Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754426Ab1F3JVS (ORCPT ); Thu, 30 Jun 2011 05:21:18 -0400 Received: from mail-ey0-f174.google.com ([209.85.215.174]:63933 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751803Ab1F3JVK (ORCPT ); Thu, 30 Jun 2011 05:21:10 -0400 Date: Thu, 30 Jun 2011 13:21:03 +0400 From: Vasiliy Kulikov To: Andrew Morton Cc: kernel-hardening@lists.openwall.com, Randy Dunlap , "Eric W. Biederman" , "Serge E. Hallyn" , Daniel Lezcano , Oleg Nesterov , Tejun Heo , Ingo Molnar , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [RFC] ipc: introduce shm_rmid_forced sysctl Message-ID: <20110630092103.GA4252@albatros> References: <20110622152514.GA9521@albatros> <20110629151436.9be479fb.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110629151436.9be479fb.akpm@linux-foundation.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2600 Lines: 84 On Wed, Jun 29, 2011 at 15:14 -0700, Andrew Morton wrote: > What a horrid patch. But given the POSIX (mis?)feature I don't see a > better way, and the feature seems desirable. Sigh. > > What sort of users would want to turn this on, and why? A shared environment, e.g. a shared web hosting. With multiple ipc namespaces (on a VPS) each namespace can steal a few megabytes of memory without any per user accounting. Even if all user's processes are killed, the orphaned shm is still kept in RAM. It doesn't lead to OOM, but it prevents from creating new segments and just annoys. > > --- a/include/linux/ipc_namespace.h > > +++ b/include/linux/ipc_namespace.h > > @@ -44,6 +44,7 @@ struct ipc_namespace { > > size_t shm_ctlall; > > int shm_ctlmni; > > int shm_tot; > > + int shm_rmid_forced; > > > > struct notifier_block ipcns_nb; > > Please send a patch which adds a nice comment to this field. OK. > Perhaps shm_rmid_forced should have had bool type. OK. The sysctl handler should parse it OK if feed it with sizeof(bool). > > --- a/ipc/shm.c > > +++ b/ipc/shm.c > > @@ -74,6 +74,7 @@ void shm_init_ns(struct ipc_namespace *ns) > > ns->shm_ctlmax = SHMMAX; > > ns->shm_ctlall = SHMALL; > > ns->shm_ctlmni = SHMMNI; > > + ns->shm_rmid_forced = 0; > > ns->shm_tot = 0; > > ipc_init_ids(&shm_ids(ns)); > > } > > The problem is that nobody will test your feature. So for testing > purposes, let's enable the feature by default. I assume this: > > --- a/ipc/shm.c~ipc-introduce-shm_rmid_forced-sysctl-ipc-introduce-shm_rmid_forced-sysctl-testing > +++ a/ipc/shm.c > @@ -74,7 +74,7 @@ void shm_init_ns(struct ipc_namespace *n > ns->shm_ctlmax = SHMMAX; > ns->shm_ctlall = SHMALL; > ns->shm_ctlmni = SHMMNI; > - ns->shm_rmid_forced = 0; > + ns->shm_rmid_forced = 1; > ns->shm_tot = 0; > ipc_init_ids(&shm_ids(ns)); > } > > will do that? Sure if it helps testing :) > > +static bool shm_may_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) > > +{ > > + return (shp->shm_nattch == 0) && > > + (ns->shm_rmid_forced || > > + (shp->shm_perm.mode & SHM_DEST)); > > +} > > Just because the existing code is crappily documented doesn't mean that > we have to copy that ;) OK ;) Thank you! -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/