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Date:   Fri, 8 Dec 2023 15:47:59 -0500
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Douglas Anderson <dianders@chromium.org>
Cc:     linux-usb@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        =?iso-8859-1?Q?Bj=F8rn?= Mork <bjorn@mork.no>,
        Eric Dumazet <edumazet@google.com>,
        Grant Grundler <grundler@chromium.org>,
        Brian Geffon <bgeffon@google.com>,
        "David S . Miller" <davem@davemloft.net>,
        Hayes Wang <hayeswang@realtek.com>,
        Simon Horman <horms@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: core: Fix crash w/ usb_choose_configuration() if no
 driver
Message-ID: <90fb5279-c1da-4d8c-8f89-b1f54175eee3@rowland.harvard.edu>
References: <20231208123119.1.If27eb3bf7812f91ab83810f232292f032f4203e0@changeid>
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On Fri, Dec 08, 2023 at 12:31:24PM -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.
> 
> 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="$(ls -d *-*)"
>   real_dir="$(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 override usb_choose_configuration()")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---

I'm not sure this is the best solution.  A USB device with no driver is 
an anomaly; in all likelihood we shouldn't be calling 
usb_choose_configuration() for such a device in the first place.

So I think a better solution would be to put this check in 
usb_authorize_device() before it does the autoresume, or else to make 
usb_choose_configuration() return immediately, right at the start, if 
there is no driver.

Alan Stern