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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 27B5CC6786E for ; Fri, 26 Oct 2018 14:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EC7E620651 for ; Fri, 26 Oct 2018 14:39:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EC7E620651 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-security-module-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726159AbeJZXRA (ORCPT ); Fri, 26 Oct 2018 19:17:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48332 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726113AbeJZXRA (ORCPT ); Fri, 26 Oct 2018 19:17:00 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 75B2D30CF544; Fri, 26 Oct 2018 14:39:41 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.106]) by smtp.corp.redhat.com (Postfix) with SMTP id A68AA60BD6; Fri, 26 Oct 2018 14:39:38 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 26 Oct 2018 16:39:41 +0200 (CEST) Date: Fri, 26 Oct 2018 16:39:37 +0200 From: Oleg Nesterov To: Tetsuo Handa Cc: serge@hallyn.com, syzbot , jmorris@namei.org, keescook@chromium.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: KASAN: use-after-free Read in task_is_descendant Message-ID: <20181026143937.GA18848@redhat.com> References: <20181022134634.GA7358@redhat.com> <201810250215.w9P2Fm2M078167@www262.sakura.ne.jp> <20181025111355.GA3725@redhat.com> <20181025121709.GD3725@redhat.com> <20181025155503.GF3725@redhat.com> <3423a470-c152-0dbf-c7a7-2775a9679194@i-love.sakura.ne.jp> <20181026130442.GB10581@redhat.com> <522c4993-4d98-be98-def2-452ed28098f9@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <522c4993-4d98-be98-def2-452ed28098f9@i-love.sakura.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 26 Oct 2018 14:39:42 +0000 (UTC) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 10/26, Tetsuo Handa wrote: > > On 2018/10/26 22:04, Oleg Nesterov wrote: > >> Suppose p1 == p2->real_parent and p2 == p3->real_parent, and p1 exited > >> when p2 tried to attach on p1, p2->real_parent was pointing to already > >> (or about to be) freed p1. > > > > No, p2->real_parent will be updated. If p1 exits it will re-parent its > > children including p2. > > My error. > > Suppose p1 == p2->real_parent and p2 == p3->real_parent, and p1 exited > when someone tried to attach on p2, p2->real_parent was pointing to already > (or about to be) freed p1. I don't see a difference. If p1 exits it will re-parent p2, p2->real_parent will be updated. > So, the puzzle part is why p2->real_parent was still pointing p1 even after > p1 was freed... I don't understand the question. Once again. TASK->real_parent can point to the freed mem only if a) TASK exits, and b) _after_ that its parent TASK->real_parent exits too. > > Again, did you read my previous email? > > Yes. But I still can't be convinced that pid_alive() test helps. Well, I don't understand which part of my explanations is not clear to you. OR. Perhaps I am wrong and do not understand your concerns. Oleg.