Re: [PATCH] Add UNSUPPORTED check in elf/tst-pldd.

[Florian Weimer <fweimer@redhat.com>]

* Stefan Liebler:

> On 8/28/19 11:24 AM, Florian Weimer wrote:
>> * Stefan Liebler:
>>
>>>   static void
>>>   target_process (void *arg)
>>>   {
>>> +  if (ptrace_scope == 1)
>>> +    {
>>> +      /* YAMA is configured to "restricted ptrace".
>>> +	 Disable the restriction for this subprocess.  */
>>> +      support_ptrace_process_set_ptracer_any ();
>>> +    }
>>> +
>>>     pause ();
>>>   }
>>
>> I think this has a race condition if pldd attaches to the process before
>> the support_ptrace_process_set_ptracer_any call.  I have no idea how
>> hard it is in practice to hit this race.  It should be possible to use a
>> process-shared barrier or some other form of synchronization to avoid
>> this issue.
>>
>> Thanks,
>> Florian
>>
>
> I've added a synchronization with stdatomic.h on a shared memory mapping.
> I've not used pthread* functions as I don't want to link against
> libpthread.so. Then further adjustments are needed.
>
> Or should I just restrict the test ptrace_scope 0 as Adhemerval has
> proposed in his post?

Is it possible to create a process tree like this?


  parent (performs output checks)
    subprocess 1 (becomes pldd via execve)
      subprocess 2

If you execve pldd from subprocess 1, wouldn't subprocess 2 in its
ptrace scope for ptrace_scope < 2?

Thanks,
Florian