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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 81759C4338F for ; Fri, 23 Jul 2021 20:19:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B44860F25 for ; Fri, 23 Jul 2021 20:19:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229530AbhGWTjT (ORCPT ); Fri, 23 Jul 2021 15:39:19 -0400 Received: from zeniv-ca.linux.org.uk ([142.44.231.140]:50180 "EHLO zeniv-ca.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229461AbhGWTjT (ORCPT ); Fri, 23 Jul 2021 15:39:19 -0400 Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m71e9-003HJ9-Rf; Fri, 23 Jul 2021 20:19:49 +0000 Date: Fri, 23 Jul 2021 20:19:49 +0000 From: Al Viro To: Jens Axboe Cc: Pavel Begunkov , io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH 3/3] io_uring: refactor io_sq_offload_create() Message-ID: References: <57758edf-d064-d37e-e544-e0c72299823d@kernel.dk> <8fb39022-ba21-2c1f-3df5-29be002014d8@kernel.dk> <591b4a1e-606a-898c-7470-b5a1be621047@kernel.dk> <640bdb4e-f4d9-a5b8-5b7f-5265b39c8044@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, Jul 23, 2021 at 07:00:40PM +0000, Al Viro wrote: > On Fri, Jul 23, 2021 at 11:56:29AM -0600, Jens Axboe wrote: > > > Will send out two patches for this. Note that I don't see this being a > > real issue, as we explicitly gave the ring fd to another task, and being > > that this is purely for read/write, it would result in -EFAULT anyway. > > You do realize that ->release() might come from seriously unexpected places, > right? E.g. recvmsg() by something that doesn't expect SCM_RIGHTS attached > to it will end up with all struct file references stashed into the sucker > dropped, and if by that time that's the last reference - welcome to ->release() > run as soon as recepient hits task_work_run(). > > What's more, if you stash that into garbage for unix_gc() to pick, *any* > process closing an AF_UNIX socket might end up running your ->release(). > > So you really do *not* want to spawn any threads there, let alone > possibly exfiltrating memory contents of happy recepient of your present... To elaborate: ->release() instance may not assume anything about current->mm, or assume anything about current, for that matter. It is entirely possible to arrange its execution in context of a process that is not yours and had not consent to doing that. In particular, it's a hard bug to have _any_ visible effects depending upon the memory mappings, memory contents or the contents of descriptor table of the process in question. There's really no way around that.