USB: mos7840: fix race in led handling

Fix race in LED handling introduced by commit 0eafe4d ("USB: serial:
mos7840: add support for MCS7810 devices") which reused the port control
urb for manipulating the LED without making sure that the urb is not
already in use. This could lead to the control urb being manipulated
while in flight.

Fix by adding a dedicated LED urb and ctrlrequest along with a LED-busy
flag to handle concurrency.

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

@@ -185,6 +185,7 @@
 
 enum mos7840_flag {
 	MOS7840_FLAG_CTRL_BUSY,
+	MOS7840_FLAG_LED_BUSY,
 };
 
 static const struct usb_device_id id_table[] = {
@@ -240,9 +241,10 @@ struct moschip_port {
 
 	/* For device(s) with LED indicator */
 	bool has_led;
-	bool led_flag;
 	struct timer_list led_timer1;	/* Timer for LED on */
 	struct timer_list led_timer2;	/* Timer for LED off */
+	struct urb *led_urb;
+	struct usb_ctrlrequest *led_dr;
 
 	unsigned long flags;
 };
@@ -535,18 +537,18 @@ static void mos7840_set_led_async(struct moschip_port *mcs, __u16 wval,
 				__u16 reg)
 {
 	struct usb_device *dev = mcs->port->serial->dev;
-	struct usb_ctrlrequest *dr = mcs->dr;
+	struct usb_ctrlrequest *dr = mcs->led_dr;
 
 	dr->bRequestType = MCS_WR_RTYPE;
 	dr->bRequest = MCS_WRREQ;
 	dr->wValue = cpu_to_le16(wval);
 	dr->wIndex = cpu_to_le16(reg);
 	dr->wLength = cpu_to_le16(0);
 
-	usb_fill_control_urb(mcs->control_urb, dev, usb_sndctrlpipe(dev, 0),
+	usb_fill_control_urb(mcs->led_urb, dev, usb_sndctrlpipe(dev, 0),
 		(unsigned char *)dr, NULL, 0, mos7840_set_led_callback, NULL);
 
-	usb_submit_urb(mcs->control_urb, GFP_ATOMIC);
+	usb_submit_urb(mcs->led_urb, GFP_ATOMIC);
 }
 
 static void mos7840_set_led_sync(struct usb_serial_port *port, __u16 reg,
@@ -572,7 +574,19 @@ static void mos7840_led_flag_off(unsigned long arg)
 {
 	struct moschip_port *mcs = (struct moschip_port *) arg;
 
-	mcs->led_flag = false;
+	clear_bit_unlock(MOS7840_FLAG_LED_BUSY, &mcs->flags);
+}
+
+static void mos7840_led_activity(struct usb_serial_port *port)
+{
+	struct moschip_port *mos7840_port = usb_get_serial_port_data(port);
+
+	if (test_and_set_bit_lock(MOS7840_FLAG_LED_BUSY, &mos7840_port->flags))
+		return;
+
+	mos7840_set_led_async(mos7840_port, 0x0301, MODEM_CONTROL_REGISTER);
+	mod_timer(&mos7840_port->led_timer1,
+				jiffies + msecs_to_jiffies(LED_ON_MS));
 }
 
 /*****************************************************************************
@@ -770,14 +784,8 @@ static void mos7840_bulk_in_callback(struct urb *urb)
 		return;
 	}
 
-	/* Turn on LED */
-	if (mos7840_port->has_led && !mos7840_port->led_flag) {
-		mos7840_port->led_flag = true;
-		mos7840_set_led_async(mos7840_port, 0x0301,
-					MODEM_CONTROL_REGISTER);
-		mod_timer(&mos7840_port->led_timer1,
-				jiffies + msecs_to_jiffies(LED_ON_MS));
-	}
+	if (mos7840_port->has_led)
+		mos7840_led_activity(port);
 
 	mos7840_port->read_urb_busy = true;
 	retval = usb_submit_urb(mos7840_port->read_urb, GFP_ATOMIC);
@@ -1454,13 +1462,8 @@ static int mos7840_write(struct tty_struct *tty, struct usb_serial_port *port,
 	data1 = urb->transfer_buffer;
 	dev_dbg(&port->dev, "bulkout endpoint is %d\n", port->bulk_out_endpointAddress);
 
-	/* Turn on LED */
-	if (mos7840_port->has_led && !mos7840_port->led_flag) {
-		mos7840_port->led_flag = true;
-		mos7840_set_led_sync(port, MODEM_CONTROL_REGISTER, 0x0301);
-		mod_timer(&mos7840_port->led_timer1,
-				jiffies + msecs_to_jiffies(LED_ON_MS));
-	}
+	if (mos7840_port->has_led)
+		mos7840_led_activity(port);
 
 	/* send it down the pipe */
 	status = usb_submit_urb(urb, GFP_ATOMIC);
@@ -2412,6 +2415,14 @@ static int mos7840_port_probe(struct usb_serial_port *port)
 	if (device_type == MOSCHIP_DEVICE_ID_7810) {
 		mos7840_port->has_led = true;
 
+		mos7840_port->led_urb = usb_alloc_urb(0, GFP_KERNEL);
+		mos7840_port->led_dr = kmalloc(sizeof(*mos7840_port->led_dr),
+								GFP_KERNEL);
+		if (!mos7840_port->led_urb || !mos7840_port->led_dr) {
+			status = -ENOMEM;
+			goto error;
+		}
+
 		init_timer(&mos7840_port->led_timer1);
 		mos7840_port->led_timer1.function = mos7840_led_off;
 		mos7840_port->led_timer1.expires =
@@ -2424,8 +2435,6 @@ static int mos7840_port_probe(struct usb_serial_port *port)
 			jiffies + msecs_to_jiffies(LED_OFF_MS);
 		mos7840_port->led_timer2.data = (unsigned long)mos7840_port;
 
-		mos7840_port->led_flag = false;
-
 		/* Turn off LED */
 		mos7840_set_led_sync(port, MODEM_CONTROL_REGISTER, 0x0300);
 	}
@@ -2447,6 +2456,8 @@ static int mos7840_port_probe(struct usb_serial_port *port)
 	}
 	return 0;
 error:
+	kfree(mos7840_port->led_dr);
+	usb_free_urb(mos7840_port->led_urb);
 	kfree(mos7840_port->dr);
 	kfree(mos7840_port->ctrl_buf);
 	usb_free_urb(mos7840_port->control_urb);
@@ -2467,6 +2478,10 @@ static int mos7840_port_remove(struct usb_serial_port *port)
 
 		del_timer_sync(&mos7840_port->led_timer1);
 		del_timer_sync(&mos7840_port->led_timer2);
+
+		usb_kill_urb(mos7840_port->led_urb);
+		usb_free_urb(mos7840_port->led_urb);
+		kfree(mos7840_port->led_dr);
 	}
 	usb_kill_urb(mos7840_port->control_urb);
 	usb_free_urb(mos7840_port->control_urb);