linux-kernel - Re: [CRAZY-RFF] debugfs: track open files and release on remove

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Message-ID: <1ec056cf3ec0953d2d1abaa05e37e89b29c7cc63.camel@sipsolutions.net>
Date:   Fri, 09 Oct 2020 10:19:02 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, nstange@...e.de, ap420073@...il.com,
        David.Laight@...lab.com, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, rafael@...nel.org
Subject: Re: [CRAZY-RFF] debugfs: track open files and release on remove

On Fri, 2020-10-09 at 10:16 +0200, Greg KH wrote:
> On Fri, Oct 09, 2020 at 10:06:14AM +0200, Johannes Berg wrote:
> > We used to say the proxy_fops weren't needed and it wasn't an issue, and
> > then still implemented it. Dunno. I'm not really too concerned about it
> > myself, only root can hold the files open and remove modules ...
> 
> proxy_fops were needed because devices can be removed from the system at
> any time, causing their debugfs files to want to also be removed.  It
> wasn't because of unloading kernel code.

Indeed, that's true. Still, we lived with it for years.

Anyway, like I said, I really just did this more to see that it _could_
be done, not to suggest that it _should_ :-)

I think adding the .owner everywhere would be good, and perhaps we can
somehow put a check somewhere like

	WARN_ON(is_module_address((unsigned long)fops) && !fops->owner);

to prevent the issue in the future?

johannes