memstick: r592: Fix UAF bug in r592_remove due to race condition

In r592_probe, dev->detect_timer was bound with r592_detect_timer.
In r592_irq function, the timer function will be invoked by mod_timer.

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

Fix it by canceling the work before cleanup in r592_remove.

CPU0                  CPU1

                    |r592_detect_timer
r592_remove         |
  memstick_free_host|
  put_device;       |
  kfree(host);      |
                    |
                    | queue_work
                    |   &host->media_checker //use

Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
---
 drivers/memstick/host/r592.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Tue, 7 Mar 2023 at 17:44, Zheng Wang <zyytlz.wz@163.com> wrote:
>
> In r592_probe, dev->detect_timer was bound with r592_detect_timer.
> In r592_irq function, the timer function will be invoked by mod_timer.
>
> If we remove the module which will call hantro_release to make cleanup,
> there may be a unfinished work. The possible sequence is as follows,
> which will cause a typical UAF bug.
>
> Fix it by canceling the work before cleanup in r592_remove.
>
> CPU0                  CPU1
>
>                     |r592_detect_timer
> r592_remove         |
>   memstick_free_host|
>   put_device;       |
>   kfree(host);      |
>                     |
>                     | queue_work
>                     |   &host->media_checker //use
>
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/memstick/host/r592.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/memstick/host/r592.c b/drivers/memstick/host/r592.c
> index 1d35d147552d..2bfa7eaae80a 100644
> --- a/drivers/memstick/host/r592.c
> +++ b/drivers/memstick/host/r592.c
> @@ -829,7 +829,7 @@ static void r592_remove(struct pci_dev *pdev)
>         /* Stop the processing thread.
>         That ensures that we won't take any more requests */
>         kthread_stop(dev->io_thread);
> -
> +       del_timer_sync(&dev->detect_timer);
>         r592_enable_device(dev, false);
>
>         while (!error && dev->req) {
> --
> 2.25.1
>

Ulf Hansson <ulf.hansson@linaro.org> 于2023年3月9日周四 23:02写道：
>
> On Tue, 7 Mar 2023 at 17:44, Zheng Wang <zyytlz.wz@163.com> wrote:
> >
> > In r592_probe, dev->detect_timer was bound with r592_detect_timer.
> > In r592_irq function, the timer function will be invoked by mod_timer.
> >
> > If we remove the module which will call hantro_release to make cleanup,
> > there may be a unfinished work. The possible sequence is as follows,
> > which will cause a typical UAF bug.
> >
> > Fix it by canceling the work before cleanup in r592_remove.
> >
> > CPU0                  CPU1
> >
> >                     |r592_detect_timer
> > r592_remove         |
> >   memstick_free_host|
> >   put_device;       |
> >   kfree(host);      |
> >                     |
> >                     | queue_work
> >                     |   &host->media_checker //use
> >
> > Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
>
> Applied for next, thanks!
>
Sorry for my late reply and thanks for your effort!

Best regards,
Zheng
>
>
> > ---
> >  drivers/memstick/host/r592.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/memstick/host/r592.c b/drivers/memstick/host/r592.c
> > index 1d35d147552d..2bfa7eaae80a 100644
> > --- a/drivers/memstick/host/r592.c
> > +++ b/drivers/memstick/host/r592.c
> > @@ -829,7 +829,7 @@ static void r592_remove(struct pci_dev *pdev)
> >         /* Stop the processing thread.
> >         That ensures that we won't take any more requests */
> >         kthread_stop(dev->io_thread);
> > -
> > +       del_timer_sync(&dev->detect_timer);
> >         r592_enable_device(dev, false);
> >
> >         while (!error && dev->req) {
> > --
> > 2.25.1
> >