using chroot option for ntpd

[Martin Pitt]

Hi!

Zach [2005-07-23 17:27 -0400]:
> But you still need the device node to mount or else have mknod, right?

So what, use mknod(2) to create it. :-)

>  At any rate chrooting a service running as root, I do not believe is
> a pointless endeavor.  Am I wrong on this?

mount(2) should work in most cases. Another method is to call fchdir()
on an open file descriptor that lives outside the chroot, then call
chdir("..") a couple of times, and then call chroot("."). This works
for processes that communicate with the outside world; if that is not
the case, then you can even create your own fake "outside directory" by
creating a directory, opening it, chrooting into it, and then using
the descriptor of that directory as your "outside file".

I have heard that there are some more ways to break out which involve
shared memory and pivot_root(), but I don't know the details of these.
Google should help. :-)

Kernel patches like grsecurity have some very cool counter measures
against breaking out of a chroot, which make escaping at least much
harder. With the default Linux kernel there is no hope, though; root
is just almighty.

Martin

-- 
Martin Pitt        http://www.piware.de
Ubuntu Developer   http://www.ubuntu.com
Debian Developer   http://www.debian.org
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