linux-kernel - Re: [PATCH v1] usb: host: Fix possible kernel crash

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Date:	Wed, 11 Jul 2012 12:34:08 +0530
From:	Venu Byravarasu <vbyravarasu@...dia.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] usb: host: Fix possible kernel crash

On Tuesday 10 July 2012 08:39 PM, Alan Stern wrote:
> On Tue, 10 Jul 2012, Venu Byravarasu wrote:
>
>> Thanks Alan for your comments.
>>
>> On Monday 09 July 2012 08:04 PM, Alan Stern wrote:
>>> On Mon, 9 Jul 2012, Venu Byravarasu wrote:
>>>
>>>> In functions itd_complete &  sitd_complete, a pointer
>>>> by name stream may get dereferenced after freeing it, when
>>>> iso_stream_put is called with stream->refcount = 2.
>>> I don't understand the problem.  Did you actually see this happen or is
>>> it only theoretical?
>> Yes it is a theoretical problem, as complained by Coverity.
>> As per the logic you explained above, this change is not needed.
>> However coverity was complaining as below:
>>
>> /kernel/drivers/usb/host/ehci-sched.c 1777 USE_AFTER_FREE Dereferencing
>> freed pointer "stream"
>>
>> Hence to pacify coverity, this change is done.
>> Please let me know if you see any other better way to handle it.
> This seems to be a false positive from Coverity.
>
> In any case, I'm about to submit some patches which get rid of the
> reference counting entirely.  So let's not worry about this.
>
> Alan Stern
>
Thanks Alan for taking care of it, in your future patch.




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