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

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Message-ID: <8fe62082d9774a1fb21894c27e140318@AcuMS.aculab.com>
Date:   Fri, 9 Oct 2020 10:56:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Johannes Berg' <johannes@...solutions.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "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>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rafael@...nel.org" <rafael@...nel.org>
Subject: RE: [RFC] debugfs: protect against rmmod while files are open

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?

	David

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