Re: seccomp ptrace selftest failures with 4.4-stable [Was: Re: LTS testing with latest kselftests - some failures]

[Andy Lutomirski]

On Thu, Jun 22, 2017 at 10:09 AM, Shuah Khan <shuah@xxxxxxxxxx> wrote:
> On 06/22/2017 10:53 AM, Kees Cook wrote:
>> On Thu, Jun 22, 2017 at 9:18 AM, Sumit Semwal <sumit.semwal@xxxxxxxxxx> wrote:
>>> Hi Kees, Andy,
>>>
>>> On 15 June 2017 at 23:26, Sumit Semwal <sumit.semwal@xxxxxxxxxx> wrote:
>>>> 3. 'seccomp ptrace hole closure' patches got added in 4.7 [3] -
>>>> feature and test together.
>>>> - This one also seems like a security hole being closed, and the
>>>> 'feature' could be a candidate for stable backports, but Arnd tried
>>>> that, and it was quite non-trivial. So perhaps  we'll need some help
>>>> from the subsystem developers here.
>>>
>>> Could you please help us sort this out? Our goal is to help Greg with
>>> testing stable kernels, and currently the seccomp tests fail due to
>>> missing feature (seccomp ptrace hole closure) getting tested via
>>> latest kselftest.
>>>
>>> If you feel the feature isn't a stable candidate, then could you
>>> please help make the test degrade gracefully in its absence?
>>
>> I don't really want to have that change be a backport -- it's quite
>> invasive across multiple architectures.
>>
>> I would say just add a kernel version check to the test. This is
>> probably not the only selftest that will need such things. :)
>
> Adding release checks to selftests is going to problematic for maintenance.
> Tests should fail gracefully if feature isn't supported in older kernels.
>
> Several tests do that now and please find a way to check for dependencies
> and feature availability and fail the test gracefully. If there is a test
> that can't do that for some reason, we can discuss it, but as a general
> rule, I don't want to see kselftest patches that check release.

If a future kernel inadvertently loses the new feature and degrades to
the behavior of old kernels, that would be a serious bug and should be
caught.

--Andy