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

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Date:   Fri, 9 Oct 2020 13:15:17 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     'Johannes Berg' <johannes@...solutions.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nstange@...e.de" <nstange@...e.de>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>
Subject: Re: [RFC] debugfs: protect against rmmod while files are open

On Fri, Oct 09, 2020 at 10:56:16AM +0000, David Laight wrote:
> From: Johannes Berg
> > Sent: 09 October 2020 11:48
> > 
> > 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.
> 
> Is there an equivalent problem for normal cdev opens
> in any modules?

What does cdev have to do with debugfs?