[PATCH v2 2/4] ACPI: NFIT: core: Fix acpi_nfit_init() error cleanup

["Rafael J. Wysocki" <rafael@kernel.org>]

From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

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>
---
 drivers/acpi/nfit/core.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 8024cd3cad14..01c73be0bd00 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -3069,6 +3069,8 @@ static void acpi_nfit_unregister(void *data)
 	struct acpi_nfit_desc *acpi_desc = data;
 
 	nvdimm_bus_unregister(acpi_desc->nvdimm_bus);
+	/* The nvdimm_bus object may have been freed, so clear the pointer. */
+	acpi_desc->nvdimm_bus = NULL;
 }
 
 int acpi_nfit_init(struct acpi_nfit_desc *acpi_desc, void *data, acpi_size sz)
@@ -3301,7 +3303,10 @@ static void acpi_nfit_notify(acpi_handle handle, u32 event, void *data)
 void acpi_nfit_shutdown(void *data)
 {
 	struct acpi_nfit_desc *acpi_desc = data;
-	struct device *bus_dev = to_nvdimm_bus_dev(acpi_desc->nvdimm_bus);
+	struct device *bus_dev;
+
+	if (!acpi_desc || !acpi_desc->nvdimm_bus)
+		return;
 
 	/*
 	 * Destruct under acpi_desc_lock so that nfit_handle_mce does not
@@ -3316,6 +3321,7 @@ void acpi_nfit_shutdown(void *data)
 	mutex_unlock(&acpi_desc->init_mutex);
 	cancel_delayed_work_sync(&acpi_desc->dwork);
 
+	bus_dev = to_nvdimm_bus_dev(acpi_desc->nvdimm_bus);
 	/*
 	 * Bounce the nvdimm bus lock to make sure any in-flight
 	 * acpi_nfit_ars_rescan() submissions have had a chance to
@@ -3388,9 +3394,14 @@ static int acpi_nfit_probe(struct platform_device *pdev)
 				sz - sizeof(struct acpi_table_nfit));
 
 	if (rc)
-		return rc;
+		acpi_nfit_shutdown(acpi_desc);
 
-	return devm_add_action_or_reset(dev, acpi_nfit_shutdown, acpi_desc);
+	return rc;
+}
+
+static void acpi_nfit_remove(struct platform_device *pdev)
+{
+	acpi_nfit_shutdown(platform_get_drvdata(pdev));
 }
 
 static void acpi_nfit_update_notify(struct device *dev, acpi_handle handle)
@@ -3474,6 +3485,7 @@ MODULE_DEVICE_TABLE(acpi, acpi_nfit_ids);
 
 static struct platform_driver acpi_nfit_driver = {
 	.probe = acpi_nfit_probe,
+	.remove = acpi_nfit_remove,
 	.driver = {
 		.name = "acpi-nfit",
 		.acpi_match_table = acpi_nfit_ids,
-- 
2.51.0