openssh unix dev - Apr 2023 - Killing the OpenSSH server doesn't cause the Windows OpenSSH client to die

I connect with the OpenSSH client on Windows to the OpenSSH server on 
FreeBSD, all in one LAN, Wifi to Eithernet.


After a while, usually when the connection is inactive for some time, it 
becomes dysfunctional: it becomes impossible to connect through reverse 
port forwards from FreeBSD to Windows.

At such times killing the ssh server process on FreeBSD, corresponding 
to the connection, doesn't cause the client to exit on Windows.

But hitting Enter on the client in Windows causes it to immediately exit.


Did anybody experience a problem like this?

Could there be a bug in OpenSSH?

Is it possible that Windows fails to deliver the signal to the client 
that the connection was terminated?


Thank you,

Yuri

Try setting

Host *
 ? ServerAliveInterval 240

in .ssh/config on the client (wherever that is in Windows).? Or pass "-o 
ServerAliveInterval=240" on the ssh client command line.

I've seen this where connections pass through some low grade external 
firewall, which drops state after a certain amount of inactivity without 
sending back RST (and apparently is immune to TCP keepalives too).

You say both boxes are on the same LAN, but it's possible that a 
badly-configured software firewall on the FreeBSD box could be the cause 
- or on Windows itself.

It depends how you "kill" the SSH server.

If you kill it by sending it a SIGKILL signal, it will NOT notify the 
client, so the client will stay running until the client discovers the 
connection is broken.

What happens if you send the SSH server a SIGHUP signal? This should cause 
an orderly shutdown on the server, which should notify the client, which 
should cause the client to do an orderly shutdown.

On Fri, 7 Apr 2023, Yuri wrote:
> I connect with the OpenSSH client on Windows to the OpenSSH server on 
> FreeBSD, all in one LAN, Wifi to Eithernet.
>
>
> After a while, usually when the connection is inactive for some time, it 
> becomes dysfunctional: it becomes impossible to connect through reverse
port
> forwards from FreeBSD to Windows.
>
> At such times killing the ssh server process on FreeBSD, corresponding to
the
> connection, doesn't cause the client to exit on Windows.
>
> But hitting Enter on the client in Windows causes it to immediately exit.
>
>
> Did anybody experience a problem like this?
>
> Could there be a bug in OpenSSH?
>
> Is it possible that Windows fails to deliver the signal to the client that 
> the connection was terminated?
>
>
> Thank you,
>
> Yuri
>
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
>
Regards,
....Bob Rasmussen,   President,   Rasmussen Software, Inc.

personal e-mail: ras at anzio.com
  company e-mail: rsi at anzio.com
           voice: (US) 503-624-0360
             fax: no longer available
             web: http://www.anzio.com
Mailing address: Rasmussen Software, Inc.   NEW AS OF JULY 1, 2022
                  6265 SW Erickson Ave.
                  Beaverton OR 97008  USA

The fact that '-o ServerAliveInterval=50' makes no difference suggests 
that there is a bug in the OpenSSH client.
It either fails to sent heartbeats, or it gets stuck in some Windows 
system call and this makes it to fail to send heartbeats.


Yuri

The OpenSSH daemon is supposed to start, and fork off additional
daemons for new connections, to prevent the loss of the main daemon
from killing vital, long-running, active connections. Various tools
have tried to mandate the end of client sessions, for various reasons
and by various mens,

Please don't try to "improve security" by breaking long-standing
features. This feature, in particular, allows a remote administrator
to revise the SSH configuration, restart it for validation, and not
lose the existing remote shell session to allow reverting a risky
chnage. Such changes would become *vastly* more risky, and very
difficult to revert due to the now broken sshd configuration. Been
there, done that. Last Tuesday.....

On Fri, Apr 7, 2023 at 12:18?PM Yuri <yuri at rawbw.com>
wrote:
>
> I connect with the OpenSSH client on Windows to the OpenSSH server on
> FreeBSD, all in one LAN, Wifi to Eithernet.
>
>
> After a while, usually when the connection is inactive for some time, it
> becomes dysfunctional: it becomes impossible to connect through reverse
> port forwards from FreeBSD to Windows.
>
> At such times killing the ssh server process on FreeBSD, corresponding
> to the connection, doesn't cause the client to exit on Windows.
>
> But hitting Enter on the client in Windows causes it to immediately exit.
>
>
> Did anybody experience a problem like this?
>
> Could there be a bug in OpenSSH?
>
> Is it possible that Windows fails to deliver the signal to the client
> that the connection was terminated?
>
>
> Thank you,
>
> Yuri
>
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev