netdev - Re: [RFC] debugfs: protect against rmmod while files are open

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Message-ID: <2a333c2a50c676c461c1e2da5847dd4024099909.camel@sipsolutions.net>
Date:   Fri, 09 Oct 2020 12:48:05 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     linux-kernel@...r.kernel.org
Cc:     nstange@...e.de, ap420073@...il.com, David.Laight@...lab.com,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        gregkh@...uxfoundation.org, rafael@...nel.org
Subject: Re: [RFC] debugfs: protect against rmmod while files are open

On Fri, 2020-10-09 at 12:41 +0200, Johannes Berg wrote:

> If the fops doesn't have a release method, we don't even need
> to keep a reference to the real_fops, we can just fops_put()
> them already in debugfs remove, and a later full_proxy_release()
> won't call anything anyway - this just crashed/UAFed because it
> used real_fops, not because there was actually a (now invalid)
> release() method.

I actually implemented something a bit better than what I described - we
never need a reference to the real_fops for the release method alone,
and that means if the release method is in the kernel image, rather than
a module, it can still be called.

That together should reduce the ~117 places you changed in the large
patchset to around a handful.

johannes