n_tty: Fix unsafe reference to "other" ldisc

commit 6d27a63caad3f13e96cf065d2d96828c2006be6b upstream.

Although n_tty_check_unthrottle() has a valid ldisc reference (since
the tty core gets the ldisc ref in tty_read() before calling the line
discipline read() method), it does not have a valid ldisc reference to
the "other" pty of a pty pair. Since getting an ldisc reference for
tty->link essentially open-codes tty_wakeup(), just replace with the
equivalent tty_wakeup().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index d239fdba29d688af2b1039b1fcbf52612313eb50..cdf72bcb3d786170dd353e9f366ffa678e35c305 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -277,16 +277,13 @@ static void n_tty_check_throttle(struct tty_struct *tty)
 
 static void n_tty_check_unthrottle(struct tty_struct *tty)
 {
-       if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
-           tty->link->ldisc->ops->write_wakeup == n_tty_write_wakeup) {
+       if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
                if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
                        return;
                if (!tty->count)
                        return;
                n_tty_set_room(tty);
-               n_tty_write_wakeup(tty->link);
-               if (waitqueue_active(&tty->link->write_wait))
-                       wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT);
+               tty_wakeup(tty->link);
                return;
        }