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 15:06:05 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Mimi Zohar <zohar@...ux.ibm.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>
Subject: Re: [PATCH bpf-next v2 3/3] bpf: Update LSM selftests for bpf_ima_inode_hash

On Mon, Nov 23, 2020 at 2:24 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> On Sat, 2020-11-21 at 00:50 +0000, KP Singh wrote:
> > From: KP Singh <kpsingh@...gle.com>
> >
> > - Update the IMA policy before executing the test binary (this is not an
> >   override of the policy, just an append that ensures that hashes are
> >   calculated on executions).
>
> Assuming the builtin policy has been replaced with a custom policy and
> CONFIG_IMA_WRITE_POLICY is enabled, then yes the rule is appended.   If
> a custom policy has not yet been loaded, loading this rule becomes the
> defacto custom policy.
>
> 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?

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?

- KP

>
> Mimi
>