	= IPPROTO_TCP;
-	iph->saddr	= *saddr;
-	iph->daddr	= *daddr;
-
-	return iph;
-}
-
-static void
-synproxy_send_tcp(struct net *net,
-		  const struct sk_buff *skb, struct sk_buff *nskb,
-		  struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
-		  struct ipv6hdr *niph, struct tcphdr *nth,
-		  unsigned int tcp_hdr_size)
-{
-	struct dst_entry *dst;
-	struct flowi6 fl6;
-
-	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
-	nskb->ip_summed   = CHECKSUM_PARTIAL;
-	nskb->csum_start  = (unsigned char *)nth - nskb->head;
-	nskb->csum_offset = offsetof(struct tcphdr, check);
-
-	memset(&fl6, 0, sizeof(fl6));
-	fl6.flowi6_proto = IPPROTO_TCP;
-	fl6.saddr = niph->saddr;
-	fl6.daddr = niph->daddr;
-	fl6.fl6_sport = nth->source;
-	fl6.fl6_dport = nth->dest;
-	security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
-	dst = ip6_route_output(net, NULL, &fl6);
-	if (dst->error) {
-		dst_release(dst);
-		goto free_nskb;
-	}
-	dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
-	if (IS_ERR(dst))
-		goto free_nskb;
-
-	skb_dst_set(nskb, dst);
-
-	if (nfct) {
-		nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
-		nf_conntrack_get(nfct);
-	}
-
-	ip6_local_out(net, nskb->sk, nskb);
-	return;
-
-free_nskb:
-	kfree_skb(nskb);
-}
-
-static void
-synproxy_send_client_synack(struct net *net,
-			    const struct sk_buff *skb, const struct tcphdr *th,
-			    const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct ipv6hdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-	u16 mss = opts->mss;
-
-	iph = ipv6_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->dest;
-	nth->dest	= th->source;
-	nth->seq	= htonl(__cookie_v6_init_sequence(iph, th, &mss));
-	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
-	tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
-	if (opts->options & XT_SYNPROXY_OPT_ECN)
-		tcp_flag_word(nth) |= TCP_FLAG_ECE;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= 0;
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
-			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
-}
 
-static void
-synproxy_send_server_syn(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts, u32 recv_seq)
-{
-	struct synproxy_net *snet = synproxy_pernet(net);
-	struct sk_buff *nskb;
-	struct ipv6hdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ipv6_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->source;
-	nth->dest	= th->dest;
-	nth->seq	= htonl(recv_seq - 1);
-	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
-	 * sequence number translation once a connection tracking entry exists.
-	 */
-	nth->ack_seq	= htonl(ntohl(th->ack_seq) - 1);
-	tcp_flag_word(nth) = TCP_FLAG_SYN;
-	if (opts->options & XT_SYNPROXY_OPT_ECN)
-		tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= th->window;
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
-			  niph, nth, tcp_hdr_size);
-}
-
-static void
-synproxy_send_server_ack(struct net *net,
-			 const struct ip_ct_tcp *state,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct ipv6hdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ipv6_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->dest;
-	nth->dest	= th->source;
-	nth->seq	= htonl(ntohl(th->ack_seq));
-	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
-	tcp_flag_word(nth) = TCP_FLAG_ACK;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
-}
-
-static void
-synproxy_send_client_ack(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 const struct synproxy_options *opts)
-{
-	struct sk_buff *nskb;
-	struct ipv6hdr *iph, *niph;
-	struct tcphdr *nth;
-	unsigned int tcp_hdr_size;
-
-	iph = ipv6_hdr(skb);
-
-	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
-	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
-			 GFP_ATOMIC);
-	if (nskb == NULL)
-		return;
-	skb_reserve(nskb, MAX_TCP_HEADER);
-
-	niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
-
-	skb_reset_transport_header(nskb);
-	nth = skb_put(nskb, tcp_hdr_size);
-	nth->source	= th->source;
-	nth->dest	= th->dest;
-	nth->seq	= htonl(ntohl(th->seq) + 1);
-	nth->ack_seq	= th->ack_seq;
-	tcp_flag_word(nth) = TCP_FLAG_ACK;
-	nth->doff	= tcp_hdr_size / 4;
-	nth->window	= htons(ntohs(th->window) >> opts->wscale);
-	nth->check	= 0;
-	nth->urg_ptr	= 0;
-
-	synproxy_build_options(nth, opts);
-
-	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
-			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
-}
-
-static bool
-synproxy_recv_client_ack(struct net *net,
-			 const struct sk_buff *skb, const struct tcphdr *th,
-			 struct synproxy_options *opts, u32 recv_seq)
-{
-	struct synproxy_net *snet = synproxy_pernet(net);
-	int mss;
-
-	mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
-	if (mss == 0) {
-		this_cpu_inc(snet->stats->cookie_invalid);
-		return false;
-	}
-
-	this_cpu_inc(snet->stats->cookie_valid);
-	opts->mss = mss;
-	opts->options |= XT_SYNPROXY_OPT_MSS;
-
-	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
-		synproxy_check_timestamp_cookie(opts);
-
-	synproxy_send_server_syn(net, skb, th, opts, recv_seq);
-	return true;
-}
+#include <net/netfilter/nf_synproxy.h>
 
 static unsigned int
 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
@@ -307,13 +46,14 @@ synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 					  XT_SYNPROXY_OPT_SACK_PERM |
 					  XT_SYNPROXY_OPT_ECN);
 
