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, 14 insertions, 13 deletions

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 617693ff9f4c..37b3c9913b08 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -157,7 +157,7 @@ EXPORT_SYMBOL(nf_nat_used_tuple);
 static int in_range(const struct nf_nat_l3proto *l3proto,
 		    const struct nf_nat_l4proto *l4proto,
 		    const struct nf_conntrack_tuple *tuple,
-		    const struct nf_nat_range *range)
+		    const struct nf_nat_range2 *range)
 {
 	/* If we are supposed to map IPs, then we must be in the
 	 * range specified, otherwise let this drag us onto a new src IP.
@@ -194,7 +194,7 @@ find_appropriate_src(struct net *net,
 		     const struct nf_nat_l4proto *l4proto,
 		     const struct nf_conntrack_tuple *tuple,
 		     struct nf_conntrack_tuple *result,
-		     const struct nf_nat_range *range)
+		     const struct nf_nat_range2 *range)
 {
 	unsigned int h = hash_by_src(net, tuple);
 	const struct nf_conn *ct;
@@ -224,7 +224,7 @@ find_appropriate_src(struct net *net,
 static void
 find_best_ips_proto(const struct nf_conntrack_zone *zone,
 		    struct nf_conntrack_tuple *tuple,
-		    const struct nf_nat_range *range,
+		    const struct nf_nat_range2 *range,
 		    const struct nf_conn *ct,
 		    enum nf_nat_manip_type maniptype)
 {
@@ -298,7 +298,7 @@ find_best_ips_proto(const struct nf_conntrack_zone *zone,
 static void
 get_unique_tuple(struct nf_conntrack_tuple *tuple,
 		 const struct nf_conntrack_tuple *orig_tuple,
-		 const struct nf_nat_range *range,
+		 const struct nf_nat_range2 *range,
 		 struct nf_conn *ct,
 		 enum nf_nat_manip_type maniptype)
 {
@@ -349,9 +349,10 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
 	/* Only bother mapping if it's not already in range and unique */
 	if (!(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL)) {
 		if (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {
-			if (l4proto->in_range(tuple, maniptype,
-					      &range->min_proto,
-					      &range->max_proto) &&
+			if (!(range->flags & NF_NAT_RANGE_PROTO_OFFSET) &&
+			    l4proto->in_range(tuple, maniptype,
+			          &range->min_proto,
+			          &range->max_proto) &&
 			    (range->min_proto.all == range->max_proto.all ||
 			     !nf_nat_used_tuple(tuple, ct)))
 				goto out;
@@ -360,7 +361,7 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
 		}
 	}
 
-	/* Last change: get protocol to try to obtain unique tuple. */
+	/* Last chance: get protocol to try to obtain unique tuple. */
 	l4proto->unique_tuple(l3proto, tuple, range, maniptype, ct);
 out:
 	rcu_read_unlock();
@@ -381,7 +382,7 @@ EXPORT_SYMBOL_GPL(nf_ct_nat_ext_add);
 
 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)
 {
 	struct net *net = nf_ct_net(ct);
@@ -459,7 +460,7 @@ __nf_nat_alloc_null_binding(struct nf_conn *ct, enum nf_nat_manip_type manip)
 		(manip == NF_NAT_MANIP_SRC ?
 		ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3 :
 		ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3);
-	struct nf_nat_range range = {
+	struct nf_nat_range2 range = {
 		.flags		= NF_NAT_RANGE_MAP_IPS,
 		.min_addr	= ip,
 		.max_addr	= ip,
@@ -702,7 +703,7 @@ static const struct nla_policy protonat_nla_policy[CTA_PROTONAT_MAX+1] = {
 
 static int nfnetlink_parse_nat_proto(struct nlattr *attr,
 				     const struct nf_conn *ct,
-				     struct nf_nat_range *range)
+				     struct nf_nat_range2 *range)
 {
 	struct nlattr *tb[CTA_PROTONAT_MAX+1];
 	const struct nf_nat_l4proto *l4proto;
@@ -730,7 +731,7 @@ static const struct nla_policy nat_nla_policy[CTA_NAT_MAX+1] = {
 
 static int
 nfnetlink_parse_nat(const struct nlattr *nat,
-		    const struct nf_conn *ct, struct nf_nat_range *range,
+		    const struct nf_conn *ct, struct nf_nat_range2 *range,
 		    const struct nf_nat_l3proto *l3proto)
 {
 	struct nlattr *tb[CTA_NAT_MAX+1];
@@ -758,7 +759,7 @@ nfnetlink_parse_nat_setup(struct nf_conn *ct,
 			  enum nf_nat_manip_type manip,
 			  const struct nlattr *attr)
 {
-	struct nf_nat_range range;
+	struct nf_nat_range2 range;
 	const struct nf_nat_l3proto *l3proto;
 	int err;