livepatch: Fix kobject refcount bug on klp_init_patch_early failure path

When enabling a klp patch with klp_enable_patch(), klp_init_patch_early()
is invoked to initialize the kobjects for the patch itself, as well as the
'struct klp_object' and 'struct klp_func' objects that comprise it.
However, there are some error paths in klp_enable_patch() where some
kobjects may have been initialized with kobject_init(), but an error code
is still returned due to e.g. a 'struct klp_object' having a NULL funcs
pointer.

In these paths, the initial reference of the kobject of the 'struct
klp_patch' may never be released, along with one or more of its objects and
their functions, as kobject_put() is not invoked on the cleanup path if
klp_init_patch_early() returns an error code.

For example, if an object entry such as the following were added to the
sample livepatch module's klp patch, it would cause the vmlinux klp_object,
and its klp_func which updates 'cmdline_proc_show', to never be released:

static struct klp_object objs[] = {
	{
		/* name being NULL means vmlinux */
		.funcs = funcs,
	},
	{
		/* NULL funcs -- would cause reference leak */
		.name = "kvm",
	}, { }
};

Without this change, if CONFIG_DEBUG_KOBJECT is enabled, and the sample klp
patch is loaded, the kobjects (the patch, the vmlinux 'struct klp_object',
and its func) are observed as initialized, but never released, in the dmesg
log output.  With the change, these kobject references no longer fail to be
released as the error case is properly handled before they are initialized.

Signed-off-by: David Vernet <void@manifault.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

kernel/livepatch/core.c

@@ -862,14 +862,11 @@ static void klp_init_object_early(struct klp_patch *patch,
 	list_add_tail(&obj->node, &patch->obj_list);
 }
 
-static int klp_init_patch_early(struct klp_patch *patch)
+static void klp_init_patch_early(struct klp_patch *patch)
 {
 	struct klp_object *obj;
 	struct klp_func *func;
 
-	if (!patch->objs)
-		return -EINVAL;
-
 	INIT_LIST_HEAD(&patch->list);
 	INIT_LIST_HEAD(&patch->obj_list);
 	kobject_init(&patch->kobj, &klp_ktype_patch);
@@ -879,20 +876,12 @@ static int klp_init_patch_early(struct klp_patch *patch)
 	init_completion(&patch->finish);
 
 	klp_for_each_object_static(patch, obj) {
-		if (!obj->funcs)
-			return -EINVAL;
-
 		klp_init_object_early(patch, obj);
 
 		klp_for_each_func_static(obj, func) {
 			klp_init_func_early(obj, func);
 		}
 	}
-
-	if (!try_module_get(patch->mod))
-		return -ENODEV;
-
-	return 0;
 }
 
 static int klp_init_patch(struct klp_patch *patch)
@@ -1024,10 +1013,17 @@ err:
 int klp_enable_patch(struct klp_patch *patch)
 {
 	int ret;
+	struct klp_object *obj;
 
-	if (!patch || !patch->mod)
+	if (!patch || !patch->mod || !patch->objs)
 		return -EINVAL;
 
+	klp_for_each_object_static(patch, obj) {
+		if (!obj->funcs)
+			return -EINVAL;
+	}
+
+
 	if (!is_livepatch_module(patch->mod)) {
 		pr_err("module %s is not marked as a livepatch module\n",
 		       patch->mod->name);
@@ -1051,11 +1047,10 @@ int klp_enable_patch(struct klp_patch *patch)
 		return -EINVAL;
 	}
 
-	ret = klp_init_patch_early(patch);
-	if (ret) {
-		mutex_unlock(&klp_mutex);
-		return ret;
-	}
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
+	klp_init_patch_early(patch);
 
 	ret = klp_init_patch(patch);
 	if (ret)