From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@kernel.org>
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 45ECFC4320A
	for <linux-fsdevel@archiver.kernel.org>; Fri, 23 Jul 2021 19:02:54 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id 2E74360F35
	for <linux-fsdevel@archiver.kernel.org>; Fri, 23 Jul 2021 19:02:54 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S229676AbhGWSWU (ORCPT
        <rfc822;linux-fsdevel@archiver.kernel.org>);
        Fri, 23 Jul 2021 14:22:20 -0400
Received: from zeniv-ca.linux.org.uk ([142.44.231.140]:49616 "EHLO
        zeniv-ca.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S229461AbhGWSWT (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Fri, 23 Jul 2021 14:22:19 -0400
Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux))
        id 1m70PY-003FS9-Fa; Fri, 23 Jul 2021 19:00:40 +0000
Date:   Fri, 23 Jul 2021 19:00:40 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3/3] io_uring: refactor io_sq_offload_create()
Message-ID: <YPsR2FgShiiYA2do@zeniv-ca.linux.org.uk>
References: <YPnqM0fY3nM5RdRI@zeniv-ca.linux.org.uk>
 <57758edf-d064-d37e-e544-e0c72299823d@kernel.dk>
 <YPn/m56w86xAlbIm@zeniv-ca.linux.org.uk>
 <a85df247-137f-721c-6056-a5c340eed90e@kernel.dk>
 <YPoI+GYrgZgWN/dW@zeniv-ca.linux.org.uk>
 <8fb39022-ba21-2c1f-3df5-29be002014d8@kernel.dk>
 <YPr4OaHv0iv0KTOc@zeniv-ca.linux.org.uk>
 <c09589ed-4ae9-c3c5-ec91-ba28b8f01424@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: <640bdb4e-f4d9-a5b8-5b7f-5265b39c8044@kernel.dk>
Sender: Al Viro <viro@ftp.linux.org.uk>
Precedence: bulk
List-ID: <linux-fsdevel.vger.kernel.org>
X-Mailing-List: linux-fsdevel@vger.kernel.org

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...