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SubjectRe: [RFC PATCH v2 1/3] ima: extend clone() with IMA namespace support
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On 03/15/2018 03:15 PM, Stefan Berger wrote:
> On 03/15/2018 03:01 PM, James Bottomley wrote:
>> On Thu, 2018-03-15 at 14:51 -0400, Stefan Berger wrote:
>>> On 03/15/2018 02:45 PM, James Bottomley wrote:
>> [...]
>>>>>> going to need some type of keyring namespace and there's
>>>>>> already
>>>>>> one hanging off the user_ns:
>>>>>>
>>>>>> commit f36f8c75ae2e7d4da34f4c908cebdb4aa42c977e
>>>>>> Author: David Howells <dhowells@redhat.com>
>>>>>> Date: Tue Sep 24 10:35:19 2013 +0100
>>>>>>
>>>>>> KEYS: Add per-user_namespace registers for persistent
>>>>>> per-UID
>>>>>> kerberos caches
>>>>> The benefit for IMA would be that this would then tie the keys
>>>>> needed for appraising to the IMA namespace's policy.
>>>>> However, if you have an appraise policy in your IMA namespace,
>>>>> which is now hooked to the user namespace, and you join that user
>>>>> namespace but your files don't have signatures, nothing will
>>>>> execute anymore. That's now a side effect of joining this user
>>>>> namespace unless we have a magic exception. My feeling is,
>>>>> people may not like that...
>>>> Agree, but I think the magic might be to populate the ima keyring
>>>> with the parent on user_ns creation. That way the user_ns owner
>>>> can delete the parent keys if they don't like them, but by default
>>>> the parent appraisal policy should just work.
>>> That may add keys to your keyring but doesn't get you signatures on
>>> your files.
>> But it doesn't need to. The only way we'd get a failure is if the file
>> is already being appraised and we lose access to the key. If the
>
> Well, the configuration I talked about above was assuming that we have
> an appraisal policy active in the IMA namespace, which is now tied to
> the user namespace that was just joined.
>
> If we are fine with the side effects of an IMA policy active as part
> of a user namespace then let's go with it. The side effects in case of
> an active IMA appraisal may then be that files cannot be
> read/accessed, or file measurements or IMA auditing may occur.
>
> The alternative is we have an independent IMA namespace. If one joins
> the USER namespace and there are no IMA-related side effects. If one
> joins the IMA namespace its IMA policy should start being enforced. If
> the current active USER namespace has the keys that go with the
> signatures of the filesystem, then we're fine from the appraisal
> perspective. If not, then IMA namespace joining may prevent file
> accesses.

With these differences pointed out, which path do we want to go now ?
Eric ? James ?

Stefan

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