linux-kernel - Re: [PATCH] KVM: dereference of NULL pointer in set_pal

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Date:	Fri, 8 Jan 2010 08:12:00 +0100
From:	Gabor Gombas <gombasg@...aki.hu>
To:	"Zhang, Xiantao" <xiantao.zhang@...el.com>
Cc:	Roel Kluin <roel.kluin@...il.com>,
	"kvm-ia64@...r.kernel.org" <kvm-ia64@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: dereference of NULL pointer in set_pal_result()

On Fri, Jan 08, 2010 at 07:28:57AM +0800, Zhang, Xiantao wrote:

> For the check "(p && p->exit_reason == EXIT_REASON_PAL_CALL", if p is NULL, the reference about "p->exit_reason == EXIT_REASON_PAL_CALL" won't be checked any more, so no issue here. 

> > diff --git a/arch/ia64/kvm/kvm_fw.c b/arch/ia64/kvm/kvm_fw.c
> > index e4b8231..d28494f 100644
> > --- a/arch/ia64/kvm/kvm_fw.c
> > +++ b/arch/ia64/kvm/kvm_fw.c
> > @@ -75,9 +75,11 @@ static void set_pal_result(struct kvm_vcpu *vcpu,
> >  	struct exit_ctl_data *p;
> > 
> >  	p = kvm_get_exit_data(vcpu);
> > -	if (p && p->exit_reason == EXIT_REASON_PAL_CALL) {
> > +	if (!p)
> > +		return;
> > +	if (p->exit_reason == EXIT_REASON_PAL_CALL) {
> >  		p->u.pal_data.ret = result;
> > -		return ;
> > +		return;
> >  	}
> >  	INIT_PAL_STATUS_UNIMPLEMENTED(p->u.pal_data.ret);

IMHO it's not the test but the INIT_PAL_STATUS_UNIMPLEMENTED() that does
the unwanted dereferencing, and that's fixed by the patch.

Gabor

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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