USB: serial: io_edgeport: fix epic-descriptor handling

Use a dedicated buffer for the DMA transfer and make sure to detect
short transfers to avoid parsing a corrupt descriptor.

Fixes: 6e8cf7751f9f ("USB: add EPIC support to the io_edgeport driver")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/io_edgeport.c

@@ -492,20 +492,24 @@ static int get_epic_descriptor(struct edgeport_serial *ep)
 	int result;
 	struct usb_serial *serial = ep->serial;
 	struct edgeport_product_info *product_info = &ep->product_info;
-	struct edge_compatibility_descriptor *epic = &ep->epic_descriptor;
+	struct edge_compatibility_descriptor *epic;
 	struct edge_compatibility_bits *bits;
 	struct device *dev = &serial->dev->dev;
 
 	ep->is_epic = 0;
+
+	epic = kmalloc(sizeof(*epic), GFP_KERNEL);
+	if (!epic)
+		return -ENOMEM;
+
 	result = usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
 				 USB_REQUEST_ION_GET_EPIC_DESC,
 				 0xC0, 0x00, 0x00,
-				 &ep->epic_descriptor,
-				 sizeof(struct edge_compatibility_descriptor),
+				 epic, sizeof(*epic),
 				 300);
-
-	if (result > 0) {
+	if (result == sizeof(*epic)) {
 		ep->is_epic = 1;
+		memcpy(&ep->epic_descriptor, epic, sizeof(*epic));
 		memset(product_info, 0, sizeof(struct edgeport_product_info));
 
 		product_info->NumPorts = epic->NumPorts;
@@ -534,8 +538,16 @@ static int get_epic_descriptor(struct edgeport_serial *ep)
 		dev_dbg(dev, "  IOSPWriteLCR     : %s\n", bits->IOSPWriteLCR	? "TRUE": "FALSE");
 		dev_dbg(dev, "  IOSPSetBaudRate  : %s\n", bits->IOSPSetBaudRate	? "TRUE": "FALSE");
 		dev_dbg(dev, "  TrueEdgeport     : %s\n", bits->TrueEdgeport	? "TRUE": "FALSE");
+
+		result = 0;
+	} else if (result >= 0) {
+		dev_warn(&serial->interface->dev, "short epic descriptor received: %d\n",
+			 result);
+		result = -EIO;
 	}
 
+	kfree(epic);
+
 	return result;
 }
 
@@ -2779,7 +2791,7 @@ static int edge_startup(struct usb_serial *serial)
 	dev_info(&serial->dev->dev, "%s detected\n", edge_serial->name);
 
 	/* Read the epic descriptor */
-	if (get_epic_descriptor(edge_serial) <= 0) {
+	if (get_epic_descriptor(edge_serial) < 0) {
 		/* memcpy descriptor to Supports structures */
 		memcpy(&edge_serial->epic_descriptor.Supports, descriptor,
 		       sizeof(struct edge_compatibility_bits));