From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751340AbcFXISc (ORCPT ); Fri, 24 Jun 2016 04:18:32 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:35576 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750971AbcFXIS1 (ORCPT ); Fri, 24 Jun 2016 04:18:27 -0400 Subject: Re: Documenting ptrace access mode checking To: "Eric W. Biederman" References: <87ziqewc3r.fsf@x220.int.ebiederm.org> <20160622215142.GA14751@redhat.com> <871t3nka3c.fsf@x220.int.ebiederm.org> Cc: mtk.manpages@gmail.com, Oleg Nesterov , Jann Horn , James Morris , linux-man , Stephen Smalley , lkml , Kees Cook , linux-security-module , Linux API From: "Michael Kerrisk (man-pages)" Message-ID: <8dc0a0ec-c46d-778f-137f-b06dae9b2a39@gmail.com> Date: Fri, 24 Jun 2016 10:18:21 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 MIME-Version: 1.0 In-Reply-To: <871t3nka3c.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/23/2016 08:56 PM, Eric W. Biederman wrote: > "Michael Kerrisk (man-pages)" writes: > >> Hi Oleg, >> >> On 06/22/2016 11:51 PM, Oleg Nesterov wrote: >>> On 06/21, Eric W. Biederman wrote: >>>> >>>> Adding Oleg just because he seems to do most of the ptrace related >>>> maintenance these days. >>> >>> so I have to admit that I never even tried to actually understand >>> ptrace_may_access ;) >>> >>>> We certainly need something that gives a high level view so people >>>> reading the man page can know what to expect. If you get down into the >>>> weeds we run the danger of people beginning to think they can depend >>>> upon bugs in the implementation. >>> >>> Personally I agree. I think "man ptrace" shouldn't not tell too much >>> about kernel internals. >> >> See my other replies on this topic. Somehow, we need a way of >> describing the behavior that user-space sees. I think it's >> inevitable that that means talking about what;s going on >> "under the hood". >> >> Regarding Eric's point that "we run the danger of people beginning >> to think they can depend upon bugs in the implementation": when it >> comes to breaking the ABI, the presence or absence of documentation >> doesn't save us on that point (Linus has a few times made his position >> wrt to documentation clear). > > Which are interesting in this respect as a bug in the implementation > that is a security issue can and will be changed, even if userspace > breaks. Breaking userspace is not desirable but when there is no other > reasonable choice it will happen. Yes, good point. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/