test: add openat2() test for invalid upper 32 bit flag value

Test that openat2() rejects unknown flags in the upper 32 bit range.

Link: https://lore.kernel.org/r/20210528092417.3942079-4-brauner@kernel.org
Cc: Richard Guy Briggs <rgb@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

tools/testing/selftests/openat2/openat2_test.c

@@ -155,7 +155,7 @@ struct flag_test {
 	int err;
 };
 
-#define NUM_OPENAT2_FLAG_TESTS 24
+#define NUM_OPENAT2_FLAG_TESTS 25
 
 void test_openat2_flags(void)
 {
@@ -229,6 +229,11 @@ void test_openat2_flags(void)
 		{ .name = "invalid how.resolve and O_PATH",
 		  .how.flags = O_PATH,
 		  .how.resolve = 0x1337, .err = -EINVAL },
+
+		/* currently unknown upper 32 bit rejected. */
+		{ .name = "currently unknown bit (1 << 63)",
+		  .how.flags = O_RDONLY | (1ULL << 63),
+		  .how.resolve = 0, .err = -EINVAL },
 	};
 
 	BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_OPENAT2_FLAG_TESTS);