Re: [uml-user] General security questions

[BlaisorBlade <bla...@ya...>]

Alle 10:18, mercoled=EC 24 dicembre 2003, Nikolaus Hammler ha scritto:
> Ist hostfs secure enough? When I mount the directory
> /mnt/media from the host system, can I make sure
> that's *not* possible to escape? To traverse other
> directories?

I don't think you should trust hostfs. Or better, if you say at the boot=20
hostfs=3Dpath(I'm not sure this is the right syntax, check), hostfs should =
be=20
safe. BUT:
1) there are some permission problems; if you are a plain user and create a=
=20
file on hostfs, you can't touch it anymore, as it will be owned by the user=
=20
running the UML
2) if anyone has root access on the UML, he can load a module; and he can l=
oad=20
even an crack_hostfs module which can access the host filesystem without=20
respecting that limit. It's a bit hard, and to know this know a bit UML; bu=
t=20
not that hard, and when UML will be shipped by all distros(which is already=
=20
happening) this will become frequent. And this can happen even if you don't=
=20
enable hostfs when compiling your UML kernel. If you disable module loading=
,=20
yet a true cracker can use some known technics(they are for i386, but=20
probably apply to UML, too) to load it anyway(if he's root on the guest).

To avoid this, you must chroot your UML; I'm not providing instructions her=
e,=20
but just search or ask.
Note: chrooting a process means that you make that process see, as its root=
=20
directory, a directory you choose before starting it. See man 1 chroot and=
=20
man 2 chroot.

> When I want to do network, there is a helper program
> that has Setuid-root. Is this a security risk?
If you care about security, avoid this(instructions on the web page). I've=
=20
never heard of exploits to it, but I neither heard of a proper security=20
auditing to it(but maybe I just missed it).

> Is it possible to gain access; even root privileges
> on the host system with that driver? I could not find
> any information concerning security on the webpage.
>
> What's the difference between UML and a real
> virtual machine? What happens when somebody attacks
> my virtual machine with a DOS attack? Does then only
> the virtual machine crash or is it possible to also
> crash the host system?
A DOS shouldn't crash a machine(at least a not-buggy/Linux one), but the lo=
ad=20
will be perceived even by the host.
> And what about buffer overflows?
> May they reach the host system?
>
> What about performance? How slow is the virtual system
> im comparison to a "real system"?
You want probably to change the TMPDIR variable to point at a place where y=
ou=20
mount a tmpfs; UML stores some files inside TMPDIR(normally /tmp) which=20
contain the guest memory, so if TMPDIR points to a RAM-based location this=
=20
will help performances(but increase memory consumption, maybe; it's not tha=
t=20
obvious, since probably tmpfs datas can be swapped out).

Bye
=2D-=20
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN