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

From: Stefano Garzarella
Date: Thu May 13 2021 - 05:41:54 EST


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