linux-kernel - Re: [PATCH] cpuidle: Avoid possible NULL pointer dereference in __cpuidle_register

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Date:	Tue, 03 Apr 2012 14:08:17 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	lenb@...nel.org, khilman@...com, deepthi@...ux.vnet.ibm.com,
	g.trinabh@...il.com, arjan@...radead.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	amit.kucheria@...aro.org
Subject: Re: [PATCH] cpuidle: Avoid possible NULL pointer dereference in __cpuidle_register_device()

On 04/03/2012 01:51 PM, Srivatsa S. Bhat wrote:
> On 04/03/2012 01:01 AM, Daniel Lezcano wrote:
>
>> On 04/02/2012 04:44 PM, Srivatsa S. Bhat wrote:
>>> In __cpuidle_register_device(), "dev->cpu" is used before checking if
>>> dev is
>>> non-NULL. Fix it.
>>>
>>> Signed-off-by: Srivatsa S. Bhat<srivatsa.bhat@...ux.vnet.ibm.com>
>>> ---
>>
>> That should be fixed at the caller level. Usually, static function does
>> not check the function parameters, it is up to the exported function to
>> do that. It is supposed the static functions are called with valid
>> parameters.
>>
>
>
> Ok, good point! I hadn't thought about that.. I just happened to notice
> that in __cpuidle_register_device(), the dev == NULL check is performed
> _after_ dereferencing it, which made the check useless. So I tried to
> fix that within that function. But thanks for pointing out the semantics..
>
>> There are two callers for __cpuidle_register_device:
>>   * cpuidle_register_device
>>   * cpuidle_enable_device
>>
>> Both of them do not check 'dev' is a valid parameter. They should as
>> they are exported and could be used by an external module. IMHO, BUG_ON
>> could be used here if dev == NULL.
>>
>
>
> BUG_ON? That would crash the system.. which might be unnecessary..

Mmh, yes, I agree. never mind.

> How about checking if dev == NULL in the 2 callers like you suggested
> and returning -EINVAL if dev is indeed NULL?
> (And of course no checks for dev == NULL in __cpuidle_register_device).

Ok for me.

> Thank you for the review!

You are welcome :)

Thanks
   -- Daniel

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