Re: [PATCH 0/1] KEYS: Measure keys in trusted keyring

[Sasha Levin <sashal@kernel.org>]

On Mon, Sep 09, 2019 at 09:31:21AM -0400, Mimi Zohar wrote:
>On Tue, 2019-09-03 at 08:54 -0700, Lakshmi Ramasubramanian wrote:
>> On 8/30/19 11:41 AM, Mimi Zohar wrote:
>>
>> > No, the measurement list ima-sig template record contains both the
>> > file hash and signature.  There's no need to maintain a white list of
>> > either the file hashes or signed hashes.  All that is needed is the
>> > set of permitted public keys (eg. keys on the trusted IMA keyring).
>>
>> You are right - Thanks for the info.
>>
>> > Even though on the local system, files signed by the system owner
>> > would be permitted, the attestation server would be able to control
>> > access to whatever service.  For example, Trusted Network Connect
>> > (TNC) could control network access.  By measuring the keys on the
>> > builtin/secondary keyrings, that control is not based on who signed
>> > the software package, but based on who signed the certificate of the
>> > key that signed the software package.  My concern is how this level of
>> > indirection could be abused.
>> Since the signer of certificate of the key that signed the software
>> package changes much less frequently compared to the certificate of the
>> key used to sign the software package, the operational overhead on the
>> server side is significantly reduced.
>>
>> I understand there is another level of indirection here. But I am also
>> not clear how this can be abused.
>
>The remote attestation server could gate any service based on the
>certificate signer.  The first gated service, based on this feature,
>will probably be network access (eg. TNC).  If/when this feature is
>upstreamed, every company, including financial institutes,

I'm not sure why upstreaming this code will matter for those entities
you're concerned about. Any entity that provides a signed kernel image
is very well capable of including out of tree patches in that image.

>organizations, and governments will become THE certificate signer for
>their organization, in order to limit access to their network and
>systems.  Once that happens, how long will it be until the same
>feature will be abused and used to limit the individual's ability to
>pick and choose which applications may run on their systems.[1]

We do not restrict end use of the kernel; this is one of the main
reasons that the kernel is licensed under GPLv2 rather than GPLv3.
Please see https://lwn.net/Articles/200422/ .

We'd love to work with you on the technical aspects of this code to make
it acceptable to the IMA maintainers, but this work can't just be NACKed
based on a perceived end use of it.

--
Thanks,
Sasha