scsi_dh: fix use-after-free when removing scsi device

The commit 1bab0de0 ("dm-mpath, scsi_dh: don't let dm detach device
handlers") removed reference counting of attached scsi device handler.
As a result, handler data is freed immediately via scsi_dh->detach()
in the context of scsi_remove_device() where activation request can be
still in flight.

This patch moves scsi_dh_handler_detach() to sdev releasing function,
scsi_device_dev_release_usercontext(), at that point the device
is already in quiesced state.

Fixes: 1bab0de0 ("dm-mpath, scsi_dh: don't let dm detach device handlers")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/scsi_dh.c

@@ -232,10 +232,14 @@ int scsi_dh_add_device(struct scsi_device *sdev)
 	return err;
 }
 
-void scsi_dh_remove_device(struct scsi_device *sdev)
+void scsi_dh_release_device(struct scsi_device *sdev)
 {
 	if (sdev->handler)
 		scsi_dh_handler_detach(sdev);
+}
+
+void scsi_dh_remove_device(struct scsi_device *sdev)
+{
 	device_remove_file(&sdev->sdev_gendev, &scsi_dh_state_attr);
 }
 

drivers/scsi/scsi_priv.h

@@ -173,9 +173,11 @@ extern struct async_domain scsi_sd_probe_domain;
 /* scsi_dh.c */
 #ifdef CONFIG_SCSI_DH
 int scsi_dh_add_device(struct scsi_device *sdev);
+void scsi_dh_release_device(struct scsi_device *sdev);
 void scsi_dh_remove_device(struct scsi_device *sdev);
 #else
 static inline int scsi_dh_add_device(struct scsi_device *sdev) { return 0; }
+static inline void scsi_dh_release_device(struct scsi_device *sdev) { }
 static inline void scsi_dh_remove_device(struct scsi_device *sdev) { }
 #endif
 

drivers/scsi/scsi_sysfs.c

@@ -399,6 +399,8 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 
 	sdev = container_of(work, struct scsi_device, ew.work);
 
+	scsi_dh_release_device(sdev);
+
 	parent = sdev->sdev_gendev.parent;
 
 	spin_lock_irqsave(sdev->host->host_lock, flags);