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 D82CAC1975A for ; Thu, 12 Mar 2020 12:27:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B2E51206EB for ; Thu, 12 Mar 2020 12:27:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726894AbgCLM1R (ORCPT ); Thu, 12 Mar 2020 08:27:17 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:54454 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725978AbgCLM1R (ORCPT ); Thu, 12 Mar 2020 08:27:17 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jCMvg-0008B2-FJ; Thu, 12 Mar 2020 06:27:12 -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 1jCMvf-0006RZ-FN; Thu, 12 Mar 2020 06:27:12 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Kirill Tkhai Cc: Bernd Edlinger , 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: <87v9nmjulm.fsf@x220.int.ebiederm.org> <202003021531.C77EF10@keescook> <20200303085802.eqn6jbhwxtmz4j2x@wittgenstein> <87v9nlii0b.fsf@x220.int.ebiederm.org> <87a74xi4kz.fsf@x220.int.ebiederm.org> <87r1y8dqqz.fsf@x220.int.ebiederm.org> <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org> Date: Thu, 12 Mar 2020 07:24:50 -0500 In-Reply-To: (Kirill Tkhai's message of "Thu, 12 Mar 2020 13:27:30 +0300") Message-ID: <87d09hn4kt.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=1jCMvf-0006RZ-FN;;;mid=<87d09hn4kt.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX197oHUB4P7o25mD2mW/iWh+TbBM6TNe7gs= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex 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 Kirill Tkhai writes: > On 09.03.2020 00:38, Eric W. Biederman wrote: >> >> The cred_guard_mutex is problematic. The cred_guard_mutex is held >> over the userspace accesses as the arguments from userspace are read. >> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other >> threads are killed. The cred_guard_mutex is held over >> "put_user(0, tsk->clear_child_tid)" in exit_mm(). >> >> Any of those can result in deadlock, as the cred_guard_mutex is held >> over a possible indefinite userspace waits for userspace. >> >> Add exec_update_mutex that is only held over exec updating process >> with the new contents of exec, so that code that needs not to be >> confused by exec changing the mm and the cred in ways that can not >> happen during ordinary execution of a process. >> >> The plan is to switch the users of cred_guard_mutex to >> exec_udpate_mutex one by one. This lets us move forward while still >> being careful and not introducing any regressions. >> >> Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/ >> Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/ >> Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/ >> Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/ >> Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/ >> Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") >> Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") >> Signed-off-by: "Eric W. Biederman" >> --- >> fs/exec.c | 9 +++++++++ >> include/linux/sched/signal.h | 9 ++++++++- >> init/init_task.c | 1 + >> kernel/fork.c | 1 + >> 4 files changed, 19 insertions(+), 1 deletion(-) >> >> diff --git a/fs/exec.c b/fs/exec.c >> index d820a7272a76..ffeebb1f167b 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -1014,6 +1014,7 @@ static int exec_mmap(struct mm_struct *mm) >> { >> struct task_struct *tsk; >> struct mm_struct *old_mm, *active_mm; >> + int ret; >> >> /* Notify parent that we're no longer interested in the old VM */ >> tsk = current; >> @@ -1034,6 +1035,11 @@ static int exec_mmap(struct mm_struct *mm) >> return -EINTR; >> } >> } >> + >> + ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); >> + if (ret) >> + return ret; > > You missed old_mm->mmap_sem unlock. See here: Duh. Thank you. I actually need to switch the lock ordering here, and I haven't yet because my son was sick yesterday. Something like this. diff --git a/fs/exec.c b/fs/exec.c index 96f89401b4d1..03d50c27ec01 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1020,9 +1020,14 @@ static int exec_mmap(struct mm_struct *mm) tsk = current; old_mm = current->mm; exec_mm_release(tsk, old_mm); + if (old_mm) + sync_mm_rss(old_mm); + + ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); + if (ret) + return ret; if (old_mm) { - sync_mm_rss(old_mm); /* * Make sure that if there is a core dump in progress * for the old mm, we get out and die instead of going @@ -1032,14 +1037,11 @@ static int exec_mmap(struct mm_struct *mm) down_read(&old_mm->mmap_sem); if (unlikely(old_mm->core_state)) { up_read(&old_mm->mmap_sem); + mutex_unlock(&tsk->signal->exec_update_mutex); return -EINTR; } } - ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); - if (ret) - return ret; - task_lock(tsk); active_mm = tsk->active_mm; membarrier_exec_mmap(mm); > diff --git a/fs/exec.c b/fs/exec.c > index 47582cd97f86..d557bac3e862 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1063,8 +1063,11 @@ static int exec_mmap(struct mm_struct *mm) > } > > ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); > - if (ret) > + if (ret) { > + if (old_mm) > + up_read(&old_mm->mmap_sem); > return ret; > + } > > task_lock(tsk); > active_mm = tsk->active_mm; Eric