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

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Date:	Fri, 8 Jan 2010 17:14:25 +0800
From:	"Zhang, Xiantao" <xiantao.zhang@...el.com>
To:	Gabor Gombas <gombasg@...aki.hu>
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()

Gabor Gombas wrote:
> 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.
Make sense. 
Xiantao
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