From 8bcd4e6a8decac251d55c4377e2e67f052777ce0 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Fri, 3 Nov 2017 15:30:55 +0100
Subject: [PATCH] serdev: ttyport: fix NULL-deref on hangup
Git-commit: 8bcd4e6a8decac251d55c4377e2e67f052777ce0
Patch-mainline: v4.15-rc3
References: bsc#1051510

Make sure to use a properly refcounted tty_struct in write_wake up to
avoid dereferencing a NULL-pointer when a port is being hung up.

Fixes: bed35c6dfa6a ("serdev: add a tty port controller driver")
Cc: stable <stable@vger.kernel.org>     # 4.11
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/serdev/serdev-ttyport.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c
@@ -57,12 +57,19 @@ static void ttyport_write_wakeup(struct
 {
 	struct serdev_controller *ctrl = port->client_data;
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	struct tty_struct *tty;
 
-	if (test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &port->tty->flags) &&
+	tty = tty_port_tty_get(port);
+	if (!tty)
+		return;
+
+	if (test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags) &&
 	    test_bit(SERPORT_ACTIVE, &serport->flags))
 		serdev_controller_write_wakeup(ctrl);
 
-	wake_up_interruptible_poll(&port->tty->write_wait, POLLOUT);
+	wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
+
+	tty_kref_put(tty);
 }
 
 static const struct tty_port_client_operations client_ops = {