USB: serial: spcp8x5: fix NULL-deref at open

commit cc090924 upstream.

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

Unable to handle kernel NULL pointer dereference at virtual address 00000030
...
PC is at spcp8x5_open+0x30/0xd0 [spcp8x5]

Fixes: 619a6f1d ("USB: add usb-serial spcp8x5 driver")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: add this check to the existing
 usb_serial_driver::attach implementation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/spcp8x5.c

@@ -176,6 +176,13 @@ static int spcp8x5_startup(struct usb_serial *serial)
 	int i;
 	enum spcp8x5_type type = SPCP825_007_TYPE;
 	u16 product = le16_to_cpu(serial->dev->descriptor.idProduct);
+	unsigned char num_ports = serial->num_ports;
+
+	if (serial->num_bulk_in < num_ports ||
+			serial->num_bulk_out < num_ports) {
+		dev_err(&serial->interface->dev, "missing endpoints\n");
+		return -ENODEV;
+	}
 
 	if (product == 0x0201)
 		type = SPCP825_007_TYPE;