[S390] cio: ensure to hold a reference for deferred deregistration

Ensure to always hold an extra device reference for scheduling a
subchannel deregistration, by moving the get_device to
ccw_device_schedule_sch_unregister. This fixes an use after free
error in ccw_device_call_sch_unregister where put_device was called
on an already freed device structure.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index 19b4469a3ca4..a7a340b1d713 100644
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -333,15 +333,15 @@ ccw_device_remove_disconnected(struct ccw_device *cdev)
          * Forced offline in disconnected state means
          * 'throw away device'.
          */
-        /* Get cdev reference for workqueue processing. */
-        if (!get_device(&cdev->dev))
-                return;
         if (ccw_device_is_orphan(cdev)) {
                 /*
                  * Deregister ccw device.
                  * Unfortunately, we cannot do this directly from the
                  * attribute method.
                  */
+                /* Get cdev reference for workqueue processing. */
+                if (!get_device(&cdev->dev))
+                        return;
                 spin_lock_irqsave(cdev->ccwlock, flags);
                 cdev->private->state = DEV_STATE_NOT_OPER;
                 spin_unlock_irqrestore(cdev->ccwlock, flags);
@@ -1032,6 +1032,9 @@ static void ccw_device_call_sch_unregister(struct work_struct *work)
 
 void ccw_device_schedule_sch_unregister(struct ccw_device *cdev)
 {
+        /* Get cdev reference for workqueue processing. */
+        if (!get_device(&cdev->dev))
+                return;
         PREPARE_WORK(&cdev->private->kick_work,
                      ccw_device_call_sch_unregister);
         queue_work(slow_path_wq, &cdev->private->kick_work);
@@ -1052,9 +1055,6 @@ io_subchannel_recog_done(struct ccw_device *cdev)
                 /* Device did not respond in time. */
         case DEV_STATE_NOT_OPER:
                 cdev->private->flags.recog_done = 1;
-                /* Remove device found not operational. */
-                if (!get_device(&cdev->dev))
-                        break;
                 ccw_device_schedule_sch_unregister(cdev);
                 if (atomic_dec_and_test(&ccw_device_init_count))
                         wake_up(&ccw_device_init_wq);
@@ -1565,8 +1565,6 @@ static int purge_fn(struct device *dev, void *data)
         spin_unlock_irq(cdev->ccwlock);
         if (!unreg)
                 goto out;
-        if (!get_device(&cdev->dev))
-                goto out;
         CIO_MSG_EVENT(3, "ccw: purging 0.%x.%04x\n", priv->dev_id.ssid,
                       priv->dev_id.devno);
         ccw_device_schedule_sch_unregister(cdev);