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=unavailable 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 B4D4EECDE46 for ; Thu, 25 Oct 2018 16:26:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 767CF20834 for ; Thu, 25 Oct 2018 16:26:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 767CF20834 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727465AbeJZA72 (ORCPT ); Thu, 25 Oct 2018 20:59:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51326 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727319AbeJZA72 (ORCPT ); Thu, 25 Oct 2018 20:59:28 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B639B308ED5F; Thu, 25 Oct 2018 16:25:58 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.106]) by smtp.corp.redhat.com (Postfix) with SMTP id D4154608F3; Thu, 25 Oct 2018 16:25:56 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 25 Oct 2018 18:25:57 +0200 (CEST) Date: Thu, 25 Oct 2018 18:25:54 +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: <20181025162554.GG3725@redhat.com> References: <76013c9e-0664-ef5e-b6c0-d48f6ce5db3c@i-love.sakura.ne.jp> <20181022134634.GA7358@redhat.com> <201810250215.w9P2Fm2M078167@www262.sakura.ne.jp> <20181025111355.GA3725@redhat.com> <20181025121709.GD3725@redhat.com> <20181025155503.GF3725@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181025155503.GF3725@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 25 Oct 2018 16:25:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/25, Oleg Nesterov wrote: > > Because our rcu read-lock critical section extends beyond the return from > synchronize_rcu(), and thus we must have a full memory barrier _between_ > that synchronize_rcu() and our rcu_read_lock(). We must see all memory updates, > including thread_pid = NULL which makes pid_alive() == F. In case I was not clear.... Suppose we have int X = 0. If some CPU does X = 1; synchronize_rcu(); and another CPU does rcu_read_lock(); x = X; rcu_read_unlock(); then x should be == 1 in case when rcu_read_unlock() happens _after_ return from synchronize_rcu(). Oleg.