linux-kernel - Re: [PATCH] usb: usbip: fix null pointer dereference

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Message-ID: <5754675B.1050104@gmail.com>
Date:	Sun, 05 Jun 2016 18:54:35 +0100
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Krzysztof Opasiak <k.opasiak@...sung.com>,
	Valentina Manea <valentina.manea.m@...il.com>,
	Shuah Khan <shuah.kh@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb: usbip: fix null pointer dereference

On Friday 03 June 2016 09:29 AM, Krzysztof Opasiak wrote:
>
>
> On 06/02/2016 03:22 PM, Sudip Mukherjee wrote:
>> We have been dereferencing udc before checking it. Lets use it after it
>> has been checked.
>>
>
> To be honest I have mixed feelings about this patch.
>
> On one hand it prevents us from dereferencing potential NULL ptr what is
> generally good. But on the other hand it seems to be a little bit
> pointless overhead. This function is called only in one place, it's
> internal function of vudc driver and in addition generally it is
> currently impossible that this function will get NULL ptr as parameter
> as it's value is taken from container_of(). Not to mention that if this
> is NULL or garbage we will end up in NULL ptr dereference much earlier
> before calling this function.
>
> So if there is something that you would like to fix with this patch and
> you have a real problem with this function could you please provide us
> some more details (for example stack trace)? If this patch is just to
> prevent us from something that will never happen then I would rather to
> not submit this. In my opinion if we get a NULL in this function this
> means that we have some serious problem in UDC core and this check will
> just mask this error.

Yes, I should have seen earlier that the only caller has already 
dereferenced udc. So maybe the following will be appropriate in this 
situation.

Regards
Sudip


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