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SubjectRe: [PATCH] mISDN: hfcpci: Fix use-after-free bug in hfcpci_Timer
On Thu, Oct 13, 2022 at 03:20:05PM +0200, Greg KH wrote:
> 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@zju.edu.cn>
> > ---
> > 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?

According to his previous response [1], the answer will be no. I'm not
super-excited that this unmaintained and old driver chosen as playground
for new tool.

[1] https://lore.kernel.org/all/17ad6913.ff8e0.1838933840d.Coremail.duoming@zju.edu.cn/#t

>
> thanks,
>
> greg k-h

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