Date:   Thu, 24 Jan 2019 19:55:12 -0800
From:   Myungho Jung <mhjungk@gmail.com>
To:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>
Cc:     linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] Bluetooth: hci_ldisc: Fix for pty driver
Message-ID: <20190125035510.GA21654@myunghoj-Precision-5530>
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tty_set_termios() should be called with slave side of pty driver. So, If
tty driver is pty master, it needs to be switched to ->link. Also,
tiocmget() and tiocmset() operations are optional so we need NULL check
for some drivers missing the operations like pty.

Reported-by: syzbot+a950165cbb86bdd023a4@syzkaller.appspotmail.com
Signed-off-by: Myungho Jung <mhjungk@gmail.com>
---
 drivers/bluetooth/hci_ldisc.c | 76 +++++++++++++++++++++--------------
 1 file changed, 46 insertions(+), 30 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index fbf7b4df23ab..169dde91b3d3 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -299,10 +299,18 @@ static int hci_uart_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
 	return 0;
 }
 
+/* If driver is pty master, return slave side */
+static struct tty_struct *hci_uart_get_real_tty(struct tty_struct *tty)
+{
+	return  (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+		 tty->driver->subtype == PTY_TYPE_MASTER) ? tty->link : tty;
+}
+
 /* Flow control or un-flow control the device */
 void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
 {
 	struct tty_struct *tty = hu->tty;
+	struct tty_struct *real_tty;
 	struct ktermios ktermios;
 	int status;
 	unsigned int set = 0;
@@ -314,45 +322,52 @@ void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
 		return;
 	}
 
+	real_tty = hci_uart_get_real_tty(tty);
 	if (enable) {
 		/* Disable hardware flow control */
-		ktermios = tty->termios;
+		ktermios = real_tty->termios;
 		ktermios.c_cflag &= ~CRTSCTS;
-		status = tty_set_termios(tty, &ktermios);
+		status = tty_set_termios(real_tty, &ktermios);
 		BT_DBG("Disabling hardware flow control: %s",
 		       status ? "failed" : "success");
 
-		/* Clear RTS to prevent the device from sending */
-		/* Most UARTs need OUT2 to enable interrupts */
-		status = tty->driver->ops->tiocmget(tty);
-		BT_DBG("Current tiocm 0x%x", status);
-
-		set &= ~(TIOCM_OUT2 | TIOCM_RTS);
-		clear = ~set;
-		set &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
-		       TIOCM_OUT2 | TIOCM_LOOP;
-		clear &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
-			 TIOCM_OUT2 | TIOCM_LOOP;
-		status = tty->driver->ops->tiocmset(tty, set, clear);
-		BT_DBG("Clearing RTS: %s", status ? "failed" : "success");
+		if (tty->driver->ops->tiocmget && tty->driver->ops->tiocmset) {
+			/* Clear RTS to prevent the device from sending */
+			/* Most UARTs need OUT2 to enable interrupts */
+			status = tty->driver->ops->tiocmget(tty);
+			BT_DBG("Current tiocm 0x%x", status);
+
+			set &= ~(TIOCM_OUT2 | TIOCM_RTS);
+			clear = ~set;
+			set &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
+				TIOCM_OUT2 | TIOCM_LOOP;
+			clear &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
+				TIOCM_OUT2 | TIOCM_LOOP;
+			status = tty->driver->ops->tiocmset(tty, set, clear);
+			BT_DBG("Clearing RTS: %s", status ? "failed" :
+			       "success");
+		}
 	} else {
-		/* Set RTS to allow the device to send again */
-		status = tty->driver->ops->tiocmget(tty);
-		BT_DBG("Current tiocm 0x%x", status);
-
-		set |= (TIOCM_OUT2 | TIOCM_RTS);
-		clear = ~set;
-		set &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
-		       TIOCM_OUT2 | TIOCM_LOOP;
-		clear &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
-			 TIOCM_OUT2 | TIOCM_LOOP;
-		status = tty->driver->ops->tiocmset(tty, set, clear);
-		BT_DBG("Setting RTS: %s", status ? "failed" : "success");
+		if (tty->driver->ops->tiocmget && tty->driver->ops->tiocmset) {
+			/* Set RTS to allow the device to send again */
+			status = tty->driver->ops->tiocmget(tty);
+			BT_DBG("Current tiocm 0x%x", status);
+
+			set |= (TIOCM_OUT2 | TIOCM_RTS);
+			clear = ~set;
+			set &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
+				TIOCM_OUT2 | TIOCM_LOOP;
+			clear &= TIOCM_DTR | TIOCM_RTS | TIOCM_OUT1 |
+				TIOCM_OUT2 | TIOCM_LOOP;
+			status = tty->driver->ops->tiocmset(tty, set, clear);
+			BT_DBG("Setting RTS: %s", status ? "failed" :
+			       "success");
+		}
 
 		/* Re-enable hardware flow control */
-		ktermios = tty->termios;
+		ktermios = real_tty->termios;
 		ktermios.c_cflag |= CRTSCTS;
-		status = tty_set_termios(tty, &ktermios);
+		status = tty_set_termios(real_tty, &ktermios);
 		BT_DBG("Enabling hardware flow control: %s",
 		       status ? "failed" : "success");
 	}
@@ -367,9 +382,10 @@ void hci_uart_set_speeds(struct hci_uart *hu, unsigned int init_speed,
 
 void hci_uart_set_baudrate(struct hci_uart *hu, unsigned int speed)
 {
-	struct tty_struct *tty = hu->tty;
+	struct tty_struct *tty;
 	struct ktermios ktermios;
 
+	tty = hci_uart_get_real_tty(hu->tty);
 	ktermios = tty->termios;
 	ktermios.c_cflag &= ~CBAUD;
 	tty_termios_encode_baud_rate(&ktermios, speed, speed);
-- 
2.17.1