Messages in this thread | | | From | Andrej Presern <> | Subject | Re: Random Register Contents | Date | Tue, 3 Nov 1998 13:51:26 +0100 |
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On Mon, 02 Nov 1998, H. Peter Anvin wrote: >> > Also in theory it is a covert channel. >> >> Now _this_ I buy. Bug status confirmed, IMO. >> > >Not a covert channel, really (Linux doesn't protect against covert >channels in the classical sense[1] -- by design, as it is far too >expensive).
It seems to be too expensive because inappropriate security mechanisms are being used.
> What it is is an *information leak* -- giving something a >peephole into something they shouldn't have.
Information leaks through covert channels. This is one and the same problem. It is called 'how to confine an object such that it cannot leak information', ie the confinement problem.
On Mon, 02 Nov 1998, Alan Cox wrote: >Xenix B2 doesnt kill the file system - you dont need to. Remembering you >cant see another persons files if you are partitioned in a suitably paranoid >way Xenix B2 has an enforced 30 second delay on df and some similar stuff >on running out of disk space.
Since in a UNIX system authority to access a filesystem is basically tied to an identity (a user's id), how exactly does Xenix prevent a process from leaking information through the filesystem (or any other means, it's the same issue anyway) to another process by the same user?
Also, I will assume Xenix doesn't perform an equivalent of a 'chroot' to a duplicate filesystem tree when a user logs in since that would be simply too inefficient (feel free to correct me if I'm wrong since I'm not a Xenix expert) but simply hides filenames from the eyes of the observer (meaning files are still there, you just can't see them via ls and friends). So the user's files share the same filename space as the rest of the system. As soon as you are able to test for the availability of a specific filename, you have a possible filesystem based covert channel.
Andrej
-- Andrej Presern, andrejp@luz.fe.uni-lj.si
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