ACPI / hotplug: Fix potential race in acpi_bus_notify()

There is a slight possibility for the ACPI device object pointed to
by adev in acpi_hotplug_notify_cb() to become invalid between the
acpi_bus_get_device() that it comes from and the subsequent dereference
of that pointer under get_device().  Namely, if acpi_scan_drop_device()
runs in parallel with acpi_hotplug_notify_cb(), acpi_device_del_work_fn()
queued up by it may delete the device object in question right after
a successful execution of acpi_bus_get_device() in acpi_bus_notify().

An analogous problem is present in acpi_bus_notify() where the device
pointer coming from acpi_bus_get_device() may become invalid before
it subsequent dereference in the "if" block.

To prevent that from happening, introduce a new function,
acpi_bus_get_acpi_device(), working analogously to acpi_bus_get_device()
except that it will grab a reference to the ACPI device object returned
by it and it will do that under the ACPICA's namespace mutex.  Then,
make both acpi_hotplug_notify_cb() and acpi_bus_notify() use
acpi_bus_get_acpi_device() instead of acpi_bus_get_device() so as to
ensure that the pointers used by them will not become stale at one
point.

In addition to that, introduce acpi_bus_put_acpi_device() as a wrapper
around put_device() to be used along with acpi_bus_get_acpi_device()
and make the (new) users of the latter use acpi_bus_put_acpi_device()
too.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

3 files changed, 40 insertions, 10 deletions

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index fcb59c21c68d..c3237774632f 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -340,7 +340,7 @@ static void acpi_bus_osc_support(void)
  */
 static void acpi_bus_notify(acpi_handle handle, u32 type, void *data)
 {
-        struct acpi_device *device = NULL;
+        struct acpi_device *device;
         struct acpi_driver *driver;
 
         ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Notification %#02x to handle %p\n",
@@ -387,12 +387,14 @@ static void acpi_bus_notify(acpi_handle handle, u32 type, void *data)
                 break;
         }
 
-        acpi_bus_get_device(handle, &device);
+        device = acpi_bus_get_acpi_device(handle);
         if (device) {
                 driver = device->driver;
                 if (driver && driver->ops.notify &&
                     (driver->flags & ACPI_DRIVER_ALL_NOTIFY_EVENTS))
                         driver->ops.notify(device, type);
+
+                acpi_bus_put_acpi_device(device);
         }
 }
 
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 7384158c7f87..59eba29a6066 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -476,7 +476,7 @@ static void acpi_device_hotplug(void *data, u32 src)
 
  out:
         acpi_evaluate_hotplug_ost(adev->handle, src, ost_code, NULL);
-        put_device(&adev->dev);
+        acpi_bus_put_acpi_device(adev);
         mutex_unlock(&acpi_scan_lock);
         unlock_device_hotplug();
 }
@@ -488,9 +488,6 @@ static void acpi_hotplug_notify_cb(acpi_handle handle, u32 type, void *data)
         struct acpi_device *adev;
         acpi_status status;
 
-        if (acpi_bus_get_device(handle, &adev))
-                goto err_out;
-
         switch (type) {
         case ACPI_NOTIFY_BUS_CHECK:
                 acpi_handle_debug(handle, "ACPI_NOTIFY_BUS_CHECK event\n");
@@ -512,12 +509,15 @@ static void acpi_hotplug_notify_cb(acpi_handle handle, u32 type, void *data)
                 /* non-hotplug event; possibly handled by other handler */
                 return;
         }
-        get_device(&adev->dev);
+        adev = acpi_bus_get_acpi_device(handle);
+        if (!adev)
+                goto err_out;
+
         status = acpi_hotplug_execute(acpi_device_hotplug, adev, type);
         if (ACPI_SUCCESS(status))
                 return;
 
-        put_device(&adev->dev);
+        acpi_bus_put_acpi_device(adev);
 
  err_out:
         acpi_evaluate_hotplug_ost(handle, type, ost_code, NULL);
@@ -1112,14 +1112,16 @@ static void acpi_scan_drop_device(acpi_handle handle, void *context)
         mutex_unlock(&acpi_device_del_lock);
 }
 
-int acpi_bus_get_device(acpi_handle handle, struct acpi_device **device)
+static int acpi_get_device_data(acpi_handle handle, struct acpi_device **device,
+                                void (*callback)(void *))
 {
         acpi_status status;
 
         if (!device)
                 return -EINVAL;
 
-        status = acpi_get_data(handle, acpi_scan_drop_device, (void **)device);
+        status = acpi_get_data_full(handle, acpi_scan_drop_device,
+                                    (void **)device, callback);
         if (ACPI_FAILURE(status) || !*device) {
                 ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No context for object [%p]\n",
                                   handle));
@@ -1127,8 +1129,32 @@ int acpi_bus_get_device(acpi_handle handle, struct acpi_device **device)
         }
         return 0;
 }
+
+int acpi_bus_get_device(acpi_handle handle, struct acpi_device **device)
+{
+        return acpi_get_device_data(handle, device, NULL);
+}
 EXPORT_SYMBOL(acpi_bus_get_device);
 
+static void get_acpi_device(void *dev)
+{
+        if (dev)
+                get_device(&((struct acpi_device *)dev)->dev);
+}
+
+struct acpi_device *acpi_bus_get_acpi_device(acpi_handle handle)
+{
+        struct acpi_device *adev = NULL;
+
+        acpi_get_device_data(handle, &adev, get_acpi_device);
+        return adev;
+}
+
+void acpi_bus_put_acpi_device(struct acpi_device *adev)
+{
+        put_device(&adev->dev);
+}
+
 int acpi_device_add(struct acpi_device *device,
                     void (*release)(struct device *))
 {
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 8256eb4ad057..94fd61a0456d 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -381,6 +381,8 @@ extern int unregister_acpi_notifier(struct notifier_block *);
  */
 
 int acpi_bus_get_device(acpi_handle handle, struct acpi_device **device);
+struct acpi_device *acpi_bus_get_acpi_device(acpi_handle handle);
+void acpi_bus_put_acpi_device(struct acpi_device *adev);
 acpi_status acpi_bus_get_status_handle(acpi_handle handle,
                                        unsigned long long *sta);
 int acpi_bus_get_status(struct acpi_device *device);