Re: [PATCH 1/2] gpio: cdev: fix missed label sanitizing in debounce_setup()

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Wed, Apr 3, 2024 at 3:15 PM Kent Gibson <warthog618@xxxxxxxxx> wrote:
>
> When adding sanitization of the label, the path through
> edge_detector_setup() that leads to debounce_setup() was overlooked.
> A request taking this path does not allocate a new label and the
> request label is freed twice when the request is released, resulting
> in memory corruption.
>
> Add label sanitization to debounce_setup().
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: b34490879baa ("gpio: cdev: sanitize the label before requesting the interrupt")
> Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
> ---
>  drivers/gpio/gpiolib-cdev.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index fa9635610251..f4c2da2041e5 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -728,6 +728,16 @@ static u32 line_event_id(int level)
>                        GPIO_V2_LINE_EVENT_FALLING_EDGE;
>  }
>
> +static inline char *make_irq_label(const char *orig)
> +{
> +       return kstrdup_and_replace(orig, '/', ':', GFP_KERNEL);
> +}
> +
> +static inline void free_irq_label(const char *label)
> +{
> +       kfree(label);
> +}
> +
>  #ifdef CONFIG_HTE
>
>  static enum hte_return process_hw_ts_thread(void *p)
> @@ -1015,6 +1025,7 @@ static int debounce_setup(struct line *line, unsigned int debounce_period_us)
>  {
>         unsigned long irqflags;
>         int ret, level, irq;
> +       char *label;
>
>         /* try hardware */
>         ret = gpiod_set_debounce(line->desc, debounce_period_us);
> @@ -1037,11 +1048,17 @@ static int debounce_setup(struct line *line, unsigned int debounce_period_us)
>                         if (irq < 0)
>                                 return -ENXIO;
>
> +                       label = make_irq_label(line->req->label);

Now that I look at the actual patch, I don't really like it. We
introduce a bug just to fix it a commit later. Such things have been
frowned upon in the past.

Let me shuffle the code a bit, I'll try to make it a bit more correct.

Bart

> +                       if (!label)
> +                               return -ENOMEM;
> +
>                         irqflags = IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING;
>                         ret = request_irq(irq, debounce_irq_handler, irqflags,
> -                                         line->req->label, line);
> -                       if (ret)
> +                                         label, line);
> +                       if (ret) {
> +                               free_irq_label(label);
>                                 return ret;
> +                       }
>                         line->irq = irq;
>                 } else {
>                         ret = hte_edge_setup(line, GPIO_V2_LINE_FLAG_EDGE_BOTH);
> @@ -1083,16 +1100,6 @@ static u32 gpio_v2_line_config_debounce_period(struct gpio_v2_line_config *lc,
>         return 0;
>  }
>
> -static inline char *make_irq_label(const char *orig)
> -{
> -       return kstrdup_and_replace(orig, '/', ':', GFP_KERNEL);
> -}
> -
> -static inline void free_irq_label(const char *label)
> -{
> -       kfree(label);
> -}
> -
>  static void edge_detector_stop(struct line *line)
>  {
>         if (line->irq) {
> --
> 2.39.2
>