test_sysctl: add dedicated proc sysctl test driver

The existing tools/testing/selftests/sysctl/ tests include two test
cases, but these use existing production kernel sysctl interfaces.  We
want to expand test coverage but we can't just be looking for random
safe production values to poke at, that's just insane!

Instead just dedicate a test driver for debugging purposes and port the
existing scripts to use it.  This will make it easier for further tests
to be added.

Subsequent patches will extend our test coverage for sysctl.

The stress test driver uses a new license (GPL on Linux, copyleft-next
outside of Linux).  Linus was fine with this [0] and later due to Ted's
and Alans's request ironed out an "or" language clause to use [1] which
is already present upstream.

[0] https://lkml.kernel.org/r/CA+55aFyhxcvD+q7tp+-yrSFDKfR0mOHgyEAe=f_94aKLsOu0Og@mail.gmail.com
[1] https://lkml.kernel.org/r/1495234558.7848.122.camel@linux.intel.com

Link: http://lkml.kernel.org/r/20170630224431.17374-2-mcgrof@kernel.org
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -1785,6 +1785,17 @@ config TEST_FIRMWARE
 
 	  If unsure, say N.
 
+config TEST_SYSCTL
+	tristate "sysctl test driver"
+	default n
+	depends on PROC_SYSCTL
+	help
+	  This builds the "test_sysctl" module. This driver enables to test the
+	  proc sysctl interfaces available to drivers safely without affecting
+	  production knobs which might alter system functionality.
+
+	  If unsure, say N.
+
 config TEST_UDELAY
 	tristate "udelay test driver"
 	default n

lib/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
 obj-y += kstrtox.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
 obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
 obj-$(CONFIG_TEST_KASAN) += test_kasan.o
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o

lib/test_sysctl.c

@@ -0,0 +1,113 @@
+/*
+ * proc sysctl test driver
+ *
+ * Copyright (C) 2017 Luis R. Rodriguez <mcgrof@kernel.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or at your option any
+ * later version; or, when distributed separately from the Linux kernel or
+ * when incorporated into other software packages, subject to the following
+ * license:
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of copyleft-next (version 0.3.1 or later) as published
+ * at http://copyleft-next.org/.
+ */
+
+/*
+ * This module provides an interface to the the proc sysctl interfaces.  This
+ * driver requires CONFIG_PROC_SYSCTL. It will not normally be loaded by the
+ * system unless explicitly requested by name. You can also build this driver
+ * into your kernel.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/async.h>
+#include <linux/delay.h>
+#include <linux/vmalloc.h>
+
+static int i_zero;
+static int i_one_hundred = 100;
+
+struct test_sysctl_data {
+	int int_0001;
+	char string_0001[65];
+};
+
+static struct test_sysctl_data test_data = {
+	.int_0001 = 60,
+	.string_0001 = "(none)",
+};
+
+/* These are all under /proc/sys/debug/test_sysctl/ */
+static struct ctl_table test_table[] = {
+	{
+		.procname	= "int_0001",
+		.data		= &test_data.int_0001,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &i_zero,
+		.extra2         = &i_one_hundred,
+	},
+	{
+		.procname	= "string_0001",
+		.data		= &test_data.string_0001,
+		.maxlen		= sizeof(test_data.string_0001),
+		.mode		= 0644,
+		.proc_handler	= proc_dostring,
+	},
+	{ }
+};
+
+static struct ctl_table test_sysctl_table[] = {
+	{
+		.procname	= "test_sysctl",
+		.maxlen		= 0,
+		.mode		= 0555,
+		.child		= test_table,
+	},
+	{ }
+};
+
+static struct ctl_table test_sysctl_root_table[] = {
+	{
+		.procname	= "debug",
+		.maxlen		= 0,
+		.mode		= 0555,
+		.child		= test_sysctl_table,
+	},
+	{ }
+};
+
+static struct ctl_table_header *test_sysctl_header;
+
+static int __init test_sysctl_init(void)
+{
+	test_sysctl_header = register_sysctl_table(test_sysctl_root_table);
+	if (!test_sysctl_header)
+		return -ENOMEM;
+	return 0;
+}
+late_initcall(test_sysctl_init);
+
+static void __exit test_sysctl_exit(void)
+{
+	if (test_sysctl_header)
+		unregister_sysctl_table(test_sysctl_header);
+}
+
+module_exit(test_sysctl_exit);
+
+MODULE_AUTHOR("Luis R. Rodriguez <mcgrof@kernel.org>");
+MODULE_LICENSE("GPL");

tools/testing/selftests/sysctl/config

@@ -0,0 +1 @@
+CONFIG_TEST_SYSCTL=y

tools/testing/selftests/sysctl/run_numerictests

@@ -1,7 +1,7 @@
 #!/bin/sh
 
-SYSCTL="/proc/sys"
-TARGET="${SYSCTL}/vm/swappiness"
+SYSCTL="/proc/sys/debug/test_sysctl/"
+TARGET="${SYSCTL}/int_0001"
 ORIG=$(cat "${TARGET}")
 TEST_STR=$(( $ORIG + 1 ))
 

tools/testing/selftests/sysctl/run_stringtests

@@ -1,7 +1,7 @@
 #!/bin/sh
 
-SYSCTL="/proc/sys"
-TARGET="${SYSCTL}/kernel/domainname"
+SYSCTL="/proc/sys/debug/test_sysctl/"
+TARGET="${SYSCTL}/string_0001"
 ORIG=$(cat "${TARGET}")
 TEST_STR="Testing sysctl"