livepatch: make object/func-walking helpers more robust

Current object-walking helper checks the presence of obj->funcs to
determine the end of objs array in klp_object structure. This is
somewhat fragile because one can easily forget about funcs definition
during livepatch creation. In such a case the livepatch module is
successfully loaded and all objects after the incorrect one are omitted.
This is very confusing. Let's make the helper more robust and check also
for the other external member, name. Thus the helper correctly stops on
an empty item of the array. We need to have a check for obj->funcs in
klp_init_object() to make it work.

The same applies to a func-walking helper.

As a benefit we'll check for new_func member definition during the
livepatch initialization. There is no such check anywhere in the code
now.

[jkosina@suse.cz: fix shortlog]
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Jessica Yu <jeyu@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

include/linux/livepatch.h

@@ -124,10 +124,12 @@ struct klp_patch {
 };
 
 #define klp_for_each_object(patch, obj) \
-	for (obj = patch->objs; obj->funcs; obj++)
+	for (obj = patch->objs; obj->funcs || obj->name; obj++)
 
 #define klp_for_each_func(obj, func) \
-	for (func = obj->funcs; func->old_name; func++)
+	for (func = obj->funcs; \
+	     func->old_name || func->new_func || func->old_sympos; \
+	     func++)
 
 int klp_register_patch(struct klp_patch *);
 int klp_unregister_patch(struct klp_patch *);

kernel/livepatch/core.c

@@ -683,6 +683,9 @@ static void klp_free_patch(struct klp_patch *patch)
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 {
+	if (!func->old_name || !func->new_func)
+		return -EINVAL;
+
 	INIT_LIST_HEAD(&func->stack_node);
 	func->state = KLP_DISABLED;