-		synproxy_send_client_synack(net, skb, th, &opts);
+		synproxy_send_client_synack_ipv6(net, skb, th, &opts);
 		consume_skb(skb);
 		return NF_STOLEN;
 
 	} else if (th->ack && !(th->fin || th->rst || th->syn)) {
 		/* ACK from client */
-		if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
+		if (synproxy_recv_client_ack_ipv6(net, skb, th, &opts,
+						  ntohl(th->seq))) {
 			consume_skb(skb);
 			return NF_STOLEN;
 		} else {
@@ -324,141 +64,6 @@ synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 	return XT_CONTINUE;
 }
 
-static unsigned int ipv6_synproxy_hook(void *priv,
-				       struct sk_buff *skb,
-				       const struct nf_hook_state *nhs)
-{
-	struct net *net = nhs->net;
-	struct synproxy_net *snet = synproxy_pernet(net);
-	enum ip_conntrack_info ctinfo;
-	struct nf_conn *ct;
-	struct nf_conn_synproxy *synproxy;
-	struct synproxy_options opts = {};
-	const struct ip_ct_tcp *state;
-	struct tcphdr *th, _th;
-	__be16 frag_off;
-	u8 nexthdr;
-	int thoff;
-
-	ct = nf_ct_get(skb, &ctinfo);
-	if (ct == NULL)
-		return NF_ACCEPT;
-
-	synproxy = nfct_synproxy(ct);
-	if (synproxy == NULL)
-		return NF_ACCEPT;
-
-	if (nf_is_loopback_packet(skb))
-		return NF_ACCEPT;
-
-	nexthdr = ipv6_hdr(skb)->nexthdr;
-	thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
-				 &frag_off);
-	if (thoff < 0 || nexthdr != IPPROTO_TCP)
-		return NF_ACCEPT;
-
-	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
-	if (th == NULL)
-		return NF_DROP;
-
-	state = &ct->proto.tcp;
-	switch (state->state) {
-	case TCP_CONNTRACK_CLOSE:
-		if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
-			nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
-						      ntohl(th->seq) + 1);
-			break;
-		}
-
-		if (!th->syn || th->ack ||
-		    CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
-			break;
-
-		/* Reopened connection - reset the sequence number and timestamp
-		 * adjustments, they will get initialized once the connection is
-		 * reestablished.
-		 */
-		nf_ct_seqadj_init(ct, ctinfo, 0);
-		synproxy->tsoff = 0;
-		this_cpu_inc(snet->stats->conn_reopened);
-
-		/* fall through */
-	case TCP_CONNTRACK_SYN_SENT:
-		if (!synproxy_parse_options(skb, thoff, th, &opts))
-			return NF_DROP;
-
-		if (!th->syn && th->ack &&
-		    CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
-			/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
-			 * therefore we need to add 1 to make the SYN sequence
-			 * number match the one of first SYN.
-			 */
-			if (synproxy_recv_client_ack(net, skb, th, &opts,
-						     ntohl(th->seq) + 1)) {
-				this_cpu_inc(snet->stats->cookie_retrans);
-				consume_skb(skb);
-				return NF_STOLEN;
-			} else {
-				return NF_DROP;
-			}
-		}
-
-		synproxy->isn = ntohl(th->ack_seq);
-		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
-			synproxy->its = opts.tsecr;
-
-		nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
-		break;
-	case TCP_CONNTRACK_SYN_RECV:
-		if (!th->syn || !th->ack)
-			break;
-
-		if (!synproxy_parse_options(skb, thoff, th, &opts))
-			return NF_DROP;
-
-		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) {
-			synproxy->tsoff = opts.tsval - synproxy->its;
-			nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
-		}
-
-		opts.options &= ~(XT_SYNPROXY_OPT_MSS |
-				  XT_SYNPROXY_OPT_WSCALE |
-				  XT_SYNPROXY_OPT_SACK_PERM);
-
-		swap(opts.tsval, opts.tsecr);
-		synproxy_send_server_ack(net, state, skb, th, &opts);
-
-		nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
-		nf_conntrack_event_cache(IPCT_SEQADJ, ct);
-
-		swap(opts.tsval, opts.tsecr);
-		synproxy_send_client_ack(net, skb, th, &opts);
-
-		consume_skb(skb);
-		return NF_STOLEN;
-	default:
-		break;
-	}
-
-	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
-	return NF_ACCEPT;
-}
-
-static const struct nf_hook_ops ipv6_synproxy_ops[] = {
-	{
-		.hook		= ipv6_synproxy_hook,
-		.pf		= NFPROTO_IPV6,
-		.hooknum	= NF_INET_LOCAL_IN,
-		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
-	},
-	{
-		.hook		= ipv6_synproxy_hook,
-		.pf		= NFPROTO_IPV6,
-		.hooknum	= NF_INET_POST_ROUTING,
-		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
-	},
-};
-
 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
 {
 	struct synproxy_net *snet = synproxy_pernet(par->net);
@@ -474,16 +79,12 @@ static int synproxy_tg6_check(const struct xt_tgchk_param *par)
 	if (err)
 		return err;
 
