Messages in this thread | | | Date | Fri, 28 Jan 2011 13:38:09 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH] System Wide Capability Bounding Set |
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Quoting Steve Grubb (sgrubb@redhat.com): > On Friday, January 28, 2011 01:49:01 pm Serge E. Hallyn wrote: > > > Using a wrapper program is a NOGO because the admin renting the machine > > > would be able to overwrite the wrapper and then they have arbitrary > > > code running with full privs and > > > > Not sure I've got this. Wrapper program in the VM he can over-write, > > but then he can overwrite the kernel too. > > No, because the kernel is only read in at boot. After that, /boot can disapear and it
And you can set it up so userspace cannot remount it, I assume?
> won't matter. It can be replaced with something and that won't matter because that's > not the real boot partition. > > > But what we are worried about is the host, so you must mean that. But if the > > wrapper program is of type noone_may_write_this_t, then wouldn't finding a way to > > replace that be as hard as overwriting the host kernel? > > No, because we aren't taking away the ability to mount or unmount. Not to mention that > root can replace his selinux policy so that next boot it doesn't define > noone_may_write_this_t. He might even put selinux in his VM in permissive. > > > Which, of course, still remains as a viable attack vector for the guest admin, > > whether you have this bounding set or not. > > No, with the bounding set, any external call the kernel makes has the bounding set > applied. This means we don't have to further restrict root in unnatural ways. > > > In other words, we have to accept that the TCB is always not just the > > kernel, but some user-space too. And yes, the wrapper program here > > would be part of the TCB. > > If you give someone root access in the VM, they probably want to set things up their > way. So, we really would like it if all the security mechanism were inside where they > can't be easily tampered with.
That's cool :)
Thanks for the elaboration, that's very interesting and helpful.
-serge
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