netfilter: add NAT support for shifted portmap ranges

This is a patch proposal to support shifted ranges in portmaps.  (i.e. tcp/udp
incoming port 5000-5100 on WAN redirected to LAN 192.168.1.5:2000-2100)

Currently DNAT only works for single port or identical port ranges.  (i.e.
ports 5000-5100 on WAN interface redirected to a LAN host while original
destination port is not altered) When different port ranges are configured,
either 'random' mode should be used, or else all incoming connections are
mapped onto the first port in the redirect range. (in described example
WAN:5000-5100 will all be mapped to 192.168.1.5:2000)

This patch introduces a new mode indicated by flag NF_NAT_RANGE_PROTO_OFFSET
which uses a base port value to calculate an offset with the destination port
present in the incoming stream. That offset is then applied as index within the
redirect port range (index modulo rangewidth to handle range overflow).

In described example the base port would be 5000. An incoming stream with
destination port 5004 would result in an offset value 4 which means that the
NAT'ed stream will be using destination port 2004.

Other possibilities include deterministic mapping of larger or multiple ranges
to a smaller range : WAN:5000-5999 -> LAN:5000-5099 (maps WAN port 5*xx to port
51xx)

This patch does not change any current behavior. It just adds new NAT proto
range functionality which must be selected via the specific flag when intended
to use.

A patch for iptables (libipt_DNAT.c + libip6t_DNAT.c) will also be proposed
which makes this functionality immediately available.

Signed-off-by: Thierry Du Tre <thierry@dtsystems.be>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

7 files changed, 21 insertions, 11 deletions

diff --git a/include/net/netfilter/ipv4/nf_nat_masquerade.h b/include/net/netfilter/ipv4/nf_nat_masquerade.h
index ebd869473603..cd24be4c4a99 100644
--- a/include/net/netfilter/ipv4/nf_nat_masquerade.h
+++ b/include/net/netfilter/ipv4/nf_nat_masquerade.h
@@ -6,7 +6,7 @@
 
 unsigned int
 nf_nat_masquerade_ipv4(struct sk_buff *skb, unsigned int hooknum,
-		       const struct nf_nat_range *range,
+		       const struct nf_nat_range2 *range,
 		       const struct net_device *out);
 
 void nf_nat_masquerade_ipv4_register_notifier(void);
diff --git a/include/net/netfilter/ipv6/nf_nat_masquerade.h b/include/net/netfilter/ipv6/nf_nat_masquerade.h
index 1ed4f2631ed6..0c3b5ebf0bb8 100644
--- a/include/net/netfilter/ipv6/nf_nat_masquerade.h
+++ b/include/net/netfilter/ipv6/nf_nat_masquerade.h
@@ -3,7 +3,7 @@
 #define _NF_NAT_MASQUERADE_IPV6_H_
 
 unsigned int
-nf_nat_masquerade_ipv6(struct sk_buff *skb, const struct nf_nat_range *range,
+nf_nat_masquerade_ipv6(struct sk_buff *skb, const struct nf_nat_range2 *range,
 		       const struct net_device *out);
 void nf_nat_masquerade_ipv6_register_notifier(void);
 void nf_nat_masquerade_ipv6_unregister_notifier(void);
diff --git a/include/net/netfilter/nf_nat.h b/include/net/netfilter/nf_nat.h
index 207a467e7ca6..da3d601cadee 100644
--- a/include/net/netfilter/nf_nat.h
+++ b/include/net/netfilter/nf_nat.h
@@ -39,7 +39,7 @@ struct nf_conn_nat {
 
 /* Set up the info structure to map into this range. */
 unsigned int nf_nat_setup_info(struct nf_conn *ct,
-			       const struct nf_nat_range *range,
+			       const struct nf_nat_range2 *range,
 			       enum nf_nat_manip_type maniptype);
 
 extern unsigned int nf_nat_alloc_null_binding(struct nf_conn *ct,
diff --git a/include/net/netfilter/nf_nat_l3proto.h b/include/net/netfilter/nf_nat_l3proto.h
index ce7c2b4e64bb..ac47098a61dc 100644
--- a/include/net/netfilter/nf_nat_l3proto.h
+++ b/include/net/netfilter/nf_nat_l3proto.h
@@ -7,7 +7,7 @@ struct nf_nat_l3proto {
 	u8	l3proto;
 
 	bool	(*in_range)(const struct nf_conntrack_tuple *t,
-			    const struct nf_nat_range *range);
+			    const struct nf_nat_range2 *range);
 
 	u32 	(*secure_port)(const struct nf_conntrack_tuple *t, __be16);
 
