linux-kernel - Re: [PATCH] Input: matrix_keypad

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Message-ID: <20190211082902.GA95126@dtor-ws>
Date:   Mon, 11 Feb 2019 00:29:02 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     linux-input@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Input: matrix_keypad - use flush_delayed_work()

Hi Sven,

On Sun, Feb 10, 2019 at 12:43:21PM -0500, Sven Van Asbroeck wrote:
> Hi Dmitry,
> 
> On Thu, Feb 7, 2019 at 5:46 PM Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> >
> > We should be using flush_delayed_work() instead of flush_work() in
> > matrix_keypad_stop() to ensure that we are not missing work that is
> > scheduled but not yet put in the workqueue (i.e. its delay timer has not
> > expired yet).
> >
> 
> Could the following scenario cause a use-after-free?
> (I am adding comments on lines starting with -->)
> 
> a) user closes the device handle:
> 
> static void matrix_keypad_stop(struct input_dev *dev)
> {
>         struct matrix_keypad *keypad = input_get_drvdata(dev);
> 
>         spin_lock_irq(&keypad->lock);
>         keypad->stopped = true;
>         spin_unlock_irq(&keypad->lock);
> 
>         flush_work(&keypad->work.work);
> -->
> --> new interrupt comes in, and schedules new delayed keypad->work (1)

It will not schedule new work because we check keypad->stopped flag
in ISR.

Thanks.

-- 
Dmitry