linux-kernel - Re: [PATCHv8 1/6] fanotify: enable close-on-exec on events' fd when requested in fanotify

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Date:	Fri, 26 Sep 2014 10:58:18 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Heinrich Schuchardt <xypron.debian@....de>
Cc:	Eric Paris <eparis@...hat.com>,
	Richard Guy Briggs <rgb@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	stable@...r.kernel.org, linux-api@...r.kernel.org,
	Jan Kara <jack@...e.cz>,
	Lino Sanfilippo <LinoSanfilippo@....de>
Subject: Re: [PATCHv8 1/6] fanotify: enable close-on-exec on events' fd when
 requested in fanotify_init()

Hi,

Le jeudi 25 septembre 2014 à 22:57 +0200, Heinrich Schuchardt a écrit :
> On 24.09.2014 15:11, 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().
> 
> I tested on kernel 3.17.0-rc5. I passed O_CLOEXEC in event_f_flags.
> When I called fcnt(event_metadata->fd, F_GETFD) it did not return 
> FD_CLOEXEC. So I can confirm your observation that O_CLOEXEC is not 
> working as expected.
> 
> I found this definition
> #define get_unused_fd() get_unused_fd_flags(0)
> 
> So essentially when get_unused_fd() is called for a fanotify event 
> O_CLOEXEC is ignored.
> 
> This is what your patch fixes.
> 
> >
> > More, there's no effective check on event_f_flags value that
> > would catch unknown / unsupported values, unlike the one on
> > f_flags argument of the syscall (see FAN_ALL_INIT_FLAGS in
> > include/uapi/linux/fanotify.h).
> 
> The fanotify_init(2) man page describes which flags are allowable in 
> event_f_flags.
> 
> Could you, please, explain why the following code in fanotify_user.c is 
> not to be considered an effective check:
> 
>      if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS)
>          return -EINVAL;
> 
>      switch (event_f_flags & O_ACCMODE) {
>      case O_RDONLY:
>      case O_RDWR:
>      case O_WRONLY:
>          break;
>      default:
>          return -EINVAL;
>      }
> 
> I CC Jan Kara as he reviewed the code.
> 

I missed the opportunity to update my commit message.

I've sent my initial version of the patch (with the same wording) on
5th, January, 2014:

http://mid.gmane.org/3d9591f81e62a78a726721c8052b3910870db35e.1388952061.git.ydroneaud@opteya.com
http://lkml.kernel.org/r/3d9591f81e62a78a726721c8052b3910870db35e.1388952061.git.ydroneaud@opteya.com

The patch was sent again on March, 11:

http://lkml.kernel.org/r/baab31b572b216d13f2149bdf07e0f79a1bae660.1394532336.git.ydroneaud@opteya.com
http://mid.gmane.org/baab31b572b216d13f2149bdf07e0f79a1bae660.1394532336.git.ydroneaud@opteya.com

And another time, on June, 1st:

http://lkml.kernel.org/r/2c6ab28980f0007ea3b9afa7ecd7497806a6a451.1401630396.git.ydroneaud@opteya.com
http://mid.gmane.org/2c6ab28980f0007ea3b9afa7ecd7497806a6a451.1401630396.git.ydroneaud@opteya.com

So as you can see, my patch predate yours:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=48149e9d3a7e924010a0daab30a6197b7d7b6580

But I have to apologize: I haven't noticed your patch was merged between
my previous submission and the current one. My bad.

I will update the commit message to remove my obsolete comment on the
input parameter check.

Thanks again for review and testing.

Regards.

-- 
Yann Droneaud
OPTEYA


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