@@ -33,7 +33,7 @@ struct nf_nat_l3proto {
 				  struct flowi *fl);
 
 	int	(*nlattr_to_range)(struct nlattr *tb[],
-				   struct nf_nat_range *range);
+				   struct nf_nat_range2 *range);
 };
 
 int nf_nat_l3proto_register(const struct nf_nat_l3proto *);
diff --git a/include/net/netfilter/nf_nat_l4proto.h b/include/net/netfilter/nf_nat_l4proto.h
index 67835ff8a2d9..b4d6b29bca62 100644
--- a/include/net/netfilter/nf_nat_l4proto.h
+++ b/include/net/netfilter/nf_nat_l4proto.h
@@ -34,12 +34,12 @@ struct nf_nat_l4proto {
 	 */
 	void (*unique_tuple)(const struct nf_nat_l3proto *l3proto,
 			     struct nf_conntrack_tuple *tuple,
-			     const struct nf_nat_range *range,
+			     const struct nf_nat_range2 *range,
 			     enum nf_nat_manip_type maniptype,
 			     const struct nf_conn *ct);
 
 	int (*nlattr_to_range)(struct nlattr *tb[],
-			       struct nf_nat_range *range);
+			       struct nf_nat_range2 *range);
 };
 
 /* Protocol registration. */
@@ -72,11 +72,11 @@ bool nf_nat_l4proto_in_range(const struct nf_conntrack_tuple *tuple,
 
 void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto,
 				 struct nf_conntrack_tuple *tuple,
-				 const struct nf_nat_range *range,
+				 const struct nf_nat_range2 *range,
 				 enum nf_nat_manip_type maniptype,
 				 const struct nf_conn *ct, u16 *rover);
 
 int nf_nat_l4proto_nlattr_to_range(struct nlattr *tb[],
-				   struct nf_nat_range *range);
+				   struct nf_nat_range2 *range);
 
 #endif /*_NF_NAT_L4PROTO_H*/
diff --git a/include/net/netfilter/nf_nat_redirect.h b/include/net/netfilter/nf_nat_redirect.h
index 5ddabb08c472..c129aacc8ae8 100644
--- a/include/net/netfilter/nf_nat_redirect.h
+++ b/include/net/netfilter/nf_nat_redirect.h
@@ -7,7 +7,7 @@ nf_nat_redirect_ipv4(struct sk_buff *skb,
 		     const struct nf_nat_ipv4_multi_range_compat *mr,
 		     unsigned int hooknum);
 unsigned int
-nf_nat_redirect_ipv6(struct sk_buff *skb, const struct nf_nat_range *range,
+nf_nat_redirect_ipv6(struct sk_buff *skb, const struct nf_nat_range2 *range,
 		     unsigned int hooknum);
 
 #endif /* _NF_NAT_REDIRECT_H_ */
diff --git a/include/uapi/linux/netfilter/nf_nat.h b/include/uapi/linux/netfilter/nf_nat.h
index a33000da7229..4a95c0db14d4 100644
--- a/include/uapi/linux/netfilter/nf_nat.h
+++ b/include/uapi/linux/netfilter/nf_nat.h
@@ -10,6 +10,7 @@
 #define NF_NAT_RANGE_PROTO_RANDOM		(1 << 2)
 #define NF_NAT_RANGE_PERSISTENT			(1 << 3)
 #define NF_NAT_RANGE_PROTO_RANDOM_FULLY		(1 << 4)
+#define NF_NAT_RANGE_PROTO_OFFSET		(1 << 5)
 
 #define NF_NAT_RANGE_PROTO_RANDOM_ALL		\
 	(NF_NAT_RANGE_PROTO_RANDOM | NF_NAT_RANGE_PROTO_RANDOM_FULLY)
@@ -17,7 +18,7 @@
 #define NF_NAT_RANGE_MASK					\
 	(NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED |	\
 	 NF_NAT_RANGE_PROTO_RANDOM | NF_NAT_RANGE_PERSISTENT |	\
-	 NF_NAT_RANGE_PROTO_RANDOM_FULLY)
+	 NF_NAT_RANGE_PROTO_RANDOM_FULLY | NF_NAT_RANGE_PROTO_OFFSET)
 
 struct nf_nat_ipv4_range {
 	unsigned int			flags;
@@ -40,4 +41,13 @@ struct nf_nat_range {
 	union nf_conntrack_man_proto	max_proto;
 };
 
+struct nf_nat_range2 {
+	unsigned int			flags;
+	union nf_inet_addr		min_addr;
+	union nf_inet_addr		max_addr;
+	union nf_conntrack_man_proto	min_proto;
+	union nf_conntrack_man_proto	max_proto;
+	union nf_conntrack_man_proto	base_proto;
+};
+
 #endif /* _NETFILTER_NF_NAT_H */