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

[Stefan Berger]

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@xxxxxxxxxx>
> > > > > > 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