[PATCH AUTOSEL 5.4 14/21] ntb: ntb_hw_switchtec: Fix use after free vulnerability in switchtec_ntb_remove due to race condition

[Sasha Levin]

From: Kaixin Wang <kxwang23@xxxxxxxxxxxxxx>

[ Upstream commit e51aded92d42784313ba16c12f4f88cc4f973bbb ]

In the switchtec_ntb_add function, it can call switchtec_ntb_init_sndev
function, then &sndev->check_link_status_work is bound with
check_link_status_work. switchtec_ntb_link_notification may be called
to start the work.

If we remove the module which will call switchtec_ntb_remove to make
cleanup, it will free sndev through kfree(sndev), while the work
mentioned above will be used. The sequence of operations that may lead
to a UAF bug is as follows:

CPU0                                 CPU1

                        | check_link_status_work
switchtec_ntb_remove    |
kfree(sndev);           |
                        | if (sndev->link_force_down)
                        | // use sndev

Fix it by ensuring that the work is canceled before proceeding with
the cleanup in switchtec_ntb_remove.

Signed-off-by: Kaixin Wang <kxwang23@xxxxxxxxxxxxxx>
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: Jon Mason <jdmason@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/ntb/hw/mscc/ntb_hw_switchtec.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/ntb/hw/mscc/ntb_hw_switchtec.c b/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
index 86ffa716eaf22..db9be3ce1cd0d 100644
--- a/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
+++ b/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
@@ -1558,6 +1558,7 @@ static void switchtec_ntb_remove(struct device *dev,
 	switchtec_ntb_deinit_db_msg_irq(sndev);
 	switchtec_ntb_deinit_shared_mw(sndev);
 	switchtec_ntb_deinit_crosslink(sndev);
+	cancel_work_sync(&sndev->check_link_status_work);
 	kfree(sndev);
 	dev_info(dev, "ntb device unregistered\n");
 }
-- 
2.43.0