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 <ebiederm@aristanetworks.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>

3 files changed, 30 insertions, 14 deletions

diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c
index a91504850195..3c9cf6a8e7fb 100644
--- a/net/8021q/vlan_netlink.c
+++ b/net/8021q/vlan_netlink.c
@@ -119,7 +119,7 @@ static int vlan_get_tx_queues(struct net *net,
 	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);
@@ -131,7 +131,7 @@ static int vlan_newlink(struct net_device *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;
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e2f3317f290f..33148a568199 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -733,6 +733,20 @@ static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
 	[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) {
@@ -756,8 +770,7 @@ static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
 	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;
@@ -976,8 +989,8 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	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;
@@ -985,7 +998,7 @@ struct net_device *rtnl_create_link(struct net *net, char *ifname,
 	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;
@@ -995,16 +1008,16 @@ struct net_device *rtnl_create_link(struct net *net, char *ifname,
 	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 (tb[IFLA_ADDRESS])
@@ -1083,6 +1096,7 @@ replay:
 
 	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]) {
@@ -1147,17 +1161,19 @@ replay:
 		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;
 	}
 }
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 71a3242fb7d0..a7de9e3a8f18 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1483,7 +1483,7 @@ static void ipgre_tap_setup(struct net_device *dev)
 	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;