From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933477AbbIVQMt (ORCPT ); Tue, 22 Sep 2015 12:12:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44950 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933288AbbIVQMr (ORCPT ); Tue, 22 Sep 2015 12:12:47 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20150922155104.GA2296@thunk.org> References: <20150922155104.GA2296@thunk.org> <20150922152450.32539.55285.stgit@warthog.procyon.org.uk> To: "Theodore Ts'o" Cc: dhowells@redhat.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com Subject: Re: [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1457.1442938362.1@warthog.procyon.org.uk> Date: Tue, 22 Sep 2015 17:12:42 +0100 Message-ID: <1458.1442938362@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Theodore Ts'o wrote: > So what this means is that on 32-bit systems, if we have a userspace > program which isn't using the Largefile-enabled, and it opens a file > which is larger than can be addressed with a 32-bit off_t, it can get > surprised and possibly cause data loss. Good point. I was initially thinking that 32-bit userspace on a 64-bit system would have O_LARGEFILE automatically enabled - but I guess it'll trap through the compat entry points which avoid that. That said, fanotify and xfs_open_by_handle() will both automatically set O_LARGEFILE irrespectively of the 32-bitness of the original caller. Further, path-based truncate() makes no checks based on file-largeness, unlike ftruncate(). > Is this something we are willing to live with? After all, there was a > originally a really good reason for the O_LARGEFILE flag in the first > place, and it was primarily about making sure that a non-LARGEFILE > capable program would hard fail on the open, instead of after it had > trashed the user's data. Okay, that seems reasonable - but it still leaves truncate() dangling. I'm not sure there's a good answer to that, though. > Was there a reason that motivated this change, other than just an > clean up? Overlayfs and one or two other places need to potentially apply O_LARGEFILE to the things that they do on behalf of userspace - but other than suppressing some size checks, it seems to be ignored by the filesystems and the VM. I vaguely seem to remember that at one point there were still filesystems that couldn't handle large files and would reject such opens - but they appear to all have been fixed. David