openssh unix dev - Jul 2007 - BUG?: Assigning a Perl script as user shell + sending commands on ssh connect

Hi,
This is sort of a strange issue. But I am experimenting with ways to
have a user log in and be presented with a perl script to interact
with. When I do either or both of the following:

     1) set the user's shell to /usr/bin/myperlscript

     2) specify ForceCommand /usr/bin/myperlscript, applied to my user

...I get strange behavior when a command is appended to the client
connect command in this way:

     ssh -l user 192.168.1.2 ls /etc

The output from the perl script is not printed immediately but waits
for a carriage return from the user before it is printed to the
screen> Here is an example using a test perl script:

     me at computer:~$ ssh -l user 192.168.1.2 /bin/bash
     user at 192.168.1.2's password:
     echo "I'm typing this line while the script seems not to be
running"
     here we go!

     enter something:

     YOU SAID: echo "I'm typing this line while the script seems not
to be running"

You can see that what I type is taken as <STDIN> by the script, so I
guess the output is stuck in a buffer somewhere. not sure if this is a
bug in OpenSSH or a perl oddity. Or maybe I really shouldn't be
setting my user's shell to be a script.

On 2007-07-26 22:30, Brandon Simmons wrote:
> You can see that what I type is taken as <STDIN> by the script, so I
> guess the output is stuck in a buffer somewhere. not sure if this is a
> bug in OpenSSH or a perl oddity. Or maybe I really shouldn't be
> setting my user's shell to be a script.
Have you tried setting autoflush on the output stream from your Perl script?

-- 
Jefferson Ogata <Jefferson.Ogata at noaa.gov>
NOAA Computer Incident Response Team (N-CIRT) <ncirt at noaa.gov>
"Never try to retrieve anything from a bear."--National Park Service

On Thu, Jul 26, 2007 at 06:30:03PM -0400, Brandon Simmons
wrote:
> Hi,
> This is sort of a strange issue. But I am experimenting with ways to
> have a user log in and be presented with a perl script to interact
> with. When I do either or both of the following:
> 
>      1) set the user's shell to /usr/bin/myperlscript
> 
>      2) specify ForceCommand /usr/bin/myperlscript, applied to my user
> 
> ...I get strange behavior when a command is appended to the client
> connect command in this way:
> 
>      ssh -l user 192.168.1.2 ls /etc
> 
> The output from the perl script is not printed immediately but waits
> for a carriage return from the user before it is printed to the
> screen> Here is an example using a test perl script:
[...]
> You can see that what I type is taken as <STDIN> by the script, so I
> guess the output is stuck in a buffer somewhere. not sure if this is a
> bug in OpenSSH or a perl oddity. Or maybe I really shouldn't be
> setting my user's shell to be a script.
Try setting stdin/out to unbuffered in your perl script:

	select STDERR; $| = 1;
	select STDOUT; $| = 1;

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.