livepatch/core: Fix reference count issues

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SFHQ

--------------------------------

Fix following reference count issues where get 'obj->mod' once but put
twice:
  1) klp_register_patch
      klp_init_patch
          klp_init_object
              klp_find_object_module
                  try_module_get    <-- 1. Get refcount once
              klp_init_object_loaded    <-- 2. If fail here!!!
              module_put    <-- 3. Put refcount first time
      klp_free_patch_start
          klp_free_objects
              __klp_free_objects
                  module_put    <-- 4. 'obj->mod' not null, put twice!!!

  2) klp_register_patch
    klp_init_patch
        klp_init_object
            klp_find_object_module
                try_module_get    <-- 1. Get refcount once
        kobject_add    <-- 2. If other objs fail here!!!
        klp_free_objects_mod_limited
            module_put    <-- 3. Put refcount first time
    klp_free_patch_start
        klp_free_objects
            __klp_free_objects
                module_put    <-- 4. 'obj->mod' not null, put twice!!!

Fixes: c33e4283 ("livepatch/core: Allow implementation without ftrace")
Signed-off-by: NZheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: NXu Kuohai <xukuohai@huawei.com>
Reviewed-by: NCheng Jian <cj.chengjian@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

kernel/livepatch/core.c

@@ -811,8 +811,10 @@ static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
 
 	klp_for_each_object_safe(patch, obj, tmp_obj) {
 #ifdef CONFIG_LIVEPATCH_STOP_MACHINE_CONSISTENCY
-		if (klp_is_module(obj))
+		if (klp_is_module(obj) && obj->mod) {
 			module_put(obj->mod);
+			obj->mod = NULL;
+		}
 #endif
 		__klp_free_funcs(obj, nops_only);
 
@@ -1118,8 +1120,10 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
 
 out:
 #ifdef CONFIG_LIVEPATCH_STOP_MACHINE_CONSISTENCY
-	if (klp_is_module(obj))
+	if (klp_is_module(obj)) {
 		module_put(obj->mod);
+		obj->mod = NULL;
+	}
 #endif
 	return ret;
 }
@@ -1137,6 +1141,9 @@ static void klp_init_object_early(struct klp_patch *patch,
 	INIT_LIST_HEAD(&obj->func_list);
 	kobject_init(&obj->kobj, &klp_ktype_object);
 	list_add_tail(&obj->node, &patch->obj_list);
+#ifdef CONFIG_LIVEPATCH_STOP_MACHINE_CONSISTENCY
+	obj->mod = NULL;
+#endif
 }
 
 static int klp_init_patch_early(struct klp_patch *patch)
@@ -1187,8 +1194,10 @@ static void klp_free_objects_mod_limited(struct klp_patch *patch,
 	klp_for_each_object_safe(patch, obj, tmp_obj) {
 		if (limit == obj)
 			break;
-		if (klp_is_module(obj))
+		if (klp_is_module(obj) && obj->mod) {
 			module_put(obj->mod);
+			obj->mod = NULL;
+		}
 	}
 }
 #endif