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

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Date:   Thu, 13 May 2021 11:41:43 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Longpeng(Mike)" <longpeng2@...wei.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        arei.gonglei@...wei.com, subo7@...wei.com,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.com>,
        Colin Ian King <colin.king@...onical.com>,
        David Brazdil <dbrazdil@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        lixianming <lixianming5@...wei.com>
Subject: Re: [RFC] vsock: notify server to shutdown when client has pending
 signal

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@...emloft.net>
>Cc: Jakub Kicinski <kuba@...nel.org>
>Cc: Stefano Garzarella <sgarzare@...hat.com>
>Cc: Jorgen Hansen <jhansen@...are.com>
>Cc: Norbert Slusarek <nslusarek@....net>
>Cc: Andra Paraschiv <andraprs@...zon.com>
>Cc: Colin Ian King <colin.king@...onical.com>
>Cc: David Brazdil <dbrazdil@...gle.com>
>Cc: Alexander Popov <alex.popov@...ux.com>
>Signed-off-by: lixianming <lixianming5@...wei.com>
>Signed-off-by: Longpeng(Mike) <longpeng2@...wei.com>
>---
> 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