-	if (snet->hook_ref6 == 0) {
-		err = nf_register_net_hooks(par->net, ipv6_synproxy_ops,
-					    ARRAY_SIZE(ipv6_synproxy_ops));
-		if (err) {
-			nf_ct_netns_put(par->net, par->family);
-			return err;
-		}
+	err = nf_synproxy_ipv6_init(snet, par->net);
+	if (err) {
+		nf_ct_netns_put(par->net, par->family);
+		return err;
 	}
 
-	snet->hook_ref6++;
 	return err;
 }
 
@@ -491,10 +92,7 @@ static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
 {
 	struct synproxy_net *snet = synproxy_pernet(par->net);
 
-	snet->hook_ref6--;
-	if (snet->hook_ref6 == 0)
-		nf_unregister_net_hooks(par->net, ipv6_synproxy_ops,
-					ARRAY_SIZE(ipv6_synproxy_ops));
+	nf_synproxy_ipv6_fini(snet, par->net);
 	nf_ct_netns_put(par->net, par->family);
 }
 
diff --git a/net/netfilter/nf_synproxy.c b/net/netfilter/nf_synproxy.c
new file mode 100644
index 000000000000..a0d540d89b74
--- /dev/null
+++ b/net/netfilter/nf_synproxy.c
@@ -0,0 +1,836 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/netfilter_ipv6.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_ecache.h>
+#include <net/netfilter/nf_synproxy.h>
+
+#include <linux/netfilter/nf_SYNPROXY.h>
+
+static struct iphdr *
+synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
+		  __be32 daddr)
+{
+	struct iphdr *iph;
+
+	skb_reset_network_header(skb);
+	iph = skb_put(skb, sizeof(*iph));
+	iph->version	= 4;
+	iph->ihl	= sizeof(*iph) / 4;
+	iph->tos	= 0;
+	iph->id		= 0;
+	iph->frag_off	= htons(IP_DF);
+	iph->ttl	= net->ipv4.sysctl_ip_default_ttl;
+	iph->protocol	= IPPROTO_TCP;
+	iph->check	= 0;
+	iph->saddr	= saddr;
+	iph->daddr	= daddr;
+
+	return iph;
+}
+
+static void
+synproxy_send_tcp(struct net *net,
+		  const struct sk_buff *skb, struct sk_buff *nskb,
+		  struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
+		  struct iphdr *niph, struct tcphdr *nth,
+		  unsigned int tcp_hdr_size)
+{
+	nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
+	nskb->ip_summed   = CHECKSUM_PARTIAL;
+	nskb->csum_start  = (unsigned char *)nth - nskb->head;
+	nskb->csum_offset = offsetof(struct tcphdr, check);
+
+	skb_dst_set_noref(nskb, skb_dst(skb));
+	nskb->protocol = htons(ETH_P_IP);
+	if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
+		goto free_nskb;
+
+	if (nfct) {
+		nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
+		nf_conntrack_get(nfct);
+	}
+
+	ip_local_out(net, nskb->sk, nskb);
+	return;
+
+free_nskb:
+	kfree_skb(nskb);
+}
+
+void
+synproxy_send_client_synack(struct net *net,
+			    const struct sk_buff *skb, const struct tcphdr *th,
+			    const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct iphdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+	u16 mss = opts->mss;
+
+	iph = ip_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->dest;
+	nth->dest	= th->source;
+	nth->seq	= htonl(__cookie_v4_init_sequence(iph, th, &mss));
+	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
+	tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
+	if (opts->options & NF_SYNPROXY_OPT_ECN)
+		tcp_flag_word(nth) |= TCP_FLAG_ECE;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= 0;
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
+			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
+}
+EXPORT_SYMBOL_GPL(synproxy_send_client_synack);
+
+static void
+synproxy_send_server_syn(struct net *net,
+			 const struct sk_buff *skb, const struct tcphdr *th,
+			 const struct synproxy_options *opts, u32 recv_seq)
+{
+	struct synproxy_net *snet = synproxy_pernet(net);
+	struct sk_buff *nskb;
+	struct iphdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ip_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->source;
+	nth->dest	= th->dest;
+	nth->seq	= htonl(recv_seq - 1);
+	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
+	 * sequence number translation once a connection tracking entry exists.
+	 */
+	nth->ack_seq	= htonl(ntohl(th->ack_seq) - 1);
+	tcp_flag_word(nth) = TCP_FLAG_SYN;
+	if (opts->options & NF_SYNPROXY_OPT_ECN)
+		tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= th->window;
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
+			  niph, nth, tcp_hdr_size);
+}
+
+static void
+synproxy_send_server_ack(struct net *net,
+			 const struct ip_ct_tcp *state,
+			 const struct sk_buff *skb, const struct tcphdr *th,
+			 const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct iphdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ip_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->dest;
+	nth->dest	= th->source;
+	nth->seq	= htonl(ntohl(th->ack_seq));
+	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
+	tcp_flag_word(nth) = TCP_FLAG_ACK;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
+}
+
+static void
+synproxy_send_client_ack(struct net *net,
+			 const struct sk_buff *skb, const struct tcphdr *th,
+			 const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct iphdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ip_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->source;
+	nth->dest	= th->dest;
+	nth->seq	= htonl(ntohl(th->seq) + 1);
+	nth->ack_seq	= th->ack_seq;
+	tcp_flag_word(nth) = TCP_FLAG_ACK;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= htons(ntohs(th->window) >> opts->wscale);
