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_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 A0EBBC10DCE for ; Tue, 10 Mar 2020 21:05:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 56CE1215A4 for ; Tue, 10 Mar 2020 21:05:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 56CE1215A4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E5EF26B0003; Tue, 10 Mar 2020 17:05:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DE8516B0006; Tue, 10 Mar 2020 17:05:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C89A66B0007; Tue, 10 Mar 2020 17:05:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0059.hostedemail.com [216.40.44.59]) by kanga.kvack.org (Postfix) with ESMTP id A96696B0003 for ; Tue, 10 Mar 2020 17:05:11 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 73EEF4DDF for ; Tue, 10 Mar 2020 21:05:11 +0000 (UTC) X-FDA: 76580682822.05.self64_2d2abcdcdc150 X-HE-Tag: self64_2d2abcdcdc150 X-Filterd-Recvd-Size: 6817 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Tue, 10 Mar 2020 21:05:10 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jBm3o-0007Ja-5Z; Tue, 10 Mar 2020 15:05:08 -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 1jBm3n-0008Ca-EI; Tue, 10 Mar 2020 15:05:08 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Kees Cook Cc: Bernd Edlinger , Christian Brauner , 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: <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> <202003101352.28BE3BEB4@keescook> Date: Tue, 10 Mar 2020 16:02:48 -0500 In-Reply-To: <202003101352.28BE3BEB4@keescook> (Kees Cook's message of "Tue, 10 Mar 2020 13:55:54 -0700") Message-ID: <87a74nsz2f.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=1jBm3n-0008Ca-EI;;;mid=<87a74nsz2f.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18PTvqUqvFHzaS8aRXcjAAB8aMmbAjVv+4= 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Kees Cook writes: > On Mon, Mar 09, 2020 at 02:02:37PM -0500, Eric W. Biederman wrote: >> exec: Add exec_update_mutex to replace cred_guard_mutex >> >> The cred_guard_mutex is problematic as it is held over possibly >> indefinite waits for userspace. The possilbe indefinite waits for >> userspace that I have identified are: The cred_guard_mutex is held in >> PTRACE_EVENT_EXIT waiting for the tracer. The cred_guard_mutex is >> held over "put_user(0, tsk->clear_child_tid)" in exit_mm(). The >> cred_guard_mutex is held over "get_user(futex_offset, ...") in >> exit_robust_list. The cred_guard_mutex held over copy_strings. > > I suspect you're not trying to make a comprehensive list here, but do > you want to mention seccomp too (since it's yet another weird case). I was calling out all of the places I have found so far where cred_guard_mutex is held over waiting for userspace to maybe do something. Those places are what cause our deadlocks. >> [...] >> Holding a mutex over any of those possibly indefinite waits for >> userspace does not appear necessary. Add exec_update_mutex that will >> just cover updating the process during exec where the permissions and >> the objects pointed to by the task struct may be out of sync. > > Should the specific resources be pointed out here? creds, mm, ... ? > > But otherwise, yup, looks sane: Probably not. The design is if exec changes it we will hold the cred_guard_mutex over it, so things are semi-atomic. > Reviewed-by: Kees Cook Eric