From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: call_usermodehelper in containers Date: Wed, 17 Feb 2016 20:57:48 -0600 Message-ID: <8737sq4teb.fsf@x220.int.ebiederm.org> References: <20131111071825.62da01d1@tlielax.poochiereds.net> <20131112004703.GB15377@kroah.com> <20131112061201.04cf25ab@tlielax.poochiereds.net> <528226EC.4050701@parallels.com> <20131112083043.0ab78e67@tlielax.poochiereds.net> <5285FA0A.2080802@parallels.com> <871u2incyo.fsf@xmission.com> <20131118172844.GA10005@redhat.com> <1455149857.2903.9.camel@themaw.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1455149857.2903.9.camel-PKsaG3nR2I+sTnJN9+BGXg@public.gmane.org> (Ian Kent's message of "Thu, 11 Feb 2016 08:17:37 +0800") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Ian Kent Cc: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Stanislav Kinsbursky , Jeff Layton , Greg KH , Linux Containers , Oleg Nesterov , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org, bharrosh-C4P08NqkoRlBDgjK7y7TUQ@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org List-Id: containers.vger.kernel.org Ccing The containers list because a related discussion is happening there and somehow this thread has never made it there. Ian Kent writes: > On Mon, 2013-11-18 at 18:28 +0100, Oleg Nesterov wrote: >> On 11/15, Eric W. Biederman wrote: >> > >> > I don't understand that one. Having a preforked thread with the >> > proper >> > environment that can act like kthreadd in terms of spawning user >> > mode >> > helpers works and is simple. > > Forgive me replying to such an old thread but ... > > After realizing workqueues can't be used to pre-create threads to run > usermode helpers I've returned to look at this. If someone can wind up with a good implementation I will be happy. >> Can't we ask ->child_reaper to create the non-daemonized kernel thread >> with the "right" ->nsproxy, ->fs, etc? > > Eric, do you think this approach would be sufficient too? > > Probably wouldn't be quite right for user namespaces but should provide > what's needed for other cases? > > It certainly has the advantage of not having to maintain a plague of > processes waiting around to execute helpers. That certainly sounds attractive. Especially for the case of everyone who wants to set a core pattern in a container. I am fuzzy on all of the details right now, but what I do remember is that in the kernel the user mode helper concepts when they attempted to scrub a processes environment were quite error prone until we managed to get kthreadd(pid 2) on the scene which always had a clean environment. If we are going to tie this kind of thing to the pid namespace I recommend simplying denying it if you are in a user namespace without an approrpriate pid namespace. AKA simply not allowing thigns to be setup if current->pid_ns->user_ns != current->user_ns. That still leaves things a little hand-wavy but I hope that helps conceptually. Eric From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out02.mta.xmission.com ([166.70.13.232]:42764 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1424050AbcBRDHk (ORCPT ); Wed, 17 Feb 2016 22:07:40 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Ian Kent Cc: Oleg Nesterov , Stanislav Kinsbursky , Jeff Layton , Greg KH , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, devel@openvz.org, bfields@fieldses.org, bharrosh@panasas.com, Linux Containers References: <20131111071825.62da01d1@tlielax.poochiereds.net> <20131112004703.GB15377@kroah.com> <20131112061201.04cf25ab@tlielax.poochiereds.net> <528226EC.4050701@parallels.com> <20131112083043.0ab78e67@tlielax.poochiereds.net> <5285FA0A.2080802@parallels.com> <871u2incyo.fsf@xmission.com> <20131118172844.GA10005@redhat.com> <1455149857.2903.9.camel@themaw.net> Date: Wed, 17 Feb 2016 20:57:48 -0600 In-Reply-To: <1455149857.2903.9.camel@themaw.net> (Ian Kent's message of "Thu, 11 Feb 2016 08:17:37 +0800") Message-ID: <8737sq4teb.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: call_usermodehelper in containers Sender: linux-nfs-owner@vger.kernel.org List-ID: Ccing The containers list because a related discussion is happening there and somehow this thread has never made it there. Ian Kent writes: > On Mon, 2013-11-18 at 18:28 +0100, Oleg Nesterov wrote: >> On 11/15, Eric W. Biederman wrote: >> > >> > I don't understand that one. Having a preforked thread with the >> > proper >> > environment that can act like kthreadd in terms of spawning user >> > mode >> > helpers works and is simple. > > Forgive me replying to such an old thread but ... > > After realizing workqueues can't be used to pre-create threads to run > usermode helpers I've returned to look at this. If someone can wind up with a good implementation I will be happy. >> Can't we ask ->child_reaper to create the non-daemonized kernel thread >> with the "right" ->nsproxy, ->fs, etc? > > Eric, do you think this approach would be sufficient too? > > Probably wouldn't be quite right for user namespaces but should provide > what's needed for other cases? > > It certainly has the advantage of not having to maintain a plague of > processes waiting around to execute helpers. That certainly sounds attractive. Especially for the case of everyone who wants to set a core pattern in a container. I am fuzzy on all of the details right now, but what I do remember is that in the kernel the user mode helper concepts when they attempted to scrub a processes environment were quite error prone until we managed to get kthreadd(pid 2) on the scene which always had a clean environment. If we are going to tie this kind of thing to the pid namespace I recommend simplying denying it if you are in a user namespace without an approrpriate pid namespace. AKA simply not allowing thigns to be setup if current->pid_ns->user_ns != current->user_ns. That still leaves things a little hand-wavy but I hope that helps conceptually. Eric