rtnetlink: add rtnl_get_net_ns_capable()

get_target_net() will be used in follow-up patches in ipv{4,6} codepaths to
retrieve network namespaces based on network namespace identifiers. So
remove the static declaration and export in the rtnetlink header. Also,
rename it to rtnl_get_net_ns_capable() to make it obvious what this
function is doing.
Export rtnl_get_net_ns_capable() so it can be used when ipv6 is built as
a module.

Signed-off-by: Christian Brauner <christian@brauner.io>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/rtnetlink.h

@@ -165,6 +165,7 @@ int rtnl_configure_link(struct net_device *dev, const struct ifinfomsg *ifm);
 
 int rtnl_nla_parse_ifla(struct nlattr **tb, const struct nlattr *head, int len,
 			struct netlink_ext_ack *exterr);
+struct net *rtnl_get_net_ns_capable(struct sock *sk, int netnsid);
 
 #define MODULE_ALIAS_RTNL_LINK(kind) MODULE_ALIAS("rtnl-link-" kind)
 

net/core/rtnetlink.c

@@ -1845,7 +1845,15 @@ static bool link_dump_filtered(struct net_device *dev,
 	return false;
 }
 
-static struct net *get_target_net(struct sock *sk, int netnsid)
+/**
+ * rtnl_get_net_ns_capable - Get netns if sufficiently privileged.
+ * @sk: netlink socket
+ * @netnsid: network namespace identifier
+ *
+ * Returns the network namespace identified by netnsid on success or an error
+ * pointer on failure.
+ */
+struct net *rtnl_get_net_ns_capable(struct sock *sk, int netnsid)
 {
 	struct net *net;
 
@@ -1862,6 +1870,7 @@ static struct net *get_target_net(struct sock *sk, int netnsid)
 	}
 	return net;
 }
+EXPORT_SYMBOL_GPL(rtnl_get_net_ns_capable);
 
 static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
@@ -1897,7 +1906,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 			ifla_policy, NULL) >= 0) {
 		if (tb[IFLA_IF_NETNSID]) {
 			netnsid = nla_get_s32(tb[IFLA_IF_NETNSID]);
-			tgt_net = get_target_net(skb->sk, netnsid);
+			tgt_net = rtnl_get_net_ns_capable(skb->sk, netnsid);
 			if (IS_ERR(tgt_net)) {
 				tgt_net = net;
 				netnsid = -1;
@@ -2765,7 +2774,7 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	if (tb[IFLA_IF_NETNSID]) {
 		netnsid = nla_get_s32(tb[IFLA_IF_NETNSID]);
-		tgt_net = get_target_net(NETLINK_CB(skb).sk, netnsid);
+		tgt_net = rtnl_get_net_ns_capable(NETLINK_CB(skb).sk, netnsid);
 		if (IS_ERR(tgt_net))
 			return PTR_ERR(tgt_net);
 	}
@@ -3175,7 +3184,7 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	if (tb[IFLA_IF_NETNSID]) {
 		netnsid = nla_get_s32(tb[IFLA_IF_NETNSID]);
-		tgt_net = get_target_net(NETLINK_CB(skb).sk, netnsid);
+		tgt_net = rtnl_get_net_ns_capable(NETLINK_CB(skb).sk, netnsid);
 		if (IS_ERR(tgt_net))
 			return PTR_ERR(tgt_net);
 	}