[PATCH 4.4 073/117] n_tty: Fix unsafe reference to "other" ldisc

Greg Kroah-Hartman
2016-02-15T00:31:25Z

From: Peter Hurley <peter@hurleysoftware.com>

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>

---
drivers/tty/n_tty.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -258,16 +258,13 @@ static void n_tty_check_throttle(struct

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;
}