Re: [PATCH] selftests/landlock: skip ptrace_test when YAMA is enabled

["Mickaël Salaün" <mic@digikod.net>]

On 16/07/2022 23:45, Guenter Roeck wrote:
> On Fri, Jul 15, 2022 at 5:17 PM Jeff Xu <jeffxu@google.com> wrote:
>>
>>> Maybe the error code returned from mount gives a hint.
>>
>> It returns -1
>>
> Sorry, I meant errno, not the return value.
> 
>>>
>>> Also, how about
>>> /proc/filesystems ?
>>
>> Yes. it has what I want:
>> nodev overlay
>>
> Excellent.
> 
> Guenter
> 
>> Thanks for your help! I can use this at runtime check.
>>
>> Jeff
>>
>>
>> On Fri, Jul 15, 2022 at 3:42 PM Guenter Roeck <groeck@google.com> wrote:
>>>
>>> On Fri, Jul 15, 2022 at 2:42 PM Jeff Xu <jeffxu@google.com> wrote:
>>>>
>>>> Jeff Xu <jeffxu@google.com>
>>>>
>>>>> Jul 14, 2022, 5:35 PM (20 hours ago)
>>>>> to Guenter, Mickaël, linux-security-module, Jorge, Guenter, Kees
>>>>>> On Thu, Jul 14, 2022 at 11:37 AM Jeff Xu <jeffxu@google.com> wrote:
>>>>>>>
>>>>>>>>>> Hmm, well, it is not related to Yama then. Could it be linked to other
>>>>>>>>>> Chromium OS non-upstream patches?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> fs_test.c 47 and 48 are failing in chromeOS because OVERLAYFS is not
>>>>>>>>> enabled in chromeOS.
>>>>>>>>> If there is a reliable way of detecting OVERLAYFS (checking mount
>>>>>>>>> overlayfs is successful ? ), this is a good candidate to add SKIP.
>>>>>>>>>
>>>>>>>
>>>>>>>> IS_ENABLED(CONFIG_OVERLAY_FS) ?
>>>>>>>
>>>>>>> Could be. Landlock selftest currently is a user space program though,
>>>>>>> IS_ENABLED will depend on the kernel header during compile time.
>>>>>>>
>>>>
>>>>
>>>>
>>>>>> Ah, sorry, I thought it was an in-kernel test. Userspace should be
>>>>>> able to determine if overlayfs is supported by checking /sys/fs/ or
>>>>>> possibly /proc/fs/.
>>>>
>>>>
>>>>> Thanks for clarifying.
>>>>
>>>>
>>>>> lsmod might be the one, such as:
>>>>> lsmod | grep overlayfs
>>>>
>>>>
>>>> I built a kernel with overlayfs on chromeos, and lsmod didn't give me
>>>> what I wanted.
>>>> /sys/fs and /proc/fs also doesn't show anything about overlayfs
>>>>
>>>> @Mickaël Salaün
>>>> Are you OK with SKIP the overlay test when mount("overlay",...) fails
>>>> in FIXTURE_SETUP() ? Mount failure can be used as an indication.

In a normal scenario, all configurations in 
tools/testing/selftests/landlock/config should be enabled, but I think 
it makes sense for some use cases like chromeOS to be able to not fail 
if overlayfs is not supported. Please patch 
FIXTURE_SETUP(layout2_overlay) to skip these tests if the related 
filesystem string is present (with or without "nodev") in 
/proc/filesystems . You can create a is_filesystem_supported(const char 
*filesystem) helper before prepare_layout() for this check, we'll need 
it for future tests.


>>>>
>>>
>>> Maybe the error code returned from mount gives a hint. Also, how about
>>> /proc/filesystems ?
>>>
>>> Guenter