mctp: Allow per-netns default networks

Currently we have a compile-time default network
(MCTP_INITIAL_DEFAULT_NET). This change introduces a default_net field
on the net namespace, allowing future configuration for new interfaces.
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/mctp.h

@@ -37,6 +37,8 @@ struct mctp_hdr {
 
 #define MCTP_HEADER_MAXLEN	4
 
+#define MCTP_INITIAL_DEFAULT_NET	1
+
 static inline bool mctp_address_ok(mctp_eid_t eid)
 {
 	return eid >= 8 && eid < 255;

include/net/netns/mctp.h

@@ -25,6 +25,9 @@ struct netns_mctp {
 	spinlock_t keys_lock;
 	struct hlist_head keys;
 
+	/* MCTP network */
+	unsigned int default_net;
+
 	/* neighbour table */
 	struct mutex neigh_lock;
 	struct list_head neighbours;

include/uapi/linux/mctp.h

@@ -26,7 +26,6 @@ struct sockaddr_mctp {
 };
 
 #define MCTP_NET_ANY		0x0
-#define MCTP_NET_DEFAULT	0x0
 
 #define MCTP_ADDR_NULL		0x00
 #define MCTP_ADDR_ANY		0xff

net/mctp/af_mctp.c

@@ -94,6 +94,9 @@ static int mctp_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 	if (!capable(CAP_NET_RAW))
 		return -EACCES;
 
+	if (addr->smctp_network == MCTP_NET_ANY)
+		addr->smctp_network = mctp_default_net(sock_net(sk));
+
 	rt = mctp_route_lookup(sock_net(sk), addr->smctp_network,
 			       addr->smctp_addr.s_addr);
 	if (!rt)

net/mctp/device.c

@@ -267,7 +267,7 @@ static struct mctp_dev *mctp_add_dev(struct net_device *dev)
 
 	spin_lock_init(&mdev->addrs_lock);
 
-	mdev->net = MCTP_INITIAL_DEFAULT_NET;
+	mdev->net = mctp_default_net(dev_net(dev));
 
 	/* associate to net_device */
 	rcu_assign_pointer(dev->mctp_ptr, mdev);

net/mctp/route.c

@@ -433,6 +433,19 @@ static struct mctp_route *mctp_route_alloc(void)
 	return rt;
 }
 
+unsigned int mctp_default_net(struct net *net)
+{
+	return READ_ONCE(net->mctp.default_net);
+}
+
+int mctp_default_net_set(struct net *net, unsigned int index)
+{
+	if (index == 0)
+		return -EINVAL;
+	WRITE_ONCE(net->mctp.default_net, index);
+	return 0;
+}
+
 /* tag management */
 static void mctp_reserve_tag(struct net *net, struct mctp_sk_key *key,
 			     struct mctp_sock *msk)
@@ -1045,6 +1058,7 @@ static int __net_init mctp_routes_net_init(struct net *net)
 	mutex_init(&ns->bind_lock);
 	INIT_HLIST_HEAD(&ns->keys);
 	spin_lock_init(&ns->keys_lock);
+	WARN_ON(mctp_default_net_set(net, MCTP_INITIAL_DEFAULT_NET));
 	return 0;
 }