USB: serial: re-implement multi-urb writes in generic driver

Use dynamic transfer buffer sizes since it is more efficient to let the
host controller do the partitioning to fit endpoint size. This way we
also do not use more than one urb per write request.

Replace max_in_flight_urbs with multi_urb_write flag in struct
usb_serial_driver to enable multi-urb writes.

Use MAX_TX_URBS=40 and a max buffer size of PAGE_SIZE to prevent DoS
attacks.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/generic.c

@@ -25,6 +25,8 @@
 
 static int debug;
 
+#define MAX_TX_URBS		40
+
 #ifdef CONFIG_USB_SERIAL_GENERIC
 
 static int generic_probe(struct usb_interface *interface,
@@ -172,78 +174,63 @@ static int usb_serial_multi_urb_write(struct tty_struct *tty,
 	struct urb *urb;
 	unsigned char *buffer;
 	int status;
-	int towrite;
-	int bwrite = 0;
-
-	dbg("%s - port %d", __func__, port->number);
-
-	if (count == 0)
-		dbg("%s - write request of 0 bytes", __func__);
 
-	while (count > 0) {
-		towrite = (count > port->bulk_out_size) ?
-			port->bulk_out_size : count;
-		spin_lock_irqsave(&port->lock, flags);
-		if (port->urbs_in_flight >
-		    port->serial->type->max_in_flight_urbs) {
-			spin_unlock_irqrestore(&port->lock, flags);
-			dbg("%s - write limit hit", __func__);
-			return bwrite;
-		}
-		port->tx_bytes_flight += towrite;
-		port->urbs_in_flight++;
+	spin_lock_irqsave(&port->lock, flags);
+	if (port->tx_urbs == MAX_TX_URBS) {
 		spin_unlock_irqrestore(&port->lock, flags);
+		dbg("%s - write limit hit", __func__);
+		return 0;
+	}
+	port->tx_urbs++;
+	spin_unlock_irqrestore(&port->lock, flags);
 
-		buffer = kmalloc(towrite, GFP_ATOMIC);
-		if (!buffer) {
-			dev_err(&port->dev,
-			"%s ran out of kernel memory for urb ...\n", __func__);
-			goto error_no_buffer;
-		}
+	urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!urb) {
+		dev_err(&port->dev, "%s - no free urbs available\n", __func__);
+		status = -ENOMEM;
+		goto err_urb;
+	}
 
-		urb = usb_alloc_urb(0, GFP_ATOMIC);
-		if (!urb) {
-			dev_err(&port->dev, "%s - no more free urbs\n",
+	count = min_t(int, count, PAGE_SIZE);
+	buffer = kmalloc(count, GFP_ATOMIC);
+	if (!buffer) {
+		dev_err(&port->dev, "%s - could not allocate buffer\n",
 				__func__);
-			goto error_no_urb;
-		}
+		status = -ENOMEM;
+		goto err_buf;
+	}
 
-		/* Copy data */
-		memcpy(buffer, buf + bwrite, towrite);
-		usb_serial_debug_data(debug, &port->dev, __func__,
-				      towrite, buffer);
-		/* fill the buffer and send it */
-		usb_fill_bulk_urb(urb, port->serial->dev,
+	memcpy(buffer, buf, count);
+	usb_serial_debug_data(debug, &port->dev, __func__, count, buffer);
+	usb_fill_bulk_urb(urb, port->serial->dev,
 			usb_sndbulkpipe(port->serial->dev,
 					port->bulk_out_endpointAddress),
-			buffer, towrite,
+			buffer, count,
 			port->serial->type->write_bulk_callback, port);
 
-		status = usb_submit_urb(urb, GFP_ATOMIC);
-		if (status) {
-			dev_err(&port->dev, "%s - error submitting urb: %d\n",
+	status = usb_submit_urb(urb, GFP_ATOMIC);
+	if (status) {
+		dev_err(&port->dev, "%s - error submitting urb: %d\n",
 				__func__, status);
-			goto error;
-		}
-
-		/* This urb is the responsibility of the host driver now */
-		usb_free_urb(urb);
-		dbg("%s write: %d", __func__, towrite);
-		count -= towrite;
-		bwrite += towrite;
+		goto err;
 	}
-	return bwrite;
+	spin_lock_irqsave(&port->lock, flags);
+	port->tx_bytes += urb->transfer_buffer_length;
+	spin_unlock_irqrestore(&port->lock, flags);
 
-error:
 	usb_free_urb(urb);
-error_no_urb:
+
+	return count;
+err:
 	kfree(buffer);
-error_no_buffer:
+err_buf:
+	usb_free_urb(urb);
+err_urb:
 	spin_lock_irqsave(&port->lock, flags);
-	port->urbs_in_flight--;
-	port->tx_bytes_flight -= towrite;
+	port->tx_urbs--;
 	spin_unlock_irqrestore(&port->lock, flags);
-	return bwrite;
+
+	return status;
 }
 
