[PATCH 4.18 135/228] tty: serial: lpuart: avoid leaking struct tty_struct

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Stefan Agner <stefan@xxxxxxxx>

commit 3216c622a24b0ebb9c159a8d1daf7f17a106b3f5 upstream.

The function tty_port_tty_get() gets a reference to the tty. Since
the code is not using tty_port_tty_set(), the reference is kept
even after closing the tty.

Avoid using tty_port_tty_get() by directly access the tty instance.
Since lpuart_start_rx_dma() is called from the .startup() and
.set_termios() callback, it is safe to assume the tty instance is
valid.

Cc: stable@xxxxxxxxxxxxxxx # v4.9+
Fixes: 5887ad43ee02 ("tty: serial: fsl_lpuart: Use cyclic DMA for Rx")
Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/fsl_lpuart.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -979,7 +979,8 @@ static inline int lpuart_start_rx_dma(st
 	struct circ_buf *ring = &sport->rx_ring;
 	int ret, nent;
 	int bits, baud;
-	struct tty_struct *tty = tty_port_tty_get(&sport->port.state->port);
+	struct tty_port *port = &sport->port.state->port;
+	struct tty_struct *tty = port->tty;
 	struct ktermios *termios = &tty->termios;
 
 	baud = tty_get_baud_rate(tty);