linux-kernel - Re: [RFC PATCH next]module: Fix mod->mkobj.kobj potentially freed too early

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Message-ID: <87vc2yciqi.fsf@rustcorp.com.au>
Date:	Thu, 22 Aug 2013 16:30:53 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	linux-next list <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, rmk+kernel@....linux.org.uk
Subject: Re: [RFC PATCH next]module: Fix mod->mkobj.kobj potentially freed too early

Greg KH <gregkh@...uxfoundation.org> writes:
> On Wed, Aug 21, 2013 at 05:49:58PM +0800, Li Zhong wrote:
> >  struct kobj_type module_ktype = {
> > +	.release   =	module_kobj_release,
> >  	.sysfs_ops =	&module_sysfs_ops,
> >  };
>
> Wait, as there is no release function here for the kobject (a different
> problem), why is the deferred release function causing any problems?
> There is no release function to call, so what is causing the oops?

Because DEBUG_KOBJECT_RELEASE does the kobject_put() sometime later,
which is what causes the oops.

Since kobjects don't have an owner field, AFAICT someone *could* grab
one in a module which is unloading, then put it after unload.   So this
fixes a real bug, albeit not one seen in the real world.

Applied,
Rusty.
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