ACPI: NFIT: core: Fix possible NULL pointer dereference

commit 027e128 upstream.

After commit 9b311b7 ("ACPI: NFIT: Install Notify() handler before
getting NFIT table"), acpi_nfit_probe() installs an ACPI notify handler
for the NFIT device before checking the presence of the NFIT table.  If
that table is not there, 0 is returned without allocating the acpi_desc
object and setting the driver data pointer of the NFIT device.  If the
platform firmware triggers an NFIT_NOTIFY_UC_MEMORY_ERROR notification
on the NFIT device at that point, acpi_nfit_uc_error_notify() will
dereference a NULL pointer.

Prevent that from occurring by adding an acpi_desc check against NULL
to acpi_nfit_uc_error_notify().

Fixes: 9b311b7 ("ACPI: NFIT: Install Notify() handler before getting NFIT table")
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/2418508.ElGaqSPkdT@rafael.j.wysocki
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: rafaeljw

drivers/acpi/nfit/core.c

@@ -3447,6 +3447,9 @@ static void acpi_nfit_uc_error_notify(struct device *dev, acpi_handle handle)
 {
 	struct acpi_nfit_desc *acpi_desc = dev_get_drvdata(dev);
 
+	if (!acpi_desc)
+		return;
+
 	if (acpi_desc->scrub_mode == HW_ERROR_SCRUB_ON)
 		acpi_nfit_ars_rescan(acpi_desc, ARS_REQ_LONG);
 	else