Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757388AbaDICaj (ORCPT ); Tue, 8 Apr 2014 22:30:39 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:55671 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756235AbaDICah (ORCPT ); Tue, 8 Apr 2014 22:30:37 -0400 Date: Wed, 9 Apr 2014 03:30:27 +0100 From: Al Viro To: "Eric W. Biederman" Cc: Linus Torvalds , "Serge E. Hallyn" , Linux-Fsdevel , Kernel Mailing List , Andy Lutomirski , Rob Landley , Miklos Szeredi , Christoph Hellwig , Karel Zak , "J. Bruce Fields" , Fengguang Wu Subject: Re: [GIT PULL] Detaching mounts on unlink for 3.15-rc1 Message-ID: <20140409023027.GX18016@ZenIV.linux.org.uk> References: <87a9kkax0j.fsf@xmission.com> <8761v7h2pt.fsf@tw-ebiederman.twitter.com> <87li281wx6.fsf_-_@xmission.com> <87ob28kqks.fsf_-_@xmission.com> <874n3n7czm.fsf_-_@xmission.com> <87wqezl5df.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wqezl5df.fsf_-_@x220.int.ebiederm.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 08, 2014 at 05:21:32PM -0700, Eric W. Biederman wrote: > This set of changes has been reviewed and been sitting idle for the last > 6 weeks. In that time the vfs has slightly shifted under me the new > version of rename and the mount hash list becoming a hlist. None of > those changes has caused changed the code in ways to invalidate these > changes, but small conflicts do result and I have attached my conflict > resolution at the end of this email in case it helps. > > To recap these changes allow a file or a directory that is a mount point > in one mount namespace to be unlinked/rmdired elsewhere where it is not > a mount point (either a remote filesystem or another mount namespace). > As has been agreed during review semantics when only a single mount > namespace exists remain unchanged. > > This removes a long standing need to lie to the vfs when a mount point > has been removed behind it's back. This also removes a DOS attack where > an unprivileged user could prevent root from renaming or deleting files > and directories by using them as mountpoints in another mount namespace. > > This change also fixes a few cases where because we were not lying to > the vfs we could leak mount points. > > When renaming or unlinking directory entries that are not mountpoints > no additional locks are taken so no performance differences can result, > and my benchmark reflected that. It also means that d_invalidate() now might trigger fs shutdown. Which has bloody huge stack footprint, for obvious reasons. And d_invalidate() can be called with pretty deep stack - walk into wrong dentry while resolving a deeply nested symlink and there you go... -- 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/