linux-kernel - Re: [RFC v1 0/3] Address potential user-after-free on module unload

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Date:   Wed, 6 Feb 2019 17:46:57 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [RFC v1 0/3] Address potential user-after-free on module unload

On Tue, Feb 05, 2019 at 02:12:31PM -0500, Sven Van Asbroeck wrote:
> On Tue, Feb 5, 2019 at 1:43 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> >
> > It really should happen when the device is removed (if it is a driver
> > that binds to a device.)
> 
> Absolutely. That's why I'm advocating adding a devm_init_work(),
> which will take care of this automatically.
> 
> But it's of course not universally applicable. Not all drivers use devm.

Ick, no, watch out for devm() calls.  Odds are this is _NOT_ what you
want to do for a device.  Remember when devm calls get freed (hint, not
at driver unbind/unload, but at device structure removal.

By creating a work queue, you are suddenly tying module code to a device
memory structure lifespan, both of which are totally independant.

It's the same issue with the devm irq call, that has been nothing but a
nightmare as everyone gets it wrong.  Try to learn from our past
mistakes please :)

thanks,

greg k-h