[PATCH net-next 2/2] netns/rtnl: return the new nsid to the user

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

When the user asks for a new nsid, he can let the kernel choose it (by
providing -1 in NETNSA_NSID). In this case, it's useful to answer to the
netlink message with the chosen nsid.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 net/core/net_namespace.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 8f5fa5d5becd..266d095296f3 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -810,8 +810,32 @@ static int rtnl_net_newid(struct sk_buff *skb, struct nlmsghdr *nlh,
 	err = alloc_netid(net, peer, nsid);
 	spin_unlock_bh(&net->nsid_lock);
 	if (err >= 0) {
+		struct net_fill_args fillargs = {
+			.portid = NETLINK_CB(skb).portid,
+			.seq = nlh->nlmsg_seq,
+			.cmd = RTM_NEWNSID,
+			.nsid = err,
+		};
+		struct sk_buff *msg;
+
+		/* The id has been allocated, thus first notify listeners */
 		rtnl_net_notifyid(net, RTM_NEWNSID, err);
-		err = 0;
+
+		/* Then, try to send the new nsid to the sender */
+		msg = nlmsg_new(rtnl_net_get_size(), GFP_KERNEL);
+		if (!msg) {
+			err = -ENOMEM;
+			NL_SET_ERR_MSG(extack, "Unable to alloc reply msg");
+			goto out;
+		}
+
+		err = rtnl_net_fill(msg, &fillargs);
+		if (err < 0) {
+			kfree_skb(msg);
+			goto out;
+		}
+
+		err = rtnl_unicast(msg, net, NETLINK_CB(skb).portid);
 	} else if (err == -ENOSPC && nsid >= 0) {
 		err = -EEXIST;
 		NL_SET_BAD_ATTR(extack, tb[NETNSA_NSID]);
-- 
2.23.0