Re: [PATCH] mmc: core: Fix struct mmc_gpio corruption

[Fabio Estevam]

Hi Marc,

On Tue, Jul 3, 2018 at 11:11 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> I recently realised that something was amiss with /proc/interrupts
> on my cubietruck:
>
>  51:          0          0     GICv2  41 Level     mv64xxx_i2c
>  59:       1047          0     GICv2 117 Level     eth0
>  66:          2          0  sunxi_pio_edge   1 Edge   XXXXX
>
> where XXXXX has some non-ASCII characters, while I was expecting:
>
>  66:          0          0  sunxi_pio_edge   1 Edge      1c0f000.mmc cd
>
> It turns out that the cd_debounce_delay_ms field was recently to
> struct mmc_gpio, and carefully placed at the one spot where it could
> cause damage: right *after* the zero-sized array that contains the
> associated label. This label ends up being passed to the IRQ
> subsystem, and then overwritten by the cd_debounce_delay_ms field.
>
> Funky!
>
> Let's move that field to a less crowded location.
>
> Fixes: bfd694d5e21c ("mmc: core: Add tunable delay before detecting card after card is inserted")
> Cc: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  drivers/mmc/core/slot-gpio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/slot-gpio.c b/drivers/mmc/core/slot-gpio.c
> index ef05e0039378..1ccf9dc07395 100644
> --- a/drivers/mmc/core/slot-gpio.c
> +++ b/drivers/mmc/core/slot-gpio.c
> @@ -27,8 +27,8 @@ struct mmc_gpio {
>         bool override_cd_active_level;
>         irqreturn_t (*cd_gpio_isr)(int irq, void *dev_id);
>         char *ro_label;
> -       char cd_label[0];
>         u32 cd_debounce_delay_ms;
> +       char cd_label[0];

Ulf has already applied a fix for this:
https://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc.git/commit/?h=fixes&id=60feca8f59a0bbdee9545ab52775cad0171151ff

which is more robust as it will give a gcc error when cd_label gets
moved in the future.