From: Wesley Cheng <wcheng@codeaurora.org>
To: Felipe Balbi <balbi@kernel.org>,
gregkh@linuxfoundation.org, peter.chen@kernel.org
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
Hemant Kumar <hemantk@codeaurora.org>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] usb: gadget: Fix double free of device descriptor pointers
Date: Sat, 24 Apr 2021 01:37:29 -0700 [thread overview]
Message-ID: <029267dd-69fb-1f07-b6ff-3384d56c9f89@codeaurora.org> (raw)
In-Reply-To: <87sg3gksyy.fsf@kernel.org>
On 4/24/2021 1:05 AM, Felipe Balbi wrote:
>
> Hi,
>
> Wesley Cheng <wcheng@codeaurora.org> writes:
>>>>> From: Hemant Kumar <hemantk@codeaurora.org>
>>>>>
>>>>> Upon driver unbind usb_free_all_descriptors() function frees all
>>>>> speed descriptor pointers without setting them to NULL. In case
>>>>> gadget speed changes (i.e from super speed plus to super speed)
>>>>> after driver unbind only upto super speed descriptor pointers get
>>>>> populated. Super speed plus desc still holds the stale (already
>>>>> freed) pointer. Fix this issue by setting all descriptor pointers
>>>>> to NULL after freeing them in usb_free_all_descriptors().
>>>>
>>>> could you describe this a little better? How can one trigger this case?
>>>> Is the speed demotion happening after unbinding? It's not clear how to
>>>> cause this bug.
>>>>
>>> Hi Felipe,
>>>
>>> Internally, we have a mechanism to switch the DWC3 core maximum speed
>>> parameter dynamically for displayport use cases. This issue happens
>>> whenever we have a maximum speed change occur on the USB gadget, which
>>> for DWC3 happens whenever we call gadget init. When we switch in and
>>> out of host mode, gadget init is being executed, leading to the change
>>> in the USB gadget max speed parameter:
>>>
>>> dwc->gadget->max_speed = dwc->maximum_speed;
>>>
>>> I know that configFS gadget has the max_speed sysfs file, which is a
>>> similar mechanism, but I haven't tried to see if we can reproduce the
>>> same issue with it. Let me see if we can reproduce this with that
>>> configfs speed setting.
>>>
>>> Thanks
>>> Wesley Cheng
>>>
>>
>> Hi Felipe,
>>
>> So I tried with doing it through the configFS max_speed, but it doesn't
>> have the same effect, as the setting done in dwc3_gadget_init() will
>> still be assigning the composite/UDC device's maximum speed to SSP/SS.
>> This is what the usb_assign_descriptor() uses to determine whether or
>> not to copy the SSP and SS descriptors.
>>
>> So in summary, at least for a DWC3 based subsystem, the only way to
>> reproduce it is if there is a way to dynamically switch the DWC3 core
>> max speed parameter.
>
> Could it be that you have a bug in your out-of-tree changes? Perhaps
> there's some assumption which your changes aren't guaranteeing.
>
Hi Felipe,
Unless there is a limitation on how the USB gadget max speed can be
used, i.e. the USB gadget max speed MUST stay the same throughout a
device's boot period, then our out of tree changes may have the wrong
assumptions. However, I don't see that stated anywhere, and I still
feel the current usb_assign_descriptors() and usb_free_all_descriptors()
aren't aligned with one another. One API decides which descriptors to
copy based on a parameter, whereas the other just frees all of them
irrespective.
Thanks
Wesley Cheng
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
next prev parent reply other threads:[~2021-04-24 8:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-21 19:47 [PATCH v2] usb: gadget: Fix double free of device descriptor pointers Wesley Cheng
2021-04-22 11:01 ` Felipe Balbi
2021-04-23 19:10 ` Wesley Cheng
2021-04-24 4:16 ` Wesley Cheng
2021-04-24 8:05 ` Felipe Balbi
2021-04-24 8:37 ` Wesley Cheng [this message]
2021-04-24 13:31 ` Felipe Balbi
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