 /**
@@ -286,7 +273,7 @@ static int usb_serial_generic_write_start(struct usb_serial_port *port)
 	}
 
 	spin_lock_irqsave(&port->lock, flags);
-	port->tx_bytes_flight += count;
+	port->tx_bytes += count;
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	return count;
@@ -318,9 +305,8 @@ int usb_serial_generic_write(struct tty_struct *tty,
 	if (!count)
 		return 0;
 
-	if (serial->type->max_in_flight_urbs)
-		return usb_serial_multi_urb_write(tty, port,
-						  buf, count);
+	if (serial->type->multi_urb_write)
+		return usb_serial_multi_urb_write(tty, port, buf, count);
 
 	count = kfifo_in_locked(&port->write_fifo, buf, count, &port->lock);
 	result = usb_serial_generic_write_start(port);
@@ -337,7 +323,7 @@ int usb_serial_generic_write_room(struct tty_struct *tty)
 	struct usb_serial_port *port = tty->driver_data;
 	struct usb_serial *serial = port->serial;
 	unsigned long flags;
-	int room = 0;
+	int room;
 
 	dbg("%s - port %d", __func__, port->number);
 
@@ -345,14 +331,10 @@ int usb_serial_generic_write_room(struct tty_struct *tty)
 		return 0;
 
 	spin_lock_irqsave(&port->lock, flags);
-	if (serial->type->max_in_flight_urbs) {
-		if (port->urbs_in_flight < serial->type->max_in_flight_urbs)
-			room = port->bulk_out_size *
-				(serial->type->max_in_flight_urbs -
-				 port->urbs_in_flight);
-	} else {
+	if (serial->type->multi_urb_write)
+		room = (MAX_TX_URBS - port->tx_urbs) * PAGE_SIZE;
+	else
 		room = kfifo_avail(&port->write_fifo);
-	}
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	dbg("%s - returns %d", __func__, room);
@@ -372,10 +354,10 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
 		return 0;
 
 	spin_lock_irqsave(&port->lock, flags);
-	if (serial->type->max_in_flight_urbs)
-		chars = port->tx_bytes_flight;
+	if (serial->type->multi_urb_write)
+		chars = port->tx_bytes;
 	else
-		chars = kfifo_len(&port->write_fifo) + port->tx_bytes_flight;
+		chars = kfifo_len(&port->write_fifo) + port->tx_bytes;
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	dbg("%s - returns %d", __func__, chars);
@@ -461,18 +443,16 @@ void usb_serial_generic_write_bulk_callback(struct urb *urb)
 
 	dbg("%s - port %d", __func__, port->number);
 
-	if (port->serial->type->max_in_flight_urbs) {
+	if (port->serial->type->multi_urb_write) {
 		kfree(urb->transfer_buffer);
 
 		spin_lock_irqsave(&port->lock, flags);
-		--port->urbs_in_flight;
-		port->tx_bytes_flight -= urb->transfer_buffer_length;
-		if (port->urbs_in_flight < 0)
-			port->urbs_in_flight = 0;
+		port->tx_bytes -= urb->transfer_buffer_length;
+		port->tx_urbs--;
 		spin_unlock_irqrestore(&port->lock, flags);
 	} else {
 		spin_lock_irqsave(&port->lock, flags);
-		port->tx_bytes_flight -= urb->transfer_buffer_length;
+		port->tx_bytes -= urb->transfer_buffer_length;
 		port->write_urb_busy = 0;
 		spin_unlock_irqrestore(&port->lock, flags);
 

include/linux/usb/serial.h

@@ -60,6 +60,8 @@ enum port_dev_state {
  * @write_urb: pointer to the bulk out struct urb for this port.
  * @write_fifo: kfifo used to buffer outgoing data
  * @write_urb_busy: port`s writing status
+ * @tx_bytes: number of bytes currently in host stack queues
+ * @tx_urbs: number of urbs currently in host stack queues
  * @bulk_out_endpointAddress: endpoint address for the bulk out pipe for this
  *	port.
  * @write_wait: a wait_queue_head_t used by the port.
@@ -98,8 +100,8 @@ struct usb_serial_port {
 	int			write_urb_busy;
 	__u8			bulk_out_endpointAddress;
 
-	int			tx_bytes_flight;
-	int			urbs_in_flight;
+	int			tx_bytes;
+	int			tx_urbs;
 
 	wait_queue_head_t	write_wait;
 	struct work_struct	work;
@@ -223,7 +225,8 @@ struct usb_serial_driver {
 	struct device_driver	driver;
 	struct usb_driver	*usb_driver;
 	struct usb_dynids	dynids;
-	int			max_in_flight_urbs;
+
+	unsigned char		multi_urb_write:1;
 
 	size_t			bulk_in_size;
 	size_t			bulk_out_size;