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, 2 insertions, 2 deletions

diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index c5904f629091..02fc343feb66 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -72,7 +72,7 @@ struct ovs_conntrack_info {
 	struct md_mark mark;
 	struct md_labels labels;
 #ifdef CONFIG_NF_NAT_NEEDED
-	struct nf_nat_range range;  /* Only present for SRC NAT and DST NAT. */
+	struct nf_nat_range2 range;  /* Only present for SRC NAT and DST NAT. */
 #endif
 };
 
@@ -710,7 +710,7 @@ static bool skb_nfct_cached(struct net *net,
  */
 static int ovs_ct_nat_execute(struct sk_buff *skb, struct nf_conn *ct,
 			      enum ip_conntrack_info ctinfo,
-			      const struct nf_nat_range *range,
+			      const struct nf_nat_range2 *range,
 			      enum nf_nat_manip_type maniptype)
 {
 	int hooknum, nh_off, err = NF_ACCEPT;