In the Linux kernel, the following vulnerability has been resolved:

parport: Fix race between port and client registration

The parport subsystem registers port devices before they are fully
initialised, resulting in a race condition where client drivers such
as lp can attach to ports that are not completely initialised or even
being torn down.

When the port and client drivers are built as modules and loaded
around the same time during boot, this occasionally results in a
crash.  I was able to make this happen reliably in a VM with a
PC-style parallel port by patching parport_pc to fail probing:

> --- a/drivers/parport/parport_pc.c
> +++ b/drivers/parport/parport_pc.c
> @@ -2069,7 +2069,7 @@ static struct parport *__parport_pc_probe_port(unsigned long int base,
>  	if (!p)
>  		goto out3;
>
> -	base_res = request_region(base, 3, p->name);
> +	base_res = NULL;
>  	if (!base_res)
>  		goto out4;
>

and then running:

    while true; do
        modprobe lp & modprobe parport_pc
	wait
	rmmod lp parport_pc
    done

for a few seconds.

In the long term I think port registration should be changed to put
the call to device_add() inside parport_announce_port(), but since the
latter currently cannot fail this will require changing all port
drivers.

For now, add a flag to indicate whether a port has been "announced"
and only try to attach client drivers to ports when the flag is set.

https://git.kernel.org/stable/c/15b1723c1472e802f9f7e69ae4e64f7dbf588848

https://git.kernel.org/stable/c/290f515c5e3b3900bc2fe24f179999fd08d23bfa

https://git.kernel.org/stable/c/51026cff1f4f3b762a0b5a07c727bd59cef45320

https://git.kernel.org/stable/c/74d6aae1df45d3414178986be743f946988fddf6

https://git.kernel.org/stable/c/a1e81b58da0179531bedf0b9f2811f5f992d5c4b

https://git.kernel.org/stable/c/d16548be2ea5058227d79799e81dab61c9bca8ec

https://git.kernel.org/stable/c/ef15ccbb3e8640a723c42ad90eaf81d66ae02017

https://git.kernel.org/stable/c/f3378b0d7bd4605de89b083b2900788157a181cc

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