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 D32F4ECDE5F for ; Thu, 19 Jul 2018 10:43:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A2152084E for ; Thu, 19 Jul 2018 10:43:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A2152084E 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 S1730732AbeGSL0W (ORCPT ); Thu, 19 Jul 2018 07:26:22 -0400 Received: from mx2.suse.de ([195.135.220.15]:52162 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727285AbeGSL0W (ORCPT ); Thu, 19 Jul 2018 07:26:22 -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 B8193ADBE; Thu, 19 Jul 2018 10:43:47 +0000 (UTC) Date: Thu, 19 Jul 2018 12:43:45 +0200 From: Michal Hocko To: Jing Xia Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com, chunyan.zhang@unisoc.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] mm: memcg: fix use after free in mem_cgroup_iter() Message-ID: <20180719104345.GV7193@dhcp22.suse.cz> References: <1531994807-25639-1-git-send-email-jing.xia@unisoc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1531994807-25639-1-git-send-email-jing.xia@unisoc.com> 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 [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. A lack of reports for 3 years is encouraging that not many people really use this mode. > Signed-off-by: Jing Xia Acked-by: Michal Hocko Thanks! > --- > mm/memcontrol.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e6f0d5e..8c0280b 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -850,7 +850,7 @@ static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg) > int nid; > int i; > > - while ((memcg = parent_mem_cgroup(memcg))) { > + for (; memcg; memcg = parent_mem_cgroup(memcg)) { > for_each_node(nid) { > mz = mem_cgroup_nodeinfo(memcg, nid); > for (i = 0; i <= DEF_PRIORITY; i++) { > -- > 1.9.1 -- Michal Hocko SUSE Labs