test_sysctl: add simple proc_dointvec() case

Test against a simple proc_dointvec() case.  While at it, add a test
against INT_MAX.  Make sure INT_MAX works, and INT_MAX+1 will fail.
Also test negative values work.

Link: http://lkml.kernel.org/r/20170630224431.17374-5-mcgrof@kernel.org
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: 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>
diff --git a/lib/test_sysctl.c b/lib/test_sysctl.c
index b2163bfb..1472e1a 100644
--- a/lib/test_sysctl.c
+++ b/lib/test_sysctl.c
@@ -41,11 +41,15 @@
 
 struct test_sysctl_data {
 	int int_0001;
+	int int_0002;
+
 	char string_0001[65];
 };
 
 static struct test_sysctl_data test_data = {
 	.int_0001 = 60,
+	.int_0002 = 1,
+
 	.string_0001 = "(none)",
 };
 
@@ -61,6 +65,13 @@
 		.extra2         = &i_one_hundred,
 	},
 	{
+		.procname	= "int_0002",
+		.data		= &test_data.int_0002,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
 		.procname	= "string_0001",
 		.data		= &test_data.string_0001,
 		.maxlen		= sizeof(test_data.string_0001),