Re: [PATCH v10 00/27] ima: Namespace IMA with audit support in IMA-ns

[Christian Brauner]

On Tue, Feb 01, 2022 at 03:37:08PM -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 is created when a user namespace is
> created, although this is done late when SecurityFS is mounted inside
> a user namespace. The advantage of piggy backing on the user namespace
> 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
> cp /sbin/busybox rootfs/bin/busybox2
> echo >> rootfs/bin/busybox2
> PATH=/bin unshare --user --map-root-user --mount-proc --pid --fork \
>   --root rootfs busybox sh -c \
>  "busybox mount -t securityfs /mnt /mnt; \
>   busybox echo 1 > /mnt/ima/active; \
>   busybox echo 'audit func=BPRM_CHECK mask=MAY_EXEC' > /mnt/ima/policy; \
>   busybox2 cat /mnt/ima/policy"
> 
> [busybox2 is used to demonstrate 2 audit messages; see below]
> 
> 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.
> 
> In the above the writing of '1' to the 'active' file is used to activate
> the IMA namespace. Future extensions to IMA namespaces will make use of
> the configuration stage after the mounting of securityfs and before the
> activation to for example choose the measurement log template.
> 
> 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 'busybox2 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.
> 
> My tree with these patches is here:
> 
> git fetch https://github.com/stefanberger/linux-ima-namespaces v5.16+imans.v10.posted
> 
> Regards,
>    Stefan
> 
> Links to previous postings:
> v1: https://lore.kernel.org/linux-integrity/20211130160654.1418231-1-stefanb@xxxxxxxxxxxxx/T/#t
> v2: https://lore.kernel.org/linux-integrity/20211203023118.1447229-1-stefanb@xxxxxxxxxxxxx/T/#t
> v3: https://lore.kernel.org/linux-integrity/6240b686-89cf-2e31-1c1b-ebdcf1e972c1@xxxxxxxxxxxxx/T/#t
> v4: https://lore.kernel.org/linux-integrity/20211207202127.1508689-1-stefanb@xxxxxxxxxxxxx/T/#t
> v5: https://lore.kernel.org/linux-integrity/20211208221818.1519628-1-stefanb@xxxxxxxxxxxxx/T/#t
> v6: https://lore.kernel.org/linux-integrity/20211210194736.1538863-1-stefanb@xxxxxxxxxxxxx/T/#t
> v7: https://lore.kernel.org/linux-integrity/20211217100659.2iah5prshavjk6v6@wittgenstein/T/#t
> v8: https://lore.kernel.org/all/20220104170416.1923685-1-stefanb@xxxxxxxxxxxxxxxxxx/#r
> v9: https://lore.kernel.org/linux-integrity/?t=20220131234353
> 
> v10:
>  - Added A-b's; addressed issues from v9
>  - Added 2 patches to support freeing of iint after namespace deletion
>  - Added patch to return error code from securityfs functions
>  - Added patch to limit number of policy rules in IMA-ns to 1024

I'm going to go take a lighter touch with this round of reviews.
First, because I have February off. :)
Second, because I think that someone who is more familiar with IMA and
its requirements should take another look to provide input and ask more
questions. Last time I spoke to Serge he did want to give this a longer
look and maybe also has additional questions.