USB: serial: keyspan_pda: verify endpoints at probe

commit 5d9b0f85 upstream.

Check for the expected endpoints in attach() and fail loudly if not
present.

Note that failing to do this appears to be benign since da280e34
("USB: keyspan_pda: clean up write-urb busy handling") which prevents a
NULL-pointer dereference in write() by never marking a non-existent
write-urb as free.

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

@@ -806,9 +806,15 @@ MODULE_FIRMWARE("keyspan_pda/xircom_pgs.fw");
 
 static int keyspan_pda_startup(struct usb_serial *serial)
 {
-
+	unsigned char num_ports = serial->num_ports;
 	struct keyspan_pda_private *priv;
 
+	if (serial->num_bulk_out < num_ports ||
+			serial->num_interrupt_in < num_ports) {
+		dev_err(&serial->interface->dev, "missing endpoints\n");
+		return -ENODEV;
+	}
+
 	/* allocate the private data structures for all ports. Well, for all
 	   one ports. */