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 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 B6770CA9EB5 for ; Mon, 4 Nov 2019 15:44:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90F5F20848 for ; Mon, 4 Nov 2019 15:44:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727989AbfKDPoU (ORCPT ); Mon, 4 Nov 2019 10:44:20 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:58238 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727796AbfKDPoT (ORCPT ); Mon, 4 Nov 2019 10:44:19 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1iReWg-0001fq-Dd; Mon, 04 Nov 2019 08:44:18 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iReWf-000835-Ge; Mon, 04 Nov 2019 08:44:18 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Topi Miettinen Cc: Luis Chamberlain , Kees Cook , Alexey Dobriyan , "linux-kernel\@vger.kernel.org" , "open list\:FILESYSTEMS \(VFS and infrastructure\)" References: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com> <87d0e8g5f4.fsf@x220.int.ebiederm.org> Date: Mon, 04 Nov 2019 09:44:05 -0600 In-Reply-To: (Topi Miettinen's message of "Sun, 3 Nov 2019 21:38:50 +0200") Message-ID: <87h83jejei.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=1iReWf-000835-Ge;;;mid=<87h83jejei.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+/SMoGN16q2hVm978SNtdL3kX2YwA8k1Q= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] Allow restricting permissions in /proc/sys X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Topi Miettinen writes: > On 3.11.2019 20.50, Eric W. Biederman wrote: >> Topi Miettinen writes: >> >>> Several items in /proc/sys need not be accessible to unprivileged >>> tasks. Let the system administrator change the permissions, but only >>> to more restrictive modes than what the sysctl tables allow. >> >> This looks quite buggy. You neither update table->mode nor >> do you ever read from table->mode to initialize the inode. >> I am missing something in my quick reading of your patch? > > inode->i_mode gets initialized in proc_sys_make_inode(). > > I didn't want to touch the table, so that the original permissions can > be used to restrict the changes made. In case the restrictions are > removed as suggested by Theodore Ts'o, table->mode could be > changed. Otherwise I'd rather add a new field to store the current > mode and the mode field can remain for reference. As the original > author of the code from 2007, would you let the administrator to > chmod/chown the items in /proc/sys without restrictions (e.g. 0400 -> > 0777)? At an architectural level I think we need to do this carefully and have a compelling reason. The code has survived nearly the entire life of linux without this capability. I think right now the common solution is to mount another file over the file you are trying to hide/limit. Changing the permissions might be better but that is not at all clear. Do you have specific examples of the cases where you would like to change the permissions? >> The not updating table->mode almost certainly means that as soon as the >> cached inode is invalidated the mode changes will disappear. Not to >> mention they will fail to propogate between different instances of >> proc. >> >> Loosing all of your changes at cache invalidation seems to make this a >> useless feature. > > At least different proc instances seem to work just fine here (they > show the same changes), but I suppose you are right about cache > invalidation. It is going to take the creation of a pid namespace to see different proc instances. All mounts of the proc within the same pid_namespace return the same instance. Eric