Re: tty locks up

[Nicholas Tufar <nt@xxxxxxxxxxxxxxx>]

On Wed, 30 Jun 1999, Sharad Joshi wrote:

> Hi,
> 
> Let user A use ttyp0
> Let user B use ttyq1
> 
> Now B can do this from his terminal:  cat < /dev/ttyp0 > /dev/null&
> And thus, A will be locked for ever. Moreover, he can not just find out
> what is happening. Nor can he log out. Also, the ps listing shows just
> "cat" for the user B and thus no one can know what is happening to the
> terminal ttyp0. User A is on the mercy of B.
> 
> Isn't this serious? Is there any way to find out who is reading a
> terminal. And how to overcome the above problem.

check the permissions of /dev/tty?? files.  When someone logs in system
sets the oner of appropriate device file to user's id and mode to 
620(rw--w----), so that other users from the same group can
send write and talk messages.  You can change it with mesg n.


Nicholas


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