BSD tty security, part 3: How to Fix It

[Dan Bernstein]

In article <128049 at tyrell.stgt.sub.org> rodney at tyrell.stgt.sub.org (Rodney Volz) writes:
> Sorry for interfering, but I really don't see the point in discussing
> "write". Write does not have any S-Bit,

It does under the tty group model in BSD 4.3. More precisely: write and
talk become setgid tty (typically group 4, btw), write either doesn't
allow shell escapes (this is easiest) or resets gids properly on shell
escapes, all ttys are set to group tty, and mesg uses only the
group-write bit. This is a required step in my plan, though it's a no-op
on most BSD systems out there. It would also not be necessary under a
sane talk/write model.

---Dan