Re: [PATCH v3] gpiolib: fix reference leaks when removing GPIO chips still in use

From: Andy Shevchenko
Date: Tue Aug 15 2023 - 05:50:57 EST


On Fri, Aug 11, 2023 at 09:30:34PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> After we remove a GPIO chip that still has some requested descriptors,
> gpiod_free_commit() will fail and we will never put the references to the
> GPIO device and the owning module in gpiod_free().
>
> Rework this function to:
> - not warn on desc == NULL as this is a use-case on which most free
> functions silently return
> - put the references to desc->gdev and desc->gdev->owner unconditionally
> so that the release callback actually gets called when the remaining
> references are dropped by external GPIO users

...

> - if (desc && desc->gdev && gpiod_free_commit(desc)) {

The commit message doesn't explain disappearing of gdev check.

> - module_put(desc->gdev->owner);
> - gpio_device_put(desc->gdev);
> - } else {
> + /*
> + * We must not use VALIDATE_DESC_VOID() as the underlying gdev->chip
> + * may already be NULL but we still want to put the references.
> + */
> + if (!desc)
> + return;
> +
> + if (!gpiod_free_commit(desc))
> WARN_ON(extra_checks);
> - }
> +
> + module_put(desc->gdev->owner);
> + gpio_device_put(desc->gdev);
> }

So, if gdev can be NULL, you will get an Oops with new code.

To keep a status quo this needs to be rewritten.

--
With Best Regards,
Andy Shevchenko