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

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Date:   Tue, 5 Feb 2019 10:22:50 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     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>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [RFC v1 0/3] Address potential user-after-free on module unload

On Tue, Feb 5, 2019 at 9:57 AM Kees Cook <keescook@...omium.org> wrote:
>
>
> Can a Coccinelle script get written to find module-use of the non-devm
> work init?

My thoughts exactly ! But sadly I'm not a Coccinelle expert. I did
look briefly at
its syntax, but I didn't immediately "get" how Cocci could find this class of
errors, without a huge false positive rate (which would make it worse than
useless).

>
> It seems like finding these in __init functions should be relatively
> easy? (Or can we add runtime detection in the existing INIT_*WORK()
> code to see if it is running from the wrong place?)
>

IMHO the problem isn't that they're called from __init functions.
Also, nothing is
wrong with the location of INIT_*WORK per se.

The real problem is that developers overlook calling cancel_work_sync()
on unload. I'm not sure how we could bolt on runtime detection to catch
a *missing* function. Again, without causing tons of false positives.