Messages in this thread | | | Date | Wed, 10 Dec 1997 14:39:53 -0500 | From | "Theodore Y. Ts'o" <> | Subject | Re: [PATCH][2.1.71] BSD revoke() syscall |
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Date: Wed, 10 Dec 1997 15:32:43 +0000 (GMT) From: Chris Evans <chris@ferret.lmh.ox.ac.uk>
On Tue, 9 Dec 1997, Theodore Y. Ts'o wrote:
> The flip side is that the tty hangup isn't a full revoke, and > there are some (small) security issues if you have a process hanging > around after the logout.
Out of interest, what are these?
User A dials up to a linux machine, runs a program which opens /dev/tty and hangs around in the background. User A logs out, and User A's program catches signals so it doesn't exit. User B logs in, and starts to do work. User A's program can still execute a few limited tty ioctl's, including ones which can reconfigure termios settings, such as the baud rate, line echoeing, etc.
Note that if you want to run a secure dialup system, you'll have used the locked_termios feature to prevent user programs from modifying the certain termios configuration fields that users should have no business modifying (baud rate, RTS/CTS, CLOCAL, etc.) (CLOCAL is the important one to restrict, really).
However, the leftover program can still cause problems for user B by diddling the certain termios features.
I suppose the hack that would improve things would be to only allow root processes to play ioctl games on a hungup file descriptor.
- Ted
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