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
+			  IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
+}
+
+bool
+synproxy_recv_client_ack(struct net *net,
+			 const struct sk_buff *skb, const struct tcphdr *th,
+			 struct synproxy_options *opts, u32 recv_seq)
+{
+	struct synproxy_net *snet = synproxy_pernet(net);
+	int mss;
+
+	mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
+	if (mss == 0) {
+		this_cpu_inc(snet->stats->cookie_invalid);
+		return false;
+	}
+
+	this_cpu_inc(snet->stats->cookie_valid);
+	opts->mss = mss;
+	opts->options |= NF_SYNPROXY_OPT_MSS;
+
+	if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
+		synproxy_check_timestamp_cookie(opts);
+
+	synproxy_send_server_syn(net, skb, th, opts, recv_seq);
+	return true;
+}
+EXPORT_SYMBOL_GPL(synproxy_recv_client_ack);
+
+unsigned int
+ipv4_synproxy_hook(void *priv, struct sk_buff *skb,
+		   const struct nf_hook_state *nhs)
+{
+	struct net *net = nhs->net;
+	struct synproxy_net *snet = synproxy_pernet(net);
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *ct;
+	struct nf_conn_synproxy *synproxy;
+	struct synproxy_options opts = {};
+	const struct ip_ct_tcp *state;
+	struct tcphdr *th, _th;
+	unsigned int thoff;
+
+	ct = nf_ct_get(skb, &ctinfo);
+	if (!ct)
+		return NF_ACCEPT;
+
+	synproxy = nfct_synproxy(ct);
+	if (!synproxy)
+		return NF_ACCEPT;
+
+	if (nf_is_loopback_packet(skb) ||
+	    ip_hdr(skb)->protocol != IPPROTO_TCP)
+		return NF_ACCEPT;
+
+	thoff = ip_hdrlen(skb);
+	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
+	if (!th)
+		return NF_DROP;
+
+	state = &ct->proto.tcp;
+	switch (state->state) {
+	case TCP_CONNTRACK_CLOSE:
+		if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
+			nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
+						      ntohl(th->seq) + 1);
+			break;
+		}
+
+		if (!th->syn || th->ack ||
+		    CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
+			break;
+
+		/* Reopened connection - reset the sequence number and timestamp
+		 * adjustments, they will get initialized once the connection is
+		 * reestablished.
+		 */
+		nf_ct_seqadj_init(ct, ctinfo, 0);
+		synproxy->tsoff = 0;
+		this_cpu_inc(snet->stats->conn_reopened);
+
+		/* fall through */
+	case TCP_CONNTRACK_SYN_SENT:
+		if (!synproxy_parse_options(skb, thoff, th, &opts))
+			return NF_DROP;
+
+		if (!th->syn && th->ack &&
+		    CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
+			/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
+			 * therefore we need to add 1 to make the SYN sequence
+			 * number match the one of first SYN.
+			 */
+			if (synproxy_recv_client_ack(net, skb, th, &opts,
+						     ntohl(th->seq) + 1)) {
+				this_cpu_inc(snet->stats->cookie_retrans);
+				consume_skb(skb);
+				return NF_STOLEN;
+			} else {
+				return NF_DROP;
+			}
+		}
+
+		synproxy->isn = ntohl(th->ack_seq);
+		if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP)
+			synproxy->its = opts.tsecr;
+
+		nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
+		break;
+	case TCP_CONNTRACK_SYN_RECV:
+		if (!th->syn || !th->ack)
+			break;
+
+		if (!synproxy_parse_options(skb, thoff, th, &opts))
+			return NF_DROP;
+
+		if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) {
+			synproxy->tsoff = opts.tsval - synproxy->its;
+			nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
+		}
+
+		opts.options &= ~(NF_SYNPROXY_OPT_MSS |
+				  NF_SYNPROXY_OPT_WSCALE |
+				  NF_SYNPROXY_OPT_SACK_PERM);
+
+		swap(opts.tsval, opts.tsecr);
+		synproxy_send_server_ack(net, state, skb, th, &opts);
+
+		nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
+		nf_conntrack_event_cache(IPCT_SEQADJ, ct);
+
+		swap(opts.tsval, opts.tsecr);
+		synproxy_send_client_ack(net, skb, th, &opts);
+
+		consume_skb(skb);
+		return NF_STOLEN;
+	default:
+		break;
+	}
+
+	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
+	return NF_ACCEPT;
+}
+EXPORT_SYMBOL_GPL(ipv4_synproxy_hook);
+
+static const struct nf_hook_ops ipv4_synproxy_ops[] = {
+	{
+		.hook		= ipv4_synproxy_hook,
+		.pf		= NFPROTO_IPV4,
+		.hooknum	= NF_INET_LOCAL_IN,
+		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+	},
+	{
+		.hook		= ipv4_synproxy_hook,
+		.pf		= NFPROTO_IPV4,
+		.hooknum	= NF_INET_POST_ROUTING,
+		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+	},
+};
+
+int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net)
+{
+	int err;
+
+	if (snet->hook_ref4 == 0) {
+		err = nf_register_net_hooks(net, ipv4_synproxy_ops,
+					    ARRAY_SIZE(ipv4_synproxy_ops));
+		if (err)
+			return err;
+	}
+
+	snet->hook_ref4++;
+	return err;
+}
+EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init);
+
+void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net)
+{
+	snet->hook_ref4--;
+	if (snet->hook_ref4 == 0)
+		nf_unregister_net_hooks(net, ipv4_synproxy_ops,
+					ARRAY_SIZE(ipv4_synproxy_ops));
+}
+EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_fini);
+
+#if IS_ENABLED(CONFIG_IPV6) /* IPv6 support */
+
+static struct ipv6hdr *
+synproxy_build_ip_ipv6(struct net *net, struct sk_buff *skb,
+		       const struct in6_addr *saddr,
+		       const struct in6_addr *daddr)
+{
+	struct ipv6hdr *iph;
+
+	skb_reset_network_header(skb);
