net: Support specifying the network namespace upon device creation.

There is no good reason to not support userspace specifying the
network namespace during device creation, and it makes it easier
to create a network device and pass it to a child network namespace
with a well known name.

We have to be careful to ensure that the target network namespace
for the new device exists through the life of the call. To keep
that logic clear I have factored out the network namespace grabbing
logic into rtnl_link_get_net.

In addtion we need to continue to pass the source network namespace
to the rtnl_link_ops.newlink method so that we can find the base
device source network namespace.

Signed-off-by: Eric W. Biederman <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>

drivers/net/can/dev.c

···
 	return -EMSGSIZE;
 }
 
-static int can_newlink(struct net_device *dev,
+static int can_newlink(struct net *src_net, struct net_device *dev,
 		       struct nlattr *tb[], struct nlattr *data[])
 {
 	return -EOPNOTSUPP;

drivers/net/macvlan.c

···
 	return 0;
 }
 
-static int macvlan_newlink(struct net_device *dev,
+static int macvlan_newlink(struct net *src_net, struct net_device *dev,
 			   struct nlattr *tb[], struct nlattr *data[])
 {
 	struct macvlan_dev *vlan = netdev_priv(dev);
···
 	if (!tb[IFLA_LINK])
 		return -EINVAL;
 
-	lowerdev = __dev_get_by_index(dev_net(dev), nla_get_u32(tb[IFLA_LINK]));
+	lowerdev = __dev_get_by_index(src_net, nla_get_u32(tb[IFLA_LINK]));
 	if (lowerdev == NULL)
 		return -ENODEV;
 

drivers/net/veth.c

···
 
 static struct rtnl_link_ops veth_link_ops;
 
-static int veth_newlink(struct net_device *dev,
+static int veth_newlink(struct net *src_net, struct net_device *dev,
 			 struct nlattr *tb[], struct nlattr *data[])
 {
 	int err;
···
 	struct veth_priv *priv;
 	char ifname[IFNAMSIZ];
 	struct nlattr *peer_tb[IFLA_MAX + 1], **tbp;
+	struct net *net;
 
 	/*
 	 * create and register peer first
···
 	else
 		snprintf(ifname, IFNAMSIZ, DRV_NAME "%%d");
 
-	peer = rtnl_create_link(dev_net(dev), ifname, &veth_link_ops, tbp);
-	if (IS_ERR(peer))
+	net = rtnl_link_get_net(src_net, tbp);
+	if (IS_ERR(net))
+		return PTR_ERR(net);
+
+	peer = rtnl_create_link(src_net, net, ifname, &veth_link_ops, tbp);
+	if (IS_ERR(peer)) {
+		put_net(net);
 		return PTR_ERR(peer);
+	}
 
 	if (tbp[IFLA_ADDRESS] == NULL)
 		random_ether_addr(peer->dev_addr);
 
 	err = register_netdevice(peer);
+	put_net(net);
+	net = NULL;
 	if (err < 0)
 		goto err_register_peer;
 

include/net/rtnetlink.h

···
 	int			(*validate)(struct nlattr *tb[],
 					    struct nlattr *data[]);
 
-	int			(*newlink)(struct net_device *dev,
+	int			(*newlink)(struct net *src_net,
+					   struct net_device *dev,
 					   struct nlattr *tb[],
 					   struct nlattr *data[]);
 	int			(*changelink)(struct net_device *dev,
···
 extern int	rtnl_link_register(struct rtnl_link_ops *ops);
 extern void	rtnl_link_unregister(struct rtnl_link_ops *ops);
 
-extern struct net_device *rtnl_create_link(struct net *net, char *ifname,
-		const struct rtnl_link_ops *ops, struct nlattr *tb[]);
+extern struct net *rtnl_link_get_net(struct net *src_net, struct nlattr *tb[]);
+extern struct net_device *rtnl_create_link(struct net *src_net, struct net *net,
+	char *ifname, const struct rtnl_link_ops *ops, struct nlattr *tb[]);
 extern const struct nla_policy ifla_policy[IFLA_MAX+1];
 
