Message-ID: <1412230855.28184.5.camel@localhost.localdomain>
From: Yann Droneaud <ydroneaud@opteya.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>, Eric Paris <eparis@redhat.com>,
        Richard Guy Briggs <rgb@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        stable@vger.kernel.org, linux-api@vger.kernel.org,
        Jan Kara <jack@suse.cz>, Lino Sanfilippo <LinoSanfilippo@gmx.de>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        Yann Droneaud <ydroneaud@opteya.com>
Date: Thu, 02 Oct 2014 08:20:55 +0200
In-Reply-To: <20141001153621.65e9258e65a6167bf2e4cb50@linux-foundation.org>
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Organization: OPTEYA
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Subject: Re: [PATCHv8.1] fanotify: enable close-on-exec on events' fd when
 requested in fanotify_init()
Sender: linux-kernel-owner@vger.kernel.org

Hi,

Le mercredi 01 octobre 2014 à 15:36 -0700, Andrew Morton a écrit :
> On Mon, 29 Sep 2014 10:49:15 +0200 Yann Droneaud <ydroneaud@opteya.com> 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?
> 

In the other hand, not enabling close-on-exec might expose unwanted file
descriptor to childs, creating security issues. YMMV.

-- 
Yann Droneaud
OPTEYA


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