[PATCH] HID: intel-ish-hid: pci-ish: Fix use after free bug in ish_remove due to race condition

[Zheng Wang <zyytlz.wz@163.com>]

In ish_probe, it calls ish_dev_init to init the device. In this function,
ishtp_device_init is called and &dev->bh_hbm_work is bound with 
bh_hbm_work_fn. recv_hbm may be called to start the timer work.

If we remove the module which will call ish_remove to make cleanup,
there may be an unfinished work. The possible sequence is as follows:

Fix it by canceling the work before cleanup in ishtp_bus_remove_all_clients

CPU0                  CPUc1

                    |bh_hbm_work_fn
ish_remove      |
ishtp_bus_remove_all_clients  |
kfree(ishtp_dev->fw_clients); |
                    |
                    |&dev->fw_clients[...]
                    |   //use

Fixes: 3703f53b99e4 ("HID: intel_ish-hid: ISH Transport layer")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
---
 drivers/hid/intel-ish-hid/ishtp/bus.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hid/intel-ish-hid/ishtp/bus.c b/drivers/hid/intel-ish-hid/ishtp/bus.c
index 81385ab37fa9..ada7cd08dbeb 100644
--- a/drivers/hid/intel-ish-hid/ishtp/bus.c
+++ b/drivers/hid/intel-ish-hid/ishtp/bus.c
@@ -744,6 +744,7 @@ void ishtp_bus_remove_all_clients(struct ishtp_device *ishtp_dev,
 		 */
 	}
 	spin_unlock_irqrestore(&ishtp_dev->cl_list_lock, flags);
+	cancel_work_sync(&ishtp_dev->bh_hbm_work);
 
 	/* Release DMA buffers for client messages */
 	ishtp_cl_free_dma_buf(ishtp_dev);
-- 
2.25.1