randstruct: Check member structs in is_pure_ops_struct()

While no uses in the kernel triggered this case, it was possible to have
a false negative where a struct contains other structs which contain only
function pointers because of unreachable code in is_pure_ops_struct().
Signed-off-by: Joonwon Kang <kjw1627@gmail.com>
Link: https://lore.kernel.org/r/20190727155841.GA13586@host
Fixes: 313dd1b6 ("gcc-plugins: Add the randstruct plugin")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

scripts/gcc-plugins/randomize_layout_plugin.c

@@ -443,13 +443,13 @@ static int is_pure_ops_struct(const_tree node)
 		if (node == fieldtype)
 			continue;
 
-		if (!is_fptr(fieldtype))
+		if (code == RECORD_TYPE || code == UNION_TYPE) {
+			if (!is_pure_ops_struct(fieldtype))
 				return 0;
-
-		if (code != RECORD_TYPE && code != UNION_TYPE)
 			continue;
+		}
 
-		if (!is_pure_ops_struct(fieldtype))
+		if (!is_fptr(fieldtype))
 			return 0;
 	}