sshnet / sshnet/SSH.NET

Connection Abort on Key Auth causes problem on reconnect

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Dominant language
C#
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Description

I'm using SSH.NET v2016.1.0 to connect to many UNIX servers. We have logic to retry connecting if an attempt fails. One of the servers uses keyboard authentication and intermittently aborts the connection during login. We have not found the cause of abort but that is not of concern here. When an abort occurs, the ConnectionInfo object is not being properly disposed when the client is Disconnected or Disposed. This is causing subsequent connection attempts to fail with client is not connected errors or errant events to be logged.

Renci.SshNet.Common.SshConnectionException: An established connection was aborted by the server.
at Renci.SshNet.Session.WaitOnHandle(WaitHandle waitHandle, TimeSpan timeout)
at Renci.SshNet.KeyboardInteractiveAuthenticationMethod.Authenticate(Session session)
at Renci.SshNet.ClientAuthentication.TryAuthenticate(ISession session, AuthenticationState authenticationState, String[] allowedAuthenticationMethods, SshAuthenticationException& authenticationException)
at Renci.SshNet.ClientAuthentication.Authenticate(IConnectionInfoInternal connectionInfo, ISession session)
at Renci.SshNet.ConnectionInfo.Authenticate(ISession session, IServiceFactory serviceFactory)
at Renci.SshNet.Session.Connect()
at Renci.SshNet.BaseClient.Connect()

We have worked around by recreating the ConnectionInfo object on each attempt and unsubscribing handlers for the AuthenticationPrompt and AuthenticationBanners events before Disposing the client when a failure occurs.

private void DisposeClient(BaseClient client)
        {
            if (client != null)
            {
                if (client.ConnectionInfo != null)
                {
                    // Unregister events
                    foreach (AuthenticationMethod authenticationMethod in client.ConnectionInfo.AuthenticationMethods)
                    {
                        if (authenticationMethod is KeyboardInteractiveAuthenticationMethod)
                        {                            
                       ((KeyboardInteractiveAuthenticationMethod)authenticationMethod).AuthenticationPrompt -= KeyboardInteractive_AuthenticationPrompt;
                            break;
                        }
                    }

                    client.ConnectionInfo.AuthenticationBanner -= ConnectionInfo_AuthenticationBanner;
                }

                client.Dispose();

                client = null;
            }
        }

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by tracing BaseClient.Dispose and Disconnect through ConnectionInfo, Session.Connect, and KeyboardInteractiveAuthenticationMethod.Authenticate, focusing on the aborted-login path shown in the stack trace. Check how authentication event handlers and connection state are retained after an abort. Done means disposing or reconnecting after a failed keyboard-authentication attempt does not produce stale events or client-is-not-connected errors.

Written by the indexing model from the issue text.

Assessment

Tech stack
csharp
Domain
networking
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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