Bug report: usb: cdns3: cdns3-gadget.c: use-after-free bug in cdns3_gadget_exit due to race condition

sicong
2024-05-11T12:50:03Z

usb: cdns3: cdns3-gadget.c: use-after-free bug in cdns3_gadget_exit due to
race condition

This bug exists in drivers/usb/cdns3/cdns3-gadget.c. Function
__cdns3_gadget_init will call cdns3_gadget_start to do the futher jobs
during the initialization proccess of cdns3 gadget. In cdns3_gadget_start,
&priv_dev->pending_status_wq is bound with cdns3_pending_setup_status_handler.
Then this work will be added to system_freezable_wq in cdns3_gadget_ep0_queue.
Here is the code.
queue_work(system_freezable_wq, &priv_dev->pending_status_wq);

If we call cdns3_gadget_exit to remove the device and make cleanup,
there are some unfinished works. This function will call cdns3_free_all_eps to
free all the endpoints. However, if cdns3_pending_setup_status_handler is
scheduled to run after the free job, it will cause use-after-free error as
cdns3_pending_setup_status_handler will use the endpoint in the following code.
request->complete(&priv_dev->eps[0]->endpoint, request);

The possible execution flow that may lead to this issue is as follows:
CPU0 CPU1
| __cdns3_gadget_init
| cdns3_gadget_start
cdns3_gadget_exit |
cdns3_free_all_eps |
devm_kfree (free) |
| cdns3_pending_setup_status_handler
| &priv_dev->eps[0]->endpoint (use)

This bug may be fixed by adding the following code in cdns3_gadget_exit.
cancel_work_sync(&priv_dev->pending_status_wq);
cancel_work_sync(&priv_dev->aligned_buf_wq);

Best regards,
Sicong Huang