Re: [PATCH] mISDN: hfcpci: Fix use-after-free bug in hfcpci_Timer

[Greg KH]

On Thu, Oct 13, 2022 at 08:57:29PM +0800, Duoming Zhou wrote:
> If the timer handler hfcpci_Timer() is running, the
> del_timer(&hc->hw.timer) in release_io_hfcpci() could
> not stop it. As a result, the use-after-free bug will
> happen. The process is shown below:
> 
>     (cleanup routine)          |        (timer handler)
> release_card()                 | hfcpci_Timer()
>   release_io_hfcpci            |
>     del_timer(&hc->hw.timer)   |
>   ...                          |  ...
>   kfree(hc) //[1]FREE          |
>                                |   hc->hw.timer.expires //[2]USE
> 
> The hfc_pci is deallocated in position [1] and used in
> position [2].
> 
> Fix by changing del_timer() in release_io_hfcpci() to
> del_timer_sync(), which makes sure the hfcpci_Timer()
> have finished before the hfc_pci is deallocated.
> 
> Fixes: 1700fe1a10dc ("Add mISDN HFC PCI driver")
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> ---
>  drivers/isdn/hardware/mISDN/hfcpci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/isdn/hardware/mISDN/hfcpci.c b/drivers/isdn/hardware/mISDN/hfcpci.c
> index af17459c1a5..5cf37fe7de2 100644
> --- a/drivers/isdn/hardware/mISDN/hfcpci.c
> +++ b/drivers/isdn/hardware/mISDN/hfcpci.c
> @@ -157,7 +157,7 @@ release_io_hfcpci(struct hfc_pci *hc)
>  {
>  	/* disable memory mapped ports + busmaster */
>  	pci_write_config_word(hc->pdev, PCI_COMMAND, 0);
> -	del_timer(&hc->hw.timer);
> +	del_timer_sync(&hc->hw.timer);

Nice, how did you test that this will work properly?  Do you have this
hardware for testing?  How was this issue found and verified that this
is the correct resolution?

thanks,

greg k-h