USB: mos7840: fix DMA to stack

Fix regression introduced by commit 0eafe4de ("USB: serial: mos7840:
add support for MCS7810 devices") which used stack-allocated buffers for
control messages.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/mos7840.c

@@ -2142,13 +2142,21 @@ static int mos7840_ioctl(struct tty_struct *tty,
 static int mos7810_check(struct usb_serial *serial)
 {
 	int i, pass_count = 0;
+	u8 *buf;
 	__u16 data = 0, mcr_data = 0;
 	__u16 test_pattern = 0x55AA;
+	int res;
+
+	buf = kmalloc(VENDOR_READ_LENGTH, GFP_KERNEL);
+	if (!buf)
+		return 0;	/* failed to identify 7810 */
 
 	/* Store MCR setting */
-	usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
+	res = usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
 		MCS_RDREQ, MCS_RD_RTYPE, 0x0300, MODEM_CONTROL_REGISTER,
-		&mcr_data, VENDOR_READ_LENGTH, MOS_WDR_TIMEOUT);
+		buf, VENDOR_READ_LENGTH, MOS_WDR_TIMEOUT);
+	if (res == VENDOR_READ_LENGTH)
+		mcr_data = *buf;
 
 	for (i = 0; i < 16; i++) {
 		/* Send the 1-bit test pattern out to MCS7810 test pin */
@@ -2158,9 +2166,12 @@ static int mos7810_check(struct usb_serial *serial)
 			MODEM_CONTROL_REGISTER, NULL, 0, MOS_WDR_TIMEOUT);
 
 		/* Read the test pattern back */
-		usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
-			MCS_RDREQ, MCS_RD_RTYPE, 0, GPIO_REGISTER, &data,
+		res = usb_control_msg(serial->dev,
+				usb_rcvctrlpipe(serial->dev, 0), MCS_RDREQ,
+				MCS_RD_RTYPE, 0, GPIO_REGISTER, buf,
 				VENDOR_READ_LENGTH, MOS_WDR_TIMEOUT);
+		if (res == VENDOR_READ_LENGTH)
+			data = *buf;
 
 		/* If this is a MCS7810 device, both test patterns must match */
 		if (((test_pattern >> i) ^ (~data >> 1)) & 0x0001)
@@ -2174,6 +2185,8 @@ static int mos7810_check(struct usb_serial *serial)
 		MCS_WR_RTYPE, 0x0300 | mcr_data, MODEM_CONTROL_REGISTER, NULL,
 		0, MOS_WDR_TIMEOUT);
 
+	kfree(buf);
+
 	if (pass_count == 16)
 		return 1;
 
@@ -2183,11 +2196,17 @@ static int mos7810_check(struct usb_serial *serial)
 static int mos7840_calc_num_ports(struct usb_serial *serial)
 {
 	__u16 data = 0x00;
+	u8 *buf;
 	int mos7840_num_ports;
 
+	buf = kzalloc(VENDOR_READ_LENGTH, GFP_KERNEL);
+	if (buf) {
 		usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
-		MCS_RDREQ, MCS_RD_RTYPE, 0, GPIO_REGISTER, &data,
+			MCS_RDREQ, MCS_RD_RTYPE, 0, GPIO_REGISTER, buf,
 			VENDOR_READ_LENGTH, MOS_WDR_TIMEOUT);
+		data = *buf;
+		kfree(buf);
+	}
 
 	if (serial->dev->descriptor.idProduct == MOSCHIP_DEVICE_ID_7810 ||
 		serial->dev->descriptor.idProduct == MOSCHIP_DEVICE_ID_7820) {