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On 2021/4/14 16:37, Stefan Hajnoczi wrote:
> On Wed, Apr 14, 2021 at 11:41:41AM +0800, Peng Tao wrote:
>> On 2021/4/12 22:46, Stefan Hajnoczi wrote:
>>> On Wed, Apr 07, 2021 at 05:07:05PM -0700, Eric Ernst wrote:
>>>> On Thu, Apr 1, 2021 at 7:58 AM Stefan Hajnoczi <stefanha at redhat.com> wrote:
>>>>> On Mon, Mar 29, 2021 at 04:49:31PM -0700, Eric Ernst wrote:
>>>
>>> BTW, one aspect of the draft that isn't clear to me:
>>>
>>>     the CSI driver will create a particular file, csiPlugin.json at the root of the volume on the host
>>>
>>> Can a malicious user put a csiPlugin.json file onto a persistent volume
>>> and then attach it to a Kata-enabled container to get the runtime and/or
>>> agent to execute mount commands either on the host or in the sandbox VM?
>>>
>> It is possible but it violates the current kata threat model, which is
>> basically we'd have to trust the host. If a user is able to gain root
>> privilege on the host, he/she is capable of doing anything to kata.
>>
>> That said, it is indeed possible to mitigate this by using an RPC based
>> approach between csi and kata.
> 
> If the host is already compromised then I don't expect Kata to protect
> anything.
> 
> My question was about k8s persistent volumes. I wanted to check that the
> csiPlugin.json file is not interpreted if present on a persistent
> volume. It should only be interpreted when the CSI driver places it
> there on the host. The text wasn't completely clear on whether the "root
> of the volume on the host" refers to the contents of the persistent
> volume itself (that's unsafe) or to the container runtime's host path
> (that's safe).
> 

Ah, good point! Kata needs to differentiate between a PV containing a 
csiPlugin.json file in it, and a CSI driver "hacked" host path. They are 
both host directories from Kata's point of view.

A possible method is to check if the host path is a mountpoint. Then
1. do not ever try to parse the csiPlugin.json file if it is a 
mountpoint, and
2. require csi to ensure that the volume host directory is not a 
mountpoint (IOW do not mount the volume to the host directory)

wdyt?

Cheers,
Tao