Re: [RFC PATCH 1/5] ima: extend clone() with IMA namespace support

[Mimi Zohar]

On Tue, 2017-07-25 at 16:08 -0500, Serge E. Hallyn wrote:
> On Tue, Jul 25, 2017 at 04:57:57PM -0400, Mimi Zohar wrote:
> > On Tue, 2017-07-25 at 15:46 -0500, Serge E. Hallyn wrote:
> > > On Tue, Jul 25, 2017 at 04:11:29PM -0400, Stefan Berger wrote:
> > > > On 07/25/2017 03:48 PM, Mimi Zohar wrote:
> > > > >On Tue, 2017-07-25 at 12:08 -0700, James Bottomley wrote:
> > > > >>On Tue, 2017-07-25 at 14:04 -0500, Serge E. Hallyn wrote:
> > > > >>>On Tue, Jul 25, 2017 at 11:49:14AM -0700, James Bottomley wrote:
> > > > >>>>On Tue, 2017-07-25 at 12:53 -0500, Serge E. Hallyn wrote:
> > > > >>>>>On Thu, Jul 20, 2017 at 06:50:29PM -0400, Mehmet Kayaalp wrote:
> > > > >>>>>>
> > > > >>>>>>From: Yuqiong Sun <suny@xxxxxxxxxx>
> > > > >>>>>>
> > > > >>>>>>Add new CONFIG_IMA_NS config option.  Let clone() create a new
> > > > >>>>>>IMA namespace upon CLONE_NEWNS flag. Add ima_ns data structure
> > > > >>>>>>in nsproxy. ima_ns is allocated and freed upon IMA namespace
> > > > >>>>>>creation and exit. Currently, the ima_ns contains no useful IMA
> > > > >>>>>>data but only a dummy interface. This patch creates the
> > > > >>>>>>framework for namespacing the different aspects of IMA (eg.
> > > > >>>>>>IMA-audit, IMA-measurement, IMA-appraisal).
> > > > >>>>>>
> > > > >>>>>>Signed-off-by: Yuqiong Sun <suny@xxxxxxxxxx>
> > > > >>>>>>
> > > > >>>>>>Changelog:
> > > > >>>>>>* Use CLONE_NEWNS instead of a new CLONE_NEWIMA flag
> > > > >>>>>Hi,
> > > > >>>>>
> > > > >>>>>So this means that every mount namespace clone will clone a new
> > > > >>>>>IMA namespace.  Is that really ok?
> > > > >>>>Based on what: space concerns (struct ima_ns is reasonably small)?
> > > > >>>>or whether tying it to the mount namespace is the correct thing to
> > > > >>>>do.  On
> > > > >>>Mostly the latter.  The other would be not so much space concerns as
> > > > >>>time concerns.  Many things use new mounts namespaces, and we
> > > > >>>wouldn't want multiple IMA calls on all file accesses by all of
> > > > >>>those.
> > > > >>>
> > > > >>>>the latter, it does seem that this should be a property of either
> > > > >>>>the mount or user ns rather than its own separate ns.  I could see
> > > > >>>>a use where even a container might want multiple ima keyrings
> > > > >>>>within the container (say containerised apache service with
> > > > >>>>multiple tenants), so instinct tells me that mount ns is the
> > > > >>>>correct granularity for this.
> > > > >>>I wonder whether we could use echo 1 > /sys/kernel/security/ima/newns
> > > > >>>as the trigger for requesting a new ima ns on the next
> > > > >>>clone(CLONE_NEWNS).
> > > > >>I could go with that, but what about the trigger being installing or
> > > > >>updating the keyring?  That's the only operation that needs namespace
> > > > >>separation, so on mount ns clone, you get a pointer to the old ima_ns
> > > > >>until you do something that requires a new key, which then triggers the
> > > > >>copy of the namespace and installing it?
> > > > >It isn't just the keyrings that need to be namespaced, but the
> > > > >measurement list and policy as well.
> > > > >
> > > > >IMA-measurement, IMA-appraisal and IMA-audit are all policy based.
> > > > >
> > > > >As soon as the namespace starts, measurements should be added to the
> > > > >namespace specific measurement list, not it's parent.
> > > 
> > > Shouldn't it be both?
> > 
> > The policy defines which files are measured. ÂThe namespace policy
> > could be different than it's parent's policy, and the parent's policy
> > could be different than the native policy. ÂBasically, file
> > measurements need to be added to the namespace measurement list,
> > recursively, up to the native measurement list.
> 
> Yes, but if a task t1 is in namespace ns2 which is a child of namespace ns1,
> and it accesses a file which ns1's policy says must be measured, then will
> ns1's required measurement happen (and be appended to the ns1 measurement
> list), whether or not ns2's policy requires it?

Yes, as the file needs to be measured only in the ns1 policy, the
measurement would exist in the ns1 measurement list, but not in the
ns2 measurement list. ÂThe pseudo code snippet below might help.

do {
   .
   .
   
   /* calculate file hash based on xattr algorithm */
   collect_measurement()
   
   /* recursively added to each namespace based on policy */
   ima_store_measurement()
   
   /* Based on the specific namespace policy and keys. */
   if (!once) {
       once = 1;
       result = ima_appraise_measurement()
   }

   ima_audit_measurement()

} while ((ns = ns->parent));

return result;

Mimi