linux-kernel - Re: [PATCH 1/1] Kobject: bail early if no new_parent in kobject

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Date:	Tue, 06 Oct 2009 11:52:09 +0300
From:	Phil Carmody <ext-phil.2.carmody@...ia.com>
To:	ext Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] Kobject: bail early if no new_parent in
	kobject_move()

On Mon, 2009-10-05 at 18:37 +0200, ext Cornelia Huck wrote:
> On Thu,  1 Oct 2009 17:50:48 +0300,
> Phil Carmody <ext-phil.2.carmody@...ia.com> wrote:
> 
> > From: Phil Carmody <ext-phil.2.carmody@...ia.com>
> > 
> > In the absense of kobj->kset, new_parent would remain NULL.
> > NULL-dereference shenanighans then ensues in the subsequent
> > sysfs_move_dir(..., new_parent) call. Bail early instead.
> 
> But sysfs_move_dir(..., NULL) should work and fall back to the sysfs
> root...

I guess there are two schools of thought - the strict and the
accommodating. I was contemplating resending an even stricter patch, but
there's nothing wrong with adopting sane safe fallbacks instead. 

> <looks at code>
> 
> It seems that has been broken for some time. Should probably be
> something like this instead (uncompiled); I can send it with proper
> description and s-o-b once I gave it a test.
> 
> ---
>  fs/sysfs/dir.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- linux-2.6.orig/fs/sysfs/dir.c
> +++ linux-2.6/fs/sysfs/dir.c
> @@ -894,7 +894,8 @@ int sysfs_move_dir(struct kobject *kobj,
>  
>  	mutex_lock(&sysfs_rename_mutex);
>  	BUG_ON(!sd->s_parent);
> -	new_parent_sd = new_parent_kobj->sd ? new_parent_kobj->sd : &sysfs_root;
> +	new_parent_sd = (new_parent_kobj && new_parent_kobj->sd) ?
> +		new_parent_kobj->sd : &sysfs_root;
>  
>  	error = 0;
>  	if (sd->s_parent == new_parent_sd)

Looks like it knocks the NULL dereference squarely on the head. Yup.

Phil
-- 
"They weren't designed to run on a computer, they were designed
to run on a Powerpoint slide projector." -- Peter Gutmann

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