rxrpc: Permit multiple service binding

Permit bind() to be called on an AF_RXRPC socket more than once (currently
maximum twice) to bind multiple listening services to it.  There are some
restrictions:

 (1) All bind() calls involved must have a non-zero service ID.

 (2) The service IDs must all be different.

 (3) The rest of the address (notably the transport part) must be the same
     in all (a single UDP socket is shared).

 (4) This must be done before listen() or sendmsg() is called.

This allows someone to connect to the service socket with different service
IDs and lays the foundation for service upgrading.

The service ID used by an incoming call can be extracted from the msg_name
returned by recvmsg().

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 40 insertions, 22 deletions

diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 1e4ac889ec00..3b982bca7d22 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -144,31 +144,48 @@ static int rxrpc_bind(struct socket *sock, struct sockaddr *saddr, int len)
 
 	lock_sock(&rx->sk);
 
-	if (rx->sk.sk_state != RXRPC_UNBOUND) {
-		ret = -EINVAL;
-		goto error_unlock;
-	}
-
-	memcpy(&rx->srx, srx, sizeof(rx->srx));
+	switch (rx->sk.sk_state) {
+	case RXRPC_UNBOUND:
+		rx->srx = *srx;
+		local = rxrpc_lookup_local(sock_net(&rx->sk), &rx->srx);
+		if (IS_ERR(local)) {
+			ret = PTR_ERR(local);
+			goto error_unlock;
+		}
 
-	local = rxrpc_lookup_local(sock_net(&rx->sk), &rx->srx);
-	if (IS_ERR(local)) {
-		ret = PTR_ERR(local);
-		goto error_unlock;
-	}
+		if (service_id) {
+			write_lock(&local->services_lock);
+			if (rcu_access_pointer(local->service))
+				goto service_in_use;
+			rx->local = local;
+			rcu_assign_pointer(local->service, rx);
+			write_unlock(&local->services_lock);
+
+			rx->sk.sk_state = RXRPC_SERVER_BOUND;
+		} else {
+			rx->local = local;
+			rx->sk.sk_state = RXRPC_CLIENT_BOUND;
+		}
+		break;
 
-	if (service_id) {
-		write_lock(&local->services_lock);
-		if (rcu_access_pointer(local->service))
-			goto service_in_use;
-		rx->local = local;
-		rcu_assign_pointer(local->service, rx);
-		write_unlock(&local->services_lock);
+	case RXRPC_SERVER_BOUND:
+		ret = -EINVAL;
+		if (service_id == 0)
+			goto error_unlock;
+		ret = -EADDRINUSE;
+		if (service_id == rx->srx.srx_service)
+			goto error_unlock;
+		ret = -EINVAL;
+		srx->srx_service = rx->srx.srx_service;
+		if (memcmp(srx, &rx->srx, sizeof(*srx)) != 0)
+			goto error_unlock;
+		rx->second_service = service_id;
+		rx->sk.sk_state = RXRPC_SERVER_BOUND2;
+		break;
 
-		rx->sk.sk_state = RXRPC_SERVER_BOUND;
-	} else {
-		rx->local = local;
-		rx->sk.sk_state = RXRPC_CLIENT_BOUND;
+	default:
+		ret = -EINVAL;
+		goto error_unlock;
 	}
 
 	release_sock(&rx->sk);
@@ -205,6 +222,7 @@ static int rxrpc_listen(struct socket *sock, int backlog)
 		ret = -EADDRNOTAVAIL;
 		break;
 	case RXRPC_SERVER_BOUND:
+	case RXRPC_SERVER_BOUND2:
 		ASSERT(rx->local != NULL);
 		max = READ_ONCE(rxrpc_max_backlog);
 		ret = -EINVAL;