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https://issues.apache.org/jira/browse/SSHD-256?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Simon Tatham updated SSHD-256:
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Attachment: 0001-Consistently-send-replies-to-channel-requests.patch
I've been investigating this same issue (having had it reported initially as a
bug against PuTTY). I agree that Michael Heemskerk's patch is sensible, but I
also think that the problem with ignoring the "want reply" flag goes
considerably further than just this one request type. I looked through the
request handling in the various channel classes and discovered that "want
reply" is often ignored in other situations, which is a source of further
latent bugs just waiting for a peer implementation to trigger them.
I've attached my own suggested patch which centralises the handling of
responses to channel requests, so as to make sure a response is _always_ sent
if "want reply" is true, and _never_ sent if it is not, regardless of the
channel type or whether the request is recognised. I haven't been conveniently
able to check the behaviour in previously failing cases, but I have run the
result through "mvn test" which reported no failures.
I would recommend applying this patch _in addition_ to Michael Heemskerk's
patch.
> 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: 0.7.0, 0.8.0, 0.9.0
> Reporter: Michael Heemskerk
> Attachments: 0001-Consistently-send-replies-to-channel-requests.patch
>
>
> 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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