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SubjectRe: [PATCH] cpuidle: Avoid possible NULL pointer dereference in __cpuidle_register_device()
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@linux.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..

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).


>
>> drivers/cpuidle/cpuidle.c | 3 ++-
>> 1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index 87411ce..75b381e 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -372,7 +372,7 @@ EXPORT_SYMBOL_GPL(cpuidle_disable_device);
>> static int __cpuidle_register_device(struct cpuidle_device *dev)
>> {
>> int ret;
>> - struct device *cpu_dev = get_cpu_device((unsigned long)dev->cpu);
>> + struct device *cpu_dev;
>> struct cpuidle_driver *cpuidle_driver = cpuidle_get_driver();
>>
>> if (!dev)
>> @@ -380,6 +380,7 @@ static int __cpuidle_register_device(struct
>> cpuidle_device *dev)
>> if (!try_module_get(cpuidle_driver->owner))
>> return -EINVAL;
>>
>> + cpu_dev = get_cpu_device((unsigned long)dev->cpu);
>> init_completion(&dev->kobj_unregister);
>>
>> per_cpu(cpuidle_devices, dev->cpu) = dev;
>>
>
>


Thank you for the review!

Regards,
Srivatsa S. Bhat



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