Re: [PATCH 1/1] Kobject: bail early if no new_parent in kobject_move()

Phil Carmody
2009-10-06T08:50:20Z

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@nokia.com> wrote:
>
> > From: Phil Carmody <ext-phil.2.carmody@nokia.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
--
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