[NETFILTER]: NAT: optional source port randomization support

This patch adds support to NAT to randomize source ports.
Signed-off-by: Eric Leblond <eric@inl.fr>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv4/ip_nat.h

@@ -16,6 +16,7 @@ enum ip_nat_manip_type
 
 #define IP_NAT_RANGE_MAP_IPS 1
 #define IP_NAT_RANGE_PROTO_SPECIFIED 2
+#define IP_NAT_RANGE_PROTO_RANDOM 4 /* add randomness to "port" selection */
 
 /* NAT sequence number modifications */
 struct ip_nat_seq {

include/net/netfilter/nf_nat.h

@@ -16,6 +16,7 @@ enum nf_nat_manip_type
 
 #define IP_NAT_RANGE_MAP_IPS 1
 #define IP_NAT_RANGE_PROTO_SPECIFIED 2
+#define IP_NAT_RANGE_PROTO_RANDOM 4
 
 /* NAT sequence number modifications */
 struct nf_nat_seq {

net/ipv4/netfilter/ip_nat_core.c

@@ -246,8 +246,9 @@ get_unique_tuple(struct ip_conntrack_tuple *tuple,
 	if (maniptype == IP_NAT_MANIP_SRC) {
 		if (find_appropriate_src(orig_tuple, tuple, range)) {
 			DEBUGP("get_unique_tuple: Found current src map\n");
-			if (!ip_nat_used_tuple(tuple, conntrack))
-				return;
+			if (!(range->flags & IP_NAT_RANGE_PROTO_RANDOM))
+				if (!ip_nat_used_tuple(tuple, conntrack))
+					return;
 		}
 	}
 
@@ -261,6 +262,13 @@ get_unique_tuple(struct ip_conntrack_tuple *tuple,
 
 	proto = ip_nat_proto_find_get(orig_tuple->dst.protonum);
 
+	/* Change protocol info to have some randomization */
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) {
+		proto->unique_tuple(tuple, range, maniptype, conntrack);
+		ip_nat_proto_put(proto);
+		return;
+	}
+
 	/* Only bother mapping if it's not already in range and unique */
 	if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)
 	     || proto->in_range(tuple, maniptype, &range->min, &range->max))

net/ipv4/netfilter/ip_nat_proto_tcp.c

@@ -8,6 +8,7 @@
 
 #include <linux/types.h>
 #include <linux/init.h>
+#include <linux/random.h>
 #include <linux/netfilter.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
@@ -75,6 +76,10 @@ tcp_unique_tuple(struct ip_conntrack_tuple *tuple,
 		range_size = ntohs(range->max.tcp.port) - min + 1;
 	}
 
+	/* Start from random port to avoid prediction */
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
+		port =  net_random();
+
 	for (i = 0; i < range_size; i++, port++) {
 		*portptr = htons(min + port % range_size);
 		if (!ip_nat_used_tuple(tuple, conntrack)) {

net/ipv4/netfilter/ip_nat_proto_udp.c

@@ -8,6 +8,7 @@
 
 #include <linux/types.h>
 #include <linux/init.h>
+#include <linux/random.h>
 #include <linux/netfilter.h>
 #include <linux/ip.h>
 #include <linux/udp.h>
@@ -74,6 +75,10 @@ udp_unique_tuple(struct ip_conntrack_tuple *tuple,
 		range_size = ntohs(range->max.udp.port) - min + 1;
 	}
 
+	/* Start from random port to avoid prediction */
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
+		port = net_random();
+
 	for (i = 0; i < range_size; i++, port++) {
 		*portptr = htons(min + port % range_size);
 		if (!ip_nat_used_tuple(tuple, conntrack))

net/ipv4/netfilter/ip_nat_rule.c

@@ -193,6 +193,10 @@ static int ipt_dnat_checkentry(const char *tablename,
 		printk("DNAT: multiple ranges no longer supported\n");
 		return 0;
 	}
+	if (mr->range[0].flags & IP_NAT_RANGE_PROTO_RANDOM) {
+		printk("DNAT: port randomization not supported\n");
+		return 0;
+	}
 	return 1;
 }
 

net/ipv4/netfilter/nf_nat_core.c

@@ -254,8 +254,9 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
 	if (maniptype == IP_NAT_MANIP_SRC) {
 		if (find_appropriate_src(orig_tuple, tuple, range)) {
 			DEBUGP("get_unique_tuple: Found current src map\n");
-			if (!nf_nat_used_tuple(tuple, ct))
-				return;
+			if (!(range->flags & IP_NAT_RANGE_PROTO_RANDOM))
+				if (!nf_nat_used_tuple(tuple, ct))
+					return;
 		}
 	}
 
@@ -269,6 +270,13 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
 
 	proto = nf_nat_proto_find_get(orig_tuple->dst.protonum);
 
+	/* Change protocol info to have some randomization */
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) {
+		proto->unique_tuple(tuple, range, maniptype, ct);
+		nf_nat_proto_put(proto);
+		return;
+	}
+
 	/* Only bother mapping if it's not already in range and unique */
 	if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
 	     proto->in_range(tuple, maniptype, &range->min, &range->max)) &&

net/ipv4/netfilter/nf_nat_proto_tcp.c

@@ -8,6 +8,7 @@
 
 #include <linux/types.h>
 #include <linux/init.h>
+#include <linux/random.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
 
@@ -75,6 +76,9 @@ tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
 		range_size = ntohs(range->max.tcp.port) - min + 1;
 	}
 
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
+		port =  net_random();
+
 	for (i = 0; i < range_size; i++, port++) {
 		*portptr = htons(min + port % range_size);
 		if (!nf_nat_used_tuple(tuple, ct))

net/ipv4/netfilter/nf_nat_proto_udp.c

@@ -8,6 +8,7 @@
 
 #include <linux/types.h>
 #include <linux/init.h>
+#include <linux/random.h>
 #include <linux/ip.h>
 #include <linux/udp.h>
 
@@ -73,6 +74,9 @@ udp_unique_tuple(struct nf_conntrack_tuple *tuple,
 		range_size = ntohs(range->max.udp.port) - min + 1;
 	}
 
+	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
+		port = net_random();
+
 	for (i = 0; i < range_size; i++, port++) {
 		*portptr = htons(min + port % range_size);
 		if (!nf_nat_used_tuple(tuple, ct))

net/ipv4/netfilter/nf_nat_rule.c

@@ -226,6 +226,10 @@ static int ipt_dnat_checkentry(const char *tablename,
 		printk("DNAT: multiple ranges no longer supported\n");
 		return 0;
 	}
+	if (mr->range[0].flags & IP_NAT_RANGE_PROTO_RANDOM) {
+		printk("DNAT: port randomization not supported\n");
+		return 0;
+	}
 	return 1;
 }