ioctl-ability, the TIOCCDTR problem

[Michael.Young%cmu-cs-g at sri-unix.UUCP]

One good reason for allowing ioctls on a tty you have a writeable
descriptor for is to allow setuid-someone-else (but maybe not root)
programs to do neat things for you (like present a visual display
of some sort).  It seems to me that writing on someone else's terminal
has almost as much negative potential as ioctl'ing it.  Don't
let your tty be writeable.  [With 4.2, one ought to be able to
set up an ipc port which can provide controlled (by tty owner)
access to one's tty.]

			Michael