+	iph = skb_put(skb, sizeof(*iph));
+	ip6_flow_hdr(iph, 0, 0);
+	iph->hop_limit	= net->ipv6.devconf_all->hop_limit;
+	iph->nexthdr	= IPPROTO_TCP;
+	iph->saddr	= *saddr;
+	iph->daddr	= *daddr;
+
+	return iph;
+}
+
+static void
+synproxy_send_tcp_ipv6(struct net *net,
+		       const struct sk_buff *skb, struct sk_buff *nskb,
+		       struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
+		       struct ipv6hdr *niph, struct tcphdr *nth,
+		       unsigned int tcp_hdr_size)
+{
+	struct dst_entry *dst;
+	struct flowi6 fl6;
+
+	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
+	nskb->ip_summed   = CHECKSUM_PARTIAL;
+	nskb->csum_start  = (unsigned char *)nth - nskb->head;
+	nskb->csum_offset = offsetof(struct tcphdr, check);
+
+	memset(&fl6, 0, sizeof(fl6));
+	fl6.flowi6_proto = IPPROTO_TCP;
+	fl6.saddr = niph->saddr;
+	fl6.daddr = niph->daddr;
+	fl6.fl6_sport = nth->source;
+	fl6.fl6_dport = nth->dest;
+	security_skb_classify_flow((struct sk_buff *)skb,
+				   flowi6_to_flowi(&fl6));
+	dst = ip6_route_output(net, NULL, &fl6);
+	if (dst->error) {
+		dst_release(dst);
+		goto free_nskb;
+	}
+	dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
+	if (IS_ERR(dst))
+		goto free_nskb;
+
+	skb_dst_set(nskb, dst);
+
+	if (nfct) {
+		nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
+		nf_conntrack_get(nfct);
+	}
+
+	ip6_local_out(net, nskb->sk, nskb);
+	return;
+
+free_nskb:
+	kfree_skb(nskb);
+}
+
+void
+synproxy_send_client_synack_ipv6(struct net *net,
+				 const struct sk_buff *skb,
+				 const struct tcphdr *th,
+				 const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct ipv6hdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+	u16 mss = opts->mss;
+
+	iph = ipv6_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip_ipv6(net, nskb, &iph->daddr, &iph->saddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->dest;
+	nth->dest	= th->source;
+	nth->seq	= htonl(nf_ipv6_cookie_init_sequence(iph, th, &mss));
+	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
+	tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
+	if (opts->options & NF_SYNPROXY_OPT_ECN)
+		tcp_flag_word(nth) |= TCP_FLAG_ECE;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= 0;
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp_ipv6(net, skb, nskb, skb_nfct(skb),
+			       IP_CT_ESTABLISHED_REPLY, niph, nth,
+			       tcp_hdr_size);
+}
+EXPORT_SYMBOL_GPL(synproxy_send_client_synack_ipv6);
+
+static void
+synproxy_send_server_syn_ipv6(struct net *net, const struct sk_buff *skb,
+			      const struct tcphdr *th,
+			      const struct synproxy_options *opts, u32 recv_seq)
+{
+	struct synproxy_net *snet = synproxy_pernet(net);
+	struct sk_buff *nskb;
+	struct ipv6hdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ipv6_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip_ipv6(net, nskb, &iph->saddr, &iph->daddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->source;
+	nth->dest	= th->dest;
+	nth->seq	= htonl(recv_seq - 1);
+	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
+	 * sequence number translation once a connection tracking entry exists.
+	 */
+	nth->ack_seq	= htonl(ntohl(th->ack_seq) - 1);
+	tcp_flag_word(nth) = TCP_FLAG_SYN;
+	if (opts->options & NF_SYNPROXY_OPT_ECN)
+		tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= th->window;
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp_ipv6(net, skb, nskb, &snet->tmpl->ct_general,
+			       IP_CT_NEW, niph, nth, tcp_hdr_size);
+}
+
+static void
+synproxy_send_server_ack_ipv6(struct net *net, const struct ip_ct_tcp *state,
+			      const struct sk_buff *skb,
+			      const struct tcphdr *th,
+			      const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct ipv6hdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ipv6_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip_ipv6(net, nskb, &iph->daddr, &iph->saddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->dest;
+	nth->dest	= th->source;
+	nth->seq	= htonl(ntohl(th->ack_seq));
+	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
+	tcp_flag_word(nth) = TCP_FLAG_ACK;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp_ipv6(net, skb, nskb, NULL, 0, niph, nth,
+			       tcp_hdr_size);
+}
+
+static void
+synproxy_send_client_ack_ipv6(struct net *net, const struct sk_buff *skb,
+			      const struct tcphdr *th,
+			      const struct synproxy_options *opts)
+{
+	struct sk_buff *nskb;
+	struct ipv6hdr *iph, *niph;
+	struct tcphdr *nth;
+	unsigned int tcp_hdr_size;
+
+	iph = ipv6_hdr(skb);
+
+	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
+	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
+			 GFP_ATOMIC);
+	if (!nskb)
+		return;
+	skb_reserve(nskb, MAX_TCP_HEADER);
+
+	niph = synproxy_build_ip_ipv6(net, nskb, &iph->saddr, &iph->daddr);
+
+	skb_reset_transport_header(nskb);
+	nth = skb_put(nskb, tcp_hdr_size);
+	nth->source	= th->source;
+	nth->dest	= th->dest;
+	nth->seq	= htonl(ntohl(th->seq) + 1);
+	nth->ack_seq	= th->ack_seq;
+	tcp_flag_word(nth) = TCP_FLAG_ACK;
+	nth->doff	= tcp_hdr_size / 4;
+	nth->window	= htons(ntohs(th->window) >> opts->wscale);
+	nth->check	= 0;
+	nth->urg_ptr	= 0;
+
+	synproxy_build_options(nth, opts);
+
