USB: serial: ti_usb_3410_5052: fix NULL-deref at open

commit ef079936 upstream.

Fix NULL-pointer dereference in open() should a malicious device lack
the expected endpoints:

Unable to handle kernel NULL pointer dereference at virtual address 00000030
..
[<bf06a6b0>] (ti_open [ti_usb_3410_5052]) from [<bf02e118>] (serial_port_activate+0x68/0x98 [usbserial])

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
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/ti_usb_3410_5052.c

@@ -438,6 +438,13 @@ static int ti_startup(struct usb_serial *serial)
 		goto free_tdev;
 	}
 
+	if (serial->num_bulk_in < serial->num_ports ||
+			serial->num_bulk_out < serial->num_ports) {
+		dev_err(&serial->interface->dev, "missing endpoints\n");
+		status = -ENODEV;
+		goto free_tdev;
+	}
+
 	/* set up port structures */
 	for (i = 0; i < serial->num_ports; ++i) {
 		tport = kzalloc(sizeof(struct ti_port), GFP_KERNEL);