From: Felipe Balbi <balbi@kernel.org>
To: Wesley Cheng <wcheng@codeaurora.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 11:05:41 +0300 [thread overview]
Message-ID: <87sg3gksyy.fsf@kernel.org> (raw)
In-Reply-To: <69253e54-771b-3b1c-1765-77bfb6288715@codeaurora.org>
[-- Attachment #1: Type: text/plain, Size: 2241 bytes --]
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.
--
balbi
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 857 bytes --]
next prev parent reply other threads:[~2021-04-24 8:36 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 [this message]
2021-04-24 8:37 ` Wesley Cheng
2021-04-24 13:31 ` Felipe Balbi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87sg3gksyy.fsf@kernel.org \
--to=balbi@kernel.org \
--cc=gregkh@linuxfoundation.org \
--cc=hemantk@codeaurora.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=peter.chen@kernel.org \
--cc=stable@vger.kernel.org \
--cc=wcheng@codeaurora.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).