linux-kernel - Re: [PATCH 00/23] gpiolib: Adopt revocable mechanism for UAF prevention

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Message-ID: <CAMRc=MdOCvEb81k0whM9dGCE8Hp=tdxZTUuiFeiL3+WsEei9EQ@mail.gmail.com>
Date: Fri, 16 Jan 2026 11:35:00 +0100
From: Bartosz Golaszewski <brgl@...nel.org>
To: Tzung-Bi Shih <tzungbi@...nel.org>
Cc: Benson Leung <bleung@...omium.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Linus Walleij <linusw@...nel.org>, 
	Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, chrome-platform@...ts.linux.dev, 
	linux-kselftest@...r.kernel.org, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, Simona Vetter <simona.vetter@...ll.ch>, 
	Dan Williams <dan.j.williams@...el.com>, Jason Gunthorpe <jgg@...dia.com>, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 00/23] gpiolib: Adopt revocable mechanism for UAF prevention

On Fri, Jan 16, 2026 at 9:11 AM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> This series transitions the UAF prevention logic within the GPIO core
> (gpiolib) to use the 'revocable' mechanism.
>
> The existing code aims to prevent UAF issues when the underlying GPIO
> chip is removed.  This series replaces that custom logic with the
> generic 'revocable' API, which is designed to handle such lifecycle
> dependencies.  There should be no change in behavior.
>
> This series depends on the 'revocable' API, introduced in [1].  Some
> build bots may report errors due to undefined symbols related to
> 'revocable' until the dependency is merged.
>

Hi Tzung-Bi!

Thank you for doing this and considering my suggestions from LPC. I
haven't looked at the code yet but I quickly tested the series with my
regular test-suites. The good news is: nothing is broken, every test
works fine. The bad news is: there seems to be a significant impact on
performance. With the user-space test-suite from libgpiod (for core C
library - gpiod-test) I'm seeing a consistent 40% impact on
performance. That's not really acceptable. :( I will try to bisect the
series later and see which part exactly breaks it.

I can also help you with user-space testing with libgpiod, if you need
it? Some documentation is available here:
https://libgpiod.readthedocs.io/en/latest/testing.html

> [1] https://lore.kernel.org/chrome-platform/20260116080235.350305-1-tzungbi@kernel.org
>
> Tzung-Bi Shih (23):
>   gpiolib: Correct wrong kfree() usage for `kobj->name`
>   gpiolib: cdev: Fix resource leaks on errors in gpiolib_cdev_register()
>   gpiolib: Fix resource leaks on errors in gpiochip_add_data_with_key()
>   gpiolib: Fix resource leaks on errors in lineinfo_changed_notify()
>   gpiolib: cdev: Correct return code on memory allocation failure
>
> => The first 5 patches are fixes.  They aren't directly related to the
>    replacement, and should be able to apply independently.
>

Awesome, I'll make them a priority.

>   gpiolib: Access `gpio_bus_type` in gpiochip_setup_dev()
>   gpiolib: Remove redundant check for struct gpio_chip
>   gpiolib: sysfs: Remove redundant check for struct gpio_chip
>   gpiolib: Ensure struct gpio_chip for gpiochip_setup_dev()
>   gpiolib: cdev: Don't check struct gpio_chip in gpio_chrdev_open()
>
> => The following 5 patches are refactors.  Makes the subsequent changes
>    easier or at least clear.
>
>   selftests: gpio: Add gpio-cdev-uaf tests
>
> => The following patch adds kselftest cases for some classic UAF
>    scenarios.
>

Thanks, these too look like v7.0 material for me. I'll try to review
these ASAP too.

Bart