From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 356536B0003 for ; Mon, 23 Jul 2018 02:44:45 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id d18-v6so5429991edp.0 for ; Sun, 22 Jul 2018 23:44:45 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id k2-v6si1227239eda.433.2018.07.22.23.44.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 22 Jul 2018 23:44:43 -0700 (PDT) Date: Mon, 23 Jul 2018 08:44:41 +0200 From: Michal Hocko 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: Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt Cc: jing.xia.mail@gmail.com, Johannes Weiner , Vladimir Davydov , chunyan.zhang@unisoc.com, Cgroups , Linux MM , LKML , Andrew Morton 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