ipv6: Nonlocal bind

Add support to allow non-local binds similar to how this was done for IPv4.
Non-local binds are very useful in emulating the Internet in a box, etc.

This add the ip_nonlocal_bind sysctl under ipv6.

Testing:

Set up nonlocal binding and receive routing on a host, e.g.:

ip -6 rule add from ::/0 iif eth0 lookup 200
ip -6 route add local 2001:0:0:1::/64 dev lo proto kernel scope host table 200
sysctl -w net.ipv6.ip_nonlocal_bind=1

Set up routing to 2001:0:0:1::/64 on peer to go to first host

ping6 -I 2001:0:0:1::1 peer-address -- to verify
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1435,6 +1435,11 @@ mtu - INTEGER
 	Default Maximum Transfer Unit
 	Default: 1280 (IPv6 required minimum)
 
+ip_nonlocal_bind - BOOLEAN
+	If set, allows processes to bind() to non-local IPv6 addresses,
+	which can be quite useful - but may break some applications.
+	Default: 0
+
 router_probe_interval - INTEGER
 	Minimum interval (in seconds) between Router Probing described
 	in RFC4191.

include/net/netns/ipv6.h

@@ -31,6 +31,7 @@ struct netns_sysctl_ipv6 {
 	int auto_flowlabels;
 	int icmpv6_time;
 	int anycast_src_echo_reply;
+	int ip_nonlocal_bind;
 	int fwmark_reflect;
 	int idgen_retries;
 	int idgen_delay;

net/ipv4/ping.c

@@ -363,7 +363,8 @@ static int ping_check_bind_addr(struct sock *sk, struct inet_sock *isk,
 						    scoped);
 		rcu_read_unlock();
 
-		if (!(isk->freebind || isk->transparent || has_addr ||
+		if (!(net->ipv6.sysctl.ip_nonlocal_bind ||
+		      isk->freebind || isk->transparent || has_addr ||
 		      addr_type == IPV6_ADDR_ANY))
 			return -EADDRNOTAVAIL;
 

net/ipv6/af_inet6.c

@@ -342,7 +342,8 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 			 */
 			v4addr = LOOPBACK4_IPV6;
 			if (!(addr_type & IPV6_ADDR_MULTICAST))	{
-				if (!(inet->freebind || inet->transparent) &&
+				if (!net->ipv6.sysctl.ip_nonlocal_bind &&
+				    !(inet->freebind || inet->transparent) &&
 				    !ipv6_chk_addr(net, &addr->sin6_addr,
 						   dev, 0)) {
 					err = -EADDRNOTAVAIL;

net/ipv6/raw.c

@@ -295,7 +295,8 @@ static int rawv6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 		 * unspecified and mapped address have a v4 equivalent.
 		 */
 		v4addr = LOOPBACK4_IPV6;
-		if (!(addr_type & IPV6_ADDR_MULTICAST))	{
+		if (!(addr_type & IPV6_ADDR_MULTICAST) &&
+		    !sock_net(sk)->ipv6.sysctl.ip_nonlocal_bind) {
 			err = -EADDRNOTAVAIL;
 			if (!ipv6_chk_addr(sock_net(sk), &addr->sin6_addr,
 					   dev, 0)) {

net/ipv6/sysctl_net_ipv6.c

@@ -75,6 +75,13 @@ static struct ctl_table ipv6_table_template[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "ip_nonlocal_bind",
+		.data		= &init_net.ipv6.sysctl.ip_nonlocal_bind,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec
+	},
 	{ }
 };
 
@@ -117,6 +124,7 @@ static int __net_init ipv6_sysctl_net_init(struct net *net)
 	ipv6_table[5].data = &net->ipv6.sysctl.idgen_retries;
 	ipv6_table[6].data = &net->ipv6.sysctl.idgen_delay;
 	ipv6_table[7].data = &net->ipv6.sysctl.flowlabel_state_ranges;
+	ipv6_table[8].data = &net->ipv6.sysctl.ip_nonlocal_bind;
 
 	ipv6_route_table = ipv6_route_sysctl_init(net);
 	if (!ipv6_route_table)