Re: [RFC] vsock: notify server to shutdown when client has pending signal

[Stefano Garzarella]

Hi,
thanks for this patch, comments below...

On Tue, May 11, 2021 at 05:41:27PM +0800, Longpeng(Mike) wrote:
> The client's sk_state will be set to TCP_ESTABLISHED if the
> server replay the client's connect request.
> However, if the client has pending signal, its sk_state will
> be set to TCP_CLOSE without notify the server, so the server
> will hold the corrupt connection.
>
>            client                        server
>
> 1. sk_state=TCP_SYN_SENT         |
> 2. call ->connect()              |
> 3. wait reply                    |
>                                 | 4. sk_state=TCP_ESTABLISHED
>                                 | 5. insert to connected list
>                                 | 6. reply to the client
> 7. sk_state=TCP_ESTABLISHED      |
> 8. insert to connected list      |
> 9. *signal pending* <--------------------- the user kill client
> 10. sk_state=TCP_CLOSE           |
> client is exiting...             |
> 11. call ->release()             |
>     virtio_transport_close
>      if (!(sk->sk_state == TCP_ESTABLISHED ||
> 	      sk->sk_state == TCP_CLOSING))
> 		return true; <------------- return at here
> As a result, the server cannot notice the connection is corrupt.
> So the client should notify the peer in this case.
>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Cc: Jorgen Hansen <jhansen@xxxxxxxxxx>
> Cc: Norbert Slusarek <nslusarek@xxxxxxx>
> Cc: Andra Paraschiv <andraprs@xxxxxxxxxx>
> Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Cc: David Brazdil <dbrazdil@xxxxxxxxxx>
> Cc: Alexander Popov <alex.popov@xxxxxxxxx>
> Signed-off-by: lixianming <lixianming5@xxxxxxxxxx>
> Signed-off-by: Longpeng(Mike) <longpeng2@xxxxxxxxxx>
> ---
> net/vmw_vsock/af_vsock.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 92a72f0..d5df908 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -1368,6 +1368,7 @@ static int vsock_stream_connect(struct socket *sock, struct sockaddr *addr,
> 		lock_sock(sk);
>
> 		if (signal_pending(current)) {
> +			vsock_send_shutdown(sk, SHUTDOWN_MASK);

I see the issue, but I'm not sure is okay to send the shutdown in any 
case, think about the server didn't setup the connection.

Maybe is better to set TCP_CLOSING if the socket state was 
TCP_ESTABLISHED, so the shutdown will be handled by the 
transport->release() as usual.

What do you think?

Anyway, also without the patch, the server should receive a RST if it 
sends any data to the client, but of course, is better to let it know 
the socket is closed in advance.

Thanks,
Stefano