target: fix use after free in target_report_luns

commit 382436f8 upstream.

Fix possible NULL pointer dereference in target_report_luns failure path.
Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/target/target_core_device.c

@@ -696,12 +696,12 @@ int target_report_luns(struct se_task *se_task)
 	 * See SPC3 r07, page 159.
 	 */
 done:
-	transport_kunmap_data_sg(se_cmd);
 	lun_count *= 8;
 	buf[0] = ((lun_count >> 24) & 0xff);
 	buf[1] = ((lun_count >> 16) & 0xff);
 	buf[2] = ((lun_count >> 8) & 0xff);
 	buf[3] = (lun_count & 0xff);
+	transport_kunmap_data_sg(se_cmd);
 
 	se_task->task_scsi_status = GOOD;
 	transport_complete_task(se_task, 1);