netdev - Re: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used

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Date:   Fri, 09 Oct 2020 07:38:59 +0200
From:   Nicolai Stange <nstange@...e.de>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        David Laight <David.Laight@...lab.com>,
        "davem\@davemloft.net" <davem@...emloft.net>,
        "kuba\@kernel.org" <kuba@...nel.org>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        Nicolai Stange <nstange@...e.de>,
        "linux-wireless\@vger.kernel.org" <linux-wireless@...r.kernel.org>,
        "wil6210\@qti.qualcomm.com" <wil6210@....qualcomm.com>,
        "brcm80211-dev-list\@cypress.com" <brcm80211-dev-list@...ress.com>,
        "b43-dev\@lists.infradead.org" <b43-dev@...ts.infradead.org>,
        "linux-bluetooth\@vger.kernel.org" <linux-bluetooth@...r.kernel.org>
Subject: Re: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used

Taehee Yoo <ap420073@...il.com> writes:

> On Fri, 9 Oct 2020 at 01:14, Johannes Berg <johannes@...solutions.net> wrote:
> On Thu, 2020-10-08 at 15:59 +0000, David Laight wrote:
>
>> From: Taehee Yoo
>> > Sent: 08 October 2020 16:49
>> >
>> > When debugfs file is opened, its module should not be removed until
>> > it's closed.
>> > Because debugfs internally uses the module's data.
>> > So, it could access freed memory.

Yes, the file_operations' ->release() to be more specific -- that's not
covered by debugfs' proxy fops.


>> > In order to avoid panic, it just sets .owner to THIS_MODULE.
>> > So that all modules will be held when its debugfs file is opened.
>>
>> Can't you fix it in common code?
>
>> Yeah I was just wondering that too - weren't the proxy_fops even already
>> intended to fix this?
>
> I didn't try to fix this issue in the common code(debugfs).
> Because I thought It's a typical pattern of panic and THIS_MODULE
> can fix it clearly.
> So I couldn't think there is a root reason in the common code.

That's correct, ->owner should get set properly, c.f. my other mail in
this thread.


Thanks,

Nicolai

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