From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C6DEECDE5F for ; Mon, 23 Jul 2018 06:44:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D822E20875 for ; Mon, 23 Jul 2018 06:44:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D822E20875 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387965AbeGWHoZ (ORCPT ); Mon, 23 Jul 2018 03:44:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:36340 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387892AbeGWHoZ (ORCPT ); Mon, 23 Jul 2018 03:44:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0AF41AE6B; Mon, 23 Jul 2018 06:44:43 +0000 (UTC) Date: Mon, 23 Jul 2018 08:44:41 +0200 From: Michal Hocko To: Shakeel Butt Cc: jing.xia.mail@gmail.com, Johannes Weiner , Vladimir Davydov , chunyan.zhang@unisoc.com, Cgroups , Linux MM , LKML , Andrew Morton Subject: Re: [PATCH] mm: memcg: fix use after free in mem_cgroup_iter() Message-ID: <20180723064441.GA17905@dhcp22.suse.cz> References: <1531994807-25639-1-git-send-email-jing.xia@unisoc.com> <20180719104345.GV7193@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 19-07-18 09:23:10, Shakeel Butt wrote: > On Thu, Jul 19, 2018 at 3:43 AM Michal Hocko wrote: > > > > [CC Andrew] > > > > On Thu 19-07-18 18:06:47, Jing Xia wrote: > > > It was reported that a kernel crash happened in mem_cgroup_iter(), > > > which can be triggered if the legacy cgroup-v1 non-hierarchical > > > mode is used. > > > > > > Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b8f > > > ...... > > > Call trace: > > > mem_cgroup_iter+0x2e0/0x6d4 > > > shrink_zone+0x8c/0x324 > > > balance_pgdat+0x450/0x640 > > > kswapd+0x130/0x4b8 > > > kthread+0xe8/0xfc > > > ret_from_fork+0x10/0x20 > > > > > > mem_cgroup_iter(): > > > ...... > > > if (css_tryget(css)) <-- crash here > > > break; > > > ...... > > > > > > The crashing reason is that mem_cgroup_iter() uses the memcg object > > > whose pointer is stored in iter->position, which has been freed before > > > and filled with POISON_FREE(0x6b). > > > > > > And the root cause of the use-after-free issue is that > > > invalidate_reclaim_iterators() fails to reset the value of > > > iter->position to NULL when the css of the memcg is released in non- > > > hierarchical mode. > > > > Well, spotted! > > > > I suspect > > Fixes: 6df38689e0e9 ("mm: memcontrol: fix possible memcg leak due to interrupted reclaim") > > > > but maybe it goes further into past. I also suggest > > Cc: stable > > > > even though the non-hierarchical mode is strongly discouraged. > > Why not set root_mem_cgroup's use_hierarchy to true by default on > init? If someone wants non-hierarchical mode, they can explicitly set > it to false. We do not change defaults under users feet usually. -- Michal Hocko SUSE Labs