USB: serial: io_ti: fix NULL-deref at open

Fix NULL-pointer dereference when clearing halt at open should a
malicious device lack the expected endpoints when in download mode.

Unable to handle kernel NULL pointer dereference at virtual address 00000030
...
[<bf011ed8>] (edge_open [io_ti]) from [<bf000118>] (serial_port_activate+0x68/0x98 [usbserial])
[<bf000118>] (serial_port_activate [usbserial]) from [<c0470ca4>] (tty_port_open+0x9c/0xe8)
[<c0470ca4>] (tty_port_open) from [<bf000da0>] (serial_open+0x48/0x6c [usbserial])
[<bf000da0>] (serial_open [usbserial]) from [<c0469178>] (tty_open+0xcc/0x5cc)

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/io_ti.c

@@ -2546,6 +2546,13 @@ static int edge_startup(struct usb_serial *serial)
 	int status;
 	u16 product_id;
 
+	/* Make sure we have the required endpoints when in download mode. */
+	if (serial->interface->cur_altsetting->desc.bNumEndpoints > 1) {
+		if (serial->num_bulk_in < serial->num_ports ||
+				serial->num_bulk_out < serial->num_ports)
+			return -ENODEV;
+	}
+
 	/* create our private serial structure */
 	edge_serial = kzalloc(sizeof(struct edgeport_serial), GFP_KERNEL);
 	if (!edge_serial)