[jira] [Updated] (SSHD-633) Race condition in command execution and SSH_MSG_CHANNEL_SUCCESS

["Goldstein Lyor (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SSHD-633?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Goldstein Lyor updated SSHD-633:
--------------------------------
    Priority: Major  (was: Critical)

> Race condition in command execution and SSH_MSG_CHANNEL_SUCCESS
> ---------------------------------------------------------------
>
>                 Key: SSHD-633
>                 URL: https://issues.apache.org/jira/browse/SSHD-633
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 1.0.0
>            Reporter: Eugene Petrenko
>            Assignee: Goldstein Lyor
>
> We use the library for production. From time to time we see timeout exceptions from clients that calls our SSH server. It was not clear what is that. Most of the time I saw command suck reading STDIN. We use JSCH as client here. The problem was reproducing rarely.
> I connect JSCH 1.51 to SSHD server to execute a command
> JSCH client expects to read {{SSH_MSG_CHANNEL_SUCCESS}} or {{SSH_MSG_CHANNEL_FAILURE}} as response to {{SSH_MSG_CHANNEL_REQUEST}} call to execute command. 
> SSHD implementation calls command's method {{start}} and than posts reply with success to the channel. It may easily command thread is able to fill send window with DATA messages. Thus {{SSH_MSG_CHANNEL_SUCCESS}} reply is not delivered. 
> This makes JSCH to wait for the message and fail on timeout. The SSHD server command is simply suck on reading stdin.
> Here goes the code I managed to reproduce the issue. What I did is to start sending a huge data block without creating a thread in command's start method. Of course this is a bit incorrect, but it easily make it fail. 
> The server contains the following command implementation
> {code}
>     final OutputStream out = getOut();
>     out.write(new byte[32 * 1024 * 1024]);
>     out.flush();
>     new Thread(new Runnable() {
>       @Override
>       public void run() {
>         try {
>           getIn().read();
>           onExit(0);
>         } catch (Throwable e) {
>           onExit(1, e.getMessage());
>         }
>       }
>     }).start();
> {code} 
> Jsch client code is follows
> {code}
>         final JSch j = new JSch();
>         final Session session = j.getSession("jonnyzzz", myResource.getHostname(), myResource.getSSHPort());
>         session.setTimeout(60_000);
>         session.connect();
>         final ChannelExec e = (ChannelExec) session.openChannel("exec");
>         e.setCommand("test-buffer-underrun");
>         final InputStream inputStream = new e.getInputStream();
>         e.connect(10_000); //meaningful timeout to reproduce the bug
>         ByteStreams.copy(inputStream, FileUtil.nullOutputStream());
> {code}



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