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

[James Bottomley]

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.ÂÂLet 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.ÂÂIs 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. ÂOn
> 
> Mostly the latter.ÂÂThe other would be not so much space concerns as
> time concerns.ÂÂMany 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. ÂI 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? ÂThat'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?

James