[PATCH 3.16 213/370] USB: serial: ch341: fix control-message error handling

[Ben Hutchings]

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

commit 2d5a9c72d0c4ac73cf97f4b7814ed6c44b1e49ae upstream.

A short control transfer would currently fail to be detected, something
which could lead to stale buffer data being used as valid input.

Check for short transfers, and make sure to log any transfer errors.

Note that this also avoids leaking heap data to user space (TIOCMGET)
and the remote device (break control).

Fixes: 6ce76104781a ("USB: Driver for CH341 USB-serial adaptor")
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/serial/ch341.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -112,6 +112,8 @@ static int ch341_control_out(struct usb_
 	r = usb_control_msg(dev, usb_sndctrlpipe(dev, 0), request,
 			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
 			    value, index, NULL, 0, DEFAULT_TIMEOUT);
+	if (r < 0)
+		dev_err(&dev->dev, "failed to send control message: %d\n", r);
 
 	return r;
 }
@@ -129,7 +131,20 @@ static int ch341_control_in(struct usb_d
 	r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), request,
 			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
 			    value, index, buf, bufsize, DEFAULT_TIMEOUT);
-	return r;
+	if (r < bufsize) {
+		if (r >= 0) {
+			dev_err(&dev->dev,
+				"short control message received (%d < %u)\n",
+				r, bufsize);
+			r = -EIO;
+		}
+
+		dev_err(&dev->dev, "failed to receive control message: %d\n",
+			r);
+		return r;
+	}
+
+	return 0;
 }
 
 static int ch341_set_baudrate_lcr(struct usb_device *dev,
@@ -180,9 +195,9 @@ static int ch341_set_handshake(struct us
 
 static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
 {
+	const unsigned int size = 2;
 	char *buffer;
 	int r;
-	const unsigned size = 8;
 	unsigned long flags;
 
 	buffer = kmalloc(size, GFP_KERNEL);
@@ -193,14 +208,9 @@ static int ch341_get_status(struct usb_d
 	if (r < 0)
 		goto out;
 
-	/* setup the private status if available */
-	if (r == 2) {
-		r = 0;
-		spin_lock_irqsave(&priv->lock, flags);
-		priv->line_status = (~(*buffer)) & CH341_BITS_MODEM_STAT;
-		spin_unlock_irqrestore(&priv->lock, flags);
-	} else
-		r = -EPROTO;
+	spin_lock_irqsave(&priv->lock, flags);
+	priv->line_status = (~(*buffer)) & CH341_BITS_MODEM_STAT;
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 out:	kfree(buffer);
 	return r;
@@ -210,9 +220,9 @@ out:	kfree(buffer);
 
 static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
 {
+	const unsigned int size = 2;
 	char *buffer;
 	int r;
-	const unsigned size = 8;
 
 	buffer = kmalloc(size, GFP_KERNEL);
 	if (!buffer)