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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 01B4FC43381 for ; Fri, 15 Mar 2019 21:39:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0036218A1 for ; Fri, 15 Mar 2019 21:39:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726404AbfCOVjs (ORCPT ); Fri, 15 Mar 2019 17:39:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34084 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725959AbfCOVjs (ORCPT ); Fri, 15 Mar 2019 17:39:48 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D20D93082B40; Fri, 15 Mar 2019 21:39:47 +0000 (UTC) Received: from sky.random (ovpn-121-1.rdu2.redhat.com [10.10.121.1]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A36055D6A6; Fri, 15 Mar 2019 21:39:45 +0000 (UTC) Date: Fri, 15 Mar 2019 17:39:44 -0400 From: Andrea Arcangeli To: zhong jiang Cc: Mike Rapoport , Peter Xu , Andrew Morton , Dmitry Vyukov , syzbot , Michal Hocko , cgroups@vger.kernel.org, Johannes Weiner , LKML , Linux-MM , syzkaller-bugs , Vladimir Davydov , David Rientjes , Hugh Dickins , Matthew Wilcox , Mel Gorman , Vlastimil Babka Subject: Re: KASAN: use-after-free Read in get_mem_cgroup_from_mm Message-ID: <20190315213944.GD9967@redhat.com> References: <00000000000006457e057c341ff8@google.com> <5C7BFE94.6070500@huawei.com> <5C7D2F82.40907@huawei.com> <5C7D4500.3070607@huawei.com> <5C7E1A38.2060906@huawei.com> <20190306020540.GA23850@redhat.com> <5C821550.50506@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5C821550.50506@huawei.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Fri, 15 Mar 2019 21:39:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 08, 2019 at 03:10:08PM +0800, zhong jiang wrote: > I can reproduce the issue in arm64 qemu machine. The issue will leave after applying the > patch. > > Tested-by: zhong jiang Thanks a lot for the quick testing! > Meanwhile, I just has a little doubt whether it is necessary to use RCU to free the task struct or not. > I think that mm->owner alway be NULL after failing to create to process. Because we call mm_clear_owner. I wish it was enough, but the problem is that the other CPU may be in the middle of get_mem_cgroup_from_mm() while this runs, and it would dereference mm->owner while it is been freed without the call_rcu affter we clear mm->owner. What prevents this race is the rcu_read_lock() in get_mem_cgroup_from_mm() and the corresponding call_rcu to free the task struct in the fork failure path (again only if CONFIG_MEMCG=y is defined). Considering you can reproduce this tiny race on arm64 qemu (perhaps tcg JIT timing variantions helps?), you might also in theory be able to still reproduce the race condition if you remove the call_rcu from delayed_free_task and you replace it with free_task.