ACPI: NFIT: core: Fix acpi_nfit_init() error cleanup

ACPI: NFIT: core: Fix acpi_nfit_init() error cleanup

If acpi_nfit_init() fails after adding the acpi_desc object to the
acpi_descs list, that object is never removed from that list because
the acpi_nfit_shutdown() devm action is not added for the NFIT device
in that case.  Next, the acpi_nfit_init() failure causes
acpi_nfit_probe() to fail, the acpi_desc object is freed, and a
dangling pointer is left behind in the acpi_descs.  Any subsequent
ACPI Machine Check Exception will trigger nfit_handle_mce() which
iterates over acpi_descs and so a use-after-free will occur.

Moreover, if acpi_nfit_probe() returns 0 after installing a notify
handler for the NFIT device and without allocating the acpi_desc
object and setting the NFIT device's driver data pointer, the
acpi_desc object will be allocated by acpi_nfit_update_notify()
and acpi_nfit_init() will be called to initialize it.  Regardless
of whether or not acpi_nfit_init() fails in that case, the
acpi_nfit_shutdown() devm action is not added for the NFIT device
and acpi_desc is never removed from the acpi_descs list.  If the
acpi_desc object is freed subsequently on driver removal, any
subsequent ACPI MCE will lead to a use-after-free like in the
previous case.

To address the first issue mentioned above, make acpi_nfit_probe()
call acpi_nfit_shutdown() directly on acpi_nfit_init() failures and
to address the other one, add a remove callback to the driver and
make it call acpi_nfit_shutdown().  Also, since it is now possible to
pass NULL to acpi_nfit_shutdown() or the acpi_desc object passed to it
may not have been initialized, add checks against NULL for acpi_desc and
its nvdimm_bus field to that function and make acpi_nfit_unregister()
clear the latter after unregistering the NVDIMM bus.

Fixes: a61fe6f7902e ("nfit, tools/testing/nvdimm: unify common init for acpi_nfit_desc")
Fixes: fbabd829fe76 ("acpi, nfit: fix module unload vs workqueue shutdown race")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: All applicable <stable@vger.kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/1963615.tdWV9SEqCh@rafael.j.wysocki