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

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Date:	Tue, 23 Feb 2010 23:45:19 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Dongdong Deng <dongdong.deng@...driver.com>,
	linux-kernel@...r.kernel.org,
	Américo Wang <xiyou.wangcong@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RESEND PATCH] module param_call: fix potential NULL pointer
	dereference

On Tue, Feb 23, 2010 at 02:26:45PM +1030, Rusty Russell wrote:
>On Mon, 22 Feb 2010 09:10:51 pm Dongdong Deng wrote:
>> The param_set_fn() function will get a parameter which is a NULL
>> pointer when insmod module via bare params as following method:
>> 
>> $insmod foo.ko foo
>> 
>> 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:
>> Using "" to replace NULL parameter, thereby the param_set_fn()
>> function will never get a NULL pointer.
>
>This changes the value of booleans, and loses checking for int params, etc.
>
>I liked Americo's approach; I've combined the two approaches below.
>
>Since I'm going away, can Andrew take this?
>
>Subject: params: don't hand NULL values to param.set callbacks.
>
>An audit by Dongdong Deng revealed that most driver-author-written param
>calls don't handle val == NULL (which happens when parameters are specified
>with no =, eg "foo" instead of "foo=1").
>
>The only real case to use this is boolean, so handle it specially for that
>case and remove a source of bugs for everyone else as suggested by Americo.
>
>Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>Cc: Dongdong Deng <dongdong.deng@...driver.com>
>Cc: Américo Wang <xiyou.wangcong@...il.com>
>
>diff --git a/kernel/params.c b/kernel/params.c
>--- a/kernel/params.c
>+++ b/kernel/params.c
>@@ -59,6 +59,9 @@ static int parse_one(char *param,
> 	/* Find parameter */
> 	for (i = 0; i < num_params; i++) {
> 		if (parameq(param, params[i].name)) {
>+			/* Noone handled NULL, so do it here. */
>+			if (!val && params[i].set != param_set_bool)
>+				return -EINVAL;

Sorry, after rethinking about this, I think it might be wrong.

With this patch, when I use non-standard bool functions, I will not
have a chance to use '!val' which should be valid for all bool
functions. Or am I missing something?

Thanks.

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