Medium [CVE-2026-68182] Linux kernel: comedi_parport driver vulnerable to denial of service via premature interrupt

In the Linux kernel, the following vulnerability has been resolved: comedi: comedi_parport: deal with premature interrupt Syzbot reported a general protection fault in `comedi_get_is_subdevice_running()`, which was called from the interrupt handler `parport_interrupt()` in the "comedi_parport" driver, but it does not currently have a C reproducer for the problem.

It's probably due to a premature interrupt for one of two reasons: 1. The driver sets up the interrupt handler before the comedi subdevices used by the interrupt handler have been allocated, but does not disable the interrupt in the parallel port's CTRL register first.

2. The driver uses a user-supplied I/O port base address which Syzbot would have supplied, but it might not be backed by real parallel port hardware.

Change the initialization order in the driver's comedi "attach" handler (`parport_attach()`) so that the hardware registers are initialized before the interrupt handler is requested. This should prevent premature interrupts occurring for real hardware.

Also add a test to the interrupt handler to ensure the comedi device is fully attached and return early if it isn't. A local user could trigger a premature interrupt, potentially due to incorrect initialization order of hardware registers or an invalid user-supplied I/O port address.