Re: [PATCH] mmc: dw_mmc: Fix potential null pointer risk

[Aleksandr Mishin]

07.03.2024 13:57, Ulf Hansson wrote:
> On Thu, 7 Mar 2024 at 09:53, Aleksandr Mishin <amishin@xxxxxxxxxx> wrote:
> > In dw_mci_runtime_resume() 'host->slot' could be null, but check is not cover all corresponding code.
> > Fix this bug by changing check place.
>
> In fact host->slot can never be NULL in dw_mci_runtime_resume() or in
> dw_mci_runtime_suspend().
>
> A better fix would thus be to remove the redundant checks.
>
> Kind regards
> Uffe
>
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Fixes: 4a835afd808a (mmc: dw_mmc: Fix potential null pointer risk)
> > Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>
> > ---
> >   drivers/mmc/host/dw_mmc.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index 829af2c98a44..a4f124452abc 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -3570,8 +3570,10 @@ int dw_mci_runtime_resume(struct device *dev)
> >                     DW_MCI_ERROR_FLAGS);
> >          mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
> >
> > +       if (!host->slot)
> > +               goto err;
> >
> > -       if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> > +       if (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 */
> > --
> > 2.30.2

At the same time there are few checks such as "if (host->slot)" in 
dw_mci_runtime_resume() and commit 
4a835afd808a3dbbac44bb399a902b822dc7445c message contains: "we 
previously assumed 'host->slot' could be null, null pointer judgment 
should be added" and replaces "if (host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)" with "if (host->slot && host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)"
So where is the truth?

--
Kind regadrds
Aleksandr