Re: [PATCH v3] gpio: Restrict usage of GPIO chip irq members before initialization

[Bartosz Golaszewski]

On Mon, Mar 21, 2022 at 2:33 PM Shreeya Patel
<shreeya.patel@xxxxxxxxxxxxx> wrote:
>
> GPIO chip irq members are exposed before they could be completely
> initialized and this leads to race conditions.
>
> One such issue was observed for the gc->irq.domain variable which
> was accessed through the I2C interface in gpiochip_to_irq() before
> it could be initialized by gpiochip_add_irqchip(). This resulted in
> Kernel NULL pointer dereference.
>
> Following are the logs for reference :-
>
> kernel: Call Trace:
> kernel:  gpiod_to_irq+0x53/0x70
> kernel:  acpi_dev_gpio_irq_get_by+0x113/0x1f0
> kernel:  i2c_acpi_get_irq+0xc0/0xd0
> kernel:  i2c_device_probe+0x28a/0x2a0
> kernel:  really_probe+0xf2/0x460
> kernel: RIP: 0010:gpiochip_to_irq+0x47/0xc0
>
> To avoid such scenarios, restrict usage of GPIO chip irq members before
> they are completely initialized.
>
> Signed-off-by: Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx>
> ---
>
> Changes in v3
>   - Move the gc->irq.initialized check inside gpiochip_to_irq().
>   - Rename gc to GPIO chip.
>   - Add barrier() to avoid compiler reordering.
>
> Changes in v2
>   - Make gc_irq_initialized flag a member of gpio_irq_chip structure.
>   - Make use of barrier() to avoid reordering of flag initialization
> before other gc irq members are initialized.
>
>
>  drivers/gpio/gpiolib.c      | 19 +++++++++++++++++++
>  include/linux/gpio/driver.h |  9 +++++++++
>  2 files changed, 28 insertions(+)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index defb7c464b87..4ff68f48b87f 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1404,6 +1404,16 @@ static int gpiochip_to_irq(struct gpio_chip *gc, unsigned int offset)
>  {
>         struct irq_domain *domain = gc->irq.domain;
>
> +#ifdef CONFIG_GPIOLIB_IRQCHIP
> +       /*
> +        * Avoid race condition with other code, which tries to lookup
> +        * an IRQ before the irqchip has been properly registered,
> +        * i.e. while gpiochip is still being brought up.
> +        */
> +       if (!gc->irq.initialized)
> +               return -EPROBE_DEFER;
> +#endif
> +
>         if (!gpiochip_irqchip_irq_valid(gc, offset))
>                 return -ENXIO;
>
> @@ -1593,6 +1603,15 @@ static int gpiochip_add_irqchip(struct gpio_chip *gc,
>
>         acpi_gpiochip_request_interrupts(gc);
>
> +       /*
> +        * Using barrier() here to prevent compiler from reordering
> +        * gc->irq.initialized before initialization of above
> +        * GPIO chip irq members.
> +        */
> +       barrier();
> +
> +       gc->irq.initialized = true;
> +
>         return 0;
>  }
>
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index b0728c8ad90c..f8996b46f430 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -218,6 +218,15 @@ struct gpio_irq_chip {
>          */
>         bool per_parent_data;
>
> +       /**
> +        * @initialized:
> +        *
> +        * Flag to track GPIO chip irq member's initialization.
> +        * This flag will make sure GPIO chip irq members are not used
> +        * before they are initialized.
> +        */
> +       bool initialized;
> +
>         /**
>          * @init_hw: optional routine to initialize hardware before
>          * an IRQ chip will be added. This is quite useful when
> --
> 2.30.2
>

I queued it for fixes, let's backport it to stable.

Bart