 #define MODULE_ALIAS_RTNL_LINK(kind) MODULE_ALIAS("rtnl-link-" kind)

net/8021q/vlan_netlink.c

···
 	return 0;
 }
 
-static int vlan_newlink(struct net_device *dev,
+static int vlan_newlink(struct net *src_net, struct net_device *dev,
 			struct nlattr *tb[], struct nlattr *data[])
 {
 	struct vlan_dev_info *vlan = vlan_dev_info(dev);
···
 
 	if (!tb[IFLA_LINK])
 		return -EINVAL;
-	real_dev = __dev_get_by_index(dev_net(dev), nla_get_u32(tb[IFLA_LINK]));
+	real_dev = __dev_get_by_index(src_net, nla_get_u32(tb[IFLA_LINK]));
 	if (!real_dev)
 		return -ENODEV;
 

net/core/rtnetlink.c

···
 	[IFLA_INFO_DATA]	= { .type = NLA_NESTED },
 };
 
+struct net *rtnl_link_get_net(struct net *src_net, struct nlattr *tb[])
+{
+	struct net *net;
+	/* Examine the link attributes and figure out which
+	 * network namespace we are talking about.
+	 */
+	if (tb[IFLA_NET_NS_PID])
+		net = get_net_ns_by_pid(nla_get_u32(tb[IFLA_NET_NS_PID]));
+	else
+		net = get_net(src_net);
+	return net;
+}
+EXPORT_SYMBOL(rtnl_link_get_net);
+
 static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[])
 {
 	if (dev) {
···
 	int err;
 
 	if (tb[IFLA_NET_NS_PID]) {
-		struct net *net;
-		net = get_net_ns_by_pid(nla_get_u32(tb[IFLA_NET_NS_PID]));
+		struct net *net = rtnl_link_get_net(dev_net(dev), tb);
 		if (IS_ERR(net)) {
 			err = PTR_ERR(net);
 			goto errout;
···
 	return 0;
 }
 
-struct net_device *rtnl_create_link(struct net *net, char *ifname,
-		const struct rtnl_link_ops *ops, struct nlattr *tb[])
+struct net_device *rtnl_create_link(struct net *src_net, struct net *net,
+	char *ifname, const struct rtnl_link_ops *ops, struct nlattr *tb[])
 {
 	int err;
 	struct net_device *dev;
···
 	unsigned int real_num_queues = 1;
 
 	if (ops->get_tx_queues) {
-		err = ops->get_tx_queues(net, tb, &num_queues,
+		err = ops->get_tx_queues(src_net, tb, &num_queues,
 					 &real_num_queues);
 		if (err)
 			goto err;
···
 	if (!dev)
 		goto err;
 
+	dev_net_set(dev, net);
+	dev->rtnl_link_ops = ops;
 	dev->real_num_tx_queues = real_num_queues;
+
 	if (strchr(dev->name, '%')) {
 		err = dev_alloc_name(dev, dev->name);
 		if (err < 0)
 			goto err_free;
 	}
-
-	dev_net_set(dev, net);
-	dev->rtnl_link_ops = ops;
 
 	if (tb[IFLA_MTU])
 		dev->mtu = nla_get_u32(tb[IFLA_MTU]);
···
 
 	if (1) {
 		struct nlattr *attr[ops ? ops->maxtype + 1 : 0], **data = NULL;
+		struct net *dest_net;
 
 		if (ops) {
 			if (ops->maxtype && linkinfo[IFLA_INFO_DATA]) {
···
 		if (!ifname[0])
 			snprintf(ifname, IFNAMSIZ, "%s%%d", ops->kind);
 
-		dev = rtnl_create_link(net, ifname, ops, tb);
+		dest_net = rtnl_link_get_net(net, tb);
+		dev = rtnl_create_link(net, dest_net, ifname, ops, tb);
 
 		if (IS_ERR(dev))
 			err = PTR_ERR(dev);
 		else if (ops->newlink)
-			err = ops->newlink(dev, tb, data);
+			err = ops->newlink(net, dev, tb, data);
 		else
 			err = register_netdevice(dev);
-
 		if (err < 0 && !IS_ERR(dev))
 			free_netdev(dev);
+
+		put_net(dest_net);
 		return err;
 	}
 }

net/ipv4/ip_gre.c

···
 	dev->features		|= NETIF_F_NETNS_LOCAL;
 }
 
-static int ipgre_newlink(struct net_device *dev, struct nlattr *tb[],
+static int ipgre_newlink(struct net *src_net, struct net_device *dev, struct nlattr *tb[],
 			 struct nlattr *data[])
 {
 	struct ip_tunnel *nt;