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

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Message-Id: <20221205123903.159838-1-brgl@bgdev.pl>
Date:   Mon,  5 Dec 2022 13:39:01 +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: [PATCH v8 0/2] gpiolib: don't allow user-space to crash the kernel with hot-unplugs

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