scsi: libiscsi: Teardown iscsi_cls_conn gracefully

Commit 1b8d0300a3 ("scsi: libiscsi: Fix UAF in
iscsi_conn_get_param()/iscsi_conn_teardown()") fixed an UAF in
iscsi_conn_get_param() and introduced 2 tmp_xxx varibles.

We can gracefully fix this UAF with the help of device_del(). Calling
iscsi_remove_conn() at the beginning of iscsi_conn_teardown would make
userspace unable to see iscsi_cls_conn. This way we we can free memory
safely.

Remove iscsi_destroy_conn() since it is no longer used.

Link: https://lore.kernel.org/r/20220310015759.3296841-4-haowenchao@huawei.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Wenchao Hao <haowenchao@huawei.com>
Signed-off-by: Wu Bo <wubo40@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -3107,8 +3107,8 @@ void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)
 {
 	struct iscsi_conn *conn = cls_conn->dd_data;
 	struct iscsi_session *session = conn->session;
-	char *tmp_persistent_address = conn->persistent_address;
-	char *tmp_local_ipaddr = conn->local_ipaddr;
+
+	iscsi_remove_conn(cls_conn);
 
 	del_timer_sync(&conn->transport_timer);
 
@@ -3130,6 +3130,8 @@ void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)
 	spin_lock_bh(&session->frwd_lock);
 	free_pages((unsigned long) conn->data,
 		   get_order(ISCSI_DEF_MAX_RECV_SEG_LEN));
+	kfree(conn->persistent_address);
+	kfree(conn->local_ipaddr);
 	/* regular RX path uses back_lock */
 	spin_lock_bh(&session->back_lock);
 	kfifo_in(&session->cmdpool.queue, (void*)&conn->login_task,
@@ -3140,9 +3142,7 @@ void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)
 	spin_unlock_bh(&session->frwd_lock);
 	mutex_unlock(&session->eh_mutex);
 
-	iscsi_destroy_conn(cls_conn);
-	kfree(tmp_persistent_address);
-	kfree(tmp_local_ipaddr);
+	iscsi_put_conn(cls_conn);
 }
 EXPORT_SYMBOL_GPL(iscsi_conn_teardown);
 

drivers/scsi/scsi_transport_iscsi.c

@@ -2137,7 +2137,11 @@ static int iscsi_iter_destroy_conn_fn(struct device *dev, void *data)
 {
 	if (!iscsi_is_conn_dev(dev))
 		return 0;
-	return iscsi_destroy_conn(iscsi_dev_to_conn(dev));
+
+	iscsi_remove_conn(iscsi_dev_to_conn(dev));
+	iscsi_put_conn(iscsi_dev_to_conn(dev));
+
+	return 0;
 }
 
 void iscsi_remove_session(struct iscsi_cls_session *session)
@@ -2414,27 +2418,6 @@ void iscsi_remove_conn(struct iscsi_cls_conn *conn)
 }
 EXPORT_SYMBOL_GPL(iscsi_remove_conn);
 
-/**
- * iscsi_destroy_conn - destroy iscsi class connection
- * @conn: iscsi cls session
- *
- * This can be called from a LLD or iscsi_transport.
- */
-int iscsi_destroy_conn(struct iscsi_cls_conn *conn)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&connlock, flags);
-	list_del(&conn->conn_list);
-	spin_unlock_irqrestore(&connlock, flags);
-
-	transport_unregister_device(&conn->dev);
-	ISCSI_DBG_TRANS_CONN(conn, "Completing conn destruction\n");
-	device_unregister(&conn->dev);
-	return 0;
-}
-EXPORT_SYMBOL_GPL(iscsi_destroy_conn);
-
 void iscsi_put_conn(struct iscsi_cls_conn *conn)
 {
 	put_device(&conn->dev);

include/scsi/scsi_transport_iscsi.h

@@ -448,7 +448,6 @@ extern int iscsi_add_conn(struct iscsi_cls_conn *conn);
 extern void iscsi_remove_conn(struct iscsi_cls_conn *conn);
 extern void iscsi_put_conn(struct iscsi_cls_conn *conn);
 extern void iscsi_get_conn(struct iscsi_cls_conn *conn);
-extern int iscsi_destroy_conn(struct iscsi_cls_conn *conn);
 extern void iscsi_unblock_session(struct iscsi_cls_session *session);
 extern void iscsi_block_session(struct iscsi_cls_session *session);
 extern struct iscsi_endpoint *iscsi_create_endpoint(int dd_size);