Phonet: resource routing backend

When both destination device and object are nul, Phonet routes the
packet according to the resource field. In fact, this is the most
common pattern when sending Phonet "request" packets. In this case,
the packet is delivered to whichever endpoint (socket) has
registered the resource.

This adds a new table so that Linux processes can register their
Phonet sockets to Phonet resources, if they have adequate privileges.

(Namespace support is not implemented at the moment.)

Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/phonet/socket.c

@@ -565,3 +565,91 @@ const struct file_operations pn_sock_seq_fops = {
 	.release = seq_release_net,
 };
 #endif
+
+static struct  {
+	struct sock *sk[256];
+} pnres;
+
+/*
+ * Find and hold socket based on resource.
+ */
+struct sock *pn_find_sock_by_res(struct net *net, u8 res)
+{
+	struct sock *sk;
+
+	if (!net_eq(net, &init_net))
+		return NULL;
+
+	rcu_read_lock();
+	sk = rcu_dereference(pnres.sk[res]);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
+	return sk;
+}
+
+static DEFINE_MUTEX(resource_mutex);
+
+int pn_sock_bind_res(struct sock *sk, u8 res)
+{
+	int ret = -EADDRINUSE;
+
+	if (!net_eq(sock_net(sk), &init_net))
+		return -ENOIOCTLCMD;
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (pn_socket_autobind(sk->sk_socket))
+		return -EAGAIN;
+
+	mutex_lock(&resource_mutex);
+	if (pnres.sk[res] == NULL) {
+		sock_hold(sk);
+		rcu_assign_pointer(pnres.sk[res], sk);
+		ret = 0;
+	}
+	mutex_unlock(&resource_mutex);
+	return ret;
+}
+
+int pn_sock_unbind_res(struct sock *sk, u8 res)
+{
+	int ret = -ENOENT;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	mutex_lock(&resource_mutex);
+	if (pnres.sk[res] == sk) {
+		rcu_assign_pointer(pnres.sk[res], NULL);
+		ret = 0;
+	}
+	mutex_unlock(&resource_mutex);
+
+	if (ret == 0) {
+		synchronize_rcu();
+		sock_put(sk);
+	}
+	return ret;
+}
+
+void pn_sock_unbind_all_res(struct sock *sk)
+{
+	unsigned res, match = 0;
+
+	mutex_lock(&resource_mutex);
+	for (res = 0; res < 256; res++) {
+		if (pnres.sk[res] == sk) {
+			rcu_assign_pointer(pnres.sk[res], NULL);
+			match++;
+		}
+	}
+	mutex_unlock(&resource_mutex);
+
+	if (match == 0)
+		return;
+	synchronize_rcu();
+	while (match > 0) {
+		sock_put(sk);
+		match--;
+	}
+}