USB: serial: io_edgeport: add missing active-port sanity check

BugLink: https://bugs.launchpad.net/bugs/1860681

commit 1568c58d upstream.

The driver receives the active port number from the device, but never
made sure that the port number was valid. This could lead to a
NULL-pointer dereference or memory corruption in case a device sends
data for an invalid port.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/usb/serial/io_edgeport.c

@@ -1666,7 +1666,8 @@ static void edge_break(struct tty_struct *tty, int break_state)
 static void process_rcvd_data(struct edgeport_serial *edge_serial,
 				unsigned char *buffer, __u16 bufferLength)
 {
-	struct device *dev = &edge_serial->serial->dev->dev;
+	struct usb_serial *serial = edge_serial->serial;
+	struct device *dev = &serial->dev->dev;
 	struct usb_serial_port *port;
 	struct edgeport_port *edge_port;
 	__u16 lastBufferLength;
@@ -1771,9 +1772,8 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 
 			/* spit this data back into the tty driver if this
 			   port is open */
-			if (rxLen) {
-				port = edge_serial->serial->port[
-							edge_serial->rxPort];
+			if (rxLen && edge_serial->rxPort < serial->num_ports) {
+				port = serial->port[edge_serial->rxPort];
 				edge_port = usb_get_serial_port_data(port);
 				if (edge_port->open) {
 					dev_dbg(dev, "%s - Sending %d bytes to TTY for port %d\n",
@@ -1783,8 +1783,8 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 							rxLen);
 					edge_port->port->icount.rx += rxLen;
 				}
-				buffer += rxLen;
 			}
+			buffer += rxLen;
 			break;
 
 		case EXPECT_HDR3:	/* Expect 3rd byte of status header */
@@ -1819,6 +1819,8 @@ static void process_rcvd_status(struct edgeport_serial *edge_serial,
 	__u8 code = edge_serial->rxStatusCode;
 
 	/* switch the port pointer to the one being currently talked about */
+	if (edge_serial->rxPort >= edge_serial->serial->num_ports)
+		return;
 	port = edge_serial->serial->port[edge_serial->rxPort];
 	edge_port = usb_get_serial_port_data(port);
 	if (edge_port == NULL) {