From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758317AbYDAOQC (ORCPT ); Tue, 1 Apr 2008 10:16:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755064AbYDAOPz (ORCPT ); Tue, 1 Apr 2008 10:15:55 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:36569 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755025AbYDAOPz (ORCPT ); Tue, 1 Apr 2008 10:15:55 -0400 Date: Tue, 1 Apr 2008 09:15:41 -0500 From: "Serge E. Hallyn" To: Pavel Emelyanov Cc: Manfred Spraul , Linux Kernel Mailing List , Andrew Morton , Serge Hallyn , Sukadev Bhattiprolu , "Eric W. Biederman" Subject: Re: [RFC, PATCH] fix SEM_UNDO with namespaces Message-ID: <20080401141540.GB13213@sergelap.ibm.com> References: <47EFFD1C.5020204@colorfullife.com> <47F08ED6.1090103@openvz.org> <47F10DF7.5010702@colorfullife.com> <47F203EC.7090806@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47F203EC.7090806@openvz.org> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Pavel Emelyanov (xemul@openvz.org): > Manfred Spraul wrote: > > Pavel Emelyanov wrote: > >> Manfred Spraul wrote: > >> > >>> Hi, > >>> > >>> the attached patch should fix the combination of CLONE_NEWIPC with > >>> shared sysv undo structures (the common case, just > >>> sys_unshare(CLONE_NEWIPC)): > >>> lookup_undo() now locates the undo array based on both semid and the > >>> namespace pointer. > >>> > >> If you start using any IPC object and then call unshare with CLONE_NEWIPC, > >> then it's your problem, but not the kernel. > >> > > The result is a kernel memory corruption, and kernel memory corruptions > > are always the kernel's problem. > > Agree. Must be fixed, but I'm not sure we should try handling this > case by trying to de-op semaphores for former task namespace. I think > that destroying this list or returning -EBUSY for this case is OK. > > > The code assumed that a semaphore id is globally unique. With > > namespaces, this is not true anymore. > > If two semaphore arrays exist with the same id, but different sizes, > > then semops will cause memory corruptions: The undo structure contains > > one element for each semaphore, thus the semop will write behind the end > > of the memory allocation. > > > >> I agree, that we should probably destroy this one when the task calls > >> unshare, but trying to keep this list relevant is useless. > >> > > A very tricky question: Let's assume we have a process with two threads. > > The undo structure is shared, as per opengroup standard. > > Now one thread calls unshare(CLONE_NEWIPC). What should happen? We > > cannot destroy the undo structure, the other thread might be still > > interested in it. > > If we allow sys_unshare() for multithreaded processes with CLONE_NEWIPC > > and without CLONE_SYSVSEM, then we must handle this case. > > Hm... I'd simply disable creating any new namespaces for threads. > I think other namespaces developers agree with me. Serge, Suka, Eric > what do you think? Absolutely. -serge