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Re: [libvirt] Notes from the KVM Forum relevant to libvirt



On Tue, Aug 23, 2011 at 4:31 PM, Daniel P. Berrange <berrange redhat com> wrote:
> On Tue, Aug 23, 2011 at 04:24:46PM +0100, Stefan Hajnoczi wrote:
>> On Tue, Aug 23, 2011 at 12:15 PM, Daniel P. Berrange
>> <berrange redhat com> wrote:
>> > I was at the KVM Forum / LinuxCon last week and there were many
>> > interesting things discussed which are relevant to ongoing libvirt
>> > development. Here was the list that caught my attention. If I have
>> > missed any, fill in the gaps....
>> >
>> >  - Sandbox/container KVM.  The Solaris port of KVM puts QEMU inside
>> >   a zone so that an exploit of QEMU can't escape into the full OS.
>> >   Containers are Linux's parallel of Zones, and while not nearly as
>> >   secure yet, it would still be worth using more containers support
>> >   to confine QEMU.
>>
>> Can you elaborate on why Linux containers are "not nearly as secure"
>> [as Solaris Zones]?
>
> Mostly because the Linux namespace functionality is far from complete,
> notably lacking proper UID/GID/capability separation, and UID/GID
> virtualization wrt filesystems. The longer answer is here:
>
>   https://wiki.ubuntu.com/UserNamespace
>
> So at this time you can't build a secure container on Linux, relying
> just on DAC alone. You have to add in a MAC layer ontop of the container
> to get full security benefits, which obviously defeats the point of
> using the container as a backup for failure in the MAC layer.

Thanks, that is interesting.  I still don't understand why that is a
problem.  Linux containers (lxc) uses a different pid namespace (no
ptrace worries), file system root (restricted to a subdirectory tree),
forbids most device nodes, etc.  Why does the user namespace matter
for security in this case?

I think it matters when giving multiple containers access to the same
file system.  Is that what you'd like to do for libvirt?

Stefan


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