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

On 9/2/19 9:37 PM, Adhemerval Zanella wrote:

On 29/08/2019 05:47, Florian Weimer wrote:
* 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.


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 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?

Do we really need that ad-hoc support on tst-pldd to make it support
ptrace_scope 1?

I don't oppose the support Stefan has added on latest iteration to
make it work, but this is a lot of code to support a very specific

As there are systems where ptrace_scope is configured to 1 by default, we should adjust the testcase as the FAIL is misleading. (I've just recognized that Steve Ellcey had also seen this FAIL:

The minimum change should be to detect ptrace_scope == 1 and mark the test as UNSUPPORTED. Or we change a bit more and let the test also run in this scenario. (Either by support_ptrace_process_set_ptracer_any or adjusting the subprocess-tree)


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