This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] Add UNSUPPORTED check in elf/tst-pldd.
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?
Bye.
Stefan
commit e2aed097192c423dcf1882cb1c39567676ef2255
Author: Stefan Liebler <stli@linux.ibm.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". In case of "restricted ptrace", we can
effectively disable the restriction by using prctl (PR_SET_PTRACER_ANY).
If ptrace_scope exists and has a higher restriction, then the test
is marked as UNSUPPORTED.
ChangeLog:
* elf/tst-pldd.c (ptrace_scope, target_barrier): New variable.
(do_test): Add UNSUPPORTED check.
(target_process): Disable restricted ptrace.
* support/Makefile (libsupport-routines): Add support_ptrace.
* support/ptrace.h: New file.
* support/support_ptrace.c: Likewise.
diff --git a/elf/tst-pldd.c b/elf/tst-pldd.c
index 6b7c94a1c0..130d1f51db 100644
--- a/elf/tst-pldd.c
+++ b/elf/tst-pldd.c
@@ -30,10 +30,27 @@
#include <support/capture_subprocess.h>
#include <support/check.h>
#include <support/support.h>
+#include <support/ptrace.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+#include <stdatomic.h>
+
+static int ptrace_scope;
+static atomic_int *target_barrier;
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 ();
+ }
+
+ /* Ensure that pldd is called after ptrace restriction has been disabled. */
+ *target_barrier = 1;
+
pause ();
}
@@ -52,9 +69,24 @@ in_str_list (const char *libname, const char *const strlist[])
static int
do_test (void)
{
+ /* Check if our subprocess can be debugged with ptrace. */
+ ptrace_scope = support_ptrace_scope ();
+ if (ptrace_scope >= 2)
+ FAIL_UNSUPPORTED ("/proc/sys/kernel/yama/ptrace_scope >= 2");
+
+ target_barrier = (atomic_int *) xmmap (NULL, sizeof (int), PROT_READ | PROT_WRITE,
+ MAP_SHARED | MAP_ANONYMOUS, -1);
+ atomic_init (target_barrier, 0);
+
/* Create a copy of current test to check with pldd. */
struct support_subprocess target = support_subprocess (target_process, NULL);
+ /* Ensure that pldd is called after ptrace restriction has been disabled in
+ target_process. Do not use pthread synchronization functions here as the
+ test below expects not to be linked against libpthread. */
+ while (*target_barrier == 0)
+ ;
+
/* Run 'pldd' on test subprocess. */
struct support_capture_subprocess pldd;
{
@@ -129,6 +161,7 @@ do_test (void)
support_capture_subprocess_free (&pldd);
support_process_terminate (&target);
+ xmunmap (target_barrier, sizeof (int));
return 0;
}
diff --git a/support/Makefile b/support/Makefile
index ab66913a02..34d14eb1bb 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -56,6 +56,7 @@ libsupport-routines = \
support_format_hostent \
support_format_netent \
support_isolate_in_subprocess \
+ support_ptrace \
support_openpty \
support_paths \
support_quote_blob \
diff --git a/support/ptrace.h b/support/ptrace.h
new file mode 100644
index 0000000000..82f79ff25c
--- /dev/null
+++ b/support/ptrace.h
@@ -0,0 +1,36 @@
+/* Support functions handling ptrace_scope.
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef SUPPORT_PTRACE_H
+#define SUPPORT_PTRACE_H
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/* Return the current YAMA mode set on the machine (0 to 3) or -1
+ if YAMA is not supported. */
+int support_ptrace_scope (void);
+
+/* Effectively disables YAMA restriction for the calling process
+ if support_ptrace_scope returns 1 "restricted ptrace". */
+void support_ptrace_process_set_ptracer_any (void);
+
+__END_DECLS
+
+#endif
diff --git a/support/support_ptrace.c b/support/support_ptrace.c
new file mode 100644
index 0000000000..e9410384b5
--- /dev/null
+++ b/support/support_ptrace.c
@@ -0,0 +1,58 @@
+/* Support functions handling ptrace_scope.
+ Copyright (C) 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <support/check.h>
+#include <support/xstdio.h>
+#include <support/ptrace.h>
+#include <sys/prctl.h>
+
+int
+support_ptrace_scope (void)
+{
+ int ptrace_scope = -1;
+
+#ifdef __linux__
+ /* YAMA may be not enabled. Otherwise it contains a value from 0 to 3:
+ - 0 classic ptrace permissions
+ - 1 restricted ptrace
+ - 2 admin-only attach
+ - 3 no attach */
+ FILE *f = fopen ("/proc/sys/kernel/yama/ptrace_scope", "r");
+ if (f != NULL)
+ {
+ TEST_COMPARE (fscanf (f, "%d", &ptrace_scope), 1);
+ xfclose (f);
+ }
+#endif
+
+ return ptrace_scope;
+}
+
+void
+support_ptrace_process_set_ptracer_any (void)
+{
+#ifdef __linux__
+ int ret = prctl (PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
+ if (ret != 0)
+ FAIL_EXIT1 ("Failed to disable YAMA restriction. (prctl returned %d: %m)",
+ ret);
+#else
+ FAIL_UNSUPPORTED ("prctl (PR_SET_PTRACER, PR_SET_PTRACER_ANY, ...) "
+ "not supported!");
+#endif
+}