n_tty: Fix unsafe reference to "other" ldisc

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().

Cc: <stable@vger.kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index d9a5fc28fef4..b280abaad91b 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -269,16 +269,13 @@ 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_kick_worker(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;
         }