linux-kernel - Re: [PATCH] gpiolib: cdev: fix NULL-pointer dereferences

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Message-ID: <Y4EBubusGqo4IroP@smile.fi.intel.com>
Date:   Fri, 25 Nov 2022 19:56:09 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: cdev: fix NULL-pointer dereferences

On Fri, Nov 25, 2022 at 05:48:02PM +0100, Bartosz Golaszewski wrote:
> On Fri, Nov 25, 2022 at 5:24 PM Kent Gibson <warthog618@...il.com> wrote:

...

> Then at the subsystem level, the GPIO device struct would need a lock
> that would be taken by every user-space operation AND the code
> unregistering the device so that we don't do what you described (i.e.
> if there's a thread doing a read(), then let's wait until it returns
> before we drop the device).

It's called a reference counting, basically you need to get device and then
put when it makes sense.

> This wouldn't fix the case in which the same situation happened in a
> kernel driver but crashing the kernel from within is a much lesser
> offense than allowing user-space to crash it.

-- 
With Best Regards,
Andy Shevchenko