On 8/29/19 10:47 AM, Florian Weimer wrote:
* Stefan Liebler:
On 8/28/19 11:24 AM, Florian Weimer wrote:
* Stefan Liebler:
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 ();
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
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)
If you execve pldd from subprocess 1, wouldn't subprocess 2 in its
ptrace scope for ptrace_scope < 2?
Yes, this is possible.
I've rearranged the subprocesses. See attached patch.
Now we have a new function pldd_process which forks target_process,
stores the pid of target_prcess to a shared memory mapping as do_test needs to know this pid.
Afterwards it execve to pldd which successfully ptrace target_process in case of "restricted ptrace".
Please review the usage of support-subprocess-functions.
Author: Stefan Liebler <email@example.com>
Date: Mon Aug 26 15:45:07 2019 +0200
Add UNSUPPORTED check in elf/tst-pldd.
The testcase forks a child process and runs pldd with PID of
this child. On systems where /proc/sys/kernel/yama/ptrace_scope
differs from zero, pldd will fail with
/usr/bin/pldd: cannot attach to process 3: Operation not permitted
This patch checks if ptrace_scope exists, is zero "classic ptrace permissions"
or one "restricted ptrace". If ptrace_scope exists and has a higher
restriction, then the test is marked as UNSUPPORTED.
The case "restricted ptrace" is handled by rearranging the processes involved
during the test. Now we have the following process tree:
-parent: do_test (performs output checks)
--subprocess 1: pldd_process (becomes pldd via execve)
---subprocess 2: target_process (ptraced via pldd)
* elf/tst-pldd.c (do_test): Add UNSUPPORTED check.
(pldd_process): New function.
* support/Makefile (libsupport-routines): Add support_ptrace.
* support/ptrace.h: New file.
* support/support_ptrace.c: Likewise.