linux-kernel - Re: [PATCH] usb: dwc2: gadget: avoid null dereference on incomplete transfer

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Date:	Mon, 04 Apr 2016 13:51:34 +0300
From:	Felipe Balbi <felipe.balbi@...ux.intel.com>
To:	John Youn <John.Youn@...opsys.com>,
	John Keeping <john@...anate.com>,
	John Youn <John.Youn@...opsys.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc2: gadget: avoid null dereference on incomplete transfer


Hi,

John Youn <John.Youn@...opsys.com> writes:
> On 3/30/2016 6:22 AM, Felipe Balbi wrote:
>> 
>> Hi,
>> 
>> John Keeping <john@...anate.com> writes:
>>> Setting up a gadget with the uac2 function results in:
>>>
>>>   Unable to handle kernel NULL pointer dereference at virtual address 00000058
>>>   ...
>>>   PC is at dwc2_hsotg_irq+0x7f0/0x908
>>>   LR is at dwc2_hsotg_irq+0x4c/0x908
>>>   Backtrace:
>>>   [<c03cd5fc>] (dwc2_hsotg_irq) from [<c00814fc>] (handle_irq_event_percpu+0x130/0x3ec)
>>>   [<c00813cc>] (handle_irq_event_percpu) from [<c0081800>] (handle_irq_event+0x48/0x6c)
>>>
>>> In all other loops we already skip endpoints that are null, so do so
>>> here as well.
>>>
>>> Signed-off-by: John Keeping <john@...anate.com>
>>> ---
>>>  drivers/usb/dwc2/gadget.c | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
>>> index 0abf73c..df43ec0 100644
>>> --- a/drivers/usb/dwc2/gadget.c
>>> +++ b/drivers/usb/dwc2/gadget.c
>>> @@ -2606,7 +2606,9 @@ irq_retry:
>>>  		for (idx = 1; idx < hsotg->num_of_eps; idx++) {
>>>  			hs_ep = hsotg->eps_in[idx];
>>>  
>>> -			if (!hs_ep->isochronous || hs_ep->has_correct_parity)
>>> +			if (!hs_ep ||
>>> +			    !hs_ep->isochronous ||
>>> +			    hs_ep->has_correct_parity)
>> 
>> this is fine (even though choice of where to break line is a bit odd),
>> but I have a question about how the rest of the code works (a bit
>> off-topic, sorry)
>> 
>>>  				continue;
>>>  
>>>  			epctl_reg = DIEPCTL(idx);
>> 
>> So, this means that the first ISO endpoint without correct parity will
>> be used. Isn't this a bit fragile ? What happens when you use a device
>> with several different interfaces using several different endpoints ?
>> 
>> Isn't there a register where we can check which physical endpoint
>> generated the IRQ ? Seems like you really wanna check what:
>> 
>
> We discussed this back when the patch was first submitted and
> determined it should work fine like this. I don't remember exactly why
> though.
>
> But this ISOC parity stuff is a workaround and we have a series of
> patches to correctly set up ISOC allowing us to remove it. We're doing
> some final tests before we send them.

fair enough, thanks

-- 
balbi

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