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>

6 files changed, 8 insertions, 8 deletions

diff --git a/net/ipv6/netfilter/ip6t_MASQUERADE.c b/net/ipv6/netfilter/ip6t_MASQUERADE.c
index 92c0047e7e33..491f808e356a 100644
--- a/net/ipv6/netfilter/ip6t_MASQUERADE.c
+++ b/net/ipv6/netfilter/ip6t_MASQUERADE.c
@@ -29,7 +29,7 @@ masquerade_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 
 static int masquerade_tg6_checkentry(const struct xt_tgchk_param *par)
 {
-	const struct nf_nat_range *range = par->targinfo;
+	const struct nf_nat_range2 *range = par->targinfo;
 
 	if (range->flags & NF_NAT_RANGE_MAP_IPS)
 		return -EINVAL;
diff --git a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
index 6b7f075f811f..56d75eb5448f 100644
--- a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
@@ -62,7 +62,7 @@ static void nf_nat_ipv6_decode_session(struct sk_buff *skb,
 #endif
 
 static bool nf_nat_ipv6_in_range(const struct nf_conntrack_tuple *t,
-				 const struct nf_nat_range *range)
+				 const struct nf_nat_range2 *range)
 {
 	return ipv6_addr_cmp(&t->src.u3.in6, &range->min_addr.in6) >= 0 &&
 	       ipv6_addr_cmp(&t->src.u3.in6, &range->max_addr.in6) <= 0;
@@ -151,7 +151,7 @@ static void nf_nat_ipv6_csum_recalc(struct sk_buff *skb,
 
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
 static int nf_nat_ipv6_nlattr_to_range(struct nlattr *tb[],
-				       struct nf_nat_range *range)
+				       struct nf_nat_range2 *range)
 {
 	if (tb[CTA_NAT_V6_MINIP]) {
 		nla_memcpy(&range->min_addr.ip6, tb[CTA_NAT_V6_MINIP],
diff --git a/net/ipv6/netfilter/nf_nat_masquerade_ipv6.c b/net/ipv6/netfilter/nf_nat_masquerade_ipv6.c
index 98f61fcb9108..9dfc2b90c362 100644
--- a/net/ipv6/netfilter/nf_nat_masquerade_ipv6.c
+++ b/net/ipv6/netfilter/nf_nat_masquerade_ipv6.c
@@ -26,14 +26,14 @@
 static atomic_t v6_worker_count;
 
 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)
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn_nat *nat;
 	struct in6_addr src;
 	struct nf_conn *ct;
-	struct nf_nat_range newrange;
+	struct nf_nat_range2 newrange;
 
 	ct = nf_ct_get(skb, &ctinfo);
 	WARN_ON(!(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
diff --git a/net/ipv6/netfilter/nf_nat_proto_icmpv6.c b/net/ipv6/netfilter/nf_nat_proto_icmpv6.c
index 57593b00c5b4..d9bf42ba44fa 100644
--- a/net/ipv6/netfilter/nf_nat_proto_icmpv6.c
+++ b/net/ipv6/netfilter/nf_nat_proto_icmpv6.c
@@ -32,7 +32,7 @@ icmpv6_in_range(const struct nf_conntrack_tuple *tuple,
 static void
 icmpv6_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/ipv6/netfilter/nft_masq_ipv6.c b/net/ipv6/netfilter/nft_masq_ipv6.c
index 4146536e9c15..dd0122f3cffe 100644
--- a/net/ipv6/netfilter/nft_masq_ipv6.c
+++ b/net/ipv6/netfilter/nft_masq_ipv6.c
@@ -22,7 +22,7 @@ static void nft_masq_ipv6_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;
diff --git a/net/ipv6/netfilter/nft_redir_ipv6.c b/net/ipv6/netfilter/nft_redir_ipv6.c
index a27e424f690d..74269865acc8 100644
--- a/net/ipv6/netfilter/nft_redir_ipv6.c
+++ b/net/ipv6/netfilter/nft_redir_ipv6.c
@@ -22,7 +22,7 @@ static void nft_redir_ipv6_eval(const struct nft_expr *expr,
 				const struct nft_pktinfo *pkt)
 {
 	struct nft_redir *priv = nft_expr_priv(expr);
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 
 	memset(&range, 0, sizeof(range));
 	if (priv->sreg_proto_min) {