linux-kernel - Re: [PATCH v8 0/2] gpiolib: don't allow user-space to crash the kernel with hot-unplugs

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Message-ID: <CAMRc=Md36QZYFd9+D_CR0mWEDoxXB1rkFf8q93ohQ=StN3jDhw@mail.gmail.com>
Date:   Wed, 7 Dec 2022 09:37:22 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Nick Hainke <vincent@...temli.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v8 0/2] gpiolib: don't allow user-space to crash the
 kernel with hot-unplugs

On Mon, Dec 5, 2022 at 1:39 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Linus Torvalds pointed out that using trylock here is wrong. This iteration
> drops it in favor of unconditional locks but keeps all the fixes that came
> later.
>
> I will also not send it for this release but make it part of the updates PR
> for v6.2 to give it some time in next.
>
> v7 -> v8:
> - don't use down_read_trylock(), just go straight for a full lock
>
> v6 -> v7:
> - fix a build issue with CDEV_V1 code disabled (giving credit to Nick Hainke)
> - protect the gdev->chip also in gpio_chrdev_open()
>
> v5 -> v6:
> - signal an error in poll callbacks instead of returning 0 which would make
>   the user-space assume a timeout occurred (which could lead to user-space
>   spinning a timeout loop forever)
>
> v4 -> v5:
> - try to acquire the semaphore for reading and bail out of syscall callbacks
>   immediately in case of lock contention
>
> v3 -> v4:
> - use function typedefs to make code cleaner
> - add a blank line after down_write()
>
> v2 -> v3:
> - drop the helper variable in patch 1/2 as we won't be using it in 2/2
> - refactor patch 2/2 to use locking wrappers around the syscall callbacks
>
> v1 -> v2:
> - add missing gdev->chip checks in patch 1/2
> - add a second patch that protects the structures that can be accessed
>   by user-space calls against concurrent removal
>
> Bartosz Golaszewski (2):
>   gpiolib: cdev: fix NULL-pointer dereferences
>   gpiolib: protect the GPIO device against being dropped while in use by
>     user-space
>
>  drivers/gpio/gpiolib-cdev.c | 204 +++++++++++++++++++++++++++++++-----
>  drivers/gpio/gpiolib.c      |   4 +
>  drivers/gpio/gpiolib.h      |   5 +
>  3 files changed, 188 insertions(+), 25 deletions(-)
>
> --
> 2.37.2
>

Reapplied again to get it back into next for testing.

Bart