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SubjectRe: [PATCH bpf-next v2 3/3] bpf: Update LSM selftests for bpf_ima_inode_hash
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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
>>

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