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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,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 8E344C18E5B for ; Tue, 10 Mar 2020 19:03:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 59C6A20637 for ; Tue, 10 Mar 2020 19:03:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727279AbgCJTDp (ORCPT ); Tue, 10 Mar 2020 15:03:45 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:60596 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726464AbgCJTDo (ORCPT ); Tue, 10 Mar 2020 15:03:44 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jBkAI-0002Hx-MC; Tue, 10 Mar 2020 13:03:42 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jBkA9-0004jE-TO; Tue, 10 Mar 2020 13:03:42 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Bernd Edlinger Cc: Christian Brauner , Kees Cook , Jann Horn , Jonathan Corbet , Alexander Viro , Andrew Morton , Alexey Dobriyan , Thomas Gleixner , Oleg Nesterov , Frederic Weisbecker , Andrei Vagin , Ingo Molnar , "Peter Zijlstra \(Intel\)" , Yuyang Du , David Hildenbrand , Sebastian Andrzej Siewior , Anshuman Khandual , David Howells , James Morris , Greg Kroah-Hartman , Shakeel Butt , Jason Gunthorpe , Christian Kellner , Andrea Arcangeli , Aleksa Sarai , "Dmitry V. Levin" , "linux-doc\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , "linux-mm\@kvack.org" , "stable\@vger.kernel.org" , "linux-api\@vger.kernel.org" References: <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org> <878sk94eay.fsf@x220.int.ebiederm.org> <87r1y12yc7.fsf@x220.int.ebiederm.org> <87k13t2xpd.fsf@x220.int.ebiederm.org> <87d09l2x5n.fsf@x220.int.ebiederm.org> <871rq12vxu.fsf@x220.int.ebiederm.org> <877dzt1fnf.fsf@x220.int.ebiederm.org> <875zfcxlwy.fsf@x220.int.ebiederm.org> Date: Tue, 10 Mar 2020 14:01:15 -0500 In-Reply-To: (Bernd Edlinger's message of "Tue, 10 Mar 2020 18:45:11 +0100") Message-ID: <87k13svxtw.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jBkA9-0004jE-TO;;;mid=<87k13svxtw.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX184oAtGUl9ErG2CEbQO/LXGywzplo5o8Mo= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 1/4] kernel/kcmp.c: Use new infrastructure to fix deadlocks in execve X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Bernd Edlinger writes: > This changes kcmp_epoll_target to use the new exec_update_mutex > instead of cred_guard_mutex. > > This should be safe, as the credentials are only used for reading, > and furthermore ->mm and ->sighand are updated on execve, > but only under the new exec_update_mutex. > Can you add a comment that the exec_update_mutex is not needed for KCMP_FILE? As both sets of credentials during exec are valid for accessing the files so exec_update_mutex does not matter. I don't think exec_update_mutex is needed for KCMP_SYSVSEM or KCMP_EPOLL_TFD either. As I don't think exec changes either one of those. Eric > Signed-off-by: Bernd Edlinger > --- > kernel/kcmp.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/kcmp.c b/kernel/kcmp.c > index a0e3d7a..b3ff928 100644 > --- a/kernel/kcmp.c > +++ b/kernel/kcmp.c > @@ -173,8 +173,8 @@ static int kcmp_epoll_target(struct task_struct *task1, > /* > * One should have enough rights to inspect task details. > */ > - ret = kcmp_lock(&task1->signal->cred_guard_mutex, > - &task2->signal->cred_guard_mutex); > + ret = kcmp_lock(&task1->signal->exec_update_mutex, > + &task2->signal->exec_update_mutex); > if (ret) > goto err; > if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) || > @@ -229,8 +229,8 @@ static int kcmp_epoll_target(struct task_struct *task1, > } > > err_unlock: > - kcmp_unlock(&task1->signal->cred_guard_mutex, > - &task2->signal->cred_guard_mutex); > + kcmp_unlock(&task1->signal->exec_update_mutex, > + &task2->signal->exec_update_mutex); > err: > put_task_struct(task1); > put_task_struct(task2);