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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Mar 04, 2026 at 05:25:25PM +0100, Ulf Hansson wrote:
> On Mon, 23 Feb 2026 at 14:48, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > Just like in commit bd2db32e7c3e ("moxart: fix potential use-after-free
> > on remove path"), we should wait until after we are finished writing to
> > the mmc host device before removing it, otherwise it could have been
> > already freed.
> 
> mmc_remove_host() doesn't actually free the host, but it reverses what
> mmc_add_host() did during probe.
> 
> Since the moxart driver uses devm_mmc_alloc_host() the last reference
> to the host will be dropped after ->remove() completes, leading to
> mmc_free_host() to be called for it.

Then how did commit bd2db32e7c3e ("moxart: fix potential use-after-free
on remove path") do anything?  It really wasn't needed either?  And so
the CVE related to it should be rejected?

> However, improvements can still be made in the ->remove() callback. See below.
> 
> >
> > Cc: Ulf Hansson <ulf.hansson@linaro.org>
> > Cc: stable <stable@kernel.org>
> > Assisted-by: gkh_clanker_2000
> 
> What's this?

My assorted hacks of scripts that found this issue.

> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> >  drivers/mmc/host/moxart-mmc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/moxart-mmc.c b/drivers/mmc/host/moxart-mmc.c
> > index 3dd8f232052f..256e16390ef3 100644
> > --- a/drivers/mmc/host/moxart-mmc.c
> > +++ b/drivers/mmc/host/moxart-mmc.c
> > @@ -690,12 +690,12 @@ static void moxart_remove(struct platform_device *pdev)
> >                 dma_release_channel(host->dma_chan_tx);
> >         if (!IS_ERR_OR_NULL(host->dma_chan_rx))
> >                 dma_release_channel(host->dma_chan_rx);
> > -       mmc_remove_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);
> > +       mmc_remove_host(mmc);
> 
> Rather than moving this to the bottom of the function, it would be
> more correct to move it to the beginning.
> 
> This way, we ensure things have been closed down properly before
> releasing the dma channels.

Ok, but I was just trying to follow the same pattern in the above
mentioned commit.  If that pattern was not actually fixing something,
then this change also doesn't do anything, so it's not needed either.

thanks,

greg k-h