USB: serial: digi_acceleport: fix incomplete rx sanity check

commit 1b0aed2b upstream.

Make sure the received data has the required headers before parsing it.

Also drop the redundant urb-status check, which has already been handled
by the caller.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/digi_acceleport.c

@@ -1660,25 +1660,30 @@ static int digi_read_inb_callback(struct urb *urb)
 	struct usb_serial_port *port = urb->context;
 	struct tty_struct *tty;
 	struct digi_port *priv = usb_get_serial_port_data(port);
-	int opcode = ((unsigned char *)urb->transfer_buffer)[0];
-	int len = ((unsigned char *)urb->transfer_buffer)[1];
-	int port_status = ((unsigned char *)urb->transfer_buffer)[2];
-	unsigned char *data = ((unsigned char *)urb->transfer_buffer) + 3;
+	unsigned char *buf = urb->transfer_buffer;
+	int opcode;
+	int len;
+	int port_status;
+	unsigned char *data;
 	int flag, throttled;
-	int status = urb->status;
-
-	/* do not process callbacks on closed ports */
-	/* but do continue the read chain */
-	if (urb->status == -ENOENT)
-		return 0;
 
 	/* short/multiple packet check */
+	if (urb->actual_length < 2) {
+		dev_warn(&port->dev, "short packet received\n");
+		return -1;
+	}
+
+	opcode = buf[0];
+	len = buf[1];
+
 	if (urb->actual_length != len + 2) {
-		dev_err(&port->dev, "%s: INCOMPLETE OR MULTIPLE PACKET, "
-			"status=%d, port=%d, opcode=%d, len=%d, "
-			"actual_length=%d, status=%d\n", __func__, status,
-			priv->dp_port_num, opcode, len, urb->actual_length,
-			port_status);
+		dev_err(&port->dev, "malformed packet received: port=%d, opcode=%d, len=%d, actual_length=%u\n",
+			priv->dp_port_num, opcode, len, urb->actual_length);
+		return -1;
+	}
+
+	if (opcode == DIGI_CMD_RECEIVE_DATA && len < 1) {
+		dev_err(&port->dev, "malformed data packet received\n");
 		return -1;
 	}
 
@@ -1693,6 +1698,9 @@ static int digi_read_inb_callback(struct urb *urb)
 
 	/* receive data */
 	if (tty && opcode == DIGI_CMD_RECEIVE_DATA) {
+		port_status = buf[2];
+		data = &buf[3];
+
 		/* get flag from port_status */
 		flag = 0;