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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 8A72DC6786E for ; Fri, 26 Oct 2018 13:52:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4ACCE20665 for ; Fri, 26 Oct 2018 13:52:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4ACCE20665 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp 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 S1727256AbeJZW3Y (ORCPT ); Fri, 26 Oct 2018 18:29:24 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:14686 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726177AbeJZW3Y (ORCPT ); Fri, 26 Oct 2018 18:29:24 -0400 Received: from fsav107.sakura.ne.jp (fsav107.sakura.ne.jp [27.133.134.234]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w9QDpsAN084405; Fri, 26 Oct 2018 22:51:54 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav107.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav107.sakura.ne.jp); Fri, 26 Oct 2018 22:51:54 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav107.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157065137.bbtec.net [60.157.65.137]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w9QDpmrC084121 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 26 Oct 2018 22:51:53 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: KASAN: use-after-free Read in task_is_descendant To: Oleg Nesterov 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 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> <3423a470-c152-0dbf-c7a7-2775a9679194@i-love.sakura.ne.jp> <20181026130442.GB10581@redhat.com> From: Tetsuo Handa Message-ID: <522c4993-4d98-be98-def2-452ed28098f9@i-love.sakura.ne.jp> Date: Fri, 26 Oct 2018 22:51:42 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181026130442.GB10581@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. So, the puzzle part is why p2->real_parent was still pointing p1 even after p1 was freed... > > Again, did you read my previous email? Yes. But I still can't be convinced that pid_alive() test helps.