Subject: Re: [PATCH] module param_call: fix potential NULL pointer dereference

From: DDD <[email-masked]>
Date: Sun, 21 Feb 2010 17:16:56 +0800

Américo Wang wrote:
> On Sun, Feb 21, 2010 at 3:24 PM, Dongdong Deng
> <[email-masked]> wrote:
>> The param_set_fn() function will get a parameter which is a NULL
>> pointer when insmod module with params via following method:
>>
>> $insmod module.ko module_params
>>
>> BTW: the normal method usually as following format:
>> $insmod module.ko module_params=example
>>
>> If the param_set_fn() function didn't check that parameter and used
>> it directly, it could caused an OOPS due to NULL pointer dereference.
>>
>> The solution is simple:
>> Just checking the parameter before using in param_set_fn().
>>
>> Example:
>> int set_module_params(const char *val, struct kernel_param *kp)
>> {
>>        /*Checking the val parameter before using */
>>        if (!val)
>>                return -EINVAL;
>>        ...
>> }
>> module_param_call(module_params, set_module_params, NULL, NULL, 0644);
>>
> 
> Why not just checking all of them in the generic code?

It is no problem that we check the params before invoking param_set_fn().

But I trend to do the checking in param_set_*fn(), because we can offer 
some special prompt infos to user if we want and handle some special 
cases like param_set_bool().

Thanks,
Dongdong

> How about my _untested_ patch below?
> 
> Thanks.
> 
> -----------
> 
> When a module parameter "foo" is not bool, 

we shouldn't accept arguments
> like this "insmod ./foo.ko foo". However, currently only standard
> ->set functions
> check this, several non-standard ->set functions ignore this, thus could cause
> NULL def oops.
> 
> Reported-by: Dongdong Deng <[email-masked]>
> Signed-off-by: WANG Cong <[email-masked]>
> 
> ---
>