scsi: iscsi: Fix iscsi_task use after free

Commit d39df15 ("scsi: iscsi: Have abort handler get ref to conn")
added iscsi_get_conn()/iscsi_put_conn() calls during abort handling but
then also changed the handling of the case where we detect an already
completed task where we now end up doing a goto to the common put/cleanup
code. This results in a iscsi_task use after free, because the common
cleanup code will do a put on the iscsi_task.

This reverts the goto and moves the iscsi_get_conn() to after we've checked
if the iscsi_task is valid.

Link: https://lore.kernel.org/r/20211004210608.9962-1-michael.christie@oracle.com
Fixes: d39df15 ("scsi: iscsi: Have abort handler get ref to conn")
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -2281,20 +2281,23 @@ int iscsi_eh_abort(struct scsi_cmnd *sc)
 		return FAILED;
 	}
 
-	conn = session->leadconn;
-	iscsi_get_conn(conn->cls_conn);
-	conn->eh_abort_cnt++;
-	age = session->age;
-
 	spin_lock(&session->back_lock);
 	task = (struct iscsi_task *)sc->SCp.ptr;
 	if (!task || !task->sc) {
 		/* task completed before time out */
 		ISCSI_DBG_EH(session, "sc completed while abort in progress\n");
 
 		spin_unlock(&session->back_lock);
-		goto success;
+		spin_unlock_bh(&session->frwd_lock);
+		mutex_unlock(&session->eh_mutex);
+		return SUCCESS;
 	}
+
+	conn = session->leadconn;
+	iscsi_get_conn(conn->cls_conn);
+	conn->eh_abort_cnt++;
+	age = session->age;
+
 	ISCSI_DBG_EH(session, "aborting [sc %p itt 0x%x]\n", sc, task->itt);
 	__iscsi_get_task(task);
 	spin_unlock(&session->back_lock);