Re: [PATCH 0/6] usbip fixes to crashes found by syzbot

[Tetsuo Handa]

On 2021/03/13 9:48, Tetsuo Handa wrote:
> On 2021/03/12 14:44, Tetsuo Handa wrote:
>> And what you are missing in your [PATCH 4,5,6/6] is
>>
>>   diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
>>   index c4457026d5ad..3c64bd06ab53 100644
>>   --- a/drivers/usb/usbip/vhci_sysfs.c
>>   +++ b/drivers/usb/usbip/vhci_sysfs.c
>>   @@ -423,6 +423,7 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
>>           /* end the lock */
>>   
>>           wake_up_process(vdev->ud.tcp_rx);
>>   +       schedule_timeout_uninterruptible(HZ); // Consider being preempted here.
>>           wake_up_process(vdev->ud.tcp_tx);
>>   
>>           rh_port_connect(vdev, speed);
>>
>> . wake_up_process(tcp_tx) can call vhci_shutdown_connection() before wake_up_process(tcp_tx) is called.
> 
> wake_up_process(tcp_rx) can call vhci_shutdown_connection() before wake_up_process(tcp_tx) is called.
> 
>> Since vhci_shutdown_connection() destroys tcp_tx thread and releases tcp_tx memory via kthread_stop_put(tcp_tx),
>> wake_up_process(tcp_tx) will access already freed memory. Your patch converted "NULL pointer dereference caused by
>> failing to call kthread_stop_put(tcp_tx)" into "use after free caused by succeeding to call kthread_stop_put(tcp_tx)".
>>
> 
> And note that
> 
>   diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
>   index c4457026d5ad..0e1a81d4632c 100644
>   --- a/drivers/usb/usbip/vhci_sysfs.c
>   +++ b/drivers/usb/usbip/vhci_sysfs.c
>   @@ -422,11 +422,11 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
>           spin_unlock_irqrestore(&vhci->lock, flags);
>           /* end the lock */
>   
>   -       wake_up_process(vdev->ud.tcp_rx);
>   -       wake_up_process(vdev->ud.tcp_tx);
>   -
>           rh_port_connect(vdev, speed);
>   
>   +       wake_up_process(vdev->ud.tcp_tx);
>   +       wake_up_process(vdev->ud.tcp_rx);
>   +
>           return count;
>    }
>    static DEVICE_ATTR_WO(attach);
> 
> is as well not sufficient, for you are still missing

Well, since tx thread can as well call usbip_event_add(USBIP_EH_SHUTDOWN), reversing
the order of wake_up_process(tcp_tx) and wake_up_process(tcp_rx) will not help.

> 
>   diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
>   index c4457026d5ad..c958f89a9196 100644
>   --- a/drivers/usb/usbip/vhci_sysfs.c
>   +++ b/drivers/usb/usbip/vhci_sysfs.c
>   @@ -422,11 +422,13 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
>           spin_unlock_irqrestore(&vhci->lock, flags);
>           /* end the lock */
>   
>   -       wake_up_process(vdev->ud.tcp_rx);
>   -       wake_up_process(vdev->ud.tcp_tx);
>   +       schedule_timeout_uninterruptible(HZ); // Consider being preempted here.
>   
>           rh_port_connect(vdev, speed);
>   
>   +       wake_up_process(vdev->ud.tcp_tx);
>   +       wake_up_process(vdev->ud.tcp_rx);
>   +
>           return count;
>    }
>    static DEVICE_ATTR_WO(attach);
> 
> because vhci_port_disconnect() from detach_store() can call usbip_event_add(&vdev->ud, VDEV_EVENT_DOWN)
> (same use after free bug regarding tcp_tx and tcp_rx) as soon as all shared states are set up and
> spinlocks are released.
> 
> What you had better consider first is how to protect event_handler()/usbip_sockfd_store()/attach_store()/detach_store() functions
>  from concurrent calls. Please respond to https://lkml.kernel.org/r/3dab66dc-2981-bc88-a370-4b3178dfd390@xxxxxxxxxxxxxxxxxxx
> before you try to make further changes.
> 

After all, I believe that there is no choice but introduce a mutex for serialization.

Greg, please pick up https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux.git/commit/?h=usbip_test&id=f345de0d2e51a20a2a1c30fc22fa1527670d2095
and below patch.