On Fri, 9 Feb 2001 [EMAIL PROTECTED] wrote:
> > the use of elevated security levels (which are necessary if
> > those flags are to have any force) has side effects that make
> > them useless on lots of systems (e.g., inability to run X).
>
> Inability to run X ?
>
> I'm running at level=3, and X is quite happy. *Starting* X is not
> possible (AFAIK) at level=3. Good thing it's fairly stable :-)
If X has open file descriptors for privileged devices for the purposes of
direct memory access, the debugging interfaces (and possibly exploits in
shared libraries) can be used to control the X server in such a way that
securelevels can be disabled or circumvented. This is because the
securelevel checks associated with devices are generally performed on the
open() event; the same effect that allows X to keep working after the
securelevel is raised allows an attacker to circumvent the protections.
Robert N M Watson FreeBSD Core Team, TrustedBSD Project
[EMAIL PROTECTED] NAI Labs, Safeport Network Services
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