vsock: each transport cycles only on its own sockets

When iterating over sockets using vsock_for_each_connected_socket, make
sure that a transport filters out sockets that don't belong to the
transport.

There actually was an issue caused by this; in a nested VM
configuration, destroying the nested VM (which often involves the
closing of /dev/vhost-vsock if there was h2g connections to the nested
VM) kills not only the h2g connections, but also all existing g2h
connections to the (outmost) host which are totally unrelated.

Tested: Executed the following steps on Cuttlefish (Android running on a
VM) [1]: (1) Enter into an `adb shell` session - to have a g2h
connection inside the VM, (2) open and then close /dev/vhost-vsock by
`exec 3< /dev/vhost-vsock && exec 3<&-`, (3) observe that the adb
session is not reset.

[1] https://android.googlesource.com/device/google/cuttlefish/

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Reviewed-by: Stefano Garzarella <[e-mail]>
Acked-by: Michael S. Tsirkin <[e-mail]>
Signed-off-by: Jiyong Park <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/vhost/vsock.c

···
 
 	/* Iterating over all connections for all CIDs to find orphans is
 	 * inefficient.  Room for improvement here. */
-	vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
+	vsock_for_each_connected_socket(&vhost_transport.transport,
+					vhost_vsock_reset_orphans);
 
 	/* Don't check the owner, because we are in the release path, so we
 	 * need to stop the vsock device in any case.

include/net/af_vsock.h

···
 struct sock *vsock_find_connected_socket(struct sockaddr_vm *src,
 					 struct sockaddr_vm *dst);
 void vsock_remove_sock(struct vsock_sock *vsk);
-void vsock_for_each_connected_socket(void (*fn)(struct sock *sk));
+void vsock_for_each_connected_socket(struct vsock_transport *transport,
+				     void (*fn)(struct sock *sk));
 int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk);
 bool vsock_find_cid(unsigned int cid);
 

net/vmw_vsock/af_vsock.c

···
 }
 EXPORT_SYMBOL_GPL(vsock_remove_sock);
 
-void vsock_for_each_connected_socket(void (*fn)(struct sock *sk))
+void vsock_for_each_connected_socket(struct vsock_transport *transport,
+				     void (*fn)(struct sock *sk))
 {
 	int i;
 
···
 	for (i = 0; i < ARRAY_SIZE(vsock_connected_table); i++) {
 		struct vsock_sock *vsk;
 		list_for_each_entry(vsk, &vsock_connected_table[i],
-				    connected_table)
+				    connected_table) {
+			if (vsk->transport != transport)
+				continue;
+
 			fn(sk_vsock(vsk));
+		}
 	}
 
 	spin_unlock_bh(&vsock_table_lock);

net/vmw_vsock/virtio_transport.c

···
 static struct workqueue_struct *virtio_vsock_workqueue;
 static struct virtio_vsock __rcu *the_virtio_vsock;
 static DEFINE_MUTEX(the_virtio_vsock_mutex); /* protects the_virtio_vsock */
+static struct virtio_transport virtio_transport; /* forward declaration */
 
 struct virtio_vsock {
 	struct virtio_device *vdev;
···
 	switch (le32_to_cpu(event->id)) {
 	case VIRTIO_VSOCK_EVENT_TRANSPORT_RESET:
 		virtio_vsock_update_guest_cid(vsock);
-		vsock_for_each_connected_socket(virtio_vsock_reset_sock);
+		vsock_for_each_connected_socket(&virtio_transport.transport,
+						virtio_vsock_reset_sock);
 		break;
 	}
 }
···
 	synchronize_rcu();
 
 	/* Reset all connected sockets when the device disappear */
-	vsock_for_each_connected_socket(virtio_vsock_reset_sock);
+	vsock_for_each_connected_socket(&virtio_transport.transport,
+					virtio_vsock_reset_sock);
 
 	/* Stop all work handlers to make sure no one is accessing the device,
 	 * so we can safely call virtio_reset_device().

net/vmw_vsock/vmci_transport.c

···
 
 static int PROTOCOL_OVERRIDE = -1;
 
+static struct vsock_transport vmci_transport; /* forward declaration */
+
 /* Helper function to convert from a VMCI error code to a VSock error code. */
 
 static s32 vmci_transport_error_to_vsock_error(s32 vmci_error)
···
 					 const struct vmci_event_data *e_data,
 					 void *client_data)
 {
-	vsock_for_each_connected_socket(vmci_transport_handle_detach);
+	vsock_for_each_connected_socket(&vmci_transport,
+					vmci_transport_handle_detach);
 }
 
 static void vmci_transport_recv_pkt_work(struct work_struct *work)