[v3] media: bttv: fix use after free error due to btv->timeout timer

  There may be some a race condition between timer function
bttv_irq_timeout and bttv_remove. The timer is setup in
probe and there is no timer_delete operation in remove
function. When it hit kfree btv, the function might still be
invoked, which will cause use after free bug.

This bug is found by static analysis, it may be false positive.

Fix it by adding del_timer_sync invoking to the remove function.

cpu0                cpu1
                  bttv_probe
                    ->timer_setup
                      ->bttv_set_dma
                        ->mod_timer;
bttv_remove
  ->kfree(btv);
                  ->bttv_irq_timeout
                    ->USE btv

Fixes: 162e6376ac58 ("media: pci: Convert timers to use timer_setup()")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
---
v3:
- Add Fix label
v2:
- stop replacing del_timer with del_timer_sync suggested by Hillf Danton
---
 drivers/media/pci/bt8xx/bttv-driver.c | 1 +
 1 file changed, 1 insertion(+)
  

Hi Zheng,

Deb Brouwer is working on converting bttv to the vb2 framework, so I want to
wait for that to finish before taking other bttv patches.

I suspect this is still valid post-vb2 conversion, but I'm not certain.

Regards,

	Hans

On 13/04/2023 05:49, Zheng Wang wrote:
> There may be some a race condition between timer function
> bttv_irq_timeout and bttv_remove. The timer is setup in
> probe and there is no timer_delete operation in remove
> function. When it hit kfree btv, the function might still be
> invoked, which will cause use after free bug.
> 
> This bug is found by static analysis, it may be false positive.
> 
> Fix it by adding del_timer_sync invoking to the remove function.
> 
> cpu0                cpu1
>                   bttv_probe
>                     ->timer_setup
>                       ->bttv_set_dma
>                         ->mod_timer;
> bttv_remove
>   ->kfree(btv);
>                   ->bttv_irq_timeout
>                     ->USE btv
> 
> Fixes: 162e6376ac58 ("media: pci: Convert timers to use timer_setup()")
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
> ---
> v3:
> - Add Fix label
> v2:
> - stop replacing del_timer with del_timer_sync suggested by Hillf Danton
> ---
>  drivers/media/pci/bt8xx/bttv-driver.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
> index d40b537f4e98..24ba5729969d 100644
> --- a/drivers/media/pci/bt8xx/bttv-driver.c
> +++ b/drivers/media/pci/bt8xx/bttv-driver.c
> @@ -4248,6 +4248,7 @@ static void bttv_remove(struct pci_dev *pci_dev)
>  
>  	/* free resources */
>  	free_irq(btv->c.pci->irq,btv);
> +	del_timer_sync(&btv->timeout);
>  	iounmap(btv->bt848_mmio);
>  	release_mem_region(pci_resource_start(btv->c.pci,0),
>  			   pci_resource_len(btv->c.pci,0));
  

Hans Verkuil <hverkuil@xs4all.nl> 于2023年4月13日周四 17:18写道：
>
> Hi Zheng,
>
> Deb Brouwer is working on converting bttv to the vb2 framework, so I want to
> wait for that to finish before taking other bttv patches.
>
> I suspect this is still valid post-vb2 conversion, but I'm not certain.
>
> Regards,
>
>         Hans
>

Hi Hans,

Thank you for your prompt response and for letting me know about the
conversion of BTTV to the vb2 framework by Deb Brouwer.
 I will wait for that to finish before submitting any other BTTV patches.

Best regards,
Zheng


> On 13/04/2023 05:49, Zheng Wang wrote:
> > There may be some a race condition between timer function
> > bttv_irq_timeout and bttv_remove. The timer is setup in
> > probe and there is no timer_delete operation in remove
> > function. When it hit kfree btv, the function might still be
> > invoked, which will cause use after free bug.
> >
> > This bug is found by static analysis, it may be false positive.
> >
> > Fix it by adding del_timer_sync invoking to the remove function.
> >
> > cpu0                cpu1
> >                   bttv_probe
> >                     ->timer_setup
> >                       ->bttv_set_dma
> >                         ->mod_timer;
> > bttv_remove
> >   ->kfree(btv);
> >                   ->bttv_irq_timeout
> >                     ->USE btv
> >
> > Fixes: 162e6376ac58 ("media: pci: Convert timers to use timer_setup()")
> > Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
> > ---
> > v3:
> > - Add Fix label
> > v2:
> > - stop replacing del_timer with del_timer_sync suggested by Hillf Danton
> > ---
> >  drivers/media/pci/bt8xx/bttv-driver.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
> > index d40b537f4e98..24ba5729969d 100644
> > --- a/drivers/media/pci/bt8xx/bttv-driver.c
> > +++ b/drivers/media/pci/bt8xx/bttv-driver.c
> > @@ -4248,6 +4248,7 @@ static void bttv_remove(struct pci_dev *pci_dev)
> >
> >       /* free resources */
> >       free_irq(btv->c.pci->irq,btv);
> > +     del_timer_sync(&btv->timeout);
> >       iounmap(btv->bt848_mmio);
> >       release_mem_region(pci_resource_start(btv->c.pci,0),
> >                          pci_resource_len(btv->c.pci,0));
>