[report?] A race condition is suspected.

[report?] A race condition is suspected.

[Hyunwoo Kim]

Dear all,

From the code, it looks like a use-after-free due to a race condition 
could be caused by the lack of a proper lock between the ncsi_dev_work() 
worker and the vlan ioctl:
```
                  cpu0                                          cpu1

         ncsi_dev_work()
           ncsi_configure_channel()
             set_one_vid()
               rcu_read_lock()
                                                            sock_ioctl()
                                                              vlan_ioctl_handler()
                                                                unregister_vlan_dev()
                                                                  vlan_vid_del()
                                                                    __vlan_vid_del()
                                                                      vlan_kill_rx_filter_info()
                                                                        ncsi_vlan_rx_kill_vid()
                                                                          list_del_rcu(&vlan->list);
                                                                          kfree(vlan);
               vid = vlan->vid;    // use-after-free?
               rcu_read_unlock()
```

However, I do not have a device that uses the ncsi_dev_work() worker, 
so I have not been able to debug this.

Can a race condition like this actually happen, and if so, it seems 
like we need to change `kfree(vlan);` to `kfree_rcu(vlan)`, or add 
an appropriate lock to the worker.


Regards,
Hyunwoo Kim

Re: [report?] A race condition is suspected.

[Hyunwoo Kim]

On Mon, Jul 03, 2023 at 11:07:34PM -0700, Hyunwoo Kim wrote:
> Dear all,
> 
> From the code, it looks like a use-after-free due to a race condition 
> could be caused by the lack of a proper lock between the ncsi_dev_work() 
> worker and the vlan ioctl:
> ```
>                   cpu0                                          cpu1
> 
>          ncsi_dev_work()
>            ncsi_configure_channel()
>              set_one_vid()
>                rcu_read_lock()
>                                                             sock_ioctl()
>                                                               vlan_ioctl_handler()
>                                                                 unregister_vlan_dev()
>                                                                   vlan_vid_del()
>                                                                     __vlan_vid_del()
>                                                                       vlan_kill_rx_filter_info()
>                                                                         ncsi_vlan_rx_kill_vid()
>                                                                           list_del_rcu(&vlan->list);
>                                                                           kfree(vlan);
>                vid = vlan->vid;    // use-after-free?
>                rcu_read_unlock()
> ```
> 
> However, I do not have a device that uses the ncsi_dev_work() worker, 
> so I have not been able to debug this.
> 
> Can a race condition like this actually happen, and if so, it seems 
> like we need to change `kfree(vlan);` to `kfree_rcu(vlan)`, or add 
> an appropriate lock to the worker.
> 
> 
> Regards,
> Hyunwoo Kim

Hi,

Can I get a review of this report?
Should I submit a patch to replace kfree_rcu()?


Regards,
Hyunwoo Kim