[PATCH] media: hantro: fix use after free bug in hantro_release 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 close the file or remove the module which will
call hantro_release and hantro_remove to make cleanup,
there may be a unfinished work. The possible sequence
is as follows, which will cause a typical UAF bug.

The same thing will happen in hantro_release, and use
ctx after freeing it.

Fix it by canceling the work before cleanup in hantro_release.

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 at 163.com>
---
 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..cf00ccaa7829 100644
--- a/drivers/media/platform/verisilicon/hantro_drv.c
+++ b/drivers/media/platform/verisilicon/hantro_drv.c
@@ -601,6 +601,7 @@ static int hantro_release(struct file *filp)
 	 * No need for extra locking because this was the last reference
 	 * to this file.
 	 */
+	cancel_delayed_work(&vpu->watchdog_work);
 	v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);
 	v4l2_fh_del(&ctx->fh);
 	v4l2_fh_exit(&ctx->fh);
-- 
2.25.1