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References: <20231211070808.v2.1.If27eb3bf7812f91ab83810f232292f032f4203e0@changeid>
 <1ec52764-7fd9-484f-bcdc-bbf97194deef@rowland.harvard.edu>
In-Reply-To: <1ec52764-7fd9-484f-bcdc-bbf97194deef@rowland.harvard.edu>
From:   Doug Anderson <dianders@chromium.org>
Date:   Mon, 11 Dec 2023 07:34:50 -0800
Message-ID: <CAD=FV=V3=Lnk-8E9GmpYtXXJBDLkPZgXWt+5MVof3Wn_JYS9rg@mail.gmail.com>
Subject: Re: [PATCH v2] usb: core: Fix crash w/ usb_choose_configuration() if
 no driver
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     linux-usb@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        netdev@vger.kernel.org,
        =?UTF-8?Q?Bj=C3=B8rn_Mork?= <bjorn@mork.no>,
        Eric Dumazet <edumazet@google.com>,
        Hayes Wang <hayeswang@realtek.com>,
        Brian Geffon <bgeffon@google.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Simon Horman <horms@kernel.org>,
        Grant Grundler <grundler@chromium.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-kernel@vger.kernel.org
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Hi,

On Mon, Dec 11, 2023 at 7:27=E2=80=AFAM Alan Stern <stern@rowland.harvard.e=
du> wrote:
>
> On Mon, Dec 11, 2023 at 07:08:14AM -0800, Douglas Anderson wrote:
> > It's possible that usb_choose_configuration() can get called when a
> > USB device has no driver. In this case the recent commit a87b8e3be926
> > ("usb: core: Allow subclassed USB drivers to override
> > usb_choose_configuration()") can cause a crash since it dereferenced
> > the driver structure without checking for NULL. Let's add a check.
> >
> > A USB device with no driver is an anomaly, so make
> > usb_choose_configuration() return immediately if there is no driver.
> >
> > This was seen in the real world when usbguard got ahold of a r8152
> > device at the wrong time. It can also be simulated via this on a
> > computer with one r8152-based USB Ethernet adapter:
> >   cd /sys/bus/usb/drivers/r8152-cfgselector
> >   to_unbind=3D"$(ls -d *-*)"
> >   real_dir=3D"$(readlink -f "${to_unbind}")"
> >   echo "${to_unbind}" > unbind
> >   cd "${real_dir}"
> >   echo 0 > authorized
> >   echo 1 > authorized
> >
> > Fixes: a87b8e3be926 ("usb: core: Allow subclassed USB drivers to overri=
de usb_choose_configuration()")
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> > Changes in v2:
> > - Return immediately if no driver, as per Alan.
> >
> >  drivers/usb/core/generic.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
> > index dcb897158228..2be1e8901e2f 100644
> > --- a/drivers/usb/core/generic.c
> > +++ b/drivers/usb/core/generic.c
> > @@ -59,7 +59,11 @@ int usb_choose_configuration(struct usb_device *udev=
)
> >       int num_configs;
> >       int insufficient_power =3D 0;
> >       struct usb_host_config *c, *best;
> > -     struct usb_device_driver *udriver =3D to_usb_device_driver(udev->=
dev.driver);
> > +     struct usb_device_driver *udriver;
> > +
> > +     if (!udev->dev.driver)
> > +             return -1;
>
> This is a rather unusual condition.  It would be good to put a comment
> just before the test, explaining that if a USB device (not an interface)
> doesn't have a driver then the kernel has no business trying to select
> or install a configuration for it.
>
> Along with the comment, feel free to add:
>
> Reviewed-by: Alan Stern <stern@rowland.harvard.edu>

Thanks for the quick reply. I've added your comment almost verbatim to
the code and sent out a quick v3 with your tag:

https://lore.kernel.org/r/20231211073237.v3.1.If27eb3bf7812f91ab83810f23229=
2f032f4203e0@changeid