syscalls/ptrace11: Add test for tracing init process

Before kernel 2.6.26, ptrace can't trace init process and will get
EPERM error. Now, it should succeed when we have enough privileges.

Signed-off-by: Yang Xu <[email protected]>

Author: xuyang0410

runtest/syscalls

@@ -1000,6 +1000,7 @@ ptrace07 ptrace07
 ptrace08 ptrace08
 ptrace09 ptrace09
 ptrace10 ptrace10
+ptrace11 ptrace11
 
 pwrite01 pwrite01
 pwrite02 pwrite02

testcases/kernel/syscalls/ptrace/.gitignore

@@ -7,3 +7,4 @@
 /ptrace08
 /ptrace09
 /ptrace10
+/ptrace11

testcases/kernel/syscalls/ptrace/ptrace11.c

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2020 FUJITSU LIMITED. All rights reserved.
+ * Author: Yang Xu <[email protected]>
+ *
+ * Before kernel 2.6.26, we can't trace init(1) process and ptrace() will
+ * get EPERM error. This case just check whether we can trace init(1)
+ * process and doesn't trigger error.
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <pwd.h>
+#include <config.h>
+#include <stdlib.h>
+#include "ptrace.h"
+#include "tst_test.h"
+
+static void verify_ptrace(void)
+{
+	TEST(ptrace(PTRACE_ATTACH, 1, NULL, NULL));
+	if (TST_RET == 0)
+		tst_res(TPASS, "ptrace() traces init process successfully");
+	else
+		tst_res(TFAIL | TTERRNO,
+			"ptrace() returns %ld, failed unexpectedly", TST_RET);
+
+	/*
+	 * Running attach/detach more times will trigger a ESRCH error because
+	 * ptrace_check_attach function in kernel will report it if its process
+	 * stats is not __TASK_TRACED.
+	 */
+	TST_RETRY_FUNC(ptrace(PTRACE_DETACH, 1, NULL, NULL), TST_RETVAL_EQ0);
+}
+
+static struct tst_test test = {
+	.test_all = verify_ptrace,
+	.needs_root = 1,
+};