[jira] [Created] (SSHD-256) SSH_MSG_CHANNEL_REQUEST for Putty handled incorrectly

["Michael Heemskerk (JIRA)" <ji...@apache.org>]

Michael Heemskerk created SSHD-256:
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             Summary: SSH_MSG_CHANNEL_REQUEST for Putty handled incorrectly
                 Key: SSHD-256
                 URL: https://issues.apache.org/jira/browse/SSHD-256
             Project: MINA SSHD
          Issue Type: Bug
    Affects Versions: 0.9.0, 0.8.0, 0.7.0
            Reporter: Michael Heemskerk


Symptom:

SSH connection is kept open after the command completes when using Putty, Plink or TortoisePlink, or rather Putty does not finish.

See:
* https://code.google.com/p/tortoisegit/issues/detail?id=1880
* https://jira.atlassian.com/browse/STASH-3824

Cause:
ChannelSession has special handling for SSH_MSG_CHANNEL_REQUEST messages that are sent by Putty:

        if (type != null && type.endsWith("@putty.projects.tartarus.org")) {
            // Ignore but accept, more doc at
            // http://tartarus.org/~simon/putty-snapshots/htmldoc/AppendixF.html
            return true;
        }

There are really two problems with this workaround that was introduced in SSHD-77:

1) This code ignores the "want reply" flag on the field and simply ignores the request. According to the SSH protocol specification, the server MUST send back a reply (success or failure) if the "want reply" flag is set to true.
2) Putty _intentionally_ sends an invalid request and _expects_ to receive a SSH_MSG_CHANNEL_FAILURE response (see http://tartarus.org/~simon/putty-snapshots/htmldoc/AppendixF.html), which is the default behaviour of ChannelSession.

I don't know whether changes in Putty or changes in MinaSSHD have made the workaround obsolete, but it is obsolete. I've verified that without the bit of code I quoted above, the Putty terminates normally.


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