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>

1 files changed, 66 insertions, 6 deletions

diff --git a/net/netfilter/xt_nat.c b/net/netfilter/xt_nat.c
index bdb689cdc829..8af9707f8789 100644
--- a/net/netfilter/xt_nat.c
+++ b/net/netfilter/xt_nat.c
@@ -37,11 +37,12 @@ static void xt_nat_destroy(const struct xt_tgdtor_param *par)
 	nf_ct_netns_put(par->net, par->family);
 }
 
-static void xt_nat_convert_range(struct nf_nat_range *dst,
+static void xt_nat_convert_range(struct nf_nat_range2 *dst,
 				 const struct nf_nat_ipv4_range *src)
 {
 	memset(&dst->min_addr, 0, sizeof(dst->min_addr));
 	memset(&dst->max_addr, 0, sizeof(dst->max_addr));
+	memset(&dst->base_proto, 0, sizeof(dst->base_proto));
 
 	dst->flags	 = src->flags;
 	dst->min_addr.ip = src->min_ip;
@@ -54,7 +55,7 @@ static unsigned int
 xt_snat_target_v0(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct;
 
@@ -71,7 +72,7 @@ static unsigned int
 xt_dnat_target_v0(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct;
 
@@ -86,7 +87,8 @@ xt_dnat_target_v0(struct sk_buff *skb, const struct xt_action_param *par)
 static unsigned int
 xt_snat_target_v1(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	const struct nf_nat_range *range = par->targinfo;
+	const struct nf_nat_range *range_v1 = par->targinfo;
+	struct nf_nat_range2 range;
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct;
 
@@ -95,13 +97,49 @@ xt_snat_target_v1(struct sk_buff *skb, const struct xt_action_param *par)
 		 (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
 		  ctinfo == IP_CT_RELATED_REPLY)));
 
-	return nf_nat_setup_info(ct, range, NF_NAT_MANIP_SRC);
+	memcpy(&range, range_v1, sizeof(*range_v1));
+	memset(&range.base_proto, 0, sizeof(range.base_proto));
+
+	return nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 }
 
 static unsigned int
 xt_dnat_target_v1(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	const struct nf_nat_range *range = par->targinfo;
+	const struct nf_nat_range *range_v1 = par->targinfo;
+	struct nf_nat_range2 range;
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *ct;
+
+	ct = nf_ct_get(skb, &ctinfo);
+	WARN_ON(!(ct != NULL &&
+		 (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED)));
+
+	memcpy(&range, range_v1, sizeof(*range_v1));
+	memset(&range.base_proto, 0, sizeof(range.base_proto));
+
+	return nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
+}
+
+static unsigned int
+xt_snat_target_v2(struct sk_buff *skb, const struct xt_action_param *par)
+{
+	const struct nf_nat_range2 *range = par->targinfo;
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *ct;
+
+	ct = nf_ct_get(skb, &ctinfo);
+	WARN_ON(!(ct != NULL &&
+		 (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
+		  ctinfo == IP_CT_RELATED_REPLY)));
+
+	return nf_nat_setup_info(ct, range, NF_NAT_MANIP_SRC);
+}
+
+static unsigned int
+xt_dnat_target_v2(struct sk_buff *skb, const struct xt_action_param *par)
+{
+	const struct nf_nat_range2 *range = par->targinfo;
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct;
 
@@ -163,6 +201,28 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 				  (1 << NF_INET_LOCAL_OUT),
 		.me		= THIS_MODULE,
 	},
+	{
+		.name		= "SNAT",
+		.revision	= 2,
+		.checkentry	= xt_nat_checkentry,
+		.destroy	= xt_nat_destroy,
+		.target		= xt_snat_target_v2,
+		.targetsize	= sizeof(struct nf_nat_range2),
+		.table		= "nat",
+		.hooks		= (1 << NF_INET_POST_ROUTING) |
+				  (1 << NF_INET_LOCAL_IN),
+		.me		= THIS_MODULE,
+	},
+	{
+		.name		= "DNAT",
+		.revision	= 2,
+		.target		= xt_dnat_target_v2,
+		.targetsize	= sizeof(struct nf_nat_range2),
+		.table		= "nat",
+		.hooks		= (1 << NF_INET_PRE_ROUTING) |
+				  (1 << NF_INET_LOCAL_OUT),
+		.me		= THIS_MODULE,
+	},
 };
 
 static int __init xt_nat_init(void)