Re: [PATCH v3 00/16] ima: Namespace IMA with audit support in IMA-ns

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On 12/7/21 10:17, Christian Brauner wrote:

On Mon, Dec 06, 2021 at 12:25:44PM -0500, Stefan Berger wrote:
The goal of this series of patches is to start with the namespacing of
IMA and support auditing within an IMA namespace (IMA-ns) as the first
step.

In this series the IMA namespace is piggy backing on the user namespace
and therefore an IMA namespace gets created when a user namespace is
created. The advantage of this is that the user namespace can provide
the keys infrastructure that IMA appraisal support will need later on.

We chose the goal of supporting auditing within an IMA namespace since it
requires the least changes to IMA. Following this series, auditing within
an IMA namespace can be activated by a user running the following lines
that rely on a statically linked busybox to be installed on the host for
execution within the minimal container environment:

mkdir -p rootfs/{bin,mnt,proc}
cp /sbin/busybox rootfs/bin
PATH=/bin unshare --user --map-root-user --mount-proc --pid --fork \
   --root rootfs busybox sh -c \
  "busybox mount -t securityfs /mnt /mnt; \
   busybox echo 'audit func=BPRM_CHECK mask=MAY_EXEC' > /mnt/ima/policy; \
   busybox cat /mnt/ima/policy"

Following the audit log on the host the last line cat'ing the IMA policy
inside the namespace would have been audited. Unfortunately the auditing
line is not distinguishable from one stemming from actions on the host.
The hope here is that Richard Brigg's container id support for auditing
would help resolve the problem.

The following lines added to a suitable IMA policy on the host would
cause the execution of the commands inside the container (by uid 1000)
to be measured and audited as well on the host, thus leading to two
auditing messages for the 'busybox cat' above and log entries in IMA's
system log.

echo -e "measure func=BPRM_CHECK mask=MAY_EXEC uid=1000\n" \
         "audit func=BPRM_CHECK mask=MAY_EXEC uid=1000\n" \
     > /sys/kernel/security/ima/policy

The goal of supporting measurement and auditing by the host, of actions
occurring within IMA namespaces, is that users, particularly root,
should not be able to evade the host's IMA policy just by spawning
new IMA namespaces, running programs there, and discarding the namespaces
again. This is achieved through 'hierarchical processing' of file
accesses that are evaluated against the policy of the namespace where
the action occurred and against all namespaces' and their policies leading
back to the root IMA namespace (init_ima_ns).

The patch series adds support for a virtualized SecurityFS with a few
new API calls that are used by IMA namespacing. Only the data relevant
to the IMA namespace are shown. The files and directories of other
security subsystems (TPM, evm, Tomoyo, safesetid) are not showing
up when secruityfs is mounted inside a user namespace.

Much of the code leading up to the virtualization of SecurityFS deals
with moving IMA's variables from various files into the IMA namespace
structure called 'ima_namespace'. When it comes to determining the
current IMA namespace I took the approach to get the current IMA
namespace (get_current_ns()) on the top level and pass the pointer all
the way down to those functions that now need access to the ima_namespace
to get to their variables. This later on comes in handy once hierarchical
processing is implemented in this series where we walk the list of
namespaces backwards and again need to pass the pointer into functions.

This patch also introduces usage of CAP_MAC_ADMIN to allow access to the
IMA policy via reduced capabilities. We would again later on use this
capability to allow users to set file extended attributes for IMA appraisal
support.

The basis for this series of patches is Linux v5.15.
My tree with these patches is here:
https://github.com/stefanberger/linux-ima-namespaces/tree/v5.15%2Bimans.v3.public
I have one small procedural favor to ask. :)

I couldn't apply your patch series directly. It if isn't too
inconvenient for you could you pass --base with a proper upstream tag,
e.g. --base=v5.15.

The branch you posted here doesn't exist afaict and I had to peruse your
github repo and figured the correct branch might be v5.15+imans.v3.posted.

In any case, --base with a proper upstream tag would make this all a bit
easier or - if it really is necessary to pull from your tree it would be
nice if you could post it in a form directly consumable by git and note
url-escaped. So something like

git clone https://github.com/stefanberger/linux-ima-namespaces v5.15+imans.v3.posted

would already help.

Sure, will do.

  Stefan



Christian



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