Re: [PATCH] gpio: cdev: sanitize the label before requesting the interrupt

[Kent Gibson <warthog618@xxxxxxxxx>]

On Wed, Mar 20, 2024 at 01:59:44PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> When an interrupt is requested, a procfs directory is created under
> "/proc/irq/<irqnum>/<label>" where <label> is the string passed to one of
> the request_irq() variants.
>
> What follows is that the string must not contain the "/" character or
> the procfs mkdir operation will fail. We don't have such constraints for
> GPIO consumer labels which are used verbatim as interrupt labels for
> GPIO irqs. We must therefore sanitize the consumer string before
> requesting the interrupt.
>

As previously mentioned, it would be nice for that constraint to be
documented in the irq header to help prevent others falling into the
same trap.  Else a short comment in the code here to explain the
need for sanitization.

> Let's replace all "/" with "-".
>

I actually prefer the ":" you originally suggested, as it more clearly
indicates a tier separation, whereas a hyphen is commonly used for
multi-word names. And as the hyphen is more commonly used the sanitized
name is more likely to conflict.

> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Stefan Wahren <wahrenst@xxxxxxx>
> Closes: https://lore.kernel.org/linux-gpio/39fe95cb-aa83-4b8b-8cab-63947a726754@xxxxxxx/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> ---
>  drivers/gpio/gpiolib-cdev.c | 32 +++++++++++++++++++++++++++-----
>  1 file changed, 27 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index f384fa278764..8b5e8e92cbb5 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -1083,10 +1083,20 @@ 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) {
> -		free_irq(line->irq, line);
> +		free_irq_label(free_irq(line->irq, line));
>  		line->irq = 0;
>  	}
>
> @@ -1110,6 +1120,7 @@ static int edge_detector_setup(struct line *line,
>  	unsigned long irqflags = 0;
>  	u64 eflags;
>  	int irq, ret;
> +	char *label;
>
>  	eflags = edflags & GPIO_V2_LINE_EDGE_FLAGS;
>  	if (eflags && !kfifo_initialized(&line->req->events)) {
> @@ -1146,11 +1157,17 @@ static int edge_detector_setup(struct line *line,
>  			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
>  	irqflags |= IRQF_ONESHOT;
>
> +	label = make_irq_label(line->req->label);
> +	if (!label)
> +		return -ENOMEM;
> +
>  	/* Request a thread to read the events */
>  	ret = request_threaded_irq(irq, edge_irq_handler, edge_irq_thread,
> -				   irqflags, line->req->label, line);
> -	if (ret)
> +				   irqflags, label, line);
> +	if (ret) {
> +		free_irq_label(label);
>  		return ret;
> +	}
>
>  	line->irq = irq;
>  	return 0;
> @@ -1973,7 +1990,7 @@ static void lineevent_free(struct lineevent_state *le)
>  		blocking_notifier_chain_unregister(&le->gdev->device_notifier,
>  						   &le->device_unregistered_nb);
>  	if (le->irq)
> -		free_irq(le->irq, le);
> +		free_irq_label(free_irq(le->irq, le));
>  	if (le->desc)
>  		gpiod_free(le->desc);
>  	kfree(le->label);
> @@ -2114,6 +2131,7 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
>  	int fd;
>  	int ret;
>  	int irq, irqflags = 0;
> +	char *label;
>
>  	if (copy_from_user(&eventreq, ip, sizeof(eventreq)))
>  		return -EFAULT;
> @@ -2198,12 +2216,16 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
>  	if (ret)
>  		goto out_free_le;
>
> +	label = make_irq_label(le->label);
> +	if (!label)
> +		goto out_free_le;
> +

Need to set ret = -ENOMEM before the goto, else you will return 0.

Cheers,
Kent.

>  	/* Request a thread to read the events */
>  	ret = request_threaded_irq(irq,
>  				   lineevent_irq_handler,
>  				   lineevent_irq_thread,
>  				   irqflags,
> -				   le->label,
> +				   label,
>  				   le);
>  	if (ret)
>  		goto out_free_le;
> --
> 2.40.1
>