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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 CA7FCC43381 for ; Mon, 25 Mar 2019 23:42:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9666B2083D for ; Mon, 25 Mar 2019 23:42:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553557351; bh=9HKKstgDeo0vs0rQiPhWD1UARtFAZEryCAqL281TzC8=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=0XDoLdejgMEQJjpXLyW9rjs4hNWFD2a1CGxdX8iicp1RP9yFkmndQ66ATp+SZ1Q/H oywXWugvQSe8ujzLbljnvk+tpQ7uhydZFRV8xc6ms5cwYXZmq1IXIn7xmoPdwFd/F9 jQc+4IK2x7jGhpxWmaBhxbC0yTVin+9bGh9NW54k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727506AbfCYXma (ORCPT ); Mon, 25 Mar 2019 19:42:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:50232 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726553AbfCYXm2 (ORCPT ); Mon, 25 Mar 2019 19:42:28 -0400 Received: from mail-wm1-f47.google.com (mail-wm1-f47.google.com [209.85.128.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3D3AE20854 for ; Mon, 25 Mar 2019 23:42:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553557347; bh=9HKKstgDeo0vs0rQiPhWD1UARtFAZEryCAqL281TzC8=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=Ep/KL1+deZDNfjqGXtXYY2NdhRdebRBYCVkEuBUYdm/oXouy1NtxYOcVOzWAQt4dt zCssZYorC9vIBLmbaA4sjJHg3cA3l3jDlLpzPNPfBQCKQIbAFXZb1KvlvSPJ5ayGnl iqDJ+CmHgaz9JQmvjSoazOPgJWtxNJDMqP6yQUMk= Received: by mail-wm1-f47.google.com with SMTP id y197so10956617wmd.0 for ; Mon, 25 Mar 2019 16:42:27 -0700 (PDT) X-Gm-Message-State: APjAAAUX3ML+Xz/Bp9aMDNTsLwn0kRlj3FP50IAwCYl7uSx8dXE4XRxi gZtsh0fufFiM5eyRpFcnFf2xgWfgVr8JFiYSduCZpw== X-Google-Smtp-Source: APXvYqy7TwbBmkrbCD21UGhsWd3I+1cLabNvWbVw1JXomyD6gXIFMeYNYciXeA+MXQTdQH5VQE5zd3Brjbbfn57vN+s= X-Received: by 2002:a7b:c257:: with SMTP id b23mr12729658wmj.83.1553557345804; Mon, 25 Mar 2019 16:42:25 -0700 (PDT) MIME-Version: 1.0 References: <20190319231020.tdcttojlbmx57gke@brauner.io> <20190320015249.GC129907@google.com> <20190320035953.mnhax3vd47ya4zzm@brauner.io> <4A06C5BB-9171-4E70-BE31-9574B4083A9F@joelfernandes.org> <20190320182649.spryp5uaeiaxijum@brauner.io> <20190320185156.7bq775vvtsxqlzfn@brauner.io> <20190320191412.5ykyast3rgotz3nu@brauner.io> In-Reply-To: From: Andy Lutomirski Date: Mon, 25 Mar 2019 16:42:14 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: pidfd design To: Daniel Colascione Cc: Jann Horn , Andy Lutomirski , Christian Brauner , Joel Fernandes , Suren Baghdasaryan , Steven Rostedt , Sultan Alsawaf , Tim Murray , Michal Hocko , Greg Kroah-Hartman , =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= , Todd Kjos , Martijn Coenen , Ingo Molnar , Peter Zijlstra , LKML , "open list:ANDROID DRIVERS" , kernel-team , Oleg Nesterov , "Serge E. Hallyn" , Kees Cook , Jonathan Kowalski , Linux API Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 25, 2019 at 1:23 PM Daniel Colascione wrote: > > On Mon, Mar 25, 2019 at 1:14 PM Jann Horn wrote: > > > > On Mon, Mar 25, 2019 at 8:44 PM Andy Lutomirski wrote: > > One ioctl on procfs roots to translate pidfds into that procfs, > > subject to both the normal lookup permission checks and only working > > if the pidfd has a translation into the procfs: > > > > int proc_root_fd = open("/proc", O_RDONLY); > > int proc_dir_fd = ioctl(proc_root_fd, PROC_PIDFD_TO_PROCFSFD, pidfd); > > > > And one ioctl on procfs directories to translate from PGIDs and PIDs to pidfds: > > > > int proc_pgid_fd = open("/proc/self", O_RDONLY); > > int self_pg_pidfd = ioctl(proc_pgid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > > int proc_pid_fd = open("/proc/thread-self", O_RDONLY); > > int self_p_pidfd = ioctl(proc_pid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > > This sounds okay to me. Or we could make it so that a procfs directory fd also works as a pidfd, but that seems more likely to be problematic than just allowing two-way translation like this > > > > And then, as you proposed, the new sys_clone() can just return a > > pidfd, and you can convert it into a procfs fd yourself if you want. > > I think that's the consensus we reached on the other thread. The > O_DIRECTORY open on /proc/self/fd/mypidfd seems like it'd work well > enough. I must have missed this particular email. IMO, if /proc/self/fd/mypidfd allows O_DIRECTORY open to work, then it really ought to do function just like /proc/self/fd/mypidfd/. and /proc/self/fd/mypidfd/status should work. And these latter two options seem nutty. Also, this O_DIRECTORY thing is missing the entire point of the ioctl interface -- it doesn't require procfs access. --Andy