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From: Yann Droneaud <ydroneaud@opteya.com>
To: Heinrich Schuchardt <xypron.glpk@gmx.de>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>,
	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>
Subject: [PATCHv8.1] fanotify: enable close-on-exec on events' fd when requested in fanotify_init()
Date: Mon, 29 Sep 2014 10:49:15 +0200	[thread overview]
Message-ID: <1411980555-10818-1-git-send-email-ydroneaud@opteya.com> (raw)
In-Reply-To: <542666B2.9080700@gmx.de>

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)

Lookup also returned some wrong usage of the syscall:

- in Gonk HAL from Mozilla Firefox OS sources[6]:

    mFd = fanotify_init(FAN_CLASS_NOTIF, FAN_CLOEXEC);

Adding support for O_CLOEXEC in fanotify_init() won't magically
enable it for Gonk since FAN_CLOEXEC is defined as 0x1, which
is likely equal to O_WRONLY when used in open flag context. In
the other hand, it won't hurt it either.

So this patch replaces call to macro get_unused_fd() by a call
to function get_unused_fd_flags() with event_f_flags value as
argument. This way O_CLOEXEC flag in the second argument of
fanotify_init(2) syscall is interpreted so that close-on-exec
get enabled when requested.

[1] http://blog.ffwll.ch/2013/11/botching-up-ioctls.html
[2] http://cgit.freedesktop.org/systemd/systemd/tree/src/readahead/readahead-collect.c?id=v208#n294
[3] https://github.com/xaionaro/clsync/blob/v0.2.1/sync.c#L1631
    https://github.com/xaionaro/clsync/blob/v0.2.1/configuration.h#L38
[4] http://www.lanedo.com/~aleksander/fanotify/fanotify-example.c
[5] http://www.lanedo.com/2013/filesystem-monitoring-linux-kernel/
[6] http://hg.mozilla.org/mozilla-central/file/325c74addeba/hal/gonk/GonkDiskSpaceWatcher.cpp#l167

Link: http://lkml.kernel.org/r/cover.1394532336.git.ydroneaud@opteya.com
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Michael Kerrisk-manpages <mtk.manpages@gmail.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: Richard Guy Briggs <rgb@redhat.com>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Cc: linux-api@vger.kernel.org
Reviewed by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
---
Hi Andrew and Henrich,

Please find an updated patch with a commit message fixed regarding
the obsolote comments on code which is now updated, thanks to
Heinrich's patch.

Changes from v8:
- fixed commit message
- added Reviewed-by:

Regards.

Yann Droneaud,
OPTEYA

 fs/notify/fanotify/fanotify_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index b13992a41bd9..c991616acca9 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -78,7 +78,7 @@ static int create_fd(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	client_fd = get_unused_fd();
+	client_fd = get_unused_fd_flags(group->fanotify_data.f_flags);
 	if (client_fd < 0)
 		return client_fd;
 
-- 
1.9.3


  reply	other threads:[~2014-09-29  8:53 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-24 13:11 [PATCHv8 0/6] Getting rid of get_unused_fd() / enable close-on-exec Yann Droneaud
2014-09-24 13:11 ` Yann Droneaud
2014-09-24 13:11 ` Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 1/6] fanotify: enable close-on-exec on events' fd when requested in fanotify_init() Yann Droneaud
2014-09-25 20:57   ` Heinrich Schuchardt
2014-09-25 20:57     ` Heinrich Schuchardt
2014-09-26  8:58     ` Yann Droneaud
2014-09-27  7:26       ` Heinrich Schuchardt
2014-09-29  8:49         ` Yann Droneaud [this message]
2014-09-29 11:50           ` [PATCHv8.1] " Jan Kara
2014-10-01 22:36           ` Andrew Morton
2014-10-01 22:36             ` Andrew Morton
2014-10-02  6:20             ` Yann Droneaud
2014-10-02  6:50               ` Mihai Donțu
2014-10-02  7:52               ` [PATCH] fanotify: add a flag to allow setting O_CLOEXEC on event fd Yann Droneaud
2014-10-02  9:13                 ` Pádraig Brady
2014-10-02  9:13                   ` Pádraig Brady
2014-10-02  9:13                   ` Pádraig Brady
2014-10-02 11:55                   ` Michael Kerrisk (man-pages)
2014-10-02 14:44                   ` Yann Droneaud
2014-10-02 14:44                     ` Yann Droneaud
2014-10-02 10:44             ` [PATCHv8.1] fanotify: enable close-on-exec on events' fd when requested in fanotify_init() Jan Kara
2014-10-02 10:44               ` Jan Kara
2014-10-02 19:46               ` Andrew Morton
2014-10-02 19:46                 ` Andrew Morton
2014-10-03  8:39                 ` [PATCHv8.2] " Yann Droneaud
2014-10-03  8:39                   ` Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 2/6] ia64: trivial: replace get_unused_fd() by get_unused_fd_flags(0) Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 3/6] ppc/cell: " Yann Droneaud
2014-09-24 13:11   ` Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 4/6] binfmt_misc: " Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 5/6] file: " Yann Droneaud
2014-09-24 13:11 ` [PATCHv8 6/6] file: remove get_unused_fd() macro Yann Droneaud

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