netdev - Re: [BUG] use-after-free after removing UDC with USB Ethernet gadget

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Message-ID: <a4732045-a8bf-cf81-6faa-0e99cabe2f4a@pengutronix.de>
Date:   Tue, 25 Oct 2022 11:28:24 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Peter Chen <peter.chen@...nel.org>,
        Felipe Balbi <balbi@...nel.org>, johannes.berg@...el.com,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Alvin Šipraga <ALSI@...g-olufsen.dk>
Subject: Re: [BUG] use-after-free after removing UDC with USB Ethernet gadget

Hello Greg,

On 25.10.22 10:12, Greg KH wrote:
> On Tue, Oct 25, 2022 at 08:54:58AM +0200, Ahmad Fatoum wrote:
>> Hi everybody,
>>
>> I am running v6.0.2 and can reliably trigger a use-after-free by allocating
>> a USB gadget, binding it to the chipidea UDC and the removing the UDC.
> 
> How do you remove the UDC?

I originally saw this while doing reboot -f on the device. The imx_usb driver's
shutdown handler is equivalent to the remove handler and that removes the UDC.

It could also be triggered with:

  echo ci_hdrc.0 > /sys/class/udc/ci_hdrc.0/device/driver/unbind

>> The network interface is not removed, but the chipidea SoC glue driver will
>> remove the platform_device it had allocated in the probe, which is apparently
>> the parent of the network device. When rtnl_fill_ifinfo runs, it will access the
>> device parent's name for IFLA_PARENT_DEV_NAME, which is now freed memory.
> 
> The gadget removal logic is almost non-existant for most of the function
> code.  See Lee's patch to try to fix up the f_hid.c driver last week as
> one example.  I imagine they all have this same issue as no one has ever
> tried the "remove the gadget device from the running Linux system"
> before as it was not an expected use case.

I see.

FTR: https://lore.kernel.org/all/20221017112737.230772-1-lee@kernel.org/
 
> Is this now an expected use case of the kernel?  If so, patches are
> welcome to address this in all gadget drivers.

I don't really care for unbinding via sysfs. I want to avoid the
use-after-free on reboot/shutdown. See the last splat in my original mail.

Cheers,
Ahmad


> 
> thanks,
> 
> greg k-h
> 


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