linux-kernel - Re: [PATCH bpf-next v2 3/3] bpf: Update LSM selftests for bpf_ima_inode

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Date:   Mon, 23 Nov 2020 19:27:43 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     James Morris <jmorris@...ei.org>,
        open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Petr Vorel <pvorel@...e.cz>
Subject: Re: [PATCH bpf-next v2 3/3] bpf: Update LSM selftests for bpf_ima_inode_hash

[...]

> > >
> > > Even if a custom policy has been loaded, potentially additional
> > > measurements unrelated to this test would be included the measurement
> > > list.  One way of limiting a rule to a specific test is by loopback
> > > mounting a file system and defining a policy rule based on the loopback
> > > mount unique uuid.
> >
> > Thanks Mimi!
> >
> > I wonder if we simply limit this to policy to /tmp and run an executable
> > from /tmp (like test_local_storage.c does).
> >
> > The only side effect would be of extra hashes being calculated on
> > binaries run from /tmp which is not too bad I guess?
>
> The builtin measurement policy (ima_policy=tcb") explicitly defines a
> rule to not measure /tmp files.  Measuring /tmp results in a lot of
> measurements.
>
> {.action = DONT_MEASURE, .fsmagic = TMPFS_MAGIC, .flags = IMA_FSMAGIC},
>
> >
> > We could do the loop mount too, but I am guessing the most clean way
> > would be to shell out to mount from the test? Are there some other examples
> > of IMA we could look at?
>
> LTP loopback mounts a filesystem, since /tmp is not being measured with
> the builtin "tcb" policy.  Defining new policy rules should be limited
> to the loopback mount.  This would pave the way for defining IMA-
> appraisal signature verification policy rules, without impacting the
> running system.

+Andrii

Do you think we can split the IMA test out,
have a little shell script that does the loopback mount, gets the
FS UUID, updates the IMA policy and then runs a C program?

This would also allow "test_progs" to be independent of CONFIG_IMA.

I am guessing the structure would be something similar
to test_xdp_redirect.sh

- KP

>
> Mimi
>