[PATCH v2] media: hantro: fix use after free bug in hantro_remove due to race condition

[Zheng Wang]

In hantro_probe, vpu->watchdog_work is bound with
hantro_watchdog. Then hantro_end_prepare_run may
be called to start the work.

If we remove the module which will call hantro_remove
to make cleanup, there may be an unfinished work.
The possible sequence is as follows, which will
cause a typical UAF bug.

Fix it by canceling the work before cleanup in hantro_remove.

CPU0                  CPU1

                    |hantro_watchdog
hantro_remove     |
  v4l2_m2m_release  |
    kfree(m2m_dev); |
                    |
                    | v4l2_m2m_get_curr_priv
                    |   m2m_dev->curr_ctx //use

Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
---
v2:
- move the cancel-work-related code to hantro_remove suggested by Hans Verkuil
---
 drivers/media/platform/verisilicon/hantro_drv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
index b0aeedae7b65..496024b21b51 100644
--- a/drivers/media/platform/verisilicon/hantro_drv.c
+++ b/drivers/media/platform/verisilicon/hantro_drv.c
@@ -1099,6 +1099,7 @@ static int hantro_remove(struct platform_device *pdev)
 
 	v4l2_info(&vpu->v4l2_dev, "Removing %s\n", pdev->name);
 
+	cancel_delayed_work_sync(&vpu->watchdog_work);
 	media_device_unregister(&vpu->mdev);
 	hantro_remove_dec_func(vpu);
 	hantro_remove_enc_func(vpu);
-- 
2.25.1