From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753943AbdAZVuh (ORCPT ); Thu, 26 Jan 2017 16:50:37 -0500 Received: from mail-pf0-f193.google.com ([209.85.192.193]:36601 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753562AbdAZVuf (ORCPT ); Thu, 26 Jan 2017 16:50:35 -0500 Date: Thu, 26 Jan 2017 16:50:31 -0500 From: Tejun Heo To: Li Zefan , Johannes Weiner , cgroups@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Konstantin Khlebnikov , kernel-team@fb.com Subject: [PATCH cgroup/for-4.10-fixes] cgroup: don't online subsystems before cgroup_name/path() are operational Message-ID: <20170126215031.GD32152@htj.duckdns.org> References: <148542370148.63697.501199781041713381.stgit@buzz> <148542370808.63697.11031298116868200840.stgit@buzz> <20170126193754.GC32152@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170126193754.GC32152@htj.duckdns.org> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>From 07cd12945551b63ecb1a349d50a6d69d1d6feb4a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 26 Jan 2017 16:47:28 -0500 While refactoring cgroup creation, a5bca2152036 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") incorrectly onlined subsystems before the new cgroup is associated with it kernfs_node. This is fine for cgroup proper but cgroup_name/path() depend on the associated kernfs_node and if a subsystem makes the new cgroup_subsys_state visible, which they're allowed to after onlining, it can lead to NULL dereference. The current code performs cgroup creation and subsystem onlining in cgroup_create() and cgroup_mkdir() makes the cgroup and subsystems visible afterwards. There's no reason to online the subsystems early and we can simply drop cgroup_apply_control_enable() call from cgroup_create() so that the subsystems are onlined and made visible at the same time. Signed-off-by: Tejun Heo Reported-by: Konstantin Khlebnikov Fixes: a5bca2152036 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") Cc: stable@vger.kernel.org # v4.6+ --- Applied to cgroup/for-4.10-fixes. Thanks. kernel/cgroup.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 2ee9ec3..688dd02 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -5221,6 +5221,11 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp, return ERR_PTR(err); } +/* + * The returned cgroup is fully initialized including its control mask, but + * it isn't associated with its kernfs_node and doesn't have the control + * mask applied. + */ static struct cgroup *cgroup_create(struct cgroup *parent) { struct cgroup_root *root = parent->root; @@ -5288,11 +5293,6 @@ static struct cgroup *cgroup_create(struct cgroup *parent) cgroup_propagate_control(cgrp); - /* @cgrp doesn't have dir yet so the following will only create csses */ - ret = cgroup_apply_control_enable(cgrp); - if (ret) - goto out_destroy; - return cgrp; out_cancel_ref: @@ -5300,9 +5300,6 @@ static struct cgroup *cgroup_create(struct cgroup *parent) out_free_cgrp: kfree(cgrp); return ERR_PTR(ret); -out_destroy: - cgroup_destroy_locked(cgrp); - return ERR_PTR(ret); } static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, -- 2.9.3