[PATCH v2 net-next 2/7] rtnetlink: Add peer_type in struct rtnl_link_ops.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

In ops->newlink(), veth, vxcan, and netkit call rtnl_link_get_net() with
a net pointer, which is the first argument of ->newlink().

rtnl_link_get_net() could return another netns based on IFLA_NET_NS_PID
and IFLA_NET_NS_FD in the peer device's attributes.

We want to get it and fill rtnl_nets->nets[] in advance in rtnl_newlink()
for per-netns RTNL.

All of the three get the peer netns in the same way:

  1. Call rtnl_nla_parse_ifinfomsg()
  2. Call ops->validate() (vxcan doesn't have)
  3. Call rtnl_link_get_net()

Let's add a new field peer_type to struct rtnl_link_ops and prefetch
netns in the peer ifla to add it to rtnl_nets in rtnl_newlink().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
v2:
  * Rename the helper to rtnl_link_get_net_ifla()
  * Unexport rtnl_link_get_net_ifla() and made it static
  * Change peer_type to u16
  * squash patch 2 & 3 (due to static requires a user)
---
 include/net/rtnetlink.h |  2 ++
 net/core/rtnetlink.c    | 55 ++++++++++++++++++++++++++++++++++++++---
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index b260c0cc9671..f17208323c08 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -75,6 +75,7 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
  *	@srcu: Used internally
  *	@kind: Identifier
  *	@netns_refund: Physical device, move to init_net on netns exit
+ *	@peer_type: Peer device specific netlink attribute number (e.g. VETH_INFO_PEER)
  *	@maxtype: Highest device specific netlink attribute number
  *	@policy: Netlink policy for device specific attribute validation
  *	@validate: Optional validation function for netlink/changelink parameters
@@ -116,6 +117,7 @@ struct rtnl_link_ops {
 	void			(*setup)(struct net_device *dev);
 
 	bool			netns_refund;
+	const u16		peer_type;
 	unsigned int		maxtype;
 	const struct nla_policy	*policy;
 	int			(*validate)(struct nlattr *tb[],
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 81f4722c1353..d5557a621099 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2518,9 +2518,10 @@ int rtnl_nla_parse_ifinfomsg(struct nlattr **tb, const struct nlattr *nla_peer,
 }
 EXPORT_SYMBOL(rtnl_nla_parse_ifinfomsg);
 
-struct net *rtnl_link_get_net(struct net *src_net, struct nlattr *tb[])
+static struct net *rtnl_link_get_net_ifla(struct nlattr *tb[])
 {
-	struct net *net;
+	struct net *net = NULL;
+
 	/* Examine the link attributes and figure out which
 	 * network namespace we are talking about.
 	 */
@@ -2528,8 +2529,17 @@ struct net *rtnl_link_get_net(struct net *src_net, struct nlattr *tb[])
 		net = get_net_ns_by_pid(nla_get_u32(tb[IFLA_NET_NS_PID]));
 	else if (tb[IFLA_NET_NS_FD])
 		net = get_net_ns_by_fd(nla_get_u32(tb[IFLA_NET_NS_FD]));
-	else
+
+	return net;
+}
+
+struct net *rtnl_link_get_net(struct net *src_net, struct nlattr *tb[])
+{
+	struct net *net = rtnl_link_get_net_ifla(tb);
+
+	if (!net)
 		net = get_net(src_net);
+
 	return net;
 }
 EXPORT_SYMBOL(rtnl_link_get_net);
@@ -3794,6 +3804,37 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
 	goto out;
 }
 
+static int rtnl_add_peer_net(struct rtnl_nets *rtnl_nets,
+			     const struct rtnl_link_ops *ops,
+			     struct nlattr *data[],
+			     struct netlink_ext_ack *extack)
+{
+	struct nlattr *tb[IFLA_MAX + 1];
+	struct net *net;
+	int err;
+
+	if (!data || !data[ops->peer_type])
+		return 0;
+
+	err = rtnl_nla_parse_ifinfomsg(tb, data[ops->peer_type], extack);
+	if (err < 0)
+		return err;
+
+	if (ops->validate) {
+		err = ops->validate(tb, NULL, extack);
+		if (err < 0)
+			return err;
+	}
+
+	net = rtnl_link_get_net_ifla(tb);
+	if (IS_ERR(net))
+		return PTR_ERR(net);
+	if (net)
+		rtnl_nets_add(rtnl_nets, net);
+
+	return 0;
+}
+
 static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 			  const struct rtnl_link_ops *ops,
 			  struct net *tgt_net, struct net *link_net,
@@ -3922,12 +3963,18 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 			if (ret < 0)
 				goto put_ops;
 		}
+
+		if (ops->peer_type) {
+			ret = rtnl_add_peer_net(&rtnl_nets, ops, data, extack);
+			if (ret < 0)
+				goto put_ops;
+		}
 	}
 
 	tgt_net = rtnl_link_get_net_capable(skb, sock_net(skb->sk), tb, CAP_NET_ADMIN);
 	if (IS_ERR(tgt_net)) {
 		ret = PTR_ERR(tgt_net);
-		goto put_ops;
+		goto put_net;
 	}
 
 	rtnl_nets_add(&rtnl_nets, tgt_net);
-- 
2.39.5 (Apple Git-154)