linux-kernel - Re: [PATCH] module param_call: fix potential NULL pointer dereference

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Message-ID: <4B825846.1030203@windriver.com>
Date:	Mon, 22 Feb 2010 18:11:18 +0800
From:	DDD <dongdong.deng@...driver.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Américo Wang <xiyou.wangcong@...il.com>,
	davem@...emloft.net, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, jason.wessel@...driver.com,
	lenb@...nel.org, dwmw2@...radead.org,
	mdharm-usb@...-eyed-alien.net, bfields@...ldses.org,
	robert.richter@....com
Subject: Re: [PATCH] module param_call: fix potential NULL pointer dereference

Rusty Russell wrote:
> On Sun, 21 Feb 2010 07:11:36 pm Américo Wang wrote:
>> On Sun, Feb 21, 2010 at 3:24 PM, Dongdong Deng
>> <dongdong.deng@...driver.com> 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 seemed useful to allow 'foo' as well as 'foo='. 

Ah, this is a good method to deal with this issue.

I will redo this patch shortly.

Thanks,
Dongdong

  But given these examples,
> obviously that was too easy to misuse.
> 
> So I like your patch; please annotate it properly and put a comment
> like:
> 	/* We used to hand NULL for bare params, but most code didn't handle it :( */
> 
> I assume none of those non-standard param parsers *want* to handle NULL?
> 
> Thanks,
> Rusty.

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