Re: problem using screen after running /bin/su

[Juergen Weigert]

On Aug 27, 04 17:50:33 +0200, Felix E. Klee wrote:
> On Fri, 27 Aug 2004 08:39:48 -0700 (PDT) Edward Quillen wrote:
> > Cannot open your terminal '/dev/pts/4' - please check.
> 
> I have the same problem under Linux. I found out that the device is
> owned by the user who started the terminal (emulator). Ordinary users
> cannot read/write from/to that device. 

And this is very good, the way it is. Otherwise, your 'ordinary user' could
try to read from the device while you were typing your password.

> The device seems to be central
> for IO; for example issuing
> 
>     echo "hello" > /dev/pts/4

Writing to a foreign tty is only a mild annouyance. 
But reading is a security risk.

> should output "hello" in the terminal. It's a while ago that I searched
> the web. All I could find were people saying that the above problem is a
> bug in screen.

What looks like a bug is actually a hand-crafted security feature.
Annoying sometimes, but protecting the innocent.

> 
> A workaround may involve setting the needed permissions before su'ing.

Correct. Best is to chown the device. A group or world readable tty is an
invitation to hackers. Or simply have your 'su' shell within the screen
session, if that is possible.

        cheers,
                Jw.

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