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Subject: Re: [PATCH] xhci: fix null-pointer dereference when destroying half-built segment rings
From: Julius Werner <jwerner@google.com>
In-Reply-To: <20121101201552.GA9472@xanatos>
Date: Thu, 1 Nov 2012 13:28:46 -0700
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>,
        Julius Werner <jwerner@chromium.org>, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Vincent Palatin <vpalatin@chromium.org>
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To: Sarah Sharp <sarah.a.sharp@linux.intel.com>
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>> Is it just
>> for (prev = *first; prev; prev = prev->next)
>>    xhci_segment_free(xhci, prev);
>> 
>> ?
> 
> Yeah, that seems cleaner.
> 
> Sarah Sharp

I can submit it that way if you want, but I would advise against it. This way you access the prev pointer after it has been freed already… that's probably not a problem in the current kernel, but it depends on how the underlying memory is managed and is generally just not a good idea in my opinion.