Re: [PATCH] moxart: fix potential use-after-free on remove path

[Ulf Hansson]

On Fri, 21 Jan 2022 at 14:54, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, Jan 21, 2022 at 01:41:27PM +0100, Ulf Hansson wrote:
> > On Fri, 14 Jan 2022 at 08:59, Greg Kroah-Hartman
> > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > It was reported that the mmc host structure could be accessed after it
> > > was freed in moxart_remove(), so fix this by saving the base register of
> > > the device and using it instead of the pointer dereference.
> > >
> > > Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> > > Cc: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
> > > Cc: Xin Xiong <xiongx18@xxxxxxxxxxxx>
> > > Cc: Xin Tan <tanxin.ctf@xxxxxxxxx>
> > > Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> > > Cc: Yang Li <yang.lee@xxxxxxxxxxxxxxxxx>
> > > Cc: linux-mmc@xxxxxxxxxxxxxxx
> > > Cc: stable <stable@xxxxxxxxxxxxxxx>
> > > Reported-by: whitehat002 <hackyzh002@xxxxxxxxx>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > >  drivers/mmc/host/moxart-mmc.c | 9 +++++----
> > >  1 file changed, 5 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/mmc/host/moxart-mmc.c b/drivers/mmc/host/moxart-mmc.c
> > > index 16d1c7a43d33..f5d96940a9b8 100644
> > > --- a/drivers/mmc/host/moxart-mmc.c
> > > +++ b/drivers/mmc/host/moxart-mmc.c
> > > @@ -697,6 +697,7 @@ static int moxart_remove(struct platform_device *pdev)
> > >  {
> > >         struct mmc_host *mmc = dev_get_drvdata(&pdev->dev);
> > >         struct moxart_host *host = mmc_priv(mmc);
> > > +       void __iomem *base = host->base;
> > >
> > >         dev_set_drvdata(&pdev->dev, NULL);
> > >
> > > @@ -707,10 +708,10 @@ static int moxart_remove(struct platform_device *pdev)
> > >         mmc_remove_host(mmc);
> > >         mmc_free_host(mmc);
> > >
> > > -       writel(0, host->base + REG_INTERRUPT_MASK);
> > > -       writel(0, host->base + REG_POWER_CONTROL);
> > > -       writel(readl(host->base + REG_CLOCK_CONTROL) | CLK_OFF,
> > > -              host->base + REG_CLOCK_CONTROL);
> >
> > Rather than doing it like this, I think it would be easier to move
> > mmc_free_host() below this part. That's usually what mmc host drivers
> > do clean up things in ->remove().
> >
> > > +       writel(0, base + REG_INTERRUPT_MASK);
> > > +       writel(0, base + REG_POWER_CONTROL);
> > > +       writel(readl(base + REG_CLOCK_CONTROL) | CLK_OFF,
> > > +              base + REG_CLOCK_CONTROL);
> > >
>
> Ok, I can do that, I didn't know if it would cause any functionality
> changes, so I was trying to preserve the same logic that the driver
> currently has.

Yes, but it's most likely just a simple mistake that was made by the
original author.

>
> Do you have this device to test this with?

No, I don't.

Although, I am confident that it should work fine too.

>
> thanks,
>
> greg k-h

Kind regards
Uffe