Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752473AbaJBKoP (ORCPT ); Thu, 2 Oct 2014 06:44:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:59450 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750987AbaJBKoN (ORCPT ); Thu, 2 Oct 2014 06:44:13 -0400 Date: Thu, 2 Oct 2014 12:44:10 +0200 From: Jan Kara To: Andrew Morton Cc: Yann Droneaud , Heinrich Schuchardt , Eric Paris , Richard Guy Briggs , Al Viro , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org, linux-api@vger.kernel.org, Jan Kara , Lino Sanfilippo , Valdis Kletnieks , Michael Kerrisk-manpages Subject: Re: [PATCHv8.1] fanotify: enable close-on-exec on events' fd when requested in fanotify_init() Message-ID: <20141002104410.GB19748@quack.suse.cz> References: <9d050a2db4f9cf68cd6cb038f16cccb0f73c6e66.1411562410.git.ydroneaud@opteya.com> <542481B3.8070300@gmx.de> <1411721898.7778.18.camel@localhost.localdomain> <542666B2.9080700@gmx.de> <1411980555-10818-1-git-send-email-ydroneaud@opteya.com> <20141001153621.65e9258e65a6167bf2e4cb50@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141001153621.65e9258e65a6167bf2e4cb50@linux-foundation.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 Wed 01-10-14 15:36:21, Andrew Morton wrote: > On Mon, 29 Sep 2014 10:49:15 +0200 Yann Droneaud wrote: > > > According to commit 80af258867648 ('fanotify: groups can specify > > their f_flags for new fd'), file descriptors created as part of > > file access notification events inherit flags from the > > event_f_flags argument passed to syscall fanotify_init(2). > > > > So while it is legal for userspace to call fanotify_init() with > > O_CLOEXEC as part of its second argument, O_CLOEXEC is currently > > silently ignored. > > > > Indeed event_f_flags are only given to dentry_open(), which only > > seems to care about O_ACCMODE and O_PATH in do_dentry_open(), > > O_DIRECT in open_check_o_direct() and O_LARGEFILE in > > generic_file_open(). > > > > But it seems logical to set close-on-exec flag on the file > > descriptor if userspace is allowed to request it with O_CLOEXEC. > > > > In fact, according to some lookup on http://codesearch.debian.net/ > > and various search engine, there's already some userspace code > > requesting it: > > > > - in systemd's readahead[2]: > > > > fanotify_fd = fanotify_init(FAN_CLOEXEC|FAN_NONBLOCK, O_RDONLY|O_LARGEFILE|O_CLOEXEC|O_NOATIME); > > > > - in clsync[3]: > > > > #define FANOTIFY_EVFLAGS (O_LARGEFILE|O_RDONLY|O_CLOEXEC) > > > > int fanotify_d = fanotify_init(FANOTIFY_FLAGS, FANOTIFY_EVFLAGS); > > > > - in examples [4] from "Filesystem monitoring in the Linux > > kernel" article[5] by Aleksander Morgado: > > > > if ((fanotify_fd = fanotify_init (FAN_CLOEXEC, > > O_RDONLY | O_CLOEXEC | O_LARGEFILE)) < 0) > > So we have a number of apps which are setting O_CLOEXEC, but it doesn't > actually work. With this change it *will* work, so the behaviour of > those apps might change, possibly breaking them? Possibly. OTOH I'd dare to say that most of the apps specifying O_CLOEXEC want that behavior and their security may be weakened by the fact that O_CLOEXEC is ignored. So we are weighting possible security issues for apps doing things right (and Mihai mentioned in this thread that at least he has an application which needs O_CLOEXEC working) against possible breakage for apps which just randomly set O_CLOEXEC without wanting. So I'm really for fixing O_CLOEXEC behavior. Honza -- Jan Kara SUSE Labs, CR -- 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/