+	synproxy_send_tcp_ipv6(net, skb, nskb, skb_nfct(skb),
+			       IP_CT_ESTABLISHED_REPLY, niph, nth,
+			       tcp_hdr_size);
+}
+
+bool
+synproxy_recv_client_ack_ipv6(struct net *net,
+			      const struct sk_buff *skb,
+			      const struct tcphdr *th,
+			      struct synproxy_options *opts, u32 recv_seq)
+{
+	struct synproxy_net *snet = synproxy_pernet(net);
+	int mss;
+
+	mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
+	if (mss == 0) {
+		this_cpu_inc(snet->stats->cookie_invalid);
+		return false;
+	}
+
+	this_cpu_inc(snet->stats->cookie_valid);
+	opts->mss = mss;
+	opts->options |= NF_SYNPROXY_OPT_MSS;
+
+	if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
+		synproxy_check_timestamp_cookie(opts);
+
+	synproxy_send_server_syn_ipv6(net, skb, th, opts, recv_seq);
+	return true;
+}
+EXPORT_SYMBOL_GPL(synproxy_recv_client_ack_ipv6);
+
+unsigned int
+ipv6_synproxy_hook(void *priv, struct sk_buff *skb,
+		   const struct nf_hook_state *nhs)
+{
+	struct net *net = nhs->net;
+	struct synproxy_net *snet = synproxy_pernet(net);
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *ct;
+	struct nf_conn_synproxy *synproxy;
+	struct synproxy_options opts = {};
+	const struct ip_ct_tcp *state;
+	struct tcphdr *th, _th;
+	__be16 frag_off;
+	u8 nexthdr;
+	int thoff;
+
+	ct = nf_ct_get(skb, &ctinfo);
+	if (!ct)
+		return NF_ACCEPT;
+
+	synproxy = nfct_synproxy(ct);
+	if (!synproxy)
+		return NF_ACCEPT;
+
+	if (nf_is_loopback_packet(skb))
+		return NF_ACCEPT;
+
+	nexthdr = ipv6_hdr(skb)->nexthdr;
+	thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
+				 &frag_off);
+	if (thoff < 0 || nexthdr != IPPROTO_TCP)
+		return NF_ACCEPT;
+
+	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
+	if (!th)
+		return NF_DROP;
+
+	state = &ct->proto.tcp;
+	switch (state->state) {
+	case TCP_CONNTRACK_CLOSE:
+		if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
+			nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
+						      ntohl(th->seq) + 1);
+			break;
+		}
+
+		if (!th->syn || th->ack ||
+		    CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
+			break;
+
+		/* Reopened connection - reset the sequence number and timestamp
+		 * adjustments, they will get initialized once the connection is
+		 * reestablished.
+		 */
+		nf_ct_seqadj_init(ct, ctinfo, 0);
+		synproxy->tsoff = 0;
+		this_cpu_inc(snet->stats->conn_reopened);
+
+		/* fall through */
+	case TCP_CONNTRACK_SYN_SENT:
+		if (!synproxy_parse_options(skb, thoff, th, &opts))
+			return NF_DROP;
+
+		if (!th->syn && th->ack &&
+		    CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
+			/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
+			 * therefore we need to add 1 to make the SYN sequence
+			 * number match the one of first SYN.
+			 */
+			if (synproxy_recv_client_ack_ipv6(net, skb, th, &opts,
+							  ntohl(th->seq) + 1)) {
+				this_cpu_inc(snet->stats->cookie_retrans);
+				consume_skb(skb);
+				return NF_STOLEN;
+			} else {
+				return NF_DROP;
+			}
+		}
+
+		synproxy->isn = ntohl(th->ack_seq);
+		if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP)
+			synproxy->its = opts.tsecr;
+
+		nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
+		break;
+	case TCP_CONNTRACK_SYN_RECV:
+		if (!th->syn || !th->ack)
+			break;
+
+		if (!synproxy_parse_options(skb, thoff, th, &opts))
+			return NF_DROP;
+
+		if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) {
+			synproxy->tsoff = opts.tsval - synproxy->its;
+			nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
+		}
+
+		opts.options &= ~(NF_SYNPROXY_OPT_MSS |
+				  NF_SYNPROXY_OPT_WSCALE |
+				  NF_SYNPROXY_OPT_SACK_PERM);
+
+		swap(opts.tsval, opts.tsecr);
+		synproxy_send_server_ack_ipv6(net, state, skb, th, &opts);
+
+		nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
+		nf_conntrack_event_cache(IPCT_SEQADJ, ct);
+
+		swap(opts.tsval, opts.tsecr);
+		synproxy_send_client_ack_ipv6(net, skb, th, &opts);
+
+		consume_skb(skb);
+		return NF_STOLEN;
+	default:
+		break;
+	}
+
+	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
+	return NF_ACCEPT;
+}
+EXPORT_SYMBOL_GPL(ipv6_synproxy_hook);
+
+static const struct nf_hook_ops ipv6_synproxy_ops[] = {
+	{
+		.hook		= ipv6_synproxy_hook,
+		.pf		= NFPROTO_IPV6,
+		.hooknum	= NF_INET_LOCAL_IN,
+		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+	},
+	{
+		.hook		= ipv6_synproxy_hook,
+		.pf		= NFPROTO_IPV6,
+		.hooknum	= NF_INET_POST_ROUTING,
+		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+	},
+};
+
+int
+nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net)
+{
+	int err;
+
+	if (snet->hook_ref6 == 0) {
+		err = nf_register_net_hooks(net, ipv6_synproxy_ops,
+					    ARRAY_SIZE(ipv6_synproxy_ops));
+		if (err)
+			return err;
+	}
+
+	snet->hook_ref6++;
+	return err;
+}
+EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init);
+
+void
+nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net)
+{
+	snet->hook_ref6--;
+	if (snet->hook_ref6 == 0)
+		nf_unregister_net_hooks(net, ipv6_synproxy_ops,
+					ARRAY_SIZE(ipv6_synproxy_ops));
+}
+EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_fini);
+#endif /* IPv6 support */
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
-- 
2.20.1

