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: Fri, 23 Apr 2021 21:16:26 -0700 [thread overview]
Message-ID: <69253e54-771b-3b1c-1765-77bfb6288715@codeaurora.org> (raw)
In-Reply-To: <c5599433-3eb0-3918-d93b-6860f7951e92@codeaurora.org>
On 4/23/2021 12:10 PM, Wesley Cheng wrote:
>
>
> On 4/22/2021 4:01 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.
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 4:17 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 [this message]
2021-04-24 8:05 ` Felipe Balbi
2021-04-24 8:37 ` Wesley Cheng
2021-04-24 13:31 ` Felipe Balbi
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