Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763293AbYBWTtF (ORCPT ); Sat, 23 Feb 2008 14:49:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760288AbYBWTsg (ORCPT ); Sat, 23 Feb 2008 14:48:36 -0500 Received: from fxip-0047f.externet.hu ([88.209.222.127]:49782 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758271AbYBWTse (ORCPT ); Sat, 23 Feb 2008 14:48:34 -0500 To: viro@ZenIV.linux.org.uk CC: miklos@szeredi.hu, hch@infradead.org, akpm@linux-foundation.org, serue@us.ibm.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, haveblue@us.ibm.com In-reply-to: <20080223185701.GS27894@ZenIV.linux.org.uk> (message from Al Viro on Sat, 23 Feb 2008 18:57:01 +0000) Subject: Re: [patch 00/10] mount ownership and unprivileged mount syscall (v8) References: <20080205213616.343721693@szeredi.hu> <20080214222103.a5d8f4fe.akpm@linux-foundation.org> <20080215090120.GA6266@infradead.org> <20080215010951.163fe10e.akpm@linux-foundation.org> <20080215091438.GA24386@infradead.org> <20080223160956.GR27894@ZenIV.linux.org.uk> <20080223185701.GS27894@ZenIV.linux.org.uk> Message-Id: From: Miklos Szeredi Date: Sat, 23 Feb 2008 20:48:26 +0100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1469 Lines: 31 > On Sat, Feb 23, 2008 at 06:33:13PM +0100, Miklos Szeredi wrote: > > > c) just what is limited by that sysctl? AFAICS, rbind is allowed > > > if mountpoint is on user vfsmount and it seems to create vfsmounts without > > > eating into that limit just fine... What's the point of limiting the > > > amount of vfsmounts marked user when you do not limit the number of vfsmount > > > one can allocate? > > > > The limit is there, so that unprivileged users cannot create insane > > number of mounts. It's just a safety thing, analogous to > > /proc/sys/fs/file-max. > > Can't they? Looks like one can create any number of vfsmounts without > getting more than one marked MNT_USER... permit_mount() will set MS_SETUSER in flags, and do_loopback() will set CL_SETUSER based on that flag. > If you are trying to limit the number of superblocks (i.e. active instances > of filesystems), then I'd say that vfsmounts make piss-poor proxies for > those and it would be better to count the objects you really want to count... I think I really want to limit vfsmounts. But not because these take so much memory or anything, just to be safe against a stupid users playing rbind and propagation, and things like that. Miklos -- 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/