[06/11] tty: fix race in tty_fasync

[Greg KH <gregkh@suse.de>]

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

------------------

From: Greg Kroah-Hartman <gregkh@suse.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@xmission.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tavis Ormandy <taviso@google.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Julien Tinnes <jln@google.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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 {