linux-kernel - Re: F_DUPFD_CLOEXEC broken in 3.7.0

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Date:	Tue, 9 Oct 2012 15:10:53 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Jim Meyering <jim@...ering.net>, eblake@...hat.com,
	Al Viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: F_DUPFD_CLOEXEC broken in 3.7.0

On Tue, Oct 09, 2012 at 10:07:22PM +0800, Cong Wang wrote:
> On Tue, Oct 9, 2012 at 6:05 AM, Richard W.M. Jones <rjones@...hat.com> wrote:
> > Let's move this to LKML ...
> >
> > On Mon, Oct 08, 2012 at 10:53:25PM +0100, Richard W.M. Jones wrote:
> >> On Mon, Oct 08, 2012 at 10:50:30PM +0100, Richard W.M. Jones wrote:
> >> [.. discussion on gnulib test-cloexec test snipped ..]
> >> > I'm suspicious this is a kernel bug:
> >> >
> >> > creat("test-cloexec.tmp", 0600)         = 3
> >> > fcntl(3, F_GETFD)                       = 0
> >> > fcntl(3, F_GETFD)                       = 0
> >> > fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
> >> > fcntl(3, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
> >> > fcntl(3, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
> >> > fcntl(3, F_SETFD, 0)                    = 0
> >> > fcntl(3, F_GETFD)                       = 0
> >> > fcntl(3, F_DUPFD_CLOEXEC, 0)            = 4
> >> > fcntl(4, F_GETFD)                       = 0
> >> > write(2, "test-cloexec.c:97: assertion failed\n", 36) = 36
> >> >
> >> > It seems to me from the description in the man page that
> >> > F_DUPFD_CLOEXEC ought to be setting the FD_CLOEXEC flag on file
> >> > descriptor 4, so either it's not or else F_GETFD isn't reading the
> >> > flag for some reason.
> >>
> >> Al Viro (CC'd) made some changes in this area recently ..
> >
> > Attached is a self-contained test program that demonstrates the bug.
> >
> 
> Seems we passed a wrong flag to f_dupfd()...
> Does the following patch help?
> 
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 8f70429..71a600a 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -258,7 +258,7 @@ static long do_fcntl(int fd, unsigned int cmd,
> unsigned long arg,
>                 err = f_dupfd(arg, filp, 0);
>                 break;
>         case F_DUPFD_CLOEXEC:
> -               err = f_dupfd(arg, filp, FD_CLOEXEC);
> +               err = f_dupfd(arg, filp, O_CLOEXEC);
>                 break;
>         case F_GETFD:
>                 err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;

Yes ..  the same patch has already been sent upstream.

Rich.

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