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workaround obsolete, but it is obsolete.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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