nf_nat: use secure_ipv4_port_ephemeral() for NAT port randomization

Use incoming network tuple as seed for NAT port randomization.
This avoids concerns of leaking net_random() bits, and also gives better
port distribution. Don't have NAT server, compile tested only.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

[ added missing EXPORT_SYMBOL_GPL ]
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/char/random.c

@@ -1571,6 +1571,7 @@ u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
 
 	return half_md4_transform(hash, keyptr->secret);
 }
+EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
 
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

net/ipv4/netfilter/nf_nat_proto_common.c

@@ -73,9 +73,13 @@ bool nf_nat_proto_unique_tuple(struct nf_conntrack_tuple *tuple,
 		range_size = ntohs(range->max.all) - min + 1;
 	}
 
-	off = *rover;
 	if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
-		off = net_random();
+		off = secure_ipv4_port_ephemeral(tuple->src.u3.ip, tuple->dst.u3.ip,
+						 maniptype == IP_NAT_MANIP_SRC
+						 ? tuple->dst.u.all
+						 : tuple->src.u.all);
+	else
+		off = *rover;
 
 	for (i = 0; i < range_size; i++, off++) {
 		*portptr = htons(min + off % range_size);