USB: CDC ACM: Fix NULL pointer dereference

If a device specifies zero endpoints in its interface descriptor,
the kernel oopses in acm_probe(). Even though that's clearly an
invalid descriptor, we should test wether we have all endpoints.
This is especially bad as this oops can be triggered by just
plugging a USB device in.
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -1104,7 +1104,8 @@ static int acm_probe(struct usb_interface *intf,
 	}
 
 
-	if (data_interface->cur_altsetting->desc.bNumEndpoints < 2)
+	if (data_interface->cur_altsetting->desc.bNumEndpoints < 2 ||
+	    control_interface->cur_altsetting->desc.bNumEndpoints == 0)
 		return -EINVAL;
 
 	epctrl = &control_interface->cur_altsetting->endpoint[0].desc;