ipv4: Use math to point per net sysctls into the appropriate struct net.

Simplify maintenance of ipv4_net_table by using math to point the per
net sysctls into the appropriate struct net, instead of manually
reassinging all of the variables into hard coded table slots.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/sysctl_net_ipv4.c

@@ -838,28 +838,15 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 
 	table = ipv4_net_table;
 	if (!net_eq(net, &init_net)) {
+		int i;
+
 		table = kmemdup(table, sizeof(ipv4_net_table), GFP_KERNEL);
 		if (table == NULL)
 			goto err_alloc;
 
-		table[0].data =
-			&net->ipv4.sysctl_icmp_echo_ignore_all;
-		table[1].data =
-			&net->ipv4.sysctl_icmp_echo_ignore_broadcasts;
-		table[2].data =
-			&net->ipv4.sysctl_icmp_ignore_bogus_error_responses;
-		table[3].data =
-			&net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr;
-		table[4].data =
-			&net->ipv4.sysctl_icmp_ratelimit;
-		table[5].data =
-			&net->ipv4.sysctl_icmp_ratemask;
-		table[6].data =
-			&net->ipv4.sysctl_ping_group_range;
-		table[7].data =
-			&net->ipv4.sysctl_tcp_ecn;
-		table[8].data =
-			&net->ipv4.sysctl_local_ports.range;
+		/* Update the variables to point into the current struct net */
+		for (i = 0; i < ARRAY_SIZE(ipv4_net_table) - 1; i++)
+			table[i].data += (void *)net - (void *)&init_net;
 
 		/* Don't export sysctls to unprivileged users */
 		if (net->user_ns != &init_user_ns)