[PATCH 2/2] USB: serial: quatech2: fix baud rate overflow

[Johan Hovold <johan@kernel.org>]

The requested baud rate is incorrectly truncated to 16 bits so that
line speeds above 65535 bps cannot be set.

Use 32 bits for the rate while rejecting rates outside of
[50,921600] to avoid having the 16-bit divisor overflow.

Fixes: f7a33e608d9a ("USB: serial: add quatech2 usb to serial driver")
Cc: stable@vger.kernel.org	# 3.5
Cc: Bill Pemberton <wfp5p@virginia.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/quatech2.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/quatech2.c b/drivers/usb/serial/quatech2.c
index dc2b39810a26..3b4df3ac7c73 100644
--- a/drivers/usb/serial/quatech2.c
+++ b/drivers/usb/serial/quatech2.c
@@ -52,6 +52,7 @@
 #define QT2_XMIT_FLUSH      0x05  /* no following info */
 #define QT2_CONTROL_ESCAPE  0xff  /* pass through previous 2 control bytes */
 
+#define  MIN_BAUD_RATE              50
 #define  MAX_BAUD_RATE              921600
 #define  DEFAULT_BAUD_RATE          9600
 
@@ -156,7 +157,7 @@ static inline int calc_baud_divisor(int baudrate)
 
 static inline int qt2_set_port_config(struct usb_device *dev,
 				      unsigned char port_number,
-				      u16 baudrate, u16 lcr)
+				      speed_t baudrate, u16 lcr)
 {
 	int divisor = calc_baud_divisor(baudrate);
 	u16 index = ((u16) (lcr << 8) | (u16) (port_number));
@@ -257,9 +258,9 @@ static void qt2_set_termios(struct tty_struct *tty,
 	struct usb_device *dev = port->serial->dev;
 	struct qt2_port_private *port_priv;
 	struct ktermios *termios = &tty->termios;
-	u16 baud;
 	unsigned int cflag = termios->c_cflag;
 	u16 new_lcr = 0;
+	speed_t baud;
 	int status;
 
 	port_priv = usb_get_serial_port_data(port);
@@ -277,6 +278,18 @@ static void qt2_set_termios(struct tty_struct *tty,
 	if (!baud)
 		baud = 9600;
 
+	if (baud < MIN_BAUD_RATE || baud > MAX_BAUD_RATE) {
+		if (old_termios)
+			baud = tty_termios_baud_rate(old_termios);
+		else
+			baud = clamp(baud, MIN_BAUD_RATE, MAX_BAUD_RATE);
+
+		tty_encode_baud_rate(tty, baud, baud);
+
+		if (!baud)
+			baud = 9600;
+	}
+
 	status = qt2_set_port_config(dev, port_priv->device_port, baud,
 				     new_lcr);
 	if (status < 0)
@@ -373,7 +386,7 @@ static int qt2_open(struct tty_struct *tty, struct usb_serial_port *port)
 	port_priv->device_port = (u8) device_port;
 
 	if (tty)
-		qt2_set_termios(tty, port, &tty->termios);
+		qt2_set_termios(tty, port, NULL);
 
 	return 0;
 
-- 
2.55.0