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>

1 files changed, 27 insertions, 11 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e2f3317..33148a5 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;
 	}
 }