Re: [PATCH nf-next v3 3/4] netfilter: synproxy: extract SYNPROXY infrastructure from {ipt,ip6t}_SYNPROXY

[Florian Westphal]

Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
> +static void
> +synproxy_send_tcp_ipv6(struct net *net,
> +		       const struct sk_buff *skb, struct sk_buff *nskb,
> +		       struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
> +		       struct ipv6hdr *niph, struct tcphdr *nth,
> +		       unsigned int tcp_hdr_size)
> +{
> +	struct dst_entry *dst;
> +	struct flowi6 fl6;
> +
> +	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
> +	nskb->ip_summed   = CHECKSUM_PARTIAL;
> +	nskb->csum_start  = (unsigned char *)nth - nskb->head;
> +	nskb->csum_offset = offsetof(struct tcphdr, check);
> +
> +	memset(&fl6, 0, sizeof(fl6));
> +	fl6.flowi6_proto = IPPROTO_TCP;
> +	fl6.saddr = niph->saddr;
> +	fl6.daddr = niph->daddr;
> +	fl6.fl6_sport = nth->source;
> +	fl6.fl6_dport = nth->dest;
> +	security_skb_classify_flow((struct sk_buff *)skb,
> +				   flowi6_to_flowi(&fl6));
> +	dst = ip6_route_output(net, NULL, &fl6);

All good, BUT the above function call also pulls in ipv6.ko.
You can fold this patch to avoid it, it coverts it to use the
nf_ip6_route() wrapper which internally uses the v6ops pointer
for ip6_route_output if needed.

diff --git a/net/netfilter/nf_synproxy.c b/net/netfilter/nf_synproxy.c
--- a/net/netfilter/nf_synproxy.c
+++ b/net/netfilter/nf_synproxy.c
@@ -434,6 +434,7 @@ synproxy_send_tcp_ipv6(struct net *net,
 {
 	struct dst_entry *dst;
 	struct flowi6 fl6;
+	int err;
 
 	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
 	nskb->ip_summed   = CHECKSUM_PARTIAL;
@@ -448,11 +449,10 @@ synproxy_send_tcp_ipv6(struct net *net,
 	fl6.fl6_dport = nth->dest;
 	security_skb_classify_flow((struct sk_buff *)skb,
 				   flowi6_to_flowi(&fl6));
-	dst = ip6_route_output(net, NULL, &fl6);
-	if (dst->error) {
-		dst_release(dst);
+	err = nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
+	if (err)
 		goto free_nskb;
-	}
+
 	dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 	if (IS_ERR(dst))
 		goto free_nskb;

[PATCH nf-next v3 4/4] netfilter: add NF_SYNPROXY symbol

[Fernando Fernandez Mancera]

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
---
 net/ipv4/netfilter/Kconfig | 2 +-
 net/ipv6/netfilter/Kconfig | 2 +-
 net/netfilter/Kconfig      | 4 ++++
 net/netfilter/Makefile     | 1 +
 4 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index 1412b029f37f..87f6ec800e54 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -197,7 +197,7 @@ config IP_NF_TARGET_SYNPROXY
 	tristate "SYNPROXY target support"
 	depends on NF_CONNTRACK && NETFILTER_ADVANCED
 	select NETFILTER_SYNPROXY
-	select SYN_COOKIES
+	select NF_SYNPROXY
 	help
 	  The SYNPROXY target allows you to intercept TCP connections and
 	  establish them using syncookies before they are passed on to the
diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index 086fc669279e..f71879f875e1 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -213,7 +213,7 @@ config IP6_NF_TARGET_SYNPROXY
 	tristate "SYNPROXY target support"
 	depends on NF_CONNTRACK && NETFILTER_ADVANCED
 	select NETFILTER_SYNPROXY
-	select SYN_COOKIES
+	select NF_SYNPROXY
 	help
 	  The SYNPROXY target allows you to intercept TCP connections and
 	  establish them using syncookies before they are passed on to the
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 02b281d3c167..ae65fca0d509 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -435,6 +435,10 @@ config NF_NAT_REDIRECT
 config NF_NAT_MASQUERADE
 	bool
 
+config NF_SYNPROXY
+	tristate
+	depends on NF_CONNTRACK && NETFILTER_ADVANCED
+
 config NETFILTER_SYNPROXY
 	tristate
 
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 72cca6b48960..7a6067513eee 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -67,6 +67,7 @@ obj-$(CONFIG_NF_NAT_TFTP) += nf_nat_tftp.o
 
 # SYNPROXY
 obj-$(CONFIG_NETFILTER_SYNPROXY) += nf_synproxy_core.o
+obj-$(CONFIG_NF_SYNPROXY) += nf_synproxy.o
 
 obj-$(CONFIG_NETFILTER_CONNCOUNT) += nf_conncount.o
 
-- 
2.20.1

Re: [PATCH nf-next v3 4/4] netfilter: add NF_SYNPROXY symbol

[Florian Westphal]

Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
> Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
> ---
>  net/ipv4/netfilter/Kconfig | 2 +-
>  net/ipv6/netfilter/Kconfig | 2 +-
>  net/netfilter/Kconfig      | 4 ++++
>  net/netfilter/Makefile     | 1 +
>  4 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
> index 1412b029f37f..87f6ec800e54 100644
> --- a/net/ipv4/netfilter/Kconfig
> +++ b/net/ipv4/netfilter/Kconfig
> @@ -197,7 +197,7 @@ config IP_NF_TARGET_SYNPROXY
>  	tristate "SYNPROXY target support"
>  	depends on NF_CONNTRACK && NETFILTER_ADVANCED
>  	select NETFILTER_SYNPROXY
> -	select SYN_COOKIES
> +	select NF_SYNPROXY

What is the difference between NETFILTER_SYNPROXY and
NF_SYNPROXY?

Any chance we can ...

> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
> index 72cca6b48960..7a6067513eee 100644
> --- a/net/netfilter/Makefile
> +++ b/net/netfilter/Makefile
> @@ -67,6 +67,7 @@ obj-$(CONFIG_NF_NAT_TFTP) += nf_nat_tftp.o
>  
>  # SYNPROXY
>  obj-$(CONFIG_NETFILTER_SYNPROXY) += nf_synproxy_core.o
> +obj-$(CONFIG_NF_SYNPROXY) += nf_synproxy.o

... make nf_synproxy.o and nf_synproxy_core.o be part
of same module?

(Or place it even in same .c file?)

Re: [PATCH nf-next v3 4/4] netfilter: add NF_SYNPROXY symbol

[Florian Westphal]

Fernando Fernandez Mancera <ffmancera@riseup.net> wrote:
> Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
> ---
>  net/ipv4/netfilter/Kconfig | 2 +-
>  net/ipv6/netfilter/Kconfig | 2 +-
>  net/netfilter/Kconfig      | 4 ++++
>  net/netfilter/Makefile     | 1 +
>  4 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
> index 1412b029f37f..87f6ec800e54 100644
> --- a/net/ipv4/netfilter/Kconfig
> +++ b/net/ipv4/netfilter/Kconfig
> @@ -197,7 +197,7 @@ config IP_NF_TARGET_SYNPROXY
>  	tristate "SYNPROXY target support"
>  	depends on NF_CONNTRACK && NETFILTER_ADVANCED
>  	select NETFILTER_SYNPROXY
> -	select SYN_COOKIES
> +	select NF_SYNPROXY

Careful.  This means I can now create a kernel config with
IP_NF_TARGET_SYNPROXY=y
SYN_COOKIES=n

... and that will fail to build.