CVE-2026-68182: comedi: comedi_parport: deal with premature interrupt

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-68182 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.29 with commit 241ab6ad7108e51c67881f7881c5e46f0400cdb1 and fixed in 6.6.148 with commit b061bb4dca49fd93063359d3805387235818778c
	Issue introduced in 2.6.29 with commit 241ab6ad7108e51c67881f7881c5e46f0400cdb1 and fixed in 6.12.101 with commit 086a9ae3c5df63ec11033a8c0b3f6a1fd295ddd1
	Issue introduced in 2.6.29 with commit 241ab6ad7108e51c67881f7881c5e46f0400cdb1 and fixed in 6.18.42 with commit cf26dd2d841583c54a87005c4934b92fddb930c3
	Issue introduced in 2.6.29 with commit 241ab6ad7108e51c67881f7881c5e46f0400cdb1 and fixed in 7.1.6 with commit 5d059ce0e6a2f6f8b97273499d47b8f917097b48
	Issue introduced in 2.6.29 with commit 241ab6ad7108e51c67881f7881c5e46f0400cdb1 and fixed in 7.2-rc5 with commit 17221216ae8ce6a24e8a4e787382e3ebc81b88a8

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68182
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/comedi/drivers/comedi_parport.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/b061bb4dca49fd93063359d3805387235818778c
	https://git.kernel.org/stable/c/086a9ae3c5df63ec11033a8c0b3f6a1fd295ddd1
	https://git.kernel.org/stable/c/cf26dd2d841583c54a87005c4934b92fddb930c3
	https://git.kernel.org/stable/c/5d059ce0e6a2f6f8b97273499d47b8f917097b48
	https://git.kernel.org/stable/c/17221216ae8ce6a24e8a4e787382e3ebc81b88a8