linux-kernel - Re: [06/11] tty: fix race in tty

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Date:	Tue, 26 Jan 2010 11:49:58 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Al Viro <viro@...IV.linux.org.uk>,
	Tavis Ormandy <taviso@...gle.com>,
	Jeff Dike <jdike@...toit.com>, Julien Tinnes <jln@...gle.com>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [06/11] tty: fix race in tty_fasync

Greg KH <gregkh@...e.de> writes:

> 2.6.27-stable review patch.  If anyone has any objections, please let us know.

Only that __f_setown by way of f_modown unconditionally enables interrupts.  So
without touching f_modown as well in mainline we have nasty sounding lockdep warnings.

Eric


> ------------------
>
> From: Greg Kroah-Hartman <gregkh@...e.de>
>
> commit 703625118069f9f8960d356676662d3db5a9d116 upstream.
>
> We need to keep the lock held over the call to __f_setown() to
> prevent a PID race.
>
> Thanks to Al Viro for pointing out the problem, and to Travis for
> making us look here in the first place.
>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Tavis Ormandy <taviso@...gle.com>
> Cc: Jeff Dike <jdike@...toit.com>
> Cc: Julien Tinnes <jln@...gle.com>
> Cc: Matt Mackall <mpm@...enic.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
>
> ---
>  drivers/char/tty_io.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/drivers/char/tty_io.c
> +++ b/drivers/char/tty_io.c
> @@ -2437,8 +2437,8 @@ static int tty_fasync(int fd, struct fil
>  			pid = task_pid(current);
>  			type = PIDTYPE_PID;
>  		}
> -		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
>  		retval = __f_setown(filp, pid, type, 0);
> +		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
>  		if (retval)
>  			goto out;
>  	} else {
--
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