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>

8 files changed, 11 insertions, 11 deletions

diff --git a/net/ipv4/netfilter/ipt_MASQUERADE.c b/net/ipv4/netfilter/ipt_MASQUERADE.c
index a03e4e7ef5f9..ce1512b02cb2 100644
--- a/net/ipv4/netfilter/ipt_MASQUERADE.c
+++ b/net/ipv4/netfilter/ipt_MASQUERADE.c
@@ -47,7 +47,7 @@ static int masquerade_tg_check(const struct xt_tgchk_param *par)
 static unsigned int
 masquerade_tg(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 	const struct nf_nat_ipv4_multi_range_compat *mr;
 
 	mr = par->targinfo;
diff --git a/net/ipv4/netfilter/nf_nat_h323.c b/net/ipv4/netfilter/nf_nat_h323.c
index ac8342dcb55e..4e6b53ab6c33 100644
--- a/net/ipv4/netfilter/nf_nat_h323.c
+++ b/net/ipv4/netfilter/nf_nat_h323.c
@@ -395,7 +395,7 @@ static int nat_h245(struct sk_buff *skb, struct nf_conn *ct,
 static void ip_nat_q931_expect(struct nf_conn *new,
 			       struct nf_conntrack_expect *this)
 {
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 
 	if (this->tuple.src.u3.ip != 0) {	/* Only accept calls from GK */
 		nf_nat_follow_master(new, this);
@@ -497,7 +497,7 @@ static int nat_q931(struct sk_buff *skb, struct nf_conn *ct,
 static void ip_nat_callforwarding_expect(struct nf_conn *new,
 					 struct nf_conntrack_expect *this)
 {
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 
 	/* This must be a fresh one. */
 	BUG_ON(new->status & IPS_NAT_DONE_MASK);
diff --git a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
index f7ff6a364d7b..4346336cee4c 100644
--- a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
+++ b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
@@ -63,7 +63,7 @@ static void nf_nat_ipv4_decode_session(struct sk_buff *skb,
 #endif /* CONFIG_XFRM */
 
 static bool nf_nat_ipv4_in_range(const struct nf_conntrack_tuple *t,
-				 const struct nf_nat_range *range)
+				 const struct nf_nat_range2 *range)
 {
 	return ntohl(t->src.u3.ip) >= ntohl(range->min_addr.ip) &&
 	       ntohl(t->src.u3.ip) <= ntohl(range->max_addr.ip);
@@ -143,7 +143,7 @@ static void nf_nat_ipv4_csum_recalc(struct sk_buff *skb,
 
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
 static int nf_nat_ipv4_nlattr_to_range(struct nlattr *tb[],
-				       struct nf_nat_range *range)
+				       struct nf_nat_range2 *range)
 {
 	if (tb[CTA_NAT_V4_MINIP]) {
 		range->min_addr.ip = nla_get_be32(tb[CTA_NAT_V4_MINIP]);
diff --git a/net/ipv4/netfilter/nf_nat_masquerade_ipv4.c b/net/ipv4/netfilter/nf_nat_masquerade_ipv4.c
index 0c366aad89cb..f538c5001547 100644
--- a/net/ipv4/netfilter/nf_nat_masquerade_ipv4.c
+++ b/net/ipv4/netfilter/nf_nat_masquerade_ipv4.c
@@ -24,13 +24,13 @@
 
 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)
 {
 	struct nf_conn *ct;
 	struct nf_conn_nat *nat;
 	enum ip_conntrack_info ctinfo;
-	struct nf_nat_range newrange;
+	struct nf_nat_range2 newrange;
 	const struct rtable *rt;
 	__be32 newsrc, nh;
 
diff --git a/net/ipv4/netfilter/nf_nat_pptp.c b/net/ipv4/netfilter/nf_nat_pptp.c
index 8a69363b4884..5d259a12e25f 100644
--- a/net/ipv4/netfilter/nf_nat_pptp.c
+++ b/net/ipv4/netfilter/nf_nat_pptp.c
@@ -48,7 +48,7 @@ static void pptp_nat_expected(struct nf_conn *ct,
 	struct nf_conntrack_tuple t = {};
 	const struct nf_ct_pptp_master *ct_pptp_info;
 	const struct nf_nat_pptp *nat_pptp_info;
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 	struct nf_conn_nat *nat;
 
 	nat = nf_ct_nat_ext_add(ct);
diff --git a/net/ipv4/netfilter/nf_nat_proto_gre.c b/net/ipv4/netfilter/nf_nat_proto_gre.c
index edf05002d674..00fda6331ce5 100644
--- a/net/ipv4/netfilter/nf_nat_proto_gre.c
+++ b/net/ipv4/netfilter/nf_nat_proto_gre.c
@@ -41,7 +41,7 @@ MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
 static void
 gre_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)
 {
diff --git a/net/ipv4/netfilter/nf_nat_proto_icmp.c b/net/ipv4/netfilter/nf_nat_proto_icmp.c
index 7b98baa13ede..6d7cf1d79baf 100644
--- a/net/ipv4/netfilter/nf_nat_proto_icmp.c
+++ b/net/ipv4/netfilter/nf_nat_proto_icmp.c
@@ -30,7 +30,7 @@ icmp_in_range(const struct nf_conntrack_tuple *tuple,
 static void
 icmp_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)
 {
diff --git a/net/ipv4/netfilter/nft_masq_ipv4.c b/net/ipv4/netfilter/nft_masq_ipv4.c
index f18677277119..f1193e1e928a 100644
--- a/net/ipv4/netfilter/nft_masq_ipv4.c
+++ b/net/ipv4/netfilter/nft_masq_ipv4.c
@@ -21,7 +21,7 @@ static void nft_masq_ipv4_eval(const struct nft_expr *expr,
 			       const struct nft_pktinfo *pkt)
 {
 	struct nft_masq *priv = nft_expr_priv(expr);
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 
 	memset(&range, 0, sizeof(range));
 	range.flags = priv->flags;