Re: [linux-lvm] devices.filter changed behaviour in 80ac8f37d6

[Peter Rajnoha <prajnoha@redhat.com>]

On 09/07/2015 03:23 PM, Peter Rajnoha wrote:
> On 09/07/2015 03:08 PM, Chris Webb wrote:
>> Just one final thought. A second reason we deliberately exclude those
>> iSCSI devices is that they're actually the drives backing customer VMs,
>> so any LVM metadata on them should be interpreted by an untrusted guest
>> kernel and not by the host. Untrusted third parties have complete
>> control over the contents of the block devices.
>>
>> Is LVM well-secured against attacks from block devices containing
>> malicious LVM metadata? If not, an unexpected change in filtering
>> behaviour might potentially be a security issue in some environments.
>>
> 
> Before, we advised use of the filters to filter out all the LVM
> layout from guest's disks that is not supposed to be visible on
> host side that may interfere heavily with the LVM layout on the
> host then (e.g. same VG/LV names used inside guest as in host).
> 
> There's a new feature called "systemid" in LVM which got included
> in lvm2 v2.02.117. This one can be also used to solve this issue
> (without a need to define filters). Check also
> https://git.fedorahosted.org/cgit/lvm2.git/tree/man/lvmsystemid.7.in.

Of course, from security point of view, you need to take care that
your systemid is not stolen so that someone doesn't fake metadata inside
guest with that systemid.

There are several sources for systemid and you can choose which one you
want to use so it's pretty configurable. One of the sources is  completely
in your own hands - the "lvmlocal.conf" settings where you can define systemid
of your own (may it be a long, random and very hard to guess string).

-- 
Peter