SSH.Net with Dropbear: Session close after 30 minutes

[ganeshkamath89]

We are using Dropbear with SSH.Net for an application.

Setup:

• The Dropbear is installed on Ubuntu 18.04 on an x86 system.
• Our SSHClient uses Key based authentication mechanism.
• Connection works normally in the beginning.
• After 30 minutes however, the session disconnects abruptly.
• This behaviour is consistant every time.

Changes attempted:

• We have checked for successful rekeying by reducing the re-keying time in Dropbear to 15 minutes.
• We have passed -K 60 to Dropbear in an attempt to extend connection time.
• We have changed SSH.Net connection with timeout and channelclosetimeout to 20 minutes
• We have used KeepAliveInterval of 1 minute (as well as 10 seconds) in SSH.Net

Environment:

• We have used the latest dropbear (version 2019.78)
• We have tried this with the SSH.Net (version 2016.1.0 (master / develpment / cwl) branches and tried it against the forks of SSH.net.core branches)
• We have tried the Nuget package (2016.1.0) available in Visual Studio as well as the Nuget package with support for .net core SSH.Net.Fork(2018.8.25.2)

Other test case combinations tried and working so far:

• OpenSSH with SSH.Net
• Putty with OpenSSH
• Putty with Dropbear

Has anybody faced this kind of disconnection?

Does anyone have any recommendation or workaround for this problem?

[msdivy]

As per - https://stackoverflow.com/questions/38613717/have-i-encountered-an-incompatibility-between-ssh-net-and-dropbear,

Please try changing the buffer size to 8K.

Code copied from above link:

using (var sftp = new SftpClient(connection)) 
{ 
	sftp.BufferSize = 8192; 
	sftp.Connect(); 
	// ...
}

[ganeshkamath89]

The object of the class SshClient does not have an attribute for Buffer size.
I tried hardcoding the values send and receive Buffer, but it did not help.

I am getting the following error @msdivy

SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelCloseMessage' to server: 'SSH_MSG_CHANNEL_CLOSE : #0'.

SshNet.Logging Verbose: 1 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelOpenMessage' to server: 'SSH_MSG_CHANNEL_OPEN'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelOpenConfirmationMessage' from server: 'SSH_MSG_CHANNEL_OPEN_CONFIRMATION : #827'.
SshNet.Logging Verbose: 1 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelRequestMessage' to server: 'SSH_MSG_CHANNEL_REQUEST : #0'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelSuccessMessage' from server: 'SSH_MSG_CHANNEL_SUCCESS : #827'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelDataMessage' from server: 'SSH_MSG_CHANNEL_DATA : #827'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelEofMessage' from server: 'SSH_MSG_CHANNEL_EOF : #827'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelRequestMessage' from server: 'SSH_MSG_CHANNEL_REQUEST : #827'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelCloseMessage' from server: 'SSH_MSG_CHANNEL_CLOSE : #827'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelCloseMessage' to server: 'SSH_MSG_CHANNEL_CLOSE : #0'.

SshNet.Logging Verbose: 1 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelOpenMessage' to server: 'SSH_MSG_CHANNEL_OPEN'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelOpenConfirmationMessage' from server: 'SSH_MSG_CHANNEL_OPEN_CONFIRMATION : #828'.
SshNet.Logging Verbose: 1 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelRequestMessage' to server: 'SSH_MSG_CHANNEL_REQUEST : #0'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelSuccessMessage' from server: 'SSH_MSG_CHANNEL_SUCCESS : #828'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelDataMessage' from server: 'SSH_MSG_CHANNEL_DATA : #828'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelEofMessage' from server: 'SSH_MSG_CHANNEL_EOF : #828'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelRequestMessage' from server: 'SSH_MSG_CHANNEL_REQUEST : #828'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Received message 'ChannelCloseMessage' from server: 'SSH_MSG_CHANNEL_CLOSE : #828'.
SshNet.Logging Verbose: 5 : [2182A24196544768B0D31071155C76D0ABC19F90] Sending message 'ChannelCloseMessage' to server: 'SSH_MSG_CHANNEL_CLOSE : #0'.
_session was null.

Exception Location
Exception: _session was null.
Exception is hit in this block of code:
protected SemaphoreLight SessionSemaphore
{
get { return _session.SessionSemaphore; }
}
In file SSH.NET\src\Renci.SshNet\Channels\Channel.cs

[msdivy]

Have a look at this: https://github.com/sshnet/SSH.NET/issues/400

[ganeshkamath89]

Hi @msdivy, the suggestion given in this link caused my application to close sooner. I am running the code from the Development brunch.