linux-kernel - Re: [RFC PATCH v2 1/3] ima: extend clone() with IMA namespace support

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Date:   Thu, 22 Mar 2018 12:47:14 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     mkayaalp@...binghamton.edu,
        Mehmet Kayaalp <mkayaalp@...ux.vnet.ibm.com>,
        sunyuqiong1988@...il.com, containers@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, david.safford@...com,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, zohar@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH v2 1/3] ima: extend clone() with IMA namespace support

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@...hat.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
> parent policy isn't appraisal, entering the IMA NS won't cause
> appraisal to be turned on unless the owner asks for it, in which case
> it's caveat emptor: As it works today, if as root I add a default
> appraisal policy to IMA without either a key or xattrs, I get an
> unusable system.

When I post a next implementation for the spawning if an IMA namespace, 
what shall be the criterion for accepting it?

     Stefan

>
> James
>
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