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

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Date:	Wed, 24 Feb 2010 11:31:16 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Dongdong Deng <dongdong.deng@...driver.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RESEND PATCH] module param_call: fix potential NULL pointer dereference

On Wed, 24 Feb 2010 02:15:19 am Américo Wang wrote:
> 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?

Sure, at that point we'd need something more sophisticated.  But to
fix this properly we want a flags word, and thus something like this
which I worked on earlier:

http://ozlabs.org/~rusty/kernel/rr-latest/param:param_ops.patch

Cheers,
Rusty.
-- 
Away travelling 25Feb-26Mar (6 .de + 1 .pl + 17 .lt + 2 .sg)
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