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From:   Vincent MAILHOL <mailhol.vincent@wanadoo.fr>
Date:   Sun, 11 Dec 2022 20:24:29 +0900
Message-ID: <CAMZ6RqJoCEW9+Z+LD1W9CORE=RUvH9tLn163mkY5Dsct5juYUA@mail.gmail.com>
Subject: Re: [PATCH v2 1/9] can: ems_usb: ems_usb_disconnect(): fix NULL
 pointer dereference
To:     Johan Hovold <johan@kernel.org>
Cc:     Marc Kleine-Budde <mkl@pengutronix.de>, linux-can@vger.kernel.org,
        Oliver Neukum <oneukum@suse.com>,
        Wolfgang Grandegger <wg@grandegger.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Frank Jungclaus <frank.jungclaus@esd.eu>, socketcan@esd.eu,
        Yasushi SHOJI <yashi@spacecubics.com>,
        =?UTF-8?Q?Stefan_M=C3=A4tje?= <stefan.maetje@esd.eu>,
        Hangyu Hua <hbh25y@gmail.com>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Peter Fink <pfink@christ-es.de>,
        Jeroen Hofstee <jhofstee@victronenergy.com>,
        =?UTF-8?Q?Christoph_M=C3=B6hring?= <cmoehring@christ-es.de>,
        John Whittington <git@jbrengineering.co.uk>,
        Vasanth Sadhasivan <vasanth.sadhasivan@samsara.com>,
        Jimmy Assarsson <extja@kvaser.com>,
        Anssi Hannula <anssi.hannula@bitwise.fi>,
        Pavel Skripkin <paskripkin@gmail.com>,
        Stephane Grosjean <s.grosjean@peak-system.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Julia Lawall <Julia.Lawall@inria.fr>,
        Dongliang Mu <dzm91@hust.edu.cn>,
        Sebastian Haas <haas@ems-wuensche.com>,
        Maximilian Schneider <max@schneidersoft.net>,
        Daniel Berglund <db@kvaser.com>,
        Olivier Sobrie <olivier@sobrie.be>,
        =?UTF-8?B?UmVtaWdpdXN6IEtvxYLFgsSFdGFq?= 
        <remigiusz.kollataj@mobica.com>,
        Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>,
        Martin Elshuber <martin.elshuber@theobroma-systems.com>,
        Bernd Krumboeck <b.krumboeck@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Alan Stern <stern@rowland.harvard.edu>,
        linux-usb@vger.kernel.org
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On Tue. 10 déc. 2022 à 20:02, Johan Hovold <johan@kernel.org> wrote:
> On Sat, Dec 10, 2022 at 06:01:49PM +0900, Vincent Mailhol wrote:
> > ems_usb sets the driver's priv data to NULL before waiting for the
> > completion of outsdanding urbs. This can results in NULL pointer
> > dereference, c.f. [1] and [2].
>
> Please stop making hand-wavy claims like this. There is no risk for a
> NULL-pointer deference here, and if you think otherwise you need to
> explain how that can happen in detail for each driver.

Understood.

*My* mistake comes from this message from Alan [1]:

| But if a driver does make the call, it should be careful to
| ensure that the call happens _after_ the driver is finished
| using the interface-data pointer.  For example, after all
| outstanding URBs have completed, if the completion handlers
| will need to call usb_get_intfdata().

I did not pay enough attention to the "if the completion handlers will
need to call usb_get_intfdata()" part and jumped into the incorrect
conclusion that any use of usb_set_intfdata(intf, NULL) before URB
completion was erroneous.

My deep apologies for all the noise. Please forget this series and one
more time, thank you for your patience.

[1] https://lore.kernel.org/linux-usb/Y4OD70GD4KnoRk0k@rowland.harvard.edu/