Re: [PATCH] mmc: dw_mmc: Add a defensive check to prevent potential null-pointer dereferences in dw_mci_runtime_resume()

[Tuo Li]

Hi Shawn,

On Fri, Dec 12, 2025 at 8:28 AM Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
>
> Hi Tuo,
>
> 在 2025/12/12 星期五 0:13, Tuo Li 写道:
> > In this function, the variable host->slot is checked and then dereferenced
> > in several places which indicates it can be NULL, for example:
> >
> >    if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> >               dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);
> >
> > However, in the following cases, host->slot is dereferenced without a
> > preceding NULL check, which introduces a risk of null-pointer dereference:
> >
> >    dw_mci_setup_bus(host->slot, true);
> >
> >    if (sdio_irq_claimed(host->slot->mmc))
> >      __dw_mci_enable_sdio_irq(host->slot, 1);
> >
> >    dw_mci_enable_cd(host);
> >
> > To prevent such issues, add a defensive check to ensure host->slot is not
> > NULL before dereferencing it.
> >
>
> Thanks for your patch. we plan to remove the slot design
> entirely soon, probably this cycle.
>

Thanks for your feedback!

> > Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
> > ---
> >   drivers/mmc/host/dw_mmc.c | 17 ++++++++++-------
> >   1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index 9e74b675e92d..e74dea0a32d4 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -3670,15 +3670,18 @@ int dw_mci_runtime_resume(struct device *dev)
> >       if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> >               dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);
> >
> > -     /* Force setup bus to guarantee available clock output */
> > -     dw_mci_setup_bus(host->slot, true);
> >
> > -     /* Re-enable SDIO interrupts. */
> > -     if (sdio_irq_claimed(host->slot->mmc))
> > -             __dw_mci_enable_sdio_irq(host->slot, 1);
> > +     if (host->slot) {
> > +             /* Force setup bus to guarantee available clock output */
> > +             dw_mci_setup_bus(host->slot, true);
> >
> > -     /* Now that slots are all setup, we can enable card detect */
> > -     dw_mci_enable_cd(host);
> > +             /* Re-enable SDIO interrupts. */
> > +             if (sdio_irq_claimed(host->slot->mmc))
> > +                     __dw_mci_enable_sdio_irq(host->slot, 1);
> > +
> > +             /* Now that slots are all setup, we can enable card detect */
> > +             dw_mci_enable_cd(host);
> > +     }
> >
> >       return 0;
> >
>

Sincerely,
Tuo Li