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

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Message-ID: <cf0d94ca-b6a0-1a1a-6cf2-a641002588bf@fb.com>
Date:   Mon, 23 Nov 2020 10:36:05 -0800
From:   Yonghong Song <yhs@...com>
To:     KP Singh <kpsingh@...omium.org>, 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>,
        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



On 11/23/20 10:27 AM, KP Singh wrote:
> [...]
> 
>>>>
>>>> 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

Look at sk_assign test.

sk_assign.c:    if (CHECK_FAIL(system("ip link set dev lo up")))
sk_assign.c:    if (CHECK_FAIL(system("ip route add local default dev lo")))
sk_assign.c:    if (CHECK_FAIL(system("ip -6 route add local default dev 
lo")))
sk_assign.c:    if (CHECK_FAIL(system("tc qdisc add dev lo clsact")))
sk_assign.c:    if (CHECK(system(tc_cmd), "BPF load failed;"

You can use "system" to invoke some bash commands to simulate a script
in the tests.

> 
> - KP
> 
>>
>> Mimi
>>