linux-kernel - Re: [PATCH] kobject: kzfree object in

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Date:	Mon, 13 Apr 2009 12:47:13 -0700
From:	Greg KH <greg@...ah.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	tom.leiming@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kobject: kzfree object in _release function

On Mon, Apr 13, 2009 at 07:37:47PM +0300, Pekka Enberg wrote:
> Hi Greg,
> 
> On Mon, Apr 13, 2009 at 7:31 PM, Greg KH <greg@...ah.com> wrote:
> > On Sun, Apr 12, 2009 at 12:16:26AM +0800, tom.leiming@...il.com wrote:
> >> From: Ming Lei <tom.leiming@...il.com>
> >>
> >> It helps to troubleshoot the __buggy__ case, in which
> >> unreferenced objects are still accessed, using kzfree
> >> to free objects safely in _release function.
> >>
> >> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> >> ---
> >>  lib/kobject.c |    4 ++--
> >>  1 files changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/lib/kobject.c b/lib/kobject.c
> >> index a6dec32..cb5a562 100644
> >> --- a/lib/kobject.c
> >> +++ b/lib/kobject.c
> >> @@ -597,7 +597,7 @@ void kobject_put(struct kobject *kobj)
> >>  static void dynamic_kobj_release(struct kobject *kobj)
> >>  {
> >>       pr_debug("kobject: (%p): %s\n", kobj, __func__);
> >> -     kfree(kobj);
> >> +     kzfree(kobj);
> >>  }
> >>
> >>  static struct kobj_type dynamic_kobj_ktype = {
> >> @@ -762,7 +762,7 @@ static void kset_release(struct kobject *kobj)
> >>       struct kset *kset = container_of(kobj, struct kset, kobj);
> >>       pr_debug("kobject: '%s' (%p): %s\n",
> >>                kobject_name(kobj), kobj, __func__);
> >> -     kfree(kset);
> >> +     kzfree(kset);
> >
> >
> > What about slab-poisoning?  Shouldn't we just rely on that instead?
> 
> Yes, you should. kzfree() strictly for cases where _correctness_ of
> the program requires it (i.e. security concerns).

Thanks for letting us know.  As such, I'll not be applying this patch.

greg k-h
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