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From "Lyor Goldstein (Jira)" <j...@apache.org>
Subject [jira] [Commented] (SSHD-968) SshClient times out during keep-alive, when SSH_MSG_GLOBAL_REQUEST is replied with SSH_MSG_UNSUPPORTED
Date Sun, 23 Feb 2020 17:58:00 GMT

    [ https://issues.apache.org/jira/browse/SSHD-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17043003#comment-17043003
] 

Lyor Goldstein commented on SSHD-968:
-------------------------------------

I am afraid I don't have good news - I have examined the code in the hopes that we can somehow
expose the sequence number of the sent message. While it is technically possible it poses
many challenges especially to the encode/decode loops - which are at the very heart of the
packets management mechanism. I am not sure the benefit is worth the risk at this time...

> SshClient times out during keep-alive, when SSH_MSG_GLOBAL_REQUEST is replied with SSH_MSG_UNSUPPORTED
> ------------------------------------------------------------------------------------------------------
>
>                 Key: SSHD-968
>                 URL: https://issues.apache.org/jira/browse/SSHD-968
>             Project: MINA SSHD
>          Issue Type: Improvement
>    Affects Versions: 2.3.0
>         Environment: Windows 10
>            Reporter: Patrik Ek
>            Assignee: Lyor Goldstein
>            Priority: Major
>
> In case SSH_MSG_GLOBAL_REQUEST is not supported by the remote SSH server, the keep-alive
heartbeat times out. The reason for this is SSH_MSG_UNIMPLEMENTED is only logged in
> {color:#172b4d}org.apache.sshd.common.session.helpers{color}.AbstractSession
> The method identifying the SSH_MSG_UNIMPLEMENTED is called AbstractSession.doHandleMessage()
> The consequense is that no reply is received and the heartbeat times out instead of calling
AbstractSession.requestFailure(). Which in turn leads to the session terminates.
> According to RFC 4253 sect. 11.4 ({color:#004000}https://tools.ietf.org/html/rfc4253#section-11.4{color})
the SSH_MSG_UNIMPLEMENTED is meant to be ignored, but this makes little sense for a heartbeat,
as even SSH_MSG_UNIMPLEMENTED is good enough to count as a reply for this. This is for example
the case in OpenSSH, where SSH_MSG_UNIMPLEMENTED replies for heartbeat, does not lead to a
termination of the SSH session.
> There is a workaround released in 2.1.1, to use ReservedSessionMessagesHandler for handling
replies, but this does not allow access to the method AbstractSession.requestFailure() (without
using reflection so to say). Further, the heartbeat is ongoing in the background, so there
is no good solution to this problem from outside of the framework.
> https://issues.apache.org/jira/browse/SSHD-887?jql=project%20%3D%20SSHD%20AND%20fixVersion%20%3D%202.1.1
> Would this be possible to fix? The reason I write it here is because the bug seems to
existing up to some version of libssh, even for the SSHv2 protocol, so just writing a bug
report on the particular server will not solve the problems for already existing implementations
using libssh.
> The following config is used,
> SshClient client = SshClient.setUpDefaultClient(){color:#cc7832};{color}{color:#808080}
> {color} {color:#172b4d}PropertyResolverUtils.updateProperty(client, ClientFactoryManager.HEARTBEAT_INTERVAL,
15000);
>  PropertyResolverUtils.updateProperty(client,ClientFactoryManager.HEARTBEAT_REPLY_WAIT,
30000);
>  PropertyResolverUtils.updateProperty(client,ClientFactoryManager.HEARTBEAT_REQUEST,
"keepalive@openssh.com");{color}
> {color:#cc7832}{color:#172b4d}BR{color}
> {color:#172b4d}Patrik{color}
> {color}



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