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

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Date:   Tue, 5 Feb 2019 19:43:55 +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 10:22:50AM -0500, Sven Van Asbroeck wrote:
> 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.

It really should happen when the device is removed (if it is a driver
that binds to a device.)  If this is not a driver, then there should be
some way to scan that cancel_work_sync() is never called or not, right?

thanks,

greg k-h