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

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Date:	Tue, 26 Jan 2010 11:14:42 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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: [06/11] tty: fix race in tty_fasync

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

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

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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