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

From: Stefan Berger
Date: Tue Jul 25 2017 - 16:11:43 EST

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.

IMA is about measuring things, logging what was executed, and finally someone looking at the measurement log and detecting 'things'. So at least one attack that needs to be prevented is a malicious person opening an IMA namespace, executing something malicious, and not leaving any trace on the host because all the logs went into the measurement list of the IMA namespace, which disappeared. That said, I am wondering whether there has to be a minimum set of namespaces (PID, UTS) providing enough 'isolation' that someone may actually open an IMA namespace and run their code. To avoid leaving no traces one could argue to implement recursive logging, so something that is logged inside the namespace will be detected in all parent containers up to the init_ima_ns (host) because it's logged (and TPM extended) there as well. The challenge with that is that logging costs memory and that can be abused as well until the machine needs a reboot... I guess the solution could be requesting an IMA namespace in one way or another but requiring several other namespace flags in the clone() to actually 'get' it. Jumping namespaces with setns() may have to be restricted as well once there is an IMA namespace.

